University of Iowa
Iowa Research Online
Theses and Dissertations
Fall 2014
Effect of aging and habitual aerobic exercise on
endothelial function, arterial stiffness, and
autonomic function in humans
Stephen Alan Harris
University of Iowa
Copyright 2014 Stephen Alan Harris
This thesis is available at Iowa Research Online: http://ir.uiowa.edu/etd/1465
Recommended Citation
Harris, Stephen Alan. "Effect of aging and habitual aerobic exercise on endothelial function, arterial stiffness, and autonomic function
in humans." MS (Master of Science) thesis, University of Iowa, 2014.
http://ir.uiowa.edu/etd/1465.
Follow this and additional works at: http://ir.uiowa.edu/etd
Part of the Exercise Physiology Commons
EFFECT OF AGING AND HABITUAL AEROBIC EXERCISE ON ENDOTHELIAL
FUNCTION, ARTERIAL STIFFNESS, AND AUTONOMIC FUNCTION IN HUMANS
by
Stephen Alan Harris
A thesis submitted in partial fulfillment
of the requirements for the
Master of Science degree in Health and Human Physiology
in the Graduate College of
The University of Iowa
December 2014
Thesis Supervisor: Assistant Professor Gary L. Pierce
Copyright by
STEPHEN ALAN HARRIS
2014
All Rights Reserved
Graduate College
The University of Iowa
Iowa City, Iowa
CERTIFICATE OF APPROVAL
_______________________
MASTER’S THESIS
_______________
This is to certify that the Master’s thesis of
Stephen Alan Harris
has been approved by the Examining Committee
for the thesis requirement for the Master of Science degree
in Health and Human Physiology at the December 2014 graduation.
Thesis Committee:
___________________________________
Gary L Pierce, Thesis Supervisor
___________________________________
Harald M. Stauss
___________________________________
Darren P. Casey
ACKNOWLEDGEMENTS
To my parents, Janell and Steve. Without your hard work and sacrifice, I would
not be where I am today. I would also like to acknowledge Dr. Pierce and Dr. Stauss
for their invaluable contributions to this manuscript.
ii
TABLE OF CONTENTS
LIST OF TABLES ................................................................................................................ v
LIST OF FIGURES ............................................................................................................. vi
CHAPTER I
INTRODUCTION ............................................................................... 1
Aging and Autonomic Dysfunction ........................................................................... 2
Baroreflex Sensitivity ................................................................................... 3
Heart Rate Variability ................................................................................... 5
Short-term BPV ....................................................................................................6
Relationship among Autonomic Measures ............................................................... 7
Aerobic Exercise and Autonomic Dysfunction in Aging .......................................... 8
Aging and Large Elastic Artery Stiffness .................................................................. 9
Large Elastic Artery Stiffness and CVD Risk ............................................ 10
Aortic Stiffness and Habitual Aerobic Exercise in Aging .......................... 11
Aging and Peripheral Vascular Endothelial Dysfunction........................................ 12
Vascular Endothelial Function and Habitual Aerobic
Exercise in Aging .............................................................................. 13
Habitual Aerobic Exercise and Autonomic Dysfunction and Large
Elastic Artery Stiffness and Peripheral Vascular Endothelial
Dysfunction in Aging ................................................................................. 14
Hypotheses and Study Aims ................................................................................... 15
CHAPTER II
METHODS ...................................................................................... 17
Subject Recruitment & Study Design ...................................... ................................17
Subject Characteristics ............................................................................................ 18
Blood Chemistry ...................................................................................................... 19
Measurements .......................................................................................................... 19
Data Analysis .................................. .........................................................................19
Baroreflex Sensitivity via the Sequence Technique ............................. ......19
Heart Rate Variability: Time Domain Analysis .......................................... 20
Heart Rate and Blood Pressure Variability: Frequency Domain
Analysis ............................................................................................... 20
Aortic Pulse Wave Velocity........................................................................ 21
Brachial Artery Flow-Mediated Dilation .................................................... 22
Brachial Artery Endothelium-Independent Dilation ................................... 22
Statistical Analysis .................................................................................................. 23
CHAPTER III
RESULTS ........................................................................................ 24
Subject Characteristics ............................................................................................ 24
Blood Chemistry ...................................................................................................... 25
Baroreflex Sensitivity .............................................................................................. 25
Heart Rate Variability: Time Domain ................................................................ 26
Heart Rate Variability: Frequency Domain ............................................................ 27
Systolic Blood Pressure Variability ........................................................................ 27
Aortic Pulse Wave Velocity. ................................................................................. ..28
Augmentation Index..... ......................................................................................... ..28
Brachial Artery Flow-Mediated Dilation ................................................................ 28
iii
Endothelium-Independent Dilation ................................................................. 29
Pearson’s Correlations ............................................................................................ 29
Exercise Intervention Subject Characteristics......................................................... 30
Exercise Intervention Blood Chemistry ...................................................... 30
Exercise and Baroreflex Sensitivity ........................................................... 31
Exercise and Time Domain Analysis of HRV ........................................................ 31
Exercise and Frequency Domain Analysis of HRV................................................ 31
Exercise and Systolic BPV ......................................................................................... 32
Exercise and Aortic Pulse Wave Velocity .............................................................. 32
Exercise and Augmentation Index .......................................................................... 32
Exercise and Brachial Artery FMD......................................................................... 32
Exercise and Endothelium-Independent Dilation ................................................... 33
Pearson’s Correlation ............................................................................ 33
CHAPTER IV
DISCUSSION .................................................................................. .34
APPENDIX A
TABLES ........................................................................................... 45
APPENDIX B
FIGURES ......................................................................................... 54
REFERENCES.................................................................................................................... 90
iv
LIST OF TABLES
Table
A1. Cross-sectional Subject Characteristics ....................................................................... 45
A2. Cross-sectional Subject Blood Chemistry .................................................................. .46
A3. Frequency Domain Analysis of HRV: Cross-sectional Study ..................................... 47
A4. Frequency Domain Analysis of BPV: Cross-sectional Study ...................................... 48
A5. Baseline Brachial Artery Diameters ......................................................................... ....49
A6. Intervention Study Subject Characteristics ............................... ...................................50
A7. Intervention Study Blood Chemistry .......................................................... .................51
A8. Frequency Domain Analysis of HRV: Intervention Study ........................ ..................52
A9. Frequency Domain Analysis of BPV: Intervention Study ........................................... 53
v
LIST OF FIGURES
Figure
B1. Aortic Pulse Wave Velocity ......................................................................................... 54
B2. Baroreflex Sensitivity ................................................................................................... 55
B3. Heart Rate Variability: Time Domain Analysis of SDNN ........................................... 56
B4. Heart Rate Variability: Time Domain Analysis of RMSSD ........................................ 57
B5. Aortic Pulse Wave Velocity ............................................................................................ 58
B6. Augmentation Index .............................................................................................. 59
B7. Absolute Change in Brachial Artery FMD................................................................... 60
B8. Percent Change in Brachial Artery FMD ..................................................................... 61
B9. Absolute Change in Endothelium-Independent Dilation ............................................. 62
B10. Percent Change in Endothelium-Independent Dilation .............................................. 63
B11. Pearson Correlation: Absolute FMD and BRS........................................................... 64
B12. Pearson Correlation: Percent FMD and BRS ...................................................... 64
B13. Pearson Correlation: Absolute FMD and SDNN ...................................................... .65
B14. Pearson Correlation: Absolute FMD and RMSSD .................................................... 66
B15. Pearson Correlation: Percent FMD and RMSSD ..................................................... 67
B16. Pearson Correlation: BRS and APWV ....................................................................... 68
B17. Pearson Correlation: SDNN and APWV.................................................................... 68
B18. Pearson Correlation: RMSSD and APWV ................................................................. 69
B19. Pearson Correlation: AI and BRS .............................................................................. 70
B20. Pearson Correlation: AI and SDNN .............................................................. .70
B21. BRS and Exercise Intervention .................................................................................. 71
B22. BRS and Attention-time Control ................................................................................ 72
B23. SDNN and Exercise Intervention ................................................................. 73
B24. SDNN and Attention-time Control ............................................................... 74
vi
B25. RMSSD and Exercise Intervention ............................................................................ 75
.
B26. RMSSD and Attention-time Control .......................................................................... 76
B27. APWV and Exercise Intervention ........................................................................... ...77
B28. APWV and Attention-time Control............................................................................ 78
B29. AI and Exercise Intervention ...................................................................................... 79
B30. AI and Attention-time Control ................................................................................... 80
B31. Absolute FMD and Exercise Intervention ................................................................. .81
B32. Absolute FMD and Attention-time Control ............................................................... 82
B33. Percent FMD and Exercise Intervention ................................................................... .83
B34. Percent FMD and Attention-time Control ................................................................. .84
B35. Absolute EID and Exercise Intervention .................................................................... 85
B36. Absolute EID and Attention-time Control ................................................................. 86
B37. Percent EID and Exercise Intervention ...................................................................... 87
B38. Percent EID and Attention-time Control ................................................................... .88
B39. Pearson Correlation: BRS and APWV after Aerobic Exercise ................................. .89
vii
1
CHAPTER I
INTRODUCTION
Advancing age in humans is characterized by alterations in the integrative
regulation by the cardiovascular and autonomic nervous system (ANS) systems. Proper
function of the ANS is achieved through a balance of parasympathetic and sympathetic
outflow from the brain, and this balance is shifted with advancing age towards decreased
parasympathetic activity and increased sympathetic discharge to the heart, vasculature,
and other organs 1, 2. The arterial baroreflex is an important negative feedback regulator of
the cardiovascular system, modulating heart-rate and blood vessel tone to maintain
arterial blood pressure during acute alterations in blood pressure from various
physiological (e.g., change in posture, exercise) and pathophysiological (e.g.,
hemorrhage) demands. This reflex is comprised of multiple parts; the receptor, consisting
of stretch-sensitive nerve endings within the walls of the carotid sinus and aortic arch,
and the effector, through which autonomic outflow is conveyed to the heart and
vasculature via the vagus nerve and sympathetic efferents. Afferent signals from the
arterial baroreceptors terminate in the nucleus tractus solitarius (NTS) within the medulla
oblongata 3. From here, the signal is integrated in the hypothalamus and directly projected
to the nucleus ambiguous, the origin of cardiac parasympathetic activity, and to the
caudal ventrolateral medulla (CVLM), a relay station responsible for inhibition of the
rostral ventrolateral medulla (RVLM), the origin of the presynaptic outflow of the
sympathetic nervous system from the brain to the spinal cord 4. Central processing in the
medulla and hypothalamus integrates this response and results in the necessary
modifications of heart-rate and vascular resistance by altering sympathetic and
parasympathetic outflow from the NTS 3. In young healthy individuals, parasympathetic
nerve activity dominates at rest, sending efferent signals to the heart by way of the vagus
nerve. Cardiac vagal tone exerts a protective effect on the heart and vasculature 5, 6 by
blunting immediate large fluctuations (increases and decreases) in arterial blood pressure
2
through the baroreflex 5. Thus, proper regulation of blood pressure by the baroreflex is
essential to preserve cardiovascular health and homeostasis 7.
Aging and Autonomic Dysfunction
The ANS has been studied extensively in humans in the context of aging, and it is
well-documented that changes in ANS function occur with advancing age. There is a
progressive shift towards chronic over-stimulation of the sympathetic nervous system
with age, indicated by increased concentrations of plasma norepinephrine, the primary
neurotransmitter necessary for synaptic transmission of sympathetic neurons, and by
increased firing rates of sympathetic fibers during muscle sympathetic nerve
microneurography recordings 8. This increased sympathetic activity is followed by a
subsequent withdrawal in parasympathetic nerve activity ultimately resulting in
sympathetic dominance. The incidence of cardiovascular disease and the activity of the
sympathetic nervous system both increase with aging 9, and increasing clinical evidence
indicates a strong association between sympathetic overactivity and the development of
cardiovascular diseases 10. Many chronic diseases are accompanied by dysfunction of the
ANS resulting from sympathetic overactivity 9. Autonomic dysfunction is implicated in
aging and a variety of disease states, such as heart failure, chronic kidney disease 11,
hypertension, and diabetes mellitus 12, and also in the triggering of sudden cardiac death
13
. Therefore, understanding the mechanisms by which autonomic dysfunction contributes
to cardiovascular dysfunction, or how cardiovascular alterations may modulate
autonomic dysfunction, may be of great clinical importance in the prevention and
treatment of cardiovascular disease.
Clinical measures of autonomic function, such as cardiac baroreflex sensitivity,
heart-rate variability, and short-term BP variability, may help stratify patients at a higher
risk of developing cardiovascular disease. Baroreflex sensitivity and heart-rate variability
are important predictors of mortality following myocardial infarction 13, and increased
3
systolic blood pressure variability is an independent predictor of cardiovascular mortality
in the general population 14. These methods are non-invasive and cost-effective to
implement, have good reproducibility, and yield valuable physiological and clinical
insight into the effect of advancing age on the function of the ANS in humans.
Baroreflex Sensitivity
Proper function of the arterial baroreflex is essential for cardiovascular system
regulation and homeostasis, whereas an impaired reflex may exacerbate the conditions of
many diseases 15. Throughout this document, baroreflex sensitivity (BRS) will be
referring to the “cardiac baroreceptor-heart rate sensitivity reflex”, but it is important to
note that this is only one efferent arm of the arterial reflex. BRS can also be assessed nonpharmacologically by measuring the “sympathetic baroreflex”, which represents the
relation between mean arterial pressure and vasoconstrictor sympathetic nerve activity.
The sympathetic reflex is typically determined in humans by assessing changes in muscle
sympathetic nerve activity (recorded at the peroneal nerve via microneurography) in
response to acute changes in blood pressure. Therefore, the sensitivity of the “cardiacheart rate” and the “sympathetic” reflexes can differ considerably in humans. Cardiac
BRS, a quantifiable measure of the baroreflex, refers to the slope of the relationship
between heart rate and systolic blood pressure in response to an acute change in arterial
pressure 5, 7, 16. Heart rate response is represented by the change in the interval between
consecutive R waves (i.e. R-R interval) on an electrocardiogram (ECG), and the degree to
which the heart rate responds to the rise and fall of arterial pressure is quantified to yield
functional information regarding the sensitivity of this reflex. BRS declines with
advancing age in sedentary adults 17, 18, and is also reduced in a variety of adults with
clinical disease, such as hypertension, heart disease, and diabetes mellitus 7.
BRS is an established technique for the evaluation of autonomic control of the
cardiovascular system, and evidence suggests that changes in the sensitivity of the
4
baroreflex reflect alterations in autonomic control of this system 19. The “gold standard”
method used to assess BRS is known as the modified Oxford technique. This procedure
involves an intravenous injection of pharmacological agents to induce rapid systemic
changes in arterial blood pressure and cardiac cycle length. First, a bolus infusion of
sodium nitroprusside, a potent nitric oxide (NO) – producing vasodilator, is administered
to decrease arterial pressure. This is followed one minute later by a subsequent infusion
of phenylephrine hydrochloride, an α-adrenergic receptor agonist that binds to receptors
located in the arterial system that elicits vasoconstriction and a pressor effect (i.e.,
increase systolic blood pressure) and lengthening of the R-R interval 19. The slope of the
regression line between the change in R-R interval and systolic blood pressure is used as
an index of the sensitivity of baroreceptor-modulation of heart rate 15.
A non-pharmacological method to test cardiac BRS is the use of Valsalva’s
maneuver, in which the subject attempts to forcefully expire against a closed airway, is
often used to reflexively stimulate the arterial baroreceptors by increasing intrathoracic
pressure and reducing cardiac filling, resulting in reduced vagal outflow to increase heart
rate and maintain cardiac output. However, both of these methods can only be performed
under standardized laboratory conditions and therefore do not reflect baroreflex control in
real-life situations, as an external stimulus is required to stimulate alterations in heart rate
and blood pressure 15.
Recent interest has shifted to the development of new techniques to assess
baroreflex function in real-life situations, without external stimuli. The “sequence
technique”, first developed by Bertinieri, identifies four or more consecutive heart beats
where R-R interval and systolic blood pressure change in the opposite direction 20.
Similar to previous techniques, a regression line is fitted between the change in systolic
blood pressure and R-R interval, and the resulting slope yields an index of the sensitivity
of the baroreflex-modulation of heart rate. The sequence technique has the advantage of
assessing spontaneous changes in heart rate in response to changes in blood pressure in
5
real-life situations 15. It is also cheaper and easier to perform, has been validated against
the Oxford technique 21, and it does not require any drug infusions, thus reducing the risk
and potential side effects to patients.
Heart Rate Variability
ANS outflow is the main regulator of heart-rate variability (HRV) 22. Variability in
heart rate is a normal physiological process that results from the coupling of heart rate
with the respiratory cycle, with transient increases and decreases in variability known as
respiratory sinus arrhythmia 23. The resulting variation in heart rate can be used as a
surrogate measure of vagal control of the heart. Reduced cardiac vagal control results in
sympathetic dominance 13, and is an independent predictor of cardiac and cerebrovascular
mortality 5, therefore developing strategies to restore autonomic function and reducing
sympathetic dominance in older adults may reduce the age-related increased risk of CVD.
HRV refers to the fluctuations in the lengthening and shortening of the R-R
interval between consecutive heart beats on a continuous ECG recording 24. Baroreceptormediated changes reflect both short-term and long-term variability components of heart
rate. Short-term variability occurs as the result of the immediate response mediated by
efferent vagal activity, while sympathetic modulation occurs more slowly and is
represented by a long-term variability component. HRV can be detected in both the time
and frequency domain. Time domain measures calculate simple indexes of HRV and are
based on a time-series of normal R-R intervals. The standard deviation of the NN
intervals (SDNN) represents the variability between consecutive heart beats and is a
common measure derived in this method. SDNN characterizes the total variability of
heart rate and includes both long- and short-term indexes of HRV 25. Another index of
HRV derived from time domain analysis is the square root of the mean squared
differences of successive NN intervals (RMSSD). RMSSD is based on the comparison of
6
the length between adjacent cycles and is an estimate of the short-term components of
HRV 26.
Frequency domain analysis is a more complex method involving spectral analysis
of heart rate. Analysis in the frequency domain confers the advantage of separating high
and low frequency components of HRV, providing insight into the differential
contributions of the ANS. Parasympathetic activity is associated with the high frequency
(HF) range of HRV through the immediate vagal response produced by fluctuations in
respiration, while the low frequency (LF) range reflects a combination of sympathetic
and parasympathetic modulation of heart rate. The ratio of LF to HF components is also
used as an index of sympathovagal balance of cardiac autonomic function 25.
HRV calculated in both the time and frequency domains has been demonstrated to
decline with advancing age in humans 24, 25, and is an independent predictor of sudden
cardiac death 13, 25 and survival after myocardial infarction 27 in older adults. HRV also
independently predicts cardiovascular mortality in older adults 22, 24, 28 and is a powerful
clinical diagnostic tool to assess autonomic control of the cardiovascular system with
aging.
Short-term BPV
Autonomic modulation of heart rate blunts large fluctuations in arterial blood
pressure through the baroreflex, and these changes in blood pressure may provide insight
regarding neural regulation of the cardiovascular system 29. Continuous monitoring of
arterial blood pressure has shown considerable variability in the 24-hour blood pressure
profile of healthy subjects as blood pressure is known to exhibit a circadian rhythm with
marked day and night differences in addition to second-to-second changes modulated
through the baroreflex 30. However, 24-hr blood pressure recordings typically require the
subject to wear an automated device (i.e. Ambulatory BP monitor) that intermittently
measures blood pressure throughout the day and night. Short-term systolic blood pressure
7
variability (BPV) is a more practical measurement because it provides prognostic
information regarding cardiovascular mortality and is easier to perform. Therefore, these
recordings provide important diagnostic information regarding variability in blood
pressure but require expensive ambulatory blood pressure monitors to perform and are
inconvenient for the subject 31.
Higher systolic BPV measured every 30 minutes through 24-hour ambulatory
monitoring (standard deviation of 24 hour systolic BPV) has been demonstrated to
independently predict cardiovascular mortality in the general population. Systolic BPV
increases with advancing age, and increased BPV is associated with an obese and
hyperlipidemic-phenotype 14, along with increased cardiovascular morbidity and
mortality 32. Ambulatory 24-hr BPV can also be assessed as daytime and nighttime BPV.
Greater 24-hr BPV is highly predictive of the incidence of CVD events and CVD risk 33.
Very short-term BPV is estimated as the standard deviation of beat by beat blood
pressure recordings, and computer analysis allows for the signal to be broken down into
time and frequency domains, therefore reflecting an estimate of autonomic balance as it
pertains to blood pressure regulation 24.
Relationship among Autonomic Measures
Autonomic modulation of heart rate results in reflex changes in arterial blood
pressure through the baroreflex. Therefore, high BRS will result in increases in HRV
with reductions in BPV 34. Laitinen et al. 29 reported an inverse association between BRS
and BPV, suggesting that BPV may provide insight to sympathetic regulation of
cardiovascular control because BRS is predominantly associated with cardiovagal
control. In hypertensive patients, BRS is positively associated with HRV, and negatively
correlated to BPV 31. This may exist because of altered control of arterial blood pressure
as a result of hypertension, ultimately resulting in broader fluctuations in pressure (i.e.,
higher BPV) as the result of improper baroreflex-control of heart-rate. However, the same
8
inverse relationship between BRS and BPV, along with a positive correlation between
BRS and HRV has been reported in healthy, normotensive subjects 6. Therefore the
presence of a hypertensive-state cannot explain these associations.
Aerobic Exercise and Autonomic Dysfunction in Aging
Aerobic exercise training may be a useful intervention to improve autonomic
dysfunction in sedentary older adults. Regular aerobic exercise has beneficial effects on
the ANS and peripheral vasculature, and is associated with a reduced risk of
cardiovascular diseases 35. Post exercise alterations in BRS are observed following one
session of moderate-to-high intensity aerobic exercise 3, and chronic habitual exercise
may potentially attenuate the age-related changes in autonomic function. Monahan et al.
16
studied the effects of habitual exercise-training on BRS in healthy adults compared to
their sedentary counterparts and found that regular aerobic exercise attenuates and
partially restores the age-associated decline in BRS. However, the endurance-trained
older adults still displayed a significantly lower BRS when compared to the young
sedentary subjects, indicating that exercise training alone does not completely abolish the
age-related reduction in BRS seen in sedentary human aging.
Dixon et al. 36 reported increased HRV among highly endurance-trained young
adults compared to age-matched sedentary controls, suggesting positive alterations in
autonomic function as a result of habitual aerobic exercise. Consistent with this, HRV
increases in parallel with aerobic capacity in sedentary and recreationally active young
adults following multi-week aerobic exercise protocol training 37. However, the effect of
life-long endurance training on systolic BPV in middle-aged and older adults has been
poorly characterized in the literature. Therefore, the objectives of this study will compare
systolic BPV, BRS, and HRV between sedentary and endurance exercise-trained middleaged and older adults to determine the extent to which autonomic function is impaired in
middle-aged/older adults compared to young adults, and whether autonomic function is
9
augmented or preserved in endurance-trained adults compared to their age-matched
sedentary peers.
Aging and Large Elastic Artery Stiffness
Sedentary aging is associated with stiffening of the elastic arteries such as the
aorta and carotid arteries even in the absence of atherosclerotic CVD 35. This is the result
of both structural and functional changes that take place within the arterial wall of the
large elastic arteries. The large elastic arteries, predominantly the aorta, act to buffer the
forceful ejection of the heart’s stroke volume, thereby exerting a protective role on the
microcirculation, such as the brain and kidneys 38. This is accomplished by a healthy
supply of the protein elastin, the primary extracellular matrix protein deposited in the
arterial wall. Elastin in the arterial wall functions as a cushion to convert pulsatile blood
flow into continuous flow by allowing the vessel wall to expand against the high pressure
during systole and subsequently recoiling to its original conformation during diastole
allowing continuous blood flow termed “run off” 39. With aging there is a progressive loss
of elastin structure along with an increased deposition of collagen, a stronger, inflexible
protein that significantly reduces the distensibility of the vessel 40. Not surprisingly, older
adults have wider pulse pressures compared to younger adults due to a diminished recoil
mechanism in their stiffer elastic arteries resulting in elevated systolic blood pressure and
a reduced diastolic blood pressure compared to young adults. Consistent with this blood
pressure phenotype, the prevalence of isolated systolic hypertension increases with
advancing age and increases the predisposition to ischemia because coronary perfusion
occurs during diastole. Furthermore, arterial stiffening negatively impacts the heart by
increasing cardiac afterload and oxygen demand, leading to left ventricular hypertrophy,
and decreasing coronary perfusion, leading to an increased risk of cardiovascular disease
events 38.
10
Progressive large artery stiffening also causes an increase in the velocity of the
pressure wave as it travels to the periphery and back to the ascending aorta. Ventricular
ejection generates a pressure wave which propagates along the vessel wall relative to the
stiffness and distending pressure, whereby the pulse wave travels faster in a stiffer versus
compliant artery. In a young healthy vasculature, the pressure wave returns to the heart in
diastole, during coronary artery perfusion, resulting in the augmentation of diastolic
blood pressure and enhancing blood flow to the myocardium 41. In older adults,
thickening of the tunica media, the muscular component of the arterial wall, along with
increased collagen deposition and fragmentation of elastin fibers, results in stiffening of
the large elastic arteries. As a result, the pulse wave travels faster and the reflected wave
returns back to the heart earlier in systole in older adults, resulting in an augmentation of
the first systolic peak rather than diastolic blood pressure in the central arteries (i.e. aorta,
carotids) 38. However, the reflected wave hemodynamics, expressed as augmentation
index (AI), are complex and the timing and amplitude of the reflected wave are
influenced by other factors in addition to arterial stiffness, such as height, heart rate, LV
ejection time, peripheral vascular tone, and the degree of impedance mismatch between
central and peripheral arteries. Nevertheless, an increase in the velocity of the reflected
wave generally causes an earlier return to the ascending aorta (during systole), resulting
in increases in cardiac afterload by forcing the heart to pump against a higher pressure
while reducing myocardial perfusion as a result of a diminished or absent augmentation
of diastolic pressure 41.
Large Elastic Artery Stiffness and CVD Risk
Pulse wave analysis with non-invasive arterial tonometry is a commonly used
method to determine central arterial stiffness. Recent evidence suggests that the
parameters derived from the arterial pressure waveform are strong independent predictors
of cardiovascular disease events 42 Aortic pulse wave velocity (APWV), as assessed by
11
carotid-femoral pulse wave velocity (CFPWV), is a noninvasive clinical estimate of
aortic stiffness. CFPWV is estimated by dividing the anatomical distance from the carotid
to the femoral arteries by the time delay between the foot of the diastolic pressure
waveform in these vessels, and is illustrated in Figure B1. Elevated CFPWV is associated
with increased mortality among high-risk clinical populations, such as patients with endstage renal disease and hypertension. Moreover, CFPWV is a robust predictor of CVD
events and death even after adjusting for blood pressure and other CVD risk factors in
generally healthy, well-functioning older adults without CVD at baseline 41, 43.
Aortic Stiffness and Habitual Aerobic Exercise in Aging
Life-long physical activity is associated with lower aortic and carotid stiffness in
healthy middle-aged and older adults 44, 45. Indeed, endurance-trained older men
demonstrate reduced CFPWV compared to their sedentary peers, suggesting that regular
aerobic exercise and/or higher fitness may lessen the degree of arterial stiffening 46. Ageassociated increases in arterial stiffness are known to occur in both men and postmenopausal healthy women. This is clinically significant because the prevalence of
cardiovascular disease increases dramatically post-menopause. Habitual endurance
exercise training mitigates the increase in arterial stiffness in this population as no
differences have been observed in CFPWV and AI between endurance-trained postmenopausal women compared to pre-menopausal women who are physically active 47.
Pierce et al. 44 confirmed in a cross-sectional study that APWV increases with age in
sedentary adults, and habitual endurance exercise training attenuates this age-related
increase. However, it is unclear whether exercise training initiated in middle-aged and
older adults can improve aortic stiffening assessed by APWV.
Aerobic exercise, both life-long and over short periods of time, causes modest
reductions in blood pressure in middle-aged and older adults, but is influenced by the
type, intensity and duration of exercise and whether hypertension is present or not 48. In
12
contrast, CFPWV did not change following 6-months of aerobic and resistance training in
previous sedentary adults with mild untreated hypertension 49. Beck et al. 50 reported
improvements in arterial stiffness and AI following 8-weeks of endurance exercising
training in young previously sedentary adults with pre-hypertension, but the effects of
exercise training on arterial stiffening in previously sedentary middle-aged and older
adults free of clinical disease remains inconclusive.
Aging and Peripheral Vascular Endothelial Dysfunction
The vascular endothelium is a single layer of cells lining the internal surface of
blood vessels. It forms a barrier between the circulating blood and the vessel wall, and
plays a pivotal role in regulating vascular health through the production of various
bioactive molecules. Blood vessel diameter (i.e., tone) is in a constant state of flux due to
competing effects of vasodilators and vasoconstrictors to maintain flow to vital organs 51.
Endothelial dysfunction refers to functional changes in the endothelial layer resulting in a
pro-constrictor phenotype presumably as the result of reduced production or bioavailabity
of the endothelium-derived vasodilator nitric oxide (NO). Vascular endothelial
dysfunction develops with advancing age, and is attributable, in part, to the development
of cardiovascular disease 52. Endothelium-dependent dilation (EDD) is one method to
quantify endothelial dysfunction by measuring the capacity of the endothelium to respond
to changes in blood flow, either by pharmacological infusion of vasoactive drugs or
through mechanical shear stress induced using reactive hyperemia blood flow in response
to reperfusion after a brief episode of limb ischemia from a blood pressure cuff 35.
Importantly, impaired EDD develops with advancing age and may contribute to the
development of atherosclerosis 53. Brachial artery flow-mediated dilation (FMD), a
clinical expression of EDD results in an acute transient increase in the diameter of the
brachial artery within one minute after release of distal cuff occlusion of the forearm.
Brachial artery FMD can be used to assess the response of the endothelium to exercise,
13
weight loss, or a pharmacological intervention. Importantly, impaired FMD is associated
with an increase in the incidence of cardiovascular events independent of CVD risk
factors in middle-aged and older adults without CVD at baseline. Therefore, brachial
artery FMD may potentially be used as a surrogate endpoint, and may be a modifiable
risk factor that may predict the effectiveness of interventions on CVD risk 54.
Vascular Endothelial Function and Habitual Aerobic Exercise in Aging
Cross-sectional and intervention studies clearly demonstrate improvements in
EDD following regular aerobic exercise training in middle-aged and older men 45, 52, 54, 55 ,
but the effects of aerobic exercise in postmenopausal women may be less effective 54
unless in the presence of estrogen replacement 56. Regular aerobic exercise prevents the
age-related reductions in EDD by increasing NO bioavailability through the activation of
NO synthase, the enzyme required for NO production. This may explain in part why
older adults who exercise regularly have a lower incidence of CVD compared to their
sedentary counterparts 35. Sedentary older men exhibit a reduction in brachial FMD
compared to their endurance-trained peers, and FMD is improved by 8 weeks of
moderate-intensity aerobic exercise 54. In contrast, no change in FMD was observed in
post-menopausal females after 8 weeks 54 or 12 weeks of aerobic exercise training 56.
Franzoni et al. 55 confirmed the age-related differences in FMD between young and old
sedentary men, and sedentary and endurance-trained adults, and found increased levels of
oxidative stress with aging and an increased antioxidant capacity in the runners,
demonstrating habitual aerobic exercise mitigates the development of endothelial
dysfunction that occurs in aging. Improvements in FMD have also been demonstrated
following intravenous infusion of the antioxidant ascorbic acid in older sedentary men
but not in endurance trained older men who have preserved EDD, with no observed
change in endothelium-independent dilation in response to sublingual nitroglycerin.
Taken together, these data suggest a mechanistic role of vascular oxidative stress in the
14
attenuation of peripheral conduit artery endothelial function in sedentary men, and that
exercise likely improves EDD in part from prevention of the development of vascular
oxidative stress mediated suppression of EDD 57.
Habitual Aerobic Exercise and Autonomic Dysfunction and Large Elastic Artery
Stiffness and Peripheral Vascular Endothelial Dysfunction in Aging
Autonomic dysfunction, aortic stiffening and endothelial dysfunction occur in the
context of healthy human sedentary aging, but little has been done to determine the
relationship between the three physiological outcomes. Age is an independent risk factor
for large artery stiffening and endothelial dysfunction 43, and also for reduced sensitivity
of the baroreflex 17, but it is unknown whether these measures of autonomic and vascular
function are related. Therefore, the purpose of this study is to characterize the extent to
which impaired autonomic function and aortic stiffening and endothelial dysfunction in
sedentary older adults is attenuated in endurance trained older adults. However, it is
unclear whether impairments in autonomic function cause dysfunction in the central and
peripheral vasculature, or if stiffer large elastic arteries and dysfunctional endothelium
lead to impaired autonomic regulation. As such, stiffening of the large elastic arteries
may itself result in reduced sensitivity of the baroreflex independent of peripheral
endothelial function by preventing normal detection of stretch in a non-compliant
vascular wall. This study will evaluate whether age-related autonomic dysfunction is
associated with impaired endothelial function and increased aortic stiffness in sedentary
young and middle-aged and older sedentary and endurance trained adults
Longitudinal studies comparing the effect of exercise training on HRV have
produced conflicting results. For example, some studies show improvements in HRV
following training between young and old subjects, and others finding no significant
increase in HRV in older subjects following exercise. Uusitalo et al. 24 reported no
significant improvements in HRV or systolic BPV following a 5-yr, low intensity,
15
aerobic exercise training intervention but greater than half of their subject population
used regular medications due to the presence of various metabolic or cardiovascular
diseases, thus potentially confounding their results. However, no studies have examined
the effects of exercise on HRV, BRS, systolic BPV, EDD, and APWV together in the
same cohort of middle-aged and older subjects. Therefore, this study will also examine
the extent to which measures of autonomic function are improved following 8 weeks of
daily aerobic exercise training in previously sedentary adults, and if this improvement is
associated with reductions in aortic stiffness and peripheral vascular endothelial function.
Hypotheses and Study Aims
To achieve the goals of this study we will conduct the following specific aims:
Aim 1: To characterize the extent to which the age-related reduction in autonomic
function is blunted in habitual physically active middle-aged and older humans, and the
association of autonomic function with central aortic stiffness and peripheral vascular
endothelial function.
Hypothesis 1: We predict that BRS, very short-term systolic BPV and HRV will be
impaired in middle-aged/older sedentary but not physically active older adults, and will
be associated with APWV and brachial artery FMD.
Aim 2: To determine the extent to which autonomic function is improved by 8 weeks of
daily aerobic exercise in previously sedentary adults and is associated with reductions in
aortic stiffness and enhanced peripheral vascular endothelial function.
16
Hypothesis 2: We predict that BRS, short-term systolic BPV and HRV will improve after
8 weeks of exercise in middle-aged/older sedentary adults but not attention-time controls,
and will be associated with reductions in APWV and increases in brachial artery FMD.
17
CHAPTER II
METHODS
The following data were derived from a subset of a subjects from NIH grant
AG013038 funded by Douglas Seals as a study conducted by Dr. Gary L. Pierce while
supported by NIH T32 AG000279.
Subject Recruitment & Study Design
A total of 45 subjects were recruited from the community for the cross-sectional
study. Subjects were subdivided into 3 groups based on age and exercise training status
including: 6 young sedentary (YS) adults (age 18-31 years), 25 middle-aged/older
sedentary (OS) adults (age 55-71 years) constituted two groups. The third group was
comprised of 15 endurance-exercise trained older (OT) adults (age 55-76 years) who had
been performing regular vigorous aerobic-endurance exercise (competitive distance
running, cycling, and/or triathlons) >45 min/day, ≥5 days/week for at least the previous 5
years.
Of the 25 OS adults, 18 were randomized to either an 8-week aerobic exercise
intervention program or an attention-control non-exercise group. Subjects in the exercise
intervention were instructed to walk 40-50 minutes/day for 6-7 days/week at 70-75% of
maximal heart rate determined during a maximal treadmill exercise test for a total of 8
weeks. Maximal oxygen consumption (VO2 max) was assessed using respiratory gas
analysis during incremental treadmill exercise using a modified Naughton protocol
performed to exhaustion. Subjects were given a Polar heart rate monitor that was preprogrammed to beep when the subject was no longer exercising in the heart rate training
range. The monitor also recorded heart rate during each training session, and this data
was downloaded every 2 weeks at the research facility. Subjects also kept an exercise log
where they recorded heart rate, rating of perceived exertion, and any other discomforts or
issues that occurred during each session. The monitors and logs were reviewed every 2
18
weeks with the study staff to confirm compliance with the exercise prescription and to
have their body weight and blood pressure assessed. The aerobic exercise intervention
used is associated with excellent subject adherence and does not produce weight loss or
other improvements in conventional risk factors for CVD that could complicate
interpretation of results. Subjects in the non-exercise control group were instructed not to
change their physical activity or diet, and met with the study staff every 2 weeks for body
weight, heart rate, and blood pressure assessment. The details of the final results of the
exercise intervention have been published elsewhere (Pierce Clin Sci 2011).
All subjects were non-smokers, non-obese, non-diabetic and free of overt
cardiovascular disease as assessed by a medical history questionnaire, physical
examination, resting and maximal exercise ECG and blood pressure, and blood
chemistry. They were not taking any prescription medications, herbal supplements, or on
antioxidant therapy. Women were postmenopausal for minimum 1 year and had not taken
hormone replace therapy for at least 6 months prior to this study.
Subject Characteristics
Body mass index (BMI) was calculated as a function of height and weight (kg/m2)
and waist and hip circumferences were measured using anthropometry. Dual energy x-ray
absorptiometry (DPX-IQ, GE/Lunar, Inc.) was used to calculate total body fat
percentage. Blood pressure and heart rate were measured at least three times in the supine
position following 15 minutes of rest using a semi-automated device (Dynamap, XL,
Johnson and Johnson), and the reported values represent the mean. Subjects completed 3day food intake records (The Food Processor 8.2, ESHA Research) from which caloric
intake and diet composition were estimated.
19
Blood Chemistry
All assays were performed at the University of Colorado at Denver and Health
Sciences Center Adult Clinical and Translational Research Center (CTRC) core
laboratory. Fasting serum concentrations of glucose, insulin, total cholesterol (TC), lowdensity lipoprotein (LDL-C) cholesterol, high-density lipoprotein (HDL-C) cholesterol,
triglycerides, and white blood cell (WBC) count were measured using standard assays.
Oxidized LDL (Alpco, Inc.) was measured using ELISA. High-sensitivity Chemistry
Immuno Analyzer (AU400e, Olympus America, Inc.) was used to measure serum
concentrations of C-reactive protein (CRP), and serum norepinephrine was determined by
high performance liquid chromatography.
Measurements
All measurements were performed at the University of Colorado at Boulder
Clinical and Translational Research Center (CTRC) following a 12-hour overnight fast
and 24-hour abstention for exercise and alcohol. Subjects were fitted with a standard 3lead electrocardiogram (ECG) for continuous monitoring of cardiac function and an intraarterial catheter to capture continuous peripheral blood pressure waveforms. The blood
pressure and ECG recordings were digitized and transmitted using Windaq Data
Acquisition software. All measurements were made in the supine position after 15
minutes of resting conditions.
Data Analysis
Baroreflex Sensitivity via the Sequence Technique
BRS was evaluated using the Analyzer component of the Hemolab software
package (Harald-Stauss Scientific, Iowa City, IA). The sequence technique identifies
sequences of four or more consecutive beats where heart rate and blood pressure
simultaneously change in the opposite direction, and an average regression slope is
20
calculated representing sensitivity of the baroreflex in milliseconds per millimeter of
mercury. The continuous blood pressure recordings were reviewed from each subject file
individually and any artifacts were removed prior to analysis. Artifacts constituted any
interruption in the signal recording, such as extrasystoles, premature beats, or patient
movement which would visibly affect the signal recording, and the resulting segments
were replaced by interpolated values generated by the software. A low-pass Butterworth
filter was then applied at a frequency of 20 Hz to further remove any background noise
and ensure analysis of the best-quality segments. A fixed delay of two beats was applied
to represent the time delay between baroreceptor activation and sympathetic outflow.
Heart Rate Variability: Time Domain Analysis
HRV in the time domain was calculated using the Hemolab software. The subject
ECG and blood pressure recordings were loaded into the Analyzer component of the
software. Prior to analysis, each ECG was reviewed to remove all artifacts, and a lowpass Butterworth filter of 20 Hz was applied to eliminate any background noise. A time
series of heart rate was then generated from the subjects ECG and the resulting file was
saved. This file was loaded into the Batch processor component of the software where the
standard deviation of all NN intervals (SDNN) and square root of the mean squared
difference between successive NN intervals (RMSSD) were calculated as time domain
HRV parameters.
Heart Rate and Blood Pressure Variability: Frequency Domain Analysis
HRV and systolic BPV were analyzed in the frequency domain to differentiate
between the relative contributions of the components of the autonomic nervous system
(e.g., sympathetic vs. parasympathetic) to heart rate and systolic BPV. Power spectral
analysis was performed using the Fast Fourier Transform (FFT), which employs a
complex algorithm to break down the signal into spectra based on frequency. Power
21
spectra were separated into three frequencies according to the standards set forth by the
Task Force of the European Society of Cardiology 58, whereby the spectra were analyzed
in the very low frequency (VLF) range (≤0.04 Hz), low frequency (LF) range (0.04-0.15
Hz), and high frequency (HF) ranges (0.15-0.4 Hz).
HRV and systolic BPV were determined from 5 minute blood pressure and ECG
recordings. First, the beat by beat time series of heart rate were converted to equidistant
time series using the Batch Processor module within the Hemolab software package.
These files were loaded into the Batch Processor a second time, and power spectra were
created and analyzed at the three frequency ranges. The areas under the curve were
calculated for the following parameters of HRV and systolic BPV: VLFa (absolute), VLFr
(relative), LFa, LFr, HFa, HFr, LF: HF ratio, and total spectral power.
Aortic Pulse Wave Velocity
Aortic pulse wave velocity (APWV) was calculated and is used as a measure of
aortic stiffness. This technique measures the velocity of the pulse wave as it travels from
the aorta to the femoral artery, where a higher APWV indicates greater stiffening of the
large elastic arteries. Each subject’s peripheral blood pressure waveforms were loaded
into the Analyzer module of the Hemolab software package, and reviewed to remove any
artifacts. A low-pass Butterworth filter was applied to the continuous blood pressure
waveforms to eliminate any background noise. A mathematical transfer function was
applied to reconstruct the aortic (central) pressure from the peripheral pressure waveform.
The aortic pressure wave was then decomposed down into the forward and reflected
waves and the time delay between them was computed as previously described 44.
Effective reflecting distance was calculated using a published regression equation that
includes age and body mass index 44, and this was divided by the computed time delay
between the forward and reflected waves to calculate APWV for each subject.
22
Brachial Artery Flow-Mediated Dilation
Brachial artery diameter in response to reactive hyperemia was imaged using
high-resolution ultrasonography as a measure of endothelium-dependent dilation. This
technique measures the change in vessel diameter in response to rapidly increased blood
flow after the release of a forearm-occluding blood pressure cuff for 5 minutes. First, the
subject lay supine with the right arm extended to the side, and images of the brachial
artery are obtained longitudinally approximately 3-6 cm proximal to the antecubital
space. The resolution was adjusted until the intimal layers of the vessel wall were
apparent. A blood pressure cuff was then placed around the forearm distal to the
olecranon, and the artery diameter and Doppler velocities were continuously recorded 30
sec. before, during, and after 2 minutes after a 5-minute cuff occlusion at a pressure of
250 mmHg. Vessel diameter measurements were determined at end-diastole, determined
by the R wave on a simultaneously recorded ECG. Brachial artery FMD is reported as the
percent change and absolute change from baseline to peak flow-induced brachial artery
diameter.
Brachial Artery Endothelium-Independent Dilation
Brachial artery diameter in response to 0.4 mg sublingual glyceryl trinitrate
(GTN) was imaged using duplex ultrasonography as a measure of endotheliumindependent dilation. The subjects were instructed to remain in the supine position for 5
minutes immediately following the conclusion of the FMD measurements. Subjects were
then given a sublingual GTN tablet to induce peripheral vasodilation. Longitudinal
images of the brachial artery were obtained 3-6 cm proximal to the antecubital space for
10 minutes after the GTN to measure the subsequent absolute and percent change of
vasodilation in the brachial artery.
23
Statistical Analysis
All analyses were performed using SPSS 19.0, (SPSS, Inc.) and Microsoft Excel.
All data are presented as mean ± standard error. Statistical significance was set an alpha
level of P < 0.05. Analysis of variance (ANOVA) was used to compare differences
between the three groups in the cross-sectional study. When a significant main effect was
observed, a least significant differences (LSD) post-hoc test was performed to determine
between group differences. For the intervention study, a 2x2 repeated measures ANOVA
was performed to identify a group (Exercise, Control) x time (Baseline, 8 weeks)
interaction between outcome variables before and after 8-weeks of aerobic exercise or
attention-control. If significant interactions were present, a paired t-test with Bonferonni
correction was performed to identify differences of within-group factors. A Pearson’s
correlation was performed to assess the relations of interest between autonomic and
vascular measurements.
24
CHAPTER III
RESULTS
Subject Characteristics
Cross-sectional subject characteristics are presented in Table A1. The average age
of the subject groups was 22 ±2 years for the young sedentary adults, 62±1 years for
the older sedentary adults, and 61±2 years for the endurance exercise-trained adults.
Older sedentary and endurance trained older adults had a greater total body mass
compared to the young sedentary adults, but not a significantly different body mass
compared to each other. Body mass index (BMI) and total body fat percentage were also
significantly greater in the older sedentary and endurance trained older adults compared
to the young sedentary adults. However, endurance trained older adults had a
significantly lower BMI and total body fat compared to their sedentary age-matched
peers likely as the result of the positive effects of chronic exercise on body composition.
Both the older sedentary and endurance trained adults had a greater waist circumference
and waist: hip ratio compared to the young sedentary adults. Hip circumference was
greater in the older sedentary compared to the young sedentary adults, but not
significantly different than the endurance trained older adults. Systolic and diastolic
blood pressures were similar in the sedentary and endurance trained older adults, and
expectedly greater than the young sedentary adults. Young sedentary adults had a lower
resting heart rate compared to older sedentary adults. As expected, endurance trained
older adults had a significantly lower resting heart rate compared to older sedentary
adults, and no difference was observed in resting heart rate between the older trained and
young sedentary adults, indicating a positive effect of chronic endurance exercise on
resting heart rate with aging.
25
Blood Chemistry
Cross-sectional subject blood chemistry is presented in Table A2. No differences
were observed in serum glucose or insulin concentrations between groups. Triglyceride
concentrations and white blood cell count were also similar between groups. Older
sedentary adults had significantly higher concentrations of serum total and LDL
cholesterol compared to young sedentary and endurance trained older adults. There was a
trend towards higher total cholesterol concentrations in the endurance trained older adults
compared to the young sedentary adults, but this did not reach significance (p=0.059).
HDL cholesterol concentrations were similar between groups. C-reactive protein (CRP)
concentrations were not significantly different between the young and older sedentary
adults, but there was a trend towards elevated serum CRP in the older sedentary adults
(p=0.063). CRP concentrations were attenuated in endurance trained older adults
compared to their age-matched sedentary peers, suggesting a possible reduction in
systemic levels of oxidative stress in older adults who perform chronic endurance
exercise training. However, no differences were observed in serum oxidized LDL
concentrations between groups. Expectedly, serum norepinephrine concentrations were
greater in older sedentary and endurance trained older adults compared to young
sedentary adults, consistent with known increases in sympathetic nervous system activity
with advancing age in humans.
Baroreflex Sensitivity
BRS data are presented in Figure B2. BRS was ~71% lower in older compared
with young sedentary adults (11.7 ± 1.4 vs. 40.7 ± 8.6 ms/mmHg, p<0.05) confirming the
age-related decline in baroreceptor-heart rate reflex sensitivity function. Endurancetrained older adults demonstrated ~52% higher BRS compared to their sedentary agematched counterparts (24.4 ± 4.0 vs. 11.7 ± 1.4 ms/mmHg, p <0.01) suggesting positive
alterations in spontaneous baroreflex-heart rate sensitivity as a result of habitual aerobic
26
exercise. No statistical difference was detected between young sedentary adults and
endurance-trained older adults (p=0.07), but there was a trend towards greater (40%)
BRS in the young sedentary adults.
Heart Rate Variability: Time Domain
Time domain analysis of HRV data are presented in Figures B3 and B4. Standard
deviation of the NN intervals (SDNN), a measure of both the low and high frequency
components of HRV and an index of the total variability of heart rate, was 43% less in
older compared with young sedentary adults (52.7 ± 5.3 vs. 93.7 ± 6.5 ms, p<0.0005),
confirming a reduced autonomic modulation of heart rate with advancing age. Aerobic
endurance-trained older adults displayed ~41% greater SDNN compared to sedentary
older adults (89.7 ± 8.4 vs. 52.7 ± 5.3 ms, p<0.0001), suggesting improvements of
autonomic control of HRV with chronic endurance exercise training. However, we
cannot rule out that differences in resting heart rate caused the age-related differences in
SDNN and preserved SDNN in older endurance trained adults. No statistical significance
was found between young sedentary adults and exercise-trained older adults for SDNN.
The root mean squared difference of successive NN intervals (RMSSD), a HRV
index highly dependent on cardiac vagal tone, was reduced ~65% in sedentary older
compared to young sedentary adults (32.5 ± 4.3 vs. 92.8 ± 10.3 ms, p<0.001). RMSSD
was ~49% higher in the endurance-trained older compared to the sedentary older adults
(63.8 ± 8.6 vs. 32.5 ± 4.3 ms, p<0.01), but did not restore it to levels observed in young
adults (63.8 ± 8.6 vs. 92.8 ± 10.3 ms, p<0.05). These data suggest that the age-related
reduction in vagal tone in older adults was only partially restored in older endurance
trained adults and that the remaining differences in RMSSD between the older endurance
trained and young sedentary adults were not explained by differences in heart rate
because heart rate was similar.
27
Heart Rate Variability: Frequency Domain
Table A3 lists the HRV parameters calculated in the frequency domain. The
frequency data were natural log transformed before statistical analysis because the data
were not normally distributed. The absolute VLF and LF components and LF/HF ratio
were similar between groups. Both the endurance trained and sedentary older adults
displayed a significantly lower absolute HF component compared to the young sedentary
adults. The relative LF component was significantly reduced in young sedentary
compared to the older sedentary and endurance trained older adults. The relative HF
component was greater in the young sedentary compared to the older sedentary adults,
but no difference was observed between the young sedentary and endurance trained older
adults. Total Power was significantly reduced in both the sedentary and endurance trained
older adults compared to the young sedentary adults, suggesting an age-related reduction
in high and low frequency HRV that is not affected by chronic endurance exercise
training.
Systolic Blood Pressure Variability: Frequency Domain
Frequency domain components of systolic BPV are presented in Table A4.
Absolute VLF and LF components were significantly greater in the sedentary and
endurance trained older adults compared to the young sedentary adults, but there was no
observed difference between either older groups. However, VLF is highly dependent on
mean blood pressure, so a higher systolic blood pressure in both older groups may have
partly explained these findings. No significant difference in the absolute HF component
was observed between groups. Older sedentary and endurance trained older adults
displayed significantly greater total power, a measure of overall variance of systolic
blood pressure, compared to the young sedentary adults. However, this is likely the result
of the increased absolute VLF and LF components in the older groups compared to the
young sedentary adults.
28
Aortic Pulse Wave Velocity
APWV data are presented in Figure B5. APWV was ~52% higher in older
sedentary adults (9.7 ± 0.2 vs. 6.1 ± 0.4 m/sec, p<0.0001) confirming previous studies
that demonstrate increased stiffening of the aorta with aging. Endurance-trained older
adults had ~18% lower APWV values compared to sedentary older adults (8.0 ± 0.3 vs.
9.7 ± 0.2 m/sec, p<0.001) suggesting that chronic endurance exercise prevents the agerelated increase in aortic stiffness. However, habitual aerobic exercise did not completely
abolish the age-related increase in aortic stiffness in older humans, because APWV in the
endurance-trained older adults remained significantly elevated compared to the young
sedentary adults (8.0 ± 0.3 vs. 6.1 ± 0.4 m/sec, p<0.0001).
Augmentation Index
AI data are presented in Figure B6. Older sedentary adults exhibited significantly
greater AI compared to young sedentary adults (35 ± 2 vs. 10 ± 3%, p<0.001) likely in
part from the greater early return and/or increased amplitude of the reflected wave from
the periphery back to the ascending aorta in older adults. AI was attenuated in exercisetrained older adults compared to their sedentary counterparts (26 ± 3 vs. 35 ± 2%,
p<0.01), suggesting beneficial effects of habitual aerobic exercise on augmentation
pressure and cardiac afterload. Not surprisingly, the endurance-trained adults displayed
greater AI compared to young sedentary adults (26 ± 3 vs. 10 ± 3%, p<0.001), therefore
habitual aerobic exercise does not completely restore the age-related increase in AI.
Brachial Artery Flow-Mediated Dilation
Figure B7 shows the absolute change in brachial artery FMD data. Baseline
brachial artery diameters were similar between young and older sedentary adults, and are
listed in Table A5. Older sedentary adults displayed a significantly reduced absolute
change in brachial artery diameter compared with young sedentary adults (0.19 ± 0.02 vs.
29
0.24 ± 0.02 mm, p< 0.05), and compared with endurance-trained older adults (0.19 ± 0.02
vs. 0.25 ± 0.03 mm, p< 0.05), confirming an age-related decline in endothelial function,
that is improved by chronic endurance exercise training. No group differences were
observed between young sedentary adults and endurance-trained older adults, suggesting
that the age-related reduction in FMD is abolished with habitual endurance exercise.
Percent change in brachial artery FMD data are presented in Figure B8. No group
differences were observed in the percent change in brachial artery FMD. This is likely
explained in part from differences in baseline diameter and the small sample size (n=6) of
the young sedentary group.
Endothelium-Independent Dilation
Absolute change in brachial artery diameter following GTN administration data
are presented in Figure B9. No statistical difference in endothelium –independent dilation
was found between sedentary and endurance-trained older adults (p=0.14).
Percent change in brachial artery diameter following GTN administration data are
presented in Figure B10. No statistical difference was found between sedentary and
endurance-trained older adults (p=0.16). GTN-mediated FMD data were available for 22
older sedentary adults and 6 exercise-trained older adults.
Pearson’s Correlations
BRS was positively correlated with both absolute and percent change in brachial
artery FMD (Figures B11 and B12). Time domain measures of HRV also positively
correlated with brachial artery FMD (Figures B13-B15). SDNN was positively correlated
with the absolute change in brachial artery FMD, and RMSSD was found to be positively
correlated with both absolute and percent change in brachial artery FMD.
A negative correlation was found between BRS and APWV (Figure B16), and
this association remained after adjusting for age and mean arterial pressure (partial r= -
30
0.55, p<0.05). Negative correlations were also observed between APWV and time
domain measures of HRV (Figure B17 and B18). A negative correlation was found
between SDNN and APWV, and between RMSSD and APWV. However, these relations
were no longer significant after adjusting for age and mean arterial pressure (SDNN vs
APWV, r= -0.29, p=0.08; RMSSD vs APWV, r= -0.20, p=0.23). AI was also found to be
negatively correlated with BRS and SDNN (Figure B19 and B20).
Exercise Intervention Subject Characteristics
Subject characteristic data for the exercise intervention and attention-time control
subjects following 8 weeks of moderate-intensity endurance exercise or attention timecontrol are presented in Table A6. Subjects in the exercise intervention and attention-time
control groups were similar in age, weight, BMI, body fat percentage, waist
circumference, hip circumference, and waist: hip ratio. No group differences were
observed for systolic and diastolic blood pressure, resting heart rate, and VO2 max.
No change in weight, BMI, body fat percentage, waist circumference, hip
circumference, and waist: hip ratio was observed following 8 weeks aerobic exercise
training in the exercise intervention or attention-time control groups. Systolic and
diastolic blood pressures also did not change following 8 weeks aerobic exercise. No
differences in resting heart rate or VO2 max were observed following 8 weeks aerobic
exercise intervention or attention-time control.
Exercise Intervention Blood Chemistry
Table A7 lists the blood chemistry before and after 8 weeks of moderate-intensity
aerobic exercise in exercise intervention and attention-time control subjects. No
differences were observed between the exercise intervention and attention-time control
groups in serum glucose, HDL cholesterol, triglycerides, oxidized LDL, CRP, and plasma
norepinephrine at baseline or following 8 weeks aerobic exercise intervention or
31
attention-time control. Total and LDL cholesterol concentrations were also similar
between the exercise intervention and attention-time control subjects.
Exercise and Baroreflex Sensitivity
BRS values before and after 8 weeks of aerobic exercise intervention or attentiontime control are presented in Figures B21 and B22. No significant differences were
observed in BRS following 8 weeks of aerobic exercise intervention or attention-time
control.
Exercise and Time Domain Analysis of HRV
Figures B23-B24 show the overall variability component of the time domain
analysis of HRV data. SDNN increased following 8 weeks of aerobic exercise in the
exercise intervention group (46.9 ± 4.7 vs. 70.5 ± 9.4 ms, p<0.05) but not in the
attention-time control group, although this may be explained in part by the nonsignificant reduction on resting heart rate from the exercise intervention. RMSSD data is
present in Figures B25-B26. No change was observed in RMSSD following 8 weeks of
attention-time control. There was a trend towards an increase in RMSSD following 8
weeks aerobic exercise in the exercise intervention, but this did not reach significance
(p=0.08).
Exercise and Frequency Domain Analysis of HRV
Frequency domain analysis of HRV data between attention-time control and
exercise intervention subjects before and after 8 weeks aerobic exercise training are
presented in Table A8. The frequency data were natural log transformed because the data
were not normally distributed. No differences in the frequency domain parameters of
HRV were observed between the exercise intervention and attention-time control groups
at baseline, and the absolute and relative spectral components of VLF, LF, HF, TP, and
32
LF/HF ratio did not change following 8 weeks of aerobic exercise training or attentiontime control.
Exercise and Systolic BPV
Table A9 lists the frequency domain data of the absolute spectral components of
systolic BPV before and after 8 weeks of aerobic exercise intervention or attention-time
control. No differences were observed in any of the spectral components of systolic BPV
at baseline or following 8 weeks of endurance exercise in the exercise intervention or
attention-time control groups.
Exercise and Aortic Pulse Wave Velocity
APWV data before and after 8 weeks of aerobic exercise in the exercise
intervention and attention-time control groups are presented in Figures B27 and B28. No
significant differences were observed following 8 weeks of endurance exercise or
attention-time control.
Exercise and Augmentation Index
Figures B29 and B30 show the AI data following 8 weeks of aerobic exercise in
the exercise intervention and attention-time control groups. No significant differences
were observed in AI following 8 weeks of aerobic exercise intervention or attention-time
control.
Exercise and Brachial Artery FMD
Absolute and percent change in brachial artery FMD between the exercise
intervention and attention-time control subjects following 8 weeks moderate-intensity
aerobic exercise are presented in Figures B31-B32 and B33-B34. No significant
differences were observed in absolute or percent change in FMD in exercise intervention
33
or attention-time control subjects following 8 weeks of aerobic exercise intervention or
attention-time control. Pierce et al. 54 observed significant improvements in both absolute
and percent change in brachial artery FMD following 8 weeks of aerobic exercise
intervention in previously sedentary men, but not post-menopausal women. However, our
study was a subset of this larger cohort, therefore our lack of differences in percent
change in FMD are likely due to the smaller sample size in this study.
Exercise and Endothelium-Independent Vasodilation
Absolute and percent change in brachial artery diameter in response to GTN
between the exercise intervention and attention-time control group data are presented in
Figures B35-B36 and B37-B38. No differences in absolute or percent change in GTNmediated endothelium-independent vasodilation were observed following 8 weeks of
aerobic exercise intervention or attention-time control.
Pearson’s Correlation
Figure B39 shows the correlation between the change in BRS and the change in
APWV. A significant negative correlation was observed between the change in BRS and
the change in APWV (r= -0.58, p<0.05) following 8 weeks of aerobic exercise
intervention suggesting that the reduction in aortic stiffness was related to the
improvement in baroreflex-heart rate function sensitivity following 8 weeks of aerobic
exercise intervention in older adults.
34
CHAPTER IV
DISCUSSION
Our study has 7 primary findings: (1) we confirmed the age-related decline in
cardiac baroreceptor-heart rate reflex sensitivity, as assessed by the sequence technique,
through a ~71% lower BRS in older compared with younger sedentary adults. However,
this age-related reduction in BRS was partially attenuated in older endurance-trained
adults in that BRS was only 40% reduced in this group; (2) we confirmed that sedentary
adults demonstrate an age-related increase in aortic stiffness that is partially attenuated in
older endurance-trained adults but not restored back to levels of young adults. We report
for the first time that higher aortic stiffness, measured by indirectly computing APWV
from a single brachial artery blood pressure waveform, was associated with lower BRS
that remained significant after adjusting for age and mean blood pressure; (3) we
observed an age-associated decline in time domain measures of HRV by demonstrating
reduced SDNN and RMSSD between older and young sedentary adults and that RMSSD
was partially improved with habitual aerobic exercise. In contrast, although relative and
total power HRV assessed in the frequency domain were reduced with aging, there was
no clear modifying effect of aerobic exercise; (4) short-term systolic BPV at the very low
and low frequencies and total power were elevated with aging in adults, but were not
altered by habitual aerobic exercise; (5) we confirmed, by deriving aortic AI from a
single peripheral blood pressure waveform, significant age-related increases in aortic AI
that was attenuated in older adults who were endurance exercise-trained; (6) we also
confirmed reductions in vascular endothelial function with sedentary aging that was
blunted in older adults who were endurance exercise-trained. Importantly, we also
determined that higher endothelial function was positively correlated with increased
autonomic control of cardiac function as assessed by cardiac BRS and time domain
measures of HRV (SDNN and RMSSD); and, (7) although we observed non-significant
improvements in baroreceptor-heart rate reflex sensitivity as assessed by BRS after 8
35
weeks of aerobic exercise training in previously sedentary older adults compared with
control group, the non-significant increases in BRS were inversely correlated with
concomitant reductions in aortic stiffness following the 8-week aerobic exercise training
intervention.
The finding of a reduced BRS in older sedentary adults is consistent with other
studies showing decreased sensitivity of the baroreceptor heart rate reflex seen with
advancing age in humans 5, 6, 16, 17. Young sedentary adults have the greatest BRS because
of greater compliance of their large elastic arteries and perhaps a high vagal tone 6.
Endurance exercise-trained adults displayed markedly improved BRS compared to their
sedentary peers to the extent that no significance was detected between the endurancetrained adults and young sedentary adults, indicating habitual aerobic exercise can
improve autonomic control of selective aspects of the cardiovascular system (i.e., heart
rate). This is likely at least in part the result of more compliant large elastic arteries in the
endurance trained older adults 45, given that the baroreceptors are anatomically located in
these arteries. However, we cannot rule out the possibility that some of the differences
observed in BRS between the young and older sedentary adults, and between the
sedentary and endurance-trained older adults in our study, may be explained in part by
the differences in resting heart rate. Our data are consistent with Monahan et al. 16, who
reported a 60% age-related decrease in cardiovagal BRS (using the Phase IV of Valsalva
maneuver) that was partially attenuated (39%) in endurance-trained older adults
compared to older sedentary adults. They also found BRS to be fully restored in middleaged but not older adults who were endurance-exercise trained, which is consistent with
our findings. Taken together, the data suggest that BRS declines with sedentary aging and
can be prevented with habitual aerobic exercise in middle-age adults but only partially
attenuated in older adults.
High variability in heart rate is important for proper cardiac autonomic regulation.
We confirmed the age-associated decline in time domain measures of HRV by
36
demonstrating reduced SDNN and RMSSD between older sedentary and young sedentary
adults. SDNN comprises both the low and high frequency components of HRV and is an
index of the total variability of heart rate. Young sedentary adults had greater SDNN
compared to older sedentary adults and thus greater overall HRV. Endurance trained
adults also had greater overall HRV compared to their age-matched peers, and similar to
levels seen in the young sedentary adults. However, resting heart rate was similar
between the young sedentary and endurance trained adults, and significantly lower in
these groups compared to the older sedentary adults. SDNN affects all frequency bands
similarly and mirrors patterns in heart rate, so these differences may be secondary to the
differences in heart rate.
RMSSD was also greatest in the young sedentary adults and reduced in the older
sedentary adults. RMSSD was decreased in the older sedentary adults compared to the
endurance trained adults, but unlike SDNN, was significantly lower in the endurance
trained older compared to the young sedentary adults. RMSSD is an estimate of the shortterm component of HRV and represents the fast fluctuations in heart rate modulated by
the parasympathetic nervous system and the vagus nerve. Young sedentary adults
presumably had the highest vagal tone and thus the highest RMSSD component of HRV,
while older sedentary adults had the lowest. RMSSD remained significantly lower in
endurance trained adults compared to young sedentary adults with similar heart rate, thus
perhaps representing a true HRV effect of a reduced cardiac vagal tone with habitual
aerobic exercise with human aging. In that, RMSSD was still significantly higher
compared to the older sedentary adults, this suggests that habitual aerobic exercise may
improve vagal control of heart rate in older adults, but not restore it to levels seen in
young adults.
Spectral analysis was used to analyze HRV in the frequency domain and
distinguish between the relative contributions of the sympathetic and parasympathetic
nervous systems to heart rate. No significant differences were found for the absolute
37
VLFa and LFa components between any groups, but there was a trend towards attenuated
VLFa and LFa components in both sedentary and endurance trained older adults. The
physiological correlate of the VLFa component is poorly defined, while the LFa
component is representative of sympathetic modulation of cardiac pacemaker function 59,
60
. The HFa component represents vagal modulation of heart rate in response to
respiratory sinus fluctuations and yields insight into the parasympathetic branch of the
ANS 61. Expectedly, absolute HFa component was significantly reduced in older
sedentary compared to young sedentary adults, but there was no difference observed
between sedentary and endurance trained older adults, indicating reduced vagal
modulation of heart rate in older sedentary adults that is not modified by chronic aerobic
exercise.
Increased sympathetic modulation of the vasculature is further supported by the
increased serum norepinephrine concentrations observed in both older adult groups.
Contrary to other studies, no difference was observed in LFr or HFr between endurance
trained and sedentary older adults. Dixon et al. 36 found significantly greater HFr and
lower LFr in endurance trained adults compared to their sedentary peers, but their subject
group was considerably younger than ours (mean age 28 vs 62 years) which may explain
this effect. Endurance exercise trained older adults also exhibited similar HFr compared
to young sedentary adults. However, this is the result of the reduced absolute VLFa and
HFa components. Total power is another general measure of HRV representing total
variability in heart rate, and is similar to the SDNN measure in time domain analysis 58.
Total power was higher in young sedentary compared to older sedentary adults likely
related to differences in resting heart rate. However, total power was attenuated in
endurance trained older adults compared to young sedentary adults with similar heart
rates, so differences in resting heart rate cannot explain this effect. No difference in total
power was found between sedentary and endurance trained older adults. Surprisingly, no
significant differences were observed in LF/HF ratio between groups, a measure which
38
reflects sympathovagal balance of HRV, although there was a trend for an age-related
increase in LF/HF ratio in the older sedentary adults.
Spectral analysis was also used to evaluate the frequency domain components of
short-term systolic BPV. The absolute VLFa component was higher in older compared to
young sedentary adults, and trended to be higher in the endurance trained older adults.
However, VLFa is highly sensitive to mean systolic blood pressure, and older sedentary
and endurance trained older adults had higher mean systolic blood pressure, so these
differences are likely explained in part by differences in mean blood pressure. The
absolute LFa component was markedly increased in both the sedentary and endurance
trained older adults compared to young sedentary adults. LFa represents sympathetic
modulation of vascular tone and could be the result of increased sympathetic drive from
the CNS or greater adrenergic responsiveness of the blood vessels, and is predictably
higher in the older compared to the young adults. Not surprisingly, no differences in the
absolute HFa component were observed between any of the groups. The HFa component
reflects the changes in respiratory mechanics and contributes very little to overall systolic
BPV, therefore is unlikely to provide insight into the ANS. Total power was also
significantly greater in sedentary and endurance trained older adults compared to young
sedentary adults, but no difference among each other. However, these differences are
probably secondary to the higher blood pressure in the older adults. The increased
systolic blood pressure likely resulted in the observed differences in the VLFa and LFa
components, which resulted in a greater overall total power in both older adult groups.
The findings of an increased APWV in sedentary and endurance trained older
adults compared to young sedentary adults, and a significantly attenuated APWV in
endurance trained compared to sedentary older adults have been reported previously 44
and are consistent with other studies demonstrating increased APWV with aging in
humans 43, 46. Travel time of the forward pressure wave to the peripheral reflecting sites is
presumably faster in older sedentary compared to young sedentary adults because they
39
have stiffer aortas, thus increasing the velocity of the forward wave (i.e., higher APWV)
in older adults. APWV was lower in endurance trained older adults compared to their
age-matched peers, suggesting habitual aerobic exercise positively attenuates the agerelated stiffening that takes place within the arterial wall of the aorta with sedentary
aging. In addition, the increased velocity of the forward and reflected waves in older
adults causes the pressure waveform to return earlier to the heart compared to young
adults, thus resulting in an elevated augmentation of systolic rather than diastolic
pressure. Not surprisingly, sedentary and endurance trained older adults have
considerably greater AI compared to young sedentary adults as the result in part from
stiffer arteries, which contributes to an earlier return of the reflected wave and a greater
augmentation of systolic blood pressure. Endurance trained older adults still displayed
significantly greater AI compared to young sedentary adults, indicating habitual aerobic
exercise does not completely prevent the age-associated increase in AI. However, AI was
significantly attenuated in endurance trained compared to sedentary older adults,
suggesting habitual aerobic exercise may improve but not normalize the extent of aortic
pressure augmentation that accompanies aging in humans.
The results of our cross-sectional analysis comparing absolute and percent change
in brachial artery FMD have been reported previously 54. The finding of attenuated
absolute change in brachial artery FMD in older compared to young sedentary adults is
consistent with other studies 55, 57 suggesting a decline in endothelial function occurs with
sedentary aging. Endurance trained older adults exhibited a markedly enhanced absolute
change in brachial artery FMD compared to their sedentary peers, and no significance
difference in absolute FMD compared to young sedentary adults, suggesting habitual
aerobic exercise may prevent and possibly restore the age-related decline in endothelial
function. No significant differences in percent change in brachial artery FMD were
observed between any of the groups in the cross-sectional study. However, this is likely
due to differences in baseline brachial artery diameter and the small sample size in the
40
young sedentary adults. No differences in absolute or percent change in endotheliumindependent dilation were observed between sedentary and endurance trained older
adults, suggesting that the differences in brachial artery FMD were specific to the
vascular endothelium. Endothelium-independent dilation data were unavailable for the
young sedentary adults.
In the present study, we observed multiple significant associations between
measures of autonomic and vascular function. A positive correlation was observed
between BRS and both absolute and percent change in brachial artery FMD. Absolute
change in brachial artery FMD also positively correlated with SDNN. Taken together,
these findings suggest that subjects with heightened cardiac autonomic control also
display greater endothelial function, or greater cardiac autonomic control may mediate
changes in endothelial function. Subjects with impaired BRS will also display impaired
peripheral endothelial function, but it is unclear whether older adults display impaired
peripheral endothelial function as the result of a weakened baroreflex or if peripheral
endothelial dysfunction compromises the cardiac baroreflex.
In addition, BRS was found to be inversely related with APWV, so that subjects
with high APWV (i.e., stiffer arteries) displayed lower BRS. It is likely that a stiffer aorta
(and carotid arteries) contributes in part to the decline in BRS with advancing age given
the anatomical location of the baroreceptors in the aortic arch and carotid bulb, but it’s
also possible that the decline in BRS and autonomic function somehow leads to
sympathetic or reduced vagal modulation of arterial properties. After adjusting for age
and mean arterial pressure, the significant association remained, indicating the
relationship between aortic stiffness and BRS was independent of any differences in age
or mean blood pressure.
RMSSD was also positively correlated to both absolute and percent change in
brachial artery FMD, suggesting a strong relationship between cardiac vagal tone and
peripheral endothelial function. Once again, impaired cardiac vagal tone may negatively
41
alter vascular endothelial function through enhanced tone, but vascular endothelial
dysfunction may mediate changes in cardiac vagal tone. Both RMSSD and SDNN were
negatively associated with APWV, indicating greater HRV is associated with a more
compliant aorta. However, after adjusting for mean pressure and age, these correlations
are no longer significant suggesting the association is explained in part by differences in
age and mean pressure rather than differences in APWV. AI was also inversely related to
both BRS and SDNN, as indicated by a significant negative correlation, and subjects with
impaired cardiac autonomic control exhibit greater augmentation of systolic blood
pressure.
Of the 25 older sedentary adults, 18 participated in 8 weeks of moderate-intensity
aerobic exercise or attention-time control to determine if a short-term aerobic exercise
intervention could improve autonomic and vascular function in previously sedentary
older adults free of CVD disease. We observed non-significant increases in BRS
following 8 weeks of aerobic exercise training in the exercise intervention group
compared with the attention-time control group. Results published by other groups
clearly demonstrate improvements in BRS following aerobic exercise training in
previously sedentary older adults 5, 16, therefore our results are likely the result of the lack
of statistical power as a result of the small sample size in the attention-control group.
SDNN, a measure of overall HRV, significantly increased following 8 weeks of
aerobic exercise intervention but not attention-time control, suggesting improved cardiac
autonomic function as the result of aerobic exercise training. SDNN mirrors patterns in
heart rate, and although resting heart rate did not significantly decrease following the
exercise intervention, this is likely the result of the small sample size in the aerobic
exercise intervention group, and the change in SDNN was most likely secondary to the
non-significant improvement in resting heart rate observed in the exercise intervention
subjects. In contrast, there was no significant difference observed in RMSSD following 8
42
weeks of aerobic exercise or attention-time control, although there was a strong trend
towards improved RMSSD in the exercise intervention group.
Frequency domain measures of HRV were largely maintained following 8 weeks
of aerobic exercise or attention-time control. This is consistent with previous studies
showing no improvements in HRV via spectral analysis following 1-year 22 and 5-years 24
of a randomized aerobic exercise intervention. Interestingly, Uusitalo et al. 22, 24 did not
report LF/HF ratio, a measure of sympathovagal balance, although we observed no
significant differences in LF/HF ratio following 8 weeks aerobic exercise intervention or
attention-time control, suggesting that aerobic exercise in previously sedentary older
adults does not improve autonomic balance. Taken together, our results and results by
others suggest little improvement in the time and frequency domain components of HRV
occur following aerobic exercise intervention in previously sedentary older adults.
Systolic BPV was also unaltered following 8 weeks of moderate-intensity aerobic
exercise or attention-time control, as no differences were observed in any of the
frequency domain components of short-term systolic BPV in exercise intervention or
attention-time control subjects. Uusitalo et al. reported no significant changes in systolic
BPV following a 1-year 22 and 5-year 24 controlled, randomized aerobic exercise training
intervention in previously sedentary adults, so no differences following 8 weeks of
aerobic exercise training in our study is not surprising. In addition, no significant changes
in APWV were observed following 8 weeks of aerobic exercise or attention-time control.
It is possible that the 8 week aerobic exercise intervention was not sufficient to evoke
significant reductions in APWV, or the lack of statistical power in the exercise
intervention group prevented the detection of a significant change in APWV.
Furthermore, no significant differences in absolute or percent change in brachial
artery FMD occurred in exercise intervention or attention-time control subjects, but there
was a trend towards enhanced FMD following training. Pierce et al. 54 found an
improvement in both absolute and percent change in brachial artery FMD following 8
43
weeks of aerobic exercise training in a larger cohort of previously sedentary men, but not
post-menopausal women, suggesting a possible sex difference in peripheral vascular
endothelial function with aging. It is important to note that 8/12 subjects in the exercise
intervention group were postmenopausal women, and improvements may have occurred
in the older men. It is also possible that the 8-week aerobic exercise stimulus was not
sufficient to evoke significant changes in FMD in our study population. Endotheliumindependent dilation was also unaffected by the exercise intervention or attention-time
control, suggesting the non-significant changes in brachial artery FMD were specific to
the endothelium and not caused by vascular smooth muscle.
We recognize several limitations in our present study. First of all, our study
included a relatively limited number of study participants, especially the young sedentary
adults. A larger sample size may have allowed for a greater statistical power and detected
more subtle differences between groups, particularly in the FMD and APWV exercise
intervention data. BRS was measured using the sequence technique which assesses
spontaneous baroreflex-heart rate sensitivity during resting conditions, therefore it does
not provide information on BRS during acute physiological perturbations in blood
pressure. Furthermore, breathing frequency was not measured, and breathing frequency is
known to affect the frequency domain components of HRV and systolic BPV.
In conclusion, our data suggest that cardiac baroreceptor heart rate reflex
sensitivity, expressed as BRS by the sequence technique, is reduced with sedentary aging
in humans and partially restored by habitual aerobic exercise training. Similarly, we
confirmed that aortic stiffness is increased with sedentary aging in humans but this is
attenuated in older adults who have been performing chronic moderate to vigorous
aerobic exercise training for more many years. Importantly, we report for the first time
that the cardiac baroreceptor heart rate reflex sensitivity, as expressed by the sequence
technique-derived BRS, was inversely associated with aortic stiffness even after adjusting
for age and mean blood pressure, suggesting that aortic stiffening may contribute in part
44
to the differential cardiac baroreceptor-heart rate reflex sensitivity that occurs with
sedentary aging and habitual physically active aging in humans. However, we cannot
determine a direct cause and effect relation between BRS and aortic stiffness in the
current study. Lastly, although improvements in cardiac baroreceptor-heart rate reflex
sensitivity and aortic stiffness after 8 weeks of daily aerobic exercise in previously
sedentary older adults compared with time-controls did not reach statistical significance,
the increase in BRS and reduction in APWV after 8 weeks of exercise training was
significantly inversely associated suggesting a integrative relation between cardiac BRS
and aortic stiffness that can altered by habitual exercise in older adults. However, future
studies using a properly powered randomized, controlled exercise intervention are needed
to directly test whether aerobic exercise training can favorably modulate cardiac
baroreceptor heart rate reflex sensitivity, as well as sensitivity of the sympathetic
baroreflex, and their relations to alterations in aortic stiffness in aged adults.
45
APPENDIX A
TABLES
Table A1: Cross- sectional Subject Characteristics
______________________________________________________________________________
Characteristic
YS (n=6)
OS (n=25)
OT (n=15)
22 ±2
62±1*
61±2*
1:5
9:16
12:3
Weight (kg)
60.7±1.9
72.0±0.2*
70.6±2.6*
Body mass index (kg/m2)
20.7±0.5
25.6±0.5*
23.5±0.6*†
Total body fat (%)
28.2±3.5
35.4±1.7*
20±1.4*†
Waist circumference (cm)
70.1±1.4
83.1±2.3*
80.3±2.2*
Hip circumference (cm)
96.5±1.6
101.4±1.1*
95.7±1.2†
Waist/Hip ratio
0.73±0.01
0.82±0.02*
0.84±0.02*
Systolic BP (mmHg)
102±10
121±3*
121±4*
Diastolic BP (mmHg)
57±2
72±2*
75±3*
Resting heart rate (beats/min)
53±2
66±2*
54±2†
Age (years)
Male: Female ratio
Data are mean  SE. *P<0.05 vs YS. †P<0.05 vs OS. BP, blood pressure
______________________________________________________________________________
Subject Characteristics in young sedentary (YS, n=6), older sedentary (OS, n=25) and
older endurance trained (n=15) adults.
46
Table A2: Cross-sectional Subject Blood Chemistry
______________________________________________________________________________
Circulating factor
YS (n=6)
OS (n=25)
OT (n=15)
Glucose (mg/dL)
83±4
88±2
88±2
Insulin (µU/mL)
7.5±1.7
6.8±0.6
5.8±1
Total cholesterol (mg/dL)
165±18
205±5*
193±7
LDL cholesterol (mg/dL)
91±14
126±4*
111±7
HDL cholesterol (mg/dL)
59±6
59±3
66±6
Triglycerides (mg/dL)
77±11
102±8
77±7
White blood count (109
cells/L)
4.4±0.3
5.0±0.2
4.6±0.2
Oxidized LDL (U/L)
46±5
56±3
54±6
C-reactive protein (mg/L)
0.41 ±0.13
1.42±0.3
0.52±0.1†
Norepinephrine (pg/mL)
159±26
351±25*
349±48*
Data are mean  SE. *P<0.05 vs YS. †P<0.05 vs OS.
LDL, low-density lipoprotein cholesterol; HDL,
high-density lipoprotein cholesterol.
______________________________________________________________________________
Subject blood chemistry in young sedentary (YS, n=6), older sedentary (OS, n=25) and
older endurance trained (n=15) adults.
47
Table A3: Frequency Domain Analysis of HRV: Cross-sectional Study
______________________________________________________________________________
HRV Parameter
YS (n=6)
OS (n=25)
OT (n=15)
VLFa, bpm2
7.67±3.71
3.35±0.66
3.81±0.71
LFa, bpm2
7.74±1.59
3.22±0.56
3.35±0.68
HFa, bpm2
7.32±1.13
1.42±0.44*
1.80±0.49*
LFr, %
37.55±4.38
54.42±5.13*
44.30±5.46*
HFr, %
39.96 ±7.85
19.96 ±2.53*
24.05±4.31
TP, bpm2
30.13±9.26
10.06±1.85*
11.35±1.72*
1.19 ±0.29
5.63±1.82
2.94±0.68
LF/HF ratio
Data are mean  SE. Log were transformed before ANOVA *P<0.05 vs YS. †P<0.05 vs
OS.
______________________________________________________________________________
Frequency domain analysis of the absolute (a) and relative (r) spectral components of
heart rate variability: very low frequency (VLF), low frequency (LF), high frequency
(HF), total power (TP), and LF/HF ratio components in young sedentary(YS, n=6), older
sedentary (OS, n=25) and older endurance trained (n=15) adults.
48
Table A4: Frequency Domain Analysis of BPV: Cross-sectional Study
______________________________________________________________________________
Systolic BPV Parameter
YS (n=6)
OS (n=25)
OT (n=14)
VLFa, mmHg2
2.18±0.59
7.92±1.01*
10.87±2.25*
LFa, mmHg2
4.16±1.28
11.15±1.48*
11.40±1.37*
HFa, mmHg2
2.20±0.48
4.59±0.90
2.35±0.43
TP, mmHg2
9.31±2.38
25.80±2.99*
25.51±3.31*
Data are mean  SE. *P<0.05 vs YS. †P<0.05 vs OS.
______________________________________________________________________________
Frequency domain analysis of the absolute (a) spectral components of systolic blood
pressure variability: very low frequency (VLF), low frequency (LF), high frequency
(HF), total power (TP), and LF/HF ratio components in young sedentary(YS, n=6), older
sedentary (OS, n=25) and older endurance trained (n=14) adults.
49
Table A5: Baseline Brachial Artery Diameters
______________________________________________________________________________
Brachial Artery Diameter
YS (n=6)
OS (n=25)
OT (n=14)
Baseline FMD diameter (mm)
3.14±0.23
3.39±0.15
3.90±0.15*†
OS (n=22)
OT (n=16)
3.40±0.15
3.64±0.15
Baseline GTN diameter (mm)
-
Data are mean  SE. *P<0.05 vs YS. †P<0.05 vs OS.
______________________________________________________________________________
Baseline brachial artery diameters of the flow-mediated dilation (FMD) and glyceryl
trinitrate (GTN) in the cross-sectional study.
50
Table A6: Intervention Study Subject Characteristics
______________________________________________________________________________
Characteristic
Age (years)
Male: Female ratio
Exercise Group
PRE
POST
Control Group
PRE
POST
63 ± 1
-
60 ± 1
-
4:12
-
3:3
-
Weight (kg)
70.9 ± 3.4
70.7 ± 3.5
75.1 ± 2.6
74.5 ± 2.4
Body mass index (kg/m2)
25.6 ± 0.8
25.5 ± 0.9
25.7 ± 0.9
25.6 ± 0.9
Total body fat (%)
34.7 ± 2.5
34.5 ± 2.8
35.8 ± 4.2
35.1 ± 4.2
Waist circumference (cm)
83.4 ± 3.0
84.5 ± 3.6
85.5 ± 3.9
85.4 ± 3.8
Hip circumference (cm)
100.5 ± 1.7
103.1 ± 1.9
103.0 ± 2.7
102.9 ± 2.5
Waist/Hip ratio
0.83 ± 0.03
0.82 ± 0.03
0.84 ± 0.05
0.84 ± 0.05
Systolic BP (mmHg)
120 ± 5
114 ± 4
122 ± 6
114 ± 6
Diastolic BP (mmHg)
73 ± 3
70 ± 2
74 ± 4
71 ± 3
Resting heart rate
(beats/min)
68 ± 4
59 ± 2
66 ± 3
61 ± 3
27.0 ± 1.3
28.7 ± 1.5
26.8 ± 2.1
27.4 ± 2.6
VO2 max (mL/kg/min)
Data are mean  SE. *P<0.05 vs Pre within-group. BP, blood
pressure; VO2 max, maximal exercise oxygen consumption.
______________________________________________________________________________
Subject characteristics in older sedentary adults who performed 8 weeks moderateintensity aerobic exercise (n=12) or attention time-control (n=6).
51
Table A7: Intervention Study Blood Chemistry
______________________________________________________________________________
Circulating Factor
Exercise Group
PRE
POST
Control Group
PRE
POST
Glucose (mg/dL)
91 ± 2
94 ± 2
89 ± 3
87 ± 3
Total cholesterol (mg/dL)
210 ± 7
202 ± 7
199 ± 10
188 ± 8
LDL cholesterol (mg/dL)
127 ± 6
122 ± 7
124 ± 7
117 ± 7
HDL cholesterol (mg/dL)
61 ± 4
59 ± 4
52 ± 5
50 ± 5
Triglycerides (mg/dL)
111 ± 12
101 ± 15
111 ± 22
101 ± 12
Oxidized LDL (U/L)
57 ± 4
59 ± 4
50 ± 4
51 ± 5
C-reactive protein (mg/L)
1.16 ± 0.22
1.05 ± 0.21
1.07 ± 0.25
1.53 ± 0.54
Norepinephrine (pg/mL)
356 ± 44
339 ± 48
383 ± 28
370 ± 32
Data are mean  SE. *P<0.05 vs Pre within-group. LDL, low-density
lipoprotein cholesterol; HDL, high-density lipoprotein cholesterol.
______________________________________________________________________________
Subject blood chemistry in older sedentary adults who performed 8 weeks moderateintensity aerobic exercise training (n=12) or attention time-control (n=6).
52
Table A8: Frequency Domain Analysis of HRV: Intervention Study
______________________________________________________________________________
Exercise Group
PRE
POST
Control Group
PRE
POST
VLFa, bpm2
2.59 ± 0.95
2.48 ± 0.45
4.06 ± 1.32
2.42 ± 0.53
LFa, bpm2
3.06 ± 0.69
3.30 ± 0.74
4.11 ± 1.69
3.83 ± 2.32
HFa, bpm2
0.90 ± 0.21
1.52 ± 0.42
2.45 ± 1.70
1.61 ± 1.17
LFr, %
41.16 ± 4.75
36.96 ± 5.30
35.57 ± 3.98
37.14 ± 6.06
HFr, %
14.31 ± 3.59
15.99 ± 2.80
15.63 ± 4.80
13.86 ± 3.60
TP, bpm2
7.75 ± 1.74
10.45 ± 2.46
12.06 ± 5.49
8.31 ± 3.73
LF/HF ratio
8.08 ± 3.50
5.26 ± 2.72
3.96 ± 1.30
3.26 ± 0.65
HRV Parameter
Data are mean  SE. *P<0.05 vs Pre within-group.
______________________________________________________________________________
Frequency domain analysis of the absolute (a) and relative (r) spectral components of
heart rate variability: very low frequency (VLF), low frequency (LF), high frequency
(HF), total power (TP), and LF/HF ratio components in 18 older sedentary adults who
performed 8 weeks moderate-intensity aerobic exercise (n=12) or attention time-control
(n=6).
53
Table A9: Frequency Domain Analysis of BPV: Intervention Study
______________________________________________________________________________
Exercise
Group
PRE
POST
PRE
POST
VLFa, mmHg2
9.05 ± 1.58
15.67 ± 4.87
8.10 ± 2.34
8.71 ± 3.74
LFa, mmHg2
16.32 ± 2.42
15.74 ± 3.48
10.66 ± 3.28
12.79 ± 4.29
HFa, mmHg2
8.49 ± 3.25
4.87 ± 1.19
4.31 ± 2.19
2.95 ± 1.17
TP, mmHg2
31.52 ± 4.52
36.88 ± 7.99
24.91 ± 6.51
25.41 ± 6.31
Systolic BPV Parameter
Control Group
Data are mean  SE. *P<0.05 vs Pre within-group.
______________________________________________________________________________
Frequency domain analysis of the absolute (a) spectral components of systolic blood
pressure variability: very low frequency (VLF), low frequency (LF), high frequency
(HF), total power (TP), and LF/HF ratio components in 18 older sedentary adults who
performed 8 weeks moderate-intensity aerobic exercise (n=12) or attention time-control
(n=6).
54
APPENDIX B
FIGURES
Figure B1: Aortic Pulse Wave Velocity
________________________________________________________________________
____________________________________________________________________________
Aortic pulse wave velocity (APWV) estimated by the gold standard carotid-femoral pulse
wave velocity (CFPWV).
55
Figure B2: Baroreflex Sensitivity
______________________________________________________________________________
Baroreflex Sensitivity (ms/mmHg)
60
50
40
†
30
*
20
10
0
YS
OS
OT
______________________________________________________________________________
Baroreflex sensitivity in young sedentary (YS, n=5), older sedentary (OS, n=24) and
older endurance trained (OT, n=14) adults. *P<0.05 vs. YS. †P<0.05 vs OS.
56
Figure B3: Heart Rate Variability: Time Domain Analysis of SDNN
______________________________________________________________________________
120
†
100
SDNN (ms)
80
*
60
40
20
0
YS
OS
OT
______________________________________________________________________________
Time Domain Analysis of the Standard Deviation of the NN Intervals (SDNN) in young
sedentary (YS, n=6), older sedentary (OS, n=25) and older endurance trained (OT, n=15)
adults. *P<0.05 vs. YS. †P<0.05 vs OS.
57
Figure B4: Heart Rate Variability: Time Domain Analysis of RMSSD
______________________________________________________________________________
120
RMSSD (ms)
100
† *
80
60
*
40
20
0
YS
OS
OT
______________________________________________________________________________
Time Domain Analysis of the Root Mean Squared Difference of Successive NN
(RMSSD) Intervals in young sedentary (YS, n=6), older sedentary (OS, n=25) and older
endurance trained (OT, n=15) adults. *P<0.05 vs. YS. †P<0.05 vs OS.
58
Figure B5: Aortic Pulse Wave Velocity
______________________________________________________________________________
12
*
10
* †
PWV (m/s)
8
6
4
2
0
YS
OS
OT
______________________________________________________________________________
Aortic pulse wave velocity (APWV) in young sedentary (YS, n=6), older sedentary (OS,
n=25) and older endurance trained (OT, n=14) adults. *P<0.05 vs. YS. †P<0.05 vs OS.
59
Figure B6: Augmentation Index
______________________________________________________________________________
40
*
Augmentation Index (%)
35
*†
30
25
20
15
10
5
0
YS
OS
OT
______________________________________________________________________________
Augmentation Index in young sedentary (YS, n=6), older sedentary (OS, n=25) and older
endurance trained (OT, n=14) adults. *P<0.05 vs. YS. †P<0.05 vs OS.
60
Figure B7: Absolute Change in Brachial Artery FMD
______________________________________________________________________________
†
Brachial Artery FMD (mmΔ)
0.3
0.25
*
0.2
0.15
0.1
0.05
0
YS
OS
OT
______________________________________________________________________________
Absolute change in brachial artery diameter in response to flow-mediated dilation (FMD)
in young sedentary (YS, n=6), older sedentary (OS, n=25) and older endurance trained
(OT, n=14) adults. *P<0.05 vs. YS. †P<0.05 vs OS. (Data are subset of published data 44).
61
Figure B8: Percent Change in Brachial Artery FMD
______________________________________________________________________________
9
Brachial Artery FMD (%Δ)
8
7
6
5
4
3
2
1
0
YS
OS
OT
______________________________________________________________________________
Percent change in brachial artery diameter in response to flow-mediated dilation (FMD)
in young sedentary (YS, n=6), older sedentary (OS, n=25) and older endurance trained
(OT, n=14) adults. *P<0.05 vs. YS. †P<0.05 vs OS. (Data are subset of published data
44
).
62
Figure B9: Absolute Change in Endothelium-Independent Dilation
______________________________________________________________________________
GTN-mediated Vasodilation (Δmm)
1.2
1
0.8
0.6
0.4
0.2
0
OS
OT
______________________________________________________________________________
Absolute change in brachial artery diameter in response to sublingual glyceryl trinitrate(GTN) induced vasodilation in older sedentary (OS, n=22) and older endurance trained
(OT, n=6) adults. *P<0.05 vs. YS. †P<0.05 vs OS. (Data are subset of published data 44).
63
Figure B10: Percent Change in Endothelium-Independent Dilation
______________________________________________________________________________
GTN-mediated Vasodilation (%Δ)
30
25
20
15
10
5
0
OS
OT
______________________________________________________________________________
Percent change in brachial artery diameter in response to sublingual glyceryl trinitrate(GTN) induced vasodilation in older sedentary (OS, n=22) and older endurance trained
(OT, n=6) adults. *P<0.05 vs. YS. †P<0.05 vs OS. (Data are subset of published data 44).
64
Figure B11: Pearson Correlation: Absolute FMD and BRS
______________________________________________________________________________
Baroreflex Sensitivity (ms/mmHg)
80
70
r= 0.396
p<0.05
60
50
40
30
20
10
0
0.000
0.100
0.200
0.300
0.400
0.500
Absolute Change in Brachial Artery FMD (Δmm)
______________________________________________________________________________
Pearson’s correlation comparing the absolute change in brachial artery flow-mediated
dilation (FMD) and baroreflex sensitivity (BRS) (n=42).
Figure B12: Pearson Correlation: Percent FMD and BRS
______________________________________________________________________________
Baroreflex Sensitivity (ms/mmHg)
80
r= 0.309
p<0.05
70
60
50
40
30
20
10
0
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
Percent Change in Brachial Artery FMD (%)
______________________________________________________________________________
Pearson’s correlation comparing percent change in brachial artery flow-mediated dilation
(FMD) and baroreflex sensitivity (BRS) (n=42).
65
Figure B13: Pearson Correlation: Absolute FMD and SDNN
______________________________________________________________________________
200
r= 0.368
p<0.05
180
160
SDNN (ms)
140
120
100
80
60
40
20
0
0.000
0.100
0.200
0.300
0.400
0.500
Absolute Change in Brachial Artery FMD (Δmm)
______________________________________________________________________________
Pearson’s correlation comparing the absolute change in brachial artery flow-mediated
dilation (FMD) with HRV in the time domain using the standard deviation of the NN
intervals (SDNN) (n=44).
66
Figure B14: Pearson Correlation: Absolute FMD and RMSSD
______________________________________________________________________________
160
r= 0.419
p<0.01
140
RMSSD (ms)
120
100
80
60
40
20
0
0.000
0.100
0.200
0.300
0.400
0.500
Absolute Change in Brachial Artery FMD (Δmm)
______________________________________________________________________________
Pearson’s correlation comparing the absolute change in brachial artery flow-mediated
dilation (FMD) with HRV in the time domain using the root of the mean squared
difference of successive NN intervals (RMSSD) (n=44).
67
Figure B15: Pearson Correlation: Percent FMD and RMSSD
______________________________________________________________________________
160
r= 0.358
p<0.05
140
RMSSD (ms)
120
100
80
60
40
20
0
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
Percent Change in Brachial Artery FMD (%)
______________________________________________________________________________
Pearson’s correlation comparing the percent change in brachial artery flow-mediated
dilation (FMD) with HRV in the time domain using the root of the mean squared
difference of successive NN intervals (RMSSD) (n=44).
68
Figure B16: Pearson Correlation: BRS and APWV
______________________________________________________________________________
Aortic Pulse Wave Velocity (m/s)
12
r= - 0.55
p<0.05
11
10
9
8
7
6
5
4
0
10
20
30
40
50
60
70
80
Baroreflex Sensitivity (ms/mmHg)
______________________________________________________________________________
Pearson’s correlation comparing baroreflex sensitivity (BRS) and aortic pulse wave
velocity (APWV) (n=42).
Figure B17: Pearson Correlation: SDNN and APWV
______________________________________________________________________________
Aortic Pulse Wave Velocity (m/s)
12
r= - 0.320
p<0.05
11
10
9
8
7
6
5
0
50
100
150
200
SDNN (ms)
______________________________________________________________________________
Pearson’s correlation comparing HRV in the time domain using the standard deviation of
the NN intervals (SDNN) with aortic pulse wave velocity (AWV) (n=42).
69
Figure B18: Pearson Correlation: RMSSD and APWV
______________________________________________________________________________
Aortic Pulse Wave Velocity (m/s)
12
r= - 0.377
p<0.05
11
10
9
8
7
6
5
0
20
40
60
80
100
120
140
160
RMSSD (ms)
______________________________________________________________________________
Pearson’s correlation comparing HRV in the time domain using the root of the mean
squared difference of successive NN intervals (RMSSD) with aortic pulse wave velocity
(APWV) (n=42).
70
Figure B19: Pearson Correlation: AI and BRS
______________________________________________________________________________
Baroreflex Sensitivity (ms/mmHg)
80
r= -0.393
p<0.05
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
Augmentation Index (%)
______________________________________________________________________________
Pearson’s correlation comparing augmentation index (AI) and baroreflex sensitivity
(BRS) (n=42).
Figure B20: Pearson Correlation: AI and SDNN
______________________________________________________________________________
200
r= -0.331
p<0.05
180
160
SDNN (ms)
140
120
100
80
60
40
20
0
0
10
20
30
40
50
60
Augmentation Index (%)
______________________________________________________________________________
Pearson’s correlation comparing augmentation index (AI) with HRV in the time domain
using the standard deviation of the NN intervals (SDNN) (n=43).
71
Figure B21: BRS and Exercise Intervention
______________________________________________________________________________
Baroreflex Sensitivity (ms/mmHg)
20
18
16
14
12
10
8
6
4
2
0
PRE
POST
______________________________________________________________________________
Baroreflex sensitivity (BRS) in 11 middle-aged and old sedentary adults before and after
8 weeks of aerobic training in the exercise intervention group. *P<0.05 vs. Pre-exercise
training.
72
Figure B22: BRS and Attention-time Control
_____________________________________________________________________________
Baroreflex Sensitivity (ms/mmHg)
16
14
12
10
8
6
4
2
0
PRE
POST
_____________________________________________________________________________
Baroreflex sensitivity (BRS) in 5 attention time-control middle-aged and old sedentary
adults before and after 8 weeks of attention-time control. *P<0.05 vs. Pre-attention-time
control.
73
Figure B23: SDNN and Exercise Intervention
______________________________________________________________________________
90
*
80
70
SDNN (ms)
60
50
40
30
20
10
0
PRE
POST
______________________________________________________________________________
Heart rate variability: time domain analysis of the standard deviation of the NN intervals
(SDNN) in 12 middle-aged and old sedentary adults before and after 8 weeks of aerobic
training in the exercise intervention group. *P<0.05 vs. Pre-exercise training.
74
Figure B24: SDNN and Attention-time Control
______________________________________________________________________________
80
70
SDNN (ms)
60
50
40
30
20
10
0
PRE
POST
______________________________________________________________________________
Heart rate variability: Time Domain Analysis of the Standard Deviation of the NN
Intervals (SDNN) in 6 attention time-control middle-aged and old sedentary adults before
and after 8 weeks of attention-time control. *P<0.05 vs. Pre-attention-time control.
75
Figure B25: RMSSD and Exercise Intervention
______________________________________________________________________________
60
RMSSD (ms)
50
40
30
20
10
0
PRE
POST
______________________________________________________________________________
Heart rate variability: time domain analysis of the root mean squared difference of
successive NN (RMSSD) intervals in 12 middle-aged and old sedentary adults before and
after 8 weeks of aerobic training in the exercise intervention group. *P<0.05 vs. Preexercise training.
76
Figure B26: RMSSD and Attention-time Control
______________________________________________________________________________
60
RMSSD (ms)
50
40
30
20
10
0
PRE
POST
______________________________________________________________________________
Heart rate variability: time domain analysis of the root mean squared difference of
successive NN (RMSSD) intervals in 6 attention time-control middle-aged and old
sedentary adults before and after 8 weeks of attention-time control. *P<0.05 vs. Preattention-time control.
77
Figure B27: APWV and Exercise Intervention
______________________________________________________________________________
Aortic Pulse Wave Velocity (m/s)
12
10
8
6
4
2
0
PRE
POST
______________________________________________________________________________
Aortic pulse wave velocity (APWV) in 12 middle-aged and old sedentary adults before
and after 8 weeks of aerobic training in the exercise intervention group. *P<0.05 vs. Preexercise training.
78
Figure B28: APWV and Attention-time Control
______________________________________________________________________________
Aortic Pulse Wave Velocity (m/s)
12
10
8
6
4
2
0
PRE
POST
______________________________________________________________________________
Aortic pulse wave velocity in (APWV) 6 attention time-control middle-aged and old
sedentary adults before and after 8 weeks of attention-time control. *P<0.05 vs. Preattention-time control.
79
Figure B29: AI and Exercise Intervention
______________________________________________________________________________
40
Augmentation Index (%)
35
30
25
20
15
10
5
0
PRE
POST
______________________________________________________________________________
Augmentation index (AI) in 12 middle-aged and old sedentary adults before and after 8
weeks of aerobic training in the exercise intervention group. *P<0.05 vs. Pre-exercise
training.
80
Figure B30: AI and Attention-time Control
______________________________________________________________________________
45
Augmentation Index (%)
40
35
30
25
20
15
10
5
0
PRE
POST
______________________________________________________________________________
Augmentation index (AI) in 6 attention time-control middle-aged and old sedentary
adults before and after 8 weeks of attention-time control. *P<0.05 vs. Pre-attention-time
control.
81
Figure B31: Absolute FMD and Exercise Intervention
______________________________________________________________________________
Brachial Artery FMD (Δmm)
0.3
0.25
0.2
0.15
0.1
0.05
0
PRE
POST
______________________________________________________________________________
Absolute change in brachial artery diameter in response to flow-mediated dilation (FMD)
in 12 middle-aged and old sedentary adults before and after 8 weeks of aerobic training in
the exercise intervention group. *P<0.05 vs. Pre-exercise training.
82
Figure B32: Absolute FMD and Attention-time Control
______________________________________________________________________________
Brachial Artery FMD (Δmm)
0.25
0.2
0.15
0.1
0.05
0
PRE
POST
______________________________________________________________________________
Absolute change in brachial artery diameter in response to flow-mediated dilation (FMD)
in 6 attention time-control middle-aged and old sedentary adults before and after 8 weeks
of attention-time control. *P<0.05 vs. Pre-attention-time control.
83
Figure B33: Percent FMD and Exercise Intervention
______________________________________________________________________________
8
Brachial Artery FMD (Δ%)
7
6
5
4
3
2
1
0
PRE
POST
______________________________________________________________________________
Percent change in brachial artery diameter in response to flow-mediated dilation (FMD)
in 12 middle-aged and old sedentary adults before and after 8 weeks of aerobic training in
the exercise intervention group. *P<0.05 vs. Pre-exercise training.
84
Figure B34: Percent FMD and Attention-time Control
______________________________________________________________________________
8
Brachial Artery FMD (Δ%)
7
6
5
4
3
2
1
0
PRE
POST
______________________________________________________________________________
Percent change in brachial artery diameter in response to flow-mediated dilation (FMD)
in 6 attention time-control middle-aged and old sedentary adults before and after 8 weeks
of attention time-control. *P<0.05 vs. Pre-attention-time control.
85
Figure B35: Absolute EID and Exercise Intervention
______________________________________________________________________________
GTN-mediated Vasodilation (Δmm)
1.2
1
0.8
0.6
0.4
0.2
0
PRE
POST
______________________________________________________________________________
Absolute change in brachial artery diameter in response to glyceryl trinitrate-(GTN)
induced vasodilation in 7 middle-aged and old sedentary adults before and after 8 weeks
of aerobic training in the exercise intervention group. *P<0.05 vs. Pre-exercise training.
86
Figure B36: Absolute EID and Attention-time Control
______________________________________________________________________________
GTN-mediated Vasodilation (Δmm)
1.4
1.2
1
0.8
0.6
0.4
0.2
0
PRE
POST
______________________________________________________________________________
Absolute change in brachial artery diameter in response to glyceryl trinitrate-(GTN)
induced vasodilation in 4 attention time-control middle-aged and old sedentary adults
before and after 8 weeks of attention-time control. *P<0.05 vs. Pre-attention-time control.
87
Figure B37: Percent EID and Exercise Intervention
______________________________________________________________________________
GTN-mediated Vasodilation (Δ%)
35
30
25
20
15
10
5
0
PRE
POST
______________________________________________________________________________
Percent change in brachial artery diameter in response to glyceryl trinitrate-(GTN)
induced vasodilation in 11 middle-aged and old sedentary adults before and after 8 weeks
of aerobic training in the exercise intervention group. *P<0.05 vs. Pre-exercise training.
88
Figure B38: Percent EID and Attention-time Control
______________________________________________________________________________
GTN-mediated Vasodilation (Δ%)
40
35
30
25
20
15
10
5
0
PRE
POST
______________________________________________________________________________
Percent change in brachial artery diameter in response to glyceryl trinitrate-(GTN)
induced vasodilation in 4 attention time-control middle-aged and old sedentary adults
before and after 8 weeks of attention time-control. *P<0.05 vs. Pre-attention-time control.
89
Figure B39: Pearson Correlation: BRS and APWV after Aerobic Exercise
______________________________________________________________________________
Change in BRS (ms/mmHg)
20
-2.5
r= -0.58
p= 0.048
15
10
5
0
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
-5
-10
Change in APWV (m/sec)
______________________________________________________________________________
Pearson’s correlation comparing the change in baroreflex sensitivity (BRS) with the
change in aortic pulse wave velocity (APWV) following 8 weeks of aerobic exercise
(n=12).
90
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