q 1999, British Geriatrics Society
Age and Ageing 1999; 28: 337–338
EDITORIAL
Ageing and the baroreflex
The baroreflex arc is important in enabling people to
function in the upright position, as it is the principal
mechanism responsible for short-term (seconds to
minutes) blood pressure control. Blood pressure
sensors in the carotid and aortic arch are linked
through glossopharyngeal and vagal nerves to central
processing centres in the brainstem, which modulate
efferent sympathetic and parasympathetic nervous
system activity to the vasculature and heart. Through
this mechanism, falls in blood pressure result in reflex
vasoconstriction and increased heart rate and stroke
volume. Conditions which cause severe disruption to
the baroreflex mechanism (such as invasive neck
tumours) can result in profound disability, with subjects being confined to the supine position. Ageassociated changes in the baroreflex are of great
physiological and clinical importance.
Measuring baroreflex sensitivity
Several methods have been used to measure baroreflex sensitivity. The traditional ‘Oxford’ approach has
been to determine the slope of the relationship
between blood pressure and heart rate changes to
bolus injections of short-lasting drugs, which either
increase or decrease blood pressure. Reduced baroreflex sensitivity is manifest by a shallower slope of
the change in heart rate against blood pressure.
Using this method, reduced baroreflex sensitivity
in normotensive older subjects and hypertensive
middle aged subjects was identified in the early
1970s. A disadvantage of the technique is the need to
administer pressor and vasodilator drugs, which are
potentially hazardous in acutely ill or frail older
subjects. For this reason, other methods were developed. These include analysis of blood pressure and
heart-rate changes during phase IV of a Valsalva
manoeuvre. Non-invasive spectral analysis and
impulse-response function analysis of continuous
heart rate and blood pressure recording are a particularly attractive method for research on older subjects.
These methods require only a brief period of simultaneous heart rate and blood pressure monitoring,
usually obtainable from a finger cuff sensor, without
the need for invasive techniques or administration
of vasoactive agents.
Increasing age is associated with increasing blood
pressure and reduced baroreflex sensitivity, and the
contribution of age per se to reduced baroreflex
sensitivity has been unclear. In this issue of Age and
Ageing, the Leicester group [1] describe the association
between age, blood pressure and baroreflex sensitivity
in a sample of 70 ‘normotensive’ subjects aged 22–82
years using several methods. They confirm that ageing
is associated with a reduction in baroreflex sensitivity
up to the fourth decade. However, beyond this there
is little further decline. Age is the dominant factor
associated with reduced baroreflex sensitivity, although
increasing blood pressure is associated with further
blunting of baroreflex sensitivity in this older normotensive population.
Interpretation of cross-sectional ageing studies is
always confounded by possible cohort changes in
lifestyle and environment, and confirmation in longitudinal observation studies is required. However, these
and other data demonstrate a profound reduction
in baroreflex sensitivity in older individuals with
additional blunting associated with hypertension. The
mechanisms responsible for this age-associated change
remain unclear. Traditional thinking has been that
increased blood vessel rigidity impairs the function of
the afferent baroreceptors in the carotids and aortic
arch, through either structural changes (due to atherosclerosis) or functional changes (such as reduced
vascular nitric oxide activity). However, since baroreflex sensitivity can be altered acutely after stroke,
altered central processing may be an additional factor.
Clinical relevance
What is the relevance of these changes to clinical care
of the older patient? First, it is surprising that these
profound changes in baroreflex sensitivity result in
no apparent adverse consequences in most healthy
subjects in middle age and beyond. Postural hypotension remains uncommon in normotensive older individuals despite this blunting of the baroreflex [2].
However, reduced baroreflex function modifies the
response of older subjects to vasodilator drugs. The
reflex tachycardia and increase in stroke volume in
response to vasodilatation is reduced, resulting in more
marked falls in blood pressure [3], which increases
the likelihood that older patients will experience druginduced orthostatic hypotension. This common clinical
observation has yet to be confirmed in well-designed
studies comparing middle-aged and older subjects
with similar cardiovascular conditions. Other adverse
consequences of impaired baroreflex function are
now being increasingly recognized. Impaired baroreflex function may be the underlying pathophysiological
abnormality in vasovagal syncope [4]. Changes in heart
rate variability and blunting of the baroreflex following
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acute stroke may contribute to cardiac dysrhythmias
and cardiac deaths seen in this condition [5]. Reduced
baroreflex sensitivity after myocardial infarction is
associated with increased cardiac mortality [6].
Optimization of use of cardiovascular therapy in
older people would be improved through a better
understanding of drug effects on baroreflex function
and its relationship to common adverse effects (such
as syncope). The development of interventions which
improve baroreflex function in older subjects may
offer treatment opportunities for the difficult problems
of orthostatic hypotension and vasovagal syncope.
Gender, hormone replacement therapy and exercise
influence baroreflex sensitivity in middle-aged subjects,
but effects in older subjects may differ [7]. Further work
is required to elucidate the effect of these and other
environmental influences on baroreflex function in
older subjects. Given the importance of cardiovascular
disease as a cause of premature death and disability
in older people, research which increases our understanding of ageing changes in cardiovascular physiology—and their relevance to cardiovascular and
cerebrovascular risk—should yield rich dividends in
improving cardiovascular therapy for the older patient.
References
1. Dawson SL, Robinson TG, Youde JH et al. Older subjects show no
age-related decrease in cardiac baroreceptor sensitivity. Age Ageing
1999; 28: 347–53.
2. Mader SL, Josephson KR, Rubenstein LZ. Low prevalence of
postural hypotension among community dwelling elderly. JAMA
1987; 285: 1511–4.
3. Robertson DRC, Waller DG, Renwick AG et al. Age-related changes
in the pharmacokinetics and pharmacodynamics of nifedipine. Br J
Clin Pharmacol 1988; 25: 297–305.
4. Thomson HL, Wright K, Frenneaux M. Baroreflex sensitivity in patients with vasovagal syncope. Circulation 1997; 95:
395–400.
5. Robinson TG, James MA, Youde J et al. Cardiac baroreceptor
sensitivity is impaired after acute stroke. Stroke 1997; 28: 1671–6.
6. LaRovere MT, Bigger JT Jr, Marcus FI et al. Baroreflex sensitivity
and heart-rate variability in prediction of total cardiac mortality
after myocardial infarction. ATRAMI Investigators. Lancet 1998; 351:
1436–7.
7. Bowman AJ, Clayton RH, Murray A et al. Effects of aerobic
exercise training and yoga on the baroreflex function in healthy
sedentary normotensive elderly persons. Eur J Clin Invest 1997; 27:
443–9.
GARY A. FORD
Department of Medicine,
University of Newcastle, Newcastle upon Tyne NE2 4HH
Email: [email protected]
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