Journal of Gerontology: MEDICAL SCIENCES
2001, Vol. 56A, No. 5, M273–M280
Copyright 2001 by The Gerontological Society of America
Orthostatic Hypotension in Elderly Persons During
Passive Standing: A Comparison With Young Persons
Takayasu Kawaguchi,1 Osamu Uyama,1 Miwako Konishi,1 Tadahiro Nishiyama,1 and Takeo Iida2
2College
1College of Nursing Art and Science Hyogo, Akashi, Japan.
of Science and Engineering, Ritsumeikan University, Kusatsu, Japan.
Background. The present study was aimed at clarifying the mechanism of orthostatic hypotension (OH) that occurs
in elderly persons and at investigating assisting methods to prevent OH by evaluating changes in autonomic nervous
system (ANS) activity and cerebral circulation of elderly persons when engaged in passive standing.
Methods. Eight elderly volunteers and 9 young volunteers gave informed consent to participate in the study. Two
experimental conditions were established: (i) “active standing,” in which the subjects stood on their own with guidance
from an assistant, and (ii) “passive standing,” in which the subjects were placed in a standing position completely by
an assistant. ANS was determined before and after standing by measuring the heart rate variability. The reaction of the
ANS was evaluated on the basis of low-frequency power (LF: 0.05–0.15 Hz) and high-frequency power (HF: 0.15–0.4
Hz), which were separated from the R-R interval data by power spectral analysis using the fast Fourier transformation.
Cerebral perfusion was measured over the right frontal region using a near-infrared spectroscopy cerebral oxygen
monitor.
Results. The main findings were: (i) Transient decreases in blood pressure occurred immediately after standing in
both the young and elderly subjects. (ii) The LF:HF ratio increased significantly ( p ⬍ .05) immediately after active
standing in the young subjects, whereas this ratio increased in the elderly subjects after some delay. (iii) The LF:HF ratio
increased significantly ( p ⬍ .01) immediately after passive standing in the young subjects, whereas this ratio decreased
significantly ( p ⬍ .05) in the elderly subjects. (iv) In the elderly subjects, the total hemoglobin (HbT) and oxyhemoglobin showed the greatest decrease during the 15-second period after standing. The maximum changes in the HbT with
passive standing differed significantly ( p ⬍ .01) from those observed during active standing.
Conclusions. Our findings emphasize the need to devise bioengineered means that allow elderly persons to exert
themselves, to maintain or improve muscle contractility and ANS function, while providing minimum assistance for
standing.
T
HE increase in the elderly population has been accompanied by a rising number of injuries and accidents due
to physical disabilities associated with aging. This includes
the problem of orthostatic hypotension (OH), which, until
recently, has been almost exclusively associated with cerebrovascular diseases. However, an epidemiologic survey
conducted by Robbins and colleagues (1) revealed that approximately 20% of elderly persons aged 65 and older, including those without cerebrovascular disease, show a propensity to develop OH. Similarly, in a survey conducted by
Ooi and colleagues (2), more than 50% of elderly residents
of retirement and nursing homes reported OH. Thus, OH
appears to be a common finding even in elderly persons
without apparent organic disabilities.
OH develops from hydrostatic pressure differences that
occur during standing, during which time blood pools in the
lower body, and the circulating blood volume decreases.
This results in decreased blood pressure due to a reduction
in cardiac output and diminished intra-arterial blood volume. Symptoms of OH, such as dizziness, lightheadedness,
weakness, blurred vision, impaired concentration, and even
loss of consciousness, may occur when cerebral perfusion is
markedly impaired (3). Blood pressure regulatory reactions
that prevent these symptoms when standing appear typically
as (i) the increase of heart rate variability due to an activated
sympathetic nervous system and (ii) the prevention of concentrated blood flow to the lower body due to the contractility of the lower limbs’ skeletal muscle (maintenance of
venous return). For patients who have been fatigued or bedridden for a long time and for persons who have recently recovered from an illness, blood pressure regulatory reaction
is made difficult because the contracting function of skeletal
muscle and the reaction of the sympathetic nervous system
have weakened. Therefore, when the patients’ postures are
to be passively changed, to prevent OH it is necessary to ask
for their positive participation in the move or to make them
aware that they are to be moved (4,5).
Several studies on OH caused by passively changed posture have been conducted in connection with autonomic nervous system (ANS) activity (6–8). However, past studies
have not examined how the passive change of posture
changes cerebral circulation or if the passive change of posture relates to OH. Moreover, few studies have clarified
what effects are given to the maintenance of cerebral circulation by the contractility of the lower limbs’ skeletal muscle or ANS activity, both of which have are caused by the
movements required for active standing. Therefore, the
present study was aimed at obtaining guidelines for preventM273
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KAWAGUCHI ET AL.
ing OH in elderly persons when they are assisted with passive standing. We evaluated cerebral circulation and ANS
activity during passive standing (standing with complete assistance, mentally and physically) and compared this evaluation with the data taken during active standing (standing
without assistance).
METHODS
Subjects
Two groups of healthy volunteers, an elderly group (4
women and 4 men; median age, 68.2 years; range, 64–79
years) and a younger group (5 women and 4 men; median
age, 23.5 years; range, 21–32 years) were enrolled in the
study. All subjects were screened by taking an accurate history, physical examination, routine laboratory tests, and
resting 12-lead ECG to ensure that they were in good health
and showed no evidence of acute illness, clinically apparent
cardiovascular disease, diabetes mellitus, or neurological
disorders. None of the subjects smoked cigarettes or were
currently taking any medication. The research protocol was
approved by the institutional review board, and each subject
gave informed consent.
Experimental Protocol
Each subject performed a series of motions to assume or
be placed into a standing position from a sitting position in a
chair (height of seat surface, 33 cm). The subjects were all
trained to stand in a uniform manner consisting of initial
forward flexion of the back and neck followed by extension
of the body. Two experimental conditions were established:
(i) “active standing,” with guidance from an assistant, and
(ii) “passive standing,” in which the subjects remained passive while an assistant placed them in a standing position.
The active standing procedure began with the assistant
holding the subject by both hands. The subject remained
with their knees in flexion until given a verbal cue, after
which the subject assumed a standing position with guidance from the assistant. The passive standing procedure began with the assistant placing a knee between both legs of
the subject, positioning the subject’s arms at their side, and
putting both hands of the subject around the neck of the assistant. While maintaining the center of gravity downward,
the assistant positioned the subject in a standing position.
To maximize the cooperation of the subjects during the study,
a female nurse served as the assistant for female subjects,
and a male nurse served as the assistant for male subjects.
After sitting at rest for 5 minutes, each subject performed
active standing, remained standing for 5 minutes, and then
sat down again. After the subject sat at rest for another 5
minutes, the passive standing procedure was performed, and
the subject again remained standing for 5 minutes. The time
required to complete active standing and passive standing
was constant at 3 seconds. ECG monitoring and continuous
measurement and recording of cerebral circulation using a
near-infrared cerebral oxygen monitor were performed during these procedures. In addition, an automated blood pressure monitor (Jentow-7700, Nihon Colin, Japan) was used
to measure pre- and post-standing blood pressure. Blood
pressure was measured at three time points: 2 minutes be-
fore standing, immediately after standing, and 3 minutes after standing.
Heart rate spectral analysis.—Heart rate variability was
measured by ECG telemetry (Syna Act MT11, NEC Medical Systems, Tokyo, Japan) from lead V5 and recorded using a data recorder (RD135T, TEAC, Tokyo, Japan). The
sampling accuracy of the recorded data was 1 kHz, and analog-digital conversion was performed on a computer (AD98,
Canopus, Kobe, Japan). An R-R interval analysis program
(Pasherver, Kissei Comtec Co., LTD, Nagano, Japan) was
used to calculate the mean R-R interval and standard deviation. Spectral analysis was performed by fast Fourier transform (FFT). The Hanning window method was used to pretreat the signal data for FFT analysis. Spectral analysis was
performed 3 minutes before and 3 minutes after standing
(FFT algorithm yielding a 256-point). The data were condensed into 2-minute sampling periods to better view the
detailed changes during each 3-minute period. Spectral analysis was performed at 30-second intervals for a total of 6
time points before and after standing to evaluate time sequence changes (Figure 1).
The total power of the heart-rate spectral data provided
by FFT was separated into a low-frequency component (LF:
0.04–0.15 Hz) and a high-frequency component (HF: 0.15–
0.4 Hz). Each respective power component was divided by
the total power (TP) and expressed as LF/TP and HF/TP.
These values were used as an index of changes in ANS activity. In particular, the LF:HF ratio was used as an index of
sympathetic nervous system activity.
To evaluate cardio-vagal nerve activity separately from
sympathetic nervous activity, testing was performed while
Figure 1. Experimental protocol.
PASSIVE STANDING IN THE ELDERLY
each subject maintained a respiratory rate of at least 9
breaths per minute.
Near-infrared spectroscopy.—For the purpose of monitoring cerebral circulation, cerebral perfusion was measured
using a near-infrared cerebral oxygen monitor (OM-200,
Shimadzu Corp., Kyoto, Japan), with its sensor unit placed
over the right eyebrow. The area was cleaned with alcohol
before the sensor unit was affixed. This device utilizes nearinfrared light rays to measure the changes in hemoglobin in
biological tissue by spatial analysis on the basis of the light
diffusion theory. The device’s light source consists of three
different wavelength laser beams (780 nm, 805 nm, and 830
nm), and the beams are irradiated in order. According to the
variations in optical density (OD) of each wavelength, oxyhemoglobin (HbO2), deoxyhemoglobin (HbD), and total hemoglobin (HbT) are calculated on the basis of the LambertBeer law (9):
Where OD ⫽ the variations in optical density from the
initial value, and Hb ⫽ changes in the concentration of hemoglobin.
In addition, this device shows the difference between actual biological tissue and theoretical concentration, and the
difference is represented by values that have been revised
on the basis of the light diffusion formula (10,11). Because
this device provides the relative changes in concentration in
each subject, we used an arbitrary unit (AU) to express the
concentration.
Statistical Analysis
The respective changes in pre- and post-standing blood
pressure for the young and elderly groups were analyzed
and compared by one-way ANOVA. For changes in other
pre- and post-standing parameters, the Student’s paired t
test was used to analyze linear distribution variables (median R-R intervals, LF/TP and HF/TP, HbT, HbO2, and
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HbD). The Wilcoxon signed rank test was used to analyze
nonlinear data variables (LF and HF power and the LF:HF
ratio). Comparison between the young and elderly subjects
was conducted using the Student’s t test and Mann-Whitney
U test. Significance was established at the p ⬍ .05 level for
all analyses.
RESULTS
Blood Pressure and Heart-Rate Spectra
Table 1 shows comparisons in heart rate variability for 3
minutes before and after standing. The mean R-R interval
(in milliseconds) decreased significantly after standing in
both the young and elderly subjects ( p ⬍ .01). This decrease
tended to be greater in the young subjects than in the elderly
subjects. The R-R standard deviation (in milliseconds) was
significantly higher in the young subjects than in the elderly
subjects. Both LF power and HF power were higher in the
young subjects than in the elderly subjects. LF power was
significantly higher ( p ⬍ .01) before active standing in the
young subjects, and HF power was significantly higher ( p ⬍
.05) before passive standing in the elderly subjects. The LF:
HF ratio increased after active standing in both the young
and elderly subjects but tended to decrease after passive
standing. In particular, the LF:HF ratio was significantly
higher ( p ⬍ .05) after active standing in the young subjects.
Blood pressure was higher in the elderly subjects than in
the young subjects at all time points. There were no significant blood pressure changes before and after standing in either of the age groups. Blood pressure decreased immediately after standing but tended to return to baseline levels
after 3 minutes. Furthermore, there were no significant differences in blood pressure changes between active standing
and passive standing (Table 2).
Figure 2 shows heart-rate variability data for 3 minutes
before and after standing in a typical case from each group.
Comparison of the waveform changes in the R-R interval
Table 1. R-R Interval Variability Before and After Standing
Active Standing
Passive Standing
Before
R-R (ms)
Young
Elderly
R-R SD
Young
Elderly
LF Power (ms)
Young
Elderly
HF Power (ms)
Young
Elderly
LF/HF
Young
Elderly
After
Before
836.5 ⫾ 91.7**
829.9 ⫾ 69.7**
774.6 ⫾ 102.5
790.9 ⫾ 72.1
838.8 ⫾ 94.0**
835.5 ⫾ 68.3*
57.6 ⫾ 24.7†
20.9 ⫾ 3.9
55.8 ⫾ 17.3‡
24.8 ⫾ 6.6
49.8 ⫾ 15.8†
21.8 ⫾ 5.0
57.6 ⫾ 16.1‡
26.8 ⫾ 8.5
34,479 ⫾ 15,911**,†
7881 ⫾ 4005
28,256 ⫾ 23,868
6416 ⫾ 5011
48,254 ⫾ 29,574†
7701 ⫾ 5535
32,943 ⫾ 29,051
4814 ⫾ 2497
51,430 ⫾ 30,346*,†
5002 ⫾ 3941
16,894 ⫾ 11,761†
2945 ⫾ 1551
40,272 ⫾ 23,994†
4315 ⫾ 2540*
27,200 ⫾ 23,920
3253 ⫾ 2107
0.96 ⫾ 0.84*
1.66 ⫾ 1.08
1.97 ⫾ 1.03
2.18 ⫾ 0.50
1.91 ⫾ 1.62
2.38 ⫾ 1.78
1.94 ⫾ 1.44
1.91 ⫾ 1.30
Notes: Values are mean ⫾ SD. n ⫽ 9 young subjects; n ⫽ 8 elderly subjects.
Before vs after: *p ⬍ .05, **p ⬍ .01.
Young vs elderly: †p ⬍ .05, ‡p ⬍ .01.
After
772.6 ⫾ 90.2
782.5 ⫾ 70.9
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Table 2. Change of Blood Pressure at Three Points in Active and Passive Standing
Active Standing
Passive Standing
2 Min Pre
Immediately Upon
3 Min Post
2 Min Pre
Immediately Upon
3 Min Post
Systolic (mm Hg)
Young
Elderly
115 ⫾ 8
150 ⫾ 15
112 ⫾ 7
147 ⫾ 20
115 ⫾ 6
150 ⫾ 32
114 ⫾ 5
141 ⫾ 17
112 ⫾ 3
138 ⫾ 16
110 ⫾ 4
139 ⫾ 23
Diastolic (mm Hg)
Young
Elderly
67 ⫾ 2
86 ⫾ 11
64 ⫾ 4
87 ⫾ 10
68 ⫾ 4
85 ⫾ 13
67 ⫾ 5
86 ⫾ 17
62 ⫾ 3
83 ⫾ 15
64 ⫾ 4
85 ⫾ 16
81 ⫾ 3
105 ⫾ 12
78 ⫾ 4
104 ⫾ 10
82 ⫾ 3
104 ⫾ 18
80 ⫾ 4
100 ⫾ 17
76 ⫾ 2
96 ⫾ 16
77 ⫾ 3
98 ⫾ 18
Mean (mm Hg)
Young
Elderly
Notes: Values are mean ⫾ SD. n ⫽ 9 young subjects; n ⫽ 8 elderly subjects.
(in milliseconds) between the young and elderly subjects revealed regular and rhythmic variations in the young subjects
but more blunted variations in the elderly subjects. We observed transient shortening of the R-R interval for approximately 10 seconds immediately after standing. The degree
of shortening was more pronounced with active standing
than with passive standing. The elderly subjects demonstrated less shortening of the R-R interval after standing, including a more gradual response, than the young subjects.
A comparison of the frequency power distribution between the young and elderly subjects revealed greater
power values in the young subjects. Evaluation of the
changes in total power showed a decrease in the HF power
component after standing in the young subjects but showed
very little change in the elderly subjects.
Serial Changes in Heart-Rate Spectra Before and
After Standing
Figure 3 shows time sequence changes in LF/TP, HF/TP,
and the LF:HF ratio before and after active standing. There
were no significant differences in the LF/TP changes. However, the young subjects showed a significantly lower HF/
TP ( p ⬍ .05) at 0 to 2 minutes and 0.5 to 2.5 minutes after
standing than immediately before standing. The young sub-
Figure 2. Example of spontaneous fluctuations in interbeat intervals of A, a young subject (a 22-year-old woman), and B, an elderly subject (a
71-year-old man), during 3 minutes before and after standing, as well as the reflection of these variations in the power spectra.
PASSIVE STANDING IN THE ELDERLY
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jects showed a significantly increased LF:HF ratio ( p ⬍
.05) immediately after standing, whereas this ratio increased
in the elderly subjects only after some delay.
Figure 4 shows time sequence changes in LF/TP, HF/TP,
and the LF:HF ratio before and after passive standing. The
young subjects showed a significantly increased LF/TP ( p ⬍
.05) at 0.5 to 2.5 minutes after standing, whereas the elderly
subjects had a significantly decreased LF/TP ( p ⬍ .05) immediately after standing. The elderly subjects showed a decreased HF/TP ( p ⬍ .05) immediately after standing. The
young subjects showed a significantly increased LF:HF ratio ( p ⬍ .01) at 0.5 to 2.5 minutes after standing, whereas
the elderly subjects had a significantly lower LF:HF ratio
( p ⬍ .05) immediately after standing, followed by a slow
subsequent increase.
Changes in Cerebral Circulation
Figure 5 shows the changes in HbT, HbO2, and HbD in
the young subjects every 2 seconds after standing. The HbT
and HbO2 showed the greatest decrease during the 10-second period after standing and returned to baseline levels approximately 20 seconds after standing. The HbD rose
slightly after standing, although not significantly, and returned to baseline values approximately 20 seconds after
standing. A comparison of the maximum variation in HbO2
and HbT during active standing and passive standing revealed significantly greater changes during passive standing
(HbT, p ⬍ .01; HbO2, p ⬍ .05).
Figure 6 shows the changes in HbT, HbO2, and HbD in
the elderly subjects every 2 seconds after standing. The HbT
and HbO2 showed the greatest decrease during the 15-second period after standing and tended to be slightly delayed
compared with the young subjects. Furthermore, unlike in
the young subjects, these values had still not returned to
baseline levels even 20 to 25 seconds after standing. A comparison of the maximum variation in HbO2 and HbT during
Figure 3. Comparison of heart-rate variability of the young and
elderly subjects in active standing.
Figure 4. Comparison of heart-rate variability of the young and
elderly subjects in passive standing.
standing revealed a significant difference in the change in
the HbT ( p ⬍ .01) during passive standing compared with
active standing.
DISCUSSION
The changes in the LF:HF ratio of the elderly subjects after passive standing was delayed significantly in comparison with the young subjects, which proves the blunt reaction
of the sympathetic nervous system of the elderly subjects
after standing. This implies that it is necessary to pay attention to activating the function of the ANS of elderly subjects
when they stand passively. As for the changes in cerebral
circulation, there appeared to be a transient decrease in the
Figure 5. A, Changes in HbT, HbO2, and HbD in the young subjects every 2 seconds after standing. B, Comparison of the maximum
variation in HbT and HbO2 in the young subjects during active and
passive standing.
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KAWAGUCHI ET AL.
Figure 6. A, Changes in HbT, HbO2, and HbD in the elderly subjects every 2 seconds after standing. B, Comparison of maximum variation in HbT and HbO2 in the elderly subjects during active and passive standing.
cerebral perfusion during a period of 10 to 20 seconds after
standing in both young and elderly subjects. In particular,
the decrease in cerebral perfusion was more significant in
passive standing than in active standing. The main reasons
are a decrease in venous return due to the lack of contractility of the lower limbs’ skeletal muscle and a decrease in
heart-rate variability caused by a decrease in venous return.
As for healthy persons, the increase in heart-rate variability
due to an activated sympathetic nerve will compensate even
under a condition of this kind. However, such a compensation can hardly be expected in elderly persons with lowered
autonomic nervous function, and, in particular, it is unlikely
that compensation will occur in elderly subjects who suffer
from diabetes and ANS dysfunction (12). ANS dysfunction
is a morbid state caused by aging; it is therefore necessary
to take into account the changes in morbid states caused by
aging.
The present study established two conditions, active
standing and passive standing, to control experimentally
whether or not skeletal muscle contractility arises. These
two methods of care are generally taken in clinical situations, and the results of the present study demonstrate the
influence given to the venous return by the difference of
skeletal muscle activity, which is applicable to actual situations where care is given.
The present study analyzed heart-rate variation to reflect
ANS activity during postural changes. This method of analysis, particularly with reference to the evaluation of the effects of changes in posture on OH, has been discussed by
other investigators (13,14). Some researchers have reported
different characteristic trends between elderly patients, who
often experience ANS dysfunction and decreased muscle
strength, and healthy younger individuals (15–17).
Pagani and colleagues (18) compared heart rate variability between young and elderly subjects and found that the
LF:HF ratio tended to be lower with a head-up tilt posture in
the elderly subjects. Lipsitz and colleagues (8) evaluated the
characteristics of heart-rate variability in elderly subjects
during a head-up tilt procedure and concluded that the low
frequency power component tended to increase less remarkably (0.06–0.10 Hz) than that observed in younger subjects,
suggesting that abrupt postural changes present a risk factor
for syncopal attacks in this group. Our results are in general
agreement with these previous findings. Thus, during assisted standing in the elderly persons, who may already be
experiencing some autonomic nervous dysfunction, sufficient precautions must be taken to ensure adequate autonomic nerve function (e.g., allowing the elderly persons to
stand up with as little assistance as possible).
Furthermore, we found that changes in heart-rate variability and cerebral perfusion were greatest during the 30second period immediately after standing. Until recently,
rapid changes in these parameters induced by standing were
difficult to measure due to limitations in the available measurement devices. However, recent improvements in measurement devices have enabled more accurate assessment of
these parameters immediately after standing. Tanaka and
colleagues (19) applied a volume clamp technique to continuously monitor finger blood-pressure variations immediately after active and passive standing and found a substantial reduction in blood pressure during the first 10 seconds
after standing. Bloomfield and colleagues (6) analyzed and
compared heart-rate variations in subjects during passive
head-up posturing and active standing up and found a
marked reduction of the R-R interval immediately after active standing. On the basis of their results, they suggested
the importance of monitoring these variations immediately
after standing in the diagnosis of OH. We noted similar
variations in the present study (Figure 2).
One purpose of the present study was to clarify the influence of changes in blood pressure when standing on cerebral circulation. However, measurements in the present
study did not find remarkable changes in blood pressure immediately after standing. That is to say, the manchette measuring method did not allow us to measure the rapid changes
in blood pressure immediately after standing, which was one
of the study purposes. The R-R interval variability shows an
abrupt increase in heart rate during an instantaneous period
of 10 to 20 seconds immediately after standing. A sharp
drop in blood pressure seems to have occurred with the increase in heart rate. It is necessary to develop in-depth studies on the changes in blood pressure by developing a testing
method that can monitor the blood pressure’s serial changes
during the entire process of the test.
The influence of postural changes on cerebral perfusion,
which was clarified by this experiment, has also been studied by others, along with the development of measuring instruments. In 1948, Shenkin and colleagues (20) measured
cerebral blood flow changes from a head-up to a head-down
position by the Kety method utilizing radioisotopes. Since
then, advanced imaging technologies, including computed
tomography, single photon emission computed tomography,
and positron emission tomography, have been developed.
These technologies assist in medical diagnosis by allowing
the monitoring of cerebral perfusion during head-up tilt testing as well as other postures. Recently, several studies have
PASSIVE STANDING IN THE ELDERLY
begun to focus on the relation between impaired cerebral
autoregulation and orthostatic hypotension. Aaslid and colleagues (21) examined the reduced cerebral blood flow associated with postural changes in healthy subjects and reported that the autoregulatory function associated with
cerebral vascular constriction was evident within 10 seconds and returned to baseline within 60 seconds. In contrast,
this autoregulatory function appears to be impaired in patients with autonomic nervous dysfunction, thus predisposing these patients to the development of symptoms such as
syncope.
The present study included the use of a near-infrared cerebral oxygen monitor to measure changes in cerebral perfusion immediately after standing. This device monitors intracerebral blood flow via a sensor placed on the forehead.
We chose this device because it is noninvasive and imposes
minimal burden on the study subjects. Several studies, including those by Hampson and colleagues (22), Kurth and
colleagues (23), and Li and colleagues (24), have verified
that this device can accurately monitor cerebral blood flow
and cerebral oxygenation. Jobsis (9) stated that the changes
in HbO2 detectable by near-infrared monitoring reflect relative changes in cerebral perfusion. Similarly, in the present
study, relative changes in HbO2 served as an index of
changes in cerebral perfusion upon standing. The measurement technique currently used, although capable of determining relative changes in a specific subject, is still not able
to provide absolute values. Thus, interpretation of the
changes at each measurement point can be considered only
on an individual basis because it is often difficult for the relation between the concentration and optical density based
on the Lambert-Beer law to be applied directly to biological
tissue. It can be pointed out that the measurement based on
the Lambert-Beer law needs contrastive materials of “zeroconcentration,” which are difficult to obtain in biological
tissue, and that it is difficult to determine optical axis distance because biological tissue is a strong scattering medium. In some studies, the variability gained from the NIRS
measurement is expressed in ␮mol/l. However, for the
above-mentioned reasons, the use of ␮mol/l when measured
with this device may result in questionable findings. We and
others (25,26) express by the arbitrary unit.
Cerebral blood flow and metabolism are known to gradually decrease after reaching adulthood as part of the aging
process. Hock and colleagues (27) reported that the magnitude of increase in HbT and HbO2 and the magnitude of decrease in HbD during brain activity (measured over the
forehead) is lower in elderly individuals than in younger individuals. In addition, the amount of brain parenchyma differs between younger and elderly individuals. Although cerebral atrophy is generally most prominent in patients with
presenile and senile dementia, these atrophy changes may
also be present in healthy elderly individuals. From the perspective of the monitoring principles used in the present
study, the distance from the skin site of the sensor to the
brain parenchyma was longer in the elderly subjects than in
the young subjects (28,29); thus, differences in the amount
of cerebrospinal fluid occupying the space between the
skull and brain parenchyma may also have influenced our
findings. Because a comparison of the differences in abso-
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lute cerebral blood flow between elderly and young subjects
was not possible, our study focused on the assessment of the
relative changes in each group of subjects.
We evaluated autonomic nervous function and cerebral
perfusion primarily on the basis of the premise that the ANS
plays a major role in the regulation of cerebral circulation.
However, regulation of cerebral circulation is not influenced only by the ANS. Higher-functioning circulatory centers in the central nervous system (CNS) have also been
shown to play an important role in this process. A study in
cats by Ninomiya and colleagues (30) describes the involvement of higher CNS centers in the regulation of increased
cardiac sympathetic nerve activity just prior to spontaneous
movement and in the regulation of increased heart rate and
myocardial contractility during actual movement. These
findings indicate that spontaneous movement may also play
a key role in circulatory regulation. Thus, sudden passive
postural changes of a person in an assisted care setting
likely contribute to the development of OH. Further indepth research should be conducted, including an investigation of the specific role of higher CNS function in these
conditions.
The worldwide increase in the aging population is expected to increase the necessity to assist elderly persons
with their postural changes, which may consequently increase accidents due to OH while they are assisted with
standing. Our findings indicate that it is important to make
elderly persons aware of the necessity to activate their autonomic nervous function before they are assisted with standing and to take care of them in a way that sufficiently utilizes the function of their skeletal muscles. Further studies
are needed that examine situations where elderly persons
are assisted with standing, and it is necessary to develop
bioengineered means that allow elderly persons to exert
themselves for the maintenance and improvement of muscle
contractility and ANS function.
Acknowledgments
This research was funded in part by a Grant-in-Aid (08672691) from the
Ministry of Education, Science and Culture, Japan.
Address correspondence to Takayasu Kawaguchi, RN, PhD, College of
Nursing Art and Science Hyogo, 13-71, Kitaoji-cho, Akashi 673-8588, Japan. E-mail: [email protected]
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Received October 15, 1999
Accepted December 15, 2000
Decision Editor: John E. Morley, MB, BCh