From the Cattedre di Medicina Interna (C.G., M.F., A.G., S.C., G.M.) and
Ortopedia (M.B., M.D.), Università di Milano and Ospedale S. Gerardo,
Monza; and the Centro di Fisiologia Clinica e Ipertensione, IRCSS Ospedale
Maggiore, Milano (G.M.), Italy.
Correspondence to Professor Giuseppe Mancia, Clinica Medica, Università di Milano, Ospedale S. Gerardo dei Tintori, via Donizetti 106, 20052 Monza, Milano, Italy. E-mail mancia.g{at}imiucca.csi.unimi.it
Abstract
Abstract—Physical training
is associated with an increase in arterial distensibility.
Whether the effect of training on this variable is evident also for
ordinary levels of exercise or no exercise is unknown, however. We have
addressed this issue by investigating the effect on radial artery
distensibility of prolonged monolateral immobilization of the
ipsilateral limb versus the following resumption of normal mobility. We
studied 7 normotensive subjects (age, 25.4±3.0 years;
systolic/diastolic blood pressure,
119±9/68±6 mm Hg, mean±SE) in whom 1 limb had been
immobilized for 30 days in plaster because of a fracture of
the elbow. At both the day after plaster removal and after 45 days of
rehabilitation, radial artery distensibility was evaluated by an
echo-tracking device (NIUS-02), which allows arterial
diameter to be measured noninvasively and continuously over all
pressures from diastole to systole (finger monitoring),
with the distensibility values being continuously derived from the
Langewouters formula. In both instances, the contralateral arm was used
as control. Immediately after removal of the plaster, radial artery
distensibility was markedly less in the previously
immobilized and fractured limb compared with the
contralateral limb (0.4±0.1 versus 0.8±0.1, 1/mm Hg
10-3, P<0.05). After rehabilitation, the
distensibility of the radial artery was markedly increased in the
previously fractured limb (0.65±0.1 1/mm Hg 10-3,
P<0.05), whereas no change was seen in the
contralateral limb. Thus, complete interruption of physical activity is
associated with a marked reduction of arterial
distensibility, indicating that even an ordinary level of activity
plays a major role in modulation of arterial
mechanical properties.
Exercise training is associated with several
changes in cardiac and arteriolar structure and
function.1 2 3 4 5 6 7 8 9 There is evidence, however, that
large and conduit artery mechanical properties are also modified by
training and that the modification consists of an increase in
distensibility10 11 12 13 that is particularly evident
in the arteries of the limbs most involved in the physical
activity.14
Whether arterial mechanical properties are modified
also by ordinary levels of physical activity (rather than becoming
manifest only during exercise training) has never been investigated. In
the present study, we addressed this issue by measuring radial
artery diameter and distensibility in subjects in whom 1 arm was
immobilized in plaster for 30 days because of an elbow
fracture. The examination was performed on the day after removal of the
plaster and after 45 days of rehabilitation, in both instances using
the contralateral radial artery as control.
Methods
Subjects
Radial Artery Evaluation
The device also uses a photoplethysmographic system (Finapres, Ohmeda)
that allows blood pressure to be recorded noninvasively from a
finger ipsilateral to the radial artery examined with an accuracy
similar to intra-arterial radial artery
pressure17 and with a resolution of 2
mm Hg.17
Blood pressure and arterial diameter signals were
directed to a computer that was programmed to calculate the
cross-sectional/pressure curve of the vessel. The curve was
analyzed according to its fit with the arctangent model of
Langewouters et al,18 which is based on the
formula
All measurements were performed by a single operator. The variation
coefficient of radial artery diameter measurements obtained by the same
operator in 2 different sessions (the within-operator variability) was
3.0%. The corresponding variation coefficient of radial artery
cross-sectional distensibility was 7.0%.
Protocol and Data Analysis
Blood pressure, heart rate, and radial artery diameter and
distensibility were obtained by averaging the values of five 30-second
periods taken at 3-minute intervals. Radial artery diameter/pressure
curves, cross-sectional distensibility/pressure curves, and diameter at
diastolic blood pressure obtained in individual subjects
were summed and expressed as mean values for the group as a whole,
separately for either arm and either experimental condition. This was
done also for the area under the curve relating cross-sectional
distensibility to blood pressure normalized for pulse pressure, ie, the
"distensibility index."20 21 22 23 24
The statistical significance of the differences in mean values
between arms and situations was assessed by 2-way ANOVA. The 2-tailed
unpaired Student t test was used to locate differences
between arms, whereas the paired Student t test was used to
locate differences before and after rehabilitation. Throughout the
text, values are mean±SEM.
Results
Figure 1
As shown in Figure 2
The forearm circumference in the healed limb was 24.0±2.1 cm before
and 26.1±2.0 cm after rehabilitation (P<0.05). The
corresponding values in the contralateral limb were 26.5±1.8 and
26.3±1.9 cm.
Discussion
Several studies have shown that exercise training is
accompanied by an increase in arterial
distensibility.10 11 12 13 14 The present study,
however, offers the first demonstration that the effect of exercise on
arterial mechanical properties is not limited to that
obtained by an increase in the exercise level but is already evident
and marked for an ordinary level of physical activity. That is, that
when arterial distensibility is quantified in a limb first
after prolonged immobilization and then after physical rehabilitation,
its value is much greater in the latter compared with the former
condition. Physical activity should thus be regarded as a mechanism
involved in the determination of arterial mechanical
function in all subjects, its role coexisting with other mechanisms
involved in the tonic modulation of these functions, eg, sympathetic
nerve activity.4 21 23 25 26 27 Our study does not
clarify the mechanisms responsible for the effect of an ordinary level
of physical activity on arterial distensibility. We can
speculate, however, that both structural and functional factors are
involved. Structural factors may reflect the fact that immobilization
may lead to a reduction of the more distensible components of the wall
tissues (eg, smooth muscle and elastin) to a greater extent than a
reduction in the stiffer components (eg,
collagen).28 29 Functional factors may reflect
the fact that immobilization leads to a local increase in sympathetic
tone, given the evidence that sympathetic tone reduces radial artery
distensibility, probably via contraction of smooth muscle in the
arterial wall.3 4 20 21 25 They may
also reflect the fact that immobilization may be accompanied by a
reduction in limb blood flow (as indirectly suggested by the reduced
forearm circumference after immobilization) and thus in the shear
stress–determined endothelial secretion of substances
(eg, nitric oxide) that relax vascular smooth muscle and make it more
distensible than in the contracted state.30 31 32 33
Unfortunately, the structural hypothesis cannot be tested because of
the need for a bioptic and thus invasive approach. The functional
hypothesis, on the other hand, can be tested by examining whether a
difference in arterial distensibility disappears in the
period immediately after prolonged ischemia (ie, when smooth
muscle tone in the arterial wall is completely
abolished).20 22 34 This was not possible in our
subjects, however, because of the difficulty of performing these
maneuvers immediately after removal of the plaster when effective
skeletal muscle contraction and limb extension were impaired.
Our findings that an ordinary level of physical activity already exerts
a positive influence on arterial distensibility has
pathophysiological implications. We can speculate
that sedentariness should be regarded as an unfavorable condition as
far as large artery function is concerned, given the adverse
consequences (increased cardiac work, greater reflection of pulse
waves, greater central blood pressure, greater trauma to the vessel
wall) that increased artery stiffness has on the
cardiovascular system.35 We can
also speculate that these consequences may develop in
cardiovascular diseases, which are accompanied and
characterized by a reduced level of physical activity, although the
neurohumoral situation is different and complex; one of these could be
congestive heart failure, in which radial artery distensibility has
indeed been shown to be reduced.21 23 26 36
Received February 2, 1998;
first decision February 17, 1998;
accepted April 8, 1998.
References
© 1998 American Heart Association, Inc.
Third Workshop on Structure and Function of Large
Arteries: Part III
Effects of Prolonged Immobilization of the Limb on Radial Artery Mechanical Properties
Key Words: arterial distensibility • training • exercise • vessels • circulation
We studied 7 healthy, right-handed young subjects (5
males, 2 females) aged from 17 to 30 years (25.4±3.0 years, mean±SE).
The subjects suffered from elbow fracture that had been treated by
complete immobilization of the limb in plaster for 30 days. All
subjects had sphygmomanometric blood pressure values <140/90
mm Hg (mean of 3 measurements). They volunteered to participate in the
study after being informed of its nature and purpose. The study
protocol was approved by the ethics committee of our hospital.
In the present study, the time-dependent changes in
arterial diameter were obtained with an A-mode ultrasonic
echo-tracking device that recorded the displacement of the radial
artery over the whole cardiac cycle (NIUS-02 system, Asulab, and
Capital Medical Service)15 and thus over the
whole diastolo-systolic pressure range. Briefly, the device
uses a highly focalized transducer operating at a frequency of 10 MHz
that was stereotaxically positioned over the radial artery
2 to 4 cm above the wrist, with gel used as a medium to prevent direct
contact with the skin. With the subject supine and the arm immobile at
the heart level, the transducer was oriented perpendicularly to
the longitudinal axis and the largest cross-sectional dimension of the
artery, based on the Doppler acoustic quality signal. After the
switch to A-mode, the echo beams corresponding to the inner posterior
and anterior walls of the artery were visualized on a computer screen
(via an analog/digital fast transducer), thus allowing internal
diameter variations to be derived. The spatial resolution was 150
µm.15 The internal diameter of the pulsating
radial artery was measured at 50 Hz, and the device resolution allowed
the identification of diameter changes of 0.0025 mm during the
blood pressure cycle15 16 (see below).
where S is the cross-sectional area of the vessel,
P is the intravascular pressure, and
, ß, and 
are 3
optimal parameters describing the spatial position of the
diameter-pressure curve.18 From this formula,
cross-sectional compliance
(C=
S/P19) was
calculated as follows:
and expressed as consecutive values for blood pressure ranging
from diastole to systole (cross-sectional
compliance/pressure curve). The above formula was then used to
calculate cross-sectional distensibility (cross-sectional compliance
divided by vessel section) over the blood pressure range from
diastole to systole (cross-sectional
distensibility/pressure curve).
The study was conducted on the morning of the day after
removal of the plaster, following a 12-hour abstinence from alcohol
consumption, caffeine consumption, and smoking. The protocol of the
study was as follows: (1) Each subject was placed in the supine
position and fitted with the finger pressure and the echo-tracking
devices after exclusion of the presence of edema at the measurement
sides. (2) After a 10-minute interval, radial artery diameter and
cross-sectional distensibility were continuously measured over a
15-minute baseline period together with blood pressure and heart rate.
The measurements were performed first in 1 limb and then in the
contralateral limb, the first measuring side being selected randomly.
(3) The whole procedure was repeated following the same sequence after
45 days of rehabilitation of the healed limb. Rehabilitation included
intermittent handgrip exercise of the forearm muscles (squeezing a
ball) and repeated flexion and extension of the forearm for 30 minutes
per day. 
, left panels, shows that in
the study performed immediately after the removal of the plaster, the
increase in blood pressure from diastole to systole was
accompanied by a slight progressive increase in radial artery diameter
and by a steep progressive and nonlinear reduction in radial artery
distensibility; this was the case in both the previously
immobilized limb and the contralateral limb. In the
previously immobilized limb, radial artery diameter was
only slightly less than in the contralateral limb (Figure 1, right
top). Radial artery distensibility, however, was much smaller, the
difference in the distensibility index being statistically significant
(Figure 1, right bottom). This was the case also when the
distensibility index was calculated for the portion of the 2 curves
that shared the same blood pressure range, ie, the "isobaric"
distensibility index.20 21 22 23 24
View larger version (24K):
[in a new window]
Figure 1. Radial artery diameter/blood pressure curves,
distensibility/blood pressure curves, diastolic diameter,
and distensibility index in the healed (H) and contralateral (C) arms.
Data are mean±SE. , systolic
blood pressure, diastolic blood pressure, and heart rate
were not modified after 45 days of rehabilitation of the healed limb,
which showed a slight and not significant increase in radial artery
diameter. Radial artery distensibility, however, increased
significantly, and the difference in the distensibility index from the
value seen immediately after removal of the plaster was statistically
significant, which was also the case for the isobaric distensibility
index. The rehabilitation period did not modify radial artery diameter
and distensibility in the contralateral limb, for which the
distensibility index value remained slightly greater than that of the
healed limb even after rehabilitation.
View larger version (21K):
[in a new window]
Figure 2. Blood pressure, heart rate, distensibility/blood
pressure curves, individual and mean distensibility indexes, and
individual and mean diastolic diameters in the healed (H)
and contralateral (C) limbs before (B) and after (A) mobilization. Data
are mean±SE. S indicates systolic; D, diastolic.
*P<0.01 vs control; §P<0.05 vs before
rehabilitation.
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