Effects
of Exercise on the Cardiovascular System
AGHE Annual Meeting
San Jose, California
February 22-25, 2001
Professor Of Biology
Quinnipiac University
Hamden, Ct 06518
Tel. (203) 582-8676
Fax (203) 582-8706
E-mail:
Page topics
Introduction
General Cardiovascular Changes With Aging
Cardiovascular Response to Exercise
Risk of Exercise in the Elderly
Effects of Estrogen on Cardiovascular System
INTRODUCTION
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Elderly (65 and over) constitute a growing proportion of
the population. Cardiovascular
disease (CVD) is a common denominator for this age group, negatively affecting
quality of life and life expectancy.
The effects of CVD in women is even more striking.
Approximately 500, 000 women (primarily postmenopausal) die each year
from CVD. Statistically, slightly
more than one out of every two women in U.S. will die of CVD.
Since 1984, the number of female deaths due to CVD has inched above the
number of male deaths (American Heart Association).
Although CVD develops 10-15 years later in women, the risk, however,
rises exponentially after menopause.
A major mechanism to counteract CVD is physical exercise.
Benefits of physical activity have been documented in healthy and
chronically ill elderly while the risks have been found to be modest.
Unfortunately, epidemiological studies indicate that only 30% of the
elderly regularly participate in some type of physical activity.
Furthermore, only 2 to 5% of the elderly report that they participate
in vigorous physical activity.
American College of Sports Medicine and Centers for Disease Control and
Prevention recommend every adult should participate in at least 30 minutes of
moderate intensity physical activity in most, but preferably all, days of the
week. In addition, they also
recommend additional hours of physical activities such as gardening, home
cleaning and repairing.
GENERAL CARDIOVASCULAR CHANGES WITH AGING
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1.
Reduction in total heart cell mass, including muscle tissue.
2.
Number of muscle fibers decrease. However, unlike the skeletal muscle fibers, cardiac muscles
compensate by increasing in size and hence, maintaining cardiac ventricular
fiber mass. In the very old
individuals, myocardial atrophy occurs. Consequently,
in the very old it is difficult to distinguish between disease versus effects
of aging.
3.
Increase in organ fat
4.
Modest decrease in metabolic rate and O2 consumption per unit of
body weight.
5.
Connective tissue, although small percentage of heart mass, increases with
aging.
6.
Mild ventricular hypertrophy with increase in end – diastolic left
ventricular volume of 5 to 10%.
7.
Increase in volume of left atrium. More pronounced in males than females.
8.
Pacemaker, Sino-Atrial Node (SA), undergoes marked age-related change.
SA node cell numbers decline by as
much as 90%. Connective tissue
spreads around SA node influencing spread of
impulses. At this time we are not
sure what is the minimum number of SA node cells
that are needed for survival. The
changes in SA node increases chances of supraventricular arrhythmias and first
degree AV blocks.
9.
Unlike SA node, AV node cell numbers are maintained.
However there is increase in the age-related
delay through the AV node.
10. Decrease of 50% in cell fiber numbers in the left branch of the Bundle of His.
11. Changes
in responsiveness to neurohormonal stimuli.
This may be the reason why spontaneous variations of heart rate over 24
hours period in men decrease with age.
12.
Intrinsic
sinus rate (measured in the presence of both sympathetic and
parasympathetic blockade) is significantly diminished with age.
13. Maximum
cardiac output (not resting) tends to decrease in a linear fashion after the
age of 30 in both males and females. This
is primarily due to decrease in heart rate with age.
14.
Arterial
walls stiffen with age and the aorta becomes dilated and elongated.
15. Age-related
reduction in compliance of arterial walls resulting in higher end-systolic
afterload. Consequently, the
aging ventricles must work against a higher end-diastolic afterload.
16. Decrease
in H2O content, more at the extracellular level.
This has important effects on blood flow and volume of distribution of
H2O – soluble molecules and drugs.
This phenomenon is also referred to as age-related “drying”.
Heart Rate
(Maximum) = 220 – age (years)
CARDIOVASCULAR RESPONSE TO EXERCISE
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1.
At beginning of exercise there is a rapid increase in heart rate (HR), stroke
volume (S.V.), and cardiac output (C.O.).
H.R. and C.O. increase within one second after muscular exercise.
If work rate is constant and below lactate threshold, a steady-state
plateau in H.R., S.V. and C.O. is reached within two to three minutes.
Recovery from short-term, low-intensity exercise is generally rapid, while the
slope of the recovery phase is the same for both trained and untrained
subjects, trained subjects however recover faster since they do not achieve as
high a H.R. as untrained subjects.
2.
Maximum aerobic capacity (VO2 max) decreases by approximately 1%
each year after age 20. This
decline can be interrupted with exercise.
For example, the expected decline in VO2 max , in middle age
and elderly individuals, over a twenty year period show half the expected
decrease. This is particularly
true in males. The decline in VO2 max in the elderly is probably due to
among many factors to the following:
a.
Decrease in physical activity
b.
Increase in body fat and decrease in body muscles (i.e. decrease in lean body
mass)
c.
Since VO2 max declines normally
with aging, the ability of the elderly to engage comfortably in normal
physical activities is reduced.
The above factors initiate a vicious cycle that leads to lower levels
of cardiorespiratory fitness.
Total Body O2 consumption = C.O.
(Arteriovenous O2 difference)
(VO2 max )
(A-
VO2 )
Possible limiting factors:
C.O. |
(A-VO2)
|
|
Declining blood volume |
Altered pulmonary function |
|
Altered circulation time |
Altered hemoglobin concentration |
|
Altered contractile state |
Declining muscle mass |
|
Altered afterload |
Altered percent extraction |
|
|
|
3.
Decrease in plasma fibrinogen (blood clotting factor) (particularly in
postmenopausal women) leading to lower risks of CVD
4. Lower H.R., higher S.V. (due to increase in end-diastolic volume, EDV)
and reduced vascular stiffness.
5. Improved
diastolic filling, particularly in males.
6. Increased
ejection fraction due to increase in S.V.
7. Increase
in HDL, decrease in LDL and triglycerides.
8.
RISK
OF EXERCISE IN THE ELDERLY
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topics
1.
Exercise-induced ventricular arrhythmias
2.
Contraindicated for the following conditions:
a.
Dementia
b.
Chronic cerebrovascular disease
c.
Pressure ulcers
d.
Gait disturbances and falls
e.
Urinary incontinence
EFFECTS OF ESTROGEN ON
CARDIOVASCULAR SYSTEM
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1.
Orally administered estrogen alone or with progesterone increase levels of HDL
in
postmenopausal women. In women
with low HDL risk of heart disease is 7X.
2.
Decreases fibrinogen (blood-clotting factor) in plasma.
3. Decreases levels of
plasminogen activator inhibitor (enzyme which blocks the actions of natural clot dissolver, tissue plasminogen activator).
4. Stimulates relaxation of
blood vessels.
5. Promotes
angiogenesis (new blood vessel development) decreasing vascular resistance
leading to decrease in blood pressure.
6.
Inhibits production of endothelin, a potent vasoconstrictor produced by endothelial
cells of vessels, leading to high blood pressure.
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Copyright 2000 Ken
Kaloustian, Ph.D.