Physical Condition for the Coronary Artery Disease Patients-Juniper Publishers
JUNIPER PUBLISHERS-OPEN ACCESS JOURNAL OF CARDIOLOGY & CARDIOVASCULAR THERAPY
Keywords: Aerobic exercise; Cardiac output; Maximal oxygen uptake
Coronary Artery Disease Considerations
A systematic review estimated that inactivity is
responsible for 6% of the burden of disease from coronary heart disease
worldwide [1]. CAD influence on work capacity and physical performance
has been widely investigated. Myocardial functional changes include
declines in maximum heart rate, stroke volume, left ventricular
contractility and an increase in peripheral vascular resistance. Oxygen
demand and supply for the Myocardium are normally balanced. Oxygen
demand above quiescent needs of the Myocardium is determined by number
of factors:
- Heart rate-the greater the frequency of contractions, the greater the oxygen demand.
- Myocardial wall tension is a function of both left ventricular systolic pressure and the ventricular radius [2].
- The contractility of the heart-relates to the vigor and force of contraction influenced by an increase in circulating Catecholamine. Changes in structure and function of the cardiovascular system in CAD patients result in maximal oxygen uptake decline [3], which is the best single indicator of physical working capacity. Oxygen supply is the most important determinant of maximum oxygen uptake in health and disease [4], the low maximal oxygen uptake in the CAD patient may be the result of a decrease in oxygen supply (cardiac output) capacity, due to the CAD process, which has a genetic component. This coupled with the reduced ability of the working muscles to extract oxygen (arterio-venous oxygen difference) due to reduced muscle mass and function at maximal effort [5], ends up in significant reduced maximal oxygen uptake [6].
Mitochondrial density was found to be lower in
skeletal muscle of CAD patients, oxidative capacity declines in some
skeletal muscles which could further diminish capacity for endurance
work [7]. CAD patients are not generally anemic and the red blood cell
content is usually well maintained [8]. However, other studies [9,10] do
not support a causal role for muscular atrophy in the decline of
maximal oxygen uptake. It seems that the related changes in maximal
oxygen uptake are dependent on a number of factors including the onset
of disease and level of physical activity. The highest rates of decline
in maximal oxygen uptake are in those individuals that have reduced
their levels of physical activity as they age. Cardiovascular system,
morphological and physiological changes have been identified in the CAD
patients.
Important factor that influence physical performance
of the cardiac patient is aging associated with a shift in mechanism by
which cardiac output is maintained during sub maximal exercise. In spite
of having lower early diastolic filling rate during sub maximal
exercise, end diastolic volume (the amount of blood filled in the
ventricle at the end of diastole) is maintained and even increased as a
function of age. As a result, CAD patients appear to have a greater
reliance on the Frank-Starling mechanism for the maintenance of cardiac
output during sub maximal exercise [11].
Following hospitalization, the patients are offered
to attend a classical rehabilitation program with moderate exercise
intensity. Aerobic exercise training is a major, and the most important,
component of cardiac rehabilitation.The beneficial effects of cardiac
rehabilitation are widely
accepted for coronary artery diseases: reduction of 25 % of the
cardiovascular mortality at 3 years after myocardial infarction,
improvement of the exercise tolerance and quality of life [12].
Moreover, patients who have left ventricular dysfunction
post myocardial infarction, (ejection fraction <45%) improve
their exercise tolerance (+23% in peak VO2) after training
without significant deleterious ventricular remodeling [13,14].
Aerobic exercise reduces the risk of cardiovascular events in
patients with prior CAD and thus, may also decrease the risk
of mortality [15,16].
Besides providing psychological benefits it exerts a positive
effect on the risk profile for CAD patients with observed
increases in circulating HDL and reductions in systolic and
diastolic blood pressure. Exercise has also been considered
to be useful for people at high risk for developing diabetes.
Studies have shown that exercise has a preventive effect in
people with a strong family history of CAD and diabetes when
compared to high-risk people who were inactive [17,18]. The
benefits of exercise can be gleaned from several short bouts of
activity throughout the day [19]. The type of exercise can be
subtle in nature, such as walking outdoors, on a treadmill, or
through a mall. Simply increasing energy expenditure through
an increase in daily living activities, such as climbing stairs or
doing house or yard work, can help to increase energy output.
After a patient establishes these routines and experiences the
rewards of exercise, such as weight loss, psychological wellbeing,
or an improvement in plasma glucose, lipids, or blood
pressure, a more positive attitude toward exercise may result
with even a further increase in activity. Recommendations
to increase physical activity should be prefaced with an
examination of current health status. If the patient has
longstanding cardiac failure, it is practical to evaluate
for left ventricular function complications that would be
affected by exercise. The presence of previously diagnosed,
and particularly undiagnosed, CHD is a critical factor in
determining the intensity of any prescribed exercise program.
Aerobic exercise reduces the risk of cardiovascular events
in patients with prior CAD and thus, may decrease the risk
of mortality [15]. Aerobic exercise decreases incidence and
severity of cardiac events during exercise among an unselected
group of patients with stable CAD [16,17]. In addition, exercise
training improves endothelium-dependent vasodilatation
both in epicardial coronary vessels and in resistance vessels in
patients with CAD [18].
Aerobic exercise reduces the risk of cardiovascular events
in patients with prior CAD and thus, may decrease the risk
of mortality [15]. Aerobic exercise decreases incidence and
severity of cardiac events during exercise among an unselected
group of patients with stable CAD [19,20]. In addition, exercise
training improves endothelium-dependent vasodilatationboth in epicardial coronary vessels and in resistance vessels in
patients with CAD [22].
Aerobic exercise decreases incidence and severity of
cardiac events during exercise among an unselected group
of patients with stable CAD [19,21]. In addition, exercise
training improves endothelium-dependent vasodilatation
both in epicardial coronary vessels and in resistance vessels in
patients with CAD [22].
Table 1 summarizes some of the changes in cardiovascular
and hemodynamic variables associated with training in CHD
patients. Endurance exercise training in the CHD patients,
decreased resting and sub maximal exercise heart rate,
systolic and diastolic blood pressure while stroke volume
increased. Marked changes are notable in the elderly subjects
during maximal effort in which stroke volume, cardiac output,
contractility, and oxygen uptake are increased, while total
peripheral resistance, systolic and diastolic blood pressure
decreased, thus lowering after-load which in turn facilitate left
ventricular systolic and diastolic function.
When previously sedentary cardiac patients are re-tested
at the same absolute sub-maximal work rate after adapting to
endurance exercise, their endurance is found to be markedly
increased. However, metabolic factors do not appear to
determine the magnitude of VO2 max. The changes in muscle
oxidative potential may play a major role in the patients
capacity to perform sub-maximal work.
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