Continued from page 1
VO2max is another important consideration of stress test and this correlates well with physical fitness at least in a cardiorespiratory and cardiovascular sense. The amount of oxygen consumed by myocardium is dependent on oxygen demand: heart rate, contractility, and wall tension. The individual will exercise until oxygen demand by myocardial cells exceeds ability of stenotic coronary artery to deliver oxygen. In other words, exercise continues until coronary reserve has been exhausted. At this point, ischemia is induced and exercise must be terminated. During exercise test, if individual experiences pectoral angina, intense dyspnea or unusual changes on electrocardiogram, or significant rhythm change due to a heart block or ventricular disturbance, an unsupervised exercise program may be contraindicated.
The test may be stopped for reasons other than reaching a VO2max upper threshold or having chest discomfort; fatigue, dyspnea, and musculoskeletal problems may cause mature adult to discontinue exercise. The test also will be terminated if blood pressure drops as work increases. Blood pressure is recorded before test, at an exercise peak, and at recovery. Diastolic BP should remain constant, but could increase slightly because of anxiety. It then could decrease once test begins. Systolic BP usually increases by 60+/-25 mm Hg in males 50-64 years of age, and by 40+/-20 mm Hg in women in same age group. For example, if systolic BP fails to increase, or initially increases then drops by more than 20 mm Hg during exercise, then it may indicate severe left ventricular dysfunction. Should systolic blood pressure fall more than 30mm Hg, then an unsupervised exercise program may be contraindicated.
Sometimes stress test shows heart complications when, in fact, extrinsic factors are responsible, and this will cause a false-positive result. These include:
-Drug use (e.g., antidepressants) - physician will take into account effects of any medication individual may be taking
-Malfunctioning ECG recording equipment
-And a host of other minor heart complications that should not stop an individual from participating in an exercise program.
It will be up to physician to remove causative agent and re-test patient. This especially is necessary to discover if patient is asymptomatic or has potential for a high exercise capacity. A false-negative test resulting from an extrinsic factor is even more disturbing as this would indicate failure to diagnose presence of abnormal coronary arteries. It then is up to physician to rely on other test procedures and for individual or fitness professional to monitor progress carefully and to supply physician with any information in regard to physical difficulty during exercise.
If test is performed properly, and there is a negative ECG response to exercise, test does not indicate coronary disease necessarily. Rather, it implies a risk factor that must be taken into consideration when an exercise program is created, and that there must be close monitoring of individualís health and fitness level.
CONTRAINDICATIONS FOR A STRESS TEST
-Acute myocardial infarction (heart attack)
-Uncontrolled congestive heart failure
-Acute inflammatory cardiac disease, e.g., active rheumatic heart disease, myocarditis
-Acute asthma or pneumonia
-Blood pressure greater than 240/120 mm Hg and uncontrolled
-Acute renal (kidney) disease
Brian D. Johnston is the Director of Education and President of the I.A.R.T. fitness certification and education institute. He has written over 12 books and is a contributing author to the Merck Medical Manual. An international lecturer, Mr. Johnston wears many hats in the fitness and health industries, and can be reached at info@ExerciseCertification.com. Visit his site at www.ExerciseCertification.com for more free articles.