Exercise and Coronary Artery Disease Research

Coronary Disease

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Many short-term studies have established the value of exercise in reversing risk factors that cause coronary artery disease. Although there were lively discussions about whether exercise is of value in preventing or managing coronary artery disease, the evidence now is so strong in support for the value of exercise that arguments against this view are no longer justified. Rather, the questions are, how much exercise, how long and what are the longterm effects. There are fewer long-term studies of the effect of exercise, but a recently reported study from Washington University School of Medicine, St. Louis, provides some answers (Journal of the American College of Cardiology, August 1987).

The study was of nine men with proven coronary artery disease, average age 57 years. All were started on a supervised vigorous exercise program that extended over a 12-month period. By the end of 12 months the men were jogging an average of 18 miles a week and they exercised at a level that caused their heart rates to be 81% of the predicted maximum heart rate (predicted maximum heart rate in men equals 220 minus age; 220 minus 57 163; 163 x Sl% = 132). Only one of the men had angina heart pain with effort before beginning the training, and he became asymptomatic during the 12-month training interval. During the 12 months, as might be predicted, the work capacity of the heart was increased with exercise, This is a mechanical effect. It is measured by the amount of oxygen the circulation can move, which increased from an average of 25.0 to 35.9 liters a minute - an improvement of 44%, The HDL-cholesterol (the cholesterol in small fatty-cholesterol particles that protects against fatty-cholesterol deposits) increased from 38 to 45, while the total cholesterol did not significantly change. These findings are all consistent with previous studies. Then the nine men continued to exercise for an additional six years. There was a further slight increase in oxygen use during exertion and they worked at an average level of 85% of their predicted maximum heart rate. Their HDL-cholesterol level increased even more, to an average of 53. Their electrocardiograms showed less evidence of insufficient coronary circulation, even at the 12-month interval, and was not changed after seven years of vigorous exercise.

The most impressive point of this study is the continued increase in HDL cholesterol, The average of 38 before the onset of training is low, and a low level is a significant factor in the in creased risk of a heart attack. The increase to 45 was an improvement, but the value should he above 50 to significantly lower the risk. That was achieved with continued exercise. This emphasizes the value of not expecting too much too soon, and the long-term benefits that can be achieved. The fact that the total cholesterol level was not changed suggests the change was brought about through the exercise and not diet. The men did not show any significant change in bodyweight, either.

The problem remains that many patients with heart disease cannot exercise at these levels, and many more are not motivated to do so on a continuing basis. But can similar benefits be obtained with less strenuous exercise that people are more likely to maintain? The answer to that question may be in the studies of 12,000 patients continuing in the large national Multiple Risk Factor Intervention Trial (MR FIT). Dr. Arthur S. Leon, a professor of epidemiology, told the American College of Sports Medicine meeting that an average of 47 minutes of moderate exercise a day was just as good as vigorous exercise. The 500 "real athletes" in the study did not have any evidence of increased protection above that noted in the moderate exercise group. The men who engaged in an avenge of 47 minutes of exercise a day had 38% fewer fatal coronary artery disease events than those who averaged only 15 minutes a day. Those whose daily exercise avenged 134 minutes or more a day did not get any additional benefit over those who averaged only 47 minutes.

This, too, was a seven-year study. What was meant by light to moderate exercise? It included gardening, home repairs and walking, as opposed to jogging or more vigorous structured activity. This study points out that there can be a significant decrease in the risk of death from coronary heart disease, even if a person engages only in moderate activity. But most people would like to avoid the actual heart attack or onset of chest pain associated coronary artery disease events. To decrease that risk, it is probably necessary to improve the risk factors.

How successful any program is in this regard irrespective of whether mild, moderate or vigorous exercise is used can only be determined by measuring each person's total cholesterol, I-IDL-cholesterol, other blood fat measurements and blood pressure. Whatever program improves the risk factors adequately is apt to improve a person's outlook and diminish his risk, both short and long-term.

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