Coronary Circulation During Heavy Exercise in Control Subjects and Patients With Coronary Heart Disease

Abstract. Coronary and systemic circulation has been measured in 10 patients with coronary heart disease (CHD) and in 11 control subjects during 2–3 periods of increasing exercise loads. The highest work load was close to the maximal tolerable exercise level. In control subjects the maximal coronary flow during heavy exercise increased to 460% of the resting value. The myocardial (a‐v)O 2 difference varied considerably inter‐ and intraindividually with increasing work load, but calculated for the group this (a‐v)O 2 difference did not change significantly. The increase in myocardial oxygen demand was thus met almost exclusively by an increase in coronary flow. The myocardial oxygen uptake increased fourfold from rest to heavy exercise with a parallel fourfold increase in the BP 8 × HR product, with a linear relationship over the whole range of values, suggesting that this product is a good index of myocardial oxygen uptake. In CHD patients the coronary flow response to moderate exercise was the same as in control subjects. During heavy exercise, however, the coronary flow increase was lower in relation to the BP 8 × HR product than in the control subjects. Coronary vascular resistance did not decrease to the same level as in the controls. The demand for increase in oxygen uptake was met through a compensatory increase in myocardial (a‐v)O 2 difference, thus making the necessary oxygen delivery possible. During the heaviest exercise, however, a significantly lower myocardial oxygen consumption was recorded in relation to the BP 8 × HR product than in the control subjects. This was interpreted as an inadequate oxygen supply, leading to decreased myocardial contractility. The impaired myocardial performance was best demonstrated in two patients with exercise‐provoked angina pectoris who developed rapidly increasing left atrial pressure.