[Evaluation of load tolerance in patients with coronary disease]

12 patients with the diagnosis of coronary heart disease and angina pectoris underwent evaluation of heart rate as an indicator of tolerance of a given work load. A floating catheter in a pulmonary artery and a peripheral arterial catheter permitted measurement of blood pressures. Oxygen uptake per minute (VO2) was measured by Douglas bags and oxygen content of arterial and mixed-venous blood was determined at rest and during each minute of submaximal and symptom-limited maximal exercise on a treadmill. In the minute of exercise, in which 60-80% (mean 71.3%) of maximal heart rate (HF max) were attained, VO2 averaged 60.3% VO2 max, cardiac output (Q) 72.5% Q max and mean pulmonary arterial pressure (PAP) 26.6 mm Hg. With one exception, Q leveled off or dropped in the last minutes of exercise beyond 85% HF max. Heart rate (HF), oxygen difference between arterial and mixed venous blood (DavO2) and PAP reached their highest values in the last minute. It is suggested that heart rates up to 70% HF max, as individually determined in a symptom-limited maximal exercise test, are the tolerable limit during occupational activities. 85% HF max should not be exceeded during exercise training. Left ventricular function may be impaired beyond that limit because of acute coronary or myocardial insufficiency, and the regulation of cardiac output becomes uneconomical.