A Study of Hemodynamics

Coronary blood flow was measured by the nitrous oxide method, and cardiac output was measured by the Fick principle, in a series of 31 human subjects with the clinical diagnosis of angina pectoris. Coronary arteriography was carried out on the same subjects as a part of the same procedure, and the extent and severity of the coronary artery lesions was determined. A numerical value was assigned to the severity of the coronary artery disease, an attempt was made to correlate the severity of coronary artery disease with the measured coronary blood flow and with various hemodynamic parameters which traditionally describe the systemic and pulmonary circulation. There was no correlation between any of the parameters measured and the severity of coronary artery disease demonstrated by angiography. It is concluded, therefore, that the nitrous oxide method for measuring coronary blood flow is not helpful in separating subjects with normal coronary arteries from those with coronary artery disease, nor are resting hemodynamic observations helpful. Maximum flow through the coronary arteries of the dog heart was measured by postmortem perfusion. This flow rate is sufficient to provide a considerable factor of safety as far as constriction of the major coronary arteries is concerned. If these data are extrapolated to the coronary vessels of man, it would seem that a very large "safety factor" exists, and this may explain why severe coronary disease is not revealed by studies of coronary blood flow.