Distribution of the coronary blood flow across the canine heart wall during systole.

The transmural distribution of left coronary blood flow during systole was studied by measuring the myocardial uptake of a bolus of Rb introduced into the coronary circulation when the perfusion was limited to the periods of systole. The measurement revealed a transmural gradient of systolic blood flow with a flow rate in the outer fourth of the left ventricle about twice that in the inner fourth. A gradient of flow encompassing all depths of myocardial tissue revealed that intramyocardial pressure during systole was not sufficient to completely collapse the vessels and, therefore, did not exceed intraventricular pressure. The results of this experiment indicate that intramyocardial pressure limits coronary blood flow through a vascular sluice mechanism.