CONTROL OF CORONARY BLOOD FLOW BY AN AUTOREGULATORY MECHANISM.

Abstract

Control of the coronary circulation has been investigated in an experimental preparation in which coronary flow was suddenly increased or decreased by the imposition of sudden changes in coronary perfusion pressure during periods of constant cardiac performance. The transient response to these changes in coronary perfusion pressure was an initial abrupt change in flow in the same direction, followed by a prompt return of flow toward the previous level. The response was completed in 10 to 15 sec, and was followed by a few cycles of damped oscillation having a period of 10 to 12 sec. Steady-state pressure-flow curves demonstrated a range of perfusion pressures over which coronary blood flow was relatively independent of pressure. Below this pressure range the coronary bed appeared to be fully dilated, and the blood flow was directly dependent upon perfusion pressure. Elevation of the level of cardiac function resulted in autoregulation of coronary flow at a higher level of flow, and decreasing the level of cardiac function resulted in regulation of coronary flow at a lower flow rate. Instantaneous pressure-flow characteristics of the coronary bed, exclusive of compensatory influences, were also determined. The experiments demonstrated an intrinsic mechanism that regulated blood flow to the myocardium. In the physiologic range of arterial pressure, coronary perfusion pressure did not appear to be a major determinant of coronary blood flow. Coronary flow appeared to be autoregulated at a level related to myocardial effort.