Effect of cardiac cooling on coronary vascular resistance in normothermic dogs

Abstract

Coronary vascular resistance was observed while the temperature of the heart was lowered to 25°C. The heart was beating but performing no external work. This was accomplished by shunting the blood around the heart and lungs, clamping the arch of the aorta and perfusing cold or warm blood at a constant rate into the ascending aorta. In most instances, coronary perfusion pressure decreased during perfusion with cold blood. The pressure suddenly fell further as perfusion with warm blood was restarted and then gradually returned to the control level. The heart spent an increased proportion of time in systole during perfusion with cold blood. These findings indicate that local cardiac cooling by the method utilized causes active dilatation of the coronary vascular bed of the dog. This dilatation may result from some direct effect of temperature change upon vascular smooth muscle.