Coronary response to transient increases in transmural pressure.

Previous studies have shown that transient increases in aortic blood pressure obtained by occlusion of the descending thoracic aorta, in anesthetized dogs with beta-blockade and vagal section, did not affect coronary vascular resistance apart from a non-significant increase just after release of the constriction. The present study examined whether this response also occurred in the normally innervated heart. Experiments were carried out in six anesthetized dogs, in which pressure in the aortic root and in the left ventricle, as well as flow in the left circumflex coronary artery, were recorded. Coronary vascular resistance was calculated as the ratio of the difference between aortic pressure and left ventricular pressure to coronary circumflex flow during the slow inflow phase. Before occlusion coronary vascular resistance was significantly lower than during the same period in the previous studies using animals with beta-blockade and vagal section. During the occlusion, in contrast with the previous investigation, the increase in aortic pressure caused a significant increase in coronary vascular resistance 10 seconds after the beginning of the occlusion. Coronary vascular resistance was further increased immediately after release of the occlusion, concomitantly with the decrease in aortic pressure, which fell abruptly below the control level. The increase immediately after the release of the constriction was qualitatively similar, but greater in extent, to that observed in the animals with vagal section and beta-blockade. These differences are assumed to depend on a lower vasomotor tone in the normally innervated hearts.(ABSTRACT TRUNCATED AT 250 WORDS)