[Coronary vascular resistance during transitory variations in aortic pressure]

The present study was aimed at studying the interaction between elastic properties and myogenic responses of the coronary wall in regulating coronary vascular resistance (CVR) during and after sudden changes in perfusion pressure. Whilst the effects of transient reductions and recoveries of the aortic blood pressure (ABP) were previously considered, in the present study attention was paid to the changes induced in CVR by the reverse procedure, i.e., by transient increases followed by abrupt decreases of ABP. The experiments were performed in 6 anesthetized dogs after section of the vagi nerves and beta-adrenergic receptor blockade. The increase of ABP was obtained by a 10 or 20 s constriction of the descending thoracic aorta. During the experimental maneuver, coronary flow increased without any significant change in CVR. Only in the late part of the 20 s constriction a reduction of CVR was observed as a likely consequence of increased myocardial metabolism. Immediately after the release of the constriction, the fall of ABP below the control was accompanied by a significant reduction of coronary flow without any significant increase in CVR. About 10 s later, a remarkable increase in flow occurred together with a significant fall of CVR, while ABP was recovering towards the control. In each animal the exact timing of these changes was independent of the duration of the constriction. When, about 20-30 s from the end of the constriction, ABP was back to the control, the hyperemia was completely over.(ABSTRACT TRUNCATED AT 250 WORDS)