Demonstration of coronary artery myogenic vasoconstriction in the awake dog

Abstract

The aim of this study was to determine whether or not coronary vasoconstriction occurs in response to a transient increase in coronary perfusion pressure. Eleven awake dogs with formalin-induced heart block, chronically instrumented with aortic and left ventricular catheters and left circumflex coronary and aortic electromagnetic flowprobes, were studied at a paced heart rate of 60 beats/min. A transient increase in aortic diastolic pressure of 17.3 +/- 1.5% for 330 +/- 20 ms and of 33.6 +/- 2.2% for 520 +/- 20 ms, via the inflation of an intra-aortic balloon, resulted in an increase in diastolic coronary vascular resistance index in the first response beat of 6 +/- 1% and 11 +/- 1%, respectively. An identical increase in diastolic coronary flow produced by the omission of a single paced beat resulted in no significant change in diastolic coronary vascular resistance index in the first response beat. Thus, the increase in diastolic coronary vascular resistance index following diastolic pressure augmentation is related to the increase in aortic diastolic pressure and not to the increase in diastolic coronary flow. These data are consistent with that of a brief myogenic response.

Microvascular response to metabolic and pressure challenge in the human coronary circulation

“…In the intact coronary circulation, myogenic activity is more difficult to demonstrate, because vasoactive pharmacological agents usually induce significant alterations in myocardial oxygen de- mand and may directly interact with the arterioles under investigation. Myogenic vasoconstriction could be observed following diastolic pressure transients in dogs, indicating a dominant role for autoregulation (31,40), whereas in the intact human heart, such direct evidence has been lacking. The coronary vascular resistance increase under ECP observed in the present study is consistent with such myogenic activity.…”