Maximal vascular conductance in right ventricular myocardial circulation

Abstract

With acutely increasing right ventricular (RV) hypertension, failure eventually occurs because of RV ischemia. This study examines the effects of RV hypertension on the diastolic right coronary circulation. Conscious dogs instrumented to measure right coronary artery pressure and blood flow were studied after maximal coronary vasodilation with chromonar. Diastolic coronary pressure-flow relations, described by slope (conductance) and zero-flow, pressure axis intercept (Pf = 0), were generated before and during RV hypertension. Diastolic Pf = 0 increased from 11.8 +/- 6.5 to 17.1 +/- 7.1 (means +/- SD, P < 0.01) Torr, with no change in conductance. During RV hypertension, RV diastolic pressure increased. To examine possible mechanisms for the increase in Pf = 0, pressure-flow relations were generated before and after volume loading, without systolic hypertension. Diastolic Pf = 0 increased from 15.5 +/- 3.1 to 20.8 +/- 4.1 Torr, suggesting that changes in Pf = 0 with RV hypertension were mediated by increased filling pressures. Pressure flow relations were derived from mean right coronary flow and RV driving pressure before and during RV hypertension. Under these conditions, Pf = 0 is close to zero; the use of RV driving pressure provides a method for calculating maximal right coronary conductance.