Effects of acute right ventricular systolic hypertension on regional myocardial blood flow in anesthetized dogs

An important determinant of right ventricular (RV) myocardial blood flow is coronary driving pressure (CDP)-the pressure difference between RV and aorta. Since right ventricular systolic hypertension (RVSH) decreases RV CDP, it might limit blood flow to RV muscle. To study this we constricted the pulmonary artery in openchest dogs to give RV to aortic systolic pressure ratios of 0.25 to 0.40 (mild RVSH) and over 0.40 (moderate RVSH). We measured regional myocardial blood flow with 8 to 10 μ diameter radioactive microspheres, RV CDP by integrating the aortic-RV pressure difference per minute (pressure index-PI), and assessed myocardial oxygen needs of each ventricle from its tensiontime index (TTI). Flow to RV wall rose with mild and fell with moderate RVSH; differences were not significant. The ratio of RV myocardial flow to TTI remained normal with mild RVSH but fell 50 per cent with moderate RVSH. The ratio of RV PI to TTI was 10.3 ± 2.7 (mean and standard deviation) in controls, 5.6 ± 1.4 in mild RVSH, 2.4 ± 1.0 in moderate RVSH, and 1.8 ± 0.6 with acute heart failure. Reducing RV PI initially causes coronary vasodilatation. After maximal vasodilatation, further reduction decreases flow relative to oxygen needs. Underperfusion of RV myocardium may be predicted from information derived from RV and aortic pressure tracings.