The role of autoregulation and tissue diastolic pressures in the transmural distribution of left ventricular blood flow in anesthetized dogs.

Publisher Website
Google Scholar
Abstract
The effects of autoregulation on transmural myocardial blood flow were studied in 21 open-chest dogs, and coronary arterial pressure was varied independently of left ventricular pressure. Total left ventricular myocardial blood flow (FLV) and subendocardial:subepicardial blood flow ratio (I:O) were measured with microspheres, 9 .mu.m in diameter, injected during autoregulation or maximal coronary vasodilation. With autoregulation, changing coronary perfusing pressures over a wide range with constant left ventricular work at steady state resulted in constant coronary flow; flows decreased below and increased above this range. When coronary flow was raised or lowered from the autoregulated flow, coronary pressures rose or fell, respectively, to reach values on the pressure-flow curve determined when coronary pressures were varied deliberately. When coronary pressure was changed in autoregulating hearts, FLV and I:O ratios were independent of the ratio of diastolic coronary pressure time index (DPTIc) to left ventricular systolic pressure time index (SPTI) over the range, 0.45-1.0, but I:O fell with pressure ratios below 0.45 and increased with pressure ratios above 1. During vasodilation, FLV and I:O ratios varied linearly with DPTIc:SPTI. Coronary autoregulation is necessary to maintain FLV and I:O distribution over a wide range of coronary:ventricular pressure relationships. With maximal vasodilation, flow at low coronary pressures increased from subendocardial to subepicardial layers, suggesting a gradient of diastolic tissue pressures.