Myocardial Blood Flow

We examined the ability of individual regions of the canine left ventricle to increase blood flow relative to baseline rates of perfusion. Regional coronary flow was measured by injecting radioactive microspheres over 90 seconds in seven anesthetized mongrel dogs. Preliminary experiments demonstrated a correlation between the regional distributions of blood flow during asphyxia and pharmacological vasodilatation with adenosine (mean r=0.75; 192 regions in each of two dogs), both of which resulted in increased coronary flow. Subsequent experiments, during which coronary perfusion pressure was held constant at 80 mm Hg, examined the pattern of blood flow in 384 regions (mean weight, 106 mg) of the left ventricular free wall during resting flow and during maximal coronary flow effected by intracoronary adenosine infusion. We found that resting and maximal flow patterns were completely uncorrelated to each other in a given dog (mean r=0.06, p=NS; n=3 dogs). Furthermore, regional coronary reserve, defined as the ratio of maximal to resting flow, ranged from 1.75 (i.e., resting flow was 57% of maximum) to 21.9 (resting flow was 4.5% of maximum). Thus, coronary reserve is spatially heterogeneous and determined by two distinct perfusion patterns: the resting (control) pattern and the maximal perfusion pattern. Normal hearts, therefore, contain small regions that may be relatively more vulnerable to ischemia. This may explain the patchy nature of infarction with hypoxia and at reduced perfusion pressures as well as the difficulty of using global parameters to predict regional ischemia. Despite the wide dispersion of coronary reserve,