Regional blood flow, microvascular blood content and tissue haematocrit in canine myocardium.

Regional myocardial blood flow, myocardial microvascular blood content and tissue haematocrit were determined in mongrel dogs. In nine dogs the intramyocardial distribution volumes of 99Tcm-albumin and 125I-fibrinogen were examined. Tracer equilibration times of 5, 10 and 30 min were used. The 125I-fibrinogen distribution volume was significantly lower than the distribution volume of 99Tcm-albumin. The 125I-fibrinogen distribution volume was not found to change with time and was thus taken to be a measure of the plasma volume. In 10 dogs intramyocardial distribution of 51Cr-labelled red cells and 125I-fibrinogen was estimated and regional myocardial blood flow was measured by 15 microns 99Tcm-albumin spheres. Plasma and red cell volumes, interpreted as myocardial microvascular blood content, ranged from 3.66 to 4.93 cm3-100 g-1. The distribution volumes indicated gradients with higher endocardial and longitudinal microvascular blood content in the left ventricular free wall and the septum. The intramyocardial haematocrits calculated from the plasma and red cell volumes were uniformly 0.3 all over the heart and amounted to 0.75 of arterial haematocrit. The mean right ventricular blood flow of 46.80 cm3 . min-1 . 100 g-1 amounted to 0.6 of a mean left ventricular blood flow of 86.65 cm3 . min-1 . 100 g-1. Transmural and longitudinal gradients of regional myocardial blood flow within the ventricular wall were observed. The patterns of transmural and longitudinal gradients of regional blood flow and microvascular blood content implies higher flow rates through more or larger vessels indicating a greater endocardial and apical vascular conductance in the vicinity of the left ventricular cavity.