Microcirculation in the ventricle of the dog and turtle.

Phasic red cell velocity and diameters of coronary arterioles, capillaries, and venules were measured in the beating turtle and dog heart using high-speed cinematography with transillumination of the left ventricle. In the turtle, arteriolar red cell velocity was diminished during systole, but during diastole arteriolar inflow increased, especially during the rapid and the slow filling period. Capillary and venule red cell velocity was in. creased during systole, particularly at the time of ejection; however, during diastole red cell velocity declined and the lowest values occurred during isovolumic relaxation. In dog arterioles, capillaries, and venules, the pattern of red cell velocity was similar. Thus, in the turtle and dog, the peak arteriolar red cell velocity occurred in unison with left coronary artery inflow, and the capillary and venule flow pattern followed that of the coronary sinus. The diameters of arterioles, capillaries, and venules in the turtle ventricle all declined about 34% during systole; similar results were obtained in the dog. Capillary arrangement appeared to be predominantly parallel and cocurrent; however, capillary loops with countercurrent flow were occasionally observed. The data on microvascular phasic red cell velocity are consistent with the macroobservations of reduced coronary artery inflow and enhanced coronary sinus outflow during ventricular contraction. The results demonstrate that the shift in the flow pattern occurs at the transition from arterioles to capillaries.