Microcirculation in the Ventricle of the Dog and Turtle

Abstract

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. KEY WORDS red cell velocitycardiac cycle arteriolar flow capillary circulation phasic capillary flow venule flow ventricular capillaries countercurrent flow• Rebatel (1) stated in 1872 that "entrance of blood into the smaller coronary vessels during systole is difficult" and that "in diastole the capillaries which have been empty of blood as a result of systolic compression, fill again from larger coronary vessels." Subsequently, numerous other investigators have confirmed the observations that coronary inflow occurs primarily during diastole and that outflow in the coronary sinus takes place mainly during systole (2-8). Consequently, there must be a point where this 180° phase shift occurs (9). However, the exact location of this shift has not been observed directly. In the atrium phasic changes in

Effects of Low Doses of Endothelin-1 on Basal Vascular Tone and Autoregulatory Vasodilation in Canine Coronary Microcirculation in Vivo

“…However, the exposed cardiac surface was always kept wet with warmed physiological solution and several reports have indicated that the effect of inserted needles is of little importance. [22][23][24] Previous reports from our laboratory have demonstrated that the reactivity of observed vessels to various vasoactive substances or to physiological stimuli is well preserved in this preparation. 11,18,20,25,26 In the present study, the vasodilation of arterial microvessels was also clearly demonstrated when the perfusion pressure was reduced, indicating that the reactivity of the observed vessels was well preserved.…”

Coronary diastolic pressure-flow relation and zero flow pressure explained on the basis of intramyocardial compliance.

“…Diameter changes of intramyocardial vessels during the cardiac cycle have been reported by Tillmanns et al (1974). They found the capillary diameter to be 4.1 nm in systole and 5.3 (im in diastole.…”

Coronary pressure-flow relationships. Controversial issues and probable implications.

“…56, No. 3, March 1985 (at least in superficial vessels) (Tillmans et al, 1974). There is evidence that venous outflow persists after cessation of arterial inflow in at least some experimental circumstances (Chilian and Marcus, 1982;Spaan, 1982;Bellamy and O'Benar, 1984).…”