No abstract

To study microcirculation of the heart in vivo, we developed a new technique of epi-illumination of the beating rat ventricular myocardium. Five tiny needles connected to the operation table were horizontally inserted into the ventricular myocardium just beneath the epicardium in order to restrict cardiac movement during contraction and to enhance the amount of light reflected from the structures under study. The in vivo light and fluorescent microscopy were performed with the Ultropak and the Fluopak systems (Leitz) combined with a highly sensitive television camera and recording system. In 142 individual in vivo measurements (6 animals) the mean capillary diameter amounted to 6.0 +/- 1.0 mu. In the same experiments, the mean intercapillary distance was 18.7 +/- 1.7 mu. In agreement with the literature, the capillaries of the epimyocardial layer of the rat heart demonstrate a mixed countercurrent flow pattern. In contrast to other authors, we observed no recruitment of resting capillaries after hypoxia.

With the use of a new fluorescent microscopic technique, we were able to measure the mean intracapillary velocities and pressures of single capillary loops of renal glomeruli of living rats. The technique involved photographing and recording the flow of fluorescent latex particles through the glomerular loops with a television monitor. In 25 rats the single glomerular loop flow velocity was 781 +/- (SD) 271 micrometers . sec-1. The mean diameter of the capillary loops measured 8.4 +/- 1.4 micrometers; their lengths were 72.3 +/- 37.5 micrometers. From the decrease in velocity of flow along the capillary loop, we were able to evaluate the filtration equivalent for the capillary surface. It was possible to measure intracapillary pressures of single glomerular loops continuously under microscopic control. High intracapillary pressures correlated with high intracapillary velocities. From the data we obtained, we were unable to calculate a filtration equilibrium at the ends of the observed capillary loops. For further correlations, we injected the glomeruli we had studied in the living state and examined them with the scanning electron microscope.