Microvasculature of the dog left ventricular myocardium

Abstract

One of the main branches of the left main coronary artery of normally beating dog hearts was perfused with a silicone elastomer which solidified within the vasculature. Prolonged immersion in increasingly concentrated ethanol and in methyl salicylate rendered the tissue translucent and the vasculature clearly visible. Surfaces were photographed by reflected or transmitted light microscopy, showing large groups of capillaries running parallel to muscle fibers and extending for up to a few centimeters. The arrangement of arteriolar inflows to the capillary network and venular outflows (two to four times as frequent) suggested that functional capillary lengths were 500-1000 μm. Estimates of capillary diameters, presumably at maximal dilatation, were 5.6 ± 1.3 μm. Capillary densities within muscle groups were 3100-3800/mm 2 , giving intercapillary distances of 19-17.5 μm. With the lesser density value, the capillary surface area is estimated to be 500 cm 2 /g of myocardium. Inclusion of interfascial spaces lowered the average density to about 2500/mm 2 . Unbranched capillary lengths averaged 100 μm, with a strongly right-skewed distribution. The anatomic arrangement provides a basis mainly for concurrent flow in neighboring capillaries, and also for some diffusional exchange between inflow and outflow regions.This study was undertaken because of the need for precise descriptions of the geometric arrangement of myocardial capillaries and of their dimensions, so that accurate values could be used for models describing the exchanges of tracers in the heart. Wearn (1928) and later Roberts and Wearn (1941) perfused isolated and beating human, cat, and rabbit hearts with dye suspensions, and reported that there were about 5000 capillaries/ mm 2 of ventricular myocardium, a value which is too high because of their failure to correct for shrinkage with fixation. They also showed that anastomoses between capillaries were numerous and that at times the branchings were so profuse as to give the impression of single muscle fibers being completely surrounded by capillaries.From studies in dead rabbits, Stoel (1925) stated that the capillary diameter in papillary muscle was 5 μm, the intercapillary distance was 18 μm (cylinder of influence = 9 μm in radius), and the capillary density was 3230/mm 2 . In the same study, the capillary diameters in the adductor magnus and the semitendinosus muscles were 2.5 and 5.0 μm, respectively. Reynolds, Kirsch, and Bing (1958) reported values of 3-5 μm for capillary diameters in dog hearts. They also stated that these can double if the once arrested hearts were reperfused. In normally beating hearts they observed large gradients in capillary density between epicardium (1200-1600/mm 2 ) and endocardium (100-340/mm 2 ) which may have been related to the experimental technique of counting only those capillaries that contained erythrocytes. Although it is commonly assumed that erythrocyte and capillary diameters are similar, Krogh (1919) showed that there was considerable variation in capi...

Fractal descriptions for spatial statistics

“…This intersection suggests that 75 μg is the size of a microvascular unit. This would suggest that these are 13 arterioles per mm 3 of tissue, in line with estimates made by others (5,6,1). But an RD of 102% is large compared to the 50% RD seen in hamster hearts (10) using quantitative autoradiography with element sizes less than 100-cubic microns, using the "molecular microsphere" iododesmethylimipramine.…”

“…The general relationship found was: (1) where m is the mass of the tissue element used to calculate RD and m o is the arbitrarily chosen mass for reference. The reason for calling this a fractal relationship rather than just a power law relationship is that the possible slopes of the relationship are bounded by limits, and the fractal dimension, D, gives insight into the nature of the data.…”

Simultaneous Blood–Tissue Exchange of Oxygen, Carbon Dioxide, Bicarbonate, and Hydrogen Ion

“…These regions are separated by the membranes of RBC, capillary, and parenchymal cells, each of which is characterized by its permeability-surface area product, PS. Because the capillary-tissue exchange length, L, that of the BTEX unit, is almost 1 mm, 6 the model uses partial differential equations 7,9,11 to account for concentration gradients along the length. The anatomical volumes of these regions are denoted by V rbc , V pl , V isf , and V pc (units ml g −1 ), their fractional water spaces by W rbc , W pl , W isf , and W pc (unitless), and corresponding volumes of distribution by , and , which are the anatomical volumes times their fractional water spaces, e.g.…”

“…The expressions for S HbO 2 and S MbO 2 are (4) where K HbO 2 (with units M −1 ) is a function of P O 2 , P CO 2 , and pH, or equivalently ∘ C rbc , c C rbc , and h C rbc , and K MbO 2 (M −1 ) are given by (5) and (with units M −1 ) is given by (6) The equilibrium constants , and and the empirical exponents n 0 , n 1 , and n 2 are as defined in Dash and Bassingthwaighte 26 (see Table 1 for values). The subscript S refers to values in standard physiological conditions at 37°C.…”

Physiology and theory of tracer washout techniques for the estimation of myocardial blood flow: Flow estimation from tracer washout

“…The capillaries parallel the cells with a density of about one per cell, or 3000/sq mm cross-section. 4 The general arrangement is shown in Fig. 2 for the dog heart.…”