TRANSMURAL DISTRIBUTION OF CAPILLARY MORPHOLOGY AS A FUNCTION OF CORONARY PERFUSION-PRESSURE IN THE RESTING CANINE HEART

Changes in coronary perfusion pressure lead to alterations in intracor onary myocardial volume that may be associated with regionally altered microvascular morphology. Transmural variations in coronary capillary geometry were quantified as a function of coronary perfusion pressure in glutaraldehyde-fixed canine hearts. Capillary volume fraction, dia meter, numerical density, anisotropy, and sarcomere length were measur ed using computer analysis of light microscopic images of sections tak en transverse or longitudinal to the muscle fiber axis. Capillary volu me was 4-6% of myocardial wall volume and exhibited a significant tran smural gradient, increasing from epicardium to endocardium. Vessels 4 to 5 mu m in diameter with a density of 2900 mm(-2) appear to increase in diameter and alter their cross-sectional shape with increasing pre ssure, rather than increasing in number, suggesting an effective diste nsibility of approximately 0.007 mm Hg-1. Quantification of vessel ani sotropy was directly related to cross-sectional shape and demonstrated that the capillaries are highly oriented. These findings indicate tha t intramyocardial capacitance is at least in part associated with nonh omogeneous changes in coronary capillary morphology with altered perfu sion pressure. (C) 1995 Academic Press, Inc.