Lognormal distribution of intercapillary distance in normal and hypertrophic rat heart as estimated by the method of concentric circles: its effect on tissue oxygenation.

The inhomogeneity of the capillary net in the cardiac muscle was estimated using our morphometric measurements in normal and hypertrophic rats hearts. As entry data we used the distribution of tissue at different distances from the nearest capillary as measured by the method of concentric circles and the mean intercapillary distance independently calculated from the capillary density. The derived distribution of intercapillary distances was approximated by lognormal distribution in which the spread can be characterized by a single parameter, namely the log standard deviation. The effect of the log standard deviation on tissue oxygenation was evaluated in normal and hypertrophic hearts, at normoxia and at hypoxia. The mean tissue PO2 and the percentage of anoxic tissue at the venous end of the tissue cylinder were calculated using Krogh's model. Two boundary situations were considered: A) the end-capillary PO2 was assumed to be equal in all capillaries due to compensatory adjustment in blood flow; B) the same flow in all capillaries was assumed resulting in varying end-capillary PO2. The real situation is expected to be between situations A and B. Increased variability of intercapillary distance proved to impair considerably the tissue oxygenation, especially when the results were expressed as a percentage of anoxic tissue. The percentage of anoxic tissue turned out to be a better index of tissue oxygenation than the mean PO2 particularly at hypoxia. The results suggest the presence of at least a partial adjustment of blood flow with respect to the width of tissue cylinder. Without such adjustment, a large part of tissue would become anoxic already in normal hearts at normoxia and this would be further aggravated by hypertrophy and/or hypoxia.