This preclinical study demonstrates transmural gradients in myocardial blood content and suggests that only a fraction of available capillaries are perfused at rest.
Blood content per gram of tissue was measured in various regions of the myocardium of the dog, by use of I 131 -labeled albumin and Cr 51 O 4 -labeled red cells. The ratio of I 131 to Cr 51 O 4 distributions was uniform, indicating that plasma skimming does not increase O 2 delivery to the inner layers. Gradients in blood content were observed from epicardium to endocardium, and in the base-apex dimension of the heart. Both the transmural gradient and the amount of blood per gram of tissue were greatest at the left ventricular apex. In this region the deeper layers contained 1.5 times as much blood as superficial ones. The data permitted estimates of the number of open capillaries, and of intercapillary distances. These estimates indicate that only a fraction of the available capillaries are perfused at rest. Mean tissue oxygen tensions were computed for various conditions of flow, capillarity, and metabolism by use of the Kety modification of the Krogh equation. Results are discussed in relation to the regulation of tissue PO 2 .
Myers et al. (Tue,) studied this question.
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