Experiments were performed on the hamster cheek pouch retractor muscle to investigate the influence of isovolemic hemodilution on microcirculatory hemodynamics and the rate of oxygen transport to striated muscle. In 23 hamsters, measurements of red blood cell velocity, hematocrit, vessel diameter, segment length (L), hemoglobin oxygen saturation (SO2), and longitudinal SO2 gradient (delta SO2/L) were made in four branching orders of arterioles before and after isovolemic exchange with plasma. Hemodilution decreased systemic hematocrit from 52 to 33%. In first- through fourth-order arterioles, this degree of hemodilution resulted in an average decrease in microcirculatory hematocrit from 42 to 28% and average increases in red blood cell velocity, computed blood flow, and systemic arterial PO2 of 50, 30, and 10%, respectively. In addition, delta SO2/L was significantly smaller in second-, third-, and fourth order arterioles compared with control values. It was estimated that approximately 84% of the oxygen that diffused across the arteriolar network was transferred by diffusion to nearby venules and capillaries; the remaining oxygen was consumed by the surrounding tissue. Following hemodilution, the magnitude of diffusional transfer declined to 73%. Oxygen flow remained at its control level in the first-order arterioles and progressively increased above control with increasing branching order. The increased oxygen delivery to the capillary network after limited hemodilution can be attributed to a compensatory increase in blood flow, an increase in systemic arterial blood oxygenation, and a decrease in precapillary oxygen loss.
The relative influence of hematocrit and red blood cell velocity on oxygen transport from capillaries to tissue
