Influence of hemoconcentration on arteriolar oxygen transport in hamster striated muscle.

We investigated the influence of isovolemic hemoconcentration on microcirculatory hemodynamics and oxygen transport in the hamster cheek pouch retractor muscle. In 17 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 packed red blood cells. Hemoconcentration increased systemic hematocrit from 50 to 65%; systemic blood gases were unchanged, but mean arterial blood pressure increased approximately 10 mmHg. Accompanying this change in systemic hematocrit the microcirculatory hematocrit increased from 40 to 50%, and red blood cell velocity and computed blood flow decreased approximately 40 and 30%, respectively. In addition, delta SO2/L was significantly increased in the four arteriolar branching orders compared with control values. We estimated that approximately 10% of the oxygen that diffused across the arteriolar network was consumed by the surrounding tissue with the remainder assumed to have diffused to venules and capillaries. After hemoconcentration, the proportion of this diffusional transfer increased by approximately 80%. Convective oxygen flow remained at its control level in the first-order arterioles and progressively decreased below control in the more distal branching orders. Our analysis of arteriolar oxygen diffusion indicated that tissue oxygenation was unchanged after hemoconcentration, a result that can be attributed to a combined effect of decreased red blood cell velocity, arteriolar vasodilation, increased precapillary oxygen loss, and a relatively modest reduction in convective oxygen flow to the capillaries.