Metabolic but not hypoxemic stimuli are related to the apparent recruitment of capillaries in the muscle

Increased metabolic rate (MR) and arterial hypoxemia are independent stimuli to increase blood flow and delivery of oxygen (O₂) into the active muscle tissue and may differ in location of their action. We speculated that blood gas analysis could provide the answer whether a given stimulus acts on the recruitment of capillaries, manifested by the apparent density of capillaries. We used the Krogh cylinder model, modified for the description at low partial pressure of O₂ (pO₂) that lead to O₂ deficit. Using data of Goodman et al. (Circ Res 43: 769-76, 1978) we calculated the apparent density of capillaries, which changed proportionally to MR, but was independent of O₂ saturation of the arterial blood, suggesting that the increased radial O₂ diffusion gradient at higher MR might be responsible for it.