Arterioles' contribution to oxygen supply to the skeletal muscles at rest

We tested the hypothesis that oxygen is supplied to the resting skeletal muscle by arterioles rather than by capillaries. This hypothesis was evaluated in rats and rabbits by combining different approaches (1) determination of the intravascular oxygen tension (PO₂) in arterioles of different diameters, (2) measurement of the perfused capillary number in response to changes in tissue PO₂, and (3) estimation of the optimum capillary number to provide oxygen efficiently to the surrounding tissue. The intravascular PO₂ values of arterioles along the vessels decreased downstream, suggesting that a significant amount of oxygen diffuses from the arterioles to the surrounding tissue. The perfused capillary number decreased as the tissue PO₂ level was elevated, and this mutual relationship displayed a nonlinear correlation. The results suggest that a boundary PO₂ level affecting the capillary recruitment exists for tissue PO₂ of less than 40 mmHg with the capillary blood-flow stops above that PO₂ level. At a high PO₂ level, therefore, the oxygen is supplied from the arterioles. Furthermore, an estimation of optimum capillary number reveals that the capillary arrangement is constructed to achieve sufficient oxygen supply to the muscle during exercise, rather than at rest. These results suggest that oxygen is supplied from arterioles to the resting skeletal muscle, whereas the oxygen is supplied from the capillaries during exercise.