Nonlinear control of microvascular blood flow against tissue pO2 in skeletal muscle

The tissue pO₂-dependent regulation of microvascular blood flow was evaluated in rabbit skeletal muscle in vivo. The rabbit tenuissimus muscle was prepared to observe the microcirculation. The capillary red blood cell velocity and perfused capillary density at various tissue pO₂ levels were measured from the images of microcirculation obtained by an intravital video-microscope. Both velocity and density were significantly decreased as tissue pO₂ was elevated, but the relationship between capillary flow and tissue pO₂ was not a linear correlation. In addition, the critical pO₂ value effected on microvascular blood flow regulation might exist in the tissue pO₂ ranging between 30 to 50 mmHg. It is suggested that the arteriolar walls might detect such a pO₂ value and control capillary blood flow directly by influencing the tonus of their smooth muscle.