Effect of oxygen on arteriolar dimensions and blood flow in cat sartorius muscle

The effect of O2 on arteriolar internal diameter, dual-slit velocity, and volume flow was studied by intravital microscopy in isolated autoperfused cat sartorius muscle. The muscle surface was covered with silicone oil, and gas mixtures containing 0, 5, 10, or 20% O2 in N2 were introduced over the muscle. When the O2 concentration was increased from 0 to 10%, arteriolar diameter, dual-slit velocity, and volume flow decreased on the average by 11 +/- 4, 30 +/- 29, and 37 +/- 13%, respectively. Under 20% O2, these parameters decrease by an additional 9 +/- 5, 29 +/- 10, and 30 +/- 14%, respectively. Percentage reduction in the diameter of large and small arterioles located at the same depth in the muscle were not significantly different. Conversely, the fall in volume flow was significantly greater in small arterioles. The lesser flow decrease in large vessels may reflect the fact that large vessels also feed deep muscle layers where the change in tissue O2 tension (PO2) is less. Our results do not support the hypothesis that small arterioles are intrinsically more sensitive to changes in tissue PO2.