Microvascular Responses to Alterations in Oxygen Tension
The changes in microvascular diameter and perivascular oxygen tension resulting from alterations in suffusion solution Po2 were investigated in a study of the participation of oxygen in the regulation of blood flow. Diffusion gradients for oxygen were altered by changing the Po2 of a solution covering the surface of the hamster cheek pouch. As the solution Po2 was raised from a low of 11 mm Hg, perivascular Po2 of the large arterioles initially decreased to a minimum at approximately 40 mm Hg and then increased progressively as solution Po2 was elevated further. Arterial capillary and tissue Po2 remained relatively constant over a range of solution oxygen tensions between 11 and 40 mm Hg, suggesting that either the precapillary sphincters or the terminal arterioles were active in regulating tissue Po2 as the input of O2 from the solution was increased. The arterioles constricted as solution Po2 was elevated. Average arteriolar diameter decreased by 13% as solution Po2 increased from 11 to 47 mm Hg. A more pronounced constriction of 20% occurred when solution Po2 was increased from 11 to 84 mm Hg. These experiments indicated that the response of large and small arterioles was not mediated by a direct effect of oxygen on the vascular smooth muscle, since decreases in perivascular oxygen tension were coincident with decreases in vascular diameter in these vessels over a range of solution Po2 between 11 and 47 mm Hg. The data did not distinguish between a direct and an indirect effect of oxygen on the vascular smooth muscle of the terminal arterioles and precapillary sphincters. However, the oxygen tensions measured at these sites (18-30 mm Hg) required that the vascular smooth muscle cells respond to altered oxygen tension at levels higher than those which have been demonstrated experimentally.
- blood flow
- precapillary sphincters
- diffusion limitation
- vascular smooth muscle
- Received November 18, 1971.
- Accepted July 25, 1972.
- © 1972 American Heart Association, Inc.