Changes in microvascular diameter and oxygen tension induced by carbon dioxide.

Microvascular diameters in the hamster cheek pouch were measured with a Vickers image-shearing eyepiece, and oxygen tension (Po 2) was measured amperometrically with 2-8 fj, microcathodes. Peri vascular Po 2 was dependent on both the type of microvessel observed and the composition of the solution bathing the tissue. During application of a solution with a mean Po 2 of 17 mm Hg and a Pco 2 of 0 mm Hg, a longitudinal gradient in perivascular Po 2 was observed: Po 2 decreased from 44 ± 2 (SE) mm Hg at the large arterioles to 18 ± 2 mm Hg at the capillary origin. Tissue Po 2 was 10 ± 1 mm Hg. Suffusion of the cheek pouch with a solution with approximately the same Po 2 and a Pco 2 of 32 mm Hg resulted in an elevation of perivascular Po 2 at all sites. Large arteriolar Po 2 under these circumstances was 47 ± 2 mm Hg, capillary origin Po 2 was 29 ± 3 mm Hg, and tissue Po 2 was 17 ± 3 mm Hg. CO 2 also produced vasodilation: the average vascular diameter increased 18 ± 7% when the solution Pco 2 was increased from 0 to 32 mm Hg. The tissue showed evidence of regulation of tissue O 2 supply both with and without CO 2 in the suffusion solution. The effects of CO 2 on the distribution of O 2 were compared with the effects of other vasodilators, and it was found that the tissue Po 2 was not consistently changed by the application of the vasodilators, whereas it was elevated 70% by CO 2. This difference is attributed in part to the effect of CO 2 on the oxyhemoglobin dissociation curve. KEY WORDS local control vasodilators oxyhemoglobin dissociation curve vascular smooth muscle blood flow regulation Bohr effect • Previous work in this laboratory has shown that the oxygen tension (Pc^) associated with various elements in the microcirculation is dependent on both the type of microvessel observed and the P02 of the solution covering the tissue (1, 2). The perivascular Po 2 decreases as measurements are made more distally along the vascular tree. This decrement of perivascular P02 indicates that oxygen (O 2) diffuses not only from the capillaries but also from the precapillary vessels. In addition, the response of the vascular bed regulates the arterial O 2 supply to maintain an almost constant …