Raising P50 increases tissue P O 2 in canine skeletal muscle but does not affect critical O2extraction ratio

Curtis, Scott E., Thomas A. Walker, W. E. Bradley, and Stephen M. Cain. Raising P50increases tissue [Formula: see text] in canine skeletal muscle but does not affect critical O2 extraction ratio. J. Appl. Physiol. 83(5): 1681–1689, 1997.—Affinity of hemoglobin (Hb) for O2 determines in part the rate of O2 diffusion from capillaries to myocytes by altering capillary [Formula: see text]. We hypothesized that a decrease in Hb O2 affinity (increased P50) would increase capillary and tissue [Formula: see text](P[Formula: see text]) and improve O2 consumption during ischemia. To test this hypothesis, blood flow to the pump-perfused left hindlimb of 18 anesthetized and paralyzed dogs was progressively decreased over 90 min while hindlimb O2 consumption and O2 delivery (Q˙o 2) and P[Formula: see text] were measured at the muscle surface. Arterial[Formula: see text] was maintained at 150 ± 10 Torr in all dogs. We increased P50by 12.3 ± 0.9 (SE) Torr in nine dogs with RSR-13, an allosteric modifier of Hb. This decreased arterial O2 saturation to 90–92% but increased mean P[Formula: see text] from 35.5 ± 11.6 to 44.1 ± 15.2 (SD) Torr ( P < 0.05) with no change in controls ( n = 9). O2 extraction ratio at criticalQ˙o 2was 74 ± 2% in controls and 79 ± 1% in RSR-13-treated dogs ( P = not significant). P[Formula: see text] was 30–40% higher in the RSR-13-treated group at anyQ˙o 2above critical but did not differ between groups below criticalQ˙o 2. Perfusion heterogeneity and convergence of the dissociation curves near criticalQ˙o 2may have mitigated any effect of increased P50 on O2 diffusion. Still, increasing P50 by 12 Torr with RSR-13 significantly increased P[Formula: see text] atQ˙o 2values above critical.