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Vol. 83, Issue 5, 1681-1689, 1997
Departments of Pediatrics and Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, Alabama 35294
Received 29 October 1996; accepted in final form 9 July 1997.
Curtis, Scott E., Thomas A. Walker, W. E. Bradley, and
Stephen M. Cain. Raising P50
increases tissue PO2 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 PO2.
We hypothesized that a decrease in Hb
O2 affinity (increased
P50) would increase capillary and tissue PO2
(PtiO2) 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 (
O2)
and PtiO2 were
measured at the muscle surface. Arterial PO2 was maintained at 150 ± 10 Torr in all dogs. We increased P50
by 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
PtiO2 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 critical
O2
was 74 ± 2% in controls and 79 ± 1% in RSR-13-treated dogs
(P = not significant).
PtiO2 was
30-40% higher in the RSR-13-treated group at any
O2
above critical but did not differ between groups below critical
O2.
Perfusion heterogeneity and convergence of the dissociation curves
near critical
O2 may have mitigated any effect of increased
P50 on
O2 diffusion. Still, increasing
P50 by 12 Torr with RSR-13
significantly increased PtiO2 at
O2
values above critical.
oxyhemoglobin dissociation curve; oxygen extraction ratio; ischemia; Mehrdraht-Dortmund-Oberfläche electrode; allosteric modifier; partial pressure of oxygen
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