Increasing P(50) does not improve DO(2CRIT) or systemic VO(2) in severe anemia.
Reducing the hemolobin (Hb)-O(2) binding affinity facilitates O(2) unloading from Hb, potentially increasing tissue mitochondrial O(2) availability. We hypothesized that a reduction of Hb-O(2) affinity would increase O(2) extraction when tissues are O(2) supply dependent, reducing the threshold of critical O(2) delivery (DO(2 CRIT)). We investigated the effects of increased O(2) tension at which Hb is 50% saturated (P(50)) on systemic O(2) uptake (VO(2) (SYS)), DO(2 CRIT), lactate production, and acid-base balance during isovolemic hemodilution in conscious rats. After infusion of RSR13, an allosteric modifier of Hb, P(50) increased from 36.6 +/- 0.3 to 48.3 +/- 0.6 but remained unchanged at 35.4 +/- 0.8 mmHg after saline (control, CON). Arterial O(2) saturations were equivalent between RSR13 and saline groups, but venous PO(2) was higher and venous O(2) saturation was lower after RSR13. Convective O(2) delivery progressively declined during hemodilution reaching the DO(2 CRIT) at 3.4 +/- 0.8 ml x min(-1) x 100 g(-1) (CON) and 3.6 +/- 0.6 ml x min(-1) x 100 g(-1) (RSR13). At Hb of 8.1 g/l VO(2) (SYS) started to decrease (CON: 1.9 +/- 0.1; RSR13: 1.8 +/- 0.2 ml x min(-1) x 100 g(-1)) and fell to 0.8 +/- 0.2 (CON) and 0.7 +/- 0.2 ml x min(-1). 100 g(-1) (RSR13). Arterial lactate was lower in RSR13-treated than in control animals when animals were O(2) supply dependent. The decrease in base excess, arterial pH, and bicarbonate during O(2) supply dependence was significantly less after RSR13 than after saline. These findings demonstrate that during O(2) supply dependence caused by severe anemia, reducing Hb-O(2) binding affinity does not affect VO(2) (SYS) or DO(2 CRIT) but appears to have beneficial effects on oxidative metabolism and acid base balance.
Eichelbrönner
Otto
O
A. C. Burton Vascular Biology Laboratory, University of Western Ontario, London, Ontario, Canada N6A 4G5.
D'Almeida
Mark
M
Sielenkämper
Andreas
A
Sibbald
William J
WJ
Chin-Yee
Ian H
IH
D000136:Acid-Base Equilibrium / Q000187:drug effects; D000740:Anemia / Q000503:physiopathology*; D000814:Aniline Compounds / Q000494:pharmacology*; D000818:Animals; D000986:Antisickling Agents / Q000494:pharmacology*; D001158:Arteries / Q000502:physiology; D001810:Blood Volume; D004195:Disease Models, Animal; D006439:Hemodynamics / Q000187:drug effects; D006454:Hemoglobins / Q000187:drug effects / Q000378:metabolism; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D019344:Lactic Acid / Q000378:metabolism; D008297:Male; D010084:Oxidation-Reduction / Q000187:drug effects; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects* / Q000502:physiology; D011422:Propionates / Q000494:pharmacology*; D051381:Rats
D000814:Aniline Compounds; D000986:Antisickling Agents; D006454:Hemoglobins; D011422:Propionates; D019344:Lactic Acid; C067396:efaproxiral; D010100:Oxygen