Abstract des Autors

These studies were conducted to compare the effects on systemic O2 transport of chronically vs. acutely increased Hb O2 affinity. O2 transport during maximal normoxic and hypoxic (inspired PO2 (PIO2) = 70 and 55 Torr, respectively) exercise was studied in rats with Hb O2 affinity that was increased chronically by sodium cyanate (group 1) or acutely by transfusion with blood obtained from cyanate-treated rats (group 2). Group 3 consisted of normal rats. Hb O2 half-saturation pressure (P50; Torr) during maximal exercise was ca. 26 in groups 1 and 2 and ca. 46 ingroup 3. In normoxia, maximal blood O2 convection (TO2max = cardiac output x arterial blood O2 content) was similar in all groups, whereas in hypoxia TO2max was significantly higher in groups 1 and 2 than in group 3. Tissue O2 extraction (arteriovenous O2 content/arterial O2 content) was lowest in group 1, intermediate in group 2, and highest in group 3 (P<0.05) at all exercise PIO2, values. In normoxia, maximal O2 utilization (VO2max) paralleled O2 extraction ratio and was lowest in group 1, intermediate in group 2, and highest in group 3 (P<0.05). In hypoxia, the lower O2 extraction ratio values of groups 1 and 2 were offset by their higher TO2max; accordingly, their differences in VO2max from group 3 were attenuated or reversed. Tissue O2 transfer capacity (VO2max/mixed venous PO2) was lowest in group 1 and comparable in groups 2 and 3. We conclude that lowering Hb P50 has opposing effects on TO2max and O2 extraction ratio, with the relative magnitude of these changes, which varies with PIO2, determining VO2max. Although the lower O2 extraction ratio of groups 2 vs. 3 suggests a decrease in tissue PO2 diffusion gradient secondary to the low P50, the lower O2 extraction ratio of groups 1 vs. 2 suggests additional negative effects of sodium cyanate and/or chronically low Hb P50 on tissue O2 transfer. Verf.-Referat