Standard and pH-affected hemoglobin-O2 binding curves of Sprague-Dawley rats under normal and shifted P50 conditions.

1. The oxygen saturation (SO2) was determined of Sprague-Dawley rat blood having increased hemoglobin (Hb)-O2 affinity (P50 < 37 mmHg) or capacity (Cmax) over a range of pH's. 2. Rats were untreated (K), or had passed 14 d drinking 0.5% saline (C; ctrl) or NaOCN (N; chronically low P50, high Cmax), 5000 m altitude acclimatization (H; high Cmax), or exchange transfusion with OCN(-)-Hb red cell blood (X; acutely low P50). 3. The P50 [mmHg], Hill's "n", and Cmax [ml O2/100 ml], measured after tonometry, were 36.0, 2.60 and 20.6 (K), 32.6, 2.50 and 21.8 (C), 18.3, 2.35 and 23.9 (N), 36.0, 2.60 and 29.4 (H), and 24.9, 2.73 and 22.3 (X). 4. Oxygen dissociation curves (ODC's), derived from simultaneous SO2 and PO2 measurements during deoxygenation (PO2: 100-0 mmHg) of blood (normal and acidified with CO2 or lactic acid), delivered Bohr coefficients (BCCO2, BCLac) each differing between groups (C vs N) above SO2 50%; within groups BCCO2 vs BCLac differed at SO2 10-90% (P < 0.05). 5. Group-specific ODC's and pH-shifted curves (+/- 0.05, +/- 0.10 and +/- 0.15 units from 7.4, relying on BCCO2) are plotted for direct reading of SO2 and, with Cmax, accurate data on blood O2 content are obtained; corrections for lactic acidosis are discussed.