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

• 1.1. The oxygen saturation (SO₂) was determined of Sprague-Dawley rat blood having increased hemoglobin (Hb)-O₂ affinity (P₅₀ < 37mmHg) or capacity (C_max) over a range of pH's.
• 2.2. Rats were untreated (K), or had passed 14 d drinking 0.5% saline (C; ctrl) or NaOCN (N; chronically low P₅₀ high C_max), 5000m altitude acclimatization (H; high C_max), or exchange transfusion with OCN⁻-Hb red cell blood (X; acutely low P₅₀).
• 3.3. The P₅₀ [mmHg], Hill's “n”, and C_max [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).
• 4.4. 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 (BC_CO2, BC_Lac) each differing between groups (C vs N) above SO₂ 50%; within groups BC_CO2 vs BC_Lac differed at SO₂ 10–90% (P < 0.05).
• 5.5. Group-specific ODC's and pH-shifted curves (± 0.05, ± 0.10 and ±0.15 units from 7.4, relying on BC_CO2) are plotted for direct reading of SO₂ and, with C_max, accurate data on blood O₂ content are obtained; corrections for lactic acidosis are discussed.