High affinity of blood for oxygen reduces oxygen uptake in contracting canine gracilis muscle

To clarify the influence of blood flow with high-oxygen (O2)-affinity blood on oxygen consumption (VO2) in submaximally exercising skeletal muscle, we perfused the isolated dog gracilis (n = 8) contracting under 1 Hz stimulation alternatively with normal and high-O2-affinity blood, with a constant arterial O2 content (Ca,O2) and varying perfusion rates. The average P50 (oxygen partial pressure (PO2) for half-saturation at pH 7.40, PCO2 of 40 mmHg at 37 degrees C) of the high-O2-affinity blood prepared by carbamylation was 15.5 mmHg, and that of the normal blood 33.7 mmHg. With normal blood perfusion, the average VO2 above 6 ml min-1 (100 g)-1 of O2 delivery (Ca,O2 x flow) was 4.38 ml min-1 (100 g)-1 (range 4.17-4.68 ml min-1 (100 g)-1, and VO2 at the O2 delivery range of 6-5 and 4-2.5 ml min-1 (100 g)-1 decreased to 3.96 and 2.43 ml min-1 (100 g)-1, respectively. The PO2 of venous effluent (Pv,O2) at the O2 delivery of 6 ml min-1 (100 g)-1 was 33 mmHg. With low-P50 blood perfusion, VO2 was significantly less than with normal blood, both below the O2 delivery level of 6 ml min-1 (100 g)-1 and above it, even in the fairly high O2 delivery range of 8.5-12 ml min-1 (100 g)-1 (P < 0.05). Thus, high blood flow did not compensate for the reduced VO2 caused by high-O2-affinity blood. At values of Pv,O2 less than 33 mmHg, VO2 with low-P50 blood was not significantly different from that with normal blood (P > 0.05). The reduced VO2 in submaximally exercising skeletal muscle might be due to a slower O2 dissociation from the high-O2-affinity red cells and to a limited O2 diffusion resulting from the lower Pv,O2 value (which reflects mean end-capillary PO2).