The magnitude of the Bohr coefficient: optimal for oxygen delivery.

This paper examines relationships between the magnitude of the blood Bohr coefficient and arterial-venous changes in blood pH, PCO2 and oxygen affinity during steady-state, aerobic gas exchange. The physical-chemical linkage of the Bohr and Haldane effects is taken into account. It is concluded that for blood in which there is negligible oxygen-linked carbamate formation: (a) arterial-venous pH and PCO2 changes would be minimized if the Bohr coefficient were approximately equal to the respiratory quotient, with opposite sign, and (b) the rightward shift of the oxygen equilibrium curve in the tissues, relative to the curve at arterial pH, would be maximal if the Bohr coefficient were about one half the respiratory quotient (Bohr coefficient -0.35 to -0.5 for RQ 07-1.0). Actual Bohr coefficients in several mammals maximize the right shift of the oxygen equilibrium curve and are therefore optimal for oxygen delivery. Actual Bohr coefficients do not minimize pH or PCO2 changes. These results suggest that the contribution of the Bohr-Haldane effect to oxygen transport is more important than its contribution to pH homeostasis or CO2 transport.