Oxygen and carbon monoxide equilibria of human adult hemoglobin at atmospheric and elevated pressure.

By F. LEE RODKEY, JOHN D. O’NEAL, AND HAROLD A. COLLISON T HE FUNDAMENTAL LAW describing the competitive combination of oxygen and carbon monoxide with hemoglobin was defined by Douglas, Haldane, and Haldane’ in 1912. At equilibrium the concentration of these two gases 1)ound to hemoglobin and in the gaseous phase were related by the equation : ( COHb) X ( 02)/( O2Hb) X ( CO ) K where K is the relative affinity constant of hemoglobin for CO and oxygen. The value of K was the same for hemoglobin in solution or in the red cells and was not altered by the presence of CO2, minor changes in pH, salt concentration, or dilution of the hemoglobin solution. Small variations in K were observed within a given species with larger changes between species and at different temperatures. Sendroy and his co-workers2’3 have reported the value of K = 210 for human hemoglobin at 38#{176} and atmospheric pressure. Conflicting reports4’5 have described changes in K as a function of plasma pH in human blood both in vivo and in vitro. Lilienthal, et al.,#{176} demonstrated that decreased barometric pressure did not alter the equilibrium distribution of CO and 02 in man. When blood was diluted 1:20 with water and equilibrated with 0.046 per cent CO in air at total pressures from 1 to 4 atmospheres, tile same percentage of COHb was observed at all pressures of equilibration.7 No other data are available on the effects of elevated pressure on the relative affinity constant. Our interest in the effect of pressure and various inert gases on the value of K arose from the peculiar problems of maintaining men under the sea for prolonged periods. In this situation tile men are provided with a respiratory gas containing less oxygen and nitrogen than is present in air in order to avoid the development of oxygen toxicity and nitrogen narcosis. Helium is often used as the major inert gas at higher pressures. The hazards of contamination of the inspired air with CO from exogenous sources or from metabolism of the divers can only be predicted if the value of K is known in such gas mixtures or is not changed by the nature of the inert gas used.