Quantitative analyses of the CO2 dissociation curve of oxygenated blood and the Haldane effect in human blood.

Abstract

The theoretical equations for the CO2 dissociation curve derived by MOCHIZUKI et al. (1983) have made it possible to estimate the CO2 contents in blood at any PCO2 by putting the intra- and extracellular bicarbonate contents at a certain PCO2 into them. Moreover, according to their Haldane effect equation, the carbamate and bicarbonate contributions are evaluated, when the Haldane effect and its plasma component are known along the PCO2 range. In order to accomplish the above calculation the water shifts due to the PCO2 and O2 saturation changes were measured as the changes of hematocrit. The hematocrit of oxygenated blood was linearly correlated to pH with a factor of -0.037, and the difference in hematocrit between oxygenated and deoxygenated bloods was 0.004 in terms of fractional hematocrit. The blood and plasma CO2 contents measured at four different PCO2's were compared with the ones calculated by use of the intra- and extracellular bicarbonate contents at 42 Torr PCO2. The measured and calculated CO2 contents coincided fairly well with each other. Using intra- and extracellular bicarbonate contents in oxygenated blood together with the Haldane effect and its plasma component, the carbamate contribution was then calculated. The carbamate content was about 1.2 mmol/liter blood over a PCO2 range of 20 to 100 Torr, and its ratio to the total Haldane effect decreased from 50 to 40%, as PCO2 was increased. The ratio of the bicarbonate shift to the total bicarbonate change due to the Haldane effect, ranging from 0.82 to 0.66, was significantly greater than that measured by changing PCO2.