The oxygen binding capacity of human haemoglobin

Summary

The internationally standardized HiCN method for measuring the total haemoglobin concentration of the blood (c ^*_Hb ) is based on the chemical composition of the haemoglobin molecule. If all haemoglobin measured in the blood by this method were active, i.e., capable of reversibly binding O₂, the O₂ binding capacity (β) would be 1.39 ml · g⁻¹ The experimental values of β to be found in the literature vary over a wide range, values as low as 1.24 ml · g⁻¹ being no exception. We determined β for 36 blood samples of healthy men, using for the determination of the O₂ content 3 independent methods, i.e., a manometric, a polarographic and a chemical one. Before the measurements the blood was equilibrated with humidified pure O₂ for 3 h. Appropriate corrections for dissolved O₂ were made. The mean β was 1.368 ml · g⁻¹, with a s.d. of 0.017 ml · g⁻¹ (median 1.372 ml · g⁻¹; range 1.322–1.387 ml · g⁻¹). This mean β corresponds to 98.4% active haemoglobin. The inactive haemoglobin consisted of 0.7% HbCO, Hi and SHb (“dyshaemoglobin”) and 0.9% unidentified inactive haemoglobin. In 4 samples a high fraction of unidentified inactive haemoglobin was found (2.8–4.3%). Taking into account that in addition to this fraction a considerable amount of dyshaemoglobin (especially HbCO) may be present in the blood of normal men, it must be concluded that calculating the O₂ carrying capacity of the blood by multiplyingc ^*_Hb by a constant value of β, may be subject to an appreciable error. If β=1.39 ml · g⁻¹ is used, the O₂ carrying capacity of the blood may easily be found 10–15% too high.