FACTORS AFFECTING THE DETERMINATION OF OXYGEN CAPACITY, CONTENT AND PRESSURE IN HUMAN ARTERIAL BLOOD

Abstract

Ammundsen''s finding that addition of Na2S2O4 to normal human blood raises the CO combining capacity by 3% on the avg. is confirmed, thus indicating that 3% of the pigment is inactive as regards gas combining power. O2 capacity of arterial blood, as obtained by 15 mins. saturation with air in a tonometer followed by analysis in the Van Slyke-Neil manometric apparatus, is considered to be about 2% higher than the value in the blood at the moment of withdrawal from the vessel. Three factors contribute to this discrepancy: a. Drainage errors in the saturator: these cause the blood sample removed for analysis to be unduly rich in red cells (avg. effect equals about 0.7%). b. Gradual reversion of some of the inactive pigment to the active gas combining form. This effect is very variable, but on the avg. equals 1.0-1.5% of the total capacity. Owing to the smallness of the effect, the nature of the inactive, reverting pigment has not been established. It may be in part met-Hb. c. Presence of traces of COHb in the blood. Correction for these factors raises the avg. % O2Hb of normal men at sea level from 95-97: the arterial pO2, as calculated from these figures and the blood dissociation curves, comes out to 1000 mm., in agreement with the alveolar pO2, rather than to the avg. figure of 80 mm. given in recent papers. The latter figure is believed to be false.