Oxygen Dissociation Curve of Arterial Blood in Men Breathing High Concentrations of Oxygen

Abstract

60 detns. of arterial O2 saturation and O2 tension were made in a series of 10 healthy men as these subjects breathed for periods of 10 or more min. the following O2-N2 mixtures: approx. 40, 50, 60, 100, 70 and 100% O2- For the detn. of O2 saturation a cuvette oximeter for whole blood was used. 02 tension was measured polarographically with a rotating platinum electrode. When the O2 tension varied between 197 and 400 mm. Hg, a significant and curvilinear increase in O2 saturation was demonstrated that amounted approx. to 0.7%. At 02 tensions of more than 400 mm. Hg and ranging up to 644 mm., no further increase in O2 saturation was observed. To exclude the possibility of conversion of an inactive heme pigment, such as methemoglobin, to oxyhemoglobin under the influence of relatively high O2 tensions, a group of 6 healthy men were studied when they breathed first 50% O2, then 100% O2 and finally 50% O2 again. An avg. increase in O2 saturation of 0.3% was observed when the subjects were changed from 50-100% O2- When they were changed from 100 to 50% O2, a decrease in saturation amounting to an avg. value of 0.7% was recorded. The changes observed were considered to be due to formation and dissociation of oxyhemoglobin. Such readily reversible changes would not be probable if the changes were due to conversion of inactive heme pigments in the blood. The findings in this study were interpreted to indicate that in vivo, a blood O2 tension of at least 400 mm. Hg is required to effect practically complete saturation of hemoglobin in arterial blood (temp.: 37[degree]C and a CO2 tension: 40 mm. Hg). Arterial O2 tensions in excess of 400 mm. Hg can be achieved in most normal subjects by inhalation of 70% O2 in N2 (avg. barometric pressure: 732.7 mm.).