Rate at Which Carbon Monoxide Replaces Oxygen From Combination With Human Hemoglobin in Solution and in the Red Cell

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Abstract
The rate at which CO replaces O2 in combination with human hemoglobin in solution and in red cell suspensions at 37°C was determined in vitro on the blood of six normal subjects at O2 tensions from 100 to over 600 mm Hg, by means of modifications of the Hartridge-Roughton rapid reaction velocity apparatus, using either a reversion spectroscope or a two-color photocolorimetric method. At low ratios of [CO] to [O2] (i.e. 2Hb]/[O2], where m∞' is a true velocity constant. Experimentally, it was not possible to use ratios of [CO] to [O2] 2Hb[/]O2], where m' is an apparent velocity constant. The measured values of m' in Hb solution ranged from 6.8 to 22.4 sec.−1 as O2 tension rose, the average value of m∞' deduced therefrom being 18.8. The apparent velocity constant for cell suspensions, mc', is less than m' owing to the limiting effects of diffusion. The ratio of mc' to m' rose from 0.46 at an O2 tension of 100 mm Hg to 0.68 at an O2 tension of 571 mm Hg.λ, the ratio of the permeability of the red cell membrane to that of the red cell interior, was calculated from these data to average 1.53. The values of mc' calculated from the in vitro experimental results cannot be used directly for calculations related to in vivo pulmonary diffusing capacity experiments, because the CO tension is over 40-fold greater in the former. Corrections for this have been made and proper values of mc' obtained for use in the calculation of true pulmonary diffusing capacity and pulmonary capillary blood volume. Submitted on February 15, 1957