The rates of disappearance of SF6, N2O, C2H2, diethyl ether and acetone from alveolar air during breath holding, following a single deep inspiration of a mixture containing one of these gases and about 15% helium, was studied in five normal seated subjects. SF6 is so insoluble that no significant change in its concentration relative to helium was found. Ether and acetone are so soluble that they dissolve in the tissues around the respiratory dead space during inspiration and evaporate during expiration, contaminating the expired alveolar gas to such an extent that the exchange of these gases cannot be properly measured at the alveolar level. N2O and C2H2 showed a) a rapid (less than 1.5 sec.) initial fall in relative alveolar concentration and b) a subsequent more gradual decrease; a) presumably results from the solution of the foreign gas in the pulmonary parenchymal tissues and can be used to calculate the pulmonary parenchymal tissue volume (Vt); b) can be used to calculate the pulmonary capillary blood flow (Qc), provided observations are not extended beyond 21 sec. The average values obtained were 3.31 l/min/m2 and 606 ml for Qc and Vt, respectively. Submitted on December 4, 1958

The over-all velocity constants, kc' and lc' (in mm−1 x sec.−1), for the combination of O2 and CO, respectively, with reduced hemoglobin in 1:80 human red cell suspensions at 37°C have been measured in a Hartridge-Roughton continuous flow apparatus. Relative pigment concentration in the flowing cell suspension was estimated from the difference in light transmission at two different colors in order to reduce the influence of light scattering. The average value of kc' was 92; that for lc' was 79. Values for corresponding velocity constants for the uptake of O2 and CO by a membrane free layer of concentrated hemoglobin solution, comparable in dimensions to the erythrocyte, have been calculated from previously reported values for the rates of reaction and diffusion in hemoglobin solutions, and are, respectively, 3.6 and 2.3 times greater than kc' and lc'. We assume that this difference reflects the additional resistance to gas diffusion into the erythrocyte imposed by the cell membrane, and on this basis we have calculated values for the ratio of the permeability of the red cell membrane to the permeability of the red cell interior (λ). For human red cells at 37°C, the value of λ is about 1.5, both for O2 and for CO penetration. Submitted on February 15, 1957

The apparent pulmonary diffusing capacity for CO (Dl) has been measured at alveolar O2 tensions from 40 to more than 600 mm Hg. Two methods were used: a) in six healthy subjects a steady state method in which the end-expiratory tension of a continuous record of respired CO concentration was considered 'alveolar' and b) in seven healthy subjects a breath holding technique. Dl, measured by either method, decreased with increasing alveolar O2 tension in all subjects, varying as much as fivefold over the entire range. All estimates of Dl were corrected for the presence of COHb in the mixed venous blood. Dl (steady state; breathing air) was on the average 0.85 of Dl (breath holding; breathing air). Submitted on February 15, 1957

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. <0.1), the rate of the reaction in Hb solution conforms theoretically to the equation d[COHb]/dt = m∞'[CO][O2Hb]/[O2], where m∞' is a true velocity constant. Experimentally, it was not possible to use ratios of [CO] to [O2] <0.2, and the results for Hb solutions were interpreted in terms of the equation d[COHb]/dt = m∞'[CO][O2Hb[/]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