Experimental analyses of pulmonary gas exchange in a standing position at rest and during treadmill exercise

Quantitative relations between O2 uptake (Vo2), arterial-venous O2 content difference [a-v)CO2), and contact time (tc) were measured at rest and during exercise in 7 normal subjects, using a rebreathing technique. By injecting a known amount of pure O2 into a rebreathing circuit, the VO2 was measured from the time interval during which the injected O2 volume was consumed. From the O2 and CO2 concentrations in rebreathing air the gas exchange ratio (R), which was linearly related to the PCO2, was determined. By using the slope of the R-PCO2 relation, the (a-v)CO2 was evaluated from the slope of the CO2 dissociation curve between the true- and oxygenated-venous PCO2. These two venous PCO2 were estimated from the R-PCO2 relation by use of the Haldane effect coefficient and by extrapolating it to the abscissa, where R = O. Furthermore, tc was evaluated by inserting the above two venous PCO2 together with the alveolar PCO2 into a contact time equation. The mean (a-v)CO2 and tc had consistent relations to the VO2 and (a-v)CO2, respectively. (a-v)CO2 = 9.5 X VO2 0.35, (vol%), and tc = 4.86 X (a-v)CO2 -1.025, (s).