DIRECT AND REBREATHING ESTIMATES OF O2 AND CO2 PRESSURES IN MIXED VENOUS BLOOD

Pulmonary artery blood was sampled from three subjects on 103 occasions before or during the rebreathing of CO2-in-N2 mixtures. Studies were made at rest and during three grades of exercise (150-900 kpm/min). The rebreathing estimate was consistently higher than that measured in blood, and the difference increased with exercise. One subject showed a similar difference in Po2. The rebreathing manoeuvre did not change the gas pressures measured in pulmonary artery blood. Differences in PCO2 may be due to a change of the bloods CO2-transport characteristics within the pulmonary capillary, or to incomplete equilibration within mixed venous blood. © 1969.