Pulmonary O2 diffusing capacity at exercise by a modified rebreathing method

The rebreathing technique for the measurement of the pulmonary O2 diffusing capacity, D(O2) previously developed for resting conditions has been modified for application to exercise and simplified to one rebreathing maneuver only. The changes consist of: 1) in administering in the course of a normoxic exercise a priming breath of an O2 free mixture just before the onset of rebreathing in order to achieve rapidly the appropriate starting P(O2) values on the linear part of the O2 dissociation curve as required by the method; 2) in calculating mixed venous blood O2 tension by extrapolation of the alveolar to mixed venous blood P(O2) equilibration curve, instead of determining it separately. While the mean D(O2) value of 21 measurements on 5 subjects at rest was 30 ml . min-1 . Torr-1 ± 3 (S.E.), in 2 subjects exercising on a bicycle ergometer, D(O2) was found to increase from a resting value of about 32 ml . min-1 . Torr-1 to 107 ml . min-1 . Torr-1 for an eightfold increase of O2 uptake. The validity and the applicability of the method are critically discussed.