One-sampling rebreathing method to measure diffusing capacity for CO

To simplify the rebreathing method to obtain the pulmonary diffusing capacity for CO (DLCO), a one-sampling method was developed, combined with a simulation technique. The change in CO fraction in rebreathing air depends on the rebreathing volume (VRB), the dead space volume (VD), the gas volume in the lung-bag-system (VS) as well as the DLCO: Using the measured VRB, VD, and VS, the changes in CO fraction in bag and alveolar air were simulated by varying the DLCO, where the expired and inspired gas volumes were represented by a sinusoidal function of time. The DLCO was determined by checking the similarity between the simulated and measured CO fractions at the 7th expiratory period. To confirm the validity of the simulation method, two-sampling rebreathing and single breath methods were additionally carried out in 6 normal subjects in the sitting position. The DLCO measured by the simulation agreed well with that measured simultaneously by the two-sampling method. The DLCO measured by this method was also compatible with that obtained from the single breath method, when the dead space was excluded from the measured lung gas volume.