An open-circuit method for determining lung diffusing capacity during exercise: Comparison to rebreathe

To avoid limitations associated with the use of single-breath and rebreathe methods for assessing the lung diffusing capacity for carbon monoxide (DL _CO) during exercise, we developed an open-circuit technique. This method does not require rebreathing or alterations in breathing pattern and can be performed with little cognition on the part of the patient. To determine how this technique compared with the traditional rebreathe (DL_CO,RB) method, we performed both the open-circuit (DL_CO,OC) and the DL _CO,RB methods at rest and during exercise (25, 50, and 75% of peak work) in 11 healthy subjects [mean age = 34 yr (SD 11)]. Both DL_CO,OC and DL_CO,RB increased linearly with cardiac output and external work. There was a good correlation between DL_CO,OC and DLCO,RB for rest and exercise (mean of individual r² = 0.88, overall r ² = 0.69, slope = 0.97). DL_CO,OC and DL_CO,RB were similar at rest and during exercise [e.g., rest = 27.2 (SD 5.8) vs. 29.3 (SD 5.2), and 75% peak work = 44.0 (SD 7.0) vs. 41.2 ml·min ^-1·mmHg^-1 (SD 6.7) for DL_CO,OC vs. DL_CO,RB]. The coefficient of variation for repeat measurements of DL_CO,OC was 7.9% at rest and averaged 3.9% during exercise. These data suggest that the DL_CO,OC method is a reproducible, well-tolerated alternative for determining DL_CO, particularly during exercise. The method is linearly associated with cardiac output, suggesting increased alveolar-capillary recruitment, and values were similar to the traditional rebreathe method.