Innovative Methodology An open-circuit method for determining lung diffusing capacity during exercise: comparison to rebreathe

Snyder, Eric M., Bruce D. Johnson, and Kenneth C. Beck. An open-circuit method for determining lung diffusing capacity during exercise: comparison to rebreathe. J Appl Physiol 99: 1985–1991, 2005. First published July 14, 2005; doi:10.1152/japplphysiol.00348.2005.—To avoid limitations associated with the use of single-breath and rebreathe methods for assessing the lung diffusing capacity for carbon monoxide (DLCO) 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 (DLCO,RB) method, we performed both the open-circuit (DLCO,OC) and the DLCO,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 DLCO,OC and DLCO,RB increased linearly with cardiac output and external work. There was a good correlation between DLCO,OC and DLCO,RB for rest and exercise (mean of individual r 0.88, overall r 0.69, slope 0.97). DLCO,OC and DLCO,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 DLCO,OC vs. DLCO,RB]. The coefficient of variation for repeat measurements of DLCO,OC was 7.9% at rest and averaged 3.9% during exercise. These data suggest that the DLCO,OC method is a reproducible, well-tolerated alternative for determining DLCO, 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.