Calculating alveolar capillary conductance and pulmonary capillary blood volume: comparing the multiple- and single-inspired oxygen tension methods

Ceridon ML, Beck KC, Olson TP, Bilezikian JA, Johnson BD. Calculating alveolar capillary conductance and pulmonary capillary blood volume: comparing the multiple- and single-inspired oxygen tension methods. J Appl Physiol 109: 643-653, 2010. First published June 10, 2010; doi: 10.1152/japplphysiol.01411.2009.-Key elements for determining alveolar-capillary membrane conductance (Dm) and pulmonary capillary blood volume (Vc) from the lung diffusing capacity (DL) for carbon monoxide (DLCO) or for nitric oxide (DLNO) are the reaction rate of carbon monoxide with hemoglobin (theta(CO)) and the Dm(CO)/DLNO relationship (alpha-ratio). Although a range of values have been reported, currently there is no consensus regarding these parameters. The study purpose was to define optimal parameters (theta(CO), alpha-ratio) that would experimentally substantiate calculations of Dm and Vc from the single-inspired O-2 tension [ inspired fraction of O-2 (Fi(O2))] method relative to the multiple- Fi(O2) method. Eight healthy men were studied at rest and during moderate exercise (80-W cycle). Dm and Vc were determined by the multiple-Fi(O2) and single-Fi(O2) methods (rebreathe technique) and were tabulated by applying previously reported theta(CO) equations (both methods) and by varying the alpha-ratio (single-Fi(O2) method) from 1.90 to 2.50. Values were then compared between methods throughout the examined alpha-ratios. Dm and Vc were critically dependent on the applied theta(CO) equation. For the multiple- Fi(O2) method, Dm was highly variable between theta(CO) equations (rest and exercise); the range of Vc was less widespread. For the single-Fi(O2) method, the theta(CO) equation by Reeves and Park (1992) combined with an alpha-ratio between 2.08 and 2.26 gave values for Dm and Vc that most closely matched those from the multiple-Fi(O2) method and were also physiologically plausible compared with predicted values. We conclude that the parameters used to calculate Dm and Vc values from the single-Fi(O2) method (using DLCO and DLNO) can significantly influence results and should be evaluated within individual laboratories to obtain optimal values.