Optimizing the calculation of DM,CO and VC via the single breath single oxygen tension DLCO/NO method

•We measure DLCO and DLNO using the single breath hold technique.•We compare DM,CO and VC calculated via the single-FiO2 vs. multiple-FiO2 method.•The Reeves and Park θCO equation is optimal when using the single-FiO2 method.•An experimental DM,NO/DM,CO ratio should be determined for each laboratory.

Alveolar-capillary membrane conductance (DM,CO) and pulmonary-capillary blood volume (VC) are calculated via lung diffusing capacity for carbon monoxide (DLCO) and nitric oxide (DLNO) using the single breath, single oxygen tension (single-FiO2) method. However, two calculation parameters, the reaction rate of carbon monoxide with blood (θCO) and the DM,NO/DM,CO ratio (α-ratio), are controversial. This study systematically determined optimal θCO and α-ratio values to be used in the single-FiO2 method that yielded the most similar DM,CO and VC values compared to the ‘gold-standard’ multiple-FiO2 method. Eleven healthy subjects performed single breath DLCO/DLNO maneuvers at rest and during exercise. DM,CO and VC were calculated via the single-FiO2 and multiple-FiO2 methods by implementing seven θCO equations and a range of previously reported α-ratios. The RP θCO equation (Reeves, R.B., Park, H.K., 1992. Respiration Physiology 88 1–21) and an α-ratio of 4.0–4.4 yielded DM,CO and VC values that were most similar between methods. The RP θCO equation and an experimental α-ratio should be used in future studies.