Steady-state measurement of NO and CO lung diffusing capacity on moderate exercise in men

Using a rapidly responding nitric oxide (NO) analyzer, we measured the stea dy-state NO diffusing capacity (DLNO) from end-tidal NO. The diffusing capa city of the alveolar capillary membrane and pulmonary capillary blood volum e were calculated from the steady-state diffusing capacity for CO (measured simultaneously) and the specific transfer conductance of blood per millili ter for NO and for CO. Nine men were studied bicycling at an average O-2 co nsumption of 1.3 +/- 0.2 l/min (mean +/- SD). DLNO was 202.7 +/- 71.2 ml . min(-1) . Torr(-1) and steady-state diffusing capacity for CO, calculated f rom end-tidal (assumed alveolar) CO2 mixed expired CO2 and mixed expired CO 2 was 46.9 +/- 12.8 ml . min(-1) . Torr(-1). NO dead space = (VT x FENO - V T x FA(NO))/ (FINO - FA(NO)) = 209 +/- 88 ml, where VT is tidal volume and FENO, FINO, and FA(NO) are mixed exhaled, inhaled, and alveolar NO concentr ations, respectively. We used the Bohr equation to estimate CO2 dead space from mixed exhaled and end-tidal (assumed alveolar) CO2 = 430 +/- 136 mi. P redicted anatomic dead space = 199 +/- 22 mi. Membrane diffusing capacity w as 333 and 166 ml . min(-1) . Torr(-1) for NO and CO, respectively, and pul monary capillary blood volume was 140 mi. Inhalation of repeated breaths of NO over 80 s did not alter DLNO at the concentrations used.