Pulmonary nitric oxide uptake reflects the entire diffusive properties of the alveolar capillary membrane.

Borland, Colin, Bryan Mist, Mariella Zammit, and Alain Vuylsteke. Steady-state measurement of NO and CO lung diffusing capacity on moderate exercise in men. J Appl Physiol 90: 538–544, 2001.—Using a rapidly responding nitric oxide (NO) analyzer, we measured the steady-state NO diffusing capacity (DLNO) from end-tidal NO. The diffusing capacity of the alveolar capillary membrane and pulmonary capillary blood volume were calculated from the steady-state diffusing capacity for CO (measured simultaneously) and the specific transfer conductance of blood per milliliter for NO and for CO. Nine men were studied bicycling at an average O2 consumption 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 from end-tidal (assumed alveolar) CO2, mixed expired CO2, and mixed expired CO, was 46.9 12.8 ml min 1 Torr 1. NO dead space (VT FENO VT FANO)/(FINO FANO) 209 88 ml, where VT is tidal volume and FENO, FINO, and FANO are mixed exhaled, inhaled, and alveolar NO concentrations, respectively. We used the Bohr equation to estimate CO2 dead space from mixed exhaled and end-tidal (assumed alveolar) CO2 430 136 ml. Predicted anatomic dead space 199 22 ml. Membrane diffusing capacity was 333 and 166 ml min 1 Torr 1 for NO and CO, respectively, and pulmonary capillary blood volume was 140 ml. Inhalation of repeated breaths of NO over 80 s did not alter DLNO at the concentrations used.