Characterizing nitric oxide exchange dynamics during tidal breathing: theory

Parametric characterization of nitric oxide (NO) gas exchange using a two-compartment model of the lungs is a potentially promising, non-invasive technique to characterize inflammatory lung diseases. Currently, this technique is limited to single breath maneuvers, including pre-expiratory breath-hold, which is cumbersome for children and individuals with compromised lung function. The current study extends the two-compartment model to parametric characterization of NO gas exchange from tidal breathing data. We assess the potential to estimate up to six flow-independent parameters, and study alternate breathing patterns by varying breathing frequency and inspiratory/expiratory flow rate ratio at constant alveolar ventilation rate. We identify three, easily characterized flow-independent parameters, which include maximum airway flux, steady state alveolar concentration, and airway volume (uncertainty <10%). Rapid inhalation followed by slow (long duration) exhalation facilitates estimates of all flow-independent parameters. Our results demonstrate the potential of parametric analysis of tidal breathing data to characterize NO pulmonary exchange.