Flow-independent nitric oxide exchange parameters in healthy adults

Currently accepted techniques utilize the plateau concentration of nitric o xide (NO) at a constant exhalation flow rate to characterize NO exchange, w hich cannot sufficiently distinguish airway and alveolar sources. Using non linear least squares regression and a two-compartment model, we recently de scribed a new technique (Tsoukias et al. J Appl Physiol 91: 477-487, 2001), which utilizes a preexpiratory breath hold followed by a decreasing flow r ate maneuver, to estimate three flow-independent NO parameters: maximum flu x of NO from the airways (J(NO,max), pl/s), diffusing capacity of NO in the airways (D-NO,D-air, pl.s(-1).ppb(-1)), and steady-state alveolar concentr ation (C-alv,C-ss, ppb). In healthy adults (n = 10), the optimal breath-hol d time was 20 s, and the mean (95% intramaneuver, intrasubject, and intrapo pulation confidence interval) J(NO,max), D-NO,D-air, and C-alv,C-ss are 640 (26, 20, and 15%) pl/s, 4.2 (168, 87, and 37%) pl.s(-1).ppb(-1), and 2.5 ( 81, 59, and 21%) ppb, respectively. J(NO,max) can be estimated with the gre atest certainty, and the variability of all the parameters within the popul ation of healthy adults is significant. There is no correlation between the flow-independent NO parameters and forced vital capacity or the ratio of f orced expiratory volume in 1 s to forced vital capacity. With the use of th ese parameters, the two-compartment model can accurately predict experiment ally measured plateau NO concentrations at a constant flow rate. We conclud e that this new technique is simple to perform and can simultaneously chara cterize airway and alveolar NO exchange in healthy adults with the use of a single breathing maneuver.