Flow-independent nitric oxide exchange parameters in cystic fibrosis

Exhaled nitric oxide (NO) remains a promising noninvasive index for monitoring inflammatory lung diseases; however, the plateau concentration (C_No,plat) is nonspecific and requires a constant exhalation flow rate. We utilized a new technique that employs a variable flow rate to estimate key flow-independent parameters characteristic of NO exchange in a group (n = 9) of 10 to 14 yr-old healthy children and children with cystic fibrosis (CF). maximum flux of NO from the airways (J_No,max, pl s^-1), diffusing capacity of NO in the airways (D_No,air, pl s^-1 ppb^-1), steady-state alveolar concentration (C_alv,ss, ppb), and mean tissue concentration of NO in the airways (C_tiss,air, ppb). We determined the following mean (± SD) values in the healthy children and patients with CF for J_No,max, D_No,air, C̄_alv,ss, and C̄_tiss,air, respectively; 784 ± 465 and 607 ± 648 pl s^-1; 4.82 ± 3.07 and 17.6 ± 12.1 pl s^-1 ppb^-1; 4.63 ± 3.59 and 1.96 ± 1.18 ppb; and 198 ± 131 and 38 ± 25 ppb. D_No,air is elevated (p = 0.007), and both C_alv,ss and C̄_tiss,air are reduced (p = 0.05 and 0.002, respectively) in CF. In contrast, C_NO,plat for healthy control subjects and patients with CF are not statistically different at both exhalation flow rates of 50 ml/s (17.5 ± 11.5 and 11.5 ± 8.97) and at 250 ml/s (7.11 ± 5.36 and 4.28 ± 3.43). We conclude that D_No,air, C̄_tiss,air, and C_alv,ss may be useful noninvasive markers of CF.