Exercise-induced bronchoconstriction alters airway nitric oxide exchange in a pattern distinct from spirometry

Abstract

Exhaled nitric oxide (NO) is altered in asthmatic subjects with exercise-induced bronchoconstriction (EIB). However, the physiological interpretation of exhaled NO is limited because of its dependence on exhalation flow and the inability to distinguish completely proximal (large airway) from peripheral (small airway and alveolar) contributions. We estimated flow-independent NO exchange parameters that partition exhaled NO into proximal and peripheral contributions at baseline, postexercise challenge, and postbronchodilator administration in steroid-naive mild-intermittent asthmatic subjects with EIB (24–43 yr old, n = 9) and healthy controls (20–31 yr old, n = 9). The mean ± SD maximum airway wall flux and airway diffusing capacity were elevated and forced expiratory flow, midexpiratory phase (FEF_25–75), forced expiratory volume in 1 s (FEV₁), and FEV₁/forced vital capacity (FVC) were reduced at baseline in subjects with EIB compared with healthy controls, whereas the steady-state alveolar concentration of NO and FVC were not different. Compared with the response of healthy controls, exercise challenge significantly reduced FEV₁(−23 ± 15%), FEF_25–75(−37 ± 18%), FVC (−12 ± 12%), FEV₁/FVC (−13 ± 8%), and maximum airway wall flux (−35 ± 11%) relative to baseline in subjects with EIB, whereas bronchodilator administration only increased FEV₁(+20 ± 21%), FEF_25–75(+56 ± 41%), and FEV₁/FVC (+13 ± 9%). We conclude that mild-intermittent steroid-naive asthmatic subjects with EIB have altered airway NO exchange dynamics at baseline and after exercise challenge but that these changes occur by distinct mechanisms and are not correlated with alterations in spirometry.