Reduced exhaled nitric oxide in children after testing of maximal expiratory pressures

Spirometry in adult subjects can induce a fall in concentration of exhaled nitric oxide (FE(NO)). Scarce information is available on the FE(NO) decrease after spirometry or after other forced lung-function maneuvers in children. We compared changes in FE(NO) induced by repeated spirometry and testing of maximal expiratory pressures (P(Emax)). Twenty-four sex- and age-matched children aged 9-18 years (mean age +/- SD, 13.3 +/- 2.8 years; 12 healthy, 12 asthmatic) were allocated to 1-week-apart sessions of repeated maneuvers of either forced vital capacity (FVC) or P(Emax). Baseline FE(NO) measurements were followed by FVC or P(Emax) maneuvers every 15 min for 45 min, whereas FE(NO) was measured at each step for 60 min. After repeated P(Emax) but not after FVC maneuvers, FE(NO) values decreased significantly from baseline in both groups. In healthy children, geometric mean FE(NO) (95% confidence intervals) decreased from 9.1 (7.0-11.8) ppb at baseline to 8.2 (6.3-10.6) ppb at 15 min and 7.7 (5.6-10.6) ppb at 30 min (P < 0.05 and P < 0.01, respectively), and remained unchanged at 45 and 60 min. In asthmatic children, FE(NO) levels fell from 21.6 (13.3-34.9) ppb at baseline to 15.1 (9.1-25.1) ppb at 15 min and remained low at 30, 45, and 60 min: 17.8 (10.7-29.5) ppb, 17.5 (10.2-30.1) ppb, and 17.6 (10.6-29.2) ppb, P < 0.01, for all differences from baseline. Repeated P(Emax) and FVC maneuvers increased FE(NO) variability, as compared with repeated FE(NO) measurements alone. Previous forced lung-function maneuvers may affect FE(NO) measurements in children. Although P(Emax) testing has a greater influence than spirometry on FE(NO) levels in children, both procedures should be avoided before measuring FE(NO).