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 (FENO). Scarce information is available on the FENO decrease after spirometry or after other forced lung-function maneuvers in children. We compared changes in FENO 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 FENO measurements were followed by FVC or P-Emax maneuvers every 15 min for 45 min, whereas FENO was measured at each step for 60 min. After repeated P-Emax but not after FVC maneuvers, FENO values decreased significantly from baseline in both groups. In healthy children, geometric mean FENO (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, FENO 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 FENO variability, as compared with repeated FENO measurements alone. Previous forced lung-function maneuvers may affect FENO measurements in children. Although P-Emax testing has a greater influence than spirometry on FENO levels in children, both procedures should be avoided before measuring FENO.