Spirometry effects on conventional and multiple flow exhaled nitric oxide in children.

OBJECTIVE: Clinical and research settings often require sequencing multiple respiratory tests in a brief visit. Guidelines recommend measuring the concentration of exhaled nitric oxide (FeNO) before spirometry, but evidence for a spirometry carryover effect on FeNO is mixed. Only one study has investigated spirometry carryover effects on multiple flow FeNO analysis. The objective of this study was to evaluate evidence for carryover effects of recent spirometry on three exhaled NO summary measures: FeNO at 50 ml/s, airway wall NO flux [J'awNO] and alveolar NO concentration [CANO] in a population-based sample of schoolchildren.
METHODS: Participants were 1146 children (191 with asthma), ages 12-15, from the Southern California Children's Health Study who performed spirometry and multiple flow FeNO on the same day. Approximately, half the children performed spirometry first. Multiple linear regression was used to estimate differences in exhaled NO summary measures associated with recent spirometry testing, adjusting for potential confounders.
RESULTS: In the population-based sample, we found no evidence of spirometry carryover effects. However, for children with asthma, there was a suggestion that exhaled NO summary measures assessed ≤6 min after spirometry were lower (FeNO: 25.8% lower, 95% CI: -6.2%, 48.2%; J'awNO: 15.1% lower 95% CI: -26.5%, 43.0%; and CANO 0.43 parts per billion lower, 95% CI: -0.12, 0.98).
CONCLUSIONS: In clinical settings, it is prudent to assess multiple flow FeNO before spirometry. In studies of healthy subjects, it may not be necessary to assess FeNO first.