Background Nitric oxide in exhaled air (eNO) is used as a marker of type 2 immune response-induced airway inflammation. We aimed to investigate the association between eNO and bronchiolitis incidence and respiratory symptoms in infancy, and its correlation with eosinophil protein X (EPX).
Methods We followed up infants at 6 weeks of age born to mothers with asthma in pregnancy and measured eNO during natural sleep using a rapid response chemiluminescense analyser (CLD88; EcoMedics), collecting at least 100 breaths, interpolated for an expiratory flow of 50 mL/s. EPX normalised to creatinine was measured in urine samples (uEPX/c). A standardised questionnaire was used to measure symptoms in first year of life. Associations were investigated using multiple linear regression and robust Poisson regression models.
Results eNO levels were obtained in 184 infants, of whom 125/184 (68%) had 12 months questionnaire data available and 51/184 (28%) had uEPX/c measured. Higher eNO was associated with less respiratory symptoms during the first 6 weeks of life (n=184, ß-coefficient: –0.49, 95% CI –0.95 to –0.04, p=0.035). eNO was negatively associated with uEPX/c (ß-coefficient: –0.004, 95% CI –0.008 to –0.001, p=0.021). Risk incidence of bronchiolitis, wheeze, cold or influenza illness and short-acting beta-agonist use significantly decreased by 18%–24% for every unit increase in eNO ppb.
Conclusion Higher eNO levels at 6 weeks of age may be a surrogate for an altered immune response that is associated with less respiratory symptoms in the first year of life.
- exhaled airway markers
- viral infection
- paediatric lung disaese
- respiratory infection
- respiratory measurement
Data availability statement
All data relevant to the study are included in the article or uploaded as online supplemental information.
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Contributors PGG, VEM, PDR, PDS and JM conducted the Breathing for Life Trial (BLT) pregnancy study; PGG, VEM, AMC and JM conducted BLT infant follow-up; PdGB and EdQA performed infant lung function; JM supervised the BLT infant follow-up; CRDSS and EP conducted analysis of eNO data; BP, CO'D, ST, TB and WG conducted uEPX/c measurements; AMC and JM supervised uEPX/c measurements; CRDSS statistical analyses; CRDSS and JM wrote a draft manuscript; all authors edited the final version of the manuscript. JM is the guarantor of this work.
Funding This research project was supported by National Health and Medical Research Council Grant number 1081667.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.