Head-to-head comparison of single-breath and tidal-breath exhaled nitric oxide measurements.

BACKGROUND

Exhaled nitric oxide (eNO) is an endogenous gas involved in airway pathophysiology and is determined in orally exhaled air by various techniques. However, traditional single-breath technique (eNO(SB)) requires active cooperation and is not always easily practicable (especially in young children); simpler techniques including tidal breathing measurements (eNO(TB)) are not standardized. The aim of this study was to evaluate the possible correlation and correspondence between eNO(SB) and eNO(TB) and the impact of potential confounders in children with chronic adenotonsillar disease.

METHODS

Eighty-six children (mean age 8.7 ± 3.2 y) underwent eNO assessment by means of eNO(SB) and eNO(TB). The correlation among eNO(TB), eNO(SB), and other potential confounders (i.e., gender, age, weight, height, BMI, and passive smoking exposure) were studied.

RESULTS

The analyses showed a poor correspondence between eNO(SB) and eNO(TB), with the latter underestimating (P < 0.001) mean eNO values: 6.4 parts per billion (ppb) (95% confidence interval (CI): 8.4-11.4 ppb) vs. 9.8 ppb (95% CI: 5.6-7.3 ppb). A greater correlation was found between eNO(SB) and eNO(TB) in children younger than 6 y. Only eNO(SB) and age predicted eNO(TB) (R2 = 43.6%).

CONCLUSION

eNO(TB) is not a good predictor of eNO(SB) in children. Constant-flow eNO(SB) is the technique of choice for eNO assessment in young children.