Measurements of exhaled nitric oxide with the single-breath technique and positive expiratory pressure in infants

The aim of this study was to adapt the single-breath technique with positiv e expiratory pressure to measure exhaled nitric oxide (eNO) in infants. We hypothesized that exhaled eNO was greater in wheezy than in healthy infants . We studied 30 infants (16 wheezy and 14 healthy). The forced expiratory v olume in 0.5 s (FEV0.5) was determined with the raised volume rapid thoraci c compression technique, and eNO was measured during constant expiratory fl ow with a rapid-response chemiluminescence analyzer. After passive inflatio n to a preset pressure of 20 cm H2O, thoracic compression with an inflatabl e jacket caused forced expiration to occur through a face-mask with an expi ratory flow resistor attached. During the forced expiration, the jacket pre ssure was increased to maintain a constant driving mouth pressure and hence a constant expiratory flow (50 ml/s). The mean level of eNO in the wheezy infants (31.8 ppb) was significantly higher than the level in healthy infan ts (18.8 ppb) (p = 0.03). A family history of atopy in parents was associat ed with increased eNO levels (p < 0.001) independent of age, sex, weight, l ength, wheezing, and FEV0.5. We conclude that the single-breath technique w ith positive expiratory pressure is a feasible method for measuring eNO in infants. Levels of eNO were significantly higher in wheezy infants and in t hose with a family history of atopy.