Fe-NO: Relationship to exhalation rates and online versus bag collection in healthy adolescents

Measurement of exhaled nitric oxide (FENO) is a noninvasive and practical m ethod for assessing airway inflammation. We conducted this investigation to determine the most appropriate flow rate for FENO measurement and to obtai n normal values for FENO We determined which expiratory flow was easy to su stain, generated reproducible values, and provided good correlation between off line and online measurements. Thirty-two healthy subjects (15-18 yr ol d) underwent spirometry and FENO measurements, using a chemiluminescent NO analyzer at expiratory flow rates of 46, 31, 23, 15, 10, 7, 5, and 4 ml/s. The major findings were as follows: (1) FENO increased as flow rates decrea sed, with strong correlation between FENO values and flow rates at the four highest flows (0.850- 0.93, p < 0.001); (2) there were no significant diff erences and good agreement between off line bag and online FENO values for the four highest flows (p < 0.09-0.83); (3) online FENO values increased wi th age 15-17 yr at all flow rates, but decreased at age 18 yr; and (4) usin g multiple regression, significant predictors of FENO were flow, body surfa ce area, age, and FEF25-75. On the basis of these results, we provide FENO values for healthy adolescents and propose that the ideal flow rate for chi ldren is between 30 and 50 ml/s.