Assessment of exhaled nitric oxide kinetics in healthy infants

Exhaled nitric oxide (FE_NO) measurements provide a noninvasive approach to the evaluation of airway inflammation. Flow-independent NO exchange parameters [airway NO transfer factor (D_NO) and airway wall NO concentration (Cw_NO)] can be estimated from FE_NO measurements at low flows and may elucidate mechanisms of disturbances in NO exchange. We measured FENO in sedated infants by using an adaptation of a raised lung volume rapid thoracic compression technique that creates forced expiration through a mass-flow controller that lasts 5-10 s, at a constant preset flow. We measured FE_NO at expired flows of 50, 25, and 15 ml/s in five healthy infants (7-31 mo). Median FE_NO increased [24, 40, and 60 parts per billion (ppb)] with decreasing expiratory flows (50, 25, and 15 ml/s). Group median (range) for D_NO and Cw_NO were 12.7 (3.2-37) × 10^-3 nl·s^-1·ppb^-1 and 108.9 (49-385) ppb, respectively, similar to values reported in healthy adults. Exhaled NO is flow dependent; flow-independent parameters of exhaled NO kinetics can be assessed in infants and are similar to values described in adults.