Bronchodilator responsiveness in normal infants and young children

Several studies have demonstrated that normal infants exhibit bronchoconstr iction after inhalation of nonspecific agonists and that the induced airway narrowing can be reversed by the inhalation of a beta -agonist. However, t here are very limited data on baseline airway tone and the airway response to a beta -agonist in this subject population. The purpose of our study was to evaluate in normal infants baseline airway responsiveness to the inhale d beta -agonist, albuterol, using changes in maximal expiratory flows. Fort y-one healthy infant volunteers with no history of respiratory disease or r ecurrent wheezing (ages 5.4 to 141.4 wk) were studied. Maximal expiratory f low-volume curves were obtained at baseline and 10 min after inhalation of albuterol (n = 28) or placebo (n = 13) using a metered-dose inhaler with a spacer. The mean percent change was significantly greater (p < 0.05) in the albuterol versus placebo group for FEV0.5 (2.2% versus -1.5%), FEF75% (10. 6% versus -3.1%), and FEF85% (12.9% versus 0.5%). Six of 28 albuterol-treat ed infants demonstrated increases in FEF75% greater than two standard devia tions from the mean change in FEF75% seen in the placebo group. These infan ts were younger and more frequently exposed to maternal smoking during preg nancy. We conclude that normal healthy infants have overall levels of basel ine airway tone that are similar to that reported in adults and older child ren; however, among the infants we evaluated the response to an inhaled bro nchodilator was greatest in the youngest infants and in those exposed to to bacco smoking.