EVALUATION OF A TIDAL EXPIRATORY FLOW INDEX IN HEALTHY AND DISEASED INFANTS

Patterns of tidal respiratory flow have been shown to relate well to a irway function in adults, and one epidemiological study in infants has demonstrated the value of the ratio of time to reach peak tidal expir atory flow to the total expiratory time (t(pef)/t(e)) in predicting su bsequent wheezing. The aim of this study was to evaluate t(pef)/t(e) a s a measure of lung function, by sequential observations over the firs t year, on a group of 22 healthy infants and on 32 infants with a hist ory of mild recurrent lower respiratory illness (LRI), and by single o bservations on 20 infants with asthma and 20 with severe chronic lung disease of prematurity. We compared t(pef)/t(e) measured in quiet, sup ine sleep (under sedation) through a face mask and pneumotachograph, w ith a measure of airway function, maximal flow at functional residual capacity (V-maxFRC), obtained from partial forced expiratory flow volu me loops using the ''squeeze'' technique. In healthy infants t(pef)/t( e) was significantly longer at 1 month than at 6 months (median values , 0.38 (95% CI, 0.36-0.43) and 0.28 (95% CI, 0.26-0.33), respectively) . Between 6 and 12 months t(pef)/t(e) did not alter significantly and it was independent of V-maxFRC. Both t(pef) and t(e) as well as their ratio varied with frequency of breathing over the first year of life, but not within each individual age band, due to the narrow spread of f requencies at each age. In assessing airway obstruction, t(pef)/t(e) w as less sensitive than V-maxFRC. There was no difference between healt hy infants, those with LRI, and infants with asthma. Values outside th e 95% CI for our control group of healthy infants were only seen in th e group of infants with severe chronic lung disease of prematurity (me dian value, 0.16; 95% CI, 0.12-0.22), most of whom demonstrated expira tory flow limitation during tidal breathing. We found the tidal breath ing index t(pef)/t(e) to be an insensitive measure of airway function in infants, compared with V-maxFRC. (C) 1994 Wiley-Liss, Inc.