ABILITY OF NEW LUNG-FUNCTION TESTS TO ASSESS METHACHOLINE-INDUCED AIRWAY-OBSTRUCTION IN INFANTS

We assessed the ability of innovative lung function tests to detect bronchial obstruction induced by methacholine bronchial challenge. Fifty-five recurrently wheezy infants (mean age 16 +/- 5.2 months) free of respiratory symptoms underwent baseline lung function tests. Forty-two completed the methacholine challenge. Maximal flow at functional residual capacity (V-maxFRC) was obtained using the squeeze technique; compliance and resistance of the respiratory system (C-rs, R(rs)) was measured with the passive expiratory flow volume technique; tidal volume breathing patterns were analyzed from recordings of respiratory rate (RR), tidal volume (V-T), and inspiratory time divided by total cycle of duration (T-i/TTtot). Expiratory tidal flow volume (V/V-T) curves were described with multiple indices such as the ratio of expiratory time necessary to reach peak tidal expiratory flow (F-pet) to expiratory time (T-me/Te). Transcutaneous oxygen tension (P-tcO2) Was measured as an indicator of response to methacholine challenge. Of 42 infants 41 responded to methacholine by a change greater than or equal to 2 standard deviations from baseline values. The mean SD unit changes were 9.8 in P-tcO2 3.7 for V-maxFRC, 2.8 for C-rs, 2.09 for R(rs), 3.1 for RR, 1.6 for T-i/T-tot, 2.2 for T-me/T-e 3.9 for PFVt. We conclude that these noninvasive lung function tests, especially V-maxFRC and F-pet, can be used to detect minor or moderate airway obstruction. Further studies are needed to determine the value of the tests in assessing bronchial disease and effects of its treatment. Pediatr Pulmonol, 1994; 18:308-316. (C) 1994 Wiley-Liss, Inc.