PNEUMOTACHOGRAPHIC NITROGEN WASHOUT METHOD FAR MEASUREMENT OF THE VOLUME OF TRAPPED GAS IN THE LUNGS

A computerized pneumotachometric multiple breath N-2-washout method for assessment of the volume of trapped gas in the lungs (V-TGN2) is presented. The V-TGN2 is measured as the volume of air mobilized from nonventilated lung spaces by five maximal breaths after a washout performed until the end-tidal nitrogen fraction is 0.02. The method demonstrated a good instrumental precision and the reproducibility of V-TGN2 method based on recordings in normal subjects was equal to that achieved with a previous V-TGN2 gas collection in bags. It was confirmed that gas trapping occurs in normal children during tidal breathing at functional residual capacity. In normal subjects V-TGN2 was directly related to lung size. In 69 healthy children and adolescents V-TGN2 showed a good correlation with vital capacity (r = 0.85; P<0.001), of and adolescents V which it comprised 1.7+/-0.4% (mean a SD). Patients with bronchial asthma or cystic fibrosis investigated had pathological gas trapping with only a few exceptions; in several cases despite normal results at forced expiratory spirometry. The relative response of V-TGN2 (reflecting peripheral airway obstruction) and forced expiratory volume in one second (FEV(1)) (reflecting conditions in central airways) to beta(2)-agonist inhalation among the patients with asthma was variable, indicating that bronchial obstruction is not uniformly distributed along the bronchial tree. Measurements of V-TGN2 can be easily performed in children from 7 years of age with the method presented. The computerized V-TGN2 method facilitates work and saves time for the operator and provides instant test results. V-TGN2 appears to be a sensitive indicator of peripheral bronchial obstruction, giving supplemental information to standard spirometry. (C) 1994 Wiiey-Liss, Inc.