Analysis of expiratory tidal flow patterns as a diagnostic tool in airflowobstruction

An index obtained from tidal expiration, the ratio of time to peak tidal ex piratory flow (tPTEF) to expiratory time (tE), discriminates between groups with and without airflow obstruction in infants and children and correlate s with other measurements of airflow obstruction in adults. The aim of this study was to determine whether the diagnosis of airflow obstruction could be made from an analysis of the later part of the expiratory tidal how time curve, i.e beyond the maximum flow, One hundred and eighteen patients attending the lung function laboratory wi th a putative diagnosis of airflow obstruction were studied. From uncoached tidal breathing, measurements were made of the average time constant of th e respiratory system (Trs) and extrapolated volume (EV), Forced expiratory spirometry and whole-body plethysmography were performed. In this cross-sectional study, Trs correlated with inspiratory airways resi stance and forced expiratory volume in one second (FEV1), according to the linear regression equations, airway resistance (Raw)=3.03 Trs+1.2, r=0.65, p<0.001, and FEV1 % predicted = 87.8-23.7 Trs, r=0.58, p<0.001,EV correlate d positively with overinflation, functional residual capacity (FRC) % pred = 152 EV+103, r=0.68, p<0.001, This study shows that there is a relationship between these measurements ma de from analysis of tidal breathing and recognized measurements of airflow obstruction and overinflation.