Analysis of expiratory tidal flow patterns as a diagnostic tool in airflow obstruction

An index obtained from tidal expiration, the ratio of time to peak tidal expiratory flow (tPTEF) to expiratory time (tE), discriminates between groups with and without airflow obstruction in infants and children and correlates 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 flow time curve, i.e beyond the maximum flow. One hundred and eighteen patients attending the lung function laboratory with a putative diagnosis of airflow obstruction were studied. From uncoached tidal breathing, measurements were made of the average time constant of the 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 resistance 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=058, p<0.001. EV correlated 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 made from analysis of tidal breathing and recognized measurements of airflow obstruction and overinflation.