Tidal expired airflow patterns in adults with airway obstruction

Earlier studies have shown that time and flow indices derived from tidal ex piratory Bow patterns can be used to distinguish the severity of airway obs truction. This study was designed to address two aspects of tidal expirator y Bow patterns: 1) how do expiratory Bow patterns differ between subjects w ith normal and obstructed Churchill Hospital airways; and 2) can a sensitiv e index of airway obstruction be derived from these pat tern differences? Tidal expiratory flow patterns from 66 adult subjects with varying degrees of air way obstructive disease with a forced expiratory volume in one secon d (FEV1) of 20-121% predicted were examined, in each subject, the expired h ow pattern from each consecutive breath was scaled and then averaged togeth er to create a single expired pattern, A detailed examination of the scaled flow patterns in 12 subjects (six with normal airways and six with airway obstruction) showed that the shape of t he post-peak expiratory Bow portion was different in the subjects with airw ay obstruction. A slope index,(S) over bar, was derived from the scaled pat terns and found to be sensitive to the severity of airway obstruction, corr elating with FEV1 (% pred) with r(2)=0.74 (p<0.05, n=57), The (S) over bar index also correlated (r(2)=0.36, p<0.05, n=47) with the functional residua l capacity (FRC) (% pred) which Mras >100% in subjects with severe airway o bstruction and lung overinflation, In subjects with normal airways, three f urther airflow patterns could be distinguished, which were different from t he patterns seen in subjects with the severest airway obstruction. Sealed Bow patterns from tidal expiration collected from uncoached subjects , can be used to derive an index of airway obstruction.