Study objectives: To explore the flow and time domain characteristics of resting tidal airflow profiles in the presence of obstructive airway disease.
Methods: Spirometry was performed on 81 adults and 46 juveniles in the lung function laboratory. All the juveniles had cystic fibrosis (CF), as did some of the adults (n = 25), with the remainder having either healthy lungs or COPD. Resting breathing profiles were recorded using a pneumotachograph. Thirteen flow and time domain parameters were extracted from each profile. Two new indexes were derived that are influenced by the shape of the post-peak expiratory flow portion of the expirogram. In this expirogram, the first index (change in post-peak expiratory flow at time 20% [Tppef20]) describes early changes in post-peak flow, while the second index (change in post-peak expiratory flow at time 80% [Tppef80]) describes later changes in flow. Multiple linear regression techniques were used to define the relationship between body size, flow and time domain parameters, and FEV1, a measure of obstructive airway disease.
Results: In juvenile subjects with CF, body weight and the time to reach peak expiratory flow are the main correlates with FEV1 (adjusted r2 = 0.74). The adult CF group are different with the expiratory flow index (Tppef20) being the major correlate with FEV1 (adjusted r2 = 0.77). In the COPD group, the second expiratory flow index (Tppef80) is the major correlate instead (adjusted r2 = 0.6).
Conclusions: Using multiple linear regression techniques has allowed the description of the interrelationships between body size, age, and tidal breathing profile in obstructive airway disease. The relationship between the flow indexes Tppef20 and Tppef80 show that in adults with CF, the loss of expiratory flow braking is an important adaptation to disease, while in COPD pulmonary hyperinflation is the predominant factor.