Thoracoabdominal asynchrony and ratio of time to peak tidal expiratory flow over total expiratory time in adolescents with cystic fibrosis

Thoracoabdominal asynchrony (TAA) and the ratio of time to peak tidal expir atory flow over total expiratory time (T-ME/T-E) have been used to assess a irway obstruction in infants and adults. We obtained these measurements usi ng calibrated respiratory inductance plethysmography (RIP) on 15 adolescent s and young adults with cystic fibrosis (CF) and varying disease severity. The measurements were then compared to 15 normal age-matched controls. TAA was expressed as a phase angle (phi) calculated from the abdominal (AB) and ribcage (RC) signals acquired from scalar strip chart recordings. Using CO DAS (DATAQ instruments, Akron, OH) software, the analog signals were digiti zed, and the differentiated sum (AB + RC) signal was used to calculate T-ME /T-E. Forced vital capacity (FVC) and forced expiratory volume in 1 sec (FE V1) were obtained using RIP in all subjects. Subjects with CF had a significantly higher mean phi than the control subje cts (15 degrees vs. 8 degrees, respectively, P = 0.01). In the CF patients the specificity of a high phi as an indicator of abnormality was 80%, while the sensitivity was 65%. There was no correlation in the magnitude of phi and disease severity as assessed by FVC or FEV1. There was no significant d ifference in T-ME/T-E between the groups. We conclude that RIP-acquired phi, but not T-ME/T-E, is a simple and useful method to detect the presence of airway obstructive disease. We speculate that the sensitivity of this method will increase in younger patients with more compliant chest walls and less air trapping. Longitudinal studies of p hi in infants and young children with lung disease could help in assessing disease severity and progression in this population, in whom repeated measu res are few and complex. (C) 1999 Wiley-Liss, Inc.