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 expiratory flow over total expiratory time (TME/TE) have been used to assess airway obstruction in infants and adults. We obtained these measurements using calibrated respiratory inductance plethysmography (RIP) on 15 adolescents 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 CODAS (DATAQ Instruments, Akron, OH) software, the analog signals were digitized, and the differentiated sum (AB + RC) signal was used to calculate TME/TE. Forced vital capacity (FVC) and forced expiratory volume in 1 sec (FEV1) were obtained using RIP in all subjects. Subjects with CF had a significantly higher mean phi than the control subjects (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 difference in TME/TE between the groups. We conclude that RIP-acquired phi, but not TME/TE, 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 phi in infants and young children with lung disease could help in assessing disease severity and progression in this population, in whom repeated measures are few and complex.