Airway distensibility by HRCT in asthmatics and COPD with comparable airway obstruction.

Introduction: Decreased airway distensibility (AD) in response to deep inspirations, as assessed by HRCT, has been associated with the severity of asthma and COPD. Aims: The current study was designed to compare the magnitude of AD by HRCT in individuals with asthma and COPD with comparable degrees of bronchial obstruction, and to explore factors that may influence it. Results: We enrolled a total of 12 asthmatics (M/F:7/5) and 8 COPD (7/1) with comparable degree of bronchial obstruction (FEV1% predicted mean +/- SEM: 69.1 +/- 5.2% and 61.2 +/- 5.0%, respectively; p = 0.31). Each subject underwent chest HRCT at FRC and at TLC. A total of 701 airways (range 20 to 38 airway per subject; 2.0 to 23.1 mm in diameter) were analyzed. AD did not differ between asthmatics and COPD (mean +/- SEM: 14 +/- 3.5% and 17 +/- 4.3%, respectively; p = 0.58). In asthmatics, AD was significantly associated with FEV1% predicted (r(2) = 0.45, p = 0.018). We found a significant correlation between the change in lung volume and the change in AD by HRCT (r(2) = 0.64, p = 0.002). In COPD, we found significant correlations between AD and the RV% predicted (r(2) = 0.51, p = 0.046) and the RV/TLC (r(2) = 0.68, p = 0.01). Conclusions: AD was primarily affected by the dynamic ability to change lung volumes in asthmatics, and by static lung volumes in COPD.