Response of individual airways in vivo to bronchial thermoplasty.

Bronchial thermoplasty (BT) is a treatment for moderate-to-severe asthma which generally improves quality-of-life scores but not conventional measures of lung function. Newer methodologies have begun to demonstrate the underlying physiological changes and elucidate the mechanism of action. We postulated that systematic, CT-based assessment of the response of individual airways to BT is feasible, and our aim was to determine the distribution of these responses and the relationship with airway size. Twenty patients meeting the ERS/ATS definition of severe asthma underwent BT and assessment including CT, Asthma Control Questionnaire (ACQ), and spirometry. Treatment was structured so that the left and right lungs are treated sequentially with a mid-treatment assessment providing an internal control. Pairs of CT scans were analysed using a new semi-automatic processing algorithm which matched individual segmented airways for quantitative comparison. Cross-sectional airway lumen area from matched airway pairs in treated lungs increased on average by 6.4% after BT (p<0.02) but showed no change in the untreated lung. Matched airway length was also unchanged. Breakdown by airway size showed amplified response in more distal airways, with the smallest quintile of measured airways dilating by 13.2% (p<0.001). ACQ improved from 3.5±0.9 to 1.9±1.2 (p<0.001). These data show that the response to BT in individual airways can be assessed by CT and that dilation is heterogeneous and predominant in distal compared with proximal airways. A CT-based approach may further our understanding of the physiological changes in BT and aid in the development of refined and personalised versions of the therapy.