Background: The purpose of this study was to use CT scanning with computational fluid dynamics to evaluate the mechanisms by which Bronchial Thermoplasty (BT) improves asthmatic symptoms. Methods: The study was conducted in a university teaching hospital, experienced in performing BT. Imaging studies were performed before, and after, BT of the left lung, and prior to treatment of the right lung, which therefore acted as a control. On each occasion, two high-resolution CT scans were performed, one at full inspiration (TLC) and the other at Functional Residual Capacity (FRC). The study protocol was offered to 10 patients, all of whom met the definition of severe asthma, despite high dose inhaled corticosteroids and dual long acting bronchodilators. Results: Significant increases in airway luminal volume were observed on the treated side, compared with control, at both full inspiration (by 27%) and at FRC (by 17%). The ratio of distal airway volume to lung volume significantly increased on the treated side. The change in airway volume with inspiration from FRC increased by 48% on the treated side compared to 5% in the control lung, suggesting treatment increased airway distensibility. No effect was observed on airway wall thickness, nor air trapping. There was a trend towards correlation between the improvement in airway volume at TLC and improvement in symptoms. Conclusion: This study demonstrates that BT increases the luminal airway volume on the treated side compared to the control lung. We suggest that this is an important link between the airway smooth muscle atrophy demonstrated pathologically, and the improvement in symptoms observed clinically.

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To assess the effects of therapeutic doses of radiation on regional pulmonary function, 28 dogs had serial chest radiographs and quantitative ventilation, perfusion, and aerosol studies at three-, six-, nine-, and twelve-month intervals after hemithorax irradiation with 60-Co-gamma photons or 15-MeV fast neutrons. Findings showed marked reductions in perfusion and aerosol deposition in the irradiated lungs of dogs in the high-dose photon and neutron groups and in the medium-dose neutron group. The effects of large photon and small neutron doses were similar (neutron RBE = 4.5). Radionuclide studies were found to be useful for detecting these alterations.