Bronchial thermoplasty increases airway volume measured by functional respiratory imaging

Abstract

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.

Bronchial thermoplasty reduces airway resistance

“…Plethysmography has demonstrated a reduction in the degree of gas trapping (measured by residual volume) after BT, but the magnitude of this change was modest [11]. The first compelling evidence for an improvement in lung physiology after BT was presented in our recent paper, which used a CT-based segmentation methodology to demonstrate that the volume of air in the airways increased following BT treatment [12].…”

Bronchial Thermoplasty Reduces Ventilation Heterogeneity Measured by Multiple Breath Nitrogen Washout

“…This allowed patients to be re-evaluated mid treatment with our CT scanning protocol, with the left lung completely treated but the right lung being untreated and serving as a control. This treatment protocol is reported elsewhere, but is included here in order to assist with the interpretation of the changes to the various lung function parameters [10,18]. In this present study, patients were evaluated by spirometry, plethysmography and MBNW at baseline (in the 4 weeks prior to BT) and then again, 6 weeks and 6 months after the completion of all BT treatment.…”

“…Nevertheless, improvements in spirometry are either non-existent or modest [4][5][6][7][8]. Mathematical modelling of the physiological behaviour of the asthmatic lung, suggests that bronchial thermoplasty should result in dilatation of the treated airways and, indeed that has been demonstrated in recent computerized tomography (CT) studies [9][10][11]. This modelling also suggests that the airway dilatation should improve the downstream distribution of ventilation to small airways and recent studies of ventilation homogeneity in the lung using hyperpolarized gas magnetic resonance imaging (MRI) would lend support to this proposal [12,13].…”

Treatment for intractable asthma: bronchial thermoplasty

“…Recently, Ishii et al have reported chest HRCT at inspiratory and expiratory levels before and after BT treatment, and reported that the expiratory lung volume decreases after BT treatment (Figure 9) (14). Langton et al also reported increase of the luminal airway volume and decrease of residual volume after BT (15,16). It can be said that measurement of expiratory lung volume can be a tool for estimating the usefulness of BT treatment.…”