Bronchial thermoplasty reduces airway resistance

Abstract

Background: The mechanism for symptomatic improvement after bronchial thermoplasty (BT) is unclear, since spirometry reveals little or no change. In this study, the effects of BT on airway resistance were examined using two independent techniques. Methods: Eighteen consecutive patients, with severe asthma (57.6 ± 14.2 years) were evaluated by spirometry and plethysmography at three time points: (i) baseline, (ii) left lung treated but right lung untreated and (iii) 6 weeks after both lungs were treated with BT. At each assessment, total and specific airway resistance (Raw, sRaw) were measured. High resolution CT scans were undertaken at the first two assessments, and measurements of lobar volume, airway volume and airway resistance were made. The Asthma Control Questionnaire (ACQ) was administered at each assessment. Results: The baseline ACQ score was 3.5 ± 0.9, and improved progressively to 1.8 ± 1.2 (p < 0.01). At baseline, severe airflow obstruction was observed, FEV1 44.8 ± 13.7% predicted, together with gas trapping, and elevated Raw at 342 ± 173%predicted. Following BT, significant improvements in Raw and sRaw were observed, as well as a reduction in Residual Volume, increase in Vital Capacity and no change in FEV1. The change in Raw correlated with the change in ACQ (r = 0.56, p < 0.05). CT scans demonstrated reduced airway volume at baseline, which correlated with the increased Raw determined by plethysmography (p = − 0.536, p = < 0.05). Following BT, the airway volume increased in the treated lung, and this was accompanied by a significant reduction in CT-determined local airway resistance. Conclusion: Symptomatic improvement after BT is mediated by increased airway volume and reduced airway resistance.

Bronchial Thermoplasty Reduces Ventilation Heterogeneity Measured by Multiple Breath Nitrogen Washout

“…There is clear dilation of airways after BT as assessed by CT, present only in lobes receiving BT actuations. We have previously adopted computational uid dynamics to show that the observed airway dilation is predicted to lower resistance at the airway level [11]. This is consistent with the reduction in plethysmographically determined airway resistance and increase in FEV 1 observed in the present study 6 months after BT.…”

“…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].…”

The effect of bronchial thermoplasty on airway volume measured 12 months post-procedure

“…We have previously used computed tomography (CT) to evaluate airway volume and have demonstrated an increase in airway volume 4 weeks after bronchial thermoplasty [13]. This correlated with a reduction in symptoms and an improvement in airway resistance [14]. A similar increase in airway volume after bronchial thermoplasty was predicted by our mathematical model of lung function [15].…”

Bronchial thermoplasty reduces ventilation heterogeneity measured by multiple breath nitrogen washout

“…There is clear dilation of airways after BT as assessed by CT, present only in lobes receiving BT actuations. We have previously adopted computational fluid dynamics to show that the observed airway dilation is predicted to lower resistance at the airway level [ 11 ]. This is consistent with the reduction in plethysmographically determined airway resistance and increase in FEV 1 observed in the present study 6 months after BT.…”

“…Nevertheless, improvements in spirometry are either non-existent or modest [ 4 – 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 – 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 ].…”