Bronchial thermoplasty reduces ventilation heterogeneity measured by multiple breath nitrogen washout

David Langton,Francis Thien,Peter B Noble,Virginia Plummer,Kim Bennetts

doi:10.1186/s12931-020-01575-x

Abstract

BackgroundDespite demonstrated symptomatic benefit from bronchial thermoplasty (BT), the underlying pathophysiological benefits have been uncertain. The purpose of the present study was to relate clinical benefit after BT to changes in lung physiology, focusing on ventilation homogeneity assessed using multiple breath nitrogen washout (MBNW), and how this may be affected by changes in airway volume and resistance.MethodsConsecutive patients (n = 21) with severe asthma scheduled for BT, were evaluated at baseline, 6 weeks and 6 months after completion of treatment. Assessments included the Asthma Control Questionnaire (ACQ), medication usage, exacerbation frequency, spirometry, plethysmography and MBNW. Eighteen of these patients underwent detailed CT evaluation for the estimation of airway volume at baseline and then after the left lung had received BT treatment but prior to right lung treatment. Data are mean ± STDEV.ResultsPatients responded to BT with an improvement in ACQ from 3.4 ± 0.8 at baseline to 2.0 ± 1.1 at 6 months (p < 0.001). Steroid requiring exacerbations fell from 3.1 ± 2.9 in the 6 months prior to BT to 1.4 ± 1.7 following BT (p < 0.001). Significant reductions in maintenance oral steroid dosing and short acting beta agonist use were observed.Airway volume measured by CT scanning significantly increased after treatment. The FEV1 improved from 1.34 ± 0.65 l to 1.52 ± 0.76 l (p = 0.024). The Residual Volume fell from 2.87 ± 0.89 l to 2.71 ± 0.93 l (p = 0.008) and Total Airway Resistance (Raw) from 10.58 ± 6.56 to 7.64 ± 3.74 cmH2O.s.l−1 (p = 0.020). The Lung Clearance Index (LCI) was 187 ± 63% predicted at baseline and improved after treatment from 12.7 ± 3.3 to 11.8 ± 2.4 (p = 0.049). The improvement in LCI correlated with the improvement in Raw (r = 0.463, p = 0.035).ConclusionClinical benefit after BT is accompanied by improvements in lung physiology, including normalisation of lung homogeneity that seems to be driven by airway dilation and reduced resistance.

Highlights

Despite demonstrated symptomatic benefit from bronchial thermoplasty (BT), the underlying pathophysiological benefits have been uncertain
Clinical benefit after BT is accompanied by improvements in lung physiology, including normalisation of lung homogeneity that seems to be driven by airway dilation and reduced resistance
Langton et al Respir Res (2020) 21:308 of the physiological behaviour of the asthmatic lung, suggests that bronchial thermoplasty should result in dilatation of the treated airways and, that has been demonstrated in recent computerized tomography (CT) studies [9,10,11]

Summary

Introduction

Despite demonstrated symptomatic benefit from bronchial thermoplasty (BT), the underlying pathophysiological benefits have been uncertain. Langton et al Respir Res (2020) 21:308 of the physiological behaviour of the asthmatic lung, suggests that bronchial thermoplasty should result in dilatation of the treated airways and, that has been demonstrated in recent computerized tomography (CT) studies [9,10,11]. This modelling 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]. MBNW indices correlate with asthma stability and airway hyper-responsiveness [16]

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