Author Conflict: No competing interests declared Running Title: Respiratory muscle EMG in methacholine challenge Abstract: Neural respiratory drive, measured via the parasternal intercostal electromyogram (EMGpara), provides a non-invasive index of the load-capacity balance of the respiratory muscle

Neural respiratory drive, measured via the parasternal intercostal electromyogram (EMGpara), provides a non-invasive index of the load-capacity balance of the respiratory muscle pump. Previous studies in patients with obstructive lung disease have shown strong relationships between EMGpara and the extent of both airflow obstruction and hyperinflation. The relative influence of the two factors has not, however, been described. Airflow obstruction was induced via methacholine challenge testing in twenty-five adult humans. Forced expiratory volume in one second (FEV1) and surface EMGpara during tidal breathing were measured following each dose, with twenty of the participants also undergoing measurements of inspiratory capacity (IC) at each stage. Linear mixed model (LMM) analysis was used to assess dose-wise changes in FEV1 and EMGpara, and thereafter to determine the Disclaimer: This is a confidential document. influence of changes in FEV1 and IC on change in EMGpara. Median (IQR) FEV1 decreased significantly (96.00 (80.00 122.30)%predicted to 67.80 (37.98 92.27)%predicted, p<0.0001) and EMGpara increased significantly (5.37 (2.25 8.92)μV to 6.27 (3.37 19.60)μV, p<0.0001) from baseline to end of test. LMM analysis showed a significant interaction between methacholine dose and induced change in EMGpara, with an increase in EMGpara of 0.24 (95% confidence interval 0.11 0.37)μV per methacholine dose2. Change in FEV1 further influenced this relationship (increase in slope of 0.002 (0.004 0.001)μV dose-2 per %predicted fall in FEV1, p=0.011), but not with change in IC. These data suggest that bronchoconstriction exerts a more potent influence on levels of EMGpara than changes in end-expiratory lung volume during methacholine challenge. New Findings: The parasternal intercostal electromyogram (EMGpara) is known to provide an accurate, non-invasive index of respiratory load-capacity balance. Although relationships between EMGpara and both airflow obstruction and hyperinflation have been shown, the independent contribution of each factor has not been examined. Reductions in airway calibre and inspiratory capacity (IC) along with increases in EMGpara were induced via methacholine challenge. A strong inverse relationship was observed between EMGpara and airway obstruction with no influence of IC. These data suggest that EMGpara is more strongly influenced by airway calibre than by changes in end-expiratory lung volume during airway challenge testing. Dual Publication: No Funding: Asthma UK: Victoria MacBean, 10/019 VM was supported by a project grant from Asthma UK during the conduct of this work Disclaimer: This is a confidential document. 1 Parasternal intercostal muscle activity during methacholine-induced bronchoconstriction Victoria MacBean PhD, Claire L. Pringle MSc, Alan C. Lunt MSc, Keith D. Sharp MSc, Ashraf Ali BSc, Anne Greenough MD , John Moxham MD, Gerrard F. Rafferty PhD King’s College London, Division of Asthma, Allergy and Lung Biology King’s College Hospital NHS Foundation Trust, Department of Respiratory Medicine National Institute for Health Research (NIHR) Biomedical Research Centre based at Guy’s and St Thomas’ NHS Foundation Trust and King’s College London Address for Correspondence: Dr Victoria MacBean Department of Respiratory Medicine King’s College London Faculty of Life Sciences & Medicine, Bessemer Road, London SE5 9PJ, UK Email victoria.macbean@kcl.ac. uk Tel +44 203 299 2080 Fax +44 203 299 3589 Running Head: Respiratory muscle EMG in methacholine challenge