Parasternal electromyography in participants with mild or moderate chronic obstructive pulmonary disease in primary care: cohort study to assess technical and clinical application.

BACKGROUND: Neural respiratory drive (NRD) measurement, reflecting the balance between respiratory muscle load and capacity, is quantified using surface parasternal electromyography (EMGpara). EMGpara tracks recovery from severe exacerbations of chronic obstructive pulmonary disease (COPD). Among stable COPD participants, we hypothesised the existence of a relationship between NRD, breathlessness and airway obstruction. STUDY AIMS: (1) assessing the feasibility of measuring EMGpara in COPD participants with forced expiratory volume in 1 s (FEV1) ≥50% predicted in primary care; (2) investigating relationships between NRD measures, self-reported breathlessness, airflow obstruction severity and health-related quality of life (HRQoL). METHODS: Participants with stable mild/moderate COPD, using inhaled corticosteroid (ICS) therapy, were recruited from 20 general practices. Participants were randomly allocated to continue using ICS (maintenance group) or to withdraw ICS (withdrawal group) over 6 weeks. EMGpara, spirometry, self-reported breathlessness (modified Borg dyspnoea scale), COPD Assessment Test and Chronic Respiratory Disease Questionnaire Self-Administered Standardised were measured at baseline, 3- and 6-month follow-up. Bland-Altman plots examined agreement between serial measurements. RESULTS: Forty COPD participants were recruited: age 70±9.2 years; body mass index 26±5.3 kg/m2; FEV1 1.74±0.54 L; and FEV1% pred 69.6±14.0%. High-quality EMGpara data were obtained from 35 participants at baseline and 31 participants on three occasions. High intra-rater and inter-rater agreement for EMGpara (intraclass correlation coefficient >0.9) and moderate correlation between EMGpara and FEV1% predicted (r=-0.42; p=0.01) were recorded. No correlation was observed between resting EMGpara and breathlessness or HRQoL measures across the three time points. CONCLUSIONS: EMGpara measurement is feasible in primary care. In this group of COPD patients, lung function was stable across the three time points and EMGpara was associated with the degree of airflow obstruction. In the resting stable state in mild/moderate disease, there was no association between EMGpara and participant-reported outcomes. Further work should investigate the utility of EMGpara in mild/moderate COPD participants during acute exacerbation and recovery.