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 (EMG para ). EMG para 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 EMG para in COPD participants with forced expiratory volume in 1 s (FEV 1 ) ≥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. EMG para , 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/m 2 ; FEV 1 1.74±0.54 L; and FEV 1 % pred 69.6±14.0%. High-quality EMG para data were obtained from 35 participants at baseline and 31 participants on three occasions. High intra-rater and inter-rater agreement for EMG para (intraclass correlation coefficient >0.9) and moderate correlation between EMG para and FEV 1 % predicted (r=−0.42; p=0.01) were recorded. No correlation was observed between resting EMG para and breathlessness or HRQoL measures across the three time points. Conclusions EMG para measurement is feasible in primary care. In this group of COPD patients, lung function was stable across the three time points and EMG para was associated with the degree of airflow obstruction. In the resting stable state in mild/moderate disease, there was no association between EMG para and participant-reported outcomes. Further work should investigate the utility of EMG para in mild/moderate COPD participants during acute exacerbation and recovery.