Limitations of surface EMG estimate of parasternal intercostal to infer neural respiratory drive

•In COPD, surface estimated “parasternal” EMG did not faithfully represent real parasternal EMG, from implanted fine wires.•During apnea, surface estimated “parasternal” EMG showed fallacious, pseudo-breathing without airflow.•Surface “parasternal” EMG was less than direct parasternal EMG during baseline, inspiratory capacity and CO2 ventilation.•Surface estimated “parasternal” EMG does not reliably express neural respiratory drive (NRD).•Surface estimated “parasternal” EMG is of limited utility as a biomarker in clinical applications including COPD. Recently, surface EMG of parasternal intercostal muscle has been incorporated in the "ERS Statement of Respiratory Muscle Testing" as a clinical technique to monitor the neural respiratory drive (NRD). However, the anatomy of the parasternal muscle risks confounding EMG "crosstalk" activity from neighboring muscles. To determine if surface “parasternal” EMG: 1) reliably estimates parasternal intercostal EMG activity, 2) is a valid surrogate expressing neural respiratory drive (NRD). Fine wire electrodes were implanted into parasternal intercostal muscle in 20 severe COPD patients along with a pair of surface EMG electrodes at the same intercostal level. We recorded both direct fine wire parasternal EMG (EMGPARA) and surface estimated “parasternal” EMG (SurfEMGpara) simultaneously during resting breathing, volitional inspiratory maneuvers, apnoea with extraneous movement of upper extremity, and hypercapnic ventilation. Surface estimated “parasternal” EMG showed spurious "pseudobreathing" activity without any airflow while real parasternal EMG was silent, during apnoea with body extremity movement. Surface estimated “parasternal” EMG did not faithfully represent real measured parasternal EMG. Surface estimated “parasternal” EMG was significantly less active than directly measured parasternal EMG during all conditions including baseline, inspiratory capacity and hypercapnic ventilation. Bland-Altman analysis showed consistent bias between direct parasternal EMG recording and surface estimated EMG during stimulated breathing. Surface “parasternal” EMG does not consistently or reliably express EMG activity of parasternal intercostal as recorded directly by implanted fine wires. A chest wall surface estimate of parasternal intercostal EMG may not faithfully express NRD and is of limited utility as a biomarker in clinical applications.