Limitations of superficial EMG estimate of parasternal intercostal muscle activity

Abstract

Introduction: Recently, surface EMG estimating parasternal intercostal muscle (PARA) activity has been presented as neural respiratory drive (NRD). Historically the deep anatomy of PARA risked undesired EMG “crosstalk” signals from neighboring chest wall muscles. To date, no study compared PARA EMG activity recorded from direct fine wire implants, to surface EMG estimates. Aims: To assess whether surface EMG reliably represents intramuscular PARA EMG activity recorded by implanted fine wires. Methods: We implanted fine wires into PARA 2nd right intercostal space, with a matching pair of surface electrodes. Ventilation, PARA activity from implanted wires, and surface estimated activity were recorded while seated: 1) during rest and hypercapnia, 2) during apnoea with extraneous upper chest wall movement. Results: During resting breathing, we found significant variability in surface EMG estimate versus implanted wire EMG. During hypercapnia, surface estimate diverged significantly away from implanted PARA EMG (slope 3.27 vs 1.30; P Conclusion: As an estimate of parasternal intercostal muscle activity, surface EMG has significant challenges that may constrain use in clinical applications.