Quantitative comparison of Pes- and respiratory muscle sEMG-derived inspiratory effort

Abstract

<b>Background:</b> Assessment of inspiratory effort under mechanical ventilation often requires invasive techniques like esophageal pressure (P_es) measurements and derived indices like respiratory muscle pressure (P_mus). Respiratory muscle surface electromyography (sEMG) is as a promising, noninvasive technique of monitoring patient activity.&nbsp;This study observed the correlation of P_mus and sEMG-derived inspiratory effort under mechanical ventilation. <b>Methods:</b> This prospective observational study was conducted with patients for elective intubation bronchoscopy. Four pressure levels were applied and airway flow/pressure, esophageal pressure, as well as diaphragmatic/intercostal sEMG were recorded. Patient efforts were quantified via the Pmus-time product (PTP_mus) and EMG-time product (ETP). The neuromechanical conversion factor (K_EMG) was used to evaluate correlation between ETP and PTP_mus. <b>Results:</b> In 43 patients, ETP of both sEMG channels correlated well with PTP_mus (diaphragm: r=0.79±0.25; intercostal: r=0.84±0.16). An automated channel selection method for optimizing the sEMG signal-to-noise ratio improved correlation with PTP_mus (r=0.87±0.09).&nbsp;The proportionality factor K_EMG between ETP and PTP_mus varied widely between patients (K_EMG=4.32±3.73 cmH2O/μV) and was highly correlated with K_EMG determined during intermittent airway occlusions (r=0.95, p&amp;lt;0.001).&nbsp;The occlusion-based method for deriving PTP_mus from ETP showed a breath-wise deviation to PTP_mus of 0.43±1.73 cmH2Os. <b>Conclusion:</b> These results show that sEMG is a promising alternative for monitoring breath-by-breath inspiratory effort during mechanical ventilation. Calculation of K_EMG allowed a concise prediction of sEMG-based inspiratory effort.