Fig. 1

An overview of the processing pipelines for surface EMG and esophageal/gastric pressure signals. Esophageal pressure (\(\textit{P}_{\mathrm{es}}\)) and gastric pressure (\(\textit{P}_{\mathrm{ga}}\)) are measured simultaneously with the double balloon technique. Cardiogenic artifacts are removed from the raw pressure signals via template subtraction. The muscular pressure (\(\textit{P}_{\mathrm{mus}}\)) is then calculated as the difference between \(\textit{P}_{\mathrm{es}}\) and the chest wall recoil pressure \(\textit{P}_{\mathrm{cw}}\) (orange curve, given by the product of the chest wall elastance \(\textit{E}_{\mathrm{cw}}\) and the volume signal \(\textit{V}\)). Transdiaphragmatic pressure (\(\textit{P}_{\mathrm{di}}\)) is calculated as the difference between \(\textit{P}_{\mathrm{es}}\) and \(\textit{P}_{\mathrm{ga}}\) curves. The respiratory surface EMG is measured via two pairs of electrodes positioned bilaterally at the second intercostal space and the costal margin. The envelopes \({\mathrm{EMG}}_{\mathrm{di}}\) and \({\mathrm{EMG}}_{\mathrm{interc}}\) are calculated on the raw ECG-gated signals using a moving RMS filter. Then, the more informative of the two channels, denoted as \({\mathrm{EMG}}_{\mathrm{sel}}\), is automatically selected and fitted to the airway pressure \(\textit{P}_{\mathrm{aw}}\) over the course of multiple subsequent occlusions, providing a scalar \(\textit{K}_{\mathrm{occl,EMG}}\). The estimate \(\textit{P}_{\mathrm{mus,EMG}}\) is calculated via the factor \(\textit{K}_{\mathrm{occl,EMG}}\) and a baseline-corrected \({\mathrm{EMG}}_{\mathrm{sel}}\) signal as in Eq. (2)