Fleisch pneumotachograph

Flow was measured with a heated Fleisch pneumotachograph, dead space 51 ml (Hans Rudolph, Kansas City, MO, USA) and airway pressure was measured by a pressure transducer (DP 15–32, Validyne, Northridge, CA, USA) for all modes. Digital EAdi signal was converted into an analog signal (National Instruments, Austin, TX, USA). During all three modes of ventilation, the EAdi waveform was simultaneously recorded with flow and airway pressure from the respective ventilator (see Additional file 1). All signals were digitized at a 100-Hz sampling rate (PowerLab/4SP, ADInstruments, Castle Hill, Australia) and recorded on a personal computer for subsequent analysis (Chart software, ADInstruments, Castle Hill, Australia).

Flow was measured with a heated Fleisch pneumotachograph placed between the endotracheal tube and the Y-piece of the ventilator circuit (Hans Rudolph, Kansas, MO) (55 (link)). Airway pressure (P_aw) was measured proximal to the endotracheal tube. Esophageal (P_es) and gastric pressures (P_ga) were measured with balloon-tipped catheters coupled to pressure transducers (54 (link)). Proper positioning of the esophageal balloon catheter was ensured with the occlusion technique (55 (link)). Transdiaphragmatic pressure (P_di) was obtained by subtracting P_es from P_ga (54 (link)).