Fig. 1

Time tracings from one individual patient. Time tracings of flow, volume, airway (Paw), esophageal (Pes) and gastric (Pga) pressures, and diaphragm electrical activity (EAdi) during pneumatically triggered and cycled-off pressure support (PS_P) at 0 % extrinsic positive end-expiratory pressure (PEEPe_0%) (top panel), PS_P at PEEPe_80% (middle panel) and neurally triggered and cycled-off pressure support (PS_N) at PEEPe_0% (bottom panel). Blue, orange and red lines indicate onset of diaphragm electrical activity (EAdi), nadir of Pes, and end of assistance, respectively. Orange bars indicate EAdi without assistance (ineffective efforts). A square wave pressure assistance profile of the same magnitude above positive end-expiratory pressure (PEEP) was obtained during all conditions (height of blue box same cm H₂O in all panels). PS_N at PEEPe_0% synchronized the assistance and eliminated ineffective efforts. Pes was reduced by PS_P at PEEPe_80% and PS_N at PEEPe_0% whereas EAdi remained unchanged. The nadir of Pes occurred prior to the peak of EAdi and resulted in a positive inspiratory Pes deflection during all conditions, suggesting assistance delivery was too high in this subject. Note that Pes reverses from a negative to a positive trajectory as assistance starts, suggesting that assistance levels are excessive despite a tidal volume (V_T) of 5.2 ml/kg of predicted body weight. Despite a low group-mean V_T, this type of Pes waveform was noted in at least 50 % of the patients