Simulated Breathing Conditions and Ventilator Settings

First, four passive breathing conditions were simulated. A Hamilton C3 ventilator (Hamilton Medical AG, Bonaduz, Switzerland), which was linked to the lung simulator without a facemask and PEV. The ventilator was calibrated and configured in the volume-controlled ventilation (VCV) mode. Then, it was configured in the pressure-controlled ventilation (PCV) mode. Finally, active conditions with a spontaneous effort were simulated, and a Respironics V60 Bilevel Ventilator (Philips) was connected to the lung simulator with a facemask and PEV, and the device was configured in the PSV mode. The pressure control (PC) and pressure support (PS) levels were adjusted for the ventilator to obtain tidal volumes (V_T) that achieved 5.0, 7.0, and 10.0 mL/kg body weight outputs, and the positive end-expiration pressure (PEEP) was set at 5.0 cmH₂O. A backup respiratory rate of 10 breaths/minute was used, and the maximal duration of the inspiratory phase was 2.0 s. A shorter inspiratory rise time was selected, which avoided overshoot.^{17 (link),18 (link)} Trigger sensitivity and cycling criteria were auto-adjusted (digital Auto-Trak™, Philips Respironics).^{16 (link)}