Fig. 5. Pressure–time products at 300 and 500 ms for each respiratory cycle (PTP³⁰⁰and PTP⁵⁰⁰), computed as the area under the time–pressure curve 300 ms (  top ) and 500 ms (  bottom ) after the onset of inspiratory effort, with normal inspiratory effort (P0.1 = 2 cm H²O) with positive end-expiratory pressure = 0 (ZEEP; Z) and positive end-expiratory pressure = 5 cm H²O (PEEP; P) for the three pressure-support ventilation (PSV) levels: 10, 15, and 20 cm H²O. *  P < 0.05 comparisons between machines. #  P < 0.05 comparisons between ZEEP and PEEP.