Comparison of Inspiratory Work of Breathing in T-Piece Breathing, PSV, and Pleural Pressure Support Ventilation (PPSV)

Abstract

We have compared the inspiratory work of breathing during T-piece breathing, pressure support ventilation (PSV), and pleural pressure support ventilation (PPSV) by using a lung model with variable compliance and resistance, under simulated spontaneous breathing. Our lung model consists of two spring-loaded bellows, representing the lung and diaphragm, placed in an airtight container. Inspiration begins with the withdrawal of air from the diaphragm bellows by a time-cycled jet-flow-creating Venturi mechanism. Expiration occurs by opening the diaphragm bellows to the atmosphere. Work of breathing (WOB) is calculated by plotting the pressure-volume curve, with pressure corresponding to intrabox pressure and volume corresponding to the tidal volume; PPSV is a new mode of mechanical ventilatory support accomplished by setting the ventilator (Servo 900C) into the PSV mode with a level of 0 cm H2O, using the pleural pressure as the input and target signal. The PPSV maximally reduces WOB under any circumstances. The PSV sufficiently reduced WOB only in the normal lung and the lung with low compliance; however, a pressure supporting time is diminished in the lung with low compliance. The serious limitations of PSV remain in its application to the lung with high resistance. It is concluded that PPSV is closer to the actual patient's signal and has a potential advantage in reducing WOB in the lung with low compliance or high resistance (or both). The lung with flow limitation is still a challenging issue for mechanical ventilatory assistance.