Figure 2

Original tracings exemplifying effects of expiratory automatic endotracheal tube compensation on lung emptying. Shown are original tracings of flow ($\dot{V}$), volume (V), airway pressure (P_aw), and tracheal pressure (P_trach) during pressure-targeted mechanical ventilation at a test lung compliance of 113 ml/cmH₂O, a respiratory rate of 30/minute, and an endotracheal tube (ETT) size of 7.0 mm inner diameter without (left-hand tracings) and with (right-hand tracings) expiratory automatic tube compensation (ATC). The arrow in the left lower tracing shows that during uncompensated expiratory ETT resistance, P_trach at the end of expiration was higher than externally applied positive end-expiratory pressure (PEEP), reflecting build-up of intrinsic PEEP because of incomplete volume emptying. During expiratory ATC, $\dot{V}$ and V increased, P_trach at the end of expiration decreased to the level of externally applied PEEP (reflecting absence of intrinsic PEEP), and peak pressure remained unchanged. These findings indicate facilitated volume emptying during expiratory ATC. STPD: standard temperature pressure dry.