Normal expiration is a passive process, characterized by an exponential decay of expiratory flow. However, in the presence of active exhalation, the expiratory flow increases, and this is often accompanied by a rise in baseline airway pressure due to the elevated intrathoracic pressure generated by expiratory muscle contraction.

A rise in baseline pressure during exhalation accompanied by an increase in expiratory flow indicates expiratory muscle contraction, which raises intrathoracic pressure. Under normal circumstances, expiration is a passive process driven by the elastic recoil of the respiratory system and produces a smooth exponential decay in the expiratory flow waveform. However, when the patient actively contracts the expiratory muscles, this normal decay pattern is lost and the expiratory

You can observe three pairs of breaths (double trigger) in this image. The first breath in double trigger is triggered by the machine, characterized by a rapid increase in pressure that reaches the pressure alarm limit, causing pressure cycling. The subsequent breath is a patient triggered mandatory breath. The pressure-time scalar deviates below the baseline due to strong inspiratory effort, known as work shifting. As the inspiratory muscles relax, the pressure-time scalar r