Assessing the Magnitude of Patient Effort in Volume Control Mode

The first breath is initiated by the ventilator through a time-triggered mechanism. Since the patient is passive (Pmus= zero), all the work is done by the ventilator to inflate the lungs. 

However, starting from the second breath and continuing through the third and fourth breaths, a noticeable deformation of the inspiratory pressure-time scalar becomes apparent. The gradual shift of pressure-time scalar toward the baseline is a result of the patient's increasing inspiratory effort, commonly referred to as work shifting (previous terminology flow starvation)