Figure 10.

Energy expenditure determined by the pressure time product (PTP) in a patient on pressure support ventilation. In all graphs, the continuous line is esophageal pressure (Pes) and the interrupted line represents the estimated recoil pressure of the chest wall (Pescw). (a) Pressure tracings have been superimposed so that Pescw is equal to Pes at the onset of the first inspiratory effort, and the integrated difference (hatched area) represents the upper bound PTPinsp. (b) Pressure tracings have been superimposed so that Pescw is equal to Pes at the first moment of transition from expiratory to inspiratory flow, and the integrated difference (hatched area) represents lower bound PTPinsp. (c) Pressure tracings are superimposed so that Pescw is equal to Pes at the second moment of transition from expiratory to inspiratory flow, and the integrated difference (hatched area) represents upper bound expiratory PTP (PTPexp). (d) Pressure tracings have been superimposed so that Pescw is equal to Pes at the onset of the second inspiratory effort, and the integrated difference (hatched area) represents lower bound PTPexp. With permission from Jubran et al. [56].