Figure 2. Estimation of the esophageal pressure-time product. The static recoil pressure of the chest wall (Pstl) is predicted from the change in lung volume and the esophageal pressure difference associated with incomplete lung emptying (Delta Pes) added to this. Delta Pesis measured from the change in Pesat the onset of inspiration. The pressure difference (indicated by the vertical distances) between the predicted value of the chest wall pressure and the esophageal pressure is the pressure produced by the respiratory muscles to generate inspiration. The integral of this pressure with respect to time during inspiration is taken as the pressure-time product per breath