Fig. 2
Examples of balloon pressure-volume curves. Panel (a) Balloon pressure (circles) and chamber pressure (dots) were plotted against balloon volume in the bench experiment. The balloon volume with transmural pressure (the difference between the balloon pressure and the chamber pressure) within ±1.0 cmH2O was defined as the minimal and maximal balloon volumes (VMIN and VMAX). The balloon volume with the closest to zero transmural pressure was defined as the best filling volume (VBEST). Least square fitting line between the chamber pressure and balloon volume (black line) and between the balloon pressure and balloon volume within VMIN to VMAX (red dash line) are also shown. Panel (b) Esophageal balloon pressure at end-expiratory (circles) and end-inspiratory occlusion (squares) were plotted against balloon volume in the clinical study. The lower and upper limits of an intermediate linear section on expiratory balloon pressure-volume curve were visually inspected, and were defined as the clinical VMIN and VMAX. The clinical VBEST was defined as the balloon volume with the largest difference between end-expiratory and end-inspiratory esophageal balloon pressure. Least square fitting line between the end-expiratory balloon pressure and balloon volume within clinical VMIN to VMAX (red dash line) is also shown