Pleural pressure volume curves

The solid circles represent a normal pressure/volume (P/V) curve of a patient with a hepatic hydrothorax, and a calculated Pel of 3 cm H₂O/L. The open circles represent the P/V curve of an entrapped lung associated with malignancy. The elastance during the first 1250 mL is normal. After 1250 mL fluid is removed, the slope of the curve becomes very steep and has a calculated elastance of 22 cm H₂O/L. The pressure/volume curve depicted by the solid triangles is from a patient with a trapped lung. The initial mean pleural liquid pressure is negative, and there is a steep slope throughout the entire thoracentesis. The calculated elastance is 216 cm H₂O/L.