THICKNESS AND PRESSURE OF PLEURAL LIQUID AT VARIOUS HEIGHTS AND WITH VARIOUS HYDROTHORACES

Pleural liquid thickness at various heights has been determined in supine and prone cats with hydrothoraces of various size. With less than 0.7 ml the thickness did not increase, suggesting that the liquid is first drawn at the bending of the lobar edges, where it releases the deformation forces. Then the thickness in the lowermost part increased linearly with the logarithm of the volume introduced. For a given amount of liquid introduced the increase of pleural liquid pressure was the same in the lower part and in the upper part, where the thickness was normal: hence pleural liquid under normal conditions should be a continuous system. The pressure of the liquid at the bottom of the pleural space became atmospheric after the introduction of about 2.5 ml; with about 20 ml the lower 10 mm of lung were collapsed. When the lowermost part of the lung is collapsed the relationship between pressure and thickness of the pleural liquid is unique irrespectively of the volume of liquid introduced. © 1969.