Interstitial fluid pressure. V. Negative pressure in the lungs.

Interstitial fluid pressures in the lung were estimated in 39 dogs from pressure measurements made in implanted perforated capsules. Special operative procedures were used to minimize operative trauma of the lungs and infection and inflammation in and around the implanted capsules. In 86X of the preparations, the x-ray findings indicated little remaining inflammation and edema around the capsules, though autopsy findings indicated that a few of these did still have some edema not detectable by x-rays. In 29 of 34 animals in which x-ray findings indicated no edema, the intracapsular pressure was negative. The average of the measurements in all 34 animals was —5.8 mm Hg (± 0.8 SEM), and in the 29 animals with negative pressure values the average was —7.3 mm Hg ( ± 0 . 6 SEM). In eight capsules the pressures were below —10 mm Hg, ranging to —16 mm Hg. Because the tissues around some of the capsules undoubtedly still had varying degrees of inflammation and edema, despite the failure of roentgenograms to show these, it is suggested that the normal interstitial fluid pressure of pulmonary tissues in dogs is somewhat more negative than the capsule pressure measurements indicate, perhaps as low as —10 mm Hg. ADDITIONAL