THICKNESS AND PRESSURE OF PLEURAL LIQUID IN SOME MAMMALS

The thickness of the pleural liquid in the superior part of the chest of dogs, rabbits, rats and mice in the lateral position was about equal to that in the inferior part, as previously shown in cats. The average value of pleural liquid thickness, except in the regions at the bending of the lobar edges, was about 10 μ in dogs and mice, as previously found in cats, 15 μ in rats, 27 μ in rabbits. The average end-expiratory pressure of the pleural liquid in the most dependent part was -2 cm H2O in dogs, -1.5 in cats, -1.2 in rats, -0.9 in rabbits. In spite of the fact that this pressure is only slightly subatmospheric, it is lower than the pressure determined by the recoil of the most dependent part of the lung, which has been shown to be nil in the lateral position. The vertical pressure gradient of the pleural liquid in dogs, cats, rabbits and rats in the lateral position was about 1 cm H2O/cm. Hense, at least for these species, the larger the chest the lower the pleural liquid pressure in the upper part. © 1969.