EFFECT OF LUNG-INFLATION ON PERIVASCULAR CUFF FLUID VOLUME IN ISOLATED DOG LUNG LOBES

Isolated, degassed dog lung lobes were suspended in a sealed container. We filled the lobes with saline to a lobe fluid pressure of 20 cm H2O. The pressure inside the container was adjusted so the lobes were inflated to transpulmonary pressures (PL) of 2 to 20 cm H2O. After 15 min of fluid inflation, the lobes were frozen in liquid nitrogen. We measured the volume of perivascular cuff fluid relative to the blood volume by a point counting procedure. In addition, we measured lobe hemoglobin content, wet weight, and dry weight. We found that perivascular cuff fluid volume increased as PL increased. There were significant (p < 0.05) increases in cuff fluid volume as PL doubled from 5 to 10 and from 10 to 20 cm H2O. The largest increases in cuff volume/cm H2O increase in PL were observed in the pressure range from 2 to 10 cm H2O. Previous investigators demonstrated that radial traction exerted by the expanding lung parenchyma results in an increase in volume of the extraalveolar vessels with lung inflation. We suggest that the same mechanism explains the measured increase in perivascular cuff fluid volume occurring with lung inflation. The relationship between perivascular interstitial fluid volume and transpulmonary pressure suggests that the compliance of the extraalveolar interstitial space decreased as the interstitial volume increased. The maximum perivascular cuff fluid volume measured in these experiments was 2.6 ml/g dry blood-free lung, which suggests that, in pulmonary edema, a substantial volume of fluid can accumulate in the perivascular interstitial space. We conclude that a decrease in interstitial fluid pressure around extraalveolar vessels with static lung inflation resulted in an increased perivascular cuff fluid volume. © 1979.