title: Fluid Exchange in the isolated perfused lung.
abstract: The advantages of an isolated, perfused lung preparation in studies of transvascular fluid shifts are described. We find the permeability characteristics of the exchange vessels in the rabbit lung preparation to be similar to those obtained in lungs in situ. The filtration coefficient is similar during plasma and during Krebs-Ringer dextran T 70 perfusion. Therefore proteins in the perfusate do not modify the permeability of the exchange vessels in these lungs as had been reported for other vascular beds. Interstitial fluid pressure in both the alveolar walls and the alveolar corner regions increases with a rise in alveolar pressure. The result is a reduction in the fluid filtration rate under both zone-III and zone-I conditions. The resistance of the extravascular pathway and the fluid pressure in the periarterial/perivenous spaces both appear to be reduced when lung volume is increased by a reduction in pleural pressure. The net effect of positive airway pressure on the transvascular fluid exchange will depend on the relative contribution of the alveolar pressure effects and the lung volume effects. Fluid reabsorption can be observed to occur in the isolated, perfused rabbit lung. This reabsorption does not take place at the level of the loose perivascular tissue spaces since the interstitial fluid pressure at these sites is much lower than the microvascular pressure. We suggest that fluid reabsorption takes place at the thick part of the air-blood barrier, which, most likely, has a higher fluid pressure.
mesh_terms: D000418:Albumins / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure; D002199:Capillary Permeability / Q000187:drug effects; D008168:Lung / Q000648:ultrastructure; D008176:Lung Volume Measurements; D008833:Microcirculation / Q000187:drug effects; D010477:Perfusion; D011650:Pulmonary Alveoli / Q000098:blood supply; D011652:Pulmonary Circulation / Q000187:drug effects; D011817:Rabbits
chemical_list: D000418:Albumins