ALVEOLAR-CAPILLARY MEMBRANE-PERMEABILITY - CORRELATION WITH FUNCTIONAL, RADIOGRAPHIC, AND POSTMORTEM CHANGES AFTER FLUID ASPIRATION

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Abstract
An index of permeability of the alveolar-capillary membrane was derived from the relative extraction from the lung into arterial blood of 2 tracers, 125I-antipyrine and 51Cr-EDTA. The effect on this index on aspirating 2 ml of isotonic saline, distilled water or 10-1 M HCl per kg body wt was studied in 3 groups of rabbits. The severity and time course of changes in the permeability index were correlated with changes in lung mechanics, gas exchange, serial chest roentgenograms, ratio of extravascular lung water to dry weight and histologic findings. Aspiration of saline produced no change in the permeability index; aspiration of water produced a large mean .+-. SEM [standard error of the mean] increase in the index, from a baseline of 0.025 .+-. 0.002 to 1.050 .+-. 0.054 (P < 0.001), but this value returned to baseline 15 min later. After HCl the permeability index increased from a baseline of 0.027 .+-. 0.003 to 1.068 .+-. 0.098 (P < 0.005), with no evidence of resolution after 60 min. Changes in lung mechanics, gas exchange and roentgenograms were smallest after aspiration of distilled water and greatest after aspiration of HCl. The functional changes after aspiration of water and saline recovered at a rate proportional to the known clearance rates of these liquids from the lung. The changes after HCl showed no tendency toward recovery or, in the case of the roentgenograms, worsened with time. There were no detectable histologic abnormalities or an increase in the ratio of extravascular lung water to dry weight after aspiration of water or saline, but there were extensive histologic abnormalities and a 70% increase in lung water after acid. The increase in the permeability index after aspiration of water was too transient to exert a deleterious effect. The persistence of the increase in the permeability index after HCl was associated with persistent functional changes attributable to the considerable increase in lung water.

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