Pulmonary extravascular chloride space and albumin content in adult dogs and puppies.

Abstract

Extract: The extravascular chloride space and albumin content of the lungs were determined in 6 adult dogs and 10 puppies. 125I-labeled human serum albumin was administered and its concentration in lung tissue was determined after equilibration with the total body albumin pool. The blood content of the lung was determined by 51Cr erythrocyte tagging, and the extravascular fluid volume by 36Cl dilution. Total water in the lung was measured by drying the lungs to constant weight. The interstitial albumin concentration, assuming uniform distribution in the chloride space, averaged 1.0 g/100 ml interstitial fluid in the adult dogs and 0.62 in the puppies; the difference between these means is statistically significant. These interstitial albumin concentrations are considerably lower than lymph protein concentrations in lung reported previously. Speculation: These data support the notion that a large net absorptive gradient of colloid osmotic pressure is present across the fluid-exchanging vessels of the lung. In view of the relatively low level of pulmonary capillary hydrostatic pressure, the application of Starling's law of capillary exchange to these data indicates that interstitial hydrostatic pressure is substantially subatmospheric [12]. Although consistent with recent measurements of interstitial pressure using perforated capsules [9], this line of argument must be considered speculative because of uncertainty as to the distribution of protein in the interstitial fluid. Information is lacking as to the mechanism whereby the protein concentration of lymph is increased relative to that of capillary filtrate or the interstitial fluid. This could occur if the hydrostatic pressure within the lymph channels were significantly higher than the surrounding interstitial pressure. The maintenance of a low protein concentration in the interstitial fluid, by virtue of limited protein filtration and efficient lymphatic removal, would constitute an important barrier against pulmonary edema formation. The present study suggests that this barrier may be more effectively maintained in the immature than in the mature animal, thus counterbalancing the increased tendency for fluid filtration in the immature lung reported previously [13].