Permeability of the Alveolar Membrane to Solutes

The lower lobe of the left lung of 54 dogs was isolated and perfused with a dextran-Tyrode's solution. The alveoli were filled with Tyrode's solution, and permeability coefficients were measured for diffusion of several substances across the alveolar membrane. The permeability coefficients of the pulmonary membrane for K 42 , urea, Na 24 , glucose, D 2 O, and dinitrophenal(DNP) were 56.5 ± 3.5, 22.9±9.2, 7.5±2.1, 3.1±0.7, 400, and 400x10 -7 cm/sec, respectively. The effect of varying the flow rate on the permeability coefficient of Na 24 was investigated, and the data failed to show any significant correlation between the flow limits of 3.8 to 12. 8 cm/min/g lung tissue. The effect of two different procedures for filling the alveoli with fluid on the permeability coefficients was also investigated and no difference could be discerned in the results. The data support the thesis that the alveolar membrane has permeability characteristics similar to those of the usual cell membrane. The interstitial fluid volume of the lung (extravascular sodium space) was measured and yielded a value in normal lungs of 0.250 ± 0.129 cc/g lung tissiue. In three edematous lungs, this space averaged three times the normal value.