Distribution of interstitial compliance and filtration coefficient in canine lung

Utilizing a modification of the isogravimetric methodology, we have estimated the perivascular interstitial compliance and filtration coefficient in the canine lung. These values averaged 1.8 g/cm H2O and 34 (g/h)/cm H2O, respectively, per 100 g lung wet weight. By studying lungs at both low and high states of inflation (where the alveolar septae are collapsed) we were also able to determine the spatial distribution of both the interstitial compliance and filtration coefficient. We estimate that of the above total interstitial compliance a maximum of 55% is around alveolar septal vessels, 20% around extra-alveolar arteries and 25% around extra-alveolar veins. Of the above total filtration coefficient, 50% represents filtration from alveolar septal vessels, 23% from extra-alveolar arteries, and 27% from extra-alveolar veins. Our results imply that there are finite interstitial compliances communicating with all permeable vessels. Significant pressures can be built up in these spaces, thereby acutely limiting the further formation of interstitial edema.