Estimation of the filtration coefficient of pulmonary exchange vessels.

Filtration characteristics of the exchange vessels in isolated dog lung were studied by calculating the volume conductance (LP,C) with use of different components of the weight-gain curve following changes in capillary pressure. In one series of lungs, capillary pressure was elevated to levels that produced alveolar edema (29.4 +/- 5.3 (mean +/- SD) mmHg), and total alveolar capillary membrane conductances (LP,T) were calculated using different components of the accumulated weight-gain measurements. These conductance values are similar to those found in the literature for studies in which alveolar edema developed and LP,T was calculated using wet-to-dry weight ratios as a measure of filtered volume. In another series of lungs, capillary pressure was altered by only 5.8 +/- 2.5 mmHg, and LP,C was calculated by estimating the initial filtration rate by an extrapolation method LP,C calculated by use of the extrapolation method (0.71 X 10(-11) cm3/dyn-s) was larger than the LP,T reported in the literature, because LP,T is an estimate of the conductance of the alveolar plus the capillary membrane. Also, for the most calculations of LP,T, tissue forces have changed which causes an overestimation of the filtration driving pressure and thus an underestimate of the capillary volume conductance. After estimating both LP,C and LP,T, the maximum volume conductance of the alveolar membrane (LP,a) was calculated to be 0.13 X 10(-11) cm3/dyn-s.