PRESSURE-DEPENDENT INCREASE IN LUNG VASCULAR-PERMEABILITY TO WATER BUT NOT PROTEIN

Simultaneous measures of vascular permeability to fluid (capillary filtration coefficient, K(f)) and to plasma proteins (solvent drag reflection coefficient, sigma) were obtained over venous pressures (Pv) from 14 to 105 Torr in the isolated ventilated canine lung lobe (n = 70) pump perfused with autologous blood. The or was obtained from the relative increase in the concentration of plasma proteins vs. erythrocytes during fluid filtration. K(f)'s were obtained from two gravimetric methods as well as from change in hematocrit. All K(f)'s increased (P < 0.05) as Pv was increased. However, sigma averaged 0.59 +/- 0.01 (range 0.54 - 0.67) and was unchanged (P > 0.05) by elevation of Pv over 20-105 Torr. In 44 lobes where all three K(f) measures were obtained, gravimetric measures of K(f) did not differ (P > 0.05) and were highly correlated with K(f) obtained from hematocrit change, V(f) K(f) (P < 0.001). However, both weight-based K(f)'s exceeded V(f) K(f) (P < 0.05), suggesting that fluid filtration was overestimated by rate of lung weight gain or underestimated by hematocrit change. Increased permeability to water but not to protein over Pv from 20 to 105 Torr indicates that permeability to both can change independently and is counter to the theory that elevated vascular pressure "stretches" vascular pores.