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The base-line capillary filtration coefficient (Kf) obtained from rates of lobe weight gain during stepwise vascular pressure elevation is reported to be threefold greater in isolated than in intact dog lung. To further evaluate the stepwise pressure elevation technique, we obtained Kf in control and oleic acid-injured isolated lung. The left lower lung lobe was removed, placed on a balance, ventilated, and pump perfused with autogenous blood. Saline (n = 6) or oleic acid (n = 6) was infused, and rate of lobe weight gain was obtained during stepwise pressure elevation. Kf averaged 0.071 +/- 0.012 and 0.243 +/- 0.027 ml X min-1 X Torr-1 X 100 g-1 in the control and injured lobes, respectively. Stepwise pressure elevation can yield a base-line Kf in isolated lung similar to Kf's obtained from this and other gravimetric methods in intact and isolated lung. Furthermore, Kf increased severalfold following lung injury with oleic acid. The stepwise pressure elevation technique for Kf determination in isolated lung can be a useful tool for quantitating changes in vascular permeability.

The elevated cardiac output associated with exercise increases lung lymph flow and may increase extravascular lung water. However, it is not known if extremely elevated cardiac output alters pulmonary vascular permeability. The hematocrit-protein method was used to determine the solvent drag reflection coefficient, an index of vascular permeability to proteins, in the isolated blood-perfused canine lung lobe. Microvascular pressure was obtained by double vascular occlusion. Lobes filtered fluid during perfusion at normal flow, 0.451 +/- 0.005 l/min (LF; n = 8), or high flow, 2.319 +/- 0.080 l/min (HF; n = 7). In the LF, venous pressure was elevated to 19.0 +/- 0.5 Torr to induce filtration, whereas Pv was 3.3 +/- 0.1 Torr in the HF. In HF vs. LF, respectively, arterial pressure was 61.4 +/- 7.1 vs. 28.0 +/- 1.0 Torr (P< 0.05), microvascular pressure was 31.9 +/- 3.0 vs. 22.2 +/- 0.9 Torr (P < 0.05), and sigma was 0.52 +/- 0.07 vs. 0.51 +/- 0.02 (P > 0.05). The fivefold increase in blood flow did not alter pulmonary vascular permeability to proteins; however, the capillary filtration coefficient was fivefold greater in the HF vs. LF group (0.328 +/- 0.059 vs. 0.067 +/- 0.007; P < 0.002). These data are compatible with enzyme activity measures indicating a direct linear relationship between blood flow rate and perfused pulmonary microvascular surface area. Although the data do not rule out the possibility of increased pulmonary vascular permeability to water during very elevated blood flow rates, the greater filtration rate during elevated flow is more likely related to increases in both microvascular pressure and surface area.