Effects of graded increases in pulmonary vascular pressures on lung fluid balance in unanesthetized sheep

SUMMARY Fourteen experiments were conducted on 12 chronically instrumented unanesthetized sheep in which we monitored pulmonary arterial, left a trial, and aortic pressures, lung lymph flow, and lymph-to-plasma ratios (L/P) of total proteins and four endogenous protein fractions during baseline and progressive elevations of left atrial pressure. We found that L/P for total proteins decreased as lung lymph flow increased until lymph flow exceeded four to five times baseline and thereafter remained nearly constant (filtration independent) at 0.26. The four protein fractions exhibited a filtration independent L/P that was related to the effective molecular radius of the protein fraction. The minimal L/P were 0.36, 0.28, 0.18, and 0.09 for the protein fractions that had effective molecular radii of 36, 38.6, 59, and 101 A, respectively. In addition, we found no evidence supporting a stretched pore phenomenon over the pressure range utilized in this investigation. Ore Res 49:1164-1172, 1981 MANY investigators have shown that an increase in left atrial pressure causes lung lymph flow to increase and lung lymph protein concentration t