The dynamics of the lung fluid filtration system in dogs with edema.

Abstract

The relationship between pulmonary microvasculature fluid filtration pressures and lung lymph flow rate (.ovrhdot.QL) as filtration pressures increased was studied to determine why lungs with functional lymphatics become edematous and, as filtration pressures decreased, to determine the effect of edema formation on lymphatic function. Edema was induced by rapid i.v. infusion of neutralized Ringer''s solution in a volume equivalent to 30% of body weight in 7 anesthetized dogs. Pulmonary microvascular pressure (Pmv) and .ovrhdot.QL increased to 58 cm H2O and 40 ml/h, respectively, during the infusion. Initially, .ovrhdot.QL increased slowly and the estimated net fluid filtration pressure (.SIGMA.p) increased rapidly with infusion. Later in the 30 min infusion period, small increases in .SIGMA.p produced greater changes in .ovrhdot.QL. Over a 3 h postinfusion period, Pmv and .ovrhdot.QL decreased but they remained significantly greater than baseline levels. During the postinfusion period .ovrhdot.QL was a linear function of Pmv and a logarithmic function of .SIGMA.p. Extravascular lung water content measured postmortem was 70% greater than normal. The relationship between .ovrhdot.QL and .SIGMA.p during and after the infusion demonstrated marked hysteresis. Extravascular fluid accumulated in the lung in part because the lymphatics responded relatively slowly to rapid increases in .SIGMA.p. Although the lymphatics may not be a quantitatively important route for removal of edema fluid, the pressure-volume characteristics of the pulmonary interstitium seem to have a major influence on lymphatic function.