Liquid Exchange Barrier In Pulmonary Microcirculation

Movement of liquid between plasma and interstitial fluid is governed by Starling's principle in which the direction and rate of liquid flux are determined by gradients of hydrostatic and oncotic pressures between the two compartments across vascular wall. Endothelium of microvasculature is the primary barrier for liquid exchange. However, pulmonary microvascular barrier properties have been difficult to quantify because surface area for liquid exchange (S) in lung is unknown.In the first part of this project, we determined barrier properties of single pulmonary microvessels using a double micropuncture (split-drop) technique in which S of the microvessel under study is known. Data were pooled from 58 isolated, blood-perfused lungs of dog, ferret, and rat since no difference among species was found. In the double micropuncture procedure, perfusion was stopped at known vascular pressure (Pmv) and a microvessel (20 μm diam) was micropunctured to inject a drop of stained oil which was split by a second microinjection with a solution of known albumin concentration. Filtration rate per unit surface area (Jv; x10^-6 cm/s) was calculated from measurements of vessel diameter and rate of change of split drop length. From measurements of Jv at different Pmv, we determined the hydraulic conductivity (Lp; 10^-7 cm/s/cmH₂O) , and the zero filtration pressure (Pzf) . From determinations of Pzf at different albumin concentrations, we quantified the albumin reflection coefficient (σ_alb) . Lp and Pzf did not differ among venules of the same lung. However, in venules, Lp (5.5±1.2 x10^-7 cm/s/cmH₂0) was 40% higher and σ_alb (0.4±0.1) 25% lower than in arterioles (4.0±1.2 and 0.5±0.1, repectively) (p<0.01). Me conclude that in...