Effect of lymphatic cannula outflow height on lung microvascular permeability estimations

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Abstract
Estimates of the pulmonary microvascular membrane reflection coefficient (.sigma.) and permeability-surface area product (PS) are frequently made with the assumption that a percent change in transmicrovascular fluid fluix (Jv) will be represented by an equal percent change in the lymph flow rate (.ovrhdot.QL) from a single cannulated lung lymph vessel. To test this, .ovrhdot.QL was measured in 7 anesthetized dogs with the outflow end of the lymph cannula set at several heights (H) above and below the lung hilus. The left atrial pressure was then elevated to increase Jv, and .ovrhdot.QL was again measured at several H. The percent increase in .ovrhdot.QL at elevated left atrial pressure depended on H. The .ovrhdot.QL data and lymph and plasma protein concentrations were used to estimate .sigma. and PS with a modified form of the Kedem and Katchalsky equations. The calculated values varied considerably with H. Changes in Jv are not represented by equal changes in .ovrhdot.QL. Therefore, techniques for estimating permeability that depend upon .ovrhdot.QL as an estimate of Jv may lead to erroneous estimates of .sigma. and PS.

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