Sites of transendothelial liquid transport in lung microcirculation.

The widely held concept that the lung transmicrovascular liquid flux occurs primarily across septal vessels has not been experimentally verified. In fact, the recent literature suggests that much if not all of the flux may occur across extraseptal vessels. Support for this idea is available from morphological studies, from segmental filtration data, and from micropuncture data concerning lung microvascular and interstitial pressures. Recent split-drop measurements of lung venular hydraulic conductivity suggest that the surface area of filtration in the lung may be considerably smaller than presumed. The view is advanced that a major portion of lung filtration may occur in the preseptal microcirculation.