Effect of changes in pleural pressure on fluid filtration rate in expanded and collapsed rabbit lungs.

Eight isolated rabbit lungs were suspended from a force-displacement transducer and perfused at constant flow. The pressure surrounding the lungs ("pleural" pressure) was then reduced from -0.5 kPa to -1.0 and -1.5 kPa, and the rate of weight gain recorded. The step reductions in "pleural" pressure produced greater increases in pulmonary vascular volume and fluid filtration rate when the lungs were collapsed than when they were expanded, thus suggesting that the change in "pleural" pressure was more effectively transmitted to the perimicrovascular space when the lung was collapsed. These observations may help to explain the phenomenon of re-expansion pulmonary oedema.