Pulmonary microvascular permeability to fluid and macromolecules.

Research in pulmonary microvascular permeability has been a hot bed of activity for the last 20 years, primarily because increases in permeability contribute to the development of some forms of pulmonary edema in humans. New techniques and animal preparations have lead to significant advances, and most of these advances have been well described in several recent reviews. Unfortunately, there is still confusion over what the techniques measure and when they can be used to make reliable permeability estimates. Furthermore, we have a different point of view than previous authors. For instance: 1) we question the assumption that lymph flow rate is proportional to filtration rate, whereas other authors have implicitly assumed this relationship to be true; 2) we believe that the wide range of filtration coefficients measured with various techniques may be narrowed by consideration of the types of errors likely to result with each technique; 3) we place more emphasis than previous authors on the potential problems caused by the collection of impure lung lymph and the possibility that lymph composition may be altered within lymph nodes. For these reasons we believe that readers may benefit from a review of the techniques used in pulmonary permeability studies written from our perspective.