Microvascular function. Transvascular exchange of fluid in the airways.

Fluid exchange in the airway microcirculation is presented relative to whether the airway epithelium is in an absorbing or a secreting state. The effects of increasing microvascular pressures and damaging the endothelial barrier are also examined relative to fluid dynamics and lymph flow, especially with regard to "filtration secretion." The microvessel pressure profile of the tracheal circulation is discussed relative to our recent data and to the published literature. These micropuncture data indicate that the major resistance to tracheal blood flow resides in arterioles with diameters less than 50 microns. It is hoped that this review will stimulate research on the airway microcirculation since the available data on the physiology and biophysics of circulation in the large and small airways are insufficient to define the microcirculatory exchange characteristics in this capillary bed.