Flow of edema fluid into pulmonary airways

An in situ rabbit preparation was used to characterize the manner in which edema fluid enters the airways when left atrial pressures are elevated. The airways were initially filled with fluid to minimize retrograde flow of edema fluid into the alveoli. The airway solution contained 125I-albumin and in some studies [14C]sucrose, and the lungs were perfused with a comparable solution which contained albumin labeled with Evans blue dye and 99mTc-diethylenetriaminepentaacetate (DTPA) or 99mTc-sulfur-colloid particles (0.4-1.7 micron diam). After 30 min of perfusion, fluid was pumped from the airways into serial tubes. When left atrial pressures were low, there was very little transfer of labels detectable between the airway and perfusate solutions. However when left atrial pressures were increased to either 15 or 22 cmH2O, fluid entered the airways containing approximately the same concentrations of Evans blue dye and 99mTc-DTPA as those present in the perfusate. In contrast, the concentration of colloid particles averaged less than 5% perfusate concentrations, indicating that the fluid had not escaped through a tear in the barriers separating the vascular and airway compartments. Concentrations of the perfusate fluid and indicators were highest in the initial samples pumped from the airways. These observations suggest that some of the fluid entering the airways may be derived from peribronchial cuffs or that there are marked regional differences in edema formation from alveoli.