Urea permeability of alveolar membrane; hemodynamic effects of liquid in the alveolar spaces

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Abstract
The blood flow through isolated lungs, excised or in situ, was measured while air or isotonic lavage solution was injected into and withdrawn from the lobar bronchus under variable pressures. Lavage of isolated lobes, intubated via the lobar bronchus with cuffed endotracheal tubes, was also performed in closed-chest experiments while certain hemodynamic parameters were recorded. Urea equilibration between the blood and the alveolar fluid could be expressed as an asymptotic line; the urea concentration of the alveolar fluid reached 30% and 55% of the blood urea concentration when the lavage solution remained in the alveoli for 5 and 15 minutes, respectively. Regardless of the presence or absence of liquid in the alveoli, vascular resistance in the isolated lobe was determined by airway pressure. In closed-chest experiments the hemodynamic effects of pulmonary lavage were minimal as long as low positive and negative pressures were used to inject and withdraw the lavage solution.