Lung fluid and protein exchange in the acute sheep preparation.

We examined the effect of left atrial hypertension on lung fluid and protein exchange in acutely prepared anesthetized sheep. The results were compared with those reported by Erdmann jet al. (Circ. Res. 37:271-284, 1975) in chronically instrumented conscious sheep. Animals were anesthetized with halothane and efferent duct of the caudal mediastinal node was cannulated. Pulmonary microvascular pressure (Pmv) was elevated by raising left atrial pressure with a left atrial balloon. For every elevation in Pmv of 1 cmH2O pulmonary lymph flow (Qlym) increased by 0.5 ml/h. Increasing the Pmv resulted in a linear decrease (p less than 0.05) in the ratio of lymph to plasma protein concentration as a result of a significant reduction in lymph protein concentration. Transvascular clearance of lymph proteins increased by 39% with a doubling of Qlym. The steady-state changes in pulmonary fluid and protein exchange induced by an increase in Pmv in acutely prepared anesthetized sheep were the same as those observed by Erdmann et al. in chronically instrumented unanesthetized sheep, indicating that the acute preparation is equally reactive to increase in Pmv and that the lung endothelial permeability is not increased.