Lung fluid and protein exchange in the acute sheep preparation

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Abstract
Effects of left atrial hypertension on lung fluid and protein exchange were examined in acutely prepared, anesthetized sheep. Results were compared to those obtained with the Erdmann preparation of chronically instrumented conscious sheep. Animals were anesthetized with halothane and N2O, and the 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 cm H2O, pulmonary lymph flow (.ovrhdot.Qlym) increased by 0.5 ml/h. Increasing the Pmv resulted in a linear decrease (P < 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 .ovrhdot.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 in the Erdmann chronically instrumented unanesthetized sheep, indicating that the acute preparation is equally reactive to increases in Pmv and that the lung endothelial permeability is not increased.

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