Effect of increased bronchial venous pressure on lung lymph flow

Abstract

We postulated that if the bronchial circulation affects lung fluid balance, increases in bronchial venous pressures may influence lung lymph flow. This hypothesis was tested in eight anesthetized sheep prepared with acute lung lymph fistulas. After control data, we increased bronchial venous pressure by infusing saline directly into the bronchial vein at a controlled infusion pressure of 20–25 cmH2O. Evans blue dye (2.5 mg/ml) was added into the saline as a marker for assessing leakage that might occur from either the catheter or the ruptured bronchial veins. Lymph flow was measured every 15 min. Lymph as well as plasma samples were collected every 30 min for measurement of protein. In five sheep we also measured Evans blue dye content both in lymph and plasma to further characterize the role of bronchial circulation in lung fluid balance. The control lymph flow was 1.9 +/- 0.2 ml/15 min, and lymph-to-plasma protein ratio was 0.65 +/- 0.3 (mean +/- SE). With infusion of saline into the bronchial vein, the mean lung lymph flow and lymph-to-plasma protein ratio did not change significantly. There was a progressive increase in dye content both in lymph and plasma. The mean Evans blue dye content in lymph was 0.087, 0.16, and 0.26 microgram/ml, whereas in plasma it was 0.43, 1.15, and 1.45 microgram/ml in samples obtained at 30, 60, and 90 min, respectively. The dye content was significantly higher in the plasma compared with the lymph in all three samples (less than 0.05). Pulmonary arterial pressure, pulmonary capillary wedge pressure, and cardiac output did not change significantly throughout the experiment.