Effect of high-frequency oscillation on lung lymph flow.

We investigated the effect of high-frequency oscillation (HFO) on lung lymphatic function under normal conditions and when lung lymph flow was increased by air microembolization. In six experiments, sheep and goats with chronic lung lymph fistulas and vascular catheters were anesthetized, paralyzed, intubated, and ventilated according to the following protocol: 1) intermittent positive-pressure ventilation (IPPV) for 1 h, 2) HFO with a frequency of 15 Hz and an estimated tidal volume of 1-2 ml/kg for 1-2 h, and 3) IPPV for 0.5 h. Ventilator settings were adjusted to maintain arterial Po2 above 100 Torr and a normal arterial Pco2. Vascular, esophageal, and mean airway pressures were monitored continuously. Lymph flow and cardiac output were recorded every 15 min. With this protocol, there were no changes in pulmonary vascular or esophageal pressures, and lymph flow remained stable throughout the experiment. In an additional five experiments, air microemboli were infused for approximately 30 min during HFO. Left atrial pressure was unchanged and lymph flow tripled. This response was qualitatively and quantitatively similar to that previously reported for unanesthetized spontaneously breathing sheep. We conclude that HFO does not impair lymphatic function under resting conditions and that lymphatics retain their ability to increase water and protein clearance during HFO.