Relationship between intracranial pressure and cervical lymphatic pressure and flow rates in sheep.

Previous reports from our group demonstrated that about one-half of the total volume of cerebrospinal fluid (CSF) removed from the cranial vault in sheep is transported into extracranial lymphatics, especially cervical lymphatic vessels in the neck. In this study, we tested the hypothesis that an elevation of intracranial pressure (ICP) would increase cervical lymphatic pressure and lymph flow rates in anesthetized sheep. Catheters were inserted into both lateral ventricles, the cisterna magna, cervical lymphatics, and the jugular vein. A ventriculo-cisternal perfusion system was employed to regulate ICP. Mean ( P = 0.008), peak ( P = 0.007), and baseline ( P = 0.013) cervical lymphatic pressures increased as ICP was elevated from 10 to 70 cmH2O in 20-cmH2O increments. Similarly, cervical lymph flow rates increased ( P < 0.001), with flows at 70 cmH2O ICP observed to be approximately fourfold higher than those at 10 cmH2O ICP. No changes were observed in mesenteric lymph flow rates (vessels not expected to drain CSF). We conclude that cervical lymphatic vessels play an important role in the transport of CSF from the cranial vault when ICP is elevated.