A Starling resistor regulates cerebral venous outflow in dogs.

This investigation was undertaken to determine whether a Starling resistor or venous waterfall effect exists between the sagittal sinus and the cerebral veins such that increases in sagittal sinus pressure (Pss) do not abolish cerebral venous outflow and to examine two possible contributions of extracranial venous valves in regulating outflow. Anesthetized dogs were subjected to positive end-expiratory pressure (PEEP) before and after intracranial pressure (Pic) was elevated by inflation of an epidural balloon. PEEP raised Pss equally in all animals, but Pic and cerebral venous pressure (Pcv) increased less in the presence of intracranial hypertension. When Pss was low, passage of a catheter in the cerebral vein in and out of the sagittal sinus demonstrated an abrupt drop in pressure as the sinus was entered. When Pss was raised and lowered independently of superior vena caval pressure (Psvc) the changes in Pic and Pcv were less when Pss was decreased than when it was increased. Sustained increases and decreases in Psvc caused increases and decreases in Pcv, Pic, Pss, and external jugular venous pressure (Pejv) regardless of whether external jugular venous valves were present or absent. We conclude that a Starling resistor between the sagittal sinus and the cerebral veins regulates cerebral venous outflow when Pss is increased by PEEP and other maneuvers that raise Psvc. The waterfall maintains Pcv and Pic at normal levels when Psvc and Pss are reduced. Extracranial venous valves are not essential to this mechanism.