Cerebrospinal fluid pressure in mannitol-treated rabbits.

Equations describing the response of cerebrospinal fluid (CSF) pressure to a rapid intravenous injection of mannitol were developed by combining equations of membrane transport with equations of CSF hydrodynamics. The physiologic variables appearing in these equations were measured in anesthetized rabbits as brain water volume = 7.9 cm3, plasma osmolality = 308 mmol/kg, fractional total body water content = 0.62, time constant of blood-brain osmotic flow = 32 min, resistance to CSF absorption = 1.92 TPa-s/m3 and brain compliance = 0.173 mm3/Pa. Mannitol (5.5-27.5 mmol/kg) was administered intravenously to anesthetized rabbits while Elliott's B solution was infused (0.13-1.27 mm3/sec) into a lateral ventricle to simulate formation of CSF. Measured CSF pressure changes corresponded closely with those predicted by theory.