Effects of changes in serum osmolarity on bulk flow of fluid into cerebral ventricles and on brain water content

Abstract

The effects of changes in serum osmolarity on the rate and osmolarity of bulk flow of fluid into the cerebral ventricles and on cortical white and grey matter water content were studied in cats. Bulk flow rates and osmolarities were measured during ventriculocisternal perfusion both before and after intravenous infusion of glucose solutions. Infusions of glucose in concentrations greater than 6% decreased fluid bulk flow rate and its osmolarity. Glucose in concentrations less than 6% increased fluid bulk flow rate and decreased its osmolarity. Bulk flow rate and serum osmolarity were found to be linearly related with a coefficient of osmotic flow of −0.835 μl/min per mOsm/l. At the extremes of induced serum osmolarities, (290 and 360 mOsm/l) bulk flow rate was either increased by 120% or completely inhibited. Effluent osmolarity also increased proportionately to serum osmolarity (0.338 mOsm/l per mOsm/l). When compared to controls, cortical grey and white matter water content increased by 1.9% and 2.9%, respectively, when the infused glucose concentration was 2.5% or less, and decreased by 1.8% and 2.9% when the concentration was 10% or more. The results of these experiments suggest that the increased bulk flow comes from the brain, rather then directly from the blood.