Variation in equation coefficients in the gravimetric method to determine brain water content.

The gravimetric method to determine the tissue water content is widely used for studying brain edema because the tissue water content can be calculated from only the density of the wet tissue using a gradient column. This method has been used in only a few studies of cerebellar water content. We estimated the water content of the cerebellar cortex by the gravimetric method and compared the results with those measured by the conventional drying-weighing method, and found a significant difference. We therefore propose modified coefficients for the equation for the water content of the cerebellar cortex as follows: % tissue water content = 456.13(1/wet tissue density) - 356.13 This equation and the drying-weighing method were used to investigate normal and edematous cerebellar cortices after compression with an epidural balloon. The modified equation provided results consistent with the drying-weighing method. Differences in the total experimental system including the breed and pre-experimental condition of the cats may be factors in variations in measured values. We recommend that investigators establish equation coefficients valid for individual experimental systems.