The role of cerebral blood volume changes in brain specific-gravity measurements

Cerebral blood volume (CBV) was calculated in gerbils from specific-gravity (SG) changes between normal and saline-perfused brains. Furthermore, changes in CBV were investigated during ischemia using carbon-14-labeled dextran (MW 70,000) as an intravascular marker. Both data were used to evaluate the possible error due to a change in CBV on the measurement of ischemic brain edema by the SG method. The methodological error found was 0.0004 for a 100% CBV change. This error is insignificant, being less than the standard deviation in the SG measured for the gerbil cortex (SG 1.0494 +/- 0.0006). Thus, CBV changes are not responsible for the SG variations observed during the first phase of ischemia. These variations are better explained as an increase of brain water content during ischemia.