The Significance of the Veins in the Determination of Cerebral Blood Volume in Clinical Cases

Summary

The changes in the intracranial blood volume (ICBV) and the cerebral blood flow (CBF) caused by decompression were monitored in clinical cases. The methods for decompression were the intravenous injection of glycerol and the lowering of cerebrospinal fluid (CSF) pressure by ventricular drainage. Changes in the ICBV were monitored in 11 patients by continuous extracranial recording of gamma activity, while monitoring CSF pressure, after the intravenous administration of ^99m Tc-labelled red blood cells. The CBF was measured in 6 cases by the ¹³³Xe inhalation method. Using these methods the changes in the ICBV were not conclusive in 3 cases of CSF drainage and 6 cases with glycerol infusion. In the other cases, the ICBV increased as a result of CSF drainage and was decreased by glycerol infusion. This indicated that there was resistance to flow distal to the vascular bed which was diminished probably by the removal of extravascular fluid after glycerol infusion, and was not diminished by simple decompression following CSF drainage. The CBF generally increased following both methods of decompression. However, glycerol infusion increased the CBF much more than CSF drainage, despite the fact that the former decreased CSF pressure less than the latter. This greater increase in the CBF following glycerol infusion also suggested the occurrence of a decrease in resistance on the venous side. The presence of such a resistance indicates that veins may have an important role in the mechanism for the determination of the ICBV in clinical cases.