Change of cerebral blood volume over the respiratory cycle during elevated intracranial pressure

The aim of this study was to test the hypothesis that during intact regulation of cerebral blood flow, difference of intracranial blood volume change between the two phases of respiration increases with increasing mean intracranial pressure. As a corollary to this hypothesis, when regulation of cerebral blood flow fails, changes of intracranial blood volume will fail to increase with increasing intracranial pressure. With the use of a laboratory model, intracranial pressure was manipulated by infusion of fluid into a balloon placed within the cranium. Electrocardiographic, arterial, intracranial, and jugular pressure signals were digitally recorded. To calculate change of blood volume during each phase of respiration, characteristics of the jugular pressure signal were used to detect the beginning and end of inhalation and the end of the expiration phase. Preliminary results indicate that during regulation of cerebral blood flow, difference in intracranial blood between the two phases of respiration increased with increasing mean intracranial pressure. In contrast, during deregulation of cerebral blood flow, difference of cerebral blood volume change between the respiratory phases failed to increase with increasing intracranial pressure.