[Changes in the intracranial pressure dynamics with head-down tilt in cats]

To determine changes in the intracranial pressure dynamics under the condition of head-down tilt, the pressure-volume relationship in the cranial cavity as well as changes in intracranial pressure were studied experimentally in 31 cats. The animals were divided into three groups; with the horizontal, with the head-down and one with the head-up position. In each group the pressure volume index (PVI) and cranial cavity compliance (C) were examined under controlled respiration. The following results were obtained. (1) The values of PVI and C were significantly greater in the head-down tilt group as compared to those in the other groups, in spite of the increase in intracranial pressure level. (2) In the situations of craniospinal blockade by epidural ligation of spinal cord at C2 level, the PVI and C were also higher in the head-down tilt group than in the horizontal group. These results indicate that the pressure buffering capacity is increased with head-down tilt with respect to intracranial volume loading. It appears that the buffering mechanism does not depend on movement of the cerebrospinal fluid, but on the increased cerebral venous vascular bed with the communication between extracranium and intracranium.