頭蓋内圧容積曲線と脳循環態動

AN EXPERIMENTAL STUDY ON CORRELATION BETWEEN INTRACRANIAL P/V CURVES AND CHANGES IN CEREBRAL BLOOD FLOW

Ⅰ．はじめに

　頭蓋内でexpanding massが徐々に増大する場合，それに伴う圧上昇パターン，すなわち頭蓋内圧容積関係pressure-volume relationshipは単純な直線関係を示さず，指数関数様に変化し，その初期には容積増大に対する何らかの圧代償機序が働くことが知られてきている^5,8,9,10）

　この圧容積関係と脳循環動態との関連，特に圧代償期に脳循環がいかなる態度をとるかについての報告は未だみられない。そこで本報告では、実験的に頭蓋内硬膜外バルーンのinflationによつて作成した圧容積関係と脳循環動態との関連，特に圧代償期の脳循環動態について脳室髄液圧，小脳脚組織圧および脳循環量を経時的に測定するにとにより検討した。また同時に脳波を記録することにより脳機能との関連についてもあわせて検討した。

Intracranial pressure/volume (P/V) relationship is not linear but of exponential fashion. This indicates possible roles of intracranial volume buffering on pressure rise in the earlier phase of mass expan-sion. It remains unresolved, however, how such spatial compensation effects on CBF and cerebral metabolism. The present study describes on the changes in CBF associated with intracranial P/V curves.

Mass expansion in the cranium was made by intermittent inflation of an epidural balloon (0.25 ml of each inflation rate at intervals of 15 min.) in artificially ventilated 14 adult mongrel cats. Ven-tricular fluid pressure (VFP), cerebellar tissue pres-sure, systemic arterial pressure and EEG were con-tinuously recorded on a polygraph. Values of hemispheric CBF were tested by means of ¹³³Xe clearance method, measured just prior to each balloon inflation.

Resting VFP remained in normal range until the attainted balloon volume below 1.5 ml, thereafter followed by a rapid increase in resting VFP, show-ing a break-point in the P/V relation. Transten-torial pressure gradients developed during steep limb of P/V curves. CBF began to decrease even in the initial stage of minimal elevation in VFPas well as of highly preserved cerebral perfusion pressure. In the stage of steep pressure rise, de-creases in CBF corresponded proportionally to the VFP increases. Slow activities in EEG also ap-peared during horizontal limb of P/V curves, re-sulting in isoelectric EEG in the stage of steep pressure rise.

The above data show that, during a gradual ex-pansion of intracranial mass, CBF can be affected even in the stage of spatial compensation of normal pressure, being presumably resulted by structural shifts and microcirculatory changes. Rapid changes in CBF and cerebral metabolism will appear cor-responding to the exhausted volumetric buffering capacity in the cranium.