後部視床下部破壊の頭蓋内圧に及ぼす影響（第2報）—加圧群と正常頭蓋内圧群の反応様式の比較

BEHAVIOR OF THE INTRACRANIAL PRESSURE FOLLOWING COAGULATION OF POSTERIOR HYPOTHALAMUS (IIND REPORT):STUDY IN REGARD TO MODERATELY RAISED ICP GROUP

I．はじめに

　著者らは，先のイヌを用いた報告^12）で，急性脳腫脹の基盤となるVasomotor paralysisの発現機序^2,3,5）として，後部視床下部機能障害の果す特異的な役割は，正常頭蓋内圧，動脈血，Pco₂Po₂pHの正常範囲内では，否定的といわざるをえない，との結論をえた。

　では，軽度一中等度に頭蓋内圧を上昇させ，脳に負荷を加えた際にも同じ結論がえられるのであろうか。

In the previous report, the authors concludedthat the dysfunction of posterior hypothalamusdidn't play a specific role in the development ofvasomotor paralysis leading acute brain swelling,under the circumstances that the ICP and thearterial Pco₂, Po₂ and pH were maintained in thenormal range.

This experiment was designed to clarify whetheror not the same conclusion could be obtained, underthe circumstances that the ICP was artificiallyelevated up to the level of 300-400 mmH₂O, precededto the procedures to the hypothalamus.

(1) Methods:

Adult mongrel dogs were anesthetized with intra-venous injection of thyamylal sodium with con-trolled ventilation. In order to elevate the ICP, asmall rubber balloon was inserted into the epiduralspace on the right fronto-temporal area and inflatedat such speed that a ICP level of 200 mmH₂Owould be obtained in one minute. After the ICPwas maintained at the level of 500 mmH₂O for tenminutes, the inflation was stopped and the balloonwas kept inflated during each procedure to thehypothalamus.

After the ICP was moderately elevated, a coag-ulation needle was stereotaxically inserted towardeither unilateral or bilateral posterior hypothalamus,which was subsequently destroyed with the coagu-lator. In order to assure the destruction of pos-terior hypothalamus, coagulation was carried outtwo times in each animal.

Before and after each procedure to the hypo-thalamus, the systemic arterial pressure (SAP) waselevated by intravenous injection of norepineph-rine (5×10^-3mg/kg) in order to investigate whetheror not the ICP increases in accordance with ele-vation of SAP.

The intracranial pressure (ICP) was continouslymonitored through a small balloon inserted insidethe dura mater and arterial Pco₂ and PO₂ weremaintained in the normal range by frequent deter-minations of blood samples.

The exact coagulated sites of hypothalamus wereconfirmed through investigation of coronal sectionafter a fixation of brain.

(2) Results:

The summary of coagulated sites of hypothalamusin 5 dogs is presented in Fig. 1. The nuclei ofhypothalamus posterior and hypothalamus dorso-medialis, which, we think, correspond to "posterior hypothalamus" were coagulated uni- or bilaterallyin all of 5 dogs.

The ICP was significantly elevated after all ofthe procedures (Fig. 2).

In regard to the degree of elevation of ICP, theresults obtained under increased ICP were signifi-cantly higher after the insertion of needle and thefirst coagulation, compared with the ones undernormal ICP (Fig. 3).

The response of ICP to intravenous injection ofnorepinephrine is demonstrated in Fig. 4, whichindicates that the elevation of ICP is moderate indegree even after each procedure. The ICP/MAPratio of elevation by intravenous injection of nor-epinephrine is summarized in Fig. 5, which revealsthe ICP/MAP ratio of elevation was not significant(NS) after all of the procedures, compared with incontrol.

In Fig. 6, the ICP/MAP ratio of elevation obtainedby injection of norepinephrine under increased ICPis presented in relation to the ones obtained undernormal ICP. The ICP/MAP ratio obtained underincreased ICP was significantly higher after all ofthe procedures than the ones under normal ICP.

The ICP/MAP ratio of elevation by injection ofnorepinephrine was closely related to the level ofICP at the time of injection of norepinephrine(Fig. 7, 8, 9) which is considered to indicate thatthe vascular tonicity is kept in good condition tocondition to autoregulate cerebral blood flow.

(3) Conclusions:

The authors think that the dysfunction of pos-terior hypothalamus doesn't play a specific role inthe development of vasomotor paralysis leadingacute brain swelling, also under moderately raisedICP with normal arterial Pco₂, and Po₂.