急性脳腫脹の成因に関する実験的研究—脳血管トーヌスに対する神経支配について

EXPERIMENTAL STUDY ON THE GENESIS OF ACUTE BRAIN SWELLING; NEURAL CONTROL OF THE CEREBRO-VASCULAR TONE

I．緒言

　脳浮腫は脳神経外科医がたえず直面する最も厄介な問題であり，これに関しては古くから多くの研究がなされてきた。この脳容積の増大を示す広い意味での"脳浮腫"は現在その成因と臨床経過より，狭義の"脳浮腫"と"急性脳腫脹"とにわけて考えられている。狭義の"脳浮腫"とは主として脳代謝機構の障害によって比較的ゆっくりと脳容積の増大をきたしてくるものを示している。"急性脳腫脹"とは脳血管トーヌスが低下して主として脳血管床の増大をきたし，その結果急激に脳容積の増大をきたしてくるものを示しており，臨床的には急性硬膜外血腫除去後などにみられるような急激な脳の腫脹がこれに含まれる。このような急性脳腫脹発生の基礎となる脳血管トーヌス低下の原因として，種々の因子が考えられるが，それらを大別すると代謝性因子と神経性因子とにわけることができる。代謝性因子については脳組織アシドーシスが関与していると考えられ，多くの報告がみられている^1）2）。今回著者は神経性因子が脳血管トーヌスの低下に関してどの程度関与しているか検討するために，次の4項目にわけ実験的に検討を試みた。1）脳血管のCO₂反応性とneural mechanism．2）脳循環の自己調節機構とneural mechanism．3）脳血管トーヌスに直接影響をおよぼすneural mechanism．4）急性脳腫脹と神経性因子との関係。以上の問題点を中心に犬を用い，脳幹，視床下部の刺激および破壊実験を行つた。

The acute brain swelling is believed to be caused by the decrease of cerebrovascular tone. For this decrease of the cerebrovascular tone, metabolic factor and/or neural factor may be involved and there are many different opinions as to the relative re-lationship and the superiority between the two factors, but no definite conclusion has been es-tablished yet.

In order to study the degree of involvement by the neural factor in relation to cerebrovascular tone, using 33 dogs, the author placed a needle stereotaxically into the brainstem and hypothalamus and made electrical stimulation and destruction by electrical coagulater. Furthermore the changes in CBF, ICP, BP and EEG by 10% CO₂ inhalation were continuously observed before and after the destruction.

CBF was measured by the double thermister and ICP by the extradural balloon method.

The results were:

(1) Response of cerebral blood vessels to CO₂ inhalation should be evaluated on the basis of CBF increase as well as cerebral vasodilatation in reaction to the CO₂ inhalation. Only when both of them have disappeared, should CO₂ response be judged negative.

(2) Even by the destruction of brainstem and hypothalamus, the CO₂ response of the cerebral blood vessels did not disappear even though there were some cases showing a decreasing tendency of the reaction. Therefore, it is believed that the effect of CO₂ on the cerebral blood vessels through the neural mechanism does not play an important role.

(3) Since autoregulation disappeared after the brainstem destruction, it was made clear that neural mechanism in some way is related to autoregulation.

(4) When autoregulation had disappeared after the severe hypoxia or brainstem destruction, in some cases CO₂ response was still positive. There-fore, the disappearence of autoregulation and that of CO₂ response are probably different in nature.

(5) By insertion of a needle into the brainstem and hypothalamus to stimulate or destruct, CBF and ICP increased independently of the BP change and by this, the presence of neural mechanism in the brainstem and hypothalamus, directly influen-cing the cerebrovascular tone was proved. However, these reactions were transient in nature and none of them developed into acute brain swelling.