炭酸ガス負荷による脳内局所循環並びに自己調節作用に関する実験的研究

EXPERIMENTAL STUDY ON REGIONAL CIRCULATION AND ITS AUTOREGULATION OF THE BRAIN IN CO2 INHALATION

Ｉ．緒言

　脳循環の調節機序および脳血管障害を主とした病態生理などの詳細を明らかにすることは脳循環の重要な研究課題である。

　全脳的脳循環測定法としてN₂0法^1）が用いられるようになつて以来，脳循環に関する研究は急速な進歩を遂げ，最近ではKr⁸⁵法^2）などのようにradioactive ga—seous indicatorを用いたclearance法，熱電対を応用したheat clearance法^3）など局所脳循環の研究が急速な発展を遂げ，皮質部循環の測定，さらに脳深部の循環への応用も試みられるようになつたが，なお問題点が多い。

Effects of CO₂ inhalation on regional circulation of dog brain and its autoregulation were studied with the oxygen electrode made of enamelled copper wire. The findings obtained were as follows :

1) Cortical blood flow was increased linearly with inhalation of air containing CO₂, 3 to 10%.

Thalamic blood flow, however, was not so much increased when the concentration of CO₂ inhaled was less than 8%, but was greatly increased when concentration more than 9%, as did the cortical blood flow. Therefore, the thalamus seemed to have a higher threshold for CO₂ to cause an in-crease of the blood flow than the cortex.

2) The particular response to CO₂ of thalamic circulation was discussed. A neurogenic factor possible for its mechanism was considered because,(1) there were the nerve fibers distributed more abundantly in the thalamus than in the cortex ;(2) the particular response to CO₂ in the thalamic circulation was prevented by phenoxybenzamine.

3) So-called autoregulation was usually noticed of both cortical and thalamic circulation. The autoregulation was inhibited with CO₂, especially in the cortex, but not in the thalamus with the concentration of CO₂ less than 8%.