連続的局所脳循環測定法の開発とその応用—Kr−81 m持続内頸動脈注入法を用いて

CONTINUOUS MEASUREMENT OF REGIONAL CEREBRAL BLOOD FLOW USING KRYPTON-81 M

I．はじめに

　臨床的に応用されている脳循環測定法の多くはclear—ance法によるものである。従つて脳循環血液量の絶対値の測定が可能である反面極く短時間に反復して測定することは不可能であり，まして脳局所の脳循環血液量の変化を経時的に連続して測定する方法は，現在のところみあたらない。最近Fazioらによつて報告された^81mKrを使用した臨床的脳循環測定法はclearance法とは違つた原理によるものであり^81mKrが超短半減期核種であることにより，極く短時間の反復測定が可能であるという利点を指摘されていた^2,3,4）。しかし，従来の報告では^1，9,10）脳循環の局所的分布の経時的変化について検討されていたにすぎない。われわれは，^81mKrを用いた脳循環測定法を応用し，脳の局所の極く短時間にdynamicに変化する脳循環血液量の連続的測定法を開発したので報告し，その臨床的有用性についても考察を加える。

In order to obtain sequential change of cerebral blood flow using the intracarotid ^81mKr infusion method, we devised a new method by using the radiation from cervical internal carotid artery as the concentration of radioisotope in the blood per-fused to the brain. Under continuous intracarotid injection of ^81mKr, the radio activity obtained from the surface of the skull is proportional to the cerebral blood flow. However, since the method depends upon the infusion of a given volume of radioisotope per unit of time into the internal carotid artery, changes in the blood flow through the internal carotid artery result in changes in the consentration of radioisotope perfused to the brain. Under such conditions, the radioactivity obtained from the surface of the skull does not indicate the changes in blood flow. In such a case, the value obtained from the radioactivity (count rate) in the ROI of the brain divided by consentration of radio-isotope in the blood perfused to the brain indicates the changes in cerebral blood flow.

Our attention was drawn to the fact that the radioactivity measured from a constant area of the cervical internal carotid artery per unit of time is an indicator of the blood concentration of radio-isotope following in the internal carotid artery, provided that, there are no changes in the size of lumen of internal carotid artery. According to this method devised by us, it had been possible to follow extremely short period changes in cerebral blood flow following CO₂inhalation, change of blood pressure (autoregulation) and administration of various drugs.