虚血脳におけるcritical flow level—I．閉塞性脳血管障害

CRITICAL. FLOW LEVELS IN CEREBRAL ISCHEMIA : I.OCCLUSIVE CEREBROVASCULAR DISEASE

Ⅰ．はじめに

　虚血性脳疾患において虚血の程度を知るには局所脳循環測定法（rCBF）が最も優れた方法であるが，¹³³XeによるrCBF測定法でどの程度の虚血が危険レベルであるかを明確に記した報告は非常に少ない。どの程度の虚血で神経脱落症状が出現し，また脳梗塞に陥るかというcritical flow levelに関しては実験的な報告がいくつかみられる^3）。しかしこのcritical fow levelもrCBF測定法によつて異なると考えられ，実験結果をそのまま臨床例にあてはめることはできない。また臨床例においてもこのcritical flow levelの検討は少なく^2），特に脳梗塞に陥るflow levelを記した報告はほとんどない^20）。したがつて現在普及しつつある¹³³Xe動注法rCBF測定法におけるcritical flow levelを知ることは非常に重要と考えられる。

　本研究の目的は閉塞性脳血管障害において神経症状の出現する血流レベル（symptomatic flow level）および脳梗塞出現レベル（infarcted flow level）を¹³³Xe動注法rCBFで求めることにある。

Critical levels of cerebral blood flow which may cause neurological symptom (symptomatic flow level) and may cause cerebral infarction (infarcted flow level) were assessed in 40 selected patients with occlusive cerebrovascular disease, by means of re-gional cerebral blood flow (rCBF) and computed tomography (CT). Embolic cases were excluded to avoid the luxury perfusion after recanalization according to our previous study. Internal carotid occlusion was also excluded because of technical reason. Regional CBF study was performed in acute stage of stroke by ¹³³Xe intracarotid injec-tion method with 16 channel multidetectors, and calculated according to the initial slope index. To estimate the symptomatic flow level, four channels corresponded to speech center were selected as "speech rCBF"in 23 patients with a lesion in dominant side, and the correlation between neuro-logical symptom (aphasia) and mean or"speech rCBF"value was investigated. To estimate the infarcted flow level, centrum semiovale of white matter which is vulnerable to middle cerebral ter-ritory was checked by CT, and the correlation between CT findings and mean rCBF value was investigated.

In 4 patients without aphasia, both mean and speech rCBF were more than 33ml/100g/min. and were less than 36ml/100g/min. in 19 patients with aphasia. In 27 patients without low density area in centrum semiovale on CT, mean rCBF was ranged 25-49 (average 35.0) ml/100g/min., and was ranged 13-26 (average 20.6) ml/100g/min. with low density area.

From these data, the symptomatic flow level was assessed at 33-36ml/100g/min. (approximately 55% of normal value) of mean rCBF or speech rCBF, and the infarcted flow level was assessed at 25-26ml/100g/min. (approximately 40%) of mean rCBF. About 40% of the patients with rCBF value be-tween two levels temporarily exacerbated after admission. These patients should be treated ag-gressively in the acute stage of stroke.