高酸素血症と脳循環—クモ膜下出血例における検討

THE EFFECTS OF HYPEROXEMIA ON CEREBRAL BLOOD FLOW IN SUBARACHNOID HEMORRHAGE PATIENTS

　抄録　大気圧下純酸素吸入（1ATA・O₂）による脳血管反応性（O₂　response）を53例の脳動脈瘤破裂によるクモ膜下出血例で検討した。CBFはValmet社製rCBF Analyzer BI−1400を用いて10mCi¹³³Xe静注法によりISIを算出した。全測定回数は100回で全脳平均血流量（mCBF）を用いて検討した。測定条件はRest （安静時）−1ATA・O₂で行った。O₂　response障害は発症後1カ月以内の症例で，ICP亢進，水頭症，広範脳障害などが障害因子であった。2カ月目に入ると障害の程度にかかわらず反応性は正常化した。重相関分析によるCBFに対するPaO₂，　PaCO₂，血圧の寄与率は全体で24％，PaO₂のそれは21％で，PaCO₂，血圧の関与は極めて小さかった。1ATA・O2下におけるCBF減少はPaO₂の上昇によるvasoconstrictionによるものと考えられた。15回のICPとCBF同時測定ではRest ICPが高いほど高酸素血症によるCBF減少率は低かった。O₂　responseは脳血管反応性テストとして臨床応用価値が高いと考えられるが，二次元的CBF測定法では限界がある。今後はpositron emission CT （PET）による検討がO₂　responseの本態解明に有用であろう。

The effects of oxygen inhalation at atmospheric pressure (1 ATA･O₂) on CBF were studied in subarachnoid hemorrhage (SAH) patients due toruptured intracranial aneurysms to prove the use-fulness of the "O₂ response" test for the evaluation of the cerebral vascular response. "O₂ response" means the CBF (or ICP) decrease during hyperoxe-mia. CBF was measured by 10 m Ci ¹³³Xe intrave-nous injection method using rCBF analyzer BI-1400 (Valmet). Two-compartmental analysis was used for the calculation of initial slope index (ISI). Stu-died cases were 53 postoperative SAH patients and 100 times examinations were done under the condi-tion of Rest-1 ATA･O₂. The incidence of global disturbance of the O₂ response was 33% from day 0 to 3, 31% during day 4 to 7, 30% during day 8 to 14, and 23% at day 15 to 30. But, after day 31, there was no case which revealed an impaired O₂ response. It was not possible to detect focal or hemispheric abnormalities of the O₂ response because of the limitation of noninvasive two-dimensional CBF measurement method employed.

The causes of O₂ response abnormality, within a month after the onset, were increased ICP, hydro-cephalus and diffuse brain damage. Multiple regres-sion analysis proved that elevated PaO₂ is the ma-jor factor in reducing CBF. CBF and ICP correla-tion study showed that the higher the Rest ICP, the fewer the CBF decreases during pure O₂ inha-lation. This may indicate that the increase in ICP in the acute stage changes the O₂ response accord-ing to the level of increased ICP. The authors' data comfirmed that the O₂ response test was useful in evaluating the cerebral vascular response of stroke patients. In the future, a three-dimensional approach using positron ECT (PET) will be fruit-ful for evaluating the pathophysiology of "O₂ re-sponse".