Reflectance spectrophotometryを用いた in vivo 局所脳血液量・局所酸素飽和度連続測定

CONTINUOUS MONITORING OF CEREBRAL BLOOD VOLUME IN CATS USING REFLECTANCE SPECTROPHOTOMETER

　抄録　Reflectance spectrophotometryを用いて，局所脳血腋量（以下r-CBV）の連続測定を行なった。1）ネコにおいて，5％および10％CO₂負荷を行い，動脈血Co₂分圧とr-CBVの問に，直線的相関を認めた。両側内頸静脈遮断に一致して，r-CBV・頭蓋内圧の上昇，およびr-CBF・血圧の低下を認めた。5％O₂負荷により，Hb等吸収点での吸収の変化を伴うことなく，スペクトルパターンのOxy-Hb型よりDeoxy-Hb型への変化を認めた。2）ネコにおいて，bemegride 100mg i．v．により，けいれん発作を誘発し，発作時のCBV変化を記録した。脳波上のepileptic burstに完全に同期して，r-CBV・頭蓋内圧・r-CBF・血圧の上昇を認めた．3）硬膜外バルーン加圧により，ネコ急性頭蓋内圧亢進モデルを作製し，約2時間放置後，急激にバルーンを開放し，減圧，その後のr-CBV・r-CBF・頭蓋内圧の変動を記録した。8例中6例において頭蓋内圧の自発的再上昇を認め，うち3例は，頭蓋内血腫形成によると思われ，残り3例は，急性脳腫脹例と考えられた。血腫形成例ではr-CBVの減少を認めたのに対し，急性脳腫脹例では，r-CBVの漸増を認め，急性頭蓋内圧亢進における脳血液量測定の重要性を確認し得た。

The importance of cerebral blood volume (CBV) as a physiological parameter has been well recog-nized, especially in its relation to the intracranial pressure (ICP). Although various methods have been applied to measure CBV, several problems and difficulties still remain to be settled. In the present study, noninvasive monitoring of CBV on the cortical surface was done with organ reflec-tance spectrophotometry.

Through the cranial window, the cat brain was illuminated by the white light via optical fibers and reflected light was analized by spectrophoto-meter equipped with microcomputer and image-sensor (Sumitomo Elec. Co., Spectrum analyzer TS-200), which enables to estimate CBV on real time as the absorbance value at the isobestic point of the spectral curve of hemoglobin (Hb).

In order to ascertain the reliability and repro-ducibility, the change of CBV was examined by 5% & 10% CO₂ inhalation, 5% O₂ inhalation and bilateral jugular vein occlusion. A linear correla-tion was found between PaCO₂ and Hb absorb-ance value on CO₂ inhalation. By the bilateral ju-gular vein occlusion, Hb increased concomitantly with ICP, while cerebral blood flow (CBF) decrea-sed. On 5% O₂ inhalation, absorbance spectral pat-tern of tissue Hb changed from that of oxy-Hb to deoxy-Hb without change of absorbance value at the isobestic point. Thus, the Hb absorbance va-lue obtained by this spectrophotometer was consi-dered to be reliable for the estimation of CBV on the cortical surface.

Using this, the change of CBV was examined on the drug-induced seizure and post-decompres-sion state after sustained intracranial hypertension.

After administration of bemegride in 3 cats, the CBV increased markedly and its change synch-ronized well with the epileptic burst of EEG in association with increase of CBF, ICP and blood pressure.

The change of CBV on the post-decompression state after sustained intracranial hypertension for 2 hours was also examined. In 6 of 8 cats, ICP gradually increased within 30 minutes after de-compression. Among them, continuous decrease of CBV was noted in 3 cats, in which large epidural hematomas were found. In the remaining 3 cats of no hematoma, CBV did not show any decrease, but even slight increase was noted. This finding well corresponded to the acute brain swelling where the increase of CBV might be the cause of increased ICP.

Thus, spectrophotometer used in this study enabled noninvasive, real time measurement of CBV on the cortical surface. This is quite useful to study the pathomechanism related to the cere-bral circulation and intracranial pressure. It will be also useful clinically to monitor CBV on the cortical surface during the operation.