Peltier熱勾配式熱クリアランス法による脳血流量測定の定量化への試み

EVALUATION OF REGIONAL CORTICAL BLOOD FLOW BY THERMAL DIFFUSION USING A PELTIER STACK

　抄録　Peltier stackを用いた熱クリアランス法による脳血流量測定の定量化に関して検討した。本法による脳血流量の表示値と水素クリアランス法による脳血流量（H₂—CBF）とに一定の関係が成り立つことは既に報告した。今回は1）この関係の動物の個体差による違い，2） in vitroでのこの関係式の算出の可能性について検討した。1）では3匹の成猫を用い，CBFを変化させそれぞれのH₂—CBFと本法による表示値とを比較した。これら3匹の各関係式は非常に類似し，また全測定での比較でも高い相関関係が得られた。2）については4種の均一な熱伝導率を持つ物質を用い，すでに関係式の判明したプローベと未知のプローベでその測定値を比較することにより未知のプロ—ベでの関係式を求めた。最後に動物実験でこの関係式を確かめた。以上より同—プローベでは，個体差に関係なく同じ関係式が成立し，また新しいプローベの関係式はin vitroで求められることが判明した。

The possibility of quantitative evaluation of cerebral blood flow (CBF) by thermal diffusion has been reported, when the thermal gradient was created by a Peltier stack. We already described the linear relationship between the CBF and the inverse of thermal gradient elsewhere when the CBF measured by hydrogen clearance (Hydrogen CBF) was compared to the values estimated by thermal diffusion. In this paper, the correlation of linear relationship between the thermal CBF and hydrogen CBF in each animal was first investga-ted. Secondary, the possibility of in vitro calibra-tion for quantitative evaluation was discussed. Two kinds of probes were manufactured. One was treat-ed not to leak the heat from the Peltier stack except the sensors for the experimental or intra-operative use, and the other was not treated to minimize the size of probe for the long-term use by implantation into the subdural space. When the thermal CBF was compared to hydrogen CBF in each of 3 cats, a linear relationship was obtain-ed in each and the values showing gradient and constant of the regression line were similar in each cat. Moreover, a good linear relationship was also observed when all measurements in 3 cats were included. These results suggested that there is no difference between each animal in the relationship of thermal and hydrogen CBF when the same probe is employed. In addition, the probe can be characterized with two values, and these are gradient and constant of the linear relationship. The fact that the blood flow is proportional to the heat conductivity indicates that the heat con-ductivity of some material is equivalent to some CBF value in the brain tissue. Accordingly, the measurements of heat conductivity by both of a new probe and the calibrated probe and its com-parison induce the characteristics of the new probe.Four kinds of materials (metal, glass, rubber and resin) were measured in this study. There was a linear relationship between the inversed values of thermal gradient measured by the new probe and those by the calibrated probe. When the gradient and constant of the regression line are a and (3, two characteristics of the new probe, gradient (Φb) and constant (Cb) are defined by

Φb=α×Φa, Cb=β×Ia+Ca,

where Φa and Ca are two characteristics of the calibrated probe. In vitro calibration of nontreat-ed probe was performed by covering with the cotton soaked by water, because it is supposed that the probe is surrounded by cerebro-spinal fluid when it is implanted into the subdural space. In the experiment using cats, it was revealed that CBF values calculated by the new probe employ-ing the characteristics induced by this in vitro calibration were well correlated with the CBF values by the calibrated probe. These results indi-cate the possibility of in vitro calibration of two kinds of flow probes.