大脳深部の微小循環動態の特異性に関する研究 ： 局所脳血流量に及ぼすhemodilutionの効果

Abstract

The object of the present investigation is to study the effects of hemodilution on regional cerebral blood flow (rCBF) in the ischemic or non-ischemic rat brain. Regional CBF was measured by Laser-Doppler flowmetry, hydrogen clearance method, and autoradiography. The Laser-Doppler flowmeter (LDF) facilitates instantaneous and continuous measurement of rCBF, while autoradiography provides the absolute rCBF values in each cerebral structure. Isovolemic hemodilution was performed to gradually exchange 7 ml of human albumin for 7 ml of rat blood, after which the values of hematocrit (Hct) decreased by about 33%. The rCBF of the thalamus measured by LDF increased by 25.8%. The increase in rCBF correlated almost linearly with the decrease in Hct. In the measurement of rCBF by LDF, the rCBF value is proportional to the product of the mean red cell dentity and red cell velocity. The decrease in density caused by hemodilution in the tissue demonstrates a factor of rCBF which supports the theoretical basis of this method. In spite of the decrease factor, measured rCBF in fact increased. These findings suggest that a remarkable increase in the velocity of red cells muso occur with hemodilution. The results of rCBF measurements in the non-ischemic rats oboained by autoradiography indicate that hemodilution significantly augments rCBF in the basal ganglia. In rats with middle cerebral artery (MCA) occlusion, rCBF decreased in the area of the MCA. When the changes in blood flow after hemodilution in the treated animals were compared with the changes at equivalent times in the animals without hemodilution, a significant recovery of rCBF in the caudate was seen, whereas the blood flow in the cerebral cortex showed no change. A heterogenous response to hemodilution was observed, which may be explained by the fact that the basal ganglia is supplied by long and narrow perforated arteries.