経頭蓋超音波ドプラ法の再現性に関する検討

ASSESSMENT OF REPRODUCIBILITY OF TRANSCRANIAL DOPPLER VELOCIMETRY

　抄録　経頭蓋超音波ドプラ法を用いて中大脳動脈（MCA），脳底動脈（BA）の血流を非侵襲的に測定して，本法の再現性について検討した。健常成人15人に対して経頭蓋超音波ドプラ装置を用いて，側頭骨，後頭骨直下にプローブをあてMCA,BAの血流速を測定し，その最大，平均のドプラ偏位周波数を求めた。この測定を検者A,Bの間で，A,B,Aさらに日を改めてAと繰り返し，最初のAの測定値を元にして以後の測定値との間の変動係数を求めた。この結果から同一測定日内のA,A間，A,B間および異なる測定日間のA,A間の測定の再現性について検討した。同一測定日内のA,A間およびA,B間の再現性は，変動係数6-18％と比較的安定した値を示した。異なる測定日間のA,A間の測定の再現性は，同一測定日内の再現性よりも劣っていた。またMCA,BAの血流測定の再現性は，前者の方がより良好な再現性を示した。特に同一測定日内のうちのMCAの血流測定の再現性は，変動係数6-11％と良好な値を示した。本法は，簡便かつ非侵襲的な脳血流測定法として良好な再現性を示しており，ベッドサイドでの脳血流モニタリングや，急性または慢性の負荷に対する脳血流反応性の評価等にも応用可能な方法であると考えられた。

In recent years, transcranial Doppler velocimetry has been widely used as a noninvasive method for measurement of blood flow velocity in basal cere-bral arteries. As for the reproducibility of this method, however, there have been only few reports so far. In the present study, we attempted to evaluate the reproducibility of this method by changing the examiners and the timing of the ex-amination. Fifteen healthy volunteers were in-vestigated by using a pulsed wave Doppler ultra-sound device with a 2 MHz transducer. Both peak and mean spatial frequencies calculated from the frequency spectrum of the Doppler signals from the middle cerebral artery (MCA) and the basilar artery (BA) were used as blood flow parameters for assessing the reproducibility. The arterial blood pressure and the end-tidal carbon dioxide partial pressure (PECO₂) were also monitored during the ultrasonic examinations. The intra- and inter-ob-server reproducibilites were evaluated by obtain-ing the coefficient of variation (CV) of the differ-ences and/or analyzing the correlation between the values from the two measurements by the same examiner and by two separate examiners, respec-tively. The intraobserver reproducibility in sepa-rate days was also evaluated. Both in the mean arterial blood pressure and in PECO₂, no significant changes were observed between the two measure-ments in each subjects.

In the present examination, the CV and r values ranged from 6. 7 to 19. 5% and from 0.69 to O. 95, respectively, showing good reproducibility of the transcranial Doppler method for measurement of blood flow velocity, though some differences were observed as follows. The intraobserver reprodu-cibility was better than the interobserver repro-ducibility. The reproducibility of the measurement in a day was better than that in separate days. Especially, the reproducibility of the measurement for MCA (CV-- 6. 7-13. 2%, r= O. 71-0. 95) was much better than that for BA (CV=--11. 1-19. 5 %, r= O. 69-0. 87). From these results, it was concluded that the measurement of the blood flow velocity in basal cerebral arteries (esp., in MCA) with the transcranial Doppler method was quite reproducible, and therefore we would be able to apply this method successfully for the evaluation of the acute or chronic changes in the blood flow velocity of the basal cerebral arteries in each individual.