動脈瘤内流れとaspect ratio(aneurysm depth/neck width)の相関  [in Japanese] Flow Vlsualization Study of Bifurcation Aneurysm: Intraaneurysmal Flow and Aspect Ratio (dome/neck)  [in Japanese]

脳動脈瘤の破裂の予知はきわめて難しい. これは脳動脈瘤の破裂のメカニズムが, 現在まで数多くの研究があるにもかかわらず, 十分に解明されていないことに起因する. われわれは動脈瘤の破裂には, 動脈瘤内の流れの状態が大きく影響をしていることを報告してきた. 今回, 動脈瘤の形態学的指標であるaspect ratio(AR=aneurysm depth/neck width)が, 動脈瘤内の流れにどのように影響を与えるか動脈瘤モデルを用いた可視化実験で検討したので報告する. 実験方法 動脈瘤モデルと流路 アクリル板を用いて三次元動脈瘤モデル作製し, これを流路として実験を行った. 動脈瘤モデルは, neckの位置は分岐部中心でかつ分岐管の径も同じにした対称型動脈瘤である. モデルの主管は, 幅20mmの円筒形であり, これは頭蓋内内頸動脈の約5倍の大きさである. 分岐血管角度は, 動脈瘤内の流れに大きな影響を及ぼす. 今回の動脈瘤モデルは, 親血管と分岐血管のなす角度そして分岐血管同士のなす角度の両者を, それぞれ115度, 130度とした.

We carried out flow visualization studies and measurement of intraaneurysmal flow velocity using a set of three-dimensional bifurcation aneurysm models of various aspect ratio (AR = dome/neck). The aneurysm models were made by an acryl according to computer specification. Flow visualization was performed using the dye injection method. Stream lines in the aneurysm models were monitored and evaluated under various flow ratios into the branches. A mean transit time was calculated by height-over-area method from the time-related concentration of the injected dye in the aneurysm that can be fitted to the exponential curve. Fundamental aneurysm flow was composed of inflow, circulation flow and outflow. A certain asymmetry of the flow ratio was necessary for a significant intraaneurysmal circulation to develop. Mean transit times correlated well with aspect ratio: 5.90 at AR 1.0, 17.74 at AR 1.5, 38.36 at AR 2.0 and 75.96 at AR 3.5. Mean transit times became dramatically slow when AR changed from 1.5 to 2.0 and almost stagnant flow was noticed at dome side of aneurysm with AR 3.5.