長谷川 英之^{1, 2}, 本江 和恵¹, 金井 浩^{1, 2}

Hideyuki HASEGAWA^{1, 2}, Kazue HONGO¹, Hiroshi KANAI^{1, 2}

¹東北大学大学院医工学研究科医工学専攻, ²東北大学大学院工学研究科電子工学専攻

¹Graduate School of Biomedical Engineering, Tohoku University, ²Graduate School of Engineering, Tohoku University

キーワード : regional pulse wave velocity, parallel beam forming, high frame rate

目的：脈波速度（pulse wave velocity: PWV）は心拍に起因する動脈に沿った圧力波の伝搬速度である．PWVは動脈硬化の進行に伴って上昇するため，動脈硬化の診断指標として用いることができる．PWVの測定は動脈硬化の診断に対する非侵襲的アプローチとして知られており，臨床の場で広く用いられている．従来のPWV測定法では平均PWVは2点間，すなわち頸動脈と大腿動脈の間の数十cm 間隔で算出する．しかしながら，PWVは動脈系の部位に依存する，すなわち遠位部動脈のPWVは近位部動脈のものよりも速くなる．したがって，局所PWVを測定する方がより好ましい．方法：本研究で局所PWVを評価するために，3,472 Hzの高時間分解能で位相差トラッキング法により動脈の長軸方向の0.2 mm間隔72ヵ所でヒト頸動脈壁の微小振動速度を測定し，これらの波形にヒルベルト変換を適用することによってPWVを推定した．結果：本研究では3名の健常被験者の頸動脈をin vivoで測定した．動脈長軸方向の14.4 mmという短区間におけるPWVはそれぞれ5.6，6.4および6.7 m/sと推定され，文献値とよく対応していた．さらに，被験者の1人に関しては，末梢から心臓の方向に伝搬している成分が認められたが，これはすなわち末梢動脈により反射された成分として知られているものである．我々の提唱した方法を用いて，反射成分の伝搬速度は−8.4 m/sと推定された．反射成分のPWVが高い原因は，進行波および反射波到達時の血圧の差であると考えられた．結論：このよう方法は（異なる部位の動脈を含む平均PWVではなく）特定の動脈で局所PWVを測定することにより，動脈硬化の進行による弾性の変化をより鋭敏に検出するのに有用であると考えられる．

Purpose: Pulse wave velocity (PWV) is the propagation velocity of the pressure wave along the artery due to the heartbeat. The PWV becomes faster with progression of arteriosclerosis and, thus, can be used as a diagnostic index of arteriosclerosis. Measurement of PWV is known as a noninvasive approach for diagnosis of arteriosclerosis and is widely used in clinical situations. In the traditional PWV method, the average PWV is calculated between two points, the carotid and femoral arteries, at an interval of several tens of centimeters. However, PWV depends on part of the arterial tree, i.e., PWVs in the distal arteries are faster than those in the proximal arteries. Therefore, measurement of regional PWV is preferable. Methods: To evaluate regional PWV in the present study, the minute vibration velocity of the human carotid arterial wall was measured at intervals of 0.2 mm at 72 points in the arterial longitudinal direction by the phased-tracking method at a high temporal resolution of 3472 Hz, and PWV was estimated by applying the Hilbert transform to those waveforms. Results: In the present study, carotid arteries of three healthy subjects were measured in vivo. The PWVs in short segments of 14.4 mm in the arterial longitudinal direction were estimated to be 5.6, 6.4, and 6.7 m/s, which were in good agreement with those reported in the literature. Furthermore, for one of the subjects, a component was clearly found propagating from the periphery to the direction of the heart, i.e., a well known component reflected by the peripheral arteries. By using the proposed method, the propagation speed of the reflection component was also separately estimated to be -8.4 m/s. The higher magnitude of PWV for the reflection component was considered to be the difference in blood pressure at the arrivals of the forward and reflection components. Conclusion: Such a method would be useful for more sensitive evaluation of the change in elasticity due to progression of arteriosclerosis by measuring the regional PWV in a specific artery of interest (not the average PWV including other arteries).