血液壓力波波速理論與水管模擬實驗之初步探討

Abstract

在心臟的週期性壓力波源下，foot-to-foot方法量測血壓波速被廣泛用來評估動脈彈性的變化。然而，主動脈傳遞的壓力波，不同位置量測到的諧頻比例並不相同，這會使得波速量測的結果受到影響。我們運用「Ｔ型管模型」來模擬整個循環系統，用兩種方式量測波速。首先，給單脈衝的壓力波，量測壓力波抵達乳膠管（Latex管）上兩不同位置的時間差，以兩量測點之間的距離除之，得到未經反射影響的正確壓力波波速。另一方面，我們也用步進馬達提供週期性壓力波來模擬心臟，然後用foot-to-foot方法來量測波速。我們用五種不同彈性模數的乳膠管來重複上述的實驗。 我們發現週期波下用foot-to-foot方法量測到的波速，不同的位置量測到不同的結果。若使用脈衝波量測波速，在Latex管上不同位置量測結果較為一致。 當我們置換不同彈性的乳膠管量測波速時，若量測位置固定，兩種方法量測的波速皆會和乳膠管的彈性有很高的相關性。最後，我們以林老師對於「徑向振動理論」為基礎，求得Ｔ型管模型中的解析解，將公式解用Matlab軟體進行數值模擬，與實驗進行比對得到與預期高度符合的結果。這結果重新詮釋了週期波壓力下，foot-to-foot方法量測到的波速和水管彈性間的關係。

Foot-to foot method is widely used to measure the pressure wave velocity (PWV) in large arteries and to assess arterial stiffness. However, the harmonic proportions of the pressure pulse varying along the large arteries may give an additional influence on the PWV measurement. Our effort is to investigate the validity of this method by a T-tube simulated arterial system. To find the true wave velocity, we generated a single impulse and measured the interval of the time as the pulse arriving at two different locations of the tube. We then replaced the impulse by a periodic water input to simulate the effect of heart. The measurements of pulse wave velocity for five tubes of different elasticity were performed. We found that the PWVs evaluated by foot-to foot method depend greatly on the locations of the pressure transducers and are not in consistent with the true wave velocity. Nevertheless, the correlation of the arterial stiffness with the PWV by foot-to foot method is significant. We would base on the “radial oscillation theory” to get the analytical solution of the T-tube system and compared the numerical answer to the experimental result. We will give a new explanation about the correlation between the PWV and the elasticity of the arterial wall.