Mynard Jonathan, Penny Daniel J, Smolich Joseph J
Heart Research Group, Murdoch Children's Heart Research Institute, Flemington Road, Parkville, Victoria 3052, Australia.
J Biomech. 2008 Dec 5;41(16):3314-21. doi: 10.1016/j.jbiomech.2008.10.002. Epub 2008 Nov 18.
Local reflection coefficients (R) provide important insights into the influence of wave reflection on vascular haemodynamics. Using the relatively new time-domain method of wave intensity analysis, R has been calculated as the ratio of the peak intensities (R(PI)) or areas (R(CI)) of incident and reflected waves, or as the ratio of the changes in pressure caused by these waves (R(DeltaP)). While these methods have not yet been compared, it is likely that elastic non-linearities present in large arteries will lead to changes in the size of waves as they propagate and thus errors in the calculation of R(PI) and R(CI). To test this proposition, R(PI), R(CI) and R(DeltaP) were calculated in a non-linear computer model of a single vessel with various degrees of elastic non-linearity, determined by wave speed and pulse amplitude (DeltaP(+)), and a terminal admittance to produce reflections. Results obtained from this model demonstrated that under linear flow conditions (i.e. as DeltaP(+)-->0), R(DeltaP) is equivalent to the square-root of R(PI) and R(CI) (denoted by R(PI)(p) and R(CI)(p)). However for non-linear flow, pressure-increasing (compression) waves undergo amplification while pressure-reducing (expansion) waves undergo attenuation as they propagate. Consequently, significant errors related to the degree of elastic non-linearity arise in R(PI) and R(CI), and also R(PI)(p) and R(CI)(p), with greater errors associated with larger reflections. Conversely, R(Delta)(P) is unaffected by the degree of non-linearity and is thus more accurate than R(PI) and R(CI).
局部反射系数（R）为研究波反射对血管血流动力学的影响提供了重要见解。使用相对较新的波强度分析时域方法，R被计算为入射波和反射波的峰值强度之比（R(PI)）或面积之比（R(CI)），或者计算为这些波引起的压力变化之比（R(DeltaP)）。虽然尚未对这些方法进行比较，但大动脉中存在的弹性非线性可能会导致波在传播时大小发生变化，从而在计算R(PI)和R(CI)时产生误差。为了验证这一观点，在一个单血管的非线性计算机模型中计算了R(PI)、R(CI)和R(DeltaP)，该模型具有不同程度的弹性非线性，由波速和脉冲幅度（DeltaP(+)）以及产生反射的终端导纳确定。从该模型获得的结果表明，在线性流动条件下（即当DeltaP(+)趋近于0时），R(DeltaP)等于R(PI)和R(CI)的平方根（分别记为R(PI)(p)和R(CI)(p)）。然而，对于非线性流动，压力增加（压缩）波在传播时会放大，而压力降低（膨胀）波在传播时会衰减。因此，R(PI)和R(CI)以及R(PI)(p)和R(CI)(p)中会出现与弹性非线性程度相关的显著误差，反射越大，误差越大。相反，R(Delta)(P)不受非线性程度的影响，因此比R(PI)和R(CI)更准确。
