Asymmetry of Doppler spectrum in stenosis differentiation

The asymmetry of the spectral distribution of ultrasonic Doppler flow velocity signals, assessed using the coefficient of skewness, is discussed as a criterion of stenosis differentiation. Its performance is compared with that of the index of turbulence intensity for both in vitro and in vivo flow Doppler signals, recorded distal to a stenosis. The power spectral distributions are computed using the direct Fourier transform and maximum likelihood method. The asymmetry of spectral distribution has proved to be a more efficient criterion than the turbulence intensity. The maximum likelihood method ensures better stenosis differentiation than the direct FFT method.     

Hemodynamic performance of small-size bileaflet valves: pressure drop and laser Doppler anemometry study comparison of three prostheses

Laser Doppler anemometry (LDA) is a single-point technique which is unparalleled to detect accurately the local properties of the velocity field in a turbulent flow, such as that generated by a prosthetic heart valve (PHV). We propose a correlation between the structure of the flow field in three 19 mm bileaflet PHVs (Sorin Bicarbon, St. Jude Standard, St. Jude HP), investigated at peak systole (6 L/min cardiac output [CO]) with LDA, in kinematic and geometric similarity, and the global parameter of transvalvular pressure drop measured in both steady and pulsatile conditions. The pressure transducers of the same apparatus were used to characterize pressure drops at different flow rates whereas the steady-flow case was studied with a highly accurate tester built in our laboratory. The 2 St. Jude models rank according to their internal orifice diameter (ID) with the standard model (with a smaller ID) providing higher pressure drops for each flow rate. Sorin Bicarbon, due to its leaflet geometry, generates a more complex flow field with respect to the 2 St. Jude flat-leaflet models and shows improved hemodynamical behavior in pulsatile conditions with respect to the stationary case due to differences in pressure recovery. This study can provide insights into a PHV's local flow structure and global hemodynamical parameters.     

正常人和急性心肌梗死患者心率震荡斜率的昼夜变化及与心率的相关性

目的观察正常人和急性心肌梗死（AMI）患者心率震荡（HRT）的昼夜变化规律,探讨不同人群心率与震荡斜率（TS）的相关性。方法选择100例AMI患者,平均年龄（60.87±13.72）岁,男66例,女34例;82例正常对照者,平均年龄（59.23±13.31）岁,男54例,女28例。两组均进行24h动态心电图检查,定量测定一昼夜中每小时的平均心率（HR）与TS的均值,采用圆形分布统计分析方法,计算两组TS值在昼夜分布中的高峰时点及集中时段。结果（1）正常对照组TS值在24h分布上有明显的集中趋势,高峰时点为04：34（P〈0.05）,集中时段为21：25～11：41;AMI组TS值在24h分布上无明显集中趋势（P〉0.05）。（2）正常对照组HR与TS呈负相关关系（r=-0.771,P〈0.01）;AMI组HR与TS不存在直线相关关系（r=-0.312,P〉0.05）。结论正常人TS值有昼夜节律性,明显受HR的影响。作为心脏的一个基本生物节律,其主要受自主神经的调控。而AMI患者的这种生物节律性消失,可能与自主神经功能紊乱有关。     

窦性心率震荡与冠心病冠脉病变累及程度的相关性分析

目的 观察窦性心率震荡各指标与冠心病患者病变累及程度之间的关系.方法 选择行冠脉造影和24h动态心电图检查的患者93例,根据冠脉造影的结果分为阳性组（69例）、阴性组（24例）,根据冠状动脉病变累及程度分为单支血管病变组（23例）、双支血管病变组（21例）和三支血管病变组（15例）,均于入院时行24h动态心电图检查,并计算震荡初始值和震荡斜率,进行统计分析.结果 阳性组HRT值[TO：（0.0463±0.0310）、TS：（3.9257±3.8741）ms/RR],阴性组值[TO：（-0.0393±8.9786）（12.9972±8.9786）ms/RR],（P ＜0.01）;单支病,TS：两组间差异有统计学意义变组HRT值[TO：（0.0069±0.0058）、TS：（6.6098±3.9966）ms/RR]、双支病变组HRT值[TO：（0.0369±0.0213）、TS：（3.6867±2.4173）ms/RR]、三支病变组HRT值[TO：（0.0985±0.0769）、TS：（0.7897±0.7327）ms/RR],HRT值除TO在单支病变组与双支病变组间差异无统计学意义（P ＞0.05）外,各组间均有统计学意义（P ＜0.01）.结论 窦性心率震荡是一种评价自主神经功能的简便的无创检测方法;窦性心率震荡与冠心病患者病变累及程度有一定的相关性,冠脉病变累及程度越重,窦性心率震荡现象越不明显.     

心肌梗死合并糖尿病患者的心率震荡变化

目的:探讨心肌梗死伴糖尿病患者和单纯心肌梗死患者的心率震荡(HRT)的变化。方法:选择24小时动态心电图有室性早搏的心肌梗死伴糖尿病患者(A组)、单纯心肌梗死患者(B组)和无器质性心脏病患者(C组)各30例,分别手工测量反映HRT的两项指标震荡初始(TO)和震荡斜率(TS),对三组患者进行比较。结果:A、B、C组TO值分别为(0.0078±0.0123)、(0.0120±0.0225)、(0.0312±0.0337)。TS值分别为(4.5182±2.3321)、(8.1430±5.7362)、(13.4520±7.5310);A、B组的TO、TS值与C组比较均有显著性差异(P<0.01),A组与B组的TO、TS值比较差异亦有显著性(分别为P<0.05,P<0.01)。结论:心肌梗死合并糖尿病患者较单纯心肌梗死患者的HRT值变化更明显,提示心肌梗死合并糖尿病患者的HRT受损更严重。     

心率震荡及其在高血压中的研究现状

心率震荡是反映自主神经功能状况的又一新的心电生理学检测方法,主要用于冠状动脉粥样硬化性心脏病、心力衰竭、糖尿病等预后的预测。有关其在高血压中的研究甚少,但已有的结果均证实高血压患者心率震荡现象明显减弱,尤其是伴左心室体积扩大、恶性室性期前收缩以及脉压增大的患者,提示高血压患者的自主神经功能明显受损,心率震荡可作为高血压患者预后不良的新指标。     

Use of an ultrasound blood-mimicking fluid for Doppler investigations of turbulence in vitro

Turbulence is an important factor in the assessment of stenotic disease and a possible causative mechanism for thromboembolism. Previous Doppler studies of turbulence have typically used whole-blood preparations or suspensions of erythrocytes. Recently, a water-glycerol based blood-mimicking fluid (BMF) has been developed for use in Doppler ultrasound studies. This fluid has desirable ultrasound properties but it has not previously been described during in vitro investigations of turbulence intensity. We report on investigations of grid-generated and constrained-jet turbulence in an in vitro test system. The BMF was found to generate significant levels of turbulence during steady flow at physiological flow rates, producing turbulent patterns in the distal region that were consistent with previous studies. Turbulence intensity increased significantly with flow rate (p < 0.005) for both the constrained jet and the constrained grid. Based on our observations, we conclude that a water-glycerol based BMF provides a suitable working fluid during in vitro investigations of turbulence using Doppler ultrasound.     

窦性心率震荡的临床研究

目的：探讨急性心肌梗死患者和扩张型心肌病患者的室性心律失常之后的窦性心率变化与预后关系。方法：检测40例急性心肌梗死患者组、25例扩张型心肌病患者组及50例冠心病非急性心肌梗死伴有室性早搏组（对照组）的室性心律失常之后的窦性心率变化[震荡初始（TO）、震荡斜率（TS）]、左室射血分数（LVEF）3项指标,并观察3项指标与1年内死亡发生率的关系。结果：①急性心肌梗死组震荡初始（TO）为（-0.38±2.34）%,震荡斜率（TS）为（2.30±1.10）ms/RR;扩张型心肌病组震荡初始为（-0.38±2.26）%,震荡斜率为（4.67±2.86）ms/RR;对照组震荡初始为（-2.26±3.16）%,震荡斜率为（8.60±6.84）ms/RR,3组比较差异有统计学意义,P〈0.01。②26例急性心肌梗死合并心力衰竭组的震荡初始为（-0.28±1.86）%,震荡斜率为（2.00±1.00）ms/RR,LVEF为（32.46±6.24）%;14例急性心肌梗死非合并心力衰竭组的震荡初始（-0.21±1.23）%,震荡斜率（2.30±1.10）ms/RR,LVEF为（50.46±8.26）%。两组比较：震荡初始差异无统计学意义,P〉0.05;震荡斜率、LVEF比较差异有统计学意义,P〈0.05。③3组各指标与恶性室性心律失常的发生率组间比较差异无统计学意义,P〉0.05。④3组各指标与1年内的死亡发生率组间比较差异无统计学意义,P〉0.05。结论：室性心律失常之后窦性心率震荡不一定能预测死亡率,死亡率的高低在于该种疾病病变的严重程度。     

Characterization of Hemodynamic Forces Induced by Mechanical Heart Valves: Reynolds vs. Viscous Stresses

Bileaflet mechanical heart valves (BMHV) are widely used to replace diseased heart valves. Implantation of BMHV, however, has been linked with major complications, which are generally considered to be caused by mechanically induced damage of blood cells resulting from the non-physiological hemodynamics environment induced by BMHV, including regions of recirculating flow and elevated Reynolds (turbulence) shear stress levels. In this article, we analyze the results of 2D high-resolution velocity measurements and full 3D numerical simulation for pulsatile flow through a BMHV mounted in a model axisymmetric aorta to investigate the mechanical environment experienced by blood elements under physiologic conditions. We show that the so-called Reynolds shear stresses neither directly contribute to the mechanical load on blood cells nor is a proper measurement of the mechanical load experienced by blood cells. We also show that the overall levels of the viscous stresses, which comprise the actual flow environment experienced by cells, are apparently too low to induce damage to red blood cells, but could potentially damage platelets. The maximum instantaneous viscous shear stress observed throughout a cardiac cycle is <15 N/m². Our analysis is restricted to the flow downstream of the valve leaflets and thus does not address other areas within the BMHV where potentially hemodynamically hazardous levels of viscous stresses could still occur (such as in the hinge gaps and leakage jets).     

横向超声多普勒技术的应用

当超声波束与流速垂直时 ,获得的横向多普勒功率谱宽度与采样单元内最大流速成正比。横向超声多普勒技术在流速测量时避免了采样单元内流速梯度造成的模糊 ,弥补了常规多普勒技术在大角度流速测量时存在盲区的缺陷 ,克服了以往B超成像与多普勒流速测量对声束要求的矛盾。本文提出了利用横向多普勒技术估计血管剪切率、进行无模糊湍流测量以及最大血流速度校正的新方法 ,设计了多通道横向多普勒系统 ,实验结果证实了横向多普勒技术在血流动力学领域应用的有效性。本文从应用方面扩展了横向多普勒技术的研究领域。