Reneman Robert S.
Department of Physiology, Biomedical Center, University of Limburg, Maastricht, The Netherlands.
Cardiovasc Dis. 1981 Sep;8(3):435-454.
Several methods are available to detect atherosclerotic lesions with a severe degree of stenosis (>70%), but the diagnosis of atherosclerotic lesions with no stenosis or with a minor degree of stenosis (<20%), is problematic. Hemodynamics associated with stenotic lesions are well described by the relationship of blood pressure and blood flow velocity, both as a function of time and localization (along the length and cross-section of the vessel). The use of this relationship in the clinic is difficult because no precise information is available about the geometry and branching of arteries, blood viscosity, and the velocity distribution over the cross-sectional area of the blood vessel. Besides, the invasiveness of the technique to measure arterial pressure as a function of time and localization does not allow routine application in patients. Because of these limitations, alternative methods have been developed. The degree and extensiveness of atherosclerotic disease can, for instance, be estimated from the changes in maximum blood flow velocity and in velocity profile, i.e., velocity distribution along the cross-section of the vessel. Moreover, the delay between simultaneously recorded arterial blood flow velocity tracings (pulse-wave velocity determination) is used to assess the elastic properties of the vessel. Changes in velocity profile occur at relatively slight degrees of arterial stenosis (around 20%), so that determination of these profiles along diseased arteries may contribute to the early diagnosis of atherosclerotic lesions. In man, transcutaneous information about the maximum and mean blood flow velocities over the cross-sectional area of the artery as an instantaneous function of time as well as the flow pattern can be obtained online with continuous wave Doppler flowmeters, at least when audio spectrum analysis is used as a processing technique. Velocity profiles can be determined with multichannel pulsed Doppler systems if the resolution of the system is adequate and a sufficient number of sample volumes can be obtained, limiting the interpolation between these samples. The on-line recording of velocity profiles can be facilitated by combining the pulsed Doppler device with either a velocity imaging system or a B-mode scan. In systems with a high resolution (sample distance 0.5 mm), one should be able to detect local disturbances in the velocity profile at the site of the lesion (due to local increases in shear stress) and proximal to the lesion (due to reflections), so that lesions with a minor degree of stenosis can be detected. In resistive systems (e.g., internal carotid arteries) in which the relationship between pressure and velocity changes during the cardiac cycle is relatively simple, the elasticity of the arterial wall can be determined by relating the relative diameter changes of the vessel, determined on-line with multichannel pulsed Doppler systems, to the instantaneous velocity pulse. Although the detection of atherosclerotic lesions at an early stage of the disease with sophisticated Doppler devices looks promising, further clinical evaluation is required.
有几种方法可用于检测狭窄程度严重（>70%）的动脉粥样硬化病变，但对于无狭窄或轻度狭窄（<20%）的动脉粥样硬化病变的诊断存在问题。狭窄病变相关的血流动力学可通过血压与血流速度的关系很好地描述，这两者都是时间和位置（沿血管长度和横截面）的函数。在临床中使用这种关系很困难，因为关于动脉的几何形状和分支、血液粘度以及血管横截面上的速度分布没有精确信息。此外，测量随时间和位置变化的动脉压的技术具有侵入性，不允许在患者中常规应用。由于这些限制，已开发出替代方法。例如，动脉粥样硬化疾病的程度和范围可根据最大血流速度和速度剖面（即沿血管横截面的速度分布）的变化来估计。此外，同时记录的动脉血流速度描记图之间的延迟（脉搏波速度测定）用于评估血管的弹性特性。速度剖面的变化发生在相对轻微的动脉狭窄程度（约20%）时，因此沿病变动脉确定这些剖面可能有助于动脉粥样硬化病变的早期诊断。在人体中，至少当使用音频频谱分析作为处理技术时，可通过连续波多普勒流量计在线获得关于动脉横截面上最大和平均血流速度随时间的瞬时函数以及血流模式的经皮信息。如果系统分辨率足够且能获得足够数量的样本容积，限制这些样本之间的插值，则可使用多通道脉冲多普勒系统确定速度剖面。将脉冲多普勒装置与速度成像系统或B型扫描相结合可便于速度剖面的在线记录。在具有高分辨率（样本间距0.5毫米）的系统中，应该能够检测到病变部位（由于剪切应力局部增加）和病变近端（由于反射）的速度剖面中的局部扰动，从而能够检测到轻度狭窄的病变。在阻力系统（如颈内动脉）中，心动周期中压力与速度之间的关系相对简单，动脉壁的弹性可通过将多通道脉冲多普勒系统在线确定的血管相对直径变化与瞬时速度脉冲相关联来确定。尽管使用精密的多普勒装置在疾病早期检测动脉粥样硬化病变看起来很有前景，但仍需要进一步的临床评估。
