膜式氧合器内流场分布的血流动力学初步研究

目的本研究从血流动力学角度,利用计算流体力学CFD初探体外生命支持系统中膜式氧合器内流场分布情况。方法利用SolidWorks建立两种典型结构氧合器模型Maquet M78000-A和Medtronic Affinity NT-B。通过Ansys CFX 14.5进行数值模拟A、B在1～7 L/min流量下,流场分布情况。计算多个指标,速度、压力、流体切应力、涡强度、入口泵功率和能量损失。同时结合体外模拟实验,复方电解质液作循环液体,测量A、B在1～7 L/min流量下各自压差,对比CFD模拟结果。结果在2 L/min平均流量辅助下,A、B入口流腔内平均流速为0.037、0.146 m/s;两侧压降为6.970、11.009 mmHg;血液经过在入口流腔产生涡强度为1.967、5.301 s~(-1);产生能量损失为0.029 8、0.043 8 W。同时体外实验中测量对应压差为5、8.67 mmHg,模拟结果为6.859、10.933 mmHg。结论 CFD可定性模拟血液在氧合器内流动和流场分布。A内涡强度、形态、位置和数量随流量增加而改变;场内形态分布也越不均匀,强涡区域主要集中在入口处。B随流量增加,流场分布也呈不均匀,高流速区域集中在入出口位置,并产生不同强度涡流,造成能量损失。不同流量下,A中血液流速、跨膜压降均低于B。但A内部仍存在涡流、流动死区等,在未来仍需做出进一步优化。体外实验与CFD模拟结果基本吻合,说明CFD模拟可为解决临床问题提供一定参考依据。     

人工心瓣脉动流试验中,主动脉根部压力、流量波形重建的实验研究

本文针对目前国内外在人工心瓣体外脉动流试验中,难以直接、准确地检测模拟主动脉根部压力、流量波形的状况,对可能导致的测试结果非客观、可比性问题进行了脉动流实验研究,并依据前文所建立的理论方法,对在现有人工心瓣体外脉动流检测装置上重建可消除测点后移误差的主动脉根部压力、流量波形,进行了流体力学实验模拟研究。     

动脉内脉动流的温度、压强和速度的径向分布

目的 动脉内脉动流的温度径向分布以及与力学量的关系。方法 在Boussinesq近似下，将脉动流作为一级小量对流体运动方程组作微扰处理。结果 导出了含温度的脉动流方程，并解出了动脉内温度、压强和速度的径向分布。结论 (1)温度和速度分布都与脉动频率有密切关系，温度波动的幅值与脉动频率成反比；(2)当脉动频率增加时，温度和速度剧烈变化的部分将局限在接近管壁的薄层中；(3)温度和轴向速度分布的变化具有相似性。     

轴流血泵入口管道流场的数值模拟与实验研究

目的研究轴流血泵入口管道内血流流场分布情况及血栓形成风险。方法利用计算流体力学(computational fluid dynamics,CFD)模拟血泵及入口管道内流动情况,获取血流速度及其分布;用二维粒子成像测速(particle image velocimetry,PIV)系统测试轴流血泵入口管道中心截面内的血液流动情况及三维粒子成像测速系统测试整个管道内的血液流动情况。CFD计算和PIV实验中血泵的转速为8000 r/min,流量为5.0 L/min。通过分析入口管道内的流场分布评价血泵入口管道内的血栓形成风险。结果整个入口管道内不存在回流、涡流和低速流动区域,血液沿管道的流动速度在管壁边界层外由0 m/s迅速增大到0.8 m/s以上。管道内的血液流速集中分布于1.2~1.5 m/s范围,管道内的平均紊流度为0.17。结论由于管道内的流动平稳且不存在回流、涡流和低速流动,因此不易形成血栓。入口管道使血流平稳,有助于改善轴流血泵内的流场。     

人工心瓣脉动流试验中,主动脉根部压力,流量波形重建的…

本文针对目前国内外在人工心瓣体外脉动脉试验中，难以直接，准确地检测模拟主动脉根部压力，流量波形的状况，对可能导致的测试结果非客观，可比性问题进行了脉动流实验研究，并依据前文（２）所建立的理论方法，对在现有人工心瓣体外脉动流检测装置上重建可消除测点后移误差的主动脉根部压力，流量波形，进行了流体力学实验模拟研究。     

含有镍钛合金丝的PET纺织瓣膜有限元分析及体外流体力学测试

目的 利用有限元方法分析径向织入镍钛金属丝的涤纶(polyethylene terephthalate, PET)基纺织瓣膜力学性能,结合体外血流动力学测试,分析金属丝数量和分布形式对PET瓣膜流体动力学性能的影响。方法 使用建模软件构建在径向方向上具有不同数量和分布的金属丝PET瓣膜和无金属丝PET瓣膜三维几何模型;根据文献和实验数据给定PET瓣膜和金属丝的材料属性;使用体外脉动流实验得到PET瓣膜的跨瓣压差曲线作为边界条件;利用有限元分析软件研究瓣膜在心动周期内的应力分布;通过体外脉动流实验评估金属丝瓣膜的流体力学性能。结果 有限元分析结果表明,径向织入镍钛金属丝可以增强对PET纺织瓣膜的支撑作用,金属丝均匀分布的瓣膜在瓣叶腹部区域的支撑力及作用区域随着金属丝数量增加而增大,金属丝分布在两侧位置的情况类似。金属丝的织入一定程度上改善PET瓣膜上的应力集中。脉动流实验结果表明,织入金属丝PET瓣膜开闭形态的稳定性、有效开口面积、反流分数和跨瓣压差等指标均优于无金属丝的纯PET瓣膜。结论 在PET纺织瓣膜的径向方向织入金属丝可以有效减少心动周期内PET纺织瓣膜上的应力集中,降低PET纺...     

平行平板流动腔中Casson流体脉动流的摄动解

高度远小于横向和纵向几何尺寸的矩形平行平板流动腔是人们用以体外研究细胞在切应力作用下力学行为的主要工具之一，考虑到通常采用的矩形平行平板流动腔内的流动属于小雷诺数流动，本文用雷诺数作为摄动参数求出了矩形平行流动腔内Casson流体脉动流的摄动解，给出了腔内切应力随压力梯度和流量的变化规律。数值结果表明，相同压力梯度下Casson流体和牛顿流体对应的腔内切应力分布无明显不同，而在相同流量条件下，Casson流体和牛顿流体对应的腔内切应力分布有明显差异，本文为Casson流体脉动流条件下平行平板流动腔切应力的确定方法提供了理论依据。     

颈动脉血液动力学的数值模拟

背景:由于颈动脉个体差异的多样性,血流量的不同等,因此建立人体真实动脉模型有其自身的局限性。目的:分析不同颈总动脉脉动入口波形和内外颈动脉出口流量分配比对颈动脉血液动力学的影响。方法:建立标准性颈动脉音叉式分叉TH-AHCB三维模型。采用不同脉动入口条件和出口流量分配比,利用ANSYS流体分析软件数值模拟颈动脉分叉管内流场,计算血液动力学参数,包括速度、壁面剪切力(WSS)等,结合数值计算结果,不同角度分析其与动脉粥样硬化的关系。结果与结论:内外颈动脉的出口流量分配比的差异对分叉管内的流场影响很大;颈总动脉入口脉动波形的变化不仅改变血液动力学参数(速度、压力、壁面切应力等)的差值,同时还会导致力学机制作用的范围改变。     

锥形血管内血液脉动流的数值模拟

将锥形血管与人体血液的脉动流动联系起来研究发展中的血液流动问题 ,给出了锥形血管的几何模型、血液流动的理论模型、生理边界条件以及计算条件 ;根据人体生理脉动流条件 ,建立了血流平均速度函数 ,并就此对三维锥形血管内的血液脉动流动进行了数值模拟 ,获得心动周期不同时刻的轴向速度、径向速度、断面压力和轴向压力分布曲线。将数值模拟计算结果与实验和分析计算结果进行对照 ,讨论了锥形血管内血液脉动流的特点。     

人工心瓣脉动流模拟试验中,主动脉根部压力、流量波形重建的理论与方法

本文针对目前国内外在人工心瓣体外脉动流试验中难以直接、准确地检测模拟主动脉根部压力、流量波形,从而影响测试结果的客观性、可比性的问题,提出了一种方法,可在现有人工心瓣体外脉动流检测装置上重建主动脉根部假想进口流动已充分发展、未受瓣膜扰动时的压力、流量波形。该方法具有数学处理简便、快速、适应性强、较为准确的特点。     

二维脉动流场中内皮细胞表面切应力分布的数值模拟

本文对三种生理相关的正弦入口速度波形的脉动流场内,VEC表面的切应力分布进行了有限差分方法的数值模拟。结果表明：（1）脉动流场与稳态流场中内皮细胞表面的流场分布完全不同,脉动流场中内皮细胞表面的切应力变化幅度远大于稳态流场中的值。（2）同一时刻,每个VEC上的切应力分布是不均匀的,细胞形状影响其表面的切应力分布。（3）在脉动周期的不同时刻,细胞表面的切应力分布也是不均匀的,切应力分布随时间的变化波形与入口波形相类似,但相位有所超前,（4）细胞的伸长主要取决于EC表面的最大平均应力大小。（5）本章的计算结果可以用于Helmilinger实验现象的解释。     

Effects of oscillation on the arteries measured by arterial impedance during left ventricular assistance

Oscillating blood flow has effects on the arteries similar to the effects of pulsatile blood flow at lower frequencies. Alternating-current theory is useful to study the pulse in the circulatory system. Arterial impedance is a good index to estimate the frequency characteristics of the artery. In this study, total vascular resistance and arterial impedance were studied in animal experiments during left ventricular assistance. A centrifugal pump was used for comparison with a VFP (vibrating-flow pump). Left ventricular assistance was performed in animal experiments using goats. Total vascular resistance and arterial impedance were studied to estimate the frequency characteristics of the artery. Total vascular resistance during steady flow assistance decreased compared with that during nonassistance. Arterial walls were extended by the blood flow assistance at steady flow. The resistance during oscillating blood flow was different at each driving frequency, showing the frequency dependency, or pulse effect, of the arterial system under nonsteady flow. Arterial impedance was also studied during oscillating blood flow and showed a slight increase at a driving frequency of 25 or 30 Hz. These fluctuations in impedance are influenced by the reflection of the pulse. Arterial impedance should be taken into consideration when analyzing pulsatile blood flow because the pulse reflection may have some effects on the arterial wall. Some variation of blood pressure and blood flow might be necessary for stable support with artificial circulatory assistance.     

Development of a flow simulator to study haemodynamic behaviour of natural and artificial blood vessels under physiologic flow conditions.

A new computer-controlled flow simulator has been designed to study the haemodynamic behaviour of natural and artificial blood vessels under physiologic flow conditions. The simulator can generate well characterized and fully developed laminar flow properties. It includes a unique perfusion case that imposes an axial tension on the vessel segment, and a commercial programmable pump to reproduce pulsatile flow rates. Response to high frequency commands was greatly attenuated and displayed a frequency dependent phase angle. Thus, for complex pulsating flow rates containing different frequency components, the system response was significantly distinct from the command. To reproduce physiologic waveforms, the transfer function of the whole system was determined for different amplitudes and frequencies of flow rate excitations. Each input command was compared to the measured flow rate, and the values of the gain and phase angle were evaluated. If the desired flow rate was composed of a sum of n sine wave components, each has a frequency fj and an amplitude Aj, a corrected command signal was then reconstructed by amplifying the attenuated components and advancing those lagged in time. The corrected signal was finally applied as the new command to the pump. The results showed an excellent agreement with physiologic waveforms. Examples of different pulsatile flow experiments to investigate the effects of frequency, pressure, and wall elasticity are presented.     

Development of a flow simulator to study haemodynamic behaviour of natural and artificial blood vessels under physiologic flow conditions

A new computer-controlled flow simulator has been designed to study the haemodynamic behaviour of natural and artificial blood vessels under physiologic flow conditions. The simulator can generate well characterized and fully developed laminar flow properties. It includes a unique perfusion case that imposes an axial tension on the vessel segment, and a commercial programmable pump to reproduce pulsatile flow rates. Response to high frequency commands was greatly attenuated and displayed a frequency dependent phase angle. Thus, for complex pulsating flow rates containing different frequency components, the system response was significantly distinct from the command. To reproduce physiologic waveforms, the transfer function of the whole system was determined for different amplitudes and frequencies of flow rate-excitations. Each input command was compared to the measured flow rate, and the values of the gain and phase angle were evaluated. If the desired flow rate was composed of a sum of n sine wave components, each has a frequency fj and an amplitude Aj, a corrected command signal was then reconstructed byamplifying the attenuated components and advancing those lagged in time. The corrected signal was finally applied as the new command to the pump. The results showed an excellent agreement with physiologic waveforms. Examples of different pulsatile flow experiments to investigate the effects of frequency, pressure, and wall elasticity are presented.     

In Vitro Studies of the Pulsatile Radiometric Signal

An in vitro model system was designed to permit simultaneous measurements of blood flow, blood pressure, and the pulsatile radiometric signal during flow studies with Ringer's solution and blood of hematocrit 32,41, and 51. When the in vitro system contained a cat carotid artery, increases in blood flow were associated with increases in the pulsatile radiometric signal. Changes in the pulsatile radiometric signal were linearly related to changes in mean flow and highly correlated with changes in the pulsatile flow, mean pressure, and pulsatile pressure. Results from the regression analyses suggest that the pulsatile radiometric signal may be attributed to reflection from the artery wall. When the in vitro system contained a glass cell, increases in blood flow were associated with decreases in the pulsatile radiometric signal. There was an inverse linear relationship between the pulsatile radiometric signal and mean flow, and changes in the pulsatile radiometric signal were highly and inversely correlated with changes in pulsatile flow and pulsatile pressure. These results suggest that when recording over the cutaneous microcirculation, the pulsatile radiometric signal is in part due to changes in the red blood cell scattering and absorption coefficients.     

Electric analogue model of the singleneedle extracorporal blood-circulatory system of an artificial kidney

Using an electric analogue model, the flow conditions (the progress over time of blood pressure and blood flow) within the single-needle extracorporal bloodcirculatory system of an artificial kidney are investigated. Two different arrangements are taken into consideration: a system with a nonpulsatile pump (a roller pump) and a system with a pulsatile pump (two roller pumps, or one bellows pump). It is demonstrated that, using a pulsatile pump and an optimised pump frequency, it is possible to achieve a reduction in pressure variations as well as flow-velocity variations (with a correspondingly reduced haemolysis rate), and also to achieve an increase in the mean blood flow (comparable to a two-needle system).     

基于电磁驱动的体外膜肺氧合搏动式泵血系统

根据电磁学原理建立梯度线圈-永磁体模型,本研究设计了一款新型电磁驱动搏动式血泵,主要包括驱动装置、泵头装置、冷却系统以及体外循环管路等.搏动式血泵运动速率接近正常人体心率,模仿心脏的节律跳动,产生搏动式血流,实现了搏动式泵血.通过搭建实验平台,采集基于电磁驱动的体外膜肺氧合(extracorporeal membran...     

一种智能化生理性心脏支持系统的设计与初步实验研究

报道了对一种用于急性心肌梗塞过渡治疗的心脏支持系统。设计用于代替心脏功能、简便易用的智能化体外循环装置。包括两个独立的机械泵和泵室、感应和控制系统、膜肺、单向活瓣等主要结构。采用血压和心电图反馈控制机制维持动脉血压和协调心脏收缩与泵输出。在体外测试了搏动泵的工作状况,并对整个系统的运行进行了模拟实验。动物实验证实可获得搏动性动脉波,在心跳停止时可给予心脏足够的血供。     

Pulsatile and nonpulsatile flows can be quantified in terms of energy equivalent pressure during cardiopulmonary bypass for direct comparisons

The purpose of this study was to quantify and compare pulsatile and nonpulsatile pressure and flow waveforms in terms of energy equivalent pressure (EEP) during cardiopulmonary bypass in a neonatal piglet model. EEP is the ratio of the area under the hemodynamic power curve and the flow curve. Piglets, mean weight of 3 kg, were used in physiologic pulsatile pump (n = 7), pulsatile roller pump (n = 6), and nonpulsatile roller pump (n = 7) groups. Data (waveforms of the femoral artery pressure, pump flow, and preaortic cannula extracorporeal circuit pressure) were collected during normothermic cardiopulmonary bypass at 35 degrees C (15 minutes on-pump), before deep hypothermic circulatory arrest (pre-DHCA) at 18 degrees C, and after cold reperfusion and rewarming (post-DHCA) at 36 degrees C. The pump flow rate was 150 ml/kg/min in all three groups. During pulsatile perfusion, the pump rate was 150 bpm in both pulsatile groups. Although there was no difference in mean pressures in all groups, EEP and the percentage increase of pressure (from mean pressure to EEP) of mean arterial pressure and preaortic cannula extracorporeal circuit pressure were higher with pulsatile perfusion compared with nonpulsatile perfusion (p < 0.001). In particular, the physiologic pulsatile pump group produced significantly higher hemodynamic energy compared with the other groups (p < 0.001). These results suggest that pulsatile and nonpulsatile flows can be quantified in terms of EEP for direct comparisons, and pulsatile flow generates higher energy, which may be beneficial for vital organ perfusion during cardiopulmonary bypass.     

Linearity and frequency response of fleisch type pneumotachometers

Some aspects of the linearity and the frequency response of flow measurement with Fleisch type pneumotachometers are considered. The transition from a uniform velocity distribution at the entrance of the capillary tubes of the transducer to a fully developed flow profile is discussed as one of the phenomena influencing the linearity of the set-up.Besides, an expression is derived for the frequency response of the Fleisch pneumotachometer. The frequency responses as derived from measurements show good agreement with theory. In the range of the lower frequencies the frequency response of the flow measuring set-up is proved to be largely determined by the frequency response of the pressure transducer with the connecting tubes. A simple way is indicated to measure the latter. This, in combination with the calculated frequency response of the flow transducer, makes it fairly casy to determine the frequency response characteristics of a flow measuring set-up containing a Fleisch type pneumotachometer.