Estimation of the Shear Stress on the Surface of an Aortic Valve Leaflet

The limited durability of xenograft heart valves and the limited supply of allografts have sparked interest in tissue engineered replacement valves. A bioreactor for tissue engineered valves must operate at conditions that optimize the biosynthetic abilities of seeded cells while promoting their adherence to the leaflet matrix. An important parameter is shear stress, which is known to influence cellular behavior and may thus be crucial in bioreactor optimization. Therefore, an accurate estimate of the shear stress on the leaflet surface would not only improve our understanding of the mechanical environment of aortic valve leaflets, but it would also aid in bioreactor design. To estimate the shear stress on the leaflet surface, two-component laser-Doppler velocimetry measurements have been conducted inside a transparent polyurethane valve with a trileaflet structure similar to the native aortic valve. Steady flow rates of 7.5, 15.0, and 22.5 L/min were examined to cover the complete range possible during the cardiac cycle. The laminar shear stresses were calculated by linear regression of four axial velocity measurements near the surface of the leaflet. The maximum shear stress recorded was 79 dyne/cm², in agreement with boundary layer theory and previous experimental and computational studies. This study has provided a range of shear stresses to be explored in bioreactor design and has defined a maximum shear stress at which cells must remain adherent upon a tissue engineered construct. © 1999 Biomedical Engineering Society. PAC99: 8719Rr, 8768+z, 8719Hh, 4262Be, 4727Nz, 0630Gv     

An automated method for analysis and visualization of laser doppler velocimetry data

The analysis and visualization of large data sets collected by use of laser Doppler velocimetry has presented a challenge to researchers using this technique to investigate complex flow fields. This paper describes an automated procedure for analysis and animation of two- and three-dimensional laser Doppler velocimetry data. The procedure consists of a suite of FORTRAN programs for calculating phase window averages of velocity and the Reynolds stress tensor, calculating the principal normal stresses, maximum shear stresses, and preparation of data files for input into Plot-3D compatible data visualization software. An example application of these techniques to data collected from anin vitro investigation of the retrograde flow field associated with a bileaflet mechanical heart valve is also presented.     

Mean Velocity and Reynolds Stress Measurements in the Regurgitant Jets of Tilting Disk Heart Valves in an Artificial Heart Environment

Laser Doppler velocimetry, with a high temporal resolution (1 ms time windows), was used to measure the flow field in two regions (major and minor orifices) near the aortic and mitral valves (Bjork Shiley monostrut Nos. 25 and 27, respectively) of the Penn State artificial heart. The motion of each valve was also investigated using a 1000 frame/s video camera in order to estimate the valve's closing velocity. Fluid velocities in excess of and opposite to valve closing velocity were detected near the valve, providing evidence of squeeze flow. Maximum Reynolds shear stresses of approximately 20,000 dyn/cm² and time-averaged Reynolds shear stresses of approximately 2000 dyn/cm² were observed during the regurgitant flow phase. These elevated Reynolds shear stresses suggest that regurgitant jets play a role in the hemolysis and thrombosis associated with tilting disk heart valves in an artificial heart environment. © 1998 Biomedical Engineering Society. PAC98: 8745Hw, 4727Wg, 4279Qx     

心淋巴流阻断急性期冠状动脉结构的观察

手术方法阻断羊心淋巴引流后，于急性期内用光，电镜观察冠状动脉主干，前室间支和心壁内小动脉的结构改变，光镜下发现动脉壁水肿，外膜及其周围组织淋巴管扩张，炎性细胞浸润，电镜下可见动脉壁内皮细胞和平滑肌细胞超微结构破坏，结果表明心淋巴引流障碍急性期内可造成冠状动脉壁病理改变。     

正常国人肾动脉粘弹性实验研究

目的　对正常国人新鲜尸体肾动脉进行应力松弛 ,蠕变实验研究 ,为临床提供生物力学参数。方法　对肾动脉进行拉伸应力松弛、蠕变粘弹性力学性质进行实验研究。结果　得出了肾动脉的应力松弛 ,蠕变数据和曲线。用回归分析的方法处理实验数据 ,得出了归一化应力松弛函数和归一化蠕变函数。结论　肾动脉 72 0 0s松弛量为0 .2 80MPa ,72 0 0s蠕变量为 13.98%。应力松弛和蠕变在最初 6 0 0s变化较大 ,72 0 0s时应力松弛、蠕变曲线基本达到平衡。肾动脉为生物粘弹性固体材料     

外周动脉管径信号及血流信号在临床诊断中的应用

本文分析了管径信号及血流速度信号的生理意义及其在临床综合应用中的重要价值，并根据实验结果，讨论了两种生理信号的应用方法及结果，证实了综合应用两种信号具有的应用价值及临床意义。并进一步讨论了这两种信号在其它方面应用的可能性。     

The effect of the skin friction on the solution of the one-dimensional equations of pulsatile flow in distensible tubes

The one-dimensional equations are used in the calculation of blood flow in arteries. The majority of the treatments use the method of characteristics and because of the nature of the method it is necessary to use a simplified value of the skin friction. A commonly used simplification is to assume the zero frequency value of the skin friction. The effect of the use of this approximation is compared with results using the full linear theory value. It is shown that the phase difference between the skin friction and the flux has an appreciable effect on the velocity wave calculated from a given pressure wave.     

Effects of posture,hypotension and locally applied vasoconstriction on the middle ear microcirculation in anaesthetized humans

Studies by laser-Doppler flowmetry of middle ear microcirculation changes induced by physical and chemical stimuli in the animal have only recently been made. This prospective study, performed in humans, was designed to compare the effects of a postural manoeuvre (headup tilt 30°), hypotension and locally applied vasoconstriction on middle ear blood flow during anaesthesia. Circulatory changes provoked by a headup tilt of 30°, and successive intravenous boluses of potent vasodilators, were compared with circulatory changes provoked by locally applied adrenaline, in ten healthy patients in good physical states undergoing middle ear surgical repair. Heart rate and direct arterial pressure were continuously recorded via a radial artery cannula. Middle ear blood flow was continuously recorded via a laser-Doppler probe placed on the promontorium cavi tympani. Metabolic parameters (partial pressure of O₂ and CO₂ in arterial blood, pH, arterial lactate concentrations) and arterial concentrations of propofol were measured just before and just after the experiment. Headup tilt did not modify heart rate, mean arterial pressure or middle ear blood flow. Vasodilators (nicardipine, nitroprusside, nitroglycerin) provoked a fall in arterial pressure (P<0.0001,P<0.0001,P<0.019, respectively), but did not induce any significant variations in heart rate; variations occurred in middle ear blood flow (P>0.05, not significant) which were different according to patients and agents. Locally applied adrenaline provoked a fall in the middle ear blood flow (P<0.0012), with no effect on heart rate and arterial pressure. There were no significant changes in metabolic values, or propofol serum concentrations. The behaviour of the middle ear blood flow submitted to hypotension, posture, or to vasoconstriction could be related to counteracting regulatory responses and/or to direct vascular effects.     

Investigation and improved performance of optical fibre probes in laser Doppler blood flow measurement

Laser Doppler flowmetry with optical-fibre beam transmission is a sensitive fast and convenient method of measuring tissue blood flow. However, its sensitivity can also be a problem because of movement artefacts. This study applies some basic considerations of fibre optics and Rayleigh light scattering to the field of laser Doppler blood flow meters. Practical suggestions are given by which movement arterfacts can be reduced by choice of optical fibres, attention to probe geometry, cladding the fibres to reduce their movements and in the method of application. Experiments which test the normalisation circuitry of laser Doppler instruments are described and the effects of movement artefacts on the interpretation of the pulsatile component of laser Doppler records are also discussed. Probe and fibre line movements cause high-frequency intensity fluctuations due to speckle movement. The intensity fluctuations produce an apparent Doppler shift much greater than the Doppler shift produced by the relative movements of probe and tissue. It has been found that it is important to ensure that the fields of view of the illuminating and detecting fibres do not overlap at the skin surface and that probe contact with the skin surface should be maintained.     

100例健康人不同部位体表血流量的测量

目的 :研究健康人不同部位的体表血流量。方法 :选择 2 0岁～60岁的健康自愿者 10 0例 ,用激光多普勒血流量图像仪 (LDPI)测量了 2 0个不同部位的体表血流量 ,比较了不同性别及不同年龄组间的差异。结果 :( 1)面部和手的血流量较高 ,下肢及躯体血流量较低。( 2 )面部与肢体左右侧体表血流量比较无明显差异。 ( 3 )男性的体表血流量除足背外其它部位均高于女性 ,尤以颜面部血流值的差异有显著意义 (P <0 .0 1)。 ( 4 )年龄 >40岁组血流量均高于年龄 <40岁组 ,除胸前及腰部外 ,其它部位的体表血流值均有显著的统计学差异(P <0 .0 1)。结论 :体表不同部位的血流量差异大 ,面部和手的血流量较躯体及下肢的高。左右侧对称部位体表血流值无明显差别 ,有男性血流量高于女性的趋势。在健康状态下 ,体表血流量不随年龄增长而减少     

胰激肽释放酶对脑缺血沙土鼠软脑膜微血管血流量的影响

胰激肽释放酶对脑缺血沙土鼠软脑膜微血管血流量的影响薛全福１吴云清１张宏１斯勤１王耀芳２蒋建平胰激肽释放酶（ＰａｎｃｒｅａｔｉｃＫａｌｉｋｒｅｉｎ，ＰＫ）是一种蛋白水解酶，在体内作用于激肽原，释放出激肽而发挥作用。在国内外已取得良好的临床效果，并已用于...     

缺血后处理对缺血再灌注家兔肾皮质血流量的影响

目的:观察缺血后处理(IPo)对缺血再灌注(I/R)家兔肾皮质血流量的影响,探讨IPo的肾保护作用。方法:24只日本大耳白兔随机分成3组:假手术组(S组),I/R组,IPo组,每组8只,均用3%戊巴比妥钠麻醉。I/R组采用结扎并切除右肾,分离并夹闭左肾动脉45min,再灌注60min制备肾I/R模型;S组麻醉后开腹,切除右肾,分离左肾及动脉;IPo组在切除右肾、夹闭左肾动脉45min后,再灌1min,缺血1min,反复4次,再全面恢复血流灌注60min;各组取股动脉血液用去蛋白终点法测定血浆肌酐(Cr)含量,二乙酰-肟显色法测定血尿素氮(BUN)含量;应用激光多普勒血流监测仪观测肾皮质血流量。结果:与S组比较,I/R组血浆Cr和BUN浓度升高(P<0.05),肾皮质血流量显著降低(P<0.05)。与I/R组相比,IPo组血浆Cr和BUN浓度降低(P<0.05),肾皮质血流量升高(P<0.05)。结论:IPo可以增加I/R后肾脏皮质的血液灌流量,改善肾功能。     

山莨菪碱对带蒂皮瓣血流量的影响及断蒂指征的探讨

我们应用激光多普勒血流仪对家兔带蒂皮瓣形成术前、后及断蒂后４８ｈ微循环血流进行测量。结果表明：①于皮瓣形成术后测量皮瓣中点血流量,实验组均高于对照组,提示山莨菪碱可以增加皮瓣的血流量。②皮瓣蒂部阻断后,中点ＬＤＦ值达到阻断前的５０％水平时断蒂,皮瓣不一定最终存活,应结合其他指征综合分析。     

微血管内红细胞的流速及白细胞对血流的调节作用

血流速度的测量是微循环研究最主要的参数之一。本实验采用30-1000幅/秒超高速显微摄像录像技术,记录及测量了正常大鼠肠系膜微循环申细动脉、毛细血管、细静脉的血流速度。8只大鼠微血管的内径从4μm—40μm的血管120根,细动脉直径最大25μm,血流速度平均5.86±0.76mm/秒。随着血管直径的减小,血流速度明显减慢,在4—6μm的毛细血管内红细胞的流速平均2.29±0.9mm/秒。在40μm直径的细静脉血流平均2.8±0.8mm/秒,比毛细血管的流速快。白细胞在微血管内流动时其流速和红细胞相同,白细胞贴附在血管壁上滚动时。速度从0.16-0.74mm/秒。白细胞贴壁不再滚动时,有的会穿过血管壁而游走到血管周围的组织,白细胞贴壁数量增多时,可使管腔变小。     

The effect of glucose and mental stress on cutaneous microvascular endothelial function

Glucose and mental stress, independently, have been found to impair arterial endothelial function (an indicator of vascular health). The present study sought to determine whether the combination of glucose and stress would have a greater effect on microvascular endothelial function than each on its own. To assess endothelial function, surges in skin blood flow (reactive hyperemia), following the release of cuff pressure to the upper arm at 200 mmHg for 5 min, were measured with laser Doppler flowmetry in 40 young, healthy females. Endothelial function did not change significantly following a 5-min mathematics stressor or the consumption of 75 g of glucose. However, the combination of glucose and stress impaired endothelium-dependent dilatation 30 min after glucose consumption. These findings suggest that combinations of vascular risk factors may be more threatening to cardiovascular health than singularly occurring factors.     

脐动脉血流测定与胎儿脐带绕颈

目的 :研究脐血流测定对脐带绕颈的预后评估。方法 :对 2 8例B超诊断为脐带绕颈的胎儿产前进行了脐动脉血流S/D值的测定 ,追踪观察围产儿出生时羊水性状、Apgar评分、脐带绕颈情况。 结果 :2 8例B超诊断为脐带绕颈的胎儿产时有 5例未发现脐带绕颈 ;而且S/D值 <3 .0的 2 4例 ,围产结局良好 ;S/D值 >3 .0的 4例 ,娩出时均是脐带绕颈很紧 ,其中 3例羊水粪染 ,Apgar评分均 <7分。结论 :S/D值可作为衡量脐带绕颈对胎儿危害程度的一种方法 ,结合B超为临床决定分娩方式提供依据     

Effect of swirling inlet condition on the flow field in a stenosed arterial vessel model

Blood flow in an artery is closely related to atherosclerosis progression. Hemodynamic environments influence platelet activation, aggregation, and rupture of atherosclerotic plaque. The existence of swirling flow components in an artery is frequently observed under in vivo conditions. However, the fluid-dynamic roles of spiral flow are not fully understood to date. In this study, the spiral blood flow effect in an axisymmetric stenosis model was experimentally investigated using particle image velocimetry velocity field measurement technique and streakline flow visualization. Spiral inserts with two different helical pitches (10D and 10/3D) were installed upstream of the stenosis to induce swirling flows. Results show that the spiral flow significantly reduces the length of recirculation flow and provokes early breakout of turbulent transition, but variation of swirling intensity does not induce significant changes of turbulence intensity. The present results about the spiral flow effects through the stenosis will contribute in achieving better understanding of the hemodynamic characteristics of atherosclerosis and in discovering better diagnosis procedures and clinical treatments.     

颈动脉流场改变对斑块稳定性影响及脑梗死分型特点分析

目的探讨颅外段颈动脉狭窄所致血流动力学变化对斑块稳定性影响;分析脑梗死分型与责任血管狭窄程度、斑块稳定性关系,为脑梗死发病机制、临床诊断、治疗和预防提供重要依据。方法对168例急性脑梗死患者分别行64排CT头颈部血管成像(CTA)及彩色多普勒血流显像仪(CDFI)检查,部分经CTA证实为中、重度狭窄及闭塞者于脑梗死恢复期行DSA检查,根据其责任血管狭窄程度,将168例患者分成颈动脉正常组、轻度狭窄组、中度狭窄组,重度狭窄组及闭塞组,结合CDFI及CTA评价斑块性质及流场改变,对梗死灶进行急性脑梗塞的牛津郡社区卒中计划(OCSP)分型,再根据CTA所示脑梗死部位,将患者分为皮质、基底节区、放射冠和后循环梗死4种亚型。观察流场改变对斑块稳定性影响并对比不同程度颈动脉狭窄后脑梗死临床分型特点。结果 168条责任血管,正常17.9%,轻度狭窄22.6%,中度狭窄30.9%,重度狭窄14.8%,闭塞14.3%,中度狭窄比例最高。狭窄程度大于50%即可导致流场改变,血流速度增快,湍流形成,斑块不稳定性增加,以脂质斑及混合斑比例最高。临床部分前循环梗死(PACI)多见,重度狭窄及闭塞组颈动脉斑块以混合斑多见,临床以分水岭梗死多见。轻度狭窄组,多为纤维斑块,临床以腔隙性梗死(LI)多见。结论颈动脉中度狭窄因特殊的血流流场变化导致斑块不稳定性增高,易发生动脉-动脉栓塞。