生物心脏瓣膜钙化前后的应力分析

生物心脏瓣膜钙化前后的应力分析李珏匡震邦（西安交通大学，西安７１００４９）刘维永（西京医院，西安７１００３２）ＳＴＲＥＳＳＡＮＡＬＹＳＩＳＯＦＮＯＲＭＡＬＡＮＤＣＡＬＣＩＦＩＥＤＢＩＯＰＲＯＳＴＨＥＴＩＣＨＥＡＲＴＶＡＬＶＥＳＬｉＪｕｅ，ＫｕａｎｇＺ...     

心脏瓣膜术联合冠状动脉旁路移植术治疗心脏瓣膜疾病患者的临床价值研究

目的:分析心脏瓣膜术联合冠状动脉旁路移植术治疗心脏瓣膜疾病患者的临床价值.方法:选取我院于2017年5月至2019年5月期间收治的80例心脏瓣膜病患者为研究对象,随机分为研究组和对照组,各40例.对比两组术后相关指标情况、手术前后心功能指标.结果:研究组呼吸机辅助通气时间、ICU监护时间以及住院时间均短于对照组(P<0...     

C-LⅢ型短柱人工机械心脏瓣膜的研制

简述了C-LⅢ型短柱人工机械心脏瓣膜的设计依据、结构特点及关键材料与工艺特性，报道了强度和疲劳试验结果，研究和比较了C-LⅢ型短柱瓣、C-LI型标准瓣、Medtronic—Hall瓣体外流体动力学性能。结果表明，C-LⅢ型短柱人工机械心脏瓣膜结构简单、性能优良，是一种新型的有希望的国产人工心脏瓣膜。     

组织工程心脏瓣膜的研究进展

组织工程心脏瓣膜(tissue engineering heart valve,TEHV)理论上能克服机械瓣及生物瓣的不足,具有广阔的发展前景.目前组织工程心脏瓣膜的研究主要集中在瓣膜支架材料的选取及制备、种子细胞的选择和种子细胞的种植及培养等三方面.本文将分别就这三方面研究进展进行介绍,分析目前存在的问题,并对其应用进行展望.     

兔眼角膜生物力学特性的年龄相关性

目的 利用兔眼角膜条的单轴拉伸实验数据,研究角膜生物力学特性与年龄的相关性。 方法 分别取3月龄和7~8月龄兔眼角膜条,实施单轴拉伸实验,获得实验数据;用指数模型和幂模型对应力 应变数据进行分析;用黏弹性力学模型对应力松弛数据进行分析。结果 兔眼角膜条呈现非线性黏弹性特征。在实验误差允许的范围内,不同月龄兔眼角膜条的非线性应力-应变关系差别不明显,7~8月龄兔眼角膜的切线模量略偏大,但其应力衰减得明显快。不同的拉伸速率对3月龄兔眼角膜条非线性应力-应变关系的影响不明显,但快速拉伸后的角膜条应力衰减明显变快。结论 兔眼角膜随月龄增加会轻微变硬,而角膜的松弛特性随月龄变化明显。     

心脏瓣膜替换术后抗凝治疗的监护

严重的风湿性心瓣膜疾病均需进行瓣膜替换手术。目前人工瓣膜均采用机械瓣膜。瓣膜替换术后，进行抗凝治疗时，如药量不足易出现血栓；药量过大可引起出血。这是抗凝治疗中最易出现的并发症。因此抗凝治疗期间病人的监护具有非常重要的意义。现将我院1999年8月至2004年2月行瓣膜替换术94例病人抗凝监护情况报告如下。     

心脏瓣膜生物力学及相关建模方式的研究进展

心脏瓣膜生物力学是一个快速发展的、高度临床相关的研究领域。研究表明大多数瓣膜病变是由于瓣膜生物力学改变导致的，因此了解心脏瓣膜与其局部力学环境之间的相互作用对于了解正常瓣膜功能和阐明瓣膜疾病进展至关重要。然而研究这些病变的技术在很大程度上受到了限制，其中缺乏良好的瓣膜力学相互作用模型是限制该领域研究深入开展的主要瓶颈之一。随着数值计算模型、体外模型和动物模型建模技术的飞速发展，心脏瓣膜相关的生物力学和介入治疗研究取得了重大进展。本文对心脏瓣膜的生物学和生物力学及相关模型进行综述，旨在使用跨学科方法加强临床心血管医生对心脏瓣膜疾病的理解。     

实验动物空腔脏器耐压力学测试系统

研制耐压力学测试系统,用以不同药物或手术方式对结肠、直肠吻合口愈合影响的实验中,测量吻合口耐压力学指标.该测试系统由双通管、三通管、加压模块和压力检测记录模块等组成,通过对本装置的操作,实现耐压检测中压力的实时检测、记录和显示.利用10只小鼠进行对比实验,共取有40段2 cm长肠管和20段2 cm长下腔静脉血管,进行耐压实验,对比吻合口破裂时压力表读数和本耐压力学测试系统的测试值,以验证系统性能.结果显示,两者的测量值具有良好的吻合度,并且测压系统所测得数据具有较小的变异系数.与以往使用压力表的测试方式相比,实验过程更为简单,观测更加直观,实验结果更为可靠.本测试系统结构简单,可优化实验流程,可应用于肠管、血管、皮肤等组织的耐压力学测试.     

组织工程心脏瓣膜支架材料的选择与应用

背景：支架材料的选择在组织工程心脏瓣膜中起着至关重要的作用,支架材料的选择也就影响着组织工程心脏瓣膜的构建效果。 目的：评价组织工程心脏瓣膜支架材料的的优缺点,并对其选择进行总结。 方法：以 “组织工程,心脏瓣膜,支架材料,生物相容性”,为中文关键词;以:“tissue engineering,heart valves, scaffold material, biocompatibility” 为英文关键词,采用计算机检索1993-01/2009-10相关文章。纳入与有关生物材料与组织工程心脏瓣膜的相关的文章;排除重复研究及Meta分析类文章。 结果与结论：人工合成高分子材料有更大的可控性,可预先塑性,大量制备,孔径和孔隙率较容易控制,成本低廉;天然生物材料和合成高分子材料都存在一定不足,将人工可降解材料与天然材料相结合构建瓣膜支架,发挥两者各自的优势构建出性能良好的组织工程心脏瓣膜。组织工程心脏瓣膜的研究前景广阔。但距离临床应用还有很长的路要走,相信随着研究的不断深入以及支架材料的不断优化对组织工程心脏瓣膜构建方法的改进,在不远的将来造福于广大心脏瓣膜病患者。     

软组织生物力学特性的测量:仪器设计

软组织的生物力学特性是诊断软组织病变的重要依据。本研究设计了一种新的仪器来在线测量软组织的生物力学特性。该仪器通过一个特别设计的集成传感器，获取软组织的应力和应变信息。集成传感器由超声传感器和应变片组成的压力传感器通过串连方式连接而成；对超声回波信号与发射信号进行互相关运算，获取软组织的应变信号，这个过程用FPGA来实现。基于软组织的生物力学模型和所获得的软组织的应力应变信号，提取软组织的特性参数。该仪器对超声回波信号和压力信号数据的采集，处理和显示通过DSP控制来实现；该仪器能测量软组织的不同层的厚度，便于运动检测和健身监测之用。     

Effects of fixation pressure on the biaxial mechanical behavior of porcine bioprosthetic heart valves with long-term cyclic loading

Zero transvalvular pressure fixation is thought to improve porcine bioprosthetic heart valve (BHV) durability by preserving the collagen fiber architecture of the native tissue, and thereby native mechanical properties. However, it is not known if the native mechanical properties are stable during long-term valve operation and thus provide additional durability. To address this question, we examined the biaxial mechanical properties of porcine BHV fixed at 0 and 4mmHg transvalvular pressure following 0, 1 x 10(6), 50 x 10(6), and 200 x 10(6) in vitro accelerated test cycles. At 0 cycles, the extensibility and degree of axial cross-coupling of the zero-pressure-fixed cusps were higher than those of the low-pressure-fixed cusps. Furthermore, extensibility of the zero-pressure-fixed tissue decreased between 1 x 10(6) and 50 x 10(6) cycles, approaching that of the low-pressure-fixed tissue, whose extensibility was unchanged over 0-200 x 10(6) cycles. The decrease in extensibility of the zero-pressure-fixed tissue between 1 x 10(6) and 50 x 10(6) cycles may be attributable to the ability of its collagen fibers to undergo larger changes in orientation and crimp with cyclic loading. These observations suggest that the collagen fiber architecture of the 0-mmHg-fixed porcine BHV, although locked in place by chemical fixation, may not be maintained over a sufficient number of cycles to be clinically beneficial. This study further underscores that chemically treated collagen fibers can undergo conformational changes under long-term cyclic loading not associated with damage.     

Material test system for the evaluation of mechanical properties of biomaterials

A new material test system has been designed to evaluate the mechanical properties of biomaterials which are very often subject to complicated dynamic and repetitive force and deformation inside the body. The test system has high versatility, being incorporated with a miniature servo-hydraulic testing machine which can smoothly apply various modes of load and deformation to materials, and a vidicon displacement analyzer for the accurate, noncontact measurement of specimen length. A minicomputer system is used for the data acquisition and processing. Performance tests of the system and preliminary experiments on elastomeric polymers have indicated that the test system is very useful for the detailed studies of the mechanical properties of various kinds of biomaterials.     

Squeeze flow measurements in mechanical heart valves

High-speed squeeze flow during mechanical valve closure is often thought to cause cavitation, either between the leaflet tip and flat contact area in the valve housing, seating lip, or strut flat seat stop, depending on design. These sites have been difficult to measure within the housing, limiting earlier research to study of squeeze flow outside the housing or with computational fluid dynamics. We directly measured squeeze flow velocity with laser Doppler velocimetry at its site of occurrence within the St. Jude Medical (SJM), Omnicarbon (OC), and Medtronic Hall Standard (MHS) 29 mm valves in a mock circulation loop. Quartz glass provided an observation window to facilitate laser penetration. Our results showed increasing squeeze flow velocity at higher heart rates: 2.39-3.44 m/s for SJM, 3.07-4.33 m/s for OC, and 3.87-5.33 m/s for MHS. Strobe lighting technique captured the images of cavitation formation. Because these results were obtained in a mock circulation loop, one can assume this may occur in vivo resulting in valve damage, hemolysis, and thromboembolism. However, velocities of this magnitude alone cannot produce the pressure drop required for cavitation, and the applicability of the Bernoulli equation under these circumstances requires further investigation.     

风湿性病变二尖瓣瓣膜的一维力学性能

目的通过测量风湿性病变的二尖瓣膜的一维拉伸力学性能,探讨二尖瓣膜力学特性变化的原因,进而从力学角度分析风湿性瓣膜病的病理生理.方法用软组织生物材料试验机对病变瓣膜前瓣的径向和环向分别进行一维拉伸试验,了解瓣膜的力学性能.结果病变瓣膜前瓣存在应力滞后现象,其径向和环向特征ε分别为0.109±0.021和0.103±0.015,特征E分别为(456±11.67)×103 N/m2和(418±24.59)×103 N/m2,两者均无显著性差别.结论病变瓣膜前瓣为粘弹性体,结构特性为各向同性, 病变瓣膜力学性能下降是风心病病理生理改变的物理学基础.     

In vivo mechanical properties of thoracic aortic aneurysmal wall estimated from in vitro biaxial tensile test

To investigate the mechanism of aneurysm rupture, it is necessary to examine the mechanical properties of aneurysm tissues in vivo. A new approach to evaluate in vivo mechanical properties of aortic aneurysmal tissues has been proposed in this study. The shape of the aneurysm was modeled as a sphere, and equi-biaxial stress in the in vivo state was estimated from the diameter and the wall thickness of each aneurysm and mean blood pressure of each patient. The mechanical properties of the aneurysm at the in vivo stress were estimated from its in vitro biaxial tensile properties. There were no significant correlations among maximum diameter D, wall thickness t, and mean infinitesimal strain in the in vivo state epsilon(m). This indicates the wall deformation during aneurysm development was not elastic but plastic. The mean incremental elastic modulus H(m), an index of tissue stiffness, had a significant positive correlation with elastic modulus anisotropy index K(H). This indicates the aneurysmal wall got more anisotropic in vivo as it becomes stiffer.     

Observation of cavitation bubbles in monoleaflet mechanical heart valves

Recently, cavitation on the surface of mechanical heart valves (MHVs) has been studied as a cause of fractures occurring in implanted MHVs. In the present study, we investigated the mechanism of MHV cavitation associated with the Björk–Shiley valve and the Medtronic Hall valve in an electrohydraulic total artificial heart (EHTAH). The valves were mounted in the mitral position in the EHTAH. The valve closing motion, pressure drop measurements, and cavitation capture were employed to investigate the mechanisms for cavitation in the MHV. There are no differences in valve closing velocity between the two valves, and its value ranged from 0.53 to 1.96m/s. The magnitude of negative pressure increased with an increase in the heart rate, and the negative pressure in the Medtronic Hall valve was greater than that in the Björk–Shiley valve. Cavitation bubbles were concentrated at the edge of the valve stop; the major cause of these cavitation bubbles was determined to be the squeeze flow. The formation of cavitation bubbles depended on the valve closing velocity and the valve leaflet geometry. From the viewpoint of squeeze flow, the Björk–Shiley valve was less likely to cause blood cell damage than the Medtronic Hall valve in our EHTAH.     

Influence of anisotropy on the mechanical behaviour of bioprosthetic heart valves

Chemically modified pericardium is commonly used in the fabrication of bioprosthetic heart valves. This material exhibits non-linear elastic behaviour and, as for most other biological soft tissues, it is orthotropicin its extensibility. The influence of the natural orthotropy of pericardium on the mechanical behaviour of pericardial heart valves during the whole cardiac cycle has been studied, using the finiteelement method. A model of the leaflet of a bicuspid valve has been created, defining the material of the tissue as orthotropic non-linear elastic. Two preferential orthogonal orientations of the tissue have been analysed (axial and circumferential). The results show that even a small amount of orthotropy (an orthotropyindex of 1.5 has been used) can significantly affect the mechanical behaviour of the valve, and that an appropriate orientation of the fibres can contribute to optimizing the stress distribution in the leaflets.     

Influence of anisotropy on the mechanical behaviour of bioprosthetic heart valves

Chemically modified pericardium is commonly used in the fabrication of bioprosthetic heart valves. This material exhibits non-linear elastic behaviour and, as for most other biological soft tissues, it is orthotropic in its extensibility. The influence of the natural orthotropy of pericardium on the mechanical behaviour of pericardial heart valves during the whole cardiac cycle has been studied, using the finite element method. A model of the leaflet of a bicuspid valve has been created, defining the material of the tissue as orthotropic non-linear elastic. Two preferential orthogonal orientations of the tissue have been analysed (axial and circumferential). The results show that even a small amount of orthotropy (an orthotropy index of 1.5 has been used) can significantly affect the mechanical behaviour of the valve, and that an appropriate orientation of the fibres can contribute to optimizing the stress distribution in the leaflets.     

Design of heart valves: A review

Each of the major cardiac valves (two arterial and two atrioventricular) is made up of a fibrous annulus with a characteristic configuration, and cusps or leaflets comprising a layer of endocardium folded over a fibrous lamina. Each of the arterial valves (aortic and pulmonary) has an annulus shaped like a three-pronged coronet to which are attached three equal-sized semilunar cusps. The arterial wall beyond each cusp forms a pocket or sinus which is crucial in the efficient closure of these valves. The coronary arterial orifices in the aorta lie high in two of the sinuses or above them and are unaffected by valve action. Narrowing of the annulus is a significant component of closure of each cardiac valve, more so for the atrioventricular valves than the arterial. Despite their traditional terminology, the left and right atrioventricular valves (mitral and tricuspid) both possess more than three leaflets each. Closure of these valves is not dependent on the number of leaflets and it is easiest to regard leaflet tissue as a continuous veil or skirt tapering towards the ventricles, where it is tethered to papillary muscles by means of chordae tendineae. Closure of these valves is biphasic, an incomplete phase in late diastole and complete closure during ventricular systole. Movement of atrioventricular leaflet tissue is slight as it is held down by tension of the chordae tendineae. © 1993 Wiley-Liss, Inc.     

Cavitation phenomenon in monoleaflet mechanical heart valves with electrohydraulic total artificial heart

Recently, cavitation on the surface of mechanical heart valves has been studied as a cause of fractures occurring in implanted mechanical heart valves. In this study, to investigate the mechanism of cavitation bubbles associated with monoleaflet mitral valves in an electrohydraulic total artificial heart (EHTAH), and to select the best valves for our EHTAH system, we measured three parameters. First, an image was created of the cavitation bubbles using a high-speed camera. Second, pressure drop in the vicinity of the valve surface was measured using mini pressure sensor. Then, the closing of the valve was observed using a Laser displacement sensor. Most of the cavitation bubbles in the Medtronic Hall valve were observed at the edge of the valve stop. With the Omnicarbon valve, the cavitation bubbles were observed at the edge of the valve and on the inner side of the leaflet. On the other hand, cavitation bubbles were observed only on the inner side of the leaflet in Bj?rk-Shiley valve. Cavitation bubbles concentrated on the edge of the valve stop; the major cause of these cavitation bubbles was determined to be the squeeze flow. The formation of cavitation bubbles depended on the valve closing velocity and the valve leaflet geometry. From a viewpoint of squeeze flow, a low closing velocity and a small size of the valve stop could minimize cavitation.