变应变率下骨骼肌连续介质本构模型

目的 针对不同结构耦合肌肉主被动行为无法考虑肌肉组织连续介质力学特性的问题,提出运用被动与主动耦合在同一个本构方程的方法,构建骨骼肌连续介质超弹性主被动本构模型。方法 为标定被动本构模型参数,给出单轴拉伸实验方法 及条件,并通过理论推导,介绍利用试验数据求解被动模型参数的具体方法。为验证主动模型的有效性,以实例对模型进行验证。结果 模型预测曲线与实验输出应力拉伸比曲线具有较好的一致性,在相同应变下的情况下,被动应力和总应力最大误差仅为20、40 kPa。结论 该连续介质超弹性本构模型能较好模拟骨骼肌的主被动行为,从而有利于下一步人体肌肉的建模与仿真。     

基于超弹性模型的动脉血管数值计算

目的：实验研究表明。血管在周向与轴向两种单轴向拉伸作用下表现出不同的力学特性,本文通过对血管单轴拉伸的数值计算,给出分别适用于周向和轴向荷载的模拟方法。方法：基于超弹性本构模型对轴向和周向两种单轴拉伸作用下血管的应力一应变关系进行数值计算,并结合血管组织结构特点及模型适用范围对结果进行分析,同时通过数值计算对Holzapfel．Gasser-Ogden模型中的各向异性参数对结果的影响展开讨论。结果：计算结果显示单一使用各向同性超弹性应变势函数无法准确完整的模拟两种情况下的单轴拉伸实验,周向拉伸采用各向同性超弹性本构模型的数值结果较好的吻合实验,而轴向拉伸宜采用Holzapfel-Gasser-Ogden模型。Holzapfel。Gasser-Ogden模型中各向异性参数1描述血管中两组增强纤维主方向的分散程度,y值越大即纤维平均主方向与轴向加载方向夹角越小,在外荷载作用下越容易使得纤维旋转到荷载方向;参数K描述血管中每组增强纤维主方向上纤维的分散程度。K值越大,纤维在基体中分散越广泛,材料性子越接近纤维,宏观表现越硬。结论：本文基于超弹性本构模型对轴向和周向两种单轴拉伸作用下血管的应力应变关系进行数值计算,提出分别用多项式形式的各向同性超弹性本构模型数值计算周向荷载作用下应力应变关系、Holzapfel-Gasser-Ogden各向异性超弹性本构模型数值模拟轴向荷载下力学性质,数值结果与实验吻合较好,为心血管系统的数值模拟提供指导,对血管系统的力学机制和临床研究具有重要意义。     

食管支架疲劳性能的研究进展

植入病体的食管支架受其结构特征和服役环境的影响,易产生疲劳破坏,从而引发严重的并发症.目前对食管支架疲劳性能的研究内容涉及载荷谱、应力-应变关系、支架疲劳裂纹和疲劳寿命预测等方面;研究方法有理论分析、数值模拟和实验研究3种.对测定食管支架疲劳性能的各种分析方法及局限性进行详细地阐述和总结,并对食管支架后期的研究进行展望...     

离体狐眼外肌被动行为的超弹性分析

目的确定眼外肌的Ogden超弹性模型参数剪切模量(μ)和曲率(α),通过数值模拟为临床眼外肌手术提供理论依据。方法通过单轴拉伸实验测试离体狐眼外肌的被动行为,并用一阶Ogden超弹性模型及ABAQUS软件对其进行超弹性分析。结果实验结果表明,狐眼外肌的被动行为是非线性的。获得了相应的超弹性参数值,其中μ=(16.57±3.76)kPa,α=8.16±1.63。当应变大于6%时,一阶Ogden模型的计算结果与实验结果之间没有显著性差异(P0.05)。计算结果与数值模拟结果都能很好地拟合实验结果。结论所确定的超弹性参数可作为狐眼外肌数值建模的输入量。     

不同力学激励对骨重建数值模拟的影响

目的研究采用应变能密度、等效应力、等效应变3种不同力学激励对骨重建数值模拟结果的影响。方法建立股骨近端的二维有限元模型,基于力学稳态理论的重建控制方程并结合有限元法,分别用3种不同力学激励模拟股骨近端的内部结构及密度分布,并与CT数据计算得到的骨密度值进行定量分析比较。结果 3种力学激励模拟得到的重建结果均能反映出股骨近端的主要特征结构,但采用等效应力作为激励时得到的股骨密度曲线图的趋势和数值都与CT图像数据更为一致。结论在骨重建力学调控机制中,应力可能起主导作用。准确预测和模拟骨重建过程将对矫形外科、骨伤治疗、人工假体的优化和个体化设计等临床实践提供理论依据。     

模拟正常动脉壁残余应变和应力的数值研究

目的 探讨残余应变对动脉壁周向应力-应变分布的影响.方法 构造残余应变数值施加方法,对在不同生理血压下的动脉壁应力-应变进行数值模拟,并且模拟了残余应变使动脉圆环张开的情形.结果 动脉壁的周向应力水平明显降低;周向应变沿壁厚的分布趋于均匀;动脉圆环的张开角α大致为7°.结论 残余应变降低了载荷状态下的应力水平;残余应变直接改变了载荷状态下动脉壁沿径向的周向应变分布;残余应变的存在会使无载荷状态的动脉圆环发生张开;血管壁优化状态体现了均匀应变优化标准.     

骨骼肌介电行为的理论模型仿真

在 10 0 Hz～ 10 0 MHz范围内 ,应用椭圆壳介电理论模型 ,经过模拟仿真蛙骨骼肌细胞的介电行为 ,确定了蛙骨骼肌细胞的椭圆壳模型各相参数。为将来对骨骼肌疲劳、肌营养不良和肌肉萎缩等病症的模型分析奠定理论基础。     

离体猪气管异向力学特性及数值模拟研究

目的 研究猪气管和主支气管各向异性的力学性能,通过有限元数值模拟确定描述气管变形的本构模型。方法 将收集的猪气管沿轴向剖开并展成平面,以展开后的气管长度方向0°为起始角度,逆时针方向获得30°、60°、90°、120°、150°、180°共6个角度方向的标本。利用电子万能试验机分别对6个角度方向标本进行单轴拉伸试验,获得标本在不同角度方向的应力和应变。采用Mooney-Rivilin超弹性模型对实验数据进行非线性拟合,得到模型材料特性参数,建立气管和主支气管有限元模型,并进行拉伸数值模拟。结果 不同角度的气管标本拉伸呈现出不同的应力-应变;在气管中,30°、120°和150°方向样本的应力范围为1.0～1.5 MPa, 60°和90°方向标本的应力范围为0.5～1.0 MPa, 180°方向标本的应力范围为2.5～3.0 MPa;在主支气管中,30°、60°和150°方向标本的应力范围为0.8～1.0 MPa, 90°和180°方向标本的应力范围为1.4～1.8 MPa, 120°方向标本的应力范围为0.4～0.6 MPa,气管与主支气管有着明显的差异。经有限元模拟验证,Mooney-...     

单轴压缩下松质骨的应力率和蠕变性能北大核心

背景:松质骨是一种多孔、非均质、各向异性和具有黏弹性的结构,是骨的重要组成部分。它在负载传输和能量吸收方面起着十分重要的作用。所以对松质骨的力学行为进行研究具有重要意义。目的:探讨单轴压缩实验中应力率对松质骨性能的影响以及不同应力值下松质骨的蠕变行为。方法:以新鲜的猪股骨松质骨为实验材料,施加不同的应力率,至试样的压缩应变达到5%卸载;在松质骨表面施加恒定的应力水平,并保持7 200 s,以便观察其蠕变应变变化。结果与结论:(1)单轴压缩实验中,在同一应变条件下,随着应力率的增加,应力值、杨氏模量也增加;(2)在不同的加载率作用下,松质骨的压缩应力-应变曲线不重合,说明松质骨的压缩力学性能具有率相关性;(3)在蠕变实验中,蠕变应变随着压缩的应力的增加而增加,蠕变柔量随着应力的增加反而减少;(4)轴压缩和蠕变实验结果说明,应力率和恒定应力水平对松质骨的力学性能影响很大,以上结果可以为如何避免松质骨损伤提供参考依据。     

局部皮瓣的生物力学特性和三维有限元模拟分析

随着整形外科医学的发展,局部皮瓣在修复皮肤缺损中的应用越来越广泛,但皮瓣的设计主要依赖于医生的经验,存在盲目性.为寻求既能指导皮瓣设计又能真实模拟皮瓣转移效果的方法,需要进行相应的生物力学研究和有限元力学分析.首先通过对局部皮瓣进行实验测试,得到局部皮瓣的生物力学特性;再根据实验得到的结果对局部推进皮瓣进行三维有限元模拟分析,得到在外载荷作用下,皮瓣和其本体组织的变形及相应的应力-应变分布情况;同时通过改变皮瓣尺寸大小模拟得到局部皮瓣设计的最佳尺寸.本模型结果能够为局部皮瓣的生物力学特性研究及其移植的数值模拟提供一定的参考.     

妊娠及分娩对盆底肌力的影响

目的比较妊娠及分娩后妇女和正常妇女的盆底肌力,了解妊娠及分娩对盆底肌力的短期影响。方法将183例在本院就诊的孕产妇分为顺产组和剖宫产组,使用盆底肌电生理仪分别检测其产前及产后盆底肌肌力,并与166例正常妇女进行评估及比较。结果妊娠组盆底肌力与正常组比较明显降低,差异有统计学意义（P〈0.05）;妊娠组和正常组中的Ⅰ类与Ⅱ类肌纤维肌力均降低,但差异无统计学意义（P〉0.05）;产后6～8周顺产组盆底肌力较剖宫产组肌力明显降低,差异有统计学意义（P〈0.05）;产后12～14周顺产组盆底肌力与剖宫产组盆底肌力均降低,差异无统计学意义（P〉0.05）。结论顺产及选择性剖宫产对盆底肌肌力的影响在产后3个月无明显差异。     

胸锁乳突肌亚部肌构筑、肌梭和神经入肌点定位

目的:为胸锁乳突肌亚部的临床应用提供形态学依据。方法:肌构筑法,组织学HE染色和体视学法。结果:(1)胸骨头亚部的肌重与生理横切面积分别是锁骨头两亚部之和的1.39倍与1.33倍;锁骨头深亚部的肌纤维长仅为胸骨头亚部肌纤维长的82%。(2)胸骨头亚部和锁骨头浅亚部的肌梭密度显著小于锁骨头深亚部。(3)副神经胸锁乳突肌支绕锁骨头深亚部后缘(占65%)入肌时距乳突尖(4.39±0.42)cm,而穿锁骨头深亚部(占35%)入肌时距乳突尖(3.96±0.34)cm。结论:胸骨头亚部是胸锁乳突肌肌力的主要提供者。锁骨头深亚部更多参与维持头部姿势。     

Electrogenesis of muscle fibers of the rat masseter muscle

It was shown by intracellular recording of resting membrane potentials (RMP) and action potentials that the superficial layers of the rat masseter muscle contain chiefly fibers with a high MPP and small overshoot, whereas the deep layers contain mainly fibers with a low MPP but a high overshoot. The excitability of the cytoplasmic membrane of muscle fibers with different MPP levels was found to be similar with respect to its electrical parameters. It is suggested that the rat masseter muscle contains a high proportion of fast phasic fibers in its superficial layers and slow phasic fibers in its deep layers.Department of Pathological Physiology, N. A. Semashko Moscow Medical Stomatologic Institute. (Presented by A. D. Ado.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 88, No. 9, pp. 265–267, September, 1979.     

Effect of single and periodic contusion on the rat soleus muscle at different stages of regeneration

This work analyzed the rat soleus muscle after single and recurrent contusions at different stages of regeneration. A noninvasive contusion was produced by a type of drop‐mass equipment. The posterior region of the right hind limb received a trauma and both right and left soleus muscles were analyzed 1, 4, and 6 days after a single contusion (1×), and 6 and 30 days after periodic contusions (10×, one trauma per week for 10 weeks). Single contusion: there was no significant difference between right and left soleus muscle weight. All animals showed abundant signs of acute damage in the right soleus. AChE activity was identified in regeneration segments of the right soleus. Periodic contusions: there was an increase in the right soleus muscle weight (α = 5%) only in the animals evaluated 6 days after periodic contusions. The right soleus muscle showed a high incidence of chronic signs of damage, such as split fibers and a centralized nucleus, which predominated when compared with the acute signs. Right soleus muscles showed split fibers with AChE activity in both the proximal and middle regions. There was no difference in the incidence of muscle fiber types (I, II, and IIC) between right and left soleus muscles after periodic contusions. Skeletal muscle contusion is common in humans, especially in sport activities, where repetitive traumas are also frequent. The results of this work indicate that despite the regeneration process there is an important change in the morphological aspect of regenerated muscle fibers, which possibly affect muscle performance. Anat Rec 254:281–287, 1999. © 1999 Wiley‐Liss, Inc.     

The human temporalis muscle: Superficial,deep, and zygomatic parts comprise one structural unit

The structure of the temporalis muscle was examined in detail from cadaveric specimens (32 specimens from 16 subjects: 5 males, average age 80.6 years; 11 females, average age 88.6 years) and Computerized Tomography (CT) and T1‐weighted Magnetic Resonance (MR) images from normal clinical patients (10 females: average age 45.0 years). Three parts of the muscle were clearly delineated in all cadaveric specimens: (1) the classically recognized superficial part, (2) a zygomatic part, and (3) a complex deep part. In one female specimen, the superficial temporalis demonstrated extensive insertions into the zygomatic process and temporomandibular joint. The zygomatic temporalis originates from the zygomatic arch to insert into the superficial part of the temporalis as it inserts into the lateral surface of the coronoid process. In all specimens, the deep temporalis contained muscle bundles that originated from various crests along the anterior surface of the temporal fossa and inserted into the internal aspect of the coronoid process and retromolar triangle, interdigitating with the buccinator, mylohyoid, and superior constrictor muscles. The confluence of muscle fibers into the buccinator muscle was confirmed in all CT/MRI images. The deep and zygomatic parts described were regarded as accessory muscle bellies previously, but are demonstrably part of the temporalis muscle as a whole. Clin. Anat. 22:655–664, 2009. © 2009 Wiley‐Liss, Inc.     

Possible effects of fatigue on muscle efficiency

The efficiency of energy transduction is defined as the ratio of the work done by a muscle to the free energy change of the chemical processes driving contraction. Two examples of the experimental measurement of muscle efficiency are: (1) the classical method of Hill which measures the value during a steady state of shortening, (2) measuring the overall efficiency during a complete cycle of a sinusoidal process, which comes closer to the situation during natural locomotion. The reasons why fatigue might lower efficiency are the following. (1) The reduction in PCr concentration and increase in Pi and Cr concentration which are characteristic of fatigued muscle, reduce the free energy of PCr splitting. This will reduce the efficiency of the recovery process. It is not known whether the efficiency of the initial process is increased to compensate. (2) There is a general conflict between efficiency and power output when motor units are chosen for a task or when the timing of activation is decided. During fatigue more powerful units have to be used to achieve a task which is no longer within the scope of less powerful units. (3) The slowing of relaxation that is sometimes found with fatigue may make it impossible to achieve the short periods of activity required for optimum efficiency during rapid cyclical movements. A reason why fatigue might increase efficiency is that muscles are thought to be more efficient energy converters when not fully activated than when fully active. Full activation is often not achieved in muscle which is considerably fatigued. Available observations do not allow us to find where the balance between these factors lies. The conclusion is thus that experiments of both the types discussed here should be performed.     

Muscle fibre types in the suprahyoid muscles of the rat

Five muscle fibre types (I, IIc, IIa, IIx and IIb) were found in the suprahyoid muscles (mylohyoid, geniohyoid, and the anterior and posterior bellies of the digastric) of the rat using immuno and enzyme histochemical techniques. More than 90% of fibres in the muscles examined were fast contracting fibres (types IIa, IIx and IIb). The geniohyoid and the anterior belly of the digastric had the greatest number of IIb fibres, whilst the mylohyoid was almost exclusively formed by aerobic fibres. The posterior belly of the digastric contained a greater percentage of aerobic fibres (83.4%) than the anterior belly (67.8%). With the exception of the geniohyoid, the percentage of type I and IIc fibres, which have slow myosin heavy chain (MHCβ), was relatively high and greater than has been previously reported in the jaw‐closing muscles of the rat, such as the superficial masseter. The geniohyoid and mylohyoid exhibited a mosaic fibre type distribution, without any apparent regionalisation, although in the later MHCβ‐containing fibres (types I and IIc) were primarily located in the rostral 2/3 region. In contrast, the anterior and posterior bellies of the digastric revealed a clear regionalisation. In the anterior belly of the digastric 2 regions were observed: both a central region, which was almost exclusively formed by aerobic fibres and where all of the type I and IIc fibres were located, and a peripheral region, where type IIb fibres predominated. The posterior belly of the digastric showed a deep aerobic region which was greater in size and where type I and IIc fibres were confined, and a superficial region, where primarily type IIx and IIb fibres were observed.     

Muscle fibre types in the suprahyoid muscles of the rat

Five muscle fibre types (I, IIc, IIa, IIx and IIb) were found in the suprahyoid muscles (mylohyoid, geniohyoid, and the anterior and posterior bellies of the digastric) of the rat using immuno and enzyme histochemical techniques. More than 90% of fibres in the muscles examined were fast contracting fibres (types IIa, IIx and IIb). The geniohyoid and the anterior belly of the digastric had the greatest number of IIb fibres, whilst the mylohyoid was almost exclusively formed by aerobic fibres. The posterior belly of the digastric contained a greater percentage of aerobic fibres (83.4%) than the anterior belly (67.8%). With the exception of the geniohyoid, the percentage of type I and IIc fibres, which have slow myosin heavy chain (MHCβ), was relatively high and greater than has been previously reported in the jaw-closing muscles of the rat, such as the superficial masseter. The geniohyoid and mylohyoid exhibited a mosaic fibre type distribution, without any apparent regionalisation, although in the later MHCβ-containing fibres (types I and IIc) were primarily located in the rostral 2/3 region. In contrast, the anterior and posterior bellies of the digastric revealed a clear regionalisation. In the anterior belly of the digastric 2 regions were observed: both a central region, which was almost exclusively formed by aerobic fibres and where all of the type I and IIc fibres were located, and a peripheral region, where type IIb fibres predominated. The posterior belly of the digastric showed a deep aerobic region which was greater in size and where type I and IIc fibres were confined, and a superficial region, where primarily type IIx and IIb fibres were observed.     

The importance of frequency and amount of electrical stimulation for contractile properties of denervated rat muscles

Soleus (SOL) and extensor digitorum longus (EDL) muscles were denervated and directly stimulated for 23–69 days through implanted electrodes employing three different patterns. The stimulation was delivered in impulse trains where the pulse frequency differed (20, 75, and 150 Hz), while the train duration (0.3 s) and train repetition rate (1 min^-1) were identical. Consequently, the number of pulses varied such that higher frequency was combined with a higher amount of stimulation. In both SOL and EDL the high-frequency pattern resulted in shorter twitch time-to-peak, greater post-tetanic potentiation, and greater tetanic force than the low frequency. Isotonic shortening velocity was increased to the same extent by all the patterns in SOL whereas in EDL fast intrinsic shortening velocity was maintained by the low-frequency pattern while it was decreased by the high-frequency pattern. We attribute this unexpected effect on the EDL to the larger number of pulses in the high-frequency pattern. By combining the present findings with previous data on directly stimulated rat muscles we conclude: in SOL the twitch duration is influenced by both the frequency and the amount of impulse activity, higher frequencies and smaller amounts leading to faster twitches. The EDL twitch duration is similarly dependent on the amount of activity, but the role of frequency is more unclear. In both SOL and EDL the isotonic shortening velocity is reduced by increasing amounts of activity and there is no evidence that impulse frequency plays a role. In EDL force output is strongly influenced by the impulse frequency, low frequencies resulting in low force outputs irrespective of the amount of activity.