Fontan术血流动力学非牛顿特性研究

目的 分析计算模拟中血液非牛顿特性对Fontan术后血流动力学的影响。方法 基于Fontan术后患者个体化三维血管模型,临床超声实测数据作为边界条件,分别选取常用的牛顿流体模型、非牛顿流体模型中的Casson模型与Carreau模型进行血流动力学模拟,计算血流分配比、能量损失、壁面切应力、非牛顿重要性系数等血流动力学参数,比较不同流体模型之间血流动力学参数差异。结果 流体模型对血流分配比影响小,非牛顿流体模型的能量损失较牛顿流体模型高,其中Casson模型最高。在下腔静脉中有明显回流、血流扰乱区域,并伴有低壁面切应力分布。在低流速时,牛顿流体模型下腔静脉血流扰乱更明显。非牛顿重要性系数显示在下腔静脉的非牛顿特性显著。结论 非牛顿特性在下腔静脉的低速回流区域影响显著,模拟患者个体化的Fontan血流动力学时应考虑血液的非牛顿特性。     

基于CT重建颅内动脉瘤非稳态血流分析

选择Navier-Stokes方程作为颅内动脉瘤三维重建模型的不可压缩血液流动的数学模型,使用计算流体力学(Computational fluid dynamics,CFD)的方法对颅内动脉瘤模型进行非牛顿(non-Newtonian fluid)模型的非定常流的数值模拟。计算3个心跳脉动周期的数值,认为第三个心跳脉动周期为稳定周期并选择第三个周期为研究对象。分析了稳定周期内不同时刻血液动力学特性参数分布情况对颅内动脉瘤的形成、生长和破裂的影响。并将此结果与牛顿(Newtonian fluid)血液模型的流线、壁面剪切力、壁面压力分布特性进行对比。结果显示,非牛顿流体血液模型比牛顿血液模型更有可信度,比较符合真实血液的流动特性,在血液流动的心跳脉动周期内,非牛顿流体的(速度、压力、壁面剪切力等)分布更加平滑。过高的壁面剪切力会直接造成动脉瘤区域处破裂,过低的壁面剪切力会使血液的营养成为和代谢物遗留在血管区域导致血液粥样化的形成。     

人体主动脉弓内非牛顿血液流动数值模拟分析

目的:通过基于三维重构技术对正常人体主动脉弓内的血流进行非牛顿血液模型数值模拟,分析血流动力学参数与血管疾病的关系,并与牛顿血液模型获得的壁面切应力(WSS)参数进行比较。方法:对临床获得的CT医学图像据进行处理重构,并转化为可用于模拟计算的三维模型。应用计算流体力学(CFD)方法进行数值模拟计算。结果:获得了正常人体主动脉弓内血流在心动周期内不同时刻的血流动力学参数。结论:主动脉弓内复杂的血流情况与血管疾病的产生与发展存在一定联系,并且非牛顿血液模型更为适合进行深入细致的主动脉弓内血液低速区域的瞬态模拟分析。     

红细胞非惯性升力对血液流动的影响

目的为准确模拟血流,研究红细胞变形性对血液流动的影响。方法基于血液流变特性和红细胞力学特性分析,对现有血液两相流流动模型进行改进,改进模型中考虑了易变形红细胞受剪切流场或血管壁面作用而产生的非惯性升力的影响。利用改进模型对多个不同直径血管内的血液流动进行模拟。结果由红细胞所受非惯性升力导致的径向运动对血管内红细胞体积分数、运动速度分布有明显影响;当血管直径为0.1~3.0 mm时,用改进模型得到的血液相对黏度的模拟值与测量值接近。结论非惯性升力是血流呈现Fahraeus-Lindqvist效应的主要原因之一。考虑非惯性升力的改进模型可以准确模拟血液流动,为循环系统诊疗机制和细胞分选等过程的模拟提供更为准确的方法。     

红细胞非惯性升力对血液流动的影响

目的 为准确模拟血流,研究红细胞变形性对血液流动的影响。方法 基于血液流变特性和红细胞力学特性分析,对现有血液两相流流动模型进行改进,改进模型中考虑了易变形红细胞受剪切流场或血管壁面作用而产生的非惯性升力的影响。利用改进模型对多个不同直径血管内的血液流动进行模拟。结果 由红细胞所受非惯性升力导致的径向运动对血管内红细胞体积分数、运动速度分布有明显影响;当血管直径为0.1~3.0 mm时,用改进模型得到的血液相对黏度的模拟值与测量值接近。结论 非惯性升力是血流呈现Fahraeus-Lindqvist效应的主要原因之一。考虑非惯性升力的改进模型可以准确模拟血液流动,为循环系统诊疗机制和细胞分选等过程的模拟提供更为准确的方法。     

红细胞非惯性升力对血液流动的影响

目的 为准确模拟血流,研究红细胞变形性对血液流动的影响。方法 基于血液流变特性和红细胞力学特性分析,对现有血液两相流流动模型进行改进,改进模型中考虑了易变形红细胞受剪切流场或血管壁面作用而产生的非惯性升力的影响。利用改进模型对多个不同直径血管内的血液流动进行模拟。结果 由红细胞所受非惯性升力导致的径向运动对血管内红细胞体积分数、运动速度分布有明显影响;当血管直径为0.1~3.0 mm时,用改进模型得到的血液相对黏度的模拟值与测量值接近。结论 非惯性升力是血流呈现Fahraeus-Lindqvist效应的主要原因之一。考虑非惯性升力的改进模型可以准确模拟血液流动,为循环系统诊疗机制和细胞分选等过程的模拟提供更为准确的方法。     

基于CT成像的冠状动脉狭窄血流动力学分析

目的基于心血管患者的冠状动脉血管模型,通过计算和分析血管内血液流动的各个动力学参数,研究冠状动脉狭窄对心血管疾病的影响。方法基于心血管患者冠状动脉造影的CT图像,用Mimics软件对左冠状动脉及其主要分支进行三维重建;利用有限元方法,对冠状动脉模型进行流体力学计算。假设血管壁不发生变形,血液为不可压缩牛顿流体,在非定常速度进口的条件下计算各血流动力学参数的变化规律。结果冠状动脉狭窄(75%面积狭窄)对下游的壁面剪切力和振荡剪切指数影响较大,并且会导致涡流和二次流的产生;在模型中装上血管支架,使得血管狭窄消失之后,涡流和二次流基本消失,而且振荡剪切指数明显变小。结论冠状动脉狭窄对血流动力学参数有重大影响,可能是引起动脉粥样硬化的原因;通过CT图像重建方法,可以诊断狭窄发生的地点以及严重性,对心血管疾病的治疗有一定的辅助作用。     

血管支架对颅内动脉瘤血液动力学的数值模拟

血管支架作为治疗颅内动脉瘤的新方法被广泛运用到临床中,而且越来越普遍。但由于某些支架植入后不能满足力学要求或对瘤内血液动力学无明显影响,反而更易形成血栓,造成动脉瘤破裂。本研究首先通过结构静力学分析比较矩形截面网格状支架和网丝编织成的圆形截面螺旋形支架的弯曲变形能力及扭转变形能力;然后将网格支架植入实际脑动脉瘤模型,进行流－固耦合模拟仿真,分析血流速度、壁面压力及壁面剪切力变化。结果表明：两种支架能够在不损失径向支撑力的情况下,提供良好的轴向顺应性,且网格状支架的变形能力高于螺旋状支架;支架植入后血液动力学各项指标明显降低。血管支架对颅内动脉瘤血液动力学有很大影响,可为临床治疗动脉瘤提供理论依据。     

颅内动脉瘤夹闭手术的血流动力学数值分析

本文利用计算流体力学(CFD)方法对颅内动脉瘤夹闭手术前后血液流场进行三维数值模拟,根据血流动力学对手术方案的可行性进行预估。采用逆向工程软件Mimics对临床CT图像进行三维数字化重构,结合相关脉动血流量,模拟心动周期不同时刻的血流动力学细节。通过计算得到了模型手术前后在心动周期不同时刻的速度场、壁面剪切应力场、压力场的分布特征,对比分析手术前后分叉处的血流速度、壁面剪切应力、壁面压力变化,结果显示术后的血流速度与壁面剪切力显著提高,而壁面压强则明显降低。     

脾静脉血栓对血流动力学影响的分析及计算流体力学模拟

本文的目的是分析脾静脉血栓(SVT)对肝门静脉系统血流动力学参数的影响。根据某肝门静脉高压症患者的CT图像和商业软件MIMICS重建了其真实的肝门静脉系统模型,采用彩色多普勒超声法测出了肝门静脉系统内的血流速度,作为模拟的入口边界条件,应用计算流体力学(CFD)方法模拟了肝门静脉系统内血流动力学参数的变化并分析了对生理过程的影响。结果显示:SVT会对肝门静脉系统的血流动力学参数造成严重影响,血液流经SVT时压强降低、流速和壁面剪切力增加,血液流动的阻力增加,门静脉主干内血流速度减缓、压力梯度减小、壁面剪切力的分布更加均匀。SVT会导致对肝脏的供血能力下降,在血栓的周围和门静脉主干内形成新血栓的可能性增加。     

压力和尾吊对大鼠骨骼肌生长的影响

目的建立尾吊和压力大鼠实验模型,比较压力与尾吊对大鼠骨骼肌生长的不同影响。方法 36只雄性SD大鼠随机分为3组:正常对照组、尾吊组和压力组,每组分两个阶段(7、14 d)进行观察。实验结束后测量比目鱼肌与趾长伸肌的湿重体重比、肌纤维横截面积和直径,以及血清中IGF-1浓度。结果压力作用7 d与尾吊7 d后,比目鱼肌湿重体重比、肌纤维横截面积、肌纤维直径都较对照组显著减少(P<0.05);压力组分别减少23.52%、14.26%、13.47%(P<0.05),尾吊组分别减少23.52%、33.07%、25.09%(P<0.05)。压力作用14 d后,各指标分别减少20.51%、-10.49%、-5.73%,都低于7 d压力组的减少量(P<0.05);而尾吊14 d后,比目鱼肌湿重体重比减少了46.15%,显著高于7 d尾吊组的减少量。血清IGF-1浓度和趾长伸肌的改变在压力、尾吊组间没有显著性差异。结论压力对比目鱼肌生长影响的过程不同于尾吊。压力作用初期是以炎症反应为主的组织损伤过程,待肌细胞适应压力环境后,可能产生一定的功能适应性生长。因此,在临床上无论假肢接受腔设计还是康复训练,考虑接受腔压力对内部肌肉损伤的影响,将有助于对残端肌肉组织的保护。     

Influence of Ageing on the Fatigability of Isolated Mouse Skeletal Muscles from Mature and Aged Mice

We investigated the influence of ageing on the fatiguing characteristics of the mouse extensor digitorum longus (EDL) muscle as compared to those of the soleus muscle. Fatigue was produced by an intermittent stimulation protocol. We report for mature and aged animals the effects of fatigue on force produced during stimulation patterns that in non-fatigued muscle gave maximum force (T(max), high frequency stimulation) and approximately half-maximum force (1/2T(max), low frequency stimulation). In 15-month-old (mature) mice, fatiguing stimulation decreased T(max) in EDL and soleus muscle to 10.3 +/- 1.0 % and 33.4 +/- 3.0 % of control, respectively. In 30-month-old (aged) mice, the decrease in T(max) in EDL and soleus was statistically equal to that of the younger animals. Fatiguing stimulation decreased 1/2T(max) in EDL and soleus from 15-month-old animals to 22.5 +/- 2.9 % and 45.7 +/- 0.3 % of control, respectively. In 30-month-old animals, the 1/2T(max) in EDL and soleus muscle decreased to 18.2 +/- 1.3 % and 35.0 +/- 3.6 % of control, respectively. Under all conditions, the soleus fatigued significantly less. Contractile recovery from fatiguing stimulation was complete for the soleus in both age groups after 30 min, but incomplete for the EDL. The 1/2T(max)/T(max) ratio significantly increased in EDL and soleus muscle from 15-month-old animals after fatiguing stimulation. This increase was less significant in EDL, and absent in soleus muscle, from 30-month-old animals. These results indicate that fatiguing stimulation induces a leftward shift in the force-frequency relationship in the young animals; this shift is either significantly less (EDL) or absent (soleus) in the older animals. We speculate that the leftward shift of the force-frequency relationship may reflect a protective mechanism in younger animals against some of the damaging effects of fatiguing stimulation (i.e. oxidative stress).     

Vinculin and meta-vinculin in fast and slow rat skeletal muscle before and after hindlimb suspension

The role of vinculin and meta-vinculin, the major components of costameres, was explored by analysing quantitatively the expression of these proteins in a slow-twitch (soleus) and in a fast-twitch (extensor digitorum longus, EDL) skeletal muscle under control conditions and after a reduced functional demand. Meta-vinculin, previously observed essentially in smooth and cardiac muscle, was also present in EDL, in the same amount as vinculin. The soleus contained exclusively vinculin, the amount of which exceeded the sum of vinculin and meta-vinculin in the EDL. After 3 weeks hypokinesia (hindlimb suspension), the vinculin content of the soleus was unchanged but after 6 weeks it had increased by 20% and, moreover, there was de novo expression of meta-vinculin. In EDL, the changes in vinculin and meta-vinculin after 3 weeks were opposite (+26% and -20% respectively). After 6 weeks the increase in vinculin was even larger (+33%) while meta-vinculin had returned to control levels. The marked expression of meta-vinculin in the atrophied soleus suggests a shift in the soleus towards the fast muscle profile with respect to cytoskeletal characteristics. On the other hand, the ability of slow muscle to maintain posture and to generate force for long periods would necessitate cytoskeletal reinforcement.     

Effects of long-term cold exposure on contractile muscles of rats

The effects of 20-week cold exposure on contractile properties of soleus and extensor digitorum longus (EDL) muscles and plasma hormone levels were studied in rats. Twenty male Wistar rats (5 week old) were randomly divided into 2 groups (n = 10 each): cage-control and cold-exposed. The rats in the cold-exposed group were immersed in shoulder-deep water (approximately 18 degrees C) for 1 h/d, 5 d/week, for 20 weeks. The temperature and humidity of the animal room with 12:12 h light-dark cycle were maintained at approximately 23 degrees C and 55%, respectively. The rats were pair-fed powdered diets. The electromyogram activities in soleus and EDL were elevated by cold exposure. The body weight and absolute soleus wet weight of the cold-exposed group were significantly less than controls at the end of experiment. The one-half relaxation time and contraction time of EDL were significantly longer in the cold-exposed group than in the control group. The rate of twitch tension development, normalized by the maximum twitch tension, in EDL of the cold-exposed group was less than in the control group. Further, the fatigue resistance of EDL, but not of soleus, in response to train stimulation at 10 Hz was improved by cold exposure. The plasma levels of thyroid hormones, 3,5,3'-triiodothyronine and thyroxine, were significantly greater in cold-exposed group. Similar changes were also seen in the plasma catecholamine levels in the cold-exposed group (p > 0.05). It is suggested that long-term cold exposure causes a shift of the contractile properties of fast-twitch EDL muscle toward the slow-twitch type. The results also indicated that the characteristics of muscles responded more strongly to an increased activity level than to the elevation of plasma hormones.     

Cross-innervation of fast and slow-twitch muscles by motor axons of the sural nerve in the mouse

The extensor digitorum longus (EDL) or soleus muscles of adult mice were cross-innervated by the sural nerve (SN) and deprived of their original innervation. The number and sizes of motor units and the location of endplates in these muscles were studied 1.5 to 16 months later. In the EDL muscle, the SN cross-innervated the original endplates. Very few ectopic endplates were seen, even when the nerve was implanted well outside of the original endplate area. Only 3% of the fibres were polyneuronally innervated. In the soleus muscle, however, the SN formed large numbers of ectopic endplates whether the nerve was implanted in the original endplate zone or outside of it. In addition, 20% of the muscle fibres were polyneuronally innervated. The SN cross-innervated both EDL and soleus muscles completely. There was no preference for a particular group of the SN motoneurones since all the cross-innervated muscles were innervated by all SN motor axons and the motor unit sizes of the SN were similar in the cross-innervated EDL and soleus muscles. It is concluded that intrinsic properties of a muscle determine the ability to form ectopic synapses. The distribution of the motor unit sizes is determined by the particular pool of motoneurones which innervates the muscle.     

Miniature end-plate potentials and sensitivity to acetylcholine in the fast and slow limb muscles of hibernating golden hamsters

Summary During hibernation reduction of frequency of the miniature end-plate potential (m.e.p.p.) was observed. This parameter was reduced in the extensor digitorum longus (EDL) muscle to 16% and in the soleus muscle to 7% of values found in awake animals. The ACh-sensitive area of the individual muscle fibres in both types of muscle increased about three times during hibernation.     

Correlation between shortening velocity,force—velocity relation and histochemical fibre-type composition in rat muscles

Summary Isometric and isotonic contractions of three muscles in the rat hind leg (soleus, extensor digitorum longus (EDL) and peroneus longus (PL)) were recordedin situ at 35° C and with nerve stimulation. Additionally, the histochemical muscle fibre-type composition of the three muscles was determined by the method of Guth and Samaha (1970). The data obtained from soleus and EDL muscles were similar to those reported in previous studies. On the basis of twitch contraction time, rate of rise of tetanic tension and maximum shortening velocity, the contraction speed of EDL was 2–3 times higher than in soleus. In the PL muscle, the twitch contraction time, rate of tension rise and shortening velocity were 17 ms, 30Po/s and 12 muscle fibre lengths/s, respectively; the data showed that the contraction speed of PL muscle was intermediate between that of the soleus and EDL muscles. In the case of soleus, more than 75% of the cross-sectional area was occupied by type 1 (slow) fibres; in both EDL and PL muscles more than 90% of the area was occupied by type 2 (fast fibres). However, the two fast muscles (EDL and PL) had different proportions of type 2B fibres; the area occupied by the type 2B fibre complement was less than 5% in PL, whereas it was around 70% in EDL muscle. The differences in shortening velocity and force—velocity relation among the three muscles could be explained on the basis of their respective muscle fibre-type compositions.     

Relationship between skin blood flow and sweating rate in prepubertal boys and young men

We have examined the effect of male sexual hormones on the regeneration of skeletal muscles. Degeneration/regeneration of the left soleus and extensor digitorum longus muscles (EDL) of Wistar male rats was induced by an injection of snake venom (2 microg, Notechis scutatus scutatus). During the muscle regeneration (25 days), rats were treated with either oil (CON), nandrolone (NAN), NAN combined with exercise (NAN + EXE) or were castrated (CAS). Muscle growth and myosin heavy chain (MyHC) isoform content of regenerating muscles were studied. Castration altered the concentrations of MyHC in venom-treated EDL (P < 0.01) and soleus (P < 0.05). NAN increased the mass (P < 0.01) of regenerating soleus and decreased the relative amount of fast MyHC protein (% of total, P < 0.05). The effect of NAN + EXE on the fast MyHC proteins of venom-treated soleus was opposite (P < 0.05). NAN and NAN + EXE were without effect on the regenerating EDL (P > 0.05). In conclusion, it is possible that male sexual hormones play a role in the growth (synthesis of contractile proteins) of regenerating muscles in rat. In addition, contrary to NAN + EXE, NAN could be beneficial to soleus regeneration.     

The Effects of Dietary Creatine Supplements on the Contractile Properties of Rat Soleus and Extensor Digitorum Longus Muscles

Daily creatine supplements (0.258 g kg(-1) ) were administered to adult male Wistar rats (n = 7) in the drinking water. Age matched rats (n = 6) acted as controls. After 5-6 days, contractile properties were examined in soleus and extensor digitorum longus (EDL) muscle strips in vitro at 30 degrees C. In soleus muscles, creatine supplements decreased the half-relaxation time of the isometric twitch from 53.6 +/- 4.3 ms in control muscles to 48.4 +/- 5.5 ms but had no effect on twitch or tetanic tension or on twitch contraction time. In EDL muscles twitch tension, tetanic tension, twitch contraction and half-relaxation times were all unaffected by creatine supplements. Creatine supplements increased the fatigue resistance of the soleus muscles but had no effect on that of the EDL muscles. After a 5 min low-frequency fatigue test, tension (expressed as a percentage of initial tension) was 56 +/- 3 % in control soleus muscles, whereas that in the creatine-supplemented muscles was 78 +/- 6 % (P < 0.01). In the EDL muscles, the corresponding values were 40 +/- 2 % and 41 +/- 9 %, respectively. The force potentiation which occurred in the EDL muscles during the initial 20-30 s of the fatigue test was 170 +/- 10 % of initial tension in the control muscles 24 s after the initial stimulus train but was reduced (P < 0.01) to 130 +/- 20 % in the creatine-supplemented muscles. In conclusion, soleus muscle endurance was increased by creatine supplements. EDL endurance was unaffected but force potentiation during repetitive stimulation was decreased. Experimental Physiology (2001) 86.2, 185-190.     

Adrenaline-mediated glycogenolysis in different skeletal muscle fibre types in the anaesthetized rat

The effect of adrenaline infusion on glycogen breakdown in different muscle fibres types in resting extensor digitorum longus (EDL) and soleus was investigated with histochemical methods. During adrenaline infusion the glycogen content in type IIB and type IIA fibres in EDL, as measured in PAS-stained sections, decreased 24.5% and 11.5% respectively. The glycogen content in type I fibres in EDL and in type I, type IIA and T-fibres in soleus did not change during adrenaline infusion. The present study shows that adrenaline infusion has different effects on glycogen breakdown in the different fibre types in EDL and a different effect on type IIA fibres in EDL and soleus. So far, the reason for these differences is unknown.