缓变狭窄幅度径向振荡血管内血流动力学

本文研究缓变狭窄幅度径向振荡血管内血液脉动流。求解线化的Ｎａｖｉｅｒ－Ｓｔ－ｏｋｅｓ血流方程和管壁方程,得出速度剖面和管壁切庆力。结果表明狭窄参数的变化对流动有很大影响。在狭窄区仙,速度变化和狭窄程度及狭窄幅度振荡频率的耦合作用有关。当狭窄幅度振荡频率接近血流基频时,血液速度变化较大,并且狭窄区最大壁切应力达到峰值。     

局部缓慢狭窄幅度径向振荡弹性直圆管内脉动血流的压强和压强梯度分析

文研究了脉动血流通过局部缓慢狭窄幅度径向振荡的弹性直圆管时压强和压强梯度的分布特征。分析表明在局部狭窄幅度径向振荡的弹性管中压强及压强梯度分布与在直圆管或局部狭窄静止的情况下明显不同、而且它与Ｗｏｒｍｅｒｓｌｅｙ数、管壁特征、及狭窄幅度振荡频率有密切关系。此项研究对进一步认识分析某些病理和治疗手法等有重要意义。     

局部缓慢狭窄幅度径向振荡弹性直圆管内脉动血流的压强和压强梯度 …

本文研究了脉动血流通过局部缓慢性狭窄幅度径向振荡的弹性直圆管时压强和压强梯度的分布特征。     

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。     

颈内动脉狭窄对大脑动脉环血流动力学影响的有限元分析

目的　大脑动脉环血流变化常与颈内动脉狭窄相联系。本研究试用有限元方法来研究颈内动脉狭窄对大脑动脉环内的血流动力学影响,以此探讨动脉环内交通动脉代偿机制。 方法　采用MIMICS10.0软件及ANSYS14.5软件,建立了一个包括血管和血流在内的流固耦合的三维有限元模型,模拟了健康模型（颈内动脉无狭窄）及各种病理模型（颈内动脉狭窄率分别为15%、 30%、 45%, 60%、 70%、 80% 和90%）。通过监测前交通动脉和后交通动脉内的血流变化,掌握动脉环内血流动力学的改变。 结果　包括血管和血流的流固耦合有限元模型首次得以建立。随着狭窄率增加,前交通动脉与患侧后交通动脉内血流逐渐增多,狭窄率达到90%后,两条血管内血流减少;健侧后交通动脉内血流也全程逐渐增加,但量极小,基本无明显变化。 结论　通过以上的结果可见,随着颈内动脉狭窄程度的加重,大脑动脉环通过前交通动脉与患侧后交通动脉开放达到代偿,狭窄率达到90%后代偿失效,从机制上印证了颈内动脉狭窄与颅内缺血性病变相关。     

支架内再狭窄的生物力学研究进展

支架介入已成为治疗心脑血管狭窄最有效的方式之一,但术后发生支架内再狭窄的问题却不可忽视。支架内再狭窄的发生,不仅与支架-血管间柔顺性失配以及支架对血管的机械性支撑引起的应力有关,而且与支架置入后血管内血流动力学环境变化引起的内膜增生有关。回顾了狭窄血管置入支架的生物力学研究历史和现状;特别从固体力学和血流动力学的角度,阐述了近年来学者对狭窄血管置入支架的生物力学数值模拟研究进展;并分析总结了支架内再狭窄的生物力学因素。从支架介入治疗过程来看,数值模拟技术可以为研究支架置入术和支架内再狭窄之间的关系提供很好的技术手段,对支架的设计以及介入治疗提供更加科学的指导。     

心电图能量谱中基频及谐频成分能量密度分布与年龄的关系

对长时间心电图能量谱中的心率基频及其谐频成分能量密度的分布,用一个指数函数进行最小二乘拟合,函数中引入的分布指数用来量化能量密度分布分散与集中的程度。用该函数对年轻(21~34岁)与年老(68~81岁)二组经过严格筛选的健康人心电图数据的能量谱进行局部拟合,计算出每个个体的心率基频及其谐频成分的中心频率f0、在中心频率f0处的能量密度、谐频与基频成分能量密度的比值、谐频与基频成分分布指数的比值以及可识别出的谐频个数等特征参数值。结果:分布指数是年轻组明显大于年老组(P<0.01),谐频与基频能量密度的比值是年轻组明显小于年老组(P<0.01),可识别出的谐频个数是年轻组明显少于年老组(P<0.01),f0及在f0处的能量密度在二个不同年龄组之间没有差异。这些结果预示着在本研究中提出的特征参数值可作为心率波动的一种新的度量。     

冠状动脉狭窄时主动脉内气囊反搏对心内膜下动脉的影响

测量了左冠状动脉狭窄前后，主动脉内气囊反搏时，各项血流动力学参数，并用超声多普勒血流仪测量了室间隔动脉血流的变化。结果表明，当ＩＡＢＰ反搏时，加强了冠脉系统血流的脉动变化，在左冠状动脉主干狭窄时，对心内膜下小动脉的灌注产生不良影响。     

兔腹主动脉狭窄后剪切力的变化对局部内皮细胞形态和通透性的影响

兔腹主动脉狭窄至正常的55.2％，伊文思蓝对动脉染色，在扫描电镜下观察内皮细胞形态，计算细胞形态指数。动脉狭窄血管内流动壁面剪切率的分布由计算机数值模拟确定。结果表明，在紧接狭窄处的近远两侧，血流受到严重干扰，内皮细胞的形态和对伊文思蓝白蛋白复合物通透性发生明显改变。研究表明，这些改变不但与剪切应力的大小有关，还与血液流动的状态有关。这与动脉粥样硬化一般好发于血液流动受到干扰，流动发生分离区域的解剖观察一致。     

一种可控性大鼠颈总动脉狭窄模型的建立及切应力测定

目的：为在体研究切应力改变诱导内皮细胞组织因了的表达建立一种可控性的大鼠颈总动脉狭窄模型。方法：54只SD大鼠随机分为9组，用自制硅胶管套扎左颈总动脉中段，术后不同时相点用TS 420型多普勒血流仪测定血流量，灌注前用DIGITEXα数字血管减影操作系统测定血管内径，用Poiseiuue流体力学公式Tw=32ηQ／πD^3计算切应力。结果：颈总动脉狭窄85％后，平均血流量减少了65％，局部切应力发生了显著变化（P〈0．01），在7d内无明显改变。结论：硅胶管套扎大鼠颈总动脉中段的狭窄模型，是比较理想的在体检测血流壁切应力改变对血管内皮细胞形态和功能影响的方法。     

Design of an artificial lung compliance chamber for pulmonary replacement

Matching the impedance of an artificial lung for pulmonary replacement to native pulmonary impedance is important in preventing right ventricular dysfunction. A lumped-parameter theoretical model and bench-top experiments were used to investigate the effect of a prototype compliance chamber on input impedance. The bench-top simulation consisted of a pulsatile flow generator, a prototype compliance chamber, and a low resistance artificial lung connected in series. Effective compliance was varied using pneumatic compression. The theoretical model considered a similar circuit with resistors before and after a compliance element. The bundle flow pulsatility (flow amplitude divided by average flow) and input impedance were calculated in the theoretical and experimental models. More compliance and lower upstream resistance result in lower bundle flow pulsatility and reduced first harmonic impedance. Matching the time scale of the circuit to the period of pulsatile flow also reduces impedance. The bench-top circuit demonstrated an optimal chamber pressure at which first harmonic impedance is reduced by 80%. The prototype compliance chamber in series with the artificial lung more closely matches native pulmonary impedance. The lumped-parameter model and the bench-top simulation will aid in the design and testing of compliance chamber modifications to improve its efficiency.     

Determination of the impedance of the guinea pig skin

The impedance of guinea-pig skin has been studied using anin vitro method which consists of placing the recording chamber containing a strip of guinea-pig skin in the feedback branch of a closed-loop amplifier having an adjustable resistor in its input circuit. The chamber consists of two cylinders filled with a circulating Krebs solution at 37°C and two platinum electrodes facing one another inside the cylinders. At a given frequency, the series resistor is adjusted to obtain a gain of unity between input and output sinewave voltages (gain=10). The value of the series resistor is then equal to the modulus of the impedance in the feedback loop and its argument is calculated by a phase/amplitude convertor on the basis of the input and output phase shift. The impedance measurement is made separately for the recording chamber and the whole system in which the tissue is inserted. Substracting vectorially both values obtained enables the impedance of the tissue itself to be deduced. This procedure is repeated over a wide frequency band and the resulting values are represented on a Bode diagram of phase and amplitude. The Bode diagram shows the variations of the electrical characteristics of the tissues as the frequency varies, and indicates nonlinear filtering especially for low-frequency values (10^?2 Hz).     

用于生物阻抗测量的双反馈电流源研究

针对生物阻抗测量中电流源在较高频率时，恒流特性较差的问题，以及对其消除直流信号能力的要求，设计了双反馈电流源方案，基于第二代电流传输器（CCII）原理设计的电压控制电流源，通过增加直流反馈单元和输入缓冲，获得了良好的输出阻抗和抗直流特性，并通过使用直接数字合成（DDS）和乘法解调技术，实现了电流幅值的闭环控制，进一步提高了电流源的恒流特性。     

Pulsatile blood flow in a stenosed artery—a theoretical model

To understand the special flow conditions which may be produced by the presence of stenosis in arteries, an analytical solution is obtained for pulsatile laminar flow in an elliptic tube. Blood is approximated by a Newtonian model and the geometry of the stenosis is introduced by specifying the change in area of cross-section of the stenosed artery with axial distance. The results for velocity, pressure, shear stress and impedance are presented. These are compared with the steady flow results as well as with those of the flow in a stenosed tube of circular cross-section. The study indicates that the fluid dynamic characteristics of the flow are affected by the percentage of stenosis as well as the geometry of the stenosis. The frequency of oscillation is also found to influence shearing stress and the impedance.     

The low frequency input impedance of the renal artery

Summary The renal artery of anesthetized dogs was perfused by a peristaltic pump with arterial blood. The pump rate could be modulated sinusoidally between 0.75 Hz and 0.0005 Hz. The frequency response of the renal arterial pressure to sinusoidal arterial flow of varying frequency and constant amplitude indicated the existence of a very slow autoregulatory pressure controlling mechanism, besides the autoregulation of flow. This fact is supported by the pressure responses to step flow increase, which show a very slow secondary pressure decrease. The time constant of this new autoregulatory phenomenon is in the order of 1000 sec. A simple linear second order model allows to simulate the renal arterial pressure flow relation (input impedance) as well as the characteristic step responses. Both the autoregulation of flow and the very slow autoregulation of pressure appear to be first order mechanisms.     

Myoelectric response of the human triceps brachii to displacement-controlled oscillations of the forearm

Summary The dynamic relations between the surface myoelectric activity in tonically contracting triceps brachii and the forearm rotation (proportional to triceps stretch) were measured by imposing small, sinusoidal, displacement-controlled perturbations on the forearm position. Three normal, adult, male subjects participated in these experiments. The amplitude of the forearm rotation, the driving frequency, and the tonic contraction level were all carefully regulated. The mean rectified triceps EMG (the output) showed a strong harmonic at the driving frequency, and the frequency-response characteristics were computed directly by comparing the amplitude and phase of this harmonic to that of the forearm flexion angle (the input). The (electrical) reflex gain is defined as the amplitude ratio of output to input. The system response was measured from 2 to 18 Hz, at two tonic contraction levels and two forearm rotation amplitudes, about a mean position of 90° forearm flexion. The results show clearly that the system response is nonlinear: the reflex gain decreases with forearm rotation amplitude. (This gain also increases with tonic contraction level for sufficiently low values of the latter variable.) The measured frequency-response characteristics of the system can be modeled approximately as a second order linear lead filter with a single time delay, followed by a saturating nonlinearity. Both model independent estimates and least-squares model fitting, yielded values of the time delay of the order of 25 ms, suggesting that a segmental mechanism mediates reflex activity. Simplified calculations and limited measurements are presented to show that a nonlinear system of the type we have identified with constant displacement driving may appear linear under constant torque driving. Our directly-measured frequency-response characteristics differ from those reported by investigators employing random, rather than periodic, driving; possible reasons for these apparent discrepancies are discussed.     

Location of membrane conductance changes by analysis of the input impedance of neurons. I. Theory

If the membrane conductance of a neuron changes, its response to injected current changes. If the change in membrane conductance is restricted to a given subregion of the neuron, that region can be located by analysis of the form of the change in the response of the neuron to current injection. The theoretical basis of this method is rigorously developed in this paper. Location of the membrane conductance change is possible because the higher-frequency components of the injected currents are progressively attenuated by the axial resistance and membrane capacitance of the neuron as they pass from the injection site to electrotonically more distant regions. For the lower-frequency components, this attenuation is less pronounced. Therefore, when a conductance change occurs relatively far from the recording/current-passing electrode, only the lower frequency components of the response are altered, because the higher-frequency components of the current do not even reach that site. When such a conductance change occurs relatively near the electrode, both the lower and the higher frequency components of the response are altered. Treating the neuron as a passive network, the input impedance at a given frequency is simply the voltage response of the neuron at that frequency divided by the current injected at that frequency. This is a complex value, having both magnitude and phase components. The change in the magnitude of the input impedance due to a conductance change occurring distally drops off more rapidly with increasing frequency than that due to a proximal conductance change. In addition, for distal conductance increases the magnitude of the input impedance can increase in the higher range of frequencies. This paradoxical effect is treated in APPENDIX I. For many neurons an estimate of the electrotonic location of a conductance change can be made knowing only the change in input resistance, the change in the magnitude of the input impedance at the characteristic frequency (omega 0 = 1/tau 0), and a reasonable estimate of the total electrotonic length of the neuron (L). The sensitivity of the method depends on the electrotonic length of the neuron. The method is most useful in neurons with dendritic trees longer than approximately 0.5 length constants. The dendritic-to-somatic conductance ratio of the neuron does not appreciably affect the forms of the responses. The time constant merely shifts the frequency range of interest.(ABSTRACT TRUNCATED AT 400 WORDS)     

Transfer properties of the slowly adapting stretch receptor of the crayfish abdomen

The slowly adapting stretch receptor in the abdomen of freshwater crayfish (Astacus fluviatilis) was investigated to determine its properties under dynamic conditions. An in situ preparation was used; the necessary dissection did not involve the receptor organ or its immediate surroundings. Sinusoidal variations in the angle of flexion in the joint to which the receptor organ was connected, were generated by a feed-back controlled stretcher. Nerve spikes recorded from the axon of the receptor neurone and information about angle of flexion in the joint obtained by position transducers, were fed into a computer. Fourier transforms were performed on both input and output data to determine the amplitude of the 0. and I. harmonic together with the phase of the 1. harmonic. The receptor organ was investigated for linearity up to 1.5 degrees input amplitude, and proved to be surprisingly linear within this range. In addition, the transfer function of the receptor organ was determined by stimulating it with small-amplitude sinusoidals with different frequencies. With a steady flexion of 35–40° in the joint, the gain of the receptor organ increased 5–6 times when the modulation frequency of the input signal was increased from 0.1 to 5 cycles/s. A maximum in gain was constantly found at about 5 cycles/s, with a rapid fall towards 0 when the modulation frequency was increased further. A change in phase lead from positive (leading output) to negative with change in sign about 1 cycle/s was also found. These results resemble the results found by investigators of isolated preparations. A “hold” property is probably a part of the overall property of the receptor organ together with an element of Maxwell type. An element of the form h(s)=ksⁿ with n=0.45 is also a part of the transfer function of the receptor organ, although the physiological parallel to this element is uncertain.     

A comparison of the response characteristics of cerebellar fastigial and vermal cortex neurons to sinusoidal stimulation of macular vestibular receptors

1. The responses of neurons located in the rostral part of the fastigial nucleus to sinusoidal tilt of the animal were recorded in precollicular decerebrate cats and compared with those elicited by the same stimulation in Purkinje (P) cells located in the vermal cortex of the cerebellar anterior lobe. In particular, by fixing the head and the body of the animal to the tilting table and by rotating the animal around its longitudinal axis, it was possible to elicit a selective labyrinth input without eliciting a neck input.
2. Among the 60 fastigial neurons tested, 43 units responded to sinusoidal tilt at the frequency of 0.026 Hz and at the peak amplitude of displacement of 10°–15°. On the other hand, among 106 P-cells tested for a mossy fiber (MF) response to the labyrinth input, 32 units were affected by the same parameters of stimulation. In both instances the response consisted in a periodic modulation of the discharge frequency, which was related to the position of the animal. Most of the responses of the fastigial units to the labyrinth input were characterized by a peak excitation in phase with side-down tilt of the animal and by inhibition during side-up tilt, whereas most of the MF-responses of the P-cells to the labyrinth input showed just the opposite behavior.
3. The threshold amplitude of tilt responsible for these responses varied in different units from 1° to 3° at the frequency of 0.026 Hz. The sensitivity of the first harmonic of the unit responses to tilt, expressed in percentage change of the average firing rate per degree of displacement, corresponded on the average to 1.73±1.16, S.D., for the fastigal neurons and to 1.61±0.94, S.D., for the P-cells. These values did not change or were only slightly modified as a result of increasing amplitude of stimulation from 1°–3° to 15°–25° at a frequency of 0.026 Hz. Moreover, changes in amplitude of stimulation at the parameters reported above did not greatly modify the phase angle of the first harmonic of the responses relative to the side-down position of the animal. Units located in the medial corticonuclear zone of the cerebellum did not show any change in sensitivity and phase angle of the responses by increasing the frequency of tilt from 0.015 to 0.20 Hz at the fixed amplitude of 10°–15°, thus indicating that these responses depended upon stimulation of macular receptors. In other units, however, these changes in frequency of rotation modified the phase angle of the responses, which became related to velocity rather than to the positional signal, due to stimulation of semicircular canal receptors.
4. The observation that most of the responsive fastigial neurons increased their firing rate, while most of the responding P-cells located in the vermal cortex of the cerebellar anterior lobe decreased their firing rate during side-down rotation of the animal is discussed in relation to the postural changes of the limbs elicited during asymmetric stimulation of macular receptors.