Intracranial Pressure Response to Non-Penetrating Ballistic Impact: An Experimental Study Using a Pig Physical Head Model and Live Pigs

This study was conducted to characterize the intracranial pressure response to non-penetrating ballistic impact using a "scalp-skull-brain" pig physical head model and live pigs. Forty-eight ballistic tests targeting the physical head model and anesthetized pigs protected by aramid plates were conducted with standard 9 mm bullets at low (279-297 m/s), moderate (350-372 m/s), and high (409-436 m/s) velocities. Intracranial pressure responses were recorded with pressure sensors embedded in similar brain locations in the physical head model and the anesthetized pigs. Three parameters of intracranial pressure were determined from the measured data: intracranial maximum pressure (P_max), intracranial maximum pressure impulse (PI_max), and the duration of the first positive phase (PPD). The intracranial pressure waves exhibited blast-like characteristics for both the physical model and l live pigs. Of all three parameters, P_max is most sensitive to impact velocity, with means of 126 kPa (219 kPa), 178 kPa (474 kPa), and 241 kPa (751 kPa) for the physical model (live pigs) for low, moderate, and high impact velocities, respectively. The mean PPD becomes increasingly short as the impact velocity increases, whereas PI_max shows the opposite trend. Although the pressure parameters of the physical model were much lower than those of the live pigs, good correlations between the physical model and the live pigs for the three pressure parameters, especially P_max, were found using linear regression. This investigation suggests that P_max is a preferred parameter for predicting the severity of the brain injury resulting from behind armor blunt trauma (BABT).     

Phase Response of Model Sinoatrial Node Cells

When a brief current pulse is incident on excitable cells in cardiac and other nervous tissue, a change in phase of the cell's response is usually observed. In cardiac tissue, the cells are exposed to external stimulation of mainly positive currents, which depolarize the cells. We performed a systematic study of the effect of depolarizing stimuli, covering timing, magnitude, and duration, and demonstrated that all of these parameters influence the phase response of the cell. The phase response of our model cell compares favorably with measurements on isolated sinoatrial node cells. We investigated the phase response to single depolarizing stimuli as a function of the stimulus parameters (phase response curves), and then studied cell responses to the combined effect of a pulse train (entrainment phenomena). The range of magnitudes and durations for the stimuli were 0.01–5 nA and 0.01–50 ms. Comparisons of the entrainment properties of the model with experimental results show good agreement with similar modes and different entrainment ratios occurring for similar basic cycle lengths (as functions of the unperturbed cell period). Our results demonstrate that any combination of parameters that provide the same charge transfer to the cell causes a similar phase response, independent of the specific magnitude and duration for the entire range of stimuli investigated. © 2003 Biomedical Engineering Society. PAC2003: 8717Nn, 8719Hh, 8719Nn     

Nonlinear transient response of electrode—electrolyte interfaces

The voltage transient response, V(t), of the electrode—electrolyte interface is known to be nonlinear. It has been shown byOnaral andSchwan in 1983 that the DC limit current of linearity, I_AL, is proportional to t^−β were β is the fractional power dependence of the linear, short pulse duration impedance. We now seek to explain the physical phenomena underlying this observation. We present an equivalent circuit model of the interface and highlight the major source of the observed nonlinear behaviour. Using the equivalent circuit model and associated formulae, an expression for the limit current of linearity is derived and compared with that found experimentally byOnaral andSchwan. According to this theoretical model, a current of as little as 22nA can be sufficient to drive an electrode system into nonlinear behaviour at longer pulse durations.     

Response properties of the periodontal mechanosensitive neurons in the trigeminal main sensory nucleus of the cat

Summary Periodontal mechanosensitive units (PM units) were recorded from the trigeminal main sensory nucleus (Vms) of the cat. The receptive fields of PM units were arranged from mandibular to maxillary divisions dorso-ventrally. The majority of PM units were single tooth units responsive to the canine tooth. They were directionally selective and had sustained responses to pressure applied to the tooth. The optimal stimulus direction of maxillary and mandibular PM units when the canine tooth was stimulated was single and it was oriented predominantly in the caudio-medial or rostrolateral direction. The threshold intensity of canine tooth stimulation was less than 0.05 N in most of the units. These findings indicate that the response properties of PM units in the Vms resemble fairly closely those of the primary afferent nerves arising from the periodontal mechanoreceptors.     

The effects of acceleration on the mechanical impedance response of a primate model exposed to sinusoidal vibration

Criteria for developing active and passive isolation mechanisms for reducing the effects of whole-body vibration exposure rely on a thorough understanding of the stiffness, damping, and resonance behaviors of the human or human surrogate body. Three Rhesus monkeys were exposed to seated whole-body sinusoidal vibration between 3 and 20 Hz at 0.69 and 3.47 msec⁻² rms (0.1 and 0.5 g peak) accelerations. The mechanical impedance magnitude and phase were calculated as the ratio and phase relation between the transmitted force and input velocity, respectively, at the seat. The resultant profiles showed a significant decrease in the primary resonance frequency with increasing acceleration. At the lower acceleration level, a second lower impedance peak was observed at approximately 5 Hz. A three-mass, two degree-of-freedom model, which included upper torso and leg representation, was used to determine the mechanical parameters that best described the measured responses. The mean stiffness coefficients and the mean undamped natural frequencies associated with the upper torso and leg subsystems showed a significant decrease with increases in the acceleration level. The results of this study strongly suggested that nonlinear stiffness properties were responsible for the observed differences in the biodynamic response of the Rhesus monkey with acceleration level.     

Automatic diagnosis system of tooth mobility for clinical use

The examination of tooth mobility gives valuable clinical findings on pathological change in the periodontium. An automatic diagnosis system has been developed for the quantitative evaluation of tooth mobility. Tooth mobility was determined from the vibration characteristics of the periodontium and expressed in terms of such objective biomechanical parameters as stiffness and two damping coefficients. These were displayed on a monitor CRT as a triangular figure. This system is composed of a probe, which comprises a vibrator and acceleration transducers, and a data analysis unit using a personal computer. A dentist can measure the tooth mobility without assistance with a foot-switch to trigger the computer operation. The reliability and the operational facility of the system are considered to be sufficient that it may be used in daily clinical practice. Data were collected from healthy and pathological teeth. The tooth mobility of the pathological tooth and the time course of the change in the mechanical parameters after implantation of the tooth were measured by this system. The advantages of this system compared with previous one, which was also developed by the authors, are discussed.     

Computerized endopharyngeal myotonometry (CEM): a new method to evaluate the tissue tone of the soft palate in patients with obstructive sleep apnoea syndrome

This study compared the tissue tone of the soft palate in nonsnoring subjects and patients with obstructive sleep apnoea syndrome (OSAS) during wakefulness. Here, tissue tone means the biomechanical property of the tissue which can be characterized by two main parameters: stiffness and elasticity. Tissue tone includes both structural and neural components. A new method to evaluate the tissue tone of the soft palate was used - computerized endopharyngeal myotonometry (CEM). This method records and analyses the response of the soft palate tissues to a brief mechanical impact. The method enabled us to evaluate the most important parameters of tissue tone: stiffness, which is expressed as a frequency; and elasticity, expressed as a logarithmic decrement of the damped oscillation. First, a self-reported questionnaire was completed about the medical history of the subjects. Subjects then underwent a physical examination of the oropharynx and polysomnography with overnight pulse oximetry. The results of the CEM method indicated that patients with OSAS show an increased stiffness of the soft palate tissues (20.3, SD 4.7 Hz) compared with nonsnoring subjects (12.2, SD 1.8 Hz). In patients with sleep apnoea, elasticity is not increased in a similar way to stiffness. Thus, the disproportion between tissue stiffness and elasticity of the soft palate is a measure of the pathological changes in patients with sleep apnoea.     

利用有限元研究非贯穿弹道冲击防弹衣后人体躯干的力学响应

目的通过建立人体躯干有限元计算模型,对弹头非贯穿性弹道冲击下人体躯干主要脏器的力学响应进行数值模拟。方法利用正常成年男性的CT扫描数据,应用医学图像重建软件Mimics和有限元前处理工具Hy-perMesh进行人体躯干有限元建模,在显式动力有限元分析软件LS-DYNA中对速度为360 m/s的9 mm手枪弹弹头撞击装配有软质防弹衣人体躯干的压力、加速度响应进行数值计算。结果建立了包括胸廓骨骼结构、脏器、纵膈和肌肉/皮肤的人体躯干有限元模型,通过数值计算获得了心脏、肺脏、肝脏、胃的压力响应以及胸骨的加速度响应,发现不同脏器之间或同一脏器的不同位置,离弹头撞击点位置的远近决定了压力峰值的大小和出现压力峰值的时间。结论装配有软质防弹衣的人体躯干有限元计算模型可作为非贯穿弹道冲击下人体力学响应的仿真分析工具,仿真结果可为防弹衣后钝性损伤机制和防护研究提供依据。     

The effects of caudocephalad (plus Gz) acceleration on the initially curved human spine

A beam-column model of the human spine subjected to a caudocephalad (+G_z) acceleration is analyzed by the finite-difference numerical technique. It was shown that the previous analytical treatment of this problem by the assumed-mode method is valid only for either very low levels of the acceleration pulse or for very early times in the response, i.e. the loading is such that the initial configuration of the spine is little changed by the dynamics. Numerical results generated, using a 20 g step acceleration input, show that the initial configuration is so appreciably changed as to invalidate the results of the assumed-mode analysis. Any future extensions of similar continuum models of the human spine, to include other additional effects, should treat the use of classical analysis with caution and consider the efficacy of computer-aided numerical analysis by either the present finite-difference solution or the currently popular finite-element method.     

Use of osteogenic bone-marrow precursor cells for reparative osteogenesis in the mandible of experimental animals

Using a model of “bony tissue tunnel defect” produced by the removal of a mandibular incisor in rats, it was found that closing the defect with a bioprosthesis prevented the washing out of osteogenic bone marrow precursor cells, which serve as a substrate for reparative osteogenesis, from the mandibular spongy bone. The reparative process was strongly stimulated if the bioprosthesis contained estrone; in this case, the time required for the tooth socket to be filled with osteogenic tissue was shortened by half. When no bone marrow elements were present in the socket, it was filled with fibrotic connective tissue, the number of bone marrow elements in spongy bone cavities was small, and the mandibular osteogenic tissue underwent atrophy. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 119, N ^o 1, pp. 72–75, January, 1995     

利用物质点法研究不同头部模型对头部碰撞动态响应的影响

目的 探讨头部肌肉及边界条件对头部碰撞动态响应的影响。方法 通过人体扫描CT图片构建3种人体头部三维物质点碰撞模型,第1种为简化的自由头部模型（SHFr）,包括头骨、膜层、脑组织,头部自由;第2种为带肌肉的自由头部模型(MHFr),包括头部肌肉、头骨、膜层、脑组织,头部自由;第3种为带肌肉的肩部固定的模型(MHSFi),包括头部肌肉、头骨、膜层、脑组织、肩部肌肉、肩颈部骨骼,肩部下缘固定。一铅质圆柱体锤以6.4 m/s初始速度垂直撞击前额部位,通过物质点法模拟计算3种模型的动态响应。结果 在本数值模拟条件下,SHFr、MHFr、MHSFi 3种模型的头部加速度峰值分别为6.018×103、4.69×103、4.76×103 m/s2。结论 头部肌肉的存在会分散头部的受力分布,扩大头部受力面积,减小受伤程度;在短时间冲击过程中,头部自由与肩部固定对头部动态响应的影响不大。     

Automatically Generating Subject-specific Functional Tooth Surfaces Using Virtual Mastication

High-accuracy geometrical models of a subject’s mandibular and maxillary teeth are combined with recordings of natural chewing trajectories of the same subject to obtain a subject-specific virtual model of mastication—the virtual masticator. The virtual masticator and a shape-optimization algorithm, which is based on removing collisions occurring between a generic maxillary tooth/teeth and the mandibular antagonists during mastication, is used to automatically reconstruct functional tooth surfaces. The process was tested using a chewing trajectory stemming from recordings made of an individual while eating elastic-type foods, a generic maxillary tooth, and the mandibular second molar of that individual. Comparing the obtained results with the actual tooth, the errors within the occlusal and functional regions of the the right second maxillary molar range between −90 and 200 μm and these errors do not change any more after three chewing cycles. These results indicate that a small number of chewing cycles is sufficient to remove occlusal interferences in the virtual tooth model. Such automatically reconstructed tooth surfaces can provide guidance during the design stage of dental fixed restorations manufactured using computer-aided design and manufacturing (CAD/CAM) systems and provide additional information for the design of dental implants or bridges.     

THE HEART RATE RESPONSE TO A BRIEF AUDITORY AND VISUAL STIMULUS

The adult heart rate (HR) response was studied in 18 male subjects following a series of 10 tones and 10 light flashes. Both stimuli were of moderate intensity (54 db and 8.0 ml) and had rise times of 30 milliseconds. The tone evoked a predominantly acceleratory response and no decrement with repetition. Initially, the light flash evoked a predominantly deceleratory response which changed to one of acceleration as the stimulus was repeated. Analysis of respiration revealed that an increase in rate and amplitude followed both stimuli and that the magnitude of respiratory changes did not diminish with stimulus repetition. Viewed according to Sokolov's criteria for identifying orienting, defensive, and adaptive responses the results support the conclusions that: (1) HR deceleration is a component of the orienting response; and (2) HR acceleration is neither an orienting, defensive, nor adaptive response but is largely secondary to respiratory changes. On the basis of the evidence, a tentative model of the HR response to simple auditory and visual stimuli is offered.     

Cross-bridge stiffness in Ca2+-activated skinned single muscle fibres

Tension transients, in response to small and rapid length changes (completed within 40 s), were obtained from skinned single frog muscle fibres incubated in activating solutions with varying concentrations of Ca²⁺. The first 2 ms of these transients were described by a linear model in which the fibre is regarded as a rod composed of infinitesimally small, identical segments containing a mass, one undamped elastic element and in the case of relaxed fibres two damped elastic elements in series, or in the case of activated fibres three such elastic elements in series. The stiffness of activated fibres, expressed in elastic constants or apparent elastic constants, increased with increasing concentrations of Ca²⁺. All the damped elastic constants that were necessary to describe the tension responses of activated fibres were proportional to isometric tension. However, the undamped elastic constant did not increase linearly with increasing isometric tension. Equatorial X-ray diffraction patterns were obtained from single frog muscle fibres under similar conditions as under which the tension transients were obtained. The filament spacing (d ₁₀)of Ca²⁺-activated single frog muscle fibres decreased with increasing isometric force, whereas the intensity ratio (I ₁₁/I₁₀)increased linearly with increasing isometric force. From experiments in which dextran (MW 200000 Da) was added, it followed that such a change in filament spacing would modify passive stiffness. The d ₁₀value of relaxed fibres decreased and stiffness increased with increasing concentrations of the polymer dextran, whereas I ₁₁/I₁₀remained constant. The relation of stiffness and filament spacing with concentration of dextran was used to eliminate the effect of decreased filament spacing on stiffness of activated fibres. After correction for changes in filament spacing the undamped complicance C ₁, normalized to tension, was not constant, but increased with increasing isometric tension. If we assume that isometric tension is proportional to the number of force generating cross-bridges, this means that only part of the undamped complicance of activated fibres is located in the crossbridges.     

Polarisation impendance of pacemaker electrodes:in vitro studies simulating practical operation

The electrical properties of pacemaker electrodes were studiedin vitro under conditions prevailing in practical pacemaker operation. Emphasis was laid on a clear distinction between the changing modes of the pacemaker action. During sensing, the electrode can be represented by an a.c. series polarisation resistance and capacitance, generally accepted for biological electrodes obeying linearity rules. During stimulation, the electrode operates in the non-linear region. A nearly constant-voltage, short, rectangular pulse applied directly to the electrode-heart system, causes the electrode voltage and current to respond as a transient exponential, characterised approximately by a single time constant. This response allows modelling of the d.c. equivalent circuit of the electrode, in the form of a polarisation capacitance with a small resistance in series, shunted by a parallel resistance. Formulae were derived for calculation of these elements. The response of the electrode-heart system to a single stimulus was tested as a function of the amplitude and duration of the applied pulse. Also, the effect of repetitive stimulations was checked at a normal pacing rate. A nearly constant-voltage pacing source, as compared with a constant-current one, appears to be advantageous for preservation of the longevity of the electrode.     

基于多刚体力学模型腰椎推拿斜扳法的优化

目的 综合考虑推拿的有效性和安全性,提出一种评价振荡激励和脉冲激励腰椎推拿斜扳法优劣的方法,并对振荡激励腰椎推拿斜扳法进行优化。方法 建立多刚体胸-腰椎生物力学模型,手法作用力作为模型的输入力,运用MATLAB/Simulink进行仿真,模拟得到腰椎各节段位移和加速度随时间变化的情况,对腰椎推拿手法行优化时,改变推拿作用力的核心要素频率f和操作次数n,比较腰椎各节段最大相对位移和最大加速度,并提出一种新的指标z,对推拿手法的有效性和安全性进行综合评价。结果 两种激励腰椎推拿斜扳法作用时,腰椎各节段最大相对位移没有差异;振荡激励腰椎推拿斜扳法作用时,腰椎各节段的最大加速度均明显小于脉冲激励腰椎推拿斜扳法作用时的最大加速度。当f=1～2.5 Hz时,推拿整体效果比较好,且整体效果与操作数无关,推拿作用力持续1个操作数即可;当f=3.33 Hz,n≥5时,推拿治疗效果最好,但此时腰椎各节段承受力也相对较大;当f≥5 Hz时,推拿整体表现不佳。结论 振荡激励腰椎推拿斜扳法比脉冲激励腰椎推拿斜扳法更安全,研究结果为医生提供一个比较合理的振荡激励腰椎推拿斜扳法操作参数的范围。     

Cardiac assessment mechanics: 1 Left ventricular mechanomyocardiography,a new approach to the detection of diseased myocardial elements and states

The inadequacies of currently employed methods for assessment of cardiac mechanics are discussed, and the need for development of more intrinsic assessment parameters is emphasised. To this end, a new technique is presented to enable determination of regional mechanical constitutive properties of the myocardium during diastole; this technique has been originally named left-ventricular mechanomyocardiography (or l.v.-m.m.c.g.). The data required for implementation of the techniques consist of left-ventricular sequential dynamic geometry and associated recorded chamber pressure. The method entails matching of the inner-boundary deformations of the instantaneous finite-element model of the left ventricle (which is loaded by the recorded instantaneous incremental pressure) with the actual instantaneous endocardial deformations (as derived from either cineangiocardiography or 2-dimensional echocardiography), to determine the regional distribution of the Young's modulus E_ne and the incremental stresses Δσ_ne (and hence the total stress σ_ne=∑_nΔσ_ne) of the myocardial elements. The mechanical constitutive properties of the myocardial elements can be then characterised by the constitutive relation E_ne=a+bσ. The constitutive parameters a and b have typical ranges for normal and pathological (ischaemic and infarcted) myocardial elements and hence can be employed to distinguish diseased elements. The values of a and b are calculated for normal and pathological subjects and their normal and pathological ranges are presented.     

Information processing by parafoveal cells in the primate nucleus of the optic tract

We recorded from single units in the pretectal nucleus of the optic tract (NOT) of the nonhuman primate. Specifically, we examined units that are modulated during smooth tracking of a small laser spot against a dark background. We used a nonlinear optimization procedure to determine whether the unit responses of these parafoveal cells are better described by a model that incorporates retinal error motion parameters or by a model that incorporates eye motion parameters. Our main finding was that all the cells in our sample group were better fit with a three-component model that incorporated retinal error motion parameters of position, velocity and acceleration (average coefficient of determination = 0.84) than a model that used position, velocity and acceleration components of eye motion (average coefficient of determination = 0.68). Other analyses involved comparison of goodness of fit between the three-component retinal error model and two-component retinal error models that excluded position or acceleration related terms. We found that there was a statistically significant degradation in the fit when position and acceleration related terms were dropped from the retinal error based model (P<0.05). Unit data from experiments in which the laser spot was extinguished for a brief period of time during tracking showed that the unit response was decreased following the target blink. We conclude on the basis of this and previous experimental data and our dynamic modeling approach that the parafoveal cells in the NOT primarily encode retinal error motion. Further they encode position, velocity and acceleration components of retinal error that could be used by other downstream structures for synthesis of a smooth-pursuit eye movement. Electronic Publication     

The contractile properties and movement dynamics of pigeon eye muscle

The lateral rectus (LR) muscle of the pigeon was directly stimulated in situ at 41°C. The length tension relationships for active and passive tension were investigated to determine the optimum muscle length (L_o). Isometric responses to single and twin pulses, tetani and sinusoidal stimulation were measuredA linear relationship was found between length and active tension during stimulation. Increase in stimulation frequency produced a corresponding shift in tension with the slope of the curves remaining the same. At L_o (1.21 times resting length) the average contraction time of single twitches was 6.03 ms and the half-relaxation time was 7.77 ms. Stimulation frequencies of 200 Hz and over gave rise to a fused tetanus. Tension increased to a maximum at 200 Hz and rate of tension rise saturated at 600 Hz. The ension response to tetanic stimulation was linear over the range 70–180 Hz. Maximum tetanic tension was around 3.48 N/cm² and the twitch: tetanus ratio was 0.164. Prolonged activation at fusion frequency showed a high fatigue resistance. Sinusoidal stimulation with pulse trains of 100–180 Hz produced a sinusoidal response over the frequency range 0.6–40 Hz, from which the gain and phase relation-ships were determined. The muscle response approximates a first order low pass filter, with a characteristic frequency of 11.2 Hz. There is an additional phase lag, equivalent to the response latency, of 2.89 ms. The results are compared to the contractile properties of mammalian eye and avian skeletal muscle. The frequency response of the LR is compared to that of cat soleus and gastrocnemius and to pigeon eye movement dynamics.