Local vibrations--mechanical impedance of the human hand's glabrous skin

The mechanical point impedance has been studied in ten different areas of the glabrous skin of the human hand on three male and three female subjects within the frequency range of 20-10 000 Hz. For all tested areas the impedance decreased with increasing frequency down to a minimum value, corresponding to the natural frequency of the skin. After that, the mechanical impedance was directly proportional to the frequency. The highest natural frequency, about 200 Hz, was measured in the distal areas of the finger and the lowest, about 80 Hz, in the proximal areas of the palm (thenar). Small differences in internal damping were also showed to exist. A great amount of handheld tools used in industry have their maximum vibrational levels within the natural frequency range of the skin. In order to avoid adverse effects the skin's mechanical properties should therefore carefully be taken into consideration at designing vibrating tools.     

Analysis of mechanical impedance in human arm movements using a virtual tennis system

The dynamic characteristics of human upper extremities are usually expressed by mechanical impedance. Although many studies have discussed human impedance characteristics, there are no reports on control abilities of task-related impedance in skilled human hand movements. This paper proposes a virtual sports system using a virtual reality technique to examine human movements. The differences in movements between skilled and unskilled subjects are investigated through a series of experiments. Then, the human impedance of a skilled player is estimated and analyzed in the preliminary phase of motion.     

Noninvasive determination of ulnar stiffness from mechanical response--in vivo comparison of stiffness and bone mineral content in humans

An approach referred to as Mechanical Response Tissue Analysis (MRTA) has been developed for the noninvasive determination of mechanical properties of the constituents of the intact limb. Of specific interest in the present study is the bending stiffness of the ulna. The point mechanical impedance properties in the low frequency regime, between 60 and 1,600 Hz are used. The procedure requires a proper design of the probe for good contact of the skin at midshaft and proper support of the proximal and distal ends of the forearm to obtain an approximation to "simple support" of the ulna. A seven-parameter model for the mechanical response is then valid, which includes the first mode of anterior-posterior beam bending of the ulna, the damping and spring effect of the soft tissue between probe and bone, and the damping of musculature. A dynamic analyzer (HP3562A) provides in seconds the impedance curve and the pole-zero curve fit. The physical parameters are obtained from a closed-form solution in terms of the curve-fit parameters. The procedure is automated and is robust and analytically reliable at about the five percent level. Some 80 human subjects have been evaluated by this mechanical response system and by the Norland single photon absorptiometer, providing for the first time in vivo, a comparison of elastic bending stiffness (ulna) and bone mineral content (radius). Three functional parameters of potential clinical value are the cross-sectional bending stiffness EI, the axial load capability Pcr (Euler buckling load) and the bone "sufficiency" S, defined as the ratio of Pcr to body weight. The correlation between EI and bone mineral (r = 0.81) is only slightly less than previous in vitro results with both measurements on the same bone (r = 0.89). When sufficiency is taken into consideration, the correlation of Pcr and bone mineral content is improved (r = 0.89). An implication is that "quality" of bone is a factor which is not indicated by bone mineral content but which is indicated by stiffness. Bone mineral is necessary for proper stiffness but not sufficient. Therefore mechanical measurement should provide a new dimension to be used toward a better understanding of the factors related to bone health and disease.     

Pneumatic processes in the temporal bone of chimpanzee (Pan troglodytes) and gorilla (Gorilla gorilla)

The ontogeny of human temporal bone pneumatization has been well studied from both comparative and clinical perspectives. While a difference in the extent of air cell distribution has been noted in our closest living relatives, chimpanzees and gorillas, the processes responsible have been relatively unexplored. To examine these processes, a large, age‐graded series of hominoid skulls was radiographed and the progress of pneumatization recorded. Additionally, a subsample of 30 chimpanzees and 12 gorillas was subjected to high‐resolution CT scanning. Neonatal specimens show a well‐developed mastoid antrum, as well as a capacious hypotympanum extending into the petrous apex. In African apes, as in humans, the mastoid antrum serves as the focus for air cell expansion into the mastoid and immediately adjacent areas. In chimpanzees and gorillas, however, a pronounced lateral structure, described as the squamous antrum, serves as the focus of pneumatization for anterior structures such as the squamous and zygomatic. The diminution of this structure in Homo sapiens explains the difference in air cell distribution in these regions. J. Morphol. 241:127–137, 1999. © 1999 Wiley‐Liss, Inc.     

Improved frequency response of pneumotachometers by digital compensation

To measure impedance one measures or estimates flow, which is commonly done by measuring the pressure drop across a pneumotachometer. The frequency response characteristics of standard pneumotachometer/pressure transducers (PPT) limit their use to relatively low frequencies. Also, the frequency response of PPTs has been reported to be "load" dependent. Thus, the frequency response characteristics measured under "no-load" conditions, which theoretically could be used to compensate subsequent measurements, may not be appropriate for measurements made under loaded conditions. Another method of measuring impedance exists which depends on a reference impedance element other than a pneumotachometer. In this method, an oscillatory flow signal with known amplitude is generated and used to force the system being tested. Unlike PPTs, this oscillatory flow generator (OFG) is a closed system that allows measurements to be made only during breath holding. Our objective was to determine whether the frequency response of a PPT could be compensated using measurements made under no-load conditions, such that it accurately measured an impedance load. The frequency response of the PPT under no-load conditions was measured by the OFG and used to compensate the output of the PPT in subsequent impedance measurements. The compensated PPT was used to measure the impedance of a mechanical structure and the impedances of four human subjects. The impedances of the mechanical structure and the subjects were also measured using the OFG.(ABSTRACT TRUNCATED AT 250 WORDS)     

Noninvasive quantitative determination of the modulus of characteristic impedance of human limb arteries

A noninvasive method of quantitative evaluation of characteristic impedance modulus of human limb arteries based on blood pressure and blood vessel volume parameters is described. The differences in the value of characteristic impedance modulus in the upper and lower limb arteries in supine and resting subjects have been shown. Under postural effects the impedance changes in the lower limb arteries are proportional to those of mean blood pressure in these vessels. No significant impedance alterations on effort have been observed in these arteries. The impedance of the upper limb arteries increased in passive orthostatic position and after physical exercises of the lower limbs. Characteristic impedance modulus of these arteries decreased after physical exercises of the upper limbs.     

Interpretation of mechanical impedance of biological tissues in the three level model with the power source of vibrations

Theoretical expressions were derived for the mechanical impedance of a round piston on the surface of a viscoelastic triple layer with sublayers linked with each other and with the rigid base. The expressions were obtained on the assumption that the piston creates an even oscillatory pressure and does not create shear stresses. The calculations in the developed model were compared with corresponding calculations in the known strict model and with experimental values obtained on a relaxed and stressed human biceps. The results obtained suggest that models of this kind can be used for reconstructing the mechanical parameters of multilayer biological tissues.     

Frequency dispersions of human skin dielectrics.

The electrical properties of many biological materials are known to exhibit frequency dispersions. In the human skin, the impedance measured at various frequencies closely describes a circular locus of the Cole-Cole type in the complex impedance plane. In this report, the formative mechanisms responsible for the anomalous circular-arc behavior of skin impedance were investigated, using data from impedance measurements taken after successive strippings of the skin. The data were analyzed with respect to changes in the parameters of the equivalent Cole-Cole model after each stripping. For an exponential resistivity profile (Tregear, 1966, Physical Functions of Skin; Yamamoto and Yamamoto, 1976, Med. Biol. Eng., 14:151--158), the profile of the dielectric constant was shown to be uniform across the epidermis. Based on these results, a structural model has been formulated in terms of the relaxation theory of Maxwell and Wagner for inhomogeneous dielectric materials. The impedance locus obtained from the model approximates a circular are with phase constant alpha = 0.82, which compares favorably with experimental data. At higher frequencies a constant-phase, frequency-dependent component having the same phase constant alpha is also demonstrated. It is suggested that an approximately rectangular distribution of the relaxation time over the epidermal dielectric sheath is adequate to account for the anomalous frequency characteristics of human skin impedance.     

Dynamical simulation of speech cooperative articulation by muscle linkages

Different kinds of articulators, such as the upper and lower lips, jaw, and tongue, are precisely coordinated in speech production. Based on a perturbation study of the production of a fricative consonant using the upper and lower lips, it has been suggested that increasing the stiffness in the muscle linkage between the upper lip and jaw is beneficial for maintaining the constriction area between the lips (Gomi et al. 2002). This hypothesis is crucial for examining the mechanism of speech motor control, that is, whether mechanical impedance is controlled for the speech motor coordination. To test this hypothesis, in the current study we performed a dynamical simulation of lip compensatory movements based on a muscle linkage model and then evaluated the performance of compensatory movements. The temporal pattern of stiffness of muscle linkage was obtained from the electromyogram (EMG) of the orbicularis oris superior (OOS) muscle by using the temporal transformation (second-order dynamics with time delay) from EMG to stiffness, whose parameters were experimentally determined. The dynamical simulation using stiffness estimated from empirical EMG successfully reproduced the temporal profile of the upper lip compensatory articulations. Moreover, the estimated stiffness variation significantly contributed to reproduce a functional modulation of the compensatory response. This result supports the idea that the mechanical impedance highly contributes to organizing coordination among the lips and jaw. The motor command would be programmed not only to generate movement in each articulator but also to regulate mechanical impedance among articulators for robust coordination of speech motor control.     

Respiratory system dynamical mechanical properties: modeling in time and frequency domain

The mechanical properties of the respiratory system are important determinants of its function and can be severely compromised in disease. The assessment of respiratory system mechanical properties is thus essential in the management of some disorders as well as in the evaluation of respiratory system adaptations in response to an acute or chronic process. Most often, lungs and chest wall are treated as a linear dynamic system that can be expressed with differential equations, allowing determination of the system’s parameters, which will reflect the mechanical properties. However, different models that encompass nonlinear characteristics and also multicompartments have been used in several approaches and most specifically in mechanically ventilated patients with acute lung injury. Additionally, the input impedance over a range of frequencies can be assessed with a convenient excitation method allowing the identification of the mechanical characteristics of the central and peripheral airways as well as lung periphery impedance. With the evolution of computational power, the airway pressure and flow can be recorded and stored for hours, and hence continuous monitoring of the respiratory system mechanical properties is already available in some mechanical ventilators. This review aims to describe some of the most frequently used models for the assessment of the respiratory system mechanical properties in both time and frequency domain.     

Phase relationship between dynamics of the subglottic pressure and oscillatory movement of the vocal folds. I. Sustained phonation

The phase relationship between subglottic pressure and vocal fold length has been studied during sustained phonation in five subjects with normal larynx. Pressure was measured by tracheal puncture and vocal fold length was deduced from simultaneous measurement of translaryngeal impedance in the horizontal plane and transglottal light flux in the vertical plane. The pressure sine wave shows a phase lead of slightly less than 90 degrees relative to the length sine wave. Thus during sustained phonation the vocal apparatus behaves like a harmonic oscillator; the frequency of oscillation is determined by the mechanical parameters of the vibrating system; the source of periodic energy supply is the subglottal pressure wave.     

Multivariable static ankle mechanical impedance with relaxed muscles

Quantitative characterization of ankle mechanical impedance is important to understand how the ankle supports lower-extremity functions during interaction with the environment. This paper reports a novel procedure to characterize static multivariable ankle mechanical impedance. An experimental protocol using a wearable therapeutic robot, Anklebot, enabled reliable measurement of torque and angle data in multiple degrees of freedom simultaneously, a combination of inversion-eversion and dorsiflexion-plantarflexion. The measured multivariable torque-angle relation was represented as a vector field, and approximated using a method based on thin-plate spline smoothing with generalized cross validation. The vector field enabled assessment of several important characteristics of static ankle mechanical impedance, which are not available from prior single degree of freedom studies: the directional variation of ankle mechanical impedance, the extent to which the ankle behaves as a spring, and evidence of uniquely neural contributions. The method was validated by testing a simple physical "mock-up" consisting of passive elements. Experiments with young unimpaired subjects quantified the behavior of the maximally relaxed human ankle, showing that ankle mechanical impedance is spring-like but strongly direction-dependent, being weakest in inversion. Remarkably, the analysis was sufficiently sensitive to detect a subtle but statistically significant deviation from spring-like behavior if subjects were not fully relaxed. This method may provide new insight about the function of the ankle, both unimpaired and after biomechanical or neurological injury.     

A simultaneous electrochemical impedance and quartz crystal microbalance study on antihuman immunoglobulin G adsorption and human immunoglobulin G reaction

The quartz crystal microbalance (QCM), in combination with electrochemical impedance spectroscopy (EIS), has been utilized to monitor in situ antihuman IgG (hIgG) adsorption on bare poly(o-phenylenediamine) (PPD)- and 1-dodecanethiol (C12SH)-modified Au electrodes and succeeding human IgG reaction, respectively. The resonant frequency (f) and the motional resistance (R(1)) of the piezoelectric quartz crystal (PQC) as well as electrochemical impedance (EI) parameters were measured and discussed. The standard heterogeneous rate constants of the ferricyanide/ferrocyanide couple before and after the antibody adsorption and antibody-antigen reactions were determined. The results show that the amount for antibody adsorption was the greatest on the most hydrophobic (1-dodecanethiol-modified) surface, while the antibody bioactivity was almost identical on the three kinds of surfaces. Two parameters simultaneously obtained, Deltaf and DeltaC(s) (interfacial capacitance), have been used for the first time to estimate both the association constant of the immunoreaction and the valence of antigen with satisfactory results. The proposed method may find wide application in interfacial biochemistry studies for its advantages in providing real-time multidimensional piezoelectric and electrochemical impedance information.     

Modeling AC current conduction through a human tooth

Impedance between the electrode inserted in a root canal of a human tooth and the outer electrode placed on the oral mucosa serves as a measure of the root canal length, a vital parameter necessary for efficient endodontic procedure in dentistry. For better understanding of current conduction through the tooth, the impedance has been measured on extracted teeth (in vitro) and further used to develop corresponding electrical lumped element models. For modeling the metal/solution interface and complex structure of the tooth, Fricke's constant phase elements are employed. More detailed insight into current conduction is given by numerical simulation. Numerical simulation demonstrates the influence on the impedance of several important parameters, such as dentin conductance, canal preparation, and solution conductance.     

Characteristics of human fingertips in the shearing direction

The shearing strain of the human fingertip plays an important role in the determination of the optimal grasping force and in the perception of texture. Most research concerned with the mechanical impedance of the human fingertips has treated the orthogonal direction to the tip surface, and little attention has been paid to the tangential direction. This paper describes impedance characteristics of the human fingertips in the tangential directions to the tip surface. In the experiment, step and ramp shearing forces were individually applied to the tips of the thumb, middle finger, and little finger. Dynamics of the fingertips were represented by the Kelvin model. Experimental results show that each fingertip had different properties with respect to the shearing strain versus the applied force, and that the thumb had the strongest shearing stiffness among these three digits. Moreover, the shearing stiffness depended on the direction of the applied force, and the stiffness in the pointing direction was stronger than that in the perpendicular direction. As the contact force in the orthogonal direction to the fingertip surface was increased, the shearing stiffness and viscosity increased without regard to the load speed of the shearing force. Furthermore, it is shown that the average strain rate of the fingertip in the tangential direction to the fingertip surface became slower and converged to a constant value with higher contact forces.     

Computer modeling of the human systemic arterial tree

A model of the human systemic arterial tree has been devised, based on a lumped-parameter-circuit approximate form. This model has been set up and studied on an analog computer. A feature of this simulation is the division of the arterial system into sections whose lengths are inversely proportional (approximately) to their cross-sectional area-or what is termed ‘equal-volume’ modeling.

Great care was exercised in the determination of the model parameters, using expressions for these parameters from a recent paper by Rideout and Dick on fluid flow in distensible tubes, with numerical values based on measurements reported in the medical literature.

The simulated pressure and flow waveforms obtained with the model compare favorably with data recorded from the normal adult human, and exhibit such well-known features as distal delay and peaking of pressure pulses. The aortic input impedance vs. frequency curve checks well against measurements on the human. The model also provides a simple means for determination of cardiac output, cardiac work and cardiac power under various assumed conditions such as variation of heart rate.     

Wave Propagation through a Newtonian Fluid Contained within a Thick-Walled,Viscoelastic Tube

The propagation of harmonic pressure waves through a Newtonian fluid contained within a thick-walled, viscoelastic tube is considered as a model of arterial blood flow. The fluid is assumed to be homogeneous and Newtonian, and its motion to be laminar and axisymmetric. The wall is assumed to be isotropic, incompressible, linear, and viscoelastic. It is also assumed that the motion is such that the convective acceleration is negligible. The motion of the fluid is described by the linearized form of the Navier-Stokes equations and the motion of the wall by classical elasticity theory. The frequency dependence of the wall mechanical properties are represented by a three parameter, relaxation-type model. Using boundary conditions describing the continuity of stress and velocity components in the fluid and the wall, explicit solutions for the system of equations of the model have been obtained. The longitudinal fluid impedance has been expressed in terms of frequency and the system parameters. The frequency equation has been solved and the propagation constant also expressed in terms of frequency and system parameters. The results indicate that the fluid impedance is smaller than predicted by the rigid tube model or by Womersley''s constrained elastic tube model. Also, the velocity of propagation is generally slower and the transmission per wavelength less than predicted by Womersley''s elastic tube model. The propagation constant is very sensitive to changes in the degree of wall viscoelasticity.     

现代中国人颞骨乳突后部的形态变异

人类颞骨因其复杂的表面及内部结构成为演化研究的重要解剖部位之一,然而由于缺乏对现代人颞骨形态与变异的细致研究及对比数据,对颞骨一些特征的定义和鉴定价值还存在争议。迄今为止,尚无学者对现代中国人群颞骨形态与变异做过专门研究。有鉴于此,本文对颞骨乳突后部一些典型性状的形态变异在现代中国人及部分古人类的表现情况进行了研究。研究结果表明:1)除乳突旁隆起的发育水平存在性别差异外(不受地区差异影响),乳突切迹、枕乳嵴、枕动脉沟的出现率和发育水平既不受地区差异影响,又无性别差异。2)现代中国人乳突后部形态总体表现为窄而深的乳突切迹、明显的乳突旁隆起、以及发育程度较弱的枕动脉沟和枕乳嵴;3)在本文所研究的性状中,乳突切迹、乳突切迹前端隆起、乳突旁隆起、枕乳嵴和枕动脉沟均呈现不同程度的个体变异;4)一些被认为属于尼安德特人衍生特征的性状在中国古人类和现代中国人的乳突后部都有出现;5)本文研究的颞骨乳突后部形态特征在中国更新世晚期人类的表现与现代中国人接近。     

Characterization of human joint impedance during impulsive motion

The objective of the present work is to make use of the limited existing information on human joint impedance and to supplement and refine it synthetically, by means of simulation. A modular concept was applied to the construction of a joint model. The basic module was an individual revolute joint which was constrained by four resistive elements. The module was adapted to represent the different anatomical joints by specifying their corresponding mechanical parameters. The modular joint model was tested by incorporating it into a two dimensional whole body model and subjecting it to known impulsive conditions such as those reported in literature with regard to vehicular collision. Fine tuning was done by examining the sensitivity of the human model kinematic response to variation of the joint parameters. The whole body model was simulated with the aid of the ADAMS computer code. A comparison of the existing experimental data related to the sled test performed on a Hybrid III dummy with synthetic collision results showed good agreement.     

Simulation of the power transmission of bone-conducted sound in a finite-element model of the human head

Bone conduction (BC) sound is the perception of sound transmitted in the skull bones and surrounding tissues. To better understand BC sound perception and the interaction with surrounding tissues, the power transmission of BC sound is investigated in a three-dimensional finite-element model of a whole human head. BC sound transmission was simulated in the FE model and the power dissipation as well as the power flow following a mechanical vibration at the mastoid process behind the ear was analyzed. The results of the simulations show that the skull bone (comprises the cortical bone and diploë) has the highest BC power flow and thereby provide most power transmission for BC sound. The soft tissues was the second most important media for BC sound power transmission, while the least BC power transmission is through the brain and the surrounding cerebrospinal fluid (CSF) inside the cranial vault. The vibrations transmitted in the skull are mainly concentrated at the skull base when the stimulation is at the mastoid. Other vibration transmission pathways of importance are located at the occipital bone at the posterior side of the head while the transmission of sound power through the face, forehead and vertex is minor. The power flow between the skull bone and skull interior indicate that some BC power is transmitted to and from the skull interior but the transmission of sound power through the brain seem to be minimal and only local to the brain–bone interface.