bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of External Bending Moments on Lumbar Muscle Force Distribution
Authors: Ladin Z. , Murthy K. R. , De Luca C. J.
Published: March 2008

A detailed biomechanical model of the low-back musculature that predicts muscleforce distribution in response to external loading is presented. The paper shows that the class of loading tasks that involve an erect posture and an arbitrary load placed on the upper limbs can be described as a loading plane whose axes are the flexion and lateral bending moments. Under these conditions, the individual muscle forces are described as a three-dimensional surface defined by the loading plane and termed the muscle activity surface (MAS). The MAS and the loading plane intersect along the switching curve which separates the load combinations that activate the muscle from those that do not. The paper suggests the existence of a recruitment order of low back muscles in response to external loads and presents a comprehensive framework for examining earlier studies that used EMG measurements to validate physiological and mechanical predictions.
Hemodynamics Analysis of a Stenosed Carotid Bifurcation and its Plaque-Mitigating Design
Authors: Kleinstreuer C. , Nazemi M. , Archie J. P.
Published: March 2008

Considering transient two-dimensional laminar flow in a diseased carotid artery segment with realistic inlet and outflow conditions, detailed velocity profiles, pressure fields, wall shear stress distributions and coupled, localized plaque formations have been simulated. The type of outflow boundary condition influences to a certain degree the extent of plaque build-up, which in turn reduces “disturbed flow” phenomena such as flow separations, recirculation zones, and wavy flow patterns in the artery branches during portions of the pulse. Based on computer experiments varying key geometric factors, a plaque-mitigating design of a carotid artery bifurcation has been proposed. Elimination of the carotid bulb, a smaller bifurcation angle, lower area ratios, and smooth wall curvatures generated a design with favorable hemodynamics parameters, leading to reduced plaque build-up by factors of 10 and 2 in the internal carotid and in the external carotid, respectively.
Separated Flow Demonstrated by Digitized Cineangiography Compared With LDV
Authors: Smedby O¨. , Fuchs L. , Tillmark N.
Published: March 2008

In order to demonstrate separated flow in vivo, a method for the computerized analysis of cineangiographies has been developed, tested in vitro, and compared with LDV. A pulsatile flow was created in a glass model bifurcation, and velocity profiles were obtained with LDV at several phase angles. The flow was cinefilmed during contrast injection and the images were digitized. The computer then transformed the image sequence into parametric images representing arrival times of the contrast. The separation regions demonstrated with LDV were identified as areas with delayed contrast arrival. A preliminary analysis of a cineangiography in vivo is also included.
Prediction of Femoral Impact Forces in Falls on the Hip
Authors: Robinovitch S. N. , Hayes W. C. , McMahon T. A.
Published: March 2008

A major determinant of the risk of hip fracture in a fall from standing height is the force applied to the femur at impact. This force is determined by the impact velocity of the hip and the effective mass, stiffness, and damping of the body at the moment of contact. We have developed a simple experiment (the pelvis release experiment) to measure the effective stiffness and damping of the body when a step change in force is applied to the lateral aspect of the hip. Results from pelvis release experiments with 14 human subjects suggest that both increased soft tissue thickness over the hip and impacting the ground in a relaxed state can decrease the effective stiffness of the body, and subsequently reduce peak impact forces. Comparison between our fall impact force predictions and in-vitro measures of femoral fracture strength suggest that any fall from standing height producing direct, lateral impact on the greater trochanter can fracture the elderly hip.
An Experimental Method for Measuring Force on the Spinal Facet Joint: Description and Application of the Method
Authors: Buttermann G. R. , Kahmann R. D. , Lewis J. L. , Bradford D. S.
Published: March 2008

A technique is described for measuring load magnitude and resultant load contact location in the facet joint in response to applied loads and moments, and the technique applied to the canine lumbar spine motion segment. Due to the cantilever beam geometry of the cranial articular process, facet joint loads result in surface strains on the lateral aspect of the cranial articular process. Strains were quantified by four strain gages cemented to the bony surface of the process. Strain measured at any one gage depended on the loading site on the articular surface of the caudal facet and on the magnitude of the facet load. Determination of facet loads during in vitro motion segment testing required calibration of the strains to known loads of various magnitudes applied to multiple sites on the caudal facet. The technique is described in detail, including placement of the strain gages. There is good repeatability of strains to applied facet loads and the strains appear independent of load distribution area. Error in the technique depends on the location of the applied facet loads, but is only significant in nonphysiologic locations. The technique was validated by two independent methods in axial torsion. Application of the technique to five in vitro canine L2–3 motion segments testing resulted in facet loads (in newtons, N) of 74 + / −23 N (mean + /−STD) in 2 newton-meter, Nm, extension, to unloaded in flexion. Lateral bending resulted in loads in the right facet of 40 + /− 32 N for 1 Nm right lateral bending and 54 + / − 29 N for 1 Nm left lateral bending. 4 Nm Torsion with and without 100 N axial compression resulted in facet loads of 92 + / − 27 N and 69 + / − 19 N, respectively. The technique is applicable to dynamic and in vivo studies.
Stiffness of Canine Stifle Joint Ligaments at Relatively High Rates of Elongation
Authors: Mabuchi Kiyoshi , Hayatsu Kazunori , Fujie Hiromichi , Yamamoto Makoto
Published: March 2008

A falling-weight impact tester was developed specifically to evaluate the tensile characteristics of animal joints at high elongation rates. The tensile force and elongation in the ligaments of the canine stifle joint were measured using a force transducer, a linear variable displacement transducer, and a digital storage oscilloscope. Stiffness and elongation rates were determined at 1 mm and at 2 mm elongation. The stiffness was calculated as the slope of the force-elongation curve, and the elongation rate was calculated as the slope of the elongation-time curve. Results demonstrated that stiffness in the canine stifle joints was not affected by the rate of elongation in the 0.1 to 1.0 m/s range.
Thermographic Stress Analysis in Cortical Bone
Authors: Vanderby Ray , Kohles Sean S.
Published: March 2008

Under adiabatic (or near adiabatic) conditions a volumetric change in an elastic material will produce a corresponding change in temperature. Based upon this principle, thermographic stress analysis (TSA) measures changes in surface heat flux (which are related to changes in surface temperature) and relates them to a coupled form of strains or stresses. To demonstrate the feasibility of using this technique for biomechanical applications, we thermographically measured heat flux from loaded specimens of cortical bone and correlated the results with strain gage data. Regular parallelepipeds were cut from the cortex of bovine femora and loaded sinusoidally at 20 Hz. At this rate of loading, mechanically induced changes in surface temperature could be sampled (via heat flux) prior to a measureable attenuation of the thermoelastic effect. Correlation coefficients demonstrated a significant linear relationship between TSA and measured and computed mechanical parameters (stress, strain, first strain invariant, and strain energy density). TSA therefore appears to be a promising technology for experimental stress analysis in cortical bone.
Species Dependence of the Zero-Stress State of Aorta: Pig Versus Rat
Authors: Han H. C. , Fung Y. C.
Published: March 2008

The zero-stress state of an aorta can be characterized by the angle with which each segment of the vessel opens up when it is cut radially. The opening angle varies with the region of the aorta: significantly with respect to the axial location, less significantly with respect to polar angle of the radial cut. Both pig and rat aortas have large opening angles in the neighborhood of 130 deg in the aortic arch region. In the thoracic region, the species difference is evident. The opening angle of the pig aorta in the middle thoracic region is rather constant in the neighborhood of 60 deg. The opening angle of the rat aorta in the thoracic region varies considerably, decreasing to 10 deg at the lower end of the thoracic region. In the abdominal region the opening angle of the pig increases from 60 to about 80 deg, that of the rat increases from about 10 to 90 deg. The potassium ion has effect on vascular smooth muscle, but has little effect on the opening angle. This suggests that the opening angle is not sensitive to smooth muscle contraction, similar to a previously known result that the opening angle is not affected by papaverine. The vessel wall thickness and vessel diameter were measured. It is shown that the ratio of the wall thickness to diameter of the pig is considerably larger than that of the rat throughout the aorta. The opening angle is shown to correlate with the vessel thickness to diameter ratio in the straight portion of the aorta, but the opening angle is large in the aortic arch region where the axial curvature of the blood vessel is large.
The Pressure-Flow Relation for Plasma in Whole Organ Skeletal Muscle and Its Experimental Verification
Authors: Sutton Don W. , Schmid-Scho¨nbein Geert W.
Published: March 2008

The whole-organ pressure-flow relation in resting rat skeletal muscle is examined for the flow of plasma. Due to the small size of the blood vessels in this organ, inertia and convective forces in the blood are negligible and viscous forces dominate. Direct measurements in the past have shown that skeletal muscle blood vessels are distensible. Theoretical formulations based on these measurements lead to a third order polynomial model for the pressure-flow relation. The purpose of the current study is to examine this relation experimentally in an isolated muscle organ. A high precision feedback controlled pump is used to perfuse artificial plasma into the vasodilated rat gracilis muscle. The results indicate that the pressure-flow curve in this tissue is nonlinear in the low flow region and almost linear at physiological flow rates, following closely the third order polynomial function. Vessel fixation with glutaraldehyde causes the curves to become linear at all pressures, indicating that vessel distention is the primary mechanism causing the nonlinearity. Furthermore, the resistance of the post-fixed tissue is determined by the pressure at which the fixative is perfused. At fixation pressures below 10 mmHg, the resistance is three times higher than in vessels fixed at normal physiological pressures. Dextran (229,000 Dalton) is used to obtain Newtonian perfusates at different viscosities. The pressure-flow relation is found to be linearly dependent on viscosity for all flow rates. Skeletal muscle has multiple arterial inflows. Separate perfusion of the two major arterial feeders in the rat gracilis muscle show that for low pressures the flow at each feeder is dependent on the pressure at the opposite feeder, whereas at normal pressures the flow becomes independent of the opposite feeder pressure. The hemodynamic resistance in plasma perfused vasodilated skeletal muscle depends on vessel distensibility, plasma viscosity, and can be closely modeled by a third order polynomial relation.
Cardiac Mechanics at the Cellular Level
Authors: Tung Leslie , Parikh Sanjay S.
Published: March 2008

The active mechanical properties of heart muscle are load, length, and time-dependent. The capability for investigating cardiac mechanics at the cellular level may help to distinguish between those properties of the myocardium which arise from myocardial cells and those which arise from the tissue architecture and extracellular matrix of connective fibers. We present here, for the first time, a general approach for subjecting single heart cells to isometric, isotonic, afterloaded, or physiological loading sequences, while obtaining on-line measures of cell force and length. This approach has been implemented and tested on freshly dissociated, adult frog ventricular myocytes. Examples are presented for each of the four loading sequences.
A Noninvasive Method of Measuring Max(dP/dt) of the Left Ventricle by Doppler Echocardiography
Authors: Senda S. , Sugawara M. , Matsumoto Y. , Kan T. , Matsuo H.
Published: March 2008

Although slightly affected by alterations in preload, the maximum first derivative of left ventricular pressure with respect to time, Max(dP/dt), is widely regarded as a simple and convenient index of cardiac contractility for clinical use. The feasibility of noninvasive, hence repeatable, measurement of Max (dP/dt) will certainly lead to re-evaluation of its usefulness. Max(dP/dt) is given by the following equation: Max(dP/dt)=ρc Max(du/dt), where ρ is the blood density, c the pulse wave velocity, and u the flow velocity in the aorta. This equation has been previously validated in animal experiments and has now been applied to the clinical setting for the first time. In 20 patients without aortic stenosis, left ventricular pressure was measured with a catheter-tip micromanometer, aortic ejection flow velocity was measured by Doppler echocardiography, and pulse wave velocity by mechanocardiography or Doppler echocardiography. Then, δc Max (du/dt was calculated from the measured data and compared with measured Max (dP/dt). A significant positive correlation was found between them (ρc Max (du/dt) = 0.96 x Max (dP/dt) + 6.52, r=0.83, p<0.001.) In 11 patients with hypertension, ρc Max (du/dt) was obtained before and after long-term (average 13.1 months) treatment with antihypertensive drugs. In spite of the expected reduction in blood pressure and the regression of left ventricular mass, ρc Max (du/dt) remaioned unchanged. In 9 patients with dilated cardiomyopathy, the effects of β1-agonist were tested at the beginning of therapy (30 mg/day denopamine) and 6 months later. The increase in ρc Max (du/dt) observed 1 hour after oral administration of he drug had not changed significantly 6 months later. We conclude that the index ρc Max (du/dt), is useful in assessing the contractile state of the left ventricle noninvasively.
Numerical Analysis of Flow in an Elastic Artery Model
Authors: Dutta A. , Wang D. M. , Tarbell J. M.
Published: March 2008

Oscillatory and pulsatile flows of Newtonian fluids in straight elastic tubes are simulated numerically with the aid of Ling and Atabek’s “local flow” assumption for the nonlinear convective acceleration terms. For the first time, a theoretical assessment of the local flow assumption is presented, and the range of validity of the assumption is estimated by comparison with perturbation solutions of the complete flow problem. Subsequent simulations with the local flow model indicate that the flow field and associated wall shear stress are extremely sensitive to the phase angle between oscillatory pressure and flow waves (impedance phase angle). This phase angle, which is a measure of the wave reflection present in the system, is known to be altered by arterial disease (e.g., hypertension) and vasoactive drugs. Thus, the paper elucidates a mechanism by which subtle changes in systemic hemodynamics (i.e., phase angles) can markedly influence local wall shear stress values.
Longitudinal Tension Variation in Collapsible Channels: A New Mechanism for the Breakdown of Steady Flow
Authors: Pedley T. J.
Published: March 2008

There are several mechanisms potentially involved in the breakdown of steady fluid flow in a collapsible tube under external pressure. Here we investigate one that has received little attention in the past: the fact that the longitudinal tension in the tube wall, T, decreases with distance downstream as a consequence of the viscous shear stress exerted by the fluid. If the tube is long enough, or the initial tension small enough, T may fall to zero before the end of the collapsible tube, and unsteady motion would presumably then ensue; this is what we mean by “breakdown.” We study the phenomenon theoretically, when the flow Reynolds number is of order one, using lubrication theory in a symmetric two-dimensional channel in which the collapsible tube is replaced by membranes occupying a segment of each wall. The resulting nonlinear ordinary differential equations are solved numerically for values of the dimensionless parameters that cover all the qualitatively different types of solution (e.g., in which the channel is distended over all its length, collapsed over all its length, or distended in the upstream part and collapsed downstream). Reducing the longitudinal tension has a marked effect on the shape of the collapsible segment, causing it to become much more deformed for the same flow rate and external pressure. Indeed, the wall slope is predicted to become very large when the downstream tension is very small, so the model is not self-consistent then. Nevertheless, the parameter values for which T becomes zero are mapped out and are expected to be qualitatively useful. The relationships between the values of T during flow and its value before the flow begins is also considered.
A Numerical Simulation of Flow in a Two-Dimensional End-to-Side Anastomosis Model
Authors: Steinman D. A. , Vinh Bach , Ethier C. Ross , Ojha M. , Cobbold R. S. C. , Johnston K. W.
Published: March 2008

In order to understand the possible role that hemodynamic factors may play in the pathogenesis of distal anastomotic intimal hyperplasia, we carried out numerical simulations of the flow field within a two-dimensional 45 degree rigid-walled end-to-side model anastomosis. The numerical code was tested and compared with experimental (photochromic dye tracer) studies using steady and near-sinusoidal waveforms, and agreement was generally very good. Using a normal human superficial femoral artery waveform, numerical simulations indicated elevated instantaneous wall shear stress magnitudes at the toe and heel of the graft-host junction and along the host artery bed. These sites also experienced highly variable wall shear stress behavior over the cardiac cycle, as well as elevated spatial gradients of wall shear stress. These observations provide additional evidence that intimal hyperplasia may be correlated to wall shear stresses over the cardiac cycle, high wall shear stress gradients, or a combination of the three. The limitations of the present work (especially in regard to the two-dimensional nature of the flow simulations) are discussed, and results are compared to previous observations about distal anastomotic intimal hyperplasia.
Improved Cartesian Coordinate Finite Difference Simulations of Small Cylindrical Objects
Authors: Chen Zong-Ping , Roemer Robert B.
Published: March 2008

An analytical, cylindrical coordinate formula for the thermal resistance around small cylindrical objects has been incorporated into finite difference equations in Cartesian coordinates to improve the accuracy of the numerical simulations of hyperthermia cancer treatments. This is done by introducing a circular finite difference control volume which is centered on the cylindrical object. The temperature distributions calculated from this new formulation and from the formulation obtained from a conventional, rectangular control volume are compared to the predictions from an analytical solution. The results show that for a given Cartesian grid spacing, the new method is superior to the conventional one. This will allow more accurate numerical solutions to be obtained at larger grid spacings when the effect of blood vessels or other cylindrical objects, such as ferromagnetic implants, hot water tubes, etc., are being investigated.
Design and Development of a New General Purpose Stereotaxic Device
Authors: Dejoz R. , Prat J. , Sa´nchez-Lacuesta J. , Peris J. L. , Vera P. , Comi´n M.
Published: March 2008

This paper describes the design and development of a new device which allows the surgeon to locate an internal point following two X-ray views with an image intensifier. Three dimensional coordinates of the target point are directly estimated by means of two ring-and-bead sights and no computer calculations are necessary. After the location of the target point it is possible to choose any track to it by means of the rotation of an arc and the circumferential sliding of the arc. The system reduces radiation doses and it can be used for many purposes such as percutaneous discectomies and chemonucleolysis, biopsies and screw insertion of interlocking nails.
Mechanical and Electrical Responses of the Squid Giant Axon to Simple Elongation
Authors: Galbraith J. A. , Thibault L. E. , Matteson D. R.
Published: March 2008

There is a limited amount of information available on the mechanical and functional response of the nervous system to loading. While deformation of cerebral, spinal, or peripheral nerve tissue can have particularly severe consequences, most research in this area has concentrated on either demonstrating in-vivo functional changes and disclosing the effected anatomical pathways, or describing material deformations of the composite structure. Although such studies have successfully produced repeatable traumas, they have not addressed the mechanisms of these mechanically induced injuries. Therefore, a single cell model is required in order to gain further understanding of this complex phenomena. An isolated squid giant axon was subjected to controlled uniaxial loading and its mechanical and physiological responses were monitored with an instrument specifically designed for these experiments. These results determined that the mechanical properties of the isolated axon are similar to those of other soft tissues, and include features such as a nonlinear load-deflection curve and a hysteresis loop upon unloading. The mechanical response was modeled with the quasi-linear viscoelastic theory (Fung, 1972). The physiological response of the axon to quasi-static loading was a small reversible hyperpolarization; however, as the rate of loading was increased, the axon depolarized and the magnitude and the time needed to recover to the original resting potential increased in a nonlinear fashion. At elongations greater than twenty percent an irreversible injury occurs and the membrane potential does not completely recover to baseline.
Effects of Stress Shielding on the Mechanical Properties of Rabbit Patellar Tendon
Authors: Yamamoto N. , Ohno K. , Hayashi K. , Kuriyama H. , Yasuda K. , Kaneda K.
Published: March 2008

Mechanical properties of the stress-shielded patellar tendon were studied in the rabbit knee. Stress shielding was accomplished by stretching a stainless-steel wire installed between the patella and tibial tubercle and thus, releasing the tension in the patellar tendon completely. Tensile tests were carried out on the specimens obtained from the patellar tendons which were exposed to the stress shielding for 1 to 6 weeks. The stress shielding changed the mechanical properties of the patellar tendon significantly: it decreased the tangent modulus and tensile strength to 9 percent of the control values after 3 weeks. There was a 131 percent increase in the cross-sectional area and a 15 percent decrease in the tendinous length. Remarkable changes were also observed in the structural properties: for example, the maximum load of the bone-tendon complex decreased to 20 percent of the control value after 3 weeks. Histological studies showed that the stress shielding increased the number of fibroblasts and decreased the longitudinally aligned collagen bundles. These results imply that if no stress is applied to the autograft in the case of augmentative reconstruction of the knee ligament, the graft strength decreases remarkably.
The Kinematometer—An Integrated Kinematic Sensor for Kinesiological Measurements
Authors: Wu Ge , Ladin Zvi
Published: March 2008

The calculation of human joint forces and moments during locomotion is usually based on the solution of the “inverse dynamics problem.” A new approach, called the Integrated Kinematic Sensor (IKS) approach, is proposed. It combines measurements of position, linear acceleration and angular velocity, coupled with six degrees of freedom analysis of rigid body motion, for the purpose of deriving high quality link kinematics and joint loads (force and moment) estimates. The IKS approach is tested on an instrumented compound pendulum to simulate the swing of a lower limb segment. The results show a high degree of correlation between the loads estimated by the IKS and those directly measured by the instrumented joint. The approach is illustrated by studying the kinematic and dynamic variables of the human shank segment during normal walking. The results agree with the basic patterns reported in the literature, while adding new information on transients during heel strike and toe off.
An Experimental Model of Gas Dispersion and Uptake at the Bronchial Wall
Authors: Kaye S. R. , Schroter R. C.
Published: March 2008

Dispersion and uptake of gas boli of a range of solubilities was examined in lung airway models; first a straight tube, then a four generation network. Airway liquid lining was simulated with gelatin. The bolus dispersion was determined from the first three moments of the concentration profile measured at two positions downstream. The disruption of the flow by the bifurcations significantly reduces the dispersion of an insoluble gas, compared to that predicted in an equivalent network of parallel straight tubes. Retention of gas in the wall increases with solubility causing increased bolus dispersion and decreased average speed. For highly soluble gases this process dominates and the effect of bifurcations becomes less significant.
The Effects of Curvature on Fluid Flow Fields in Pulmonary Artery Models: Flow Visualization Studies
Authors: Lynch P. G. , Saylor A. , Ha B. , Lucas C. , Henry G. W. , Ferreiro J. I. , Yoganathan A. P.
Published: March 2008

In vitro pulsatile flow visualization studies were conducted to assess the effects of varying radii of curvature of the right ventricular outflow tract (RVOT) and main pulmonary artery (MPA) on the flow fields in the main, right, and left pulmonary arteries of a one month lamb pulmonary artery model. Three glass flow-through models were studied; one with no curvature, one with the correct anatomic curvature, and one with an overaccentuated curvature on the RVOT and MPA. All other geometric parameters were held constant. Pulsatile flow visualization studies were conducted at nine flow conditions; heart rates of 70, 100, and 140 bpm, and cardiac outputs of 1.5, 2.5 and 3.5 l/min with corresponding mean pulmonary pressures of 10, 20, and 30 mmHg. Changes were observed in the pulmonary flow fields as the curvature of the outflow tract, heart rate and mean pulmonary pressure were varied. An increase in vessel curvature led to an increase in the overall radial nature of the flow field as well as flow separation regions which formed faster, originated further downstream, and occupied more of the vessel area. At higher heart rates, the maximum size of the separation regions decreased, while flow separation regions appeared earlier in the cardiac cycle and grew more quickly. Heart rate also affected the initiation of flow reversal; flow reversal occurred later in the cardiac cycle at lower heart rates. Both heart rate and mean pulmonary pressure influenced the stability of the pulmonary flow field and the appearance of coherent structures. In addition, an increase in mean pulmonary pressure increased the magnitude of reverse flow. These flow visualization observations have directed more quantitative studies such as pulsed Doppler ultrasound and laser Doppler anemometry velocity measurements.
Relationship Between Achilles Tendon Mechanical Properties and Gastrocnemius Muscle Function
Authors: Trestik C. L. , Lieber R. L.
Published: March 2008

Strain was measured along the length of frog (Rana pipiens) gastrocnemius muscle-tendon units (MTU). Maximum muscle tension (P0) was measured, and the MTU was passively loaded to P0. Strain at P0 was measured at eight intervals along the tendon and aponeurosis and was approximately two percent for all regions except the aponeurosis region closest to the muscle fibers where it was about six percent. A computer model predicted sarcomere shortening of up to 0.5 μm due to tendon lengthening which demonstrates that tendons provide a more complex physiological function than simply transmitting muscle force to bones.
Multiple Minima in Inverse Hyperthermia Temperature Estimation Problems
Authors: Liauh C.-T. , Roemer R. B.
Published: March 2008

Using one-, two-, and three-dimensional numerical simulation models it is shown that multiple minima solutions exist for some inverse hyperthermia temperature estimation problems. This is a new observation that has important implications for all potential applications of these inverse techniques. The general conditions under which these multiple minima occur are shown to be solely due to the existence of symmetries in the bio-heat transfer model used to solve the inverse problem. General rules for determining the number of these global minimum points in the unknown parameter (perfusion) space are obtained for several geometrically symmetric (with respect to the sensor placement and the inverse case blood perfusion model) one-, two- and three-dimensional problem formulations with multiple perfusion regions when no model mismatch is present. As the amount of this symmetry is successively reduced, all but one of these global minima caused by symmetry become local minima. A general approach for (a) detecting when the inverse algorithm has converged to a local minimum, and (b) for using that knowledge to direct the search algorithm toward the global minimum is presented. A three-dimensional, random perfusion distribution example is given which illustrates the effects of the multiple minima on the performance of a state and parameter estimation algorithm. This algorithm attempts to reconstruct the entire temperature field during simulated hyperthermia treatments based on knowledge of measured temperatures from a limited number of locations.
Numerical Simulation of the Thermal Fields Occurring in the Treatment of Malignant Tumors by Local Hyperthermia
Authors: O’Brien K. T. , Mekkaoui A. M.
Published: March 2008

Dual beam microwave heating is known to deposit heat at depth in a medium. Thus transient heating times may be reduced and more even heating may be obtained. Such a system has potential in the treatment of cancer by hyperthermia. A theoretical analysis of this situation is presented here. A simulation has been made of the thermal fields generated in the treatment of malignant tumors using local hyperthermia. The simulation utilizes the alternating direction implicit method which is particularly suited to the solution of the governing equations, and provides rapid convergence in multiple dimensions. The simulation is three dimensional in temperature, with variations occurring through two spatial coordinates and one time coordinate. The simulation can accommodate the transient flow of heat due to conductive heat transfer through tissues such as healthy tissue, malignant tumors, cartilage and bone, convective heat transfer through perfusion in the tissue and flow through the arteries, and heat generation from sources such as microwave beams. Small changes in the thermophysical properties of the tissue, and the blood perfusion rates are shown to exhibit only minor effects on the thermal fields, whereas the power of the heat sources, and the conductive flux are shown to have major effects on the thermal fields. The effects of adjacent physiological structures such as arteries and bones have also been determined. The temperature fields have been found to be weakly dependent on the increased perfusion rates encountered in the arteries except when the perfusion rate in the artery exceeds that in the tissue by at least one order of magnitude. A similar effect is noticed if the tumor is close to a bone. The greater thermal insulation exhibited by the bone restricts the flow of heat into it, and therefore causes the tissue to increase in temperature. Once the transient heating has been employed and the heating proceeds under steady-state conditions, the dual beam microwave applicator must be controlled to avoid overheating. The effect of on/off control and proportional + integral + derivative control is discussed.
Viscous Airflow Through a Rigid Tube With a Compliant Lining: A Simple Model for the Air-Mucus Interaction in Pulmonary Airways
Authors: Evrensel Cahit A. , Khan Md. Raquib U. , Elli Shahram , Krumpe Peter E.
Published: March 2008

The respiratory tract of mammals is lined with a layer of mucus, described as viscoelastic semi-solid, above a layer of watery serous fluid. The interaction of these compliant layers with pulmonary airflow plays a major role in lung clearance by two-phase gas-liquid flow and in increased flow resistance in patients with obstructive airway diseases such as cystic fibrosis, chronic bronchitis and asthma. Experiments have shown that such coupled systems of flow-compliant-layers are quite susceptible to sudden shear instabilities, leading to formation of relatively large amplitude waves at the interface. Although these waves enhance the lung clearance by mobilizing the secretions, they increase the flow resistance in airways. The objective of this paper is to understand the basic interaction mechanism between the two media better by studying airflow through a rigid pipe that is lined by a compliant layer. The mathematical model that has been developed for this purpose is capable of explaining some of the published experimental observations. Wave instability theory is applied to the coupled air-mucus system to explore the stability of the interface. The results show that the onset flow speed for the initiation of unstable surface waves, and the resulting wavelength, are both very sensitive to mucus thickness. The model predicts that the instabilities initiate in the form of propagating waves for the elastic mucus where the wave speed is about 40 percent of the flow speed. The wavelength and phase speed to air velocity ratio are shown to increase with increasing mucus thickness. Also, results show that the mucus viscosity causes the onset air velocity to increase and the wave speed to decrease. The predictions of the model for the viscoelastic case are in good qualitative and quantitative agreement with some of the published experimental observations.
Laser Anemometry Measurements of Steady Flow Past Aortic Valve Prostheses
Authors: Chew Y. T. , Low H. T. , Lee C. N. , Kwa S. S.
Published: March 2008

An experimental investigation was conducted in steady flow to examine the fluid dynamics performance of three prosthetic heart valves of 27 mm diameter: Starr-Edwards caged ball valve, Bjork-Shiley convexo-concave tilting disk valve, and St. Vincent tilting disk valve. It was found that the pressure loss across the St. Vincent valve is the least and is, in general, about 70 percent of that of the Starr-Edwards valve. The pressure recovery is completed about 4 diameters downstream. The velocity profiles for the ball valve reveal a large single reversed flow region behind the occluder while those for the tilting disks valves reveal two reversed flow regions immediately behind the occluders. Small regions of stasis are also found near the wall in the minor opening of Bjork-Shiley valve and in the major opening of St. Vincent valve. The maximum wall shear stresses of the three valves at a flow rate of 30 l/min are in the range 30–50 dyn/cm2 which can cause hemolysis of attached red blood cells. The corresponding maximum Reynolds normal stresses are in the range of 1600–3100 dyn/cm2. The Reynolds normal stresses decay quickly and return approximately to the upstream undisturbed level at about 4 diameters downstream while the wall shear stresses decay at a slower rate. The maximum Reynolds normal stresses occur at about 1 diameter downstream while the maximum wall shear stress is at about 2 diameters downstream. In general, the St. Vincent valve has better performance. A method to compensate for refractive index variations and curvature effect of the sinus region of the aorta root using laser doppler anemometer measurements is also proposed.
Application of the Joint Coordinate System to Three-Dimensional Joint Attitude and Movement Representation: A Standardization Proposal
Authors: Cole G. K. , Nigg B. M. , Ronsky J. L. , Yeadon M. R.
Published: March 2008

The selection of an appropriate and/or standardized method for representing 3-D joint attitude and motion is a topic of popular debate in the field of biomechanics. The joint coordinate system (JCS) is one method that has seen considerable use in the literature. The JCS consists of an axis fixed in the proximal segment, an axis fixed in the distal segment, and a “floating” axis. There has not been general agreement in the literature on how to select the body fixed axes of the JCS. The purpose of this paper is to propose a single definition of the body fixed axes of the JCS. The two most commonly used sets of body fixed axes are compared and the differences between them quantified. These differences are shown to be relevant in terms of practical applications of the JCS. Argumentation is provided to support a proposal for a standardized selection of body fixed axes of the JCS consisting of the axis eˆ1 embedded in the proximal segment and chosen to represent flexion-extension, the “floating” axis eˆ2 chosen to represent ad-abduction, and the axis eˆ3 embedded in the distal segment and chosen to represent axial rotation of that segment. The algorithms for the JCS are then documented using generalized terminology.
A Two-Dimensional Dynamic Anatomical Model of the Human Knee Joint
Authors: Abdel-Rahman Eihab , Hefzy Mohamed Samir
Published: March 2008

The objective of this study is to develop a two-dimensional dynamic model of the knee joint to simulate its response under sudden impact. The knee joint is modeled as two rigid bodies, representing a fixed femur and a moving tibia, connected by 10 nonlinear springs representing the different fibers of the anterior and posterior cruciate ligaments, the medial and lateral collateral ligaments, and the posterior part of the capsule. In the analysis, the joint profiles were represented by polynomials. Model equations include three nonlinear differential equations of motion and three nonlinear algebraic equations representing the geometric constraints. A single point contact was assumed to exist at all times. Numerical solutions were obtained by applying Newmark constant-average-acceleration scheme of differential approximation to transform the motion equations into a set of nonlinear simultaneous algebraic equations. The equations reduced thus to six nonlinear algebraic equations in six unknowns. The Newton-Raphson iteration technique was then used to obtain the solution. Knee response was determined under sudden rectangular pulsing posterior forces applied to the tibia and having different amplitudes and durations. The results indicate that increasing pulse amplitude and/or duration produced a decrease in the magnitude of the tibio-femoral contact force, indicating thus a reduction in the joint stiffness. It was found that the anterior fibers of the posterior cruciate and the medial collateral ligaments are the primary restraints for a posterior forcing pulse in the range of 20 to 90 degrees of knee flexion; this explains why most isolated posterior cruciate ligament injuries and combined injuries to the posterior cruciate ligament and the medial collateral results from a posterior impact on a flexed knee.
Dynamic Behavior Analysis of Mechanical Monoleaflet Heart Valve Prostheses in the Opening Phase
Authors: Cheon Gill-Jeong , Chandran K. B.
Published: March 2008

In this paper, fluttering behavior of a mechanical monoleaflet tilting disk heart valve prostheses during the opening phase was analyzed. The impact between the occluder and the guiding strut at the fully open position was included in the analysis with a Bjork-Shiley monoleaflet aortic valve. The motion of the valve occluder was modeled as a rotating system, and equations were derived by employing the moment equilibrium principle. Forces due to lift, drag, gravity, and buoyancy were considered as external forces acting on the occluder. The 4th-order Runge-Kutta method was used to solve the governing equations. The results demonstrated that the occluder reaches the steady equilibrium position only after damped vibration. Fluttering frequency varies as a function of time after opening and is in the range of 8–84 Hz. Valve opening appears to be affected by the orientation of the valve relative to gravitational force. The opening velocities are in the range of 0.56–1.37 m/sec and the dynamic loads by impact of the occluder and the strut are in the range of 60–190 N.
Biomechanics of Diarthrodial Joints: A Review of Twenty Years of Progress
Authors: Mow Van C. , Ateshian Gerard A. , Spilker Robert L.
Published: March 2008

A survey of some of the advances made over the past twenty years in understanding diarthrodial joint biomechanics is presented. Topics covered in this review include: biotribology (i.e., friction, lubrication and wear of diarthrodial joints); contact area determinations; stereophotogrammetric rendering of articular surfaces; deformational field analysis using canonical problems; and finite element formulations for both infinitesimal and finite deformations of diphasic materials and precise anatomic surfaces. Suggestions are made for future research directions as well.
Experimental Approaches on Measuring the Mechanical Properties and Constitutive Laws of Arterial Walls
Authors: Hayashi Kozaburo
Published: March 2008

Studies on the elastic properties of arterial walls which have been done for the past two decades are surveyed briefly. After several in vitro and in vivo experimental methods and clinical techniques for the measurements of the mechanical behavior of arterial walls have been reviewed, data obtained of the basic characteristics of the arterial wall, including wall incompressiblity and anisotropy, are discussed. The author then reviews constitutive laws proposed for the description of stress-strain relationships of arterial walls and methods for the parametric expression of pressure-diameter data, and shows data on the effects of aging and vascular diseases on arterial mechanics. Finally, residual stress in the arterial wall is discussed.
Active Motion of Polymorphonuclear Leukocytes in Response to Chemoattractant in a Micropipette
Authors: Skierczynski B. A. , Usami S. , Chien S. , Skalak R.
Published: March 2008

A novel experimental method of producing and observing the active motion of polymorphonuclear leukocytes (PMNs) using a micropipette technique has been recently developed (Usami et al., 1992). The present paper develops a quantitative theory for the chemoattractant gradients and cell locomotion observed in these experiments. In previous experimental methods (e.g., the Boyden chamber, the Zygmond chamber and the Dunn chamber) for study chemotaxis of leukocytes, fibroblasts, and PMNs, the exact nature of the concentration gradient of the chemoattractant is unknown. The cells may themselves modify the local gradient of the chemoattractant. In experiments using the micropipette, an internal source of chemoattractant provides well-defined boundary and initial conditions which allow the computation of the chemoattractant concentration gradient during the active locomotion of the PMNs. Since the cell completely fills the pipette lumen, convection is limited to the motion of the cells themselves. In coordinates moving with cell, it is assumed that diffusion is the only mechanism of mass transport of the chemoattractant (fMLP). Computations of the fMLP concentration during locomotion of the cell were carried out for a range of rates of fMLP binding by the receptors expressed on the front face of the cell membrane. The results show that the front face of the cell is subjected to increasing fMLP concentration during the cell motion. The sequence of events involve receptor binding of fMLP, signal transduction, polymerization of the cell cytoskeleton at the membrane of the front face, spatially dependent adhesion to the pipette wall, and localized contraction of the cytoskeleton. This sequence of events leads to the steady locomotion of the leukocytes in the micropipette. The computation of the distribution of the fMLP concentration during cell locomotion with constant velocity in micropipette experiments shows that the cell is exposed to increasing concentration of fMLP. This suggests that chemotaxis maybe induced by temporal gradient of an attractant.
Scanning Acoustic Microscope Studies of the Elastic Properties of Osteons and Osteon Lamellae
Authors: Katz J. Lawrence , Meunier Alain
Published: March 2008

Scanning acoustic microscopy (SAM) provides the means for studying the elastic properties of a material at a comparable level of resolution to that obtained by optical microscopy for structural studies. SAM is nondestructive and permits observation of properties in the interior of materials which are optically opaque. Two modes of ultrasonic signals have been used in a Model UH3 Scanning Acoustic Microscope (Olympus Co., Tokyo, Japan) as part of a continuing study of the microstructural properties of bone. The pulse mode, using a single narrow pulse in the range of 30 MHz to 100 MHz, has been used to survey the surface and interior of specimens of human and canine femoral compact cortical bone at resolutions down to approximately 30μm. To obtain more detailed information at significantly higher resolution, the burst mode, comprised of tens of sinusoids, has been used at frequencies from 200 MHz to 600 MHz. This has provided details of both human and canine single osteons (or haversion systems) and osteonic lamellae at resolutions down to approximately 1.7μm, well within the thickness of a lamella as viewed in a specimen cut transverse to the femoral axis.
The Coronary Circulation
Authors: Mates Robert E.
Published: March 2008

Dramatic advances have been made in the last two decades in the diagnosis and treatment of coronary artery disease. The development of open heart surgical techniques for bypassing occluded arteries made quantitative diagnostic techniques more important. Computer enhanced angiographic methods, together with measurements using tomography, ultrasound and magnetic resonance imaging have greatly improved the precision of the diagnosis. A more complete understanding of coronary mechanics and control has enabled physicians to better interpret the significance of geometric information and to supplement this information with functional assessment of stenosed arteries. Finally, traditional bypass surgery is now supplemented with closed-chest techniques such as balloon angioplasty. Biomedical engineers have been involved in all of these developments. This paper will review these developments and attempt to identify remaining questions.