bluuebunny/crossref_metadata_2025 huggingface dataset:
Velocity Profiles in Stenosed Tube Models Using Magnetic Resonance Imaging
Authors: Rittgers S. E. , Fei Ding-yu , Kraft K. A. , Fatouros P. P. , Kishore P. R. S.
Published: June 2009

A time-of-flight MRI velocity measurement technique is evaluated against corresponding LDV measurements in a constriction tube model over a range of physiologic flow conditions. Results from this study show that MR displacement images can: 1) be obtained within both laminar and turbulent jets (maximum stenotic Re≅4,200), 2) measure mean jet velocities up to 172 cm/s, and, 3) detect low forward and reverse stenosis (0≤L/D≤2). Regions between the jet termination point and re-establishment of laminar flow (Re≥1500, ≥1000, and ≥110 downstream of 40, 60, and 80 percent stenosis, respectively) cannot presently be detected by this technique.
Mechanical Properties of the Lateral Collateral Ligament: Effect of Cruciate Instability in the Rabbit
Authors: Tozilli P. A. , Arnoczky S. P.
Published: June 2009

Concomitant soft tissue injury resulting from knee instability following cruciate rupture is a serious clinical problem. To study this injury mechanism, the biomechanical properties of the lateral collateral ligament were measured at 0, 4, 8, 12, and 16 weeks post-operatively in rabbits having the anterior and posterior cruciate ligaments sectioned. No significant changes were found in the ligament’s cross-sectional area, tensile mechanical response, or in its hexosamine content. The predominant mode of ligament failure was by bone avulsion at the insertion sites (78 percent) with 86 percent of paired limbs failing in a similar manner.
Nonlinear Gross Response Analysis of a Lumbar Motion Segment in Combined Sagittal Loadings
Authors: Shirazi-Adl A. , Drouin G.
Published: June 2009

A 3-D nonlinear mathematical model is used to analyze the mechanical response of a lumbar L2–3 motion segment including the posterior elements when subjected to combined sagittal plane loads. The loadings consist of axial compression force, anterior and posterior shear forces, and flexion and extension moments. The facet articulation is modelled as a general moving contact problem and the ligaments as a collection of uniaxial elements. The disk nucleus is considered as an inviscid fluid and the annulus as a composite of collagenous fibers embedded in a matrix of ground substance. The presence of axial compression force reduces the segmental stiffness in flexion whereas a reverse trend is predicted in extension. In the presence of axial compression with and without sagittal shear force, flexion considerably increases the intradiscal pressure while extension reduces it. In other words, under an identical compression force, disk pressure is predicted to be noticeably larger in flexion than in extension. The segmental mechanical response in extension loadings is markedly influenced by the changes in the relative geometry of the articular surfaces at the lower regions. Finally, the deformation of the bony structures plays a significant role in the segmental mechanics under relatively large loads.
An Analytical Solution Countercurrent Heat Transfer Between Parallel Vessels With a Linear Axial Temperature Gradient
Authors: Wissler E. H.
Published: June 2009

Presented in this paper is a solution for countercurrent heat exchange between two parallel vessels embedded in an infinite medium with a linear temperature gradient along the axes of the vessels. The velocity profile within the vessel is assumed to be parabolic. This solution describes the temperature field within the vessels, as well as in the tissue, and establishes that the intravessel temperature is not uniform, as is generally assumed to be the case. An explicit expression for the intervessel thermal resistance based on the difference between cup-mixed mean temperatures is derived.
A Combined Macro and Microvascular Model for Whole Limb Heat Transfer
Authors: Song W. J. , Weinbaum S. , Jiji L. M. , Lemons D.
Published: June 2009

A new prototype model for whole limb heat transfer is proposed wherein the countercurrent heat exchange from the large central arteries and veins in the core of the limb is coupled to microvascular models for the surrounding muscle and the cutaneous tissue layers. The local microvascular temperature field in the muscle tissue is described by the bioheat equation of Weinbaum and Jiji [1]. The new model allows for an arbitrary axial variation of cross-sectional area and blood distribution between the muscle and cutaneous tissue, accounts for the blood flow to and heat loss from the hand and treats the venous return temperature and surface temperature distribution as unknowns that are determined as part of the solution to the overall boundary value problem. Representative solutions are presented for a wide range of environmental conditions for a limb in both the resting state and during exercise.
Thermal Modeling of the Malignant Woman’s Breast
Authors: Osman M. M. , Afify E. M.
Published: June 2009

In this paper the conceptual three-dimensional model of the normal woman’s breast presented in Osman and Afify [1], is developed into a detailed quantitative model of the malignant woman’s breast. This model takes into consideration the effect of tumor size and location on the metabolic heat production, blood perfusion rate, and thermal contour plot of the malignant breast for each tumor size, depth, and location. Also the results of this investigation show that a hot spot in the malignant woman’s breast thermal contour plot may not be directly related to an embedded tumor beneath the breast surface.
Heat Transfer Normal to Paired Arterioles and Venules Embedded in Perfused Tissue During Hyperthermia
Authors: Charny C. K. , Levin R. L.
Published: June 2009

A numerical model of the heat transer normal to an arteriole-venule pair embedded in muscle tissue has been constructed. Anatomical data describing the blood vessel size, spacing, and density have been incorporated into the model. This model computes temperatures along the vessel walls as well as the temperature throughout the tissue which comprises an infinitely long Krogh cylinder around the vessel pair. Tissue temperatures were computed in the steady-state under resting conditions, while transient calculations were made under hyperthermic conditions. Results show that for both large- (1st generation) and medium-sized (5th generation) vessel pairs, the mean tissue temperature within the tissue cylinder is not equal to the mean of the arteriole and venule blood temperatures under both steady-state and transient conditions. The numerical data were reduced so that a comparison could be made with the predictions of a simple two-dimensional superposition of line sources and sinks presented by Baish et al. [1]. This comparison reveals that the superposition model accurately describes the heat transfer effects during hyperthermia, permitting subsequent incorporation of this theory into a realistic three-dimensional model of heat transfer in a whole limb during hyperthermia.
Flow Measurements in a Human Femoral Artery Model With Reverse Lumen Curvature
Authors: Back L. H. , Back M. R. , Kwack E. Y. , Crawford D. W.
Published: June 2009

Flow visualization and wall pressure measurements were made in a smooth reverse curvature model that conformed to the gentle “s” shape of a left femoral artery angiogram of a patient in a clinical trial. Observed lesion localization at the inner (lesser) curvatures appeared to be associated with secondary flows in the wall vicinity directed toward the inner curvatures that tended to reverse direction in the flow entering the reverse curvature region. Moderate flow resistance increases of about 20 percent above the Poiseuille flow relation were found at the higher physiological Reynolds numbers Re above about 600–700 and thus Dean numbers for steady flow. For pulsatile flow simulation, flow resistances did not increase up to the largest Re of 470 tested. Apparently, the large variations in velocity during the cardiac cycle disrupted the stronger secondary flow patterns observed at the higher Reynolds numbers for steady flow.
Flow Measurements in an Atherosclerotic Curved, Tapered Femoral Artery Model of Man
Authors: Back L. H. , Kwack E. Y. , Crawford D. W.
Published: June 2009

Flow visualization and pressure measurements were made for physiological conditions in a model derived from a femoral angiorgram of a patient with lesion localization on the inner curvature wall and with vessel taper. Effects of curvature and taper were evaluated separately in other curved, tapered, smooth and straight, tapered, smooth models. Double helical secondary flow patterns were modified by plaque on the inner wall, and flow separations were observed between plaques at higher flow rates and Reynolds numbers. Pressure drop data for the plaque simulation model were similar in trend with Reynolds number as for the smooth model, but flow resistances were 25 to 40 percent higher. Significant pressure drops were measured due to the mild taper which could be estimated from momentum considerations, and smaller increased pressure drops were found due to curvature effects at the higher Dean numbers. Flow resistances for in vivo pulsatile flow simulation were about 10 percent higher than for steady flow for the plaque model, whereas no differences were observed for the smooth model.
Relationship Between Mechanical Properties and Collagen Structure of Closed and Open Wounds
Authors: Doillon Charles J. , Dunn Michael G. , Silver Frederick H.
Published: June 2009

Mechanical properties and collagen structure of excisional wounds left open are compared with wounds closed by clips. In both wound models, collagen fiber diameter increases with time post-wounding and is related to tensile strength. Clipped wounds show a higher ultimate tensile strength and tangent modulus compared with open wounds. In clipped wounds, newly deposited collagen appears as a biaxially oriented network as observed in normal skin. In open wounds a delay in the organization of the collagen network is observed and parallel wavy-shaped ribbons of collagen fibers are deposited. At long term, the high extensibility observed in open wounds may be due to the sliding of ribbons of collagen fibers past each other.
Analytical Description of Minimum Energy Expenditure Surfaces
Authors: Winarski D. J. , Pearson J. R.
Published: June 2009

Mechanical energy expenditure during level walking was evaluated and graphed for two unilateral, below-knee amputees over time and a range of adjustments of the flexion-extension alignment angle. The resulting mechanical energy surfaces were then least-squared fitted with an analytical function that was linear in time and quadratic in flexion-extension alignment angle. The least-squares analysis showed that there was a flexion-extension adjustment that minimized the mechanical energy expenditure and that this optimal adjustment was very close to the design point set by certified prosthetists.
Three-Dimensional Kinematic Modelling of the Human Shoulder Complex—Part II: Mathematical Modelling and Solution Via Optimization
Authors: Tu¨mer S. T. , Engin A. E.
Published: June 2009

In this paper, individual joint sinus cones associated with the sternoclavicular, claviscapular, and glenohumeral joints of the three-dimensional kinematic model introduced in Part I for the human shoulder complex are quantitatively determined. First, mathematical description of the humerus orientation with respect to torso is given in terms of eight joint variables. Since the system is a kinematically redundant one, solution for the joint variables satisfying a prescribed humerus orientation is possible only if additional requirements are imposed; and the “minimum joint motion” criterion is introduced for this purpose. Two methods, namely the Lagrange multipliers and flexible tolerance methods, are formulated and tested for the optimization problem. The statistical in-vivo data base for the circumductory motion of the upper arm is employed to determine a set of joint variables via optimization, which are then utilized to establish the sizes and orientations of the elliptical cones for the individual joint sinuses. The results are discussed and compared with those given on the basis of measurements made on cadaveric specimens.
A Theoretical Model of Localized Heat and Water Vapor Transport in the Human Respiratory Tract
Authors: Hanna L. M. , Scherer P. W.
Published: June 2009

A steady-state, one-dimensional theoretical model of human respiratory heat and water vapor transport is developed. Local mass transfer coefficients measured in a cast replica of the upper respiratory tract are incorporated into the model along with heat transfer coefficients determined from the Chilton-Colburn analogy and from data in the literature. The model agrees well with reported experimental measurements and predicts that the two most important parameters of the human air-conditioning process are: 1) the blood temperature distribution along the airway walls, and 2) the total cross-sectional area and perimeter of the nasal cavity. The model also shows that the larynx and pharynx can actually gain water over a respiratory cycle and are the regions of the respiratory tract most subject to drying. With slight modification, the model can be used to investigate respiratory heat and water vapor transport in high stress environments, pollutant gas uptake in the respiratory tract, and the connection between respiratory air-conditioning and the function of the mucociliary escalator.
Stress Analysis and Failure Prediction in the Proximal Femur Before and After Total Hip Replacement
Authors: Vichnin H. H. , Batterman S. C.
Published: June 2009

An investigation was performed to determine the effects of the presence of two lengths of proximal Mu¨ller prosthesis on predicted failure loads, as compared to those for an intact femur. Three-dimensional stresses in a bone/cement/prosthesis system were determined using finite element methods, with both isotropic and transversely isotropic material properties used for the diaphyseal cortex. Significant increases in prosthesis stem stresses were found when the transversely isotropic material properties were employed in the diaphyseal cortex. This leads to the conclusion that accurate anisotropic material properties for bone are essential for precise stress determination and optimum design in prosthetic implants. Failure loads were also predicted for vertical compression and axial torque, similar to available experimental conditions, and were within the range of the experimental failure data found in the literature. The technique developed herein can be used to systematically assess existing as well as future implant designs, taking into account the complex three-dimensional interaction effects of the overall bone/cement/prosthesis system.
Sensitivity of Insertion Locations on Length Patterns of Anterior Cruciate Ligament Fibers
Authors: Hefzy M. S. , Grood E. S.
Published: June 2009

A technique is demonstrated, employing an instrumented spatial linkage, for the determination of the length patterns of discrete fiber bundles within a ligament under controlled loading conditions. The instrumented spatial linkage was used to measure the three-dimensional joint motion. The linkage was also used as a three-dimensional coordinate digitizer to determine the spatial location of bony landmarks and the ligament’s insertion areas. The length of pseudo fiber bundles was determined as the straight line distance between bone attachments. A comparison is presented, showing good agreement, between elongation patterns obtained from this method and those measured using an instrumented fine wire cable fiber. A sensitivity analysis was performed to evaluate the influence of tibial and femoral attachment location on the length pattern of fiber bundles of the anterior cruciate ligament. It was found that the relationship between fiber elongation and knee flexion depended strongly on the fibers femoral attachment location but not on its tibial attachment location.
Parametric Studies on the Three-Layer Microcirculatory Model for Surface Tissue Energy Exchange
Authors: Dagan Z. , Weinbaum S. , Jiji L. M.
Published: June 2009

The new three-layer microvascular mathematical model for surface tissue heat transfer developed in [1, 2], which is based on detailed vascular casts and tissue temperature measurements in the rabbit thigh, is used to investigate the thermal characteristics of surface tissue under a wide variety of physiological conditions. Studies are carried out to examine the effects of vascular configuration, arterial blood supply rate, distribution of capillary perfusion, cutaneous blood circulation and metabolic heat production on the average tissue temperature profile, the local arterial-venous blood temperature difference in the thermally significant counter-current vessels, and surface heat flux.
A Three-Dimensional Finite Element Analysis of the Upper Tibia
Authors: Little R. B. , Wevers H. W. , Siu D. , Cooke T. D. V.
Published: June 2009

A three-dimensional finite element model of the proximal tibia has been developed to provide a base line for further modeling of prosthetic resurfaced tibiae. The geometry for the model was developed by digitizing coronal and transverse sections made with the milling machine, from one fresh tibia of average size. The load is equally distributed between the medial and lateral compartments over contact areas that were reported in the literature. An indentation test has been used to measure the stiffness and the ultimate strength of cancellous bone in four cadaver tibiae. These values provided the statistical basis for characterising the inhomogeneous distribution of the cancellous bone properties in the proximal tibia. All materials in the model were assumed to be linearly elastic and isotropic. Mechanical properties for the cortical bone and cartilage have been taken from the literature. Results have been compared with strain gage tests and with a two-dimensional axisymmetric finite element model both from the literature. Qualitative comparison between trabecular alignment, and the direction of the principal compressive stresses in the cancellous bone, showed a good relationship. Maximum stresses in the cancellous bone and cortical bone, under a load which occurs near stance phase during normal gait, show safety factors of approximately eight and twelve, respectively. The load sharing between the cancellous bone and the cortical bone has been plotted for the first 40 mm distally from the tibial eminence.
A Comparison of the Mechanical Behavior of the Cat Soleus Muscle With a Distribution-Moment Model
Authors: Zahalak G. I.
Published: June 2009

A state-variable model for skeletal muscle, termed the “Distribution-Moment Model,” is derived from A. F. Huxley’s 1957 model of molecular contraction dynamics. The state variables are the muscle stretch and the three lowest-order moments of the bond-distribution function (which represent, respectively, the contractile tissue stiffness, the muscle force, and the elastic energy stored in the contractile tissue). The rate equations of the model are solved under various conditions, and compared to experimental results for the cat soleus muscle subjected to constant stimulation. The model predicts several observed effects, including (i) yielding of the muscle force in constant velocity stretches, (ii) different “force-velocity relations” in isotonic and isovelocity experiments, and (iii) a decrease of peak force below the isometric level in small-amplitude sinusoidal stretches. Chemical energy and heat rates predicted by the model are also presented.
The Material Properties of Bone-Particle Impregnated PMMA
Authors: Park H. C. , Liu Y. K. , Lakes R. S.
Published: June 2009

The elastic Young’s modulus and shear modulus of bone-particle impregnated polymethylmethacrylate (PMMA) has been measured experimentally at room temperature as a function of bone particle concentration. It was found that the moduli increased with increasing bone particle content. This increase was less than the stiffness increase predicted by higher-order composite theory [1, 2] under the assumption of perfect bonding between particles and matrix. It was concluded that a bond existed but that it was not a perfect bond.
Design and Performance of a Modified Buckle Transducer for the Measurement of Ligament Tension
Authors: Barry D. , Ahmed A. M.
Published: June 2009

The basic features of a modified buckle transducer for the direct in-situ measurement of tension in ligamentous or tendonous tissues are described. The slender shape of the modified design allows measurement in ligaments located in confined spaces with reduced risk of physical interference between the transducer and adjacent bony structures. In addition, simultaneous measurements in different fiber groups of the same ligament are made convenient. The design procedure of the proposed transducer and its performance characteristics are described.
Viscoelastic Properties of Microvessels in Rat Spinotrapezius Muscle
Authors: Skalak T. C. , Schmid-Scho¨nbein G. W.
Published: June 2009

In order to establish a quantitative model of blood flow in skeletal muscle, the mechanical properties of the blood vessels need to be measured. We present measurements of the viscoelastic properties of arterioles, venules, and capillaries in exteriorized rat spinotrapezius muscle. Muscles were perfused with an inert silicone polymer and a uniform static pressure was established by occlusion of the venous outflow. Vessel diameters were then measured as a function of the static pressure. This study provides the first measurements of the viscoelastic properties of microvessels in skeletal muscle in situ. Over a pressure range of 20–200 mmHg, the transverse arterioles are the most distensible vessels, while the arcade venules are the stiffest. In response to a step change in pressure, all vessels show an initial elastic deformation, followed by a nonlinear creep. Based on the experimental results for different pressure histories a constitutive equation relating vessel diameter to the local transmural pressure is proposed. Diameter changes are expressed in the form of a diameter strain, analogous to a Green’s strain, and are related to the local transmural pressure using a standard linear solid model. This model has only three empirical coefficients and could be fitted to all experimental results for all vessels within error of measurement.
Measurement of the Extensional and Flexural Rigidities of a Subcellular Structure: Marginal Bands Isolated From Erythrocytes of the Newt
Authors: Waugh R. E. , Erwin G. , Bouzid A.
Published: June 2009

The elastic properties of marginal band, a microtubular structure isolated from the newt (notophthalmus viridescens) have been measured. Bands were isolated using Triton X-100 and pepsin at pH 6.8 according to the method of Cohen (1978). Isolated bands were manipulated with a glass microhook in a buffer-filled chamber under the microscope. Single bands were stretched between the hook and a thin glass fiber. The fiber was calibrated so that the force on the band could be calculated from the displacement of the fiber. The data pairs of force versus band deflection were analyzed according to the theoretical work of Libai and Simmonds (1983) to obtain the flexural and extensional rigidities of the band. Band dimensions calculated from the data were consistent with microscopically determined values. The average flexural rigidity of the bands (EI) was 5.3 × 10−13 dyn•cm2 and the average extensional rigidity (EA) was 0.017 dyn. Compared to the cell membrane, the marginal band is nearly inextensible and has a much greater resistance to bending, indicating that the band makes an important contribution to the deformability of the circulating cell.
Thermal Pulse Decay Method for Simultaneous Measurement of Local Thermal Conductivity and Blood Perfusion: A Theoretical Analysis
Authors: Arkin H. , Holmes K. R. , Chen M. M. , Bottje W. G.
Published: June 2009

Presented here is a theoretical analysis of the recently developed thermal pulse decay (TPD) method for a simultaneous measurement of local tissue conductivity and blood perfusion rate. The paper describes the theoretical model upon which the TPD method is based and details its capabilities and limitations. The theoretical aspects that affected the development of the measurement protocol are also discussed. The performance of the method is demonstrated with an experimental example which compares the measurements of local kidney blood perfusion rates made using the TPD method with the total renal blood flow obtained coincidentally using a blood flowmeter, in an anesthetized dog.
Statistical Data Base for the Biomechanical Properties of the Human Shoulder Complex—I: Kinematics of the Shoulder Complex
Authors: Engin A. E. , Chen S.-M.
Published: June 2009

In the last two decades, several multi-segmented mathematical models of the total-human-body have appeared in the literature. While these models can handle very sophisticated load-motion situations, their effectiveness depends heavily on the proper biomechanical description and simulation of the major articulating joints of the human body. Among these joints, the most complicated and the least successfully modeled one has been the shoulder complex mainly due to the lack of an appropriate biomechanical data base as well as the anatomical complexity of the shoulder region. In 1984, the senior author and his associates proposed a new kinematic data collection methodology by means of sonic emitters and associated data analysis technique. Based on this data collection methodology, Part I of this paper establishes a statistical data base for the shoulder complex sinus of the male population of ages 18–32. Estimates for the population mean and standard deviation as well as their confidence intervals are presented. The results are expressed in functional expansion form relative to a locally defined joint axis system as well as relative to the torso-fixed coordinate system in the form of globographic representation.
Statistical Data Base for the Biomechanical Properties of the Human Shoulder Complex—II: Passive Resistive Properties Beyond the Shoulder Complex Sinus
Authors: Engin A. E. , Chen S.-M.
Published: June 2009

In mathematical modeling of multi-segmented articulating total-human-body, there is no doubt that the shoulder complex plays one of the most important roles. However, proper biomechanical passive resistive force data have been lacking in the literature. This paper presents determination of the three-dimensional passive resistive joint properties beyond the maximal voluntary shoulder complex sinus. A functional expansion with two spherical angular variables in the local joint axis system is proposed to fit the overall restoring force (moment) data. A constant restoring force (moment) contour map as well as a three-dimensional perspective view of the results are presented in a new coordinate system defined in this study. Finally, a statistical data base is established by utilizing the statistical analysis procedures discussed in Part I [9] of this paper.
Flush-Mounted Hot Film Anemometer Accuracy in Pulsatile Flow
Authors: Nandy S. , Tarbell J. M.
Published: June 2009

The accuracy of a flush-mounted hot film anemometer probe for wall shear stress measurements in physiological pulsatile flows was evaluated in fully developed pulsatile flow in a rigid straight tube. Measured wall shear stress waveform based on steady flow anemometer probe calibrations were compared to theoretical wall shear stress waveforms based on well-established theory and measured flow rate waveforms. The measured and theoretical waveforms were in close agreement during systole (average deviation of 14 percent at peak systole). As expected, agreement was poor during diastole because of flow reversal and diminished frequency response at low shear rate.
Small-Scale Temperature Fluctuations in Perfused Tissue During Local Hyperthermia
Authors: Baish J. W. , Ayyaswamy P. S. , Foster K. R.
Published: June 2009

We develop analytical expressions (scaling laws) for the local temperature fluctuations near isolated and countercurrent blood vessels during hyperthermia. These scaling laws relate the magnitude of such fluctuations to the size of the heated region and to the thermal equilibration length of the vessels. A new equilibration length is identified for countercurrent vessels. Significant temperature differences are predicted between the vessels and the immediately adjacent tissue when the equilibration length is comparable to or longer than the size of the heated tissue region. Countercurrent vessels are shown to have shorter equilibration lengths and produce smaller temperature fluctuations than isolated vessels of the same size.
Three-Dimensional Strain Fields in a Uniform Osteotomy Gap
Authors: DiGioia A. M. , Cheal E. J. , Hayes W. C.
Published: June 2009

Stable internal fixation usually results in a unique histological healing pattern which involves direct cortical reconstruction and an absence of periosteal bridging callus. While it has been suggested that longitudinal interfragmentary strain levels control this healing pattern, the complex, multiaxial strain fields in the interfragmentary region are not well understood. Based on an in-vivo study of gap healing in the sheep tibia by Mansmann et al. [13], we used several finite element models of simplified geometry to: 1) explore modeling assumptions on material linearity and deformation kinematics, and 2) examine the strain distribution in a healing fracture gap subjected to known levels of interfragmentary strain. We found that a general nonlinear material, nonlinear geometric analysis is necessary to model an osteotomy gap subjected to a maximum longitudinal strain of 100 percent. The large displacement, large strain conditions which were used in the in-vivo study result in complex, multiaxial strain fields in the gap. Restricting the maximum longitudinal strain to 10 percent allows use of a linear goemetric formulation without compromising the numerical results. At this reduced strain level a linear material model can be used to examine the extent of material yielding within a homogeneous osteotomy gap. Severe local strain variations occurred both through the thickness of the gap and radially from the endosteal to periosteal gap surfaces. The bone/gap interface represented a critical plane of high distortional and volumetric change and principal strain magnitudes exceeded the maximum longitudinal strains.
Deformation Analyses in Cell and Developmental Biology. Part I—Formal Methodology
Authors: Cheng L. Y.
Published: June 2009

This study presents a computational approach for the deformation analyses of problems in cell and developmental biology. Cells and embryos are viewed mechanically as axisymmetric shell-like bodies containing a body of incompressible material. The analysis approach is based on the finite element method. It is comprised of three finite element ingredients: (1) an axisymmetric shell/membrane element valid for modeling finite bending, shearing and stretching; (2) a volume constraint algorithm for modeling the membrane-bound incompressible material; and (3) a contact algorithm for modeling the mechanical interactions between deformable bodies. Part II of this study will demonstrate how these three ingredients can be applied to analyze mechanical experiments on cells. This same method is also useful for simulating embryonic shape changes during development.
Deformation Analyses in Cell and Developmental Biology. Part II—Mechanical Experiments on Cells
Authors: Cheng L. Y.
Published: June 2009

This study employs the finite element approach developed in Part I to analyze mechanical experiments on cells. It views cells as axisymmetric membrane structures containing a body of incompressible material, and models the mechanical contact between a cell and the loading apparatus by a contact algorithm. Since the method is valid for analyzing axisymmetric shell-like bodies with arbitrary shapes, it treates various mechanical experiments on cells in a unified manner. For demonstration purposes, three commonly used mechanical experiments on cells are considered; (1) the compression experiment; (2) the suction (micropipette aspiration) experiment; and (3) the magnetic particle experiment. Based on an estimate of the mechanical property data for unfertilized sea urchin eggs, this analysis method predicts the responses for all three experiments using the same assumptions and approximations. This parallel treatment gives a broad basis for data correlation with experiments. The method also provides insights into mechanical experiments not offered by other approximate methods. For example, it gives the distributions of tensions and stretches on the cell cortex, and suggests the role of friction in the suction experiment.
Choking Phenomena in a Lung-Like Model
Authors: Elad David , Kamm Roger D. , Shapiro Ascher H.
Published: June 2009

A simple, continuous, one-dimensional model for the geometry and structure of the bronchial airways is used for the analysis of fluid flow patterns which have been observed in forced expiration maneuvers. Various phenomena within the conducting system associated with flow limitation are investigated: (a) the conditions in which a “choke” (flow limitation) can occur in a compliant system; (b) theoretical flows that are physically impossible; (c) the possibility of having elastic jumps downstream of the choke point; (d) perturbations in the physical parameters of the conducting system.
Correlation Among Shear Rate Measures in Vascular Flows
Authors: Friedman Morton H. , Deters Owen J.
Published: June 2009

A variety of shear rate measures have been calculated from hemodynamic data obtained by laser Doppler anemometry in flow-through casts of human aortic bifurcations. Included are measures sensitive to the mean and amplitude of the shear rate, its maximum rate of change, the duration of stasis and flow reversal near the wall, and the unidirectionality of the flow. Many of these measures are highly correlated with one another. This suggests that that it will be difficult to identify from in vivo measurements those aspects of the flow field to which the vessel wall is most sensitive. It may be possible to separate the effects of purely temporal factors (e.g., the duration of flow reversal) from those related to wall shear stress.
Design of a New Pulse Duplicator System for Prosthetic Heart Valves
Authors: Kitamura T. , Affeld K. , Mohnhaupt A.
Published: June 2009

This paper discusses results of a computer simulation for designing a new pulse duplicator system for mechanical heart valves. The design objective of the system is to obtain a compact, efficient pulse duplicator system capable of accurately measuring the volume flow rate across a valve. The volume flow rate is determined as the derivative of the volume displacement of an actuator piston which directly drives the fluid. The system does not need any circulatory loop, since the piston is controlled on-line to follow command signals representing an aortic impedance. The results of the computer simulation show: (1) the designed PI-controllers of the actuator can precisely control valve motion to follow given command signals, (2) the eigenvalues of the controllers have to be carefully chosen to prevent unstable behaviors of a valve in diastole, and (3) the dimensions of the actuator is optimized by minimizing a cost function of the total efficiency of the system.
The Recovery of Terminal Lymph Flow Following Occlusion
Authors: Miller G. E. , Seale J. L.
Published: June 2009

The effects of external pressure on the relative terminal lymphatic flow rate following occlusion of the lumph system were studied. Sulfur colloid tagged with 99mTc was injected into the hind thigh of dogs prior to compressive loading. Initially, the lymphatic clearance of the tracer was measured for approximately forty minutes with no applied external pressure. The terminal lymph vessels were then occluded for thirty minutes with the application of an applied external pressure of 75 mm Hg. Finally, the lymphatic clearance following occlusion was measured with the application of a nonocclusive pressure. External pressures of 0, 30, and 45 mm Hg were tested to determine the effects of post-occlusive pressure application on terminal lymphatic clearance. Results indicated that terminal lymphatic clearance did not resume for an applied pressure of 45 mm Hg following occlusion. The relative lymphatic clearance rate at an external pressure of 30 mm Hg following occlusion was 54% of the clearance rate for a 0 mm Hg applied pressure prior to lymph occlusion. The results for a 0 mm Hg external pressure following occlusion indicated a 23 percent clearance rate compared to the pre-occlusive state. A two compartment model was utilized to determine the lymphatic clearance rate per unit tissue volume of subcutaneous tissue from the experimental data for each pressure phase.
Temperature Dependent Behavior of the Canine Medial Collateral Ligament
Authors: Woo Savio L.-Y. , Lee Thay Q. , Gomez Mark A. , Sato Shigeru , Field Frederic P.
Published: June 2009

The temperature dependent tensile behavior of ligament was investigated from 2°C to 37°C. Nondestructive cyclic tests were performed on ten canine femur-medial collateral ligament-tibia (FMT) complexes at sequential temperatures of 22°C, 22°C, 27°C, 32°C, 37°C, and again at 22°C. The samples were rested at zero load between tests for sufficient time periods to allow for full recovery from the ligament’s time and history dependent viscoelastic properties. Ten additional FMT complexes were sequentially tested in a similar fashion, but at temperatures of 22°C, 22°C, 2°C, 6°C, 14°C, and 22°C. All canine FMT complexes showed temperature dependent viscoelastic properties: the measured area of hysteresis decreased with increasing temperature; the cyclic load relaxation behavior plateaued to a higher value at lower temperatures; and the tensile load at a predetermined ligament substance strain level had an inversely proportional relationship with respect to temperature.
The Kinetics of Chemically Induced Nonequilibrium Swelling of Articular Cartilage and Corneal Stroma
Authors: Eisenberg S. R. , Grodzinsky A. J.
Published: June 2009

An electromechanical model for charged, hydrated tissues is developed to predict the kinetics of changes in swelling and isometric compressive stress induced by changes in bath salt concentration. The model focuses on ionic transport as the rate limiting step in chemically modulating electrical interactions between the charged macromolecules of the extracellular matrix. The swelling response to such changes in local interaction forces is determined by the relative rates of chemical diffusion and fluid redistribution in the tissue sample. We have tested the model by comparing the experimentally observed salt-induced stress relaxation response in bovine articular cartilage and corneal stroma to the response predicted by the model using constitutive relations for the concentration dependent material properties of the tissues reported in a related study. The qualitatively good agreement between our experimental measurements and the predictions of the model supports the physical basis of the model and demonstrates the model’s ability to discriminate between the two soft connective tissues that were examined.
Fluid Particle Motion and Lagrangian Velocities for Pulsatile Flow Through a Femoral Artery Branch Model
Authors: Back M. R. , Cho Y. I. , Crawford D. W. , Back L. H.
Published: June 2009

A flow visualization study using selective dye injection and frame by frame analysis of a movie provided qualitative and quantitative data on the motion of marked fluid particles in a 60 degree artery branch model for simulation of physiological femoral artery flow. Physical flow features observed included jetting of the branch flow into the main lumen during the brief reverse flow period, flow separation along the main lumen wall during the near zero flow phase of diastole when the core flow was in the downstream direction, and inference of flow separation conditions along the wall opposite the branch later in systole at higher branch flow ratios. There were many similarities between dye particle motions in pulsatile flow and the comparative steady flow observations.
Characterization of Penile Erectile States Using External Computer-Based Monitoring
Authors: Frohrib D. A. , Goldstein I. , Payton T. R. , Padma-Nathan H. , Krane R. J.
Published: June 2009

The states of penile erection have not been quantified to establish their relationship to intracorporal fluid pressure and to soft tissue constraint. Computer-based circumferential rigidity sensing during erectile cycles now permits circumferential size and rigidity characterization. Measurements during dynamic infusion cavernometry and cavernosography relate intracorporal pressure and axial rigidity to circumference and circumferential rigidity characterization. Tumescence/rigidity coupling and tissue elastic contributions are identified from the combined data.
Pseudoelasticity of Excised Visceral Pleura
Authors: Humphrey J. D. , Vawter D. L. , Vito R. P.
Published: June 2009

A pseudostrain-energy function is proposed for describing the behavior of excised sheets of canine visceral pleura. Pseudoelastic material constants are determined from experimental biaxial data by employing a nonlinear least-squares algorithm. The agreement between theory and experiment is shown to be quite good. Furthermore, the visceral pleura studied appears to be inelastic and to exhibit in-plane isotropy. Comparison with previous works is discussed.
Analysis of Opening Shock of a Chest Mounted Reserve Parachute
Authors: Khader G. A. , Huston R. L.
Published: June 2009

The effect of opening shock of a chest-mounted reserve parachute on the head/neck dynamics is studied. Comparisons are made with similar effects of a back-mounted reserve parachute. The analysis employs a biodynamic computer model developed in earlier research. The results show that there are significant advantages of a chest-mounted over a back-mounted reserve parachute.
Biomechanical Analysis of Manual Lifting Tasks
Authors: Kromodihardjo S. , Mital A.
Published: June 2009

This paper presents the findings of a study conducted to determine peak forces generated in the human spine while the individual is engaged in lifting maximum acceptable weight. Calculations of forces and moments, acting on each body segment, were based on film data collected on four individuals for twelve variations of the manual lifting task. The variations were defined by: (i) box-size (three different boxes were used), (ii) presence or absence of handles, and (iii) symmetry and asymmetry of the lifting task (sagittal and nonsagittal lifting). In general, lower loads were accepted for lift when lifting asymmetrically or when lifting boxes without handles or when lifting bigger boxes. However, peak forces (compressive and shear forces in the spine and ground reaction forces) for these situations were not always lower than those generated when handling either compact boxes or boxes with handles or when lifting boxes symmetrically in the sagittal plane. On the basis of these results, it was concluded that lifting loads asymmetrically or in boxes without handles or in bulky boxes is relatively much more stressful than lifting the same load symmetrically or in boxes with handles or in compact boxes.
Reversible and Irreversible Components of Central-Airway Flow Resistance
Authors: Snyder B. , Olson D. E. , Hammersley J. R. , Peterson C. V. , Jaeger M. J.
Published: June 2009

The flow energy loss (head loss) through a cast of canine central airways is found to be nearly independent of flow direction. By contrast, head loss in geometrically-simpler branching sections at comparable flow conditions is highly irreversible, with inspiratory loss being greater by nearly two units of dynamic pressure (2•1/2ρV2). In these branching sections head loss appears to be independent of important geometric parameters such as the branch length/diameter ratio and the exit/inlet flow-area ratio. An analysis of these observations suggests that kinetic energy factors, not shear stresses, account for most of the energy dissipated in central airways and in simple bifurcating sections. Inspiratory loss in bifurcations is greatly increased by the onset of flow separation: irreversibility is minimal in central airways, where separation either is absent or else is much less pronounced.
Measurement of the Mechanical Properties of the Human Lung Tissue
Authors: Zeng Y. J. , Yager D. , Fung Y. C.
Published: June 2009

The mechanical properties of human lung tissue were measured in a state of biaxial tension. The experimental data were fitted with a pseudo-elastic constitutive equation proposed earlier and the physical constants were identified.
A Constitutive Description of Contracting Papillary Muscle and Its Implications to the Dynamics of the Intact Heart
Authors: Pinto J. G.
Published: June 2009

A simple mathematical model capable of simulating the major biomechanical attributes of contracting cardiac muscle is presented. This model is based on the phenomenological observations on heart muscle. The form of the equation can be readily extended to describe the pressure-volume-time-velocity of the intact heart as well, thus allowing a direct bridge between the dynamics of papillary muscle and the dynamics of intact heart. Parameters that are sensitive to inotropic state of the muscle can be obtained directly from the isometric tension-time record of the muscle or the isovolumic pressure-time record of the ventricle. These parameters have the potential to serve as quantitative measures of cardiac health.
A Three-Dimenstional Nonlinear Finite Element Model of Lumbar Intervertebral Joint in Torsion
Authors: Ueno K. , Liu Y. K.
Published: June 2009

Torsion as a cause of failure in the lumbar intervertebral joint was studied using a three-dimensional nonlinear finite element model. The role of facets and ligaments as well as the stress distributions in the posterior elements, the disk, the ligaments, and the vertebral body were examined. For physiological range of torsion, the facets carried 10 to 40 percent of the torque. The fiber stresses in the disk were the highest at the lateral margin of the outer layer of the annulus. Therefore, torsion itself is unlikely to cause posterior or posterolateral disk prolapse.
Modeling of Human Reactions to Whole-Body Vibration
Authors: Amirouche Farid M. L.
Published: June 2009

A computer-automated approach for studying the human body vibration is presented. This includes vertical, horizontal, and torsional vibration. The procedure used is based on Finite Segment Modeling (FSM) of the human body, thus treating it as a mechanical structure. Kane’s equations as developed by Huston et al. are used to formulate the governing equations of motion. The connective tissues are modeled by springs and dampers. In addition, the paper presents the transient response of different parts of the body due to a sinusoidal forcing function as well as an impulse function applied to the lower torso in the vertical direction.
A Simple Unconstrained Dynamic Knee Simulator
Authors: Szklar O. , Ahmed A. M.
Published: June 2009

The design of a simple dynamic knee simulator is described. In the simulator the joint dynamics are reproduced in-vitro in a knee specimen by controlling the time-histories of the tensions in two flexible cables acting as lumped muscle group equivalents, without constraining the natural conjunct and passive motions of the specimen. The two cable tensions acting individually are used to control the active flexion/extension motion, while their simultaneous action is used to control joint compressive force. The characteristics of the electrohydraulic servo system acting under real-time microprocessor control are described. The system performance during simulation of an idealized level-walking function is evaluated.