bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Characterization of Membranelike Biological Tissue
Authors: Thibault L. E. , Fry D. L.
Published: July 2009

Experimental and analytical methods are presented which enable one to examine the local rheological properties of biological tissues which can be captured as flat sheets between matching pressure manifolds and deformed under experimentally prescribed hydrostatic loading conditions. In spite of the fact that most biological tissues, including arteries, are nonlinearly elastic when considered over wide ranges of strain, it was found that the deformation of swine and canine arterial wall specimens in the physiological range of wall strain can be approximated by an isotropic, linearily elastic membrane model. In view of this, the elastic behavior was characterized approximately by an incremental modulus over the range of 0.45 to 0.65 strain. The incremental modulus in both species was shown to increase by a factor of three along the descending thoracic aorta from the ductus scar to the celiac orifice.
Rhesus Monkey Intervertebral Disk Viscoelastic Response to Shear Stress
Authors: Kelley B. S. , Lafferty J. F. , Bowman D. A. , Clark P. A.
Published: July 2009

A viscoelastic model of the shear response of the Rhesus monkey intervertebral disk, represented by a series chain of four Kelvin units is presented. Two types of investigations are carried out to assess the validity of the model: 1) determination of material properties by comparison with experimental strain creep behavior of the disk; and 2) validation of this viscoelastic model by accurately predicting the experimental results of stress relaxation tests. The use of the series Kelvin units approach provides the first analytical mechanical model capable of predicting the creep and relaxation functions for the intervertebral disk in shear.
Joint Models, Degrees of Freedom, and Anatomical Motion Measurement
Authors: Kinzel G. L. , Gutkowski L. J.
Published: July 2009

When the motion associated with an anatomical joint is to be measured, a kinematic model for the joint must first be established. The joint model will have from one to six degrees of freedom, and both the measurement technique and the means used to describe the motion will be influenced by the model and its degrees of freedom. This paper discusses the modeling and measurement of anatomical joint motion from a kinematics viewpoint. A review of the literature pertaining to measurement techniques, kinematic assumptions, and motion descriptions for anatomical joint motion is presented. One, two, three and six degree-of-freedom models for various anatomical joints have appeared in the literature, and the applicability of these models is compared and discussed.
A Programmable Limb Testing System (and Some Measurements of Intrinsic Muscular and Reflex-Mediated Stiffnesses)
Authors: Billian C. , Zahalak G. I.
Published: July 2009

A new versatile apparatus for investigating the neuromusculoskeletal dynamics of the upper limb, termed the Programmable Limb Testing System (PLTS) has been designed, built, and tested. The planning, construction, and operation of this system are described in this paper. Results are presented from a limited set of experiments, measuring intrinsic muscular and reflex-mediated stiffnesses of the triceps brachii, which exhibit the system’s performance and some of its capabilities.
Mechanical Behavior of Fetal Dura Mater Under Large Axisymmetric Inflation
Authors: Kriewall T. J. , Akkas N. , Bylski D. I. , Melvin J. W. , Work B. A.
Published: July 2009

The nonlinear mechanical behavior of fetal dura mater was tested experimentally and compared to two published nonlinear material strain energy functions, the Mooney-Rivlin and the Skalak, Tozeren, Zarda, and Chien (STZC). The STZC constitutive relations best fit the behavior of the dura mater and were used to describe quantitatively its stiffness. Runge-Kutta numerical procedures were used to fit the theoretical data to the experimental results. The material’s stiffness was positively correlated with fetal weight (r = 0.67, p<0.05). These results are discussed and directions for future research indicated.
Determination of the Local Erosion Stress of the Canine Endothelium Using a Jet Impingement Method
Authors: Vaishnav R. N. , Patel D. J. , Atabek H. B. , Deshpande M. D. , Plowman F. , Vossoughi J.
Published: July 2009

A method to determine local endothelial erosion stress is presented. Freshly excised segments of middle descending thoracic aortas of dogs were slit open longitudinally and stretched in a specially designed rack to various circumferential and longitudinal dimensions. Jets of physiological saline were impinged normally on the endothelium of these segments. Lesions caused by the jet were made visible by staining the tissue with Evans blue dye. The dye solution was absorbed by regions where the endothelial layer had been damaged or destroyed. Characteristically, the lesions were annular in shape. This indicates that the endothelium can withstand large normal stresses where the jet impinges, but is eroded by the shear stress resulting from the jet efflux. Erosion stress of the endothelium was determined by correlating the external radius of a lesion with the shear stress expected at that radial distance from the center of the jet. Results from 185 lesions created in 17 aortic segments indicate that: 1) the in-vitro endothelial erosion stress as measured by a 30-s duration of exposure to shear stress is 7761 ± 155 (SEM) dynes/cm2 at room temperature (23° C) and 2645 ± 155 (SEM) dynes/cm2 at body temperature (37°C); 2) the erosion stress decreases markedly with an increase in the duration of exposure to shear stress; 3) the results for long-duration exposure are consistent with those of the well-known in-vivo study of Fry on endothelial erosion stress. The importance of the method is its ability to measure local endothelial erosion stress which is of particular significance in the study of the discrete process of atherogenesis.
Stresses in a Harrington Distraction Rod: Their Origin and Relationship to Fatigue Fractures In Vivo
Authors: Brunski J. B. , Hill D. C. , Moskowitz A.
Published: July 2009

As illustrated by the case study described in this paper, in-vivo fractures of distraction rods often occur by metallurgical fatigue at the junction between the smooth and ratcheted parts of the rod (i.e., at the first ratchet junction, FRJ). To clarify causative factors of fatigue at the FRJ, stresses are analyzed in a standard 11-in. rod using both experimental and theoretical methods. The analyses reveal how distraction force, eccentricity of loading, rod geometry and material determine the stresses at the FRJ. These stresses can exceed the fatigue endurance limit for certain clinically encountered conditions.
Monitoring Fracture Site Properties With External Fixation
Authors: Beaupre G. S. , Hayes W. C. , Jofe M. H. , White A. A.
Published: July 2009

An in-vitro system has been devised to monitor the properties of an idealized fracture site immobilized with a Hoffman-Vidal external fixator. A dial gage was used to measure the relative pin displacements under controlled axial loading. The displacement measurements were then used in conjunction with a finite element model to predict the modulus of an idealized fracture site. Five fracture sites made of neoprene disks of different mechanical properties were monitored in order to simulate the increasing modulus of a healing fracture. Good agreement was observed between directly measured mechanical properties of the neoprene and those inferred from the combined finite element and pin displacement tests.
A Joint Coordinate System for the Clinical Description of Three-Dimensional Motions: Application to the Knee
Authors: Grood E. S. , Suntay W. J.
Published: July 2009

The experimental study of joint kinematics in three dimensions requires the description and measurement of six motion components. An important aspect of any method of description is the ease with which it is communicated to those who use the data. This paper presents a joint coordinate system that provides a simple geometric description of the three-dimensional rotational and translational motion between two rigid bodies. The coordinate system is applied to the knee and related to the commonly used clinical terms for knee joint motion. A convenient characteristic of the coordinate system shared by spatial linkages is that large joint displacements are independent of the order in which the component translations and rotations occur.
An Analytical Technique for Modeling Knee Joint Stiffness—Part II: Ligamentous Geometric Nonlinearities
Authors: Hefzy M. S. , Grood E. S.
Published: July 2009

An analytical technique previously developed to evaluate the contribution of the ligaments to the nonlinear, coupled stiffness characteristics of the human knee joint [1] is extended here to include geometric nonlinearities. In [1], we assumed that the ligaments act as tensile bands running in a straight line between tibial and femoral insertion sites. Here, two forms of geometric nonlinearities are introduced and analyzed: ligaments wrapping around bone surfaces, such as occurs with the medial collateral ligament, the posterior capsule, and the anterior cruciate in hyperextension, and wrapping of ligaments around each other, such as occurs with the cruciate ligaments as the knee is flexed and internally rotated.
Pre-Collapse Stress Redistributions in Femoral Head Osteonecrosis—A Three-Dimensional Finite Element Analysis
Authors: Brown T. D. , Hild G. L.
Published: July 2009

Three-dimensional finite element analysis is used to explore the influence of several lesion characteristics upon mechanical stress distributions in segmentally necrotic human femoral heads. Variables studied parametrically included apparent modulus deficits within the lesion proper, as well as the depth, width, and location of the infarcted head regions. The detailed patterns of stress redistribution were complex and were found to be a strong function of the specific lesion characteristics. The salient phenomenon, however, was one of preferential load uptake by the stiffer bone surrounding the lesion. Since computed stress reductions within the infarctions were usually much smaller than experimentally observed strength reductions, the data suggest a strong tendency for an elevated incidence of trabecular fatigue fractures in the affected regions.
Continuum Mechanical Model of Leukocytes During Protopod Formation
Authors: Schmid-Scho¨nbein G. W. , Skalak R.
Published: July 2009

A new continuum mechanical theory for protopod extension in leukocytes is developed. Protopod formation is an active process which is the basis for amoeboid displacement on substrates. Leukocytes may form protopods both when adhering to a substrate and when freely suspended in plasma. Therefore the required energy is derived from the cell itself. Protopods are depleted of granules and other organelles, they have a fine fibrillar ultrastructure, and they are covered by a cell membrane. They grow at about 5 μm/min until they reach a length of 4–5 μm. A period of protopod retraction follows during which granules re-enter via the protopod base by Brownian motion. Micropipette experiments have indicated that the protoplasm in the leukocyte has viscoelastic properties, whereas the protopod is stiffer and shows elastic behavior. We propose a continuum theory based on the polymerization of the actin matrix in the cell which results in gelation with a preferred orientation. It is triggered by influx of Ca++ across local regions of the cell membrane and the polymerization occurs along an interface at the base of the polymerized protopod. As cytoplasm passes through the interface it is subject both to a volumetric strain due to exclusion of granules and a shear strain due to alignment of actin molecules. The polymerization provides an active force leading to projection of the protopod and cell deformation. The base of the protopod rests on the unpolymerized cytoplasm along the interface. As the external plasma medium and the cell membrane, if it is not stretched taut, offer little resistance, the projection of the protopod proceeds outward with simultaneous unfolding of the membrane. On the other hand, in osmotically swollen cells the membrane offers considerable resistance as it is under tension and the actin polymerization proceeds inward. A general set of equations are formulated and some special solutions are discussed.
Tissue Culture Cells on Deformable Substrata: Biomechanical Implications
Authors: Harris Albert K.
Published: July 2009

A method has been developed for the study of the forces which individual cells exert during their locomotion. Polydimethyl-siloxane (silicone fluid) was crosslinked on its surface by brief flaming to form a thin layer of silicone rubber. Tissue culture cells of many types were then plated out onto these rubber substrata and the propulsive forces these cells exert as they adhere and spread became visible as wrinkles and other distortions in the rubber. From time-lapse films of these distortions, it appears that the component cells of the body move by exerting shearing forces through their plasma membranes. How these forces are exerted and how this technique for observing them could be made more quantitative are discussed.
Passive Stiffness of Rat Cardiac Myocytes
Authors: Brady A. J.
Published: July 2009

Intact single cells were isolated from adult rat hearts by enzymatic digestion and suspended in 0.25 mM Ca++ Tyrode’s solution. Quiescent, clearly striated rodlike cells were selected for study of the elastic properties of the cells at various stages of membrane and myofilament extraction. Selected cells were placed in a relaxing solution (pCa + 9, 10 mn EGTA) and then each end gently pulled into the tip of a closely fitting suction micropipette for attachment to a force transducer and length perturbation driver. This procedure was performed in low Ca++ to prevent Ca++ loading of the cell during attachment and at room temperature to prevent chemical skinning of the cell [1]. Stiffness was measured by applying a 5-Hz sinusoidal length perturbation (5 percent L0) to one end of the cell while measuring the induced tension change at the other. The ratio of sinusoidal tension change to applied length change (stiffness) was determined for each cell over a length range of about 1–1.3 L0 before removal of the contractile filaments and up to 3.0 L0 after treatment with 0.6 M KI. The stiffness-length relation was measured first in relaxing solution and then in 0.25 mM Ca++ Tyrode’s. If spontaneous contractions or contracture occurred the cell was rejected. If the cell remained quiescent and relaxed it was treated again with relaxing solution and 1 percent Triton X-100 to remove the membranes. The stiffness-length relation was again measured and then the cell was superfused with 0.47 M KCl/10 mM pyrophosphate solution to remove the myosin filaments. The stiffness-length relation was again determined and the cell finally perfused with 0.6 M KI to remove all the contractile filaments. A rodlike, faintly striated structure remained at this point whose stiffness could still be measured. In cells which remained quiescent during the entire extraction procedure and did not develop contracture the following results were obtained. In the relaxing solution and in 0.25 mM Ca++ the stiffness-length relation was similar to that of rat papillary muscle [2]. When the cell membranes were removed with detergent a transient increase in stiffness sometimes occurred which declined within a few minutes to a level near that in the relaxing solution. With KC1 treatment the stiffness declined variably to about half its control value. Immediately upon treatment of the cell with KI solution the major striation pattern disappeared and stiffness fell dramatically. Also the cell became highly extensible such that is could be reversibly extended in length to 2.5–3 L0 with the faintly striated pattern uniformly following the extension. At 3 L0 the sinusoidally measured stiffness was about equal to that of the intact cell at L0. These data indicate that a significant source of the high resting stiffness of rat heart muscle resides within the muscle cells and is dependent to a large extent on the presence of the myofilaments [3]. Also, a measurable stiffness remains in the cells after contractile filament extraction, which may be attributable to the cytoskeletal intermediate filaments.
Analytical Solutions for Shear Deformation and Flow of Red Cell Membrane
Authors: Hochmuth R. M. , Berk D. A.
Published: July 2009

Studies of red blood cell deformation have shown that there are a number of membrane material properties that affect the deformation process. In this paper various types of deformation are modeled using geometrical and constitutive simplifications so that the effect of intrinsic elastic and viscous membrane properties and of major geometric constraints is made obvious while other factors are ignored. To this end, numerical solutions are shunned in favor of exact analytical (“closed-form”) solutions to simple and basic membrane deformation problems in order to reveal functional dependence.
Models of Cell Interaction Based on Differential Adhesion
Authors: Childress S.
Published: July 2009

Recent efforts to model the mechanical interaction of aggregates of biological cells are reviewed. Differential adhesion is discussed as a means of creating a field of stress equivalent to tension elements at interfaces between unlike cell types. Several numerical algorithms are described and applied to shortening and folding of cell sheets, three-dimensional monolayers, and two-dimensional cell aggregates.
A Pulsed Wire Probe for the Measurement of Velocity and Flow Direction in Slowly Moving Air
Authors: Olson D. E. , Parker K. H. , Snyder B.
Published: July 2009

This report describes the theory and operation of a pulsed-probe anemometer designed to measure steady three-dimensional velocity fields typical of pulmonary tracheo-bronchial airflows. Local velocities are determined by measuring the transport time and orientation of a thermal pulse initiated at an upstream wire and sensed at a downstream wire. The transport time is a reproducible function of velocity and the probe wire spacing, as verified by a theoretical model of convective heat transfer. When calibrated the anemometer yields measurements of velocity accurate to ±5 percent and resolves flow direction to within 1 deg at airspeeds ≥10 cm/s. Spatial resolution is ±0.5 mm. Measured flow patterns typical of curved circular pipes are included as examples of its application.
Comparison of Steady and Pulsatile Flow Near the Ventral and Dorsal Walls of Casts of Human Aortic Bifurcations
Authors: Deters O. J. , Mark F. F. , Bargeron C. B. , Friedman M. H. , Hutchins G. M.
Published: July 2009

Steady and pulsatile flows were passed through casts of human aortic bifurcations and, by means of a laser Doppler anemometer, fluid velocities were measured at selected sites near the ventral and dorsal walls. At these sites, in the vicinity of the bifurcation, the influence of secondary flow is significant and therefore an appreciation of the phasic variation of secondary flow patterns is important. Results are presented comparing the flow direction in both steady and pulsatile flow at sites in three casts. The common features of the flow at these sites were the persistence of the flow direction during the accelerating and decelerating phases of the pulsatile cycle, and the consistently smaller angle (measured from the inlet centerline) of the pulsatile flow direction as compared to the angle of the flow direction in steady flow.
Incremental Formulations in Vascular Mechanics
Authors: Vaishnav R. N. , Vossoughi J.
Published: July 2009

The pulsatile deformations of the large arteries can be viewed as small time-varying deformations superposed on large deformations. This motivates the study of the incremental deformations of the vascular tissue. Unfortunately, because of the variety of possible choices of definitions of stresses and strains, the choice of the characterizing incremental moduli is not unique, which has led to much ambiguity and confusion in the literature. This communication systematically presents some of the options available for characterization of orthotropic incremental deformations of the vascular tissue, and provides explicit formulas for interconversions of incremental elastic moduli for uniaxial tests on strips of incompressible tissue. Relative merits of various choices are discussed.
A Note on the Blood Analog for In-Vitro Testing of Heart Valve Bioprostheses
Authors: Chandran K. B. , Khalighi B.
Published: July 2009

Glycerol solution with the viscosity coefficient similar to that of blood is used in evaluating the performance characteristics of prosthetic heart valves in the laboratory. However, physiological saline solution is used as a test fluid in testing tissue heart valves even though the viscosity coefficient does not match that of human blood. It is commonly believed that glycerol is absorbed by the tissue valves and hence the leaflets become stiff, making the test results invalid. However, in our laboratory a comparison of tissue valves exposed to glycerine solution at various times does not indicate any difference in the leaflet opening characteristics. Hence, it is suggested that glycerine solution be used as a test fluid for the evaluation of tissue valves also.
On the Propagation of a Wave Front in Viscoelastic Arteries
Authors: Holenstein R. , Nerem R. M. , Niederer P. F.
Published: July 2009

In formulating a mathematical model of the arterial system, the one-dimensional flow approximation yields realistic pressure and flow pulses in the proximal as well as in distal regions of a simulated arterial conduit, provided that the viscoelastic damping induced by the vessel wall is properly taken into account. Models which are based on a purely elastic formulation of the arterial wall properties are known to produce shocklike transitions in the propagating pulses which are not observed in man under physiological conditions. The viscoelastic damping characteristics are such that they are expected to reduce the tendency of shock formation in the model. In order to analyze this phenomenon, the propagation of first and second-order pressure waves is calculated with the aid of a wave front expansion, and criteria for the formation of shocks are derived. The application of the results to the human arterial system show that shock waves are not to be expected under normal conditions, while in case of a pathologically increased pressure rise at the root of the aorta, shocklike transitions may develop in the periphery. In particular, it is shown that second-order waves never lead to shock formation in finite time for the class of initial conditions and mechnaical wave guides which are of interest in the mammalian circulation.
Morphometry of Cat’s Pulmonary Arterial Tree
Authors: Yen R. T. , Zhuang F. Y. , Fung Y. C. , Ho H. H. , Tremer H. , Sobin S. S.
Published: July 2009

Morphometic data of the pulmonary artery in the cat’s right lung are presented. Silicone elastomer casts of cat’s right lung were made, and measured, counted and analyzed. The Strahler system is used to describe the branching pattern of the arterial vascular tree. These data are needed for any quantitative approach to the study of the pulmonary circulation. For all the pulmonary blood vessels of the cat lying between the main pulmonary artery and the capillary beds, there are a total of 10 orders of vessels in the right upper lobe, 9 orders of vessels in the right middle lobe and 11 orders of vessels in the right lower lobe. The ratio of the number of branches in successive orders of vessels or the branching ratio, is 3.58. The corresponding average diameter ratio is 1.72, whereas the average length ratio is 1.81.
Histological Staining as a Measure of Stress in Collagen Fibers
Authors: Lanir Y. , Walsh J. , Soutas-Little R. W.
Published: July 2009

It has been reported previously that collagen fibers will stain either red or green by Masson’s and other trichrome methods depending on whether they have been respectively stressed or relaxed prior to fixation. This was shown in skin [1, 2, 3] tendon [4, 5] bone[6] and films of collagen [7]. If this stain-stress dependence is of a unique quantitative nature, then staining could be used as a tension probe for collagen fibers. Relaxed and stressed collagen bundles of rat tail tendon and rat Achilles tendon have been stained using various staining periods, and results indicate that the change in staining may be associated with denser packing of the fibers in the bundle under stress rather than directly due to the stress itself. Denser packing may reduce the rate of penetration of the counterstain thus causing the staining differences. Since this rate of penetration is dependent on a number of other variables (unrelated to stress), it is concluded that collagen staining is not a reliable tension probe.
Strain Topography of Human Tendon and Fascia
Authors: Zernicke R. F. , Butler D. L. , Grood E. S. , Hefzy M. S.
Published: July 2009

Discretized surface strains for human tendon and fascia were photogrammetrically determined with high-speed cinematography and were displayed topographically using three-dimensional computer graphics. Substantial differences were found between estimates of tissue strain measured from grip motion versus discretized strain estimates from highspeed films. The computer-generated contour maps also provide a useful technique for analyzing the nonhomogeneity of tendon and fascial strains during high rate tests.
Effect of Aortic Valve Orientation on Arterial Flow Distribution
Authors: Doo Irene , Rodkiewicz Cz. M.
Published: July 2009

This short note presents the results from experiments performed on an artificial heart valve, in particular, the aortic valve located at the exit of the left ventricle of the heart. The valve was tested in a full-scale elastic model of the arterial system, with a cam-piston unit duplicating the pumping action of the heart. The dependence of the arterial flow distribution on the angular orientation of the valve was investigated and it was found that there was no discernible influence of valve orientation on the arterial flow distribution.
Parameter Estimation Using the Quasi-Linear Viscoelastic Model Proposed by Fung
Authors: Dortmans L. J. M. G. , Sauren A. A. H. J. , Rousseau E. P. M.
Published: July 2009

Using the quasi-linear viscoelastic model proposed by Fung for the description of the viscoelastic properties of soft biological tissues, the parameters governing their time-dependent behavior are commonly estimated from relaxation experiments. Exact quantification is possible from the response to a step change in the strain. Since it is physically impossible to realize a true step change in the strain, in practice the response to a steplike strain change is used. In the present study the discrepancies between the exact and the estimated parameter values are investigated using a hypothetical quasi-linear viscoelastic material. The parameter τ1, governing the fast viscous phenomena, is found to be subject to the largest errors. Methods for obtaining better estimates of τ1 are outlined in a number of special cases.
Kinematic and Force Data Collection in Biomechanics by Means of Sonic Emitters—I: Kinematic Data Collection Methodology
Authors: Engin A. E. , Peindl R. D. , Berme N. , Kaleps I.
Published: July 2009

In this paper, first, the principles of sonic digitizing are presented. Next, a description of quantitative determination of the relative motion between two body segments by utilization of sonic emitters is provided. A new kinematic data collection methodology and data analysis is proposed to check continuously the accuracy of the data collected by means of the sonic emitters. The first part of the paper is terminated by establishment of an accuracy criteria and selection of the most accurate data set and associated error analysis. Quantitative results based upon the kinematic data collection methodology of Part I were obtained for the forced kinematic motion of the human shoulder complex and are presented in Part II.
Large Deformation Mechanics of the Enucleated Eyeball
Authors: Taber L. A.
Published: July 2009

Large deformation of enucleated pig eyeballs under rigid cylindrical indenters was studied analytically and experimentally. The analytic model for the eyeball consists of a fluid-filled spherical membrane composed of an incompressible, elastic material with an exponential strain energy function. The Rayleigh-Ritz technique provided an approximate solution via a potential energy formulation. Comparison with results from tests on eyeballs and a water-filled rubber (Mooney-Rivlin) shell shows good agreement at large deflection, where membrane action dominates. Due to the highly nonlinear stress-strain relations for the sclera, the load remains relatively small until the indenter displacement approaches 40–60 percent of the eyeball radius, and then the load increases rapidly. Depending on the indenter size, either a perforation or a rupture type of failure occurs.
Calculation of Long Jump Performance by Numerical Integration of the Equations of Motion
Authors: Ward-Smith A. J.
Published: July 2009

The aerial phase of the long jump is calculated by numerical integration of the equations of motion. Consideration is given to the effects on performance of the horizontal and vertical components of velocity at takeoff, aerodynamic drag, wind assistance and the vertical displacement of the center of mass which occurs during the course of the jump. For still air conditions it is shown that an analytical solution due to Lamb [6] compares very favorably with the numerical solution, providing an excellent description of the trajectory. Calculations neglecting the effect of aerodynamic drag are shown to overestimate the jump distance of world-class athletes by from 9 to 11 cm under still air conditions.
Electro-Mechanical Behavior of Wet Bone—Part I: Theory
Authors: Guzelsu N. , Saha S.
Published: July 2009

The remodeling properties of bones due to various stimuli have been of substantial interest to the scientists. Examination of electro-mechanical properties of bone and their relation to remodeling and osteogenesis have been investigated mainly by experimental means. In this study, by using continuum physics, it is shown that the remodeling of bones can be formulated theoretically in terms of electrical and mechanical effects. The interactions among the constituents of bone (bone matrix, bone salts, electrolytes and hydrogen ions) and effects of various stimuli (mechnical, electrical and chemical) on the remodeling mechanism of bone tissue are interpreted with this model. Moreover, the stimulation of osteogenesis by electrical means is predicted.
Measurement of the Laser Exposure Levels for Burn Threshold in Biological Tissue
Authors: Laufer G. , Joachims H. Z. , Eliachar I. , Mordechovitz D.
Published: July 2009

Experiments for the evaluation of the laser energy density required to induce burn threshold in biological tissue are presented. The results are compared with a theoretical model. The values obtained for soft tissue are higher than the pain threshold and the safety standards for the maximum permissible exposure. This is due to the different nature of injury associated with the surgical process.
Governing Equations of Motion for the Otolith Organs and Their Response to a Step Change in Velocity of the Skull
Authors: Grant J. W. , Best W. A. , LoNigro R.
Published: July 2009

The otolith organs are the linear motion sensors of the inner ear. They comprise an overdamped second-order system and respond to gravity and skull acceleration. The governing equations of motion which describe the relative displacement of the mass with respect to the skull are developed. When these equations are non-dimensionalized they indicate that the elastic term is almost negligible with respect to the viscous and inertial terms. For a step change in skull velocity an analytic solution is given for the elastic term equal to zero and numeric solutions are given for small values of the elastic term.
An Experimental Study of Pressure Losses in Pulsatile Flows Through Rigid and Pulsating Stenosis
Authors: Rabinovitz R. , Degani D. , Gutfinger C. , Milo S.
Published: July 2009

The time-dependent pressure curves of a pulsatile flow across rigid and pulsating stenoses were investigated experimentally in a laboratory simulator of the outflow tract of the heart right ventricle. The experiments were performed within the range of physiological conditions of frequency and flow rate. The experimental setup consisted of a closed flow system which was operated by a pulsatile pump, and a test chamber which enabled checking different modes of stenosis. Rigid constrictions were simulated by means of axisymmetric blunt-ended annular plugs with moderate-to-severe area reductions. The pulsating stenosis consisted of a short starling resistor device operated by a pulsating external pressure which was synchronized by the pulsatile flow. It was found that the shape of the time-dependent pressure curve upstream of the stenosis was different in the case of rigid stenosis than in the pulsating one. Potential clinical applications of the work may relate to diagnosis of the type of stenosis in the congenital heart disease known as Tetralogy of Fallot.
Gas Transport During Oscillatory Flow in a Network of Branching Tubes
Authors: Kamm R. D. , Collins J. , Whang J. , Slutsky A. S. , Greiner M.
Published: July 2009

A transport coefficient was measured for a range of oscillatory flow conditions in a branching network of tubes. Measurements were made both across the first generation of a three-generation network and the second generation of a four-generation network. The results for these two series of tests were similar, indicating that there was no significant effect due to the system boundaries. The results are cast in terms of an effective axial diffusion coefficient of the form Deff=(ϰ+0.50Vt1.66f0.94)cm2/s where ϰ is the molecular diffusivity, Vt is the local stroke volume (cc), and f is the oscillation frequency (Hz). These results are compared to those obtained by other investigators in branching systems of similar geometry. At low frequency, this result is found to be in approximate agreement with the steady flow result of Scherer, et al. [15]. This expression differs from the oscillatory flow results of Tarbell, et al. [19] for liquids, primarily in terms of the effects of oscillation frequency.
On the Damping Properties of the Shoulder Complex
Authors: Engin A. E.
Published: July 2009

Effectiveness of the multi-segmented total-human-body models to predict accurately live human response depends heavily on the task of proper biomechanical description and simulation of the articulating joints. Determination of the damping properties in articulating joints is an important part of this task and constitutes the subject of this paper. A new method which is based on the damped oscillations of a body segment is introduced by considering the shoulder complex as an example. The numerical results for the angular damping coefficients at the shoulder complex are presented for forty different orientations of the arm with respect to torso. The angular damping coefficients exhibit a nonlinear behavior as a function of the arm orientation.
Nonquasi-Steady Character of Pulsatile Flow in Human Coronary Arteries
Authors: Mark F. F. , Bargeron C. B. , Deters O. J. , Friedman M. H.
Published: July 2009

This experiment was conducted to determine if the pulsatile flow through the proximal portion of the left coronary artery system in man exhibits quasi-steady characteristics. Steady and pulsatile flows were passed through an idealized model whose dimensions were based on a vascular cast. The mean Reynolds number was 180 and the unsteadiness number was 2.7. Velocity profiles were measured by laser Doppler anemometry at several locations along diameters in the parent and both daughter channels in the neighborhood of the “left main” bifurcation. Analysis of the results along one diameter in the “left main” channel shows that unsteady flow in the larger coronary arteries may not be simulated by a series of steady flow experiments.
Regulation of Transmural Myocardial Blood Flow
Authors: Hoffman J. I. E. , Baer R. W. , Hanley F. L. , Messina L. M.
Published: July 2009

A major problem in understanding how myocardial blood flow is regulated is the common occurrence of subendocardial ischemia in many diseases, with or without coronary arterial disease. Two commonly held explanatory hypotheses were that high systolic intramyocardial pressures prevented flow to deep but not superficial muscle, or that in diastole tissue pressures were highest subendocardially. Neither hypothesis is tenable today, and the likeliest hypothesis is that retrograde systolic flow from the deeper muscle produces a longer time constant for diastolic flow in deep than in superficial muscle.
Arteriovenous Difference of the Blood Density in the Coronary Circulation
Authors: Kenner T. , Moser M. , Mohl W.
Published: July 2009

The mechanical oscillator technique permits determining blood density continuously with high accuracy. Using this technique arteriovenous density gradients were recorded in the coronary vascular bed of anesthetized dogs. It was found that the coronary sinus blood has a higher density than arterial blood due to the loss of filtered fluid in the microcirculation. The amount of fluid loss corresponds to the lymph flow in the myocardium. Increase of venous pressure leads to an increase of the density gradient. Intermittent coronary sinus occlusion (ICSO) surprisingly leads to a reduction of the density gradient. Injection of osmotically hypertensive fluids influences the arteriovenous gradient by shifting extravascular fluid into the blood. The method permits the determination of filtration coefficients and to estimate the tissue volume available for fluid exchange.
Interaction Between Intramyocardial Pressure (IMP) and Myocardial Circulation
Authors: Arts T. , Reneman R. S.
Published: July 2009

In our concept of the interaction between intramyocardial pressure (IMP) and myocardial perfusion, IMP is defined as the hydrostatic pressure in the soft tissue surrounding the myocardial fibers. In a mathematical model of the mechanics of the left ventricle the latter definition results in values for IMP equal to left ventricular pressure in the inner layers of the wall, and a continuous decrease across the wall to zero in the outer layers. Modulation of coronary artery flow during the cardiac cycle is predominantly due to compression of the coronary vasculature by the IMP during the systolic phase of the cardiac cycle, resulting in back-squeezing components in this flow. In a mathematical model of the dynamics of the coronary circulation, containing a large capacitance at the level of the coronary microvasculature, the modulations of coronary artery flow were found to be similar to those found in animal experiments in open-chest dogs.
Pressure Change and Gas Mixing Induced by Oscillations in a Closed System
Authors: Isabey D. , Harf A. , Chang H. K.
Published: July 2009

In an attempt to delineate some mechanical behaviors found in branching airways, pressure transmission, gas motion, and mixing were studied during high-frequency oscillation (HFO) in an idealized system consisting of a large straight tube and a rigid sphere linked together by a small straight tube. Depending on the frequency f, and on the unsteadiness dimensionless parameter α, pressure amplitude in the large tube is either strongly attenuated or amplified in the sphere. This finding may provide a theoretical basis for the pressure resonance phenomenon observed in the lung by previous investigators. Gas compression in the closed volume causes convective mixing throughout the system. The measured dispersion was found to be proportional to f(VT/A)2, in agreement with a recent report. However, bulk convective mixing was sufficient to explain the dispersion for oscillatory volumes (VT) as small as 80 percent of the small tube volume, as has been previously suggested.
Steady-State Analysis of Self-Heated Thermistors Using Finite Elements
Authors: Hayes L. J. , Valvano J. W.
Published: July 2009

The purpose of this work is to validate, using numerical, finite element methods, the thermal assumptions made in the analytical analysis of a coupled thermistor probe-tissue model upon which a thermal conductivity measurement scheme has been based. Analytic, closed form temperature profiles generated by the self-heated thermistors can be found if three simplifying assumptions are made: 1)  the thermistor is spherical; 2)  heat is generated in all regions of the bead; and 3)  heat is generated uniformly in the bead. This analytic solution is used to derive a linear relationship between tissue thermal conductivity and the ratio of thermistor temperature rise over electrical power required to maintain that temperature rise. This derived, linear relationship is used to determine thermal conductivity from the observed experimental data. However, in reality, the thermistor bead is a prolate spheroid surrounded by a passive shell, and the heating pattern in the bead is highly nonuniform. In the physical system, the exact relationship between the tissue thermal conductivity and parameters measured by the thermistor is not known. The finite element method was used to calculate the steady-state temperature profiles generated by thermistor beads with realistic geometry and heating patterns. The results of the finite element analysis show that the empirical, linear relationship remains valid when all three simplifying assumptions are significantly relaxed.
A Strain Energy Function for Lung Parenchyma
Authors: Stamenovic D. , Wilson T. A.
Published: July 2009

The strain energy for the air-filled lung is calculated from a model of the parenchymal microstructure. The energy is the sum of the surface energy and the elastic energies of two tissue components. The first of these is the peripheral tissue system that provides the recoil pressure of the saline-filled lung, and the second is the system of line elements that form the free edges of the alveolar walls bordering the alveolar ducts. The computed strain energy is consistent with the observed linear elastic behavior of parenchyma and the data on large deformations around blood vessels.
Biomechanical Factors Affecting Fracture Stability and Femoral Bursting in Closed Intramedullary Rod Fixation of Femur Fractures
Authors: Tencer A. F. , Sherman M. C. , Johnson K. D.
Published: July 2009

Intramedullary rodding of femur fractures, although a safe and rapidly performed procedure, can result in several complications. If the rod fit is too loose, fracture instability, rod migration, and delayed union may result. If the rod fit is too tight, cracking of the femur may occur during rod insertion. These complications were investigated in terms of geometric and mechanical parameters of the bone-implant system. Results showed that rods of the same nominal size from different manufacturers showed more than twofold difference in flexural rigidity and a threefold difference in torsional modulus. These differences appear to be due to differences in cross sectional shape and wall thickness of the rods. Measurements of pushout force and hoop stress in cadaver femora showed a large difference in pushout force with different rods, and significantly lower forces in distal than in proximal femoral fracture components. Pushout force decreased with fracture component length proximally and dropped to zero in distal components less than 170 mm long. An increase in ream diameter in the distal components of just 1 mm was found to decrease the mean pushout force from 740N to 90N. The most significant variable was found to be anterior offset of the starting hole more than 6 mm from the centerline of the medullary canal which resulted in consistent lifting of the anterior cortex during insertion of the rod.
A New Simplified Bioheat Equation for the Effect of Blood Flow on Local Average Tissue Temperature
Authors: Weinbaum S. , Jiji L. M.
Published: July 2009

A new simplified three-dimensional bioheat equation is derived to describe the effect of blood flow on blood-tissue heat transfer. In two recent theoretical and experimental studies [1, 2] the authors have demonstrated that the so-called isotropic blood perfusion term in the existing bioheat equation is negligible because of the microvascular organization, and that the primary mechanism for blood-tissue energy exchange is incomplete countercurrent exchange in the thermally significant microvessels. The new theory to describe this basic mechanism shows that the vascularization of tissue causes it to behave as an anisotropic heat transfer medium. A remarkably simple expression is derived for the tensor conductivity of the tissue as a function of the local vascular geometry and flow velocity in the thermally significant countercurrent vessels. It is also shown that directed as opposed to isotropic blood perfusion between the countercurrent vessels can have a significant influence on heat transfer in regions where the countercurrent vessels are under 70-μm diameter. The new bioheat equation also describes this mechanism.
The Relationship Between Crimp Pattern and Mechanical Response of Human Patellar Tendon-Bone Units
Authors: Stouffer D. C. , Butler D. L. , Hosny D.
Published: July 2009

The objectives of this study are twofold. First, to further develop the understanding of the relationship between the observed mechanical response and changes in the crimp pattern in human patellar tendon bone units. This is accomplished through the use of a specially constructed test frame and microscope system that permits observation and measurement of the crimp patterns as a function of load. Second, the results of the experimental study are used to develop a constitutive equation that includes spatial variation in the crimp pattern. The results of both the experimental and analytical study imply that local strain in the proximity of the attachment site is significantly larger than the strain in the central region of the tendon. The experimental and histological results are for specimens taken from four human bone-patellar tendon-bone units.
Cyclic Loading on the Red Cell Membrane in a Shear Flow: A Possible Cause of Hemolysis
Authors: Niimi H. , Sugihara M.
Published: July 2009

The fluid force acting on single human red cells in a high shear flow was analyzed. A two-dimensional elliptical microcapsule as a model of the deformed red cells was adopted to numerically calculate the distributions of the shear forces on both sides of the cell membrane. It is theoretically shown that the cell membrane undergoes an unsteady cyclic loading under the rotational motion around the interior. The mechanism leading to blood cell trauma is examined by repeatedly loading the continuously moving cell membrane.
Running on Flat Turns: Experiments, Theory, and Applications
Authors: Greene P. R.
Published: July 2009

Theoretical and experimental results are presented which demonstrate the mechanical effects of running along a circular turn. The theory is a simple one-parameter model, requiring only the top speed v0 of the runner as an input. The dimensionless parameter (Rg/v02), a reciprocal Froude number or dimensionless radius, appears as a natural result of the theory. This radial Froude number allows for the comparison of the theory and experiment for a large number of individuals on the same set of axes. The parameters of speed, foot contact time, ballistic air time, step length, stride length, and stride time are all predicted and measured for 23 different subjects. The agreement between theory and experiment is good. Exact solutions and approximate asymptotic results for the speed-radius relation are presented. Applications are made to the practical problem of the design of indoor and outdoor running tracks for athletic competition.