bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural Properties of Immature Canine Bone
Authors: Torzilli P. A. , Takebe K. , Burstein A. H. , Heiple K. G.
Published: June 2009

Structural properties of growing canine long bones were determined from three and four-point bending tests. Mechanical and geometric properties were found to follow a biphasic growth process, with a rapid increase in bending strength and moment of inertia from 1 to 24 wk of age and a substantially decreased rate thereafter to maturity. Predicted bone tissue material properties were also found to follow this biphasic developmental process.
Analysis of Model Variables and Fixation Post Length Effects on Stresses Around a Prosthesis in the Proximal Tibia
Authors: Askew M. J. , Lewis J. L.
Published: June 2009

A two-dimensional, finite element model of a single-posted, metal, tibial prosthetic component implanted with PMMA in the proximal tibia is developed. The effects upon the stresses at the PMMA-bone interface and in the cancellous bone around the component due to the inclusion in the model of the cortical shell and the heterogeneity and anisotropy of the cancellous bone, are demonstrated. Various lengths of the fixation post are considered. The cortical shell adds support and stiffness to the bone structure, and allows generation of significant stresses proximally. The heterogeneity of the cancellous bone, as assumed here, dictates the form of the stress distributions and the magnitudes and locations of the peak stress values around the post of the component. Peak stress values can occur at locations proximal to the post tip. The anisotropy of the cancellous bone significantly alters the magnitudes of the stresses. Lower stresses along the post interface and higher stresses beneath the plate of the prosthesis are seen in the anisotropic models. Lengthening of the fixation post reduces stresses proximally, but the effects of post lengthening upon the maximum stress values around the post are highly dependent upon the assumed properties of the cancellous bone.
Experimental Measurements of the Flow-Induced Shear Stress Distribution in the Vicinity of Prosthetic Heart Valves
Authors: Herkes W. H. , Lloyd J. R.
Published: June 2009

The present study examines the local shear stress distribution occurring during flow through prosthetic valves. The electrochemical technique is a powerful tool for the study of mass transfer related phenomena and was selected for this investigation. The present investigation attempts to establish the viability of the particular application of the technique. Three test section geometries were analyzed: a straight tube, a ball-in-cage valve, and a model disk-in-cage valve, and the tests were conducted at six Reynolds numbers ranging from 1000 to 6000 under steady-state conditions. The model disk valve provided a base-case check on the validity of the technique since it has been employed in several previous studies and the flow through it is well documented. High shear and low shear regions are clearly evident and their locations can be pinpointed. The ball-in-cage valve was tested over the full range of Reynolds numbers. The shear profiles demonstrate a double peak in the region of the ball, a result which was unexpected. Careful study revealed that this was a result of the test section geometry and provides another demonstration of the importance of test section geometry. The frequency of the fluctuations in wall shear for the ball valve were found to be different than those for the disk valve indicating that the environment at the aortic wall is definitely affected by valve design. This study showed the electrochemical technique to be a valuable tool for the study of the flow through prosthetic heart valves.
Transient Study of Couple Stress Effects in Compact Bone: Torsion
Authors: Yang J. F. C. , Lakes R. S.
Published: June 2009

Couple stress theory, which admits an internal moment per unit area as well as the usual force per unit area, is a generalization of classical elasticity. Experimentally we have demonstrated the existence of couple stress by measuring the effect of size on apparent stiffness of compact bone in quasi-static torsion. From these measurements, we obtain the characteristic length for bone in couple stress theory.
The Material Properties of Immature Bone
Authors: Torzilli P. A. , Takebe K. , Burstein A. H. , Zika J. M. , Heiple K. G.
Published: June 2009

The age-related material properties of developing immature canine bone were determined for the femora, tibiae, humeri, radii, and ulnae in animals from 1 wk of age to maturity. These properties included bone geometry changes, material tissue properties, and qualitative and quantitative morphological evaluations. All bones exhibited a two-phase growth cycle, an initial rapid phase (20 wk) followed by a substantially slower growth to maturation (48 wk). All properties showed age-related changes except bone tissue strain to failure.
Transient and Residual Stresses and Displacements in Self-Curing Bone Cement—Part II: Thermoelastic Analysis of the Stem Fixation System
Authors: Ahmed A. M. , Nair R. , Burke D. L. , Miller J.
Published: June 2009

In this second part of a two-part report, an idealized model of the stem fixation system is analyzed to determine the adverse effects of the thermal stresses and displacements of bone cement during its curing process. The Shaffer-Levitsky stress-rate strain-rate law for chemically hardening material has been used. The results show that if the cement is surrounded by cancellous bone, as opposed to cortical bone, then transient tensile circumferential stresses in the cement and similar radial stresses at the stem/cement interface are generated. The former may cause flaws and voids within the still curing cement, while the latter may cause gaps at the interface.
Selection of Body Segment Parameters by Optimization Methods
Authors: Vaughan C. L. , Andrews J. G. , Hay J. G.
Published: June 2009

The selection of body segment parameters (BSPs) is a difficult yet essential task in many biomechanical studies. The methods used to date—cadaver, reaction board, mathematical modeling, gamma scanning, and kinematics—all have a number of drawbacks. The purpose of the present paper is to present an alternative method, based on kinematic data and optimization theory, for selecting BSPs. The design variables are the BSPs and the objective function to be minimized is based on the difference between calculated and measured distal extremity kinetics, while the equality constraints are based on Newtonian principles as well as bilateral symmetry of the BSPs. Three different activities are used to generate “optimal” sets of BSPs and these values are different, but not markedly so, from cadaver values. Further detailed investigation appears warranted.
Respiratory Heat Transfer in Cold Water and During Rewarming
Authors: Hayes P. A. , Padbury E. H. , Florio J. T. , Fyfield T. P.
Published: June 2009

Respiratory heat loss was measured during cold water (5–6° C) excursions to depths of 300 m. Losses were computed with and without respiratory gas heating when wearing a diving helmet in current commercial and Service use. A magnitude of heat loss, sufficient to cause undue stress to the respiratory tract, was observed even with gas heating provided, particularly at maximum depth. If the hyperbaric gas is both heated and humidified to a maximum comfort level then respiratory gains in the order of 40 W are possible at 250 m. This technique of utilizing warm wet gas introduced into the respiratory tract was tested as a rewarming technique following immersion in cold water (4–5° C) to the limit of peripheral endurance.
Interaction of Fluid Movement and Particle Diffusion Across Capillary Walls
Authors: Salathe´ Eric P. , Venkataraman R.
Published: June 2009

The rate of transcapillary exchange of substances delivered to or removed from the tissue by blood depends on the concentration difference across the capillary wall. This concentration difference results in an osmotic effect that can have considerable influence on capillary-tissue fluid exchange. However, fluid exchange also affects the plasma and tissue concentrations of the various substances. Therefore, the determination of substrate concentration profiles involves an interaction of many microcirculatory phenomena, including capillary-tissue fluid exchange. In this paper a general mathematical model is presented that describes the interaction of multiple exchangeable solutes. The resulting equations are solved to give the concentration profiles of different substances and their effect on fluid exchange for various normal and pathological situations of physiological interest.
In-Vivo Elastic and Damping Response of the Human Leg to Impact Forces
Authors: Mizrahi J. , Susak Z.
Published: June 2009

The transmission of impact forces in a straight leg from the foot to the level of the greater trochanter was investigated by a two-degree of freedom linear damped-spring model. Foot ground forces measured during a vertical jump and accelerations measured at the level of the greater trochanter were used as model input. The model elastic constant and damping coefficient were determined by solving the dynamic equations of the system. The model was used to predict peak acceleration values for a given input force. Satisfactory prediction of the magnitudes of the first two peaks of the acceleration (maximum difference of 3 percent) was achieved in the two subjects studied.
The Effect of Incomplete Fixation of Elastin on the Appearance of Pulmonary Alveoli
Authors: Sobin S. S. , Fung Y.-C. B. , Tremer H. M.
Published: June 2009

Pulmonary alveolar geometry in histological sections prepared by quick-freezing the lung, with freeze-substitution of ice, fixation of the dry lung with osmium tetroxide in nonaqueous and nonpolar solvent and celloidin embedding is remarkably different from the geometry seen in preparations made by instilling aqueous aldehyde or osmium tetroxide solution in the airways. The alveolar walls in the quick-frozen lung are linear; those in the others are wrinkled. The difference was demonstrated to be due to incomplete fixation of elastin.
Kinematic Analysis and Simulation of Vertebral Motion Under Static Load—Part I: Kinematic Analysis
Authors: Soni A. H. , Sullivan J. A. , Patwardhan A. G. , Gudavalli M. R. , Chitwood J.
Published: June 2009

The paper presents the kinematic analysis of motion segments of ten, human-lumbar spines. In order to achieve this objective, a spine fixture and a linkage transducer were designed. The spine fixture is capable of holding the motion segment in a prescribed plane of loading. With the designed fixture it becomes possible to apply three types of shear loads, and three types of bending loads. In addition, if desired, a compressive preload may be applied to a motion segment. The linkage transducer consists of six rotary potentiometers connected by seven rigid links. The transducer is capable of measuring all possible components of vertebral motion. The motion data in the motion segments of ten lumbar spine were collected under the influence of combined shear and bending loads applied in an incremental manner. Maximum shear load was 35.6 N and maximum bending load was 6780 N·mm. The motion segments did not show any appreciable difference in their motion beyond these loads. The motion segments were not subjected to any compressive preload. The range of motion data were collected in twelve loading planes 15 deg apart. The characteristic vertebral motion may be described in terms of range of motion, its components, and the parameters associated with the screw motion. The paper presents data in the chart form to describe the kinematic characteristics of the lumbar motion segment.
A Three-Layer Semi-Empirical Model for Flow of Blood and Other Particular Suspensions Through Narrow Tubes
Authors: Gupta B. B. , Nigam K. M. , Jaffrin M. Y.
Published: June 2009

A three-layer mathematical model has been developed and tested for calculating the velocity profile and wall layer thickness for the flow of blood and other particulate suspensions in narrow tubes, from measurements of apparent viscosity and mean concentration in tube. The model consists of a thin cell-free layer, accounting for wall exclusion effect, a cell-depleted one due to radial cell migration and a central core with uniform cell concentration. It is shown that this model contains several previously published models as particular cases and that it gives more realistic predictions of velocity profiles from the same data than less refined models. With proper adjustment of its parameters it is applicable satisfactorily to a wide variety of suspensions. The model results confirm the importance of cell deformability on blood rheological properties in capillaries less than 100 μ.
On Relationship Between Bulk Modulus and Relative Volume of Lung During Inflation-Deflation Maneuvers
Authors: Pao Y. C. , Shy D. S. , Chevalier P. A.
Published: June 2009

An equation of the form K = C/[1 − (V/Vmax)]n relating the bulk modulus K to the relative volume V/Vmax of lung region during inflation-deflation maneuvers is proposed. It well represents the observed fact that the bulk modulus becomes infinitely large when the regional volume approaches its maximum capacity Vmax. The parameter C describes the bulk modulus at low regional volume whereas the parameter n quantifies the rate at which the bulk modulus changes during the inflation-deflation maneuvers. The mathematical expressions for the regional pressure, P, and volume V, are obtained by integrating the equation K = VdP/dV. They fit exceedingly well with the experimental data recorded during inflation-deflation tests of six excised canine lung lobes.
Computer Modeling of the Human Left Ventricle
Authors: Yettram A. L. , Vinson C. A. , Gibson D. G.
Published: June 2009

A computer graphical technique is described for reconstructing the three-dimensional geometry of the human left ventricle of the heart from biplane cineangiograms. The views used are right and left anterior oblique. The reconstructed shape is intended for three-dimensional mesh generation for finite element stress analysis, but may also be useful for clinical diagnostic purposes and for cavity volume calculation throughout the cardiac cycle.
Steady Expiratory Flow-Pressure Relationship in a Model of the Human Bronchial Tree
Authors: Reynolds D. B.
Published: June 2009

Static pressure differences across a human bronchial tree model were obtained for steady expiratory flows of several gases producing Reynolds numbers (Re1) in the bronchus carrying the entire flow (first bronchus) between 150 and 50,000. The model was constructed from an air-dried lung and was complete to bronchi about 2 mm in diameter. Dimensionless static pressure plotted against Re1 consolidated the data on a single curve, phenomenologically described by an equation of the form: ΔPs/ΔPd1 = A + B Re1 where ΔPd1 is a pressure drop for Poiseuille flow. Velocity profile measurements at two sites along the first bronchus for laminar and turbulent flows indicate a dependence on the latter and distance from the first junction. Loss in total pressure was computed and may result from both frictional dissipation and changes in momentum flux associated with development of velocity profiles near the junctions. An average loss in total pressure within a single bronchus was calculated after making several simplifying assumptions, and this result may be useful in modeling both the resistance of the entire bronchial tree and the more complex phenomenon of maximal expiratory flow.
Peribronchial Stress Analysis Utilizing Concentric Cylindrical Shells of Parenchyma
Authors: Tani J. , Nakamura M. , Sasaki H. , O¯kubo T. , Takishima T. , Hildebrandt J.
Published: June 2009

The mechanical dependence of bronchial volume on parenchymal properties and on intrabronchial and pleural pressures was investigated utilizing finite elasticity theory. Treating the lung parenchyma as a compressible continuum, and using a simple strain-energy-density function fitted to pressure-volume curves of saline-filled lungs, we analyzed nonhomogeneous large deformations of the fluid-filled excised dog lobe by numerical procedures. For the purpose of obtaining peribronchial stress distributions, the lung was represented by a hollow very thick-walled cylinder corresponding to an axial bronchus with surrounding parenchyma. Finite elements consisted of concentric cylindrical shells. In general, we found that the theoretical results corresponded well to published stress and strain data for bronchial collapse. Peribronchial radial and circumferential stresses were found to be concentrated at the bronchial wall, but dissipated rapidly within 1–2 bronchial radii away from the wall. We conclude that the magnitude of regional lung recoil around bronchi during collapse can be reasonably well estimated by a theoretical analysis based on total lung pressure-volume relationships.
A Generalized Method for the Minimization of Cellular Osmotic Stresses and Strains During the Introduction and Removal of Permeable Cryoprotectants
Authors: Levin R. L.
Published: June 2009

The successful freeze preservation of mammalian cells and tissues usually requires the presence of high concentrations of cryoprotective agents (CPAs) such as glycerol, ethylene glycol, or dimethylsulfoxide. Unfortunately, the addition of these permeable agents to cells and tissues prior to freezing and their removal after thawing has been documented to be as damaging as the freeze-thaw process itself. This damaging process has been hypothesized to result from the drastic alterations in cell size caused by the osmotic stresses usually imposed upon cells during the introduction and removal of the cryoprotectants. Consequently, on the basis of a nonequilibrium thermodynamic model for the transport of water and a permeable CPA across cell membranes, a method has been developed to minimize these potentially lethal transient changes in cell size. This method involves the simultaneous variation of both the extracellular CPA and electrolyte or osmotic extender osmolalities in a balanced, prescribed manner so that both the cellular water content and the total intracellular ionic strength remain constant as the intracellular CPA osmolaity is either raised or lowered. The theoretical analysis indicates that many of the resulting protocols are practical from the clinical point of view.
Bioengineering Studies of Periodic External Compression as Prophylaxis Against Deep Vein Thrombosis—Part I: Numerical Studies
Authors: Kamm R. D.
Published: June 2009

This paper presents the results of a numerical study of the technique of periodic external compression for the prevention of deep vein thrombosis. In the model the veins of the lower leg are portrayed as a continuous system rather than as discrete elements as in previous models. Consequently, we are able to explore the detailed effects of different modes of compression including (i) uniform compression, the simultaneous application of uniform pressure over the entire lower leg, (ii) graded compression, the application of nonuniform pressure, maximum at the ankle and minimum at the knee, and (iii) wavelike compression, a wave of compression proceeding from the ankle toward the knee. These numerical results indicate that the effectiveness of uniform compression is severely compromised by the formation of a flow-limiting throat at the proximal end of the compression cuff that reduces both the rate at which blood is discharged from the lower leg and the total blood volume removed. Both of these detrimental effects can be avoided by the use of either wavelike or graded compression. Both alternate methods are shown to produce more uniform augmentation of volume flow rate, flow velocity, and shear stress, throughout the entire lower leg. In the companion paper, Part II [18] (see following article), these same compression modes are tested using a simple hydraulic model consisting of a single latex tube inside a foam cylinder as a highly simplified representation of a human leg.
An In-Vivo Study of Normal Wrist Kinematics
Authors: Brumbaugh R. B. , Crowninshield R. D. , Blair W. F. , Andrews J. G.
Published: June 2009

The motion of the hand relative to a reference frame embedded in the radius is described using the screw displacement axis (SDA) concept. A three-dimensional sonic digitizer was utilized in a study of the dominant wrist of 15 normal subjects to determine the location and orientation of the SDAs based on the endpoints of flexion-extension motion (FEM) and radial-ulnar deviation (RUD) of the hand. The length of the common perpendicular between the SDAs of FEM and RUD was as large as 6 mm in some individuals; however, in some subjects the FEM SDA was distal of the RUD SDA while in others it was proximal. Considering the group of 15 subjects, the SDAs of FEM and RUD for the normal group nearly intersect in the head of the capitate in the neutrally positioned wrist and forearm.
Peristaltic Transport of a Power-Law Fluid With Variable Consistency
Authors: Shukla J. B. , Gupta S. P.
Published: June 2009

Effects of the consistency variation on the peristaltic transport of a non-Newtonian power-law fluid fluid through a tube have been investigated by taking into account the existence of a peripheral layer. It is shown that the flow rate flux, for zero pressure drop, increases as the amplitude of the peristaltic wave increases but it decreases due to the pseudoplastic nature of the fluid. It is also noted that, for zero pressure drop, the flux does not depend on the consistency of peripheral layer while the friction decreases as this consistency decreases. However, for nonzero pressure drop, the flux increases and the friction force decreases as the consistency of peripheral layer fluid decreases.
Bulging of Lumbar Intervertebral Disks
Authors: Reuber M. , Schultz A. , Denis F. , Spencer D.
Published: June 2009

Lateral, posterolateral, posterior, and end plate bulges in the intervertebral disks of 14 fresh human cadaver lumbar motion segments were measured. Loads were applied in compression of up to 800 N; and in right lateral bending, extension, flexion, and torsion of up to 12 Nm. Mean disk bulges up to 2.7 mm were found. Disk bulges differed little after fluid injection or after posterior element removal.
Some Static Mechanical Properties of the Lumbar Intervertebral Joint, Intact and Injured
Authors: Tencer A. F. , Ahmed A. M. , Burke D. L.
Published: June 2009

The in-vitro static load-displacement properties of the intact and the injured human lumber intervertebral joint have been investigated in a loading apparatus which allows entirely unconstrained relative displacement between the joint members. The spatial relative displacement produced by a given load, alone or in combination with another load (preload), were measured using 14 specimens and emphasizing strict control of the secondary variables which are known to affect the results. An attempt has been made to interpret the results in terms of the relative load-bearing roles of the disk, the facets and the posterior ligaments as a function of the type of load. The results indicate that the disk is the major load-bearing element in lateral and anterior (with respect to a fixed superior vertebra) shears, axial compression and flexion, while the facets play a major role in posterior shear and axial torque.
Transient Temperature Profiles in Tissues With Nonuniform Blood Flow Distributions
Authors: Elkowitz A. B. , Shitzer A. , Eberhart R. C.
Published: June 2009

Numerical methods and the bio-heat transfer equation are employed to calculate temperature profiles in tissues subjected to nonuniform blood flow distributions, for initial and boundary conditions which simulate experimental physiological situations. Results indicate that one can infer, from sudden changes in temperature distribution, the occurrence of sudden changes in tissue blood flow. However, prediction of blood flow distribution from near equilibrium or steady-state temperature profiles is of poor resolution, and does not appear useful as a practical technique. The methods and results are useful for predictions of temperature profiles in the absence of significant endogenous or exogenous heating; they can be extended to such applications by straightforward methods.
Extending the Theory of Dash Running
Authors: Senator M.
Published: June 2009

I extend the theory of dash running by allowing resisting force to be proportional to any positive power of speed and by allowing the runner to be tractive-force-limited at the beginning of the dash and developable-force-limited subsequently. I solve the equation of motion and express the maximum value of developable force as a function of limiting dash velocity, resisting-force/velocity exponent, and indoor and outdoor-track asymptotic intercept times (the intercepts with the time axis of asymptotic lines that are fitted to the distance-time curves) and limiting tractive coefficients. For a 20-yr-mean world record limiting dash velocity of 10.33 m/s and indoor and outdoor asymptotic intercept times of 0.617 and 0.265 s, I find that a composite dash world record holder is tractive-force-limited on indoor tracks, that limiting indoor tractive coefficient is about 0.9, and that the maximum value of developable force exceeds 2.0 times the record holder’s weight.
Effect of Aortic Stenosis on Coronary Flow Dynamics: Studies in an In-Vitro Pulse Duplicating System
Authors: Sabbah H. N. , Stein P. D.
Published: June 2009

The dynamics of retrograde coronary flow in aortic valvular stenosis was investigated in an in-vitro pulse duplicating system which had the capability of simulating coronary flow. The ventricular chamber of the pulse duplicator consisted of an opaque elastic sac molded from rubber in the shape of a left ventricle. The aortic test section consisted of an acrylic mold of the root of the aorta of a calf, which included the sinuses of Valsalva and the entrance region of both the left and right coronary arteries. Flow in the left coronary artery was modeled to deliver both a systolic and a diastolic component of flow. Studies were performed with normal porcine valves in the aortic and mitral positions and were repeated with a human stenotic valve in the aortic position. Pressures were measured in the aorta, left ventricle, and at the ostium of the left coronary artery with catheter-tip micromanometers. In the presence of a normal aortic valve, total coronary flow was adjusted to 120 ml/min of which 21 percent of the flow occurred during systole. The phasic pattern of coronary flow was similar to that shown in vivo. In the presence of a stenotic aortic valve, a small amount of retrograde coronary flow (<1 percent of total coronary flow) was observed; and this occurred during the initial phase of systole. Retrograde coronary flow during systole appears to have resulted from compression of the collapsible segment of the simulated coronary artery. This was caused by the elevated simulated intramural pressure.
Accuracy Enchancement of In-Vivo Bone Strain Measurements and Analysis
Authors: Bessman E. S. , Carter D. R. , McCarthy J. C. , Harris W. H.
Published: June 2009

A numerical technique is presented to evaluate and correct the zero-strain reference points determined experimentally for certain in-vivo strain rosette applications on long bones. The method is used to determine whether significant transverse stresses are present at the gage site during in-vivo activities. If transverse stresses are shown to be negligible, the experimentally determined zeroes can be appropriately adjusted to provide an increased accuracy of the strain measurements. In addition, the transverse Poisson’s ratio is calculated and can be incorporated in subsequent in-vivo stress calculations.
Errors in the Center and Angle of Rotation of a Joint: An Experimental Study
Authors: Panjabi M. M. , Goel V. K. , Walter S. D. , Schick S.
Published: June 2009

The error sensitivity in the determination of center and angle of rotations of a body joint performing planar motion is studied. A simple experiment is described to measure the errors in these two kinematic parameters as functions of errors in the input coordinates of markers. The effect of varying the marker locations and the size of motion-step is also studied. The errors in the center of rotation are found to increase dramatically when the two markers subtend angles of about 0 deg or 180 deg and when the motion step size decreases to 1 deg or less. Similar results are found for errors in the angle of rotation which, in addition, increase with decrease in the radius of the markers.
Turbulent Stresses in the Region of Aortic and Pulmonary Valves
Authors: Stein P. D. , Walburn F. J. , Sabbah H. N.
Published: June 2009

The specific features of turbulent flow that are likely to be damaging to the blood cells and platelets are the stresses which are intrinsic to turbulence, known as Reynolds stresses. These include normal stresses as well as shear stresses. The purpose of this study is to determine the magnitude of the turbulent stresses that may occur during ejection in the vicinity of normal and diseased aortic valves near normal pulmonary valves. Both Reynolds normal stresses and Reynolds shear stresses were calculated from velocities obtained in vitro with a laser Doppler anemometer in the region of two severely stenotic and regurgitant human aortic valves. Reynolds normal stresses were also calculated from velocities obtained with a hot-film anemometer in 21 patients in the region of normal and diseased aortic valves. In seven of these patients, it was calculated in the region of the normal pulmonary valve. The Reynolds normal stress in patients with combined aortic stenosis and insufficiency was prominently higher than in patients with normal valves. In the former, the Reynolds normal stress during ejection transiently reached 18,000 dynes/cm2. This was in the range of the Reynolds normal stress observed in vitro. The Reynolds shear stress measured in vitro transiently reached 11,900 dynes/cm2 during ejection. Because the Reynolds normal stresses in the presence of the severely stenotic and regurgitant valves were comparable in vitro and in patients, it is likely that the Reynolds shear stress in patients is also comparable to values measured in vitro. These values were well above the stresses which, when sustained, have been shown to have a damaging effect upon blood cells and platelets.
Surgical Drilling: Design and Performance of an Improved Drill
Authors: Saha S. , Pal S. , Albright J. A.
Published: June 2009

The majority of twist drills used in orthopaedics are very similar to chisel pointed metal drilling bits. Modifications usually observed are reduction of the point angle to 90 deg and sometimes grinding of the entire cutting lip at 0 deg rake angle, which appeared to have been made arbitrarily without any advantage. We have attempted to design a surgical drill bit with the objective of minimization of the drilling thrust and temperature and effective removal of bone chips. Our results showed that the presence of the chisel edge was mainly responsible for increasing the thrust force and the temperature developed. The effects of a constant feed rate and thrust on the peak temperature were also examined. The combined effect of the helix and the point angles on the rake angle which in turn determines the cutting efficiency was analyzed for various types of surgical bits. Based on our results and previously published data from the literature an optimized drill bit was designed with a split point, a point angle of 118 deg, a parabolic flute, and a helix angle of 36 deg and its performance was compared with other existing surgical drill bits. For drilling in compact bone, the new design decreased the thrust load by 45 percent and the peak temperature rise by 41 percent. Simlar improvements were also recorded for drilling bone cement. The time of drilling a bone cortex was also significantly reduced and “walking” on the curved bone surface was eliminated and dimensional tolerance on hole sizes was improved. The new design is likely to reduce the time of surgery and also minimize the tissue damage.
Conditioning Surfaces to Suit the Biomedical Environment: Recent Progress
Authors: Baier R. E.
Published: June 2009

One major determinant of the suitability of various engineering materials for use in biological settings is the relative strength of adhesion obtained between those materials and their contacting viable phases. Maximal adhesive strength and immobility are desired for orthopedic and dental implants, for example, while minimal bioadhesion is critical to preventing unwanted thrombus formation in cardiovascular devices, plaque buildup on dental prostheses, and bacterial fouling of heat exchangers. This article reviews the principles of adhesive phenomena in such harsh environments, introduces some novel test methods and materials available for sensitive analysis of the earliest interfacial events, and provides a brief illustration of their use in the study of surface fouling of food processing equipment. Attention is then directed to adhesive phenomena in the oral environment, examining new surface conditioning methods for the prevention of micro-organism deposits, as well as the promotion of excellent tissue bonding to implanted prosthetic devices. Other bioadhesive phenomena considered include those important to the safe and effective function of new cardiovascular devices, such as the artificial heart and substitute blood vessels, and the prevention of biological fouling of materials in the sea. Comparisons of the primary interfacial events in these diverse systems—all wet, salty, and biochemically active—illustrate that Nature has been very conservative in accommodating encounters with strange boundaries. As with a classic drama, the players and timing may vary, but the script remains the same.
Determination of Perfusion Field During Local Hyperthermia With the Aid of Finite Element Thermal Models
Authors: Sekins K. M. , Emery A. F. , Lehmann J. F. , MacDougall J. A.
Published: June 2009

Two-dimensional transient thermal models of human thighs undergoing microwave diathermy are developed with the aid of experimental data to shed light on the blood flow response occurring during local hyperthermia in muscle. The experimental data were taken from tests on six human subjects treated with a 915-Mz, direct-contact microwave diathermy device which incorporated a system for simultaneously cooling the skin surface with a cold air stream. The numerically calculated perfusion fields were determined by systematically varying a model’s blood flow response to the temperature stimulus until good agreement between the experimental and model temperature fields were achieved. The model blood flow values were then checked against those measured in the human experiments via xenon 133 washout and good agreement here was also found. The future use of models of this type in clinical diagnosis and hyperthermic treatment is proposed.
Force Generation From Orthodontic Appliances
Authors: Greif R. , Coltman M. , Gailus M. , Shapiro E.
Published: June 2009

The design of orthodontic archwires often incorporates complex bends, loops and twists to generate force fields. The determination of the magnitude and direction of these forces requires the solution of three-dimensional problems of geometric nonlinearity. To solve these problems, a computer program is developed based on a combined incremental/iterative algorithm. The findings are verified by comparison with analytic solutions of nonlinear engineering problems, as well as by laboratory testing of orthodontic archwires.
A Model of Lower Extremity Muscular Anatomy
Authors: Brand R. A. , Crowninshield R. D. , Wittstock C. E. , Pedersen D. R. , Clark C. R. , van Krieken F. M.
Published: June 2009

The mathematical prediction of muscle and joint force requires a quantitative knowledge of muscle origins and insertions. A model is presented based upon marking the origins and insertions in three cadavers (six limbs). Right-to-left biological variations and/or making errors are sometimes significant, but they rarely result in moment arm calculation variations of greater than 20 percent and usually the variations are less than 10 percent. The muscle origin and insertion differences between small and large cadavers is great, as would be expected, and the use of single specimen or average data will result in large errors in muscle force predictions. A scaling scheme is presented which substantially reduces those errors. The inherent limitations of developing a straight line muscle model include: 1) right-to-left biological variations and/or marking errors; 2) difficulties in establishing “effective” origins or insertions when the locations of the actual origin or insertion do not accurately reflect muscle function; and 3) intersubject variability which cannot be accounted for by simple scaling schemes.
Direct In-Vivo Measurements of the Elastic Properties of Canine Trachea
Authors: Winter D. C. , Pimmel R. L. , Lewis B. F.
Published: June 2009

The specific compliance of the tracheas of seven anesthetized dogs were measured in vivo under control conditions and with the cervical vagi cut and then stimulated. Specific compliances ranged from 7.9 to 12.2 × 10−6 (dynes/cm2)−1 for the control measurements and were not significantly different after vagotomy. Stimulation of the vagi reduced the compliance of the trachea by 40–70 percent. These results agree with other reported in-vivo results but the specific compliance values are noticeably less than the values reported for excised trachea.
The Effect of Gelled-Pad Design on the Performance of Electrosurgical Dispersive Electrodes
Authors: Caruso P. M. , Pearce J. A. , DeWitt D. P.
Published: June 2009

A two-dimensional model of a simplified configuration of the gelled-pad electrode applied to human tissue was developed. As a consequence of the boundary discontinuity near the edge of the pad, the model predicted high peripheral and low central surface temperature rises. By comparison with base conditions, increased gelled-pad area and gel electrical resistivity and decreased initial pad temperature reduce the temperature rise across the pad surface. Temperature distributions measured on the thighs of human subjects were shown to have similar characteristics to those predicted by the model. Even though three-dimensional and blood flow effects were not considered, the model is satisfactory for evaluating the effect of electrode design changes on thermal performance.
Soft Tissue Strain and Facet Face Interaction in the Lumbar Intervertebral Joint—Part I: Input Data and Computational Technique
Authors: Tencer A. F. , Mayer T. G.
Published: June 2009

A numerical simulation was devised to determine ligament strains, facet face interaction, and disk fiber strain in the lumbar intervertebral joint under load. This technique uses experimentally derived load deflection and morphologic data from lumbar cadaver specimens from which initial and displaced soft tissue attachment points can be calculated. This allows the strain data to be derived. The effect of disk bulge is also considered. The calculated strains of most ligaments except the facet capsular ligaments were found to be insensitive to anatomical measurement variability of ± 1 mm.
A Direct Substitution, Equation Error Technique for Solving the Thermographic Tomography Problem
Authors: Kleinman A. M. , Roemer R. B.
Published: June 2009

A new technique for solving the combined state and parameter estimation problem in thermographic tomography is presented. The technique involves the direct substitution of known skin temperatures into the finite difference form of the bio-heat transfer equation as formulated for solving an initial value problem with a convection boundary condition at the skin surface. These equations are then used to solve the inverse bio-heat transfer problem for the unknown subcutaneous tissue temperatures and physiological parameters. For a small number of nodal points, closed form algebraic solutions are obtained. For larger sets of equations, a hybrid technique is used in which the problem is initially posed as an unconstrained optimization problem in which the model equation error is minimized using the conjugate gradient descent technique to get close to a solution. Then a generalized Newton-Raphson technique was used to solve the equations. A numerical simulation of a one-dimensional problem is investigated both with and without noise superimposed on the input (transient) skin temperature data. The results show that the technique gives very accurate results if the skin temperature data contains little noise. It is also shown that if the physical properties of the tissue and the metabolism are known, that a given set of proper transient skin temperature inputs yields a unique solution for the unknown internal temperatures and blood perfusion rates. However, the similar problem with known blood perfusion rates and unknown metabolisms does not yield a unique solution for the internal temperatures and metabolisms.
Identification of In-Vivo Vibration Modes of Human Tibiae by Modal Analysis
Authors: Van der Perre G. , Van Audekercke R. , Martens M. , Mulier J. C.
Published: June 2009

When attempting to evaluate the mechanical properties of human bones in vivo by mechanical vibration analysis, some essential requirements must be met. A quantitative relation between measured vibration parameters (e.g., natural frequency) and mechanical bone properties must be available, in-vivo vibration modes should correctly be identified and the associated natural frequencies reproducibly and accurately measured, the influence of joints and soft tissues must be known. These problems were addressed by modal analysis (i.e., experimental determination of natural frequencies, mode shapes and damping ratios) of human tibiae in the following situations: 1) dry excised tibiae, 2) fresh excised tibiae, 3) in-vivo tibiae, 4) tibiae in an amputated leg, in different steps of dissection. In the in-vivo measuring conditions used by the authors, the tibia vibration is practically free-free. Two single bending modes (at ± 270 Hz and ± 340 Hz, respectively), each of them corresponding with one principal direction for bending, were identified. The difference between the natural frequencies observed in vivo and those of fresh excised tibiae is almost completely caused by the effect of muscles (added mass and damping), whereas joints and skin play only a minor role. Frequency differences between fresh and dry excised tibiae are largely accounted for by the absence of bone marrow in the latter.
Pressure Difference-Flow Rate Variation in a Femoral Artery Branch Casting of Man for Steady Flow
Authors: Cho Y. I. , Back L. H. , Crawford D. W.
Published: June 2009

In-vitro, steady flow in a casting of the profunda femoris branch of the femoral artery of man was studied by measuring pressure differences in the main lumen and also in the branch over a large Reynolds number range from 200 to 1600. Effects of viscous and inviscid flows in this femoral artery branch were demonstrated quantitatively. The critical ratio of the flow rate in the branch to the upstream main lumen, m˙3/m˙1, in this casting was found to be 0.4, above which the inviscid flow analysis indicated a pressure rise and below which it yielded a pressure drop in the main lumen across the branch junction. Pressure rises were experimentally found to occur both in the main lumen and in the branch for certain ranges of m˙3/m˙1.
Turbulent Flows Through a Disk-Type Prosthetic Heart Valve
Authors: Yang W. J. , Wang J. H.
Published: June 2009

A numerical model is developed to predict the complex velocity, shear and pressure fields in steady turbulent flow through a disk-type prosthetic heart valve in a constant diameter chamber. The governing Navier-Stokes equations are reduced to a set of simultaneous algebraic finite-difference equations which are solved by a fast-converging line-iterations technique. A two-parameter, two-equation model is employed to determine the turbulent viscosity. Numerical results are obtained for stream function, vorticity, and shear and normal stresses. The regions of very high shear and normal stresses in the fluid and at the walls are identified. The maximum value of the shear stress occurring near the upstream corner of the disk may cause hemolysis. The technique can be used together with in-vitro physcial experiments to evaluate existing or future prosthetic heart valve designs.
Three-Dimensional Stress Distribution in Arteries
Authors: Chuong C. J. , Fung Y. C.
Published: June 2009

A three-dimensional stress-strain relationship derived from a strain energy function of the exponential form is proposed for the arterial wall. The material constants are identified from experimental data on rabbit arteries subjected to inflation and longitudinal stretch in the physiological range. The objectives are: 1) to show that such a procedure is feasible and practical, and 2) to call attention to the very large variations in stresses and strains across the vessel wall under the assumptions that the tissue is incompressible and stress-free when all external load is removed.
Leg Motion Analysis During Gait by Multiaxial Accelerometry: Theoretical Foundations and Preliminary Validations
Authors: Hayes W. C. , Gran J. D. , Nagurka M. L. , Feldman J. M. , Oatis C.
Published: June 2009

A theoretical formulation for studying limb motions and joint kinetics by multiaxial accelerometry is developed. The technique is designed to study the swing phase of human gait, modeling the lower leg as a rigid body. Major advantages of the approach are that acceleration information needed for the calculation of forces and moments is generated directly, and that the method automatically generates its own initial conditions. Results of validation experiments using both artificial and experimental data demonstrate that the method is theoretically valid, but that it taxes available instrumentation and requires further development before it can be applied in a clinical setting.
Fiber Stabilization of Bent Cylinders, With an Application to Intervertebral Disks
Authors: Schreiner K. E.
Published: June 2009

Fibers cannot carry compression, and reinforcing fibers in a cylinder can only carry load if they are kept taut by the deformations of the cylinder. In the present study it is found that in pure bending, deformations that change the pitch, i.e., the angle between the fibers and the cross-sectional plane, towards 30 deg will slacken the fibers. With an initial pitch different than 30 deg, fibers in one half of the cross section will then be slackened by bending, and this half of the cylinder becomes unstable. Applied to the mechanics of the intervertebral disks, this may help explain mechanisms leading to nucleus prolaps.
A Finite Element Model of Burn Injury in Blood-Perfused Skin
Authors: Diller K. R. , Hayes L. J.
Published: June 2009

The burn process resulting from the application of a hot, cylindrical source to the skin surface was modeled using the finite element technique. A rotationally symmetric 125-element mesh was defined within the tissue beneath and outlying to an applied heating disk. The disk temperature and duration of contact were varied, respectively, between 50 and 100°C for up to 30 s. Natural convection with ambient air was assumed for areas of skin surface not in direct contact with the disk. The simulated thermal history was used in a damage integral model to calculate the extent and severity of injury in the radial and axial dimensions.