Showing papers in "Journal of Biomechanical Engineering-transactions of The Asme in 1980"

Heat transfer to blood vessels

Abstract: Heat transfer to individual blood vessels has been investigated in three configurations: a single vessel, two vessels in counterflow, and a single vessel near the skin surface. For a single vessel the Graetz number is the controlling parameter. The arterioles, capillaries, and venules have very low Graetz numbers, Gz < 0.4, and act as perfect heat exchangers in which the blood quickly reaches the tissue temperature. The large arteries and veins with Graetz numbers over 10(3) have virtually no heat exchange with the tissue, and blood leaves them at near the entering temperature. Heat transfer between parallel vessels in counterflow is influenced most strongly by the relative distance of separation anad by the mass transferred from the artery to the vein along the length. These two effects are of the same order of magnitude, whereas the film coefficients in the blood flow are of significant but lesser importance. The effect of a blood vessel on the temperature distribution of the skin directly above it and on the heat transfer to the environment increases with decreasing depth-to-radius ratio and decreasing Biot number based on radius. The absolute magnitude of these effects is independent of other linear effects, such as internal heat generation or a superimposed one-dimensional heat flux.

The meaning of the point of maximum oscillations in cuff pressure in the indirect measurement of blood pressure--part ii

Abstract: When measuring blood pressure indirectly, oscillations in the cuff pressure are observed. The cuff pressure for which these oscillations reach a maximum and its relationship to the true mean arterial pressure was investigated using a simple one-dimensional theoretical model of the cuff-arm-artery system. Results from this model indicate that the cuff pressure for maximal oscillation is strongly dependent on compression chanber air volume, pulse pressure, and arterial elasticity. Parallel experimental studies indicate general agreement with the theoretical model. The cuff pressure for maximal oscillations appears to provide a reasonable estimation of the true mean arterial pressure provided compression chamber air volume is kept small.

Quasi-Linear Viscoelastic Properties of Normal Articular Cartilage

Abstract: A combined experimental and analytical approach was used to determine the history-dependent viscoelastic properties of normal articular cartilage in tension. Specimens along the surface split line direction, taken from the middle zone of articular cartilage were subjected to relaxation and cyclic tests. A quasi-linear viscoelastic theory proposed by Fung [31] was used in combination with the experimental results to determine the nonlinear viscoelastic properties and the elastic stress-strain relationship of normal articular cartilage.

The role of fluid mechanics in atherogenesis.

Abstract: A specialists meeting on "The Role of Fluid Mechanics in Atherogenesis" was held August 24-25, 1978, at The Ohio State University This meeting was a followup to a similar meeting held in 1974 [1, 2] The present status of our knowledge of the importance of fluid mechanics in the initiation and progression of arterial lesions is summarized on the basis of the experimental data presented at the meeting; no attempt is made to provide a comprehensive review of the relevant literature Three basic aspects are addressed: firstly, the localization of arterial lesions; secondly, the local hemodynamics of arterial segments with a high predilection to the development of lesions; and thirdly, the interaction of hemodynamic factors with the arterial wall The many unresolved questions, apparently conflicting experimental data and areas in need of future research on the role of fluid mechanics in atherogenesis are identified specifically

Controlled Destruction and Temperature Distributions in Biological Tissues Subjected to Monoactive Electrocoagulation

Abstract: An analysis of the temperature fields developed in a biological tissue undergoing a monoactive electrical coagulating process is presented, including thermal recovery following prolonged heating. The analysis is performed for the passage of alternating current and assumes a homogeneous and isotropic tissue model which is uniformly perfused by blood at arterial temperature. Solution for the one-dimensional spherical geometry is obtained by a Laplace transform and numerical integrations. Results obtained indicate the major role which blood perfusion plays in determining the effects of the coagulating process; tissue temperatures and depth of destruction are drastically reduced as blood perfusion increases. Metabolic heat generation rate is found to have negligible effects on tissue temperatures whereas electrode thermal inertia affects temperature levels appreciably. However, electrodes employed in practice would have a low thermal inertia which might be regarded as zero for all practical purposes. It is also found that the depth of tissue destruction is almost directly proportional to the electrical power and duration of application. To avoid excessively high temperatures and charring, it would be advantageous to reduce power and increase the time of application. Results of this study should be regarded as a first approximation to the rather complex phenomena associated with electrocoagulation. They may, nevertheless, serve as preliminary guidelines to practicing surgeons applying this technique.

Effects of Transmural Pressure and Muscular Activity on Pulse Waves in Arteries

Abstract: Propagation of small amplitude harmonic waves through a viscous incompressible fluid contained in an initially stressed elastic cylindrical tube is considered as a model of the pulse wave propagation in arteries. The nonlinearity and orthotropy of the vascular material is taken into account. Muscular activity is introduced by means of an "active" tension in circumferential direction of the vessel. The frequency equation is obtained and it is solved numerically for the parameters of a human abdominal aorta. Conclusions concerning pressure-dependence, age-dependence, and muscular activation-dependence of the wave characteristics are drawn which are in accord with available experimental data.

A viscoelastic model for use in predicting arterial pulse waves.

Abstract: In nonlinear mathematical models of the arterial circulation, the viscoelasticity of the vessel walls has generally been neglected or only taken into account in a highly approximate manner. A new method is proposed to simulate the nonlinear viscoelastic properties of the wall material with the aid of a convolution integral of the creep function and the pressure history. With this simulation it is possible to properly describe the measured characteristics of arterial viscoelasticity. Moreover, it is utilized in a mathematical model of arterial pulse propagation to study the influence of the internal wall friction on the shape, amplitude and mean value of pressure and flow pulses. The corresponding predictions are in much better agreement with in-vivo measurements, especially for the distal part of the circulation, than those obtained without viscoelasticity.

The Contribution of the Cruciate Ligaments to the Load-Displacement Characteristics of the Human Knee Joint

Abstract: Human knee specimens were subjected to anterior-posterior, medial-lateral, varus-valgus, and torsional displacement tests. Loads were recorded for the intact joint and for the joint with all soft tissues cut except for the cruciate ligaments. The effect of condylar interference was determined for anterior-posterior, medial-lateral, and torsional displacements. The variation in load with flexion angle was considerable for medial-lateral (0-90-deg flexion) displacements, and less for varus-valgus (0-45-deg flexion) displacements. The cruciates were found to carry almost the entire anterior-posterior load; they carried a significant percentage of the medial-lateral load which varied considerably with flexion angle. A small, but not insignificant percentage of the varus-valgus load was carried by the cruciates and the variations with flexion angle were small. In torsion, the cruciates resisted only internal rotation. In the tested displacement ranges, condylar interference had a small effect on the medial-lateral load but did not affect anterior-posterior or torsional loads.

A technique for kinematic modeling of anatomical joints.

Abstract: This paper describes a general technique for fitting a spatial kinematic model to an in-vivo anatomical joint under typical physiological loading conditions. The method employs a nonlinear least squares algorithm to minimize the aggregate deviation between postulated model motion and experimentally measured anatomical joint motion over multiple joint positions. Estimation of the parameters of a universal joint with skew-oblique revolutes to best reproduce wrist motion was used as an example. Experimental motion data from the right wrists of five subjects were analyzed. The technique performed very well and produced repeatable results consistent with previous biomechanical wrist findings.

A microstructure model for the rheology of mammalian tendon.

Abstract: The rheological behavior of mammalian tendon is analyzed in terms of its constituents structure and their properties. The elastic fibers are assumed to be straight and linearly elastic. They are of predominant role in the low ranges of strain. The collagen fibers are nonuniformly undulated. Upon stretch they gradually become straight, thus increasing the stiffness of the tissue. They are assumed to be linearly viscoelastic with negligible bending strength. It is shown that the nonuniformity of the collagen fiber structure can account for the observed nonlinear load-strain relations as well as for the nonlinear viscoelastic behavior of the tendon. An experimental procedure is developed through which the material functions and parameters can be determined.

Load elongation behavior of the canine anterior cruciate ligament.

Abstract: This paper describes the results of an investigation on the mechanical properties of canine anterior cruciate ligaments. A total of 38 ligaments were tested. It is shown that the completely reversible (elastic) range of strain is limited to 14 percent elongation, corresponding to an applied load of 200 N. Within this range each specimen was tested at different strain rates varying from 0.12 percent/s to 220 percent/s and it is demonstrated that the mechanical behavior of the ligaments is not sensitive to strain rate in the range investigated. After completion of tests in the reversible range, of strain ten ligaments were frozen and similar tests were performed after thawing. It is shown that freezing produces alterations of the mechanical properties. The ligaments become more rigid than when they are tested in fresh conditions. From room temperature up to 45C, the load-elongation relationship is not significantly dependent upon test temperature.

Electrogoniometer for the Measurement of Human Elbow Joint Rotation

Abstract: Since the electrogoniometric method has been justified for the measurement of lower extremity joint motion, a similar device is developed for the measurement of elbow joint and forearm rotations. In this design, the axis of forearm rotation coincides with the anatomical axis which eliminates the cross talk existing in the regular triaxial goniometer. Although the axis of abduction-adduction is still offset from the elbow joint, special linkage arrangement was used to obtain equivalent motion. Experimental method was used to validate the accuracy of the device and model simulation was performed to emphasize the importance of accurate placement of the instrument on test subjects. Application of the present apparatus to normal subjects was studied to illustrate the range of elbow motion required in performing normal activities of daily living. This device is currently used in the functional evaluation of patients with elbow and forearm problems.

Visco-Elasticity of Passive Cardiac Muscle

Abstract: A quantitative mechanical description of the heart organ requires information on the mechanical behavior of its muscle in reasonable unity and completeness. In this respect, a fundamental constitutive law for soft biological tissures was proposed by Fung in 1972. This article presents evidence to show that Fung's law is a useful law to describe the mechanical behavior of heart muscle in the unstimulated (diastolic) state with sufficient generality. A visco-elastic relaxation phenomenon is studied in the isolated cardiac muscle of cat and rabbit with the purpose of constructing a mathematical model for relaxation. Experimental results show that passive relaxation behavior of heart muscle can be adequately described by a generalized standard linear solied with a continuous distribution of relaxation times. The form of the relaxation function devised permits the application of linear visco-elasticity theory to the nonlinear cardiac muscle. The relaxation model is used to predict the force-length (stress-strain) behavior of papillary muscle with reasonable accuracy.

A Miniature Fiber Optic pH Sensor for Physiological Use

Abstract: A flexible 0.4-mm-dia pH probe potentially suitable for physiological use has been developed. It is based on the concept of utilizing two single plastic fiber optic strands to illuminate and remotely sense the color change of a dye indicator contained within an acutely implanted sealed cellulosic hollow fiber permeable to hydrogen ions. A supporting electronic module provides tungsten filament illumination, light sensing with a photodiode/operational amplifier, analog and digital circuitry to provide appropriate signal averaging and processing, and a mechanical assembly to enable the optical density measurements to be made both at 560 nm and, for normalization purposes, in the red. Over the physiological pH range from 7.0 to 7.4, the fiber optic probe agrees with a standard glass pH electrode to within 0.01 pH units in buffer solutions, to within 0.017 pH units in heparinized dog blood in vitro, and it has performed successfully while implanted in the jugular vein of a sheep.

Laboratory evaluation of a unified theory for simultaneous multiple axis artificial arm control.

Abstract: This paper reports on the application of a "postulate-based" control method for multi-axis artificial arm control. This method uses shoulder muscle EMG's as control sites, but, unlike previous techniques, the theory is the first that can be rigorously defined in terms of musculoskeletal anatomy, EMG muscle-force relationships, EMG transmission characteristics, muscle recruitment, limb dynamics and normal motion constraints. The control theory results in a deterministic, mathematically expressible set of controller equations, which use the vector of natural limb torques estimated by shoulder EMG signals and a "constraint" for input. The output of the controller equations is a vector of prosthetic torques to be applied to the artificial limb. We report on the implementation of the theory up to the point of laboratory feasibility trials of actual simultaneous above-elbow amputee control of elbow flexion and humeral rotation. Implementation of the theory required: 1) deviation of the controller equations from Newton's dynamic equations of motion into controller form in conformity with the postulate theory; 2) development of a methodology for estimating natural musculoskeletal torques from EMG signals; 3) hardware and software for experimental testing with actual closed loop amputee control of the prosthesis; and 4) a methodology for evaluating the performance of the prosthesis relative to both alternative prosthetic systems and the natural arm. These tasks were completed and simultaneous multiple-axis control of a prosthetic arm was accomplished by both amputee and nonamputee subjects. Key questions of control compatibility, naturalness, stability, and performance evaluation relative to other prostheses and the natural arm were addressed. Various problems are discussed with the conclusion that this method, despite some difficulties, holds great promise as a practical rehabilitation tool.

A measurement of proximal femur strain with total hip arthroplasty.

Abstract: Strain measurement was performed on loaded fresh human cadaveric proximal femurs before and after total hip femoral component implantation. Changes in the femurs' strain state associated with loading through stainless steel and titanium femoral components were recorded. The role of proximal femur remodeling in femoral component loosening is discussed along with the likely effect of femoral component elastic modulus on the remodeling process.

A Mathematical Model of Lung Parenchyma

Abstract: The geometry of the proposed model of the parenchyma of a mammalian lung reproduces a cluster of alveoli arranged around a lowest-level air duct. The alveolar walls are assumed to be nonlinear elastic membranes, whose properties are described in terms of a strain energy function which reflects the hardening character of the stress-strain curve. The effect of the surfactant is included in terms of a variable (area-dependent) surface tension. Analyses of various mechanical processes in the parenchyma are performed with the aid of the finite element method, with the geometric and physical nonlinearities of the problem taken into account.

The design, fabrication and evaluation of a trileaflet prosthetic heart valve.

Abstract: Although prosthetic heart valves have been in existence for many years, the need for new improved designs and in-vitro evaluation techniques are apparent. This paper presents details on the design considerations, fabrication techniques and heart valve evaluation equipment. A valve performance index is discussed in light of various valve and mock circulatory test section designs. The need for national and indeed international valve evaluation techniques is made apparent.

A Finite Element Model for Macroscopic Deformation of the Lung

Abstract: A finite element model is formulated for determining the macroscopic stress, strain and deformation of the lung parenchyma. The effects of nonlinear elastic behavior, finite deformation, and interfacial tension are included. An incremental approach is used. Illustrative results for deformation of the lung due to its weight are included. The necessity of including surface tension explicitly is demonstrated.

Changes in the deformational behavior of human hip cartilage with age.

Abstract: The deformation occurring in the articular cartilage covering the human femoral head has been measured both when the femoral head is loaded in its natural acetabulum and when the cartilage is loaded with a small indentor. The results indicate that the material response is substantially different in these two situations. In the intact joint the cartilage deformation is substantially greater in older joints, but the response of cartilage to loading with an indentor does not change significantly with age. Theoretical elastic models of the cartilage behavior in these two situations were analyzed. For old cartilage which is idealized as an elastic material the increased deformation which is observed in the intact joint can be attributed to changes in Poisson's ratio, though in the real material increased fluid flux under load is the more probable cause.

Force systems from orthodontic appliances: an analytical and experimental comparison.

Abstract: Experimental data is compared with the simulated displacements from a computer program for the clinical activations of two separate orthodontic appliances undergoing a total of four separate loading conditions. Good agreement is shown over the entire range of activation. Suggestions for future strengthening of both the analytical and the experimental methods are given. An interactive design graphics system is shown to be imminently available to the research orthodontist.

Automatic control of human thermal comfort by a liquid-cooled garment.

Abstract: Water cooling in a liquid-cooled garment is used to maintain the thermal comfort of crewmembers during extravehicular activity. The feasibility of a simple control that will operate automatically to maintain the thermal comfort is established. Data on three test subjects are included to support the conclusion that heat balance can be maintained well within allowable medical limits. The controller concept was also successfully demonstrated for ground-based applications and shows potential for any tasks involving the use of liquid-cooled garments.

Devolution of Inhomogeneities in Bone Structure—Predictions of Adaptive Elasticity Theory

Abstract: In this paper we consider an initially inhomogeneous adaptive elastic body subjected to a steady homogeneous stress state. The adaptive elastic body, which is a model for living bone tissue, is inhomogeneous in both its anisotropic elastic properties and its density. The principal result of the paper is the determination of the devolution of the initially inhomogeneous body to a homogeneous body under the influence of the steady homogeneous stress state. A cylindrical body that is inhomogeneous along the axis of the cylinder, but homogeneous in each transverse plane of the cylinder, is used as an example. This cylindrical body is loaded by a steady uniform stress directed along the cylindrical axis. The temporal devolution of an inhomogeneity in the initial shape of a sine wave is illustrated. As time progresses the amplitude of the sine wave decreases, rapidly at first and then more slowly. As time becomes very large the sine wave becomes a straight line signifying that the cylinder has become homogeneous.

Volumetric changes in cells during freezing and thawing.

Abstract: A thermodynamic model is presented to describe the combined freezing and thawing process for living cells. Continuous changes in the cell volume are predicted according to the thermal protocol imposed on the system. Experimental verification of the model is sought by monitoring continuously the volume of cells as frozen on a cryomicroscope. The volumes of individual cells are measured from sequential photomicrographs by a computerized image analysis technique. The model and experimental data are in quite close agreement for the freezing process, but upon thawing the experimentally measured volumes consistently increased much more rapidly than predicted by the model. The model can be made to conform to the data by accounting for a substantial influx of electrolyte to the cell at subfreezing temperatures.

Correlation of field injuries and GM hybrid III dummy responses for lap-shoulder belt restraint.

Abstract: Simulated frontal, lap-shoulder belted, barrier impact tests were performed using a Volvo sedan and General Motors Hybrid III anthropomorphic test dummy. Swedish field accident injury data for this vehicle are available from another published study. For the purpose of this program, the injuries were logically subdivided into four body regions: head, neck, thorax, and lower torso. The Hybrid III has instrumentation in each of these regions. The results of three replicated tests at barrier equivalent velocities of nominally 32 and 48 km/h are discussed in terms of the field injuries, thereby providing a basis for more intelligent interpretation of future Hybrid III test results. Language: en

Hemodynamic measurements in human arterial casts, and their correlation with histology and luminal area.

Abstract: A new approach is presented for studying the vascular response to hemodynamic stress. A laser doppler anemometer is used to make velocity measurements very near the walls of human arterial casts; these measurements are then correlated with the histology of the artery from which the cast was made. Several illustrative results are given which suggest that the velocity profiles along the outer walls of aortic bifurcations may be significantly determined by the longitudinal variation of cross-sectional area. The shapes of these profiles were qualitatively different for each cast studied. In one specimen, the location of initial lipid deposits appeared to correlate with flow acceleration.

Shear-Induced Augmentation of Oxygen Transfer in Blood

Abstract: An experimental study was performed to determine the extent of shear-induced augmentation of oxygen diffusion in blood. The results were obtained using whole human blood in laminar flow through semipermeable membrane tubes. Transfer enchancement in whole blood was found to be dependent on the fluid shear rate and the hemoglobin saturation level. Very little agumentation was observed in saturated blood for shear rates up to 2500 s-1. However, with partially unsaturated blood, oxygen transfer was increased up to 250 percent at the higher shear rates. The implications for modeling oxygen transfer in blood are discussed.

Derivation of myocardial fiber stiffness equation based on theory of laminated composite

Abstract: The constitutive equation with stress-dependent coefficients for laminated composite is derived and employed for iterative determination of myocardial fiber's stiffness equation E(f) = Ksigma(f) + C from myocardial strip's stiffness equation E(s) = K(s)sigma(s) + C(s). The strip's stiffness constants K(s) and C(s) are estimated by the least-square curve fitting of the stress-strain data experimentally obtained from uniaxially stretching of strips of left ventricular heart wall excised from seven canine hearts. The values of K and C computed at selected fiber orientations across the thickness of the strip and using three, five, and ten-layer approximations are reported.