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EDITORIAL

J Biomech Eng. 1983;105(4):315. doi:10.1115/1.3138426.
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Abstract
Commentary by Dr. Valentin Fuster

RESEARCH PAPERS

J Biomech Eng. 1983;105(4):316-320. doi:10.1115/1.3138427.

Two unembalmed and one embalmed human cadaveric head-neck systems were instrumented and subjected to central forehead impact of ballistically suspended 3.07-kg aluminum shell at velocities ranging from 50 to 345 cm/s. Occipital skull accelerations and disk pressures were measured by transducers, while the deformation of the system was determined by framing camera data. The results were found to be in accord with those from corresponding tests in artifical head-neck replica. Initial and terminal X-ray examination of the structure revealed no evidence of either skull or vertebral fractures.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):321-331. doi:10.1115/1.3138428.

A three-dimensional analytical model of the cervical spine is described. The cervical vertebrae and the head are modeled as rigid bodies which are interconnected by deformable elements representing the intervertebral disks, facet joints, ligaments and muscles. A special pentahedral continuum element for representing the articular facets is described which effectively maintains stability of the cervical spine in both lateral and frontal plane accelerations, which is very difficult with multispring models of the facets. A simplified representation is used for the spine and body below the level of T1. The neck musculature is modeled by over 100 muscle elements representing 22 major muscle groups in the neck. The model has been validated for frontal and sideways impact accelerations by simulating published experimental data. Results are also presented to show the effects of the stretch reflex response on the dynamics of the head and neck under moderate acceleration.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):332-337. doi:10.1115/1.3138429.

A strain energy density (SED) criterion based on a fracture mechanics approach was used to assess the possible failure of acetabular bone cement after total hip replacement. Stress distributions in the cement at the bone-cement interface were calculated using two-dimensional finite element analyses. The results indicate that increasing the thickness of bone cement reduces the risk of cement fracture. The addition of a metal backing to the polyethylene cup and retention of the sub-chondral bone further reduces the risk of failure. The SED criterion was found to predict the same critical regions as zones of possible cement failure as the von Mises’ criterion. Although either criterion can be used for predicting failure in this acetabular analysis both criteria are excessively conservative in predicting failure in regions where high principal compressive stresses are present. Further development of cement failure criteria are indicated.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):338-345. doi:10.1115/1.3138430.

The need for better and longer lasting trileaflet valves has led to the design and development of the Abiomed polymeric trileaflet valve prosthesis. In-vitro fluid dynamic studies on sizes 25 and 21 mm valves in the aortic position indicate an overall improvement in performance compared to the Carpentier-Edwards and Ionescu-Shiley tissue valves in current clinical use. The pressure drop studies yielded effective orifice areas of 1.99 and 1.54 cm2 , and performance indices of 0.41 and 0.45 for the Nos. 25 and 21 valves, respectively. Leaflet photography studies indicated that the two valve sizes had maximum opening areas of 225 and 145 mm2 , respectively, at a normal resting cardiac output. Steady and pulsatile flow velocity measurements with a laser-Doppler anemometer (LDA) system indicate that the flow field downstream of the Abiomed valve is jetlike and turbulent. Maximum mean square axial velocity fluctuations of 55 and 83 cm/s, and turbulent shear stresses of 220 and 450 N/m2 were measured in the immediate vicinity of the nos. 25 and 21 valves, respectively. The Abiomed valves studied had been originally configured for use in valved conduits, and it is therefore our opinion that further improvements can be made to the valve and stent design, which would enhance its fluid dynamic performance.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):346-352. doi:10.1115/1.3138431.

Possible models of shear-induced augmentation of oxygen transfer in laminar blood flow are discussed and evaluated in the light of recently published experimental results [1]. A new transfer augmentation model is presented which evaluates the effect of microscopic translational motions of the red blood cells back and forth across the flow streamlines. The results of this model appear to be consistent with the experimentally measured diffusion augmentation.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):353-359. doi:10.1115/1.3138432.

A simple model is presented to analyze the effect of stenoses of different severities in a long elastic tube or artery on the pressure and flow-rate wave forms incident upon them. Wave propagation in the undisturbed tube is taken to be linear; nonlinearity arises from the quadratic dependence of stenosis pressure drop on flow rate. Before the model can be applied in practice, important physiological questions must be answered; e.g.: (a) Can the incident wave form and mean proximal pressure be regarded as given input? (b) Is the mean flow rate given, or does the peripheral resistance remain constant? Results are given on the assumption that the answer to (a) is yes. The principal conclusion is that the input impedance spectrum of a stenosed artery depends strongly on the incident waveform, as well as on the severity of the stenosis and on the distance from it at which measurements are made. There is good qualitative agreement with the results of experiments and of other models.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):360-366. doi:10.1115/1.3138433.

The plasma membrane water permeability of human granulocytes in the presence of extracellular ice was determined experimentally on a cryomicroscope. Transient volumes of individual cells were measured at constant subzero temperatures subsequent to ice nucleation. Permeability values were deduced by adjustment of multiple parameters in a model to obtain an optimal fit to the data. The permeability was determined to be a function of both temperature and intracellular solute osmolality, with a reference value at 0°C of 0.407 μm/atm·min and temperature and solute coefficients of 218kJ/mol and 1.09 Osm/kg.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):367-373. doi:10.1115/1.3138434.

Muscle fiber pathways in the heart wall are described. Procedures are introduced which permit data to be standardized from cadaver and animal hearts fixed at different points of the cardiac cycle or obtained in vivo from patients with different ejection fractions and heart masses. Design criteria are also developed here to construct a hypothetical standard left ventricle to compare the data from different hearts. The equations allow the nested set of toroidal fiber-shells to be depicted with typical muscle fiberpaths. With this formulation the heart wall and typical elements in it can be shown computergraphically as they move from the contracted state to the distended. Man-made fiber structures that simulate the fail-safe shockload absorbing features of the heart can now be designed and tested computergraphically by use of the mathematical procedures described here.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):374-380. doi:10.1115/1.3138435.

The mechanical behavior of the lung tissue (expressed by its constitutive equations) has considerable influence on the normal and pathological function of the lung. It determines the stress field in the tissue, thus affecting the impedence and energy consumption during breathing as well as the localization of certain lung diseases. The lung tissue has a complex mechanical response. It arises from the tissue’s structure—a cluster of a very large number of closely packed airsacks (alveoli) and air ducts. Each of the alveoli has a shape of irregular polyhedron. It is bounded by the alveolar wall membrane. In the present study, a stochastic approach to the tissue’s structure will be employed. The density distribution function of the membrane’s orientation in space is considered as the predominant structural parameter. Based on this model the present theory relates the behavior of both the alveolar membrane and that of its liquid interface to the tissue’s general constitutive properties. The resulting equations allow for anisotropic and visco-elastic effects. A protocol for material characterization along the present model is proposed as well. The methodology of the present theory is quite general and can be similarly used with other structural models of the lung tissue (e.g., models in which the effect of the alveolar ducts is included).

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):381-388. doi:10.1115/1.3138436.

A mechanical lung model with branching up to five generations, developed from an actual human lung, is used to study experimentally the velocity profiles in the trachea and the main branches. Three different flow rates representing light, medium, and heavy breathings have been simulated for both inhalation and exhalation. The velocity profiles, except for the one in the trachea in the frontal direction due to exhalation, are in good agreement with the velocity profiles in simplified models of published literature.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):389-392. doi:10.1115/1.3138437.

The nonlinear two-layer arterial wall model introduced by von Maltzahn, et al. [11] is subjected to a rigorous parameter sensitivity and range of validity analysis. The model is based on the assumption that in large muscular conduit arteries the two mechanically significant layers are media and adventitia. Using curve-fitting techniques, the media is determined to be isotropic and the adventitia to be anisotropic. As a result of the range of validity analysis, the polynomial relationship for the energy density function of the media is changed to an exponential relationship. This leads to new coefficients for the polynomial of the adventitia. All coefficients have specific mechanical meanings. The parameter sensitivity analysis demonstrates convincingly that all model parameters are significantly important.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):393-397. doi:10.1115/1.3138438.

Tensile fatigue tests of acrylic bone cement were conducted under strain control in a wet environment at 37°C. A constant strain rate of 0.02s−1 was used, resulting in physiologic loading frequencies. Comparison of the tensile fatigue data with the results of previous tension-compression fatigue tests indicates that fatigue failure is governed primarily by the maximum cyclic tensile strain. The compressive portion of the loading cycle has little effect on the number of cycles to failure. A new empirically derived equation is introduced to describe the influence of mean strain and strain amplitude on fatigue endurance. The results emphasize the critical role tensile strains may play in cement failure and loosening of total joint replacements.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):401-404. doi:10.1115/1.3138440.
Abstract
Topics: Blood flow
Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):404-406. doi:10.1115/1.3138441.
Abstract
Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):406-410. doi:10.1115/1.3138442.

Measurement of local velocity fluctuations was made with an L-shaped conical hot-film probe in a submerged circular jet. The experiment was carried out in solutions of washed human red blood cells (RBC) in a phosphate buffer solution (PBS), at hematocrit concentrations (Ht percent) of 10, 19, 29, and 38 percent. The viscosity of the testing solutions was kept at 3.2 c.p. by adding proper amount of dextran. The experiment was conducted at Reynolds numbers (N R ) 674, 963, 1255 and 1410, based on the jet exit velocity and exit diameter. Statistical analyses were performed on the recorded instantaneous velocity signals to obtain the root-mean-square (rms) values, the probability density functions (PDF) and the power spectral density functions (PSDF) of the signals. Within the range tested, we noticed an incidental rise in rms values at 19 to 29 Ht percent for N R = 963 similar to those reported earlier in the literature. Further analyses using PDF and PSDF, however, showed neither a trend nor any physical significance of this rise. Based on the analyses of both the PDF and the PSDF, we believe that the incidental rise in rms value can be partially attributed to the high spikes registered by the probe in a high RBC concentrations fluid flow. The bombardment of RBC on the probe thermal boundary layer may cause a characteristic change in the probe response to certain flow phenomenon, at least within the Reynolds number range used in this study. Additional theoretical and experimental information is needed to pin point the nature of this response. We thus suggest that the second and higher moments of the HFA signals obtained in a fluctuating flow field involving a liquid with relatively high contaminant concentrations cannot be interpreted as a simple flow phenomenon.

Commentary by Dr. Valentin Fuster

BOOK REVIEWS

J Biomech Eng. 1983;105(4):411. doi:10.1115/1.3138443.
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Abstract
Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):411. doi:10.1115/1.3138444.
FREE TO VIEW
Abstract
Topics: Blood flow
Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):412. doi:10.1115/1.3138445.
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Abstract
Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):412. doi:10.1115/1.3138446.
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Abstract
Topics: Membranes , Physiology
Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(4):412-413. doi:10.1115/1.3138447.
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Abstract
Commentary by Dr. Valentin Fuster

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