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  • Articles  (10)
  • Other Sources
  • Biomechanics  (10)
  • Springer  (10)
  • 1995-1999  (10)
  • Technology  (10)
  • 1
    Electronic Resource
    Electronic Resource
    Mechanical Contribution of Endocardium During Finite Extension and Torsion Experiments on Papillary Muscles (1999)
    Springer
    Annals of biomedical engineering 27 (1999), S. 123-130 
    Details
    ISSN: 1573-9686
    Keywords: Biomechanics ; Constitutive behavior ; Cardiac mechanics ; Myocardium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Finite extension and torsion tests on cardiac papillary muscles are presently the best way to directly measure the response to shear along myocardial fibers. Quantifying this response is necessary for determining the complete three-dimensional constitutive behavior of myocardium as a transversely isotropic material. Analysis of such tests is complicated, however, since papillary muscles are materially inhomogeneous, consisting of a myocardial core surrounded by an endocardial sheath that is rich in collagen. In this article, we show that the papillary muscle response to extension and torsion additively decouples into the response of the bare myocardial core plus the response of an endocardial sheath filled with fluid (assuming the muscle is a radially inhomogeneous and incompressible continuum with cylindrical symmetry). This result allows the endocardial response to be subtracted from the intact papillary muscle response to obtain the response of the bare myocardial core. An initial estimate suggests that the endocardial sheath affects the axial moment significantly (50% of torque for all twists at low stretch) but affects the axial force only slightly (〈10% at moderate twists). © 1999 Biomedical Engineering Society. PAC99: 8719Hh, 8719Rr, 8719Ff
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.218
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of Cell Migration on the Maintenance of Tension on a Collagen Matrix (1999)
    Springer
    Annals of biomedical engineering 27 (1999), S. 721-730 
    Details
    ISSN: 1573-9686
    Keywords: Fibroblast ; Cornea ; Biomechanics ; Collagen matrix ; Finite-element modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Although it is known that cells promote structural reorganization of the collagen architecture, how individual cells exert mechanical tension on the matrix is not clearly understood. In the present study we have investigated the mechanical interaction of individual corneal fibroblasts with a collagen matrix using an improved version of our previously described in vitro force-measurement system (Roy, P. et al. Exp. Cell Res. 232:106–117, 1997). The elastic distortion of the collagen matrix exerted by cells was temporally recorded and analyzed using a two-dimensional finite-element model to quantify the forces exerted on the matrix. Time-lapse videomicroscopy of serum-cultured cells on the matrix for up to 6 h revealed that individual fibroblasts generated measurable tension on the matrix during pseudopodial extension and slow retraction. Fast retraction, an event observed during active cell migration, was associated with dramatic release of tension on the matrix. An apparent inverse correlation was observed between cell translocation and maintenance of matrix tension. Additional experiments with cells under serum-free conditions revealed that these cells fail to generate any detectable tension on the matrix despite undergoing filopodial extension and retraction. Since serum-free cells do not form focal adhesions or stress fibers, these experimental data suggest that contractility of nonmotile cells, coupled with strong cell–matrix adhesion, is the most favorable mechanism of generating and maintaining tension on the extracellular matrix. © 1999 Biomedical Engineering Society. PAC99: 8718Ed, 8715La, 8714Ee, 4266Ct, 0270Dh
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.227
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  • 3
    Electronic Resource
    Electronic Resource
    Assessment of Active and Passive Restraint During Guided Reaching After Chronic Brain Injury (1999)
    Springer
    Annals of biomedical engineering 27 (1999), S. 805-814 
    Details
    ISSN: 1573-9686
    Keywords: Rehabilitation ; Neurological control systems ; Bioinstrumentation ; Biomechanics ; Spasticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract We report the use of a mechatronic device for assessing arm movement impairment after chronic brain injury. The device, called the “Assisted Rehabilitation and Measurement Guide,” is designed to guide reaching movements across the workspace, to measure movement and force generation, and to apply controlled forces to the arm along linear reaching paths. We performed a series of experiments using the device in order to identify the contribution of active muscle and passive tissue restraint to decreased active range of motion of guided reaching (i.e., “workspace deficits”) in a group of five chronic, spastic hemiparetic, brain-injured subjects. Our findings were that passive tissue restraint was increased in the spastic arms, as compared to the contralateral, nonparetic arms. Active muscle restraint, on the other hand, was typically comparable in the two arms, as quantified by measurements of active arm stiffness at the workspace boundary during reaching. In all subjects, there was evidence of movement-generated weakness, consistent with a small contribution of spasticity to workspace deficits. These results demonstrate the feasibility of mechatronic assessment of the causes of decreased functional movement, and could provide a basis for enhanced treatment planning and monitoring following brain injury. © 1999 Biomedical Engineering Society. PAC99: 8719La, 8719St, 8780Vt, 8719Nn, 8719Ff
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.233
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  • 4
    Electronic Resource
    Electronic Resource
    Reflex Torque Response to Movement of the Spastic Elbow: Theoretical Analyses and Implications for Quantification of Spasticity (1999)
    Springer
    Annals of biomedical engineering 27 (1999), S. 815-829 
    Details
    ISSN: 1573-9686
    Keywords: Spasticity ; Stretch reflex ; Biomechanics ; Stroke ; Hemiparesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A parametric model of the human reflex torque response to a large-amplitude, constant angular velocity elbow extension was developed in order to help quantify spasticity in hemiparetic stroke patients, and to better understand its pathophysiology. The model accounted for the routinely observed leveling of torque (i.e., a plateau) at a mean angular increment of 51°±10° s.d. (n=98) after the initial rise. This torque “plateau” was observed in all eight subjects, and in 98 of 125 trials across 25 experimental sessions. The occurrence of this plateau cannot be explained by decreases in elbow flexor moment arms during elbow extension. Rather, the plateau is attributable to a consistent leveling in muscle activation as confirmed both qualitatively from recordings of rectified, smoothed electromyograph (EMG) activity, and quantitatively using an EMG coefficient model. A parametric model was developed in which the pattern of muscle activation in the stretch reflex response of elbow flexors was described as a cumulative normal distribution with respect to joint angle. Two activation functions, one related to biceps and the other to brachioradialis/brachialis, were incorporated into the model in order to account for observations of a bimodal angular stiffness profile. The resulting model yielded biologically plausible parameters of the stretch reflex response which may prove useful for quantifying spasticity. In addition, the model parameters had clear pathophysiological analogs, which may help us understand the nature of the stretch reflex response in spastic muscles. © 1999 Biomedical Engineering Society. PAC99: 8719Rr, 8719Xx, 8719St, 8719Nn, 8719Ff, 8710+e
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.234
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  • 5
    Electronic Resource
    Electronic Resource
    History-Dependent Mechanical Behavior of Guinea-Pig Small Intestine (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 850-858 
    Details
    ISSN: 1573-9686
    Keywords: Biomechanics ; Jejunum ; Preconditioning ; Pressure–volume relation ; Stiffness ; Strain softening ; Viscoelasticity ; Mechanics ; Small intestine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Measurement of pressure–volume relations is a commonly used technique to elucidate small intestinal stiffness. There is a lack of data on the relation between stiffness and history-dependent mechanical properties of the gastrointestinal tract. We aimed to distinguish between passive properties of the tissue that depend on the time-history of load (viscoelastic effects) versus those that depend on the maximum previous load (strain softening effects). Ten repeated pressure–volume relations were measured at each peak pressure level in six isolated, passive guinea-pig jejuni in vitro during balloon inflation and deflation cycles. With inflation to a new higher peak pressure (ranging from 3 to 15 mm Hg), the pressure–volume relation became less stiff, particularly in the low pressure range, without a significant change in unloaded jejunal volume. We computed the jejunal normalized volume change as a function of the integrated volume–time history and maximum volume. Analysis of covariance revealed significant dependence of the normalized volume change on the volume–time history (P 〈; 0.001) and the maximum volume history (P 〈; 0.001). Multiple linear regression analysis showed that approximately 90% of the history dependence could be attributed to the maximum volume. Most softening (loss of stiffness) happens in the low pressure range of the curve (0–3 mm Hg). We adopted the Johnson and Beatty strain softening theory and computed the volume amplification factor. This factor was shown to be a linear function of the normalized peak volume (r2 〉 0.999). Since strain softening effects were significantly greater than viscoelastic effects, we conclude that history-dependent changes in jejunal stiffness are more likely to involve alterations to elastic rather than viscous structures in the tissue. These effects must be taken into account when performing balloon distension studies in the gastrointestinal tract for studying physiological and pathophysiological problems in which loading conditions are altered, e.g., mechanoreceptor studies in normal intestine and in acute and chronic obstruction, in order to have an accurate description of the biomechanics. © 1998 Biomedical Engineering Society. PAC98: 8745Bp
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.109
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  • 6
    Electronic Resource
    Electronic Resource
    Noninvasive acceleration measurements to characterize knee arthritis and chondromalacia (1995)
    Springer
    Annals of biomedical engineering 23 (1995), S. 78-84 
    Details
    ISSN: 1573-9686
    Keywords: Diagnosis ; Rheumatoid arthritis ; Quantitative assessment ; Rheumatology ; Biomechanics ; Patofemoral joint ; Acceleration measurement ; Tibiofemoral joint ; Osteoarthritis ; Vibration arthroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Devising techniques and instrumentation for early detection of knee arthritis and chondromalacia presents a challenge in the domain of biomedical engineering. The purpose of the present investigation was to characterize normal knees and knees affected by osteoarthritis, rheumatoid arthritis, and chondromalacia using a set of noninvasive acceleration measurements. Ultraminiature accelerometers were placed on the skin over the patella in four groups of subjects, and acceleration measurements were obtained during leg rotation. Acceleration measurements were significantly different in the four groups of subjects in the time and frequency domains. Power spectral analysis revealed that the average power was significantly different for these groups over a 100–500 Hz range. Noninvasive acceleration measurements can characterize the normal, arthritis, and chondromalacia knees. However, a study on a larger group of subjects is indicated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02368303
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  • 7
    Electronic Resource
    Electronic Resource
    An improved muscle-reflex actuator for use in large-scale neuromusculoskeletal models (1995)
    Springer
    Annals of biomedical engineering 23 (1995), S. 359-374 
    Details
    ISSN: 1573-9686
    Keywords: Neuromuscular ; Muscle mechanics ; Muscle spindle ; Posture ; Movement ; Stability ; Biomechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract This paper extends the systematic approach described in Winters and Stark (62) for developing muscle models. The underlying motivation is our finding that for larger scale shoulder and head-neck postural systems to be mechanically stable, open-loop muscle properties are often not sufficient. There are three primary contributions. First, the previous muscle mechanical model structure and parameter estimation process of (62) is updated to reflect recent experimental findings. Second, an intrafusal (IF) muscle model is developed that includes a γ static motoneuron (MN) drive, a Hill muscle model, and a muscle spindle sensor across the IF series element; this provides a more appropriate muscle spindle output signal, especially for studies of posture. Third, the conceptual cut between the neurocontrol input and the actuator is raised from just below the MN summing junction to a higher location, allowing a “musclereflex actuator” to be defined that satisfies the formal theoretical requirement for possessing passive spring-like behavior when the neurocontrol input is constant. α−ψ MN coactivation is assumed, and three types of intrinsic autogenic reflex responses (spindle, Golgi tendon organ, Rhenshaw cell) are developed. Default feedback gains are set based on the criteria that inherent feedback should not sculpt the feedforward excitation drive by more than ±10% of maximum. This new actuator model only mildly affects voluntary goal-directed dynamic performance, but enhances spring-like performance around the postural equilibrium state, in line with available animal and human studies and with several theories on postural regulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00000004
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  • 8
    Electronic Resource
    Electronic Resource
    New models of the oculomotor mechanics based on data obtained with chronic muscle force transducers (1995)
    Springer
    Annals of biomedical engineering 23 (1995), S. 346-358 
    Details
    ISSN: 1573-9686
    Keywords: Saccade ; Extraocular muscles ; Muscle crossbridge models ; Biomechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Several phenomenological models of the oculomotor mechanics that produce saccadic eye movements have been developed. These models have been based on measurements of macroscopic muscle and orbital tissue properties and measurements of eye kinematics during saccades. We recorded the forces generated by the medial and lateral recti during saccades in an alert, behaving monkey using chronically implanted force transducers. With this new data, we tested the ability of the classic saccade models to generate realistic muscle force profiles. Errors in the predictions of the classic saccade models led to a reexamination of the current models of extraocular muscle. Both a phenomenological, Hill-type muscle model and an approximation to Huxley's molecular level muscle model based on the crossbridge mechanism of contraction (distribution moment model) were derived and studied for monkey extraocular muscle. Simulations of the distribution moment model led to insights suggesting (i) specific modifications in the lumped force/velocity relationship in the Hill-type model that resulted in this type of phenomenological model being able to generate realistic dynamics in extraocular muscle during saccades; (ii) the distribution of activity in the different fiber types in extraocular muscle may be central to the characteristics exhibited by the muscle during saccades; (iii) the transient properties of lengthening muscle such as yielding are not significant during saccades; and (iv) the series elastic component in active muscle may be predominantly generated by the elastic properties of the cross-bridges.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00000003
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  • 9
    Electronic Resource
    Electronic Resource
    A Unified Method for Calculating the Center of Pressure during Wheelchair Propulsion (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 328-336 
    Details
    ISSN: 1573-9686
    Keywords: Kinematics ; Kinetics ; Rehabilitation ; Biomechanics ; Generalized center of pressure ; Center of pressure ; Wheelchair propulsion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The measurement of the center of pressure (COP) has been and continues to be a successful tool for gait analysis. The definition of a similar COP for wheelchair propulsion, however, is not straightforward. Previously, a COP definition similar to that used in force plate analysis had been proposed. Unfortunately, this solution has the disadvantage of requiring a separate COP definition for each plane of analysis. A definition of the generalized center of pressure (GCOP) which is consistent in all planes of analysis is derived here. This definition is based on the placement of a force-moment system, equivalent to the force-moment system at the hub, on a line in space where the moment vector (wrench moment) is parallel to the force vector. The parallel force-moment system is then intersected with three planes defined by anatomical landmarks on the hand. Data were collected using eight subjects at propulsion speeds of 1.34 m/s and 2.24 m/s (1.34 m/s only for subject 1, 0.894 m/s and 1.79 m/s for subject 8). Each subject propelled a wheelchair instrumented with a SMARTWheel. A PEAK 5 video system was used to determine the position of anatomical markers attached to each subject’s upper extremity. The GCOP in the transverse plane of the wrist formed clusters for all subject’s except subject 2 at 1.34 m/s. The clustering of the GCOP indicates that the line of action for the force applied by the hand is approximately perpendicular to the transverse plane through the wrist. When comparing the magnitude of the moment vector part of the wrench with the moment of the force vector of the wrench about the hub, the wrench moment is approximately an order of magnitude smaller. This indicates that the role of the wrist for wheelchair propulsion is primarily to stabilize the force applied by the arm and shoulder. © 1998 Biomedical Engineering Society. PAC98: 8745Dr, 8710+e
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.80
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  • 10
    Electronic Resource
    Electronic Resource
    Estimation of Tendon Moment Arms from Three-Dimensional Magnetic Resonance Images (1999)
    Springer
    Annals of biomedical engineering 27 (1999), S. 247-256 
    Details
    ISSN: 1573-9686
    Keywords: Medical imaging ; Magnetic resonance imaging ; Biomechanics ; Tendon moment arm ; Functional neuromuscular stimulation ; Tendon transfer surgery ; Hand biomechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract New three-dimensional (3D) magnetic resonance imaging (MRI) methods for measuring the tendon moment arm were created and were evaluated on the tendon moment arm of the flexor digitorum profundus at the third metacarpophalangeal joint. Using an open magnet MRI system and a hand holder, a series of static images were acquired at four joint angles and analyzed using specially created computer programs. Three methods were evaluated: (1) a 3D tendon excursion method that extended the method of Landsmeer; (2) a 3D geometric method whereby the moment arm was the perpendicular distance between the joint axis of rotation and the tendon path, and (3) a two-dimensional (2D) geometric method whereby single image slices were analyzed. Repeating the imaging and measurement processes, the 3D tendon excursion method was more reproducible (6% variation) than the 3D geometric method (12%), and both were much more reproducible than the 2D geometric method (27%). By having three operators analyze a single set of image data, we found that the precision of the 3D tendon excursion method was much less affected by segmentation error than the 3D geometric method. With the 3D imaging methods, tendon bowstringing and a displacement of the joint center of rotation toward the dorsal side of the hand were evident, leading to as much as a 60% increase in moment arm with joint flexion. Because of the dependence on flexion and variation between subjects, we recommend patient-specific measurements for target applications in functional neuromuscular stimulation interventions and tendon transfer surgery. © 1999 Biomedical Engineering Society. PAC99: 8761Pk, 8719Rr, 0705Pj
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.180
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