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Biomedical subjects

A Sances

Publications and source records attributed to A Sances.

At least 19 recordsLinked to original sources
PubMed1992

Biomechanical properties of human lumbar spine ligaments.

Biomechanical properties of the six major lumbar spine ligaments were determined from 38 fresh human cadaveric subjects for direct incorporation into mathematical and finite element models. Anterior and posterior longitudinal ligaments, joint capsules, ligamentum flavum, interspinous, and supraspinous ligaments were evaluated. Using the results from in situ isolation tests, individual force-deflection responses from 132 samples were transformed with a normalization procedure into mean force-deflection properties to describe the nonlinear characteristics. Ligament responses based on the mechanical characteristics as well as anatomical considerations, were grouped into T12-L2, L2-L4, and L4-S1 levels maintaining individuality and nonlinearity. A total of 18 data curves are presented. Geometrical measurements of original length and cross-sectional area for these six major ligaments were determined using cryomicrotomy techniques. Derived parameters including failure stress and strain were computed using the strength and geometry information. These properties for the lumbar spinal ligaments which are based on identical definitions used in mechanical testing and geometrical assay will permit more realistic and consistent inputs for analytical models.

Adult↗
PubMed1991

Strength and kinematic response of dynamic cervical spine injuries.

This study was conducted to evaluate the biodynamic strength and localized kinematic response of the human cervical spine under axial loading applied to the head. Intact ligamentous fresh human cadaveric head-neck complexes were subjected to dynamic compressive forces with a custom-designed electrohydraulic testing device at varying rates. The structure included the effects of anterior and posterior cervical spine muscles with a system of pulleys, dead weights, and spring tension. Localized kinematic data were obtained from retroreflective targets placed on the bony landmarks of the specimen at every level of the spinal column. Input forces, accelerations, displacement, and output generalized force histories were recorded as a function of time with a digital data acquisition system at dynamic sampling rates in excess of 8,000 Hz. High-speed photography at 1,000-1,200 frames/sec also was used. Pathologic alterations to the head-neck complex were evaluated with conventional radiography, computed tomography, and cryomicrotomy. In all specimens, cervical spine injuries occurred as a result of impact. Compressive forces recorded at the distal end of the preparation indicated large-duration, short-magnitude pulses in contrast to short-duration, high-amplitude input waveforms at the head, suggesting decoupling characteristics of the head-neck system. Cervical vertebral body accelerations were consistently smaller than the accelerations recorded on the head. Kinematic data demonstrated temporal deformation characteristics as well as a plausible sequence of spinal deformations leading to injury, which were correlated with the pathoanatomic alterations documented with the post-test computed tomographic and sequential cryomicrotome sections.

Acceleration↗
PubMed1991

Strength and motion analysis of the human head-neck complex.

This study was conducted to correlate the pathology of the experimentally tested human cervical spine with biomechanical strength information and localized temporal movements of the various spinal components. Eight fresh human cadaveric head-neck complexes were subjected to compressive forces at a quasistatic rate of 2.5 mm/s until failure. Biomechanical force and deflection data were collected. Localized kinematic data as a function of time were obtained from retroreflective targets placed in the anterior and posterior regions of the vertebral body, facet column, and spinous process at every level of the cervical spine. The specimens were radiographed prior to, during, and following failure; they were then deep frozen at the level of failure to preserve the localized tissue deformations. Specimens underwent computed tomography scanning and sequential sectioning using a cryomicrotome. The failure forces and compressions ranged from 1.3 to 3.6 kN and 0.9 to 3.7 cm. Stiffness and energy-absorbing characteristics ranged from 96.1 to 220.5 kN/m and 12.2 to 53.6 J, respectively. Varying localized temporal motions among spinal components were found to exist at all levels of the head-neck complex. With increasing compressive loads, the specimen components reorient as demonstrated by kinematic changes in the spinal elements; failure was imminent when the structure no longer resisted any further increase in external load. The study demonstrated that an evaluation of the human head-neck complex in a relaxed state, as in clinical observations on posttraumatic radiographs, is often different from that documented immediately following the traumatic insult; this underscores the importance of conducting controlled in vitro investigations to determine the injury biomechanics of the human cervical spine.

Aged↗
PubMed1979

Spinal cord evaluation by cortical evoked responses.

In ten monkeys, selective segmental lesions of the dorsal columns at the upper thoracic and middle cervical levels resulted in almost total attenuation of the cortical evoked potential responses to peripheral nerve stimulation. Conversely isolated segmental dorsal column preservation showed intact transmission of the evoked responses at rostral spinal cord, nucleus ventralis posterior lateralis, and cortical levels. Responses recorded from the intralaminar thalamic nuclei in the region of nucleus centrum medianum were unaffected by dorsal column ablation, but were markedly attenuated following bilateral ventral column ablation.

Animals↗
PubMed1978

Early somatosensory evoked potentials.

The early somatosensory evoked potential secondary to median nerve stimulation in the human had an onset latency of 9--12 msec when recorded from scalp electrodes at vertex-to-mastoid, vertex-to-inion or at the base of the skull. Similar latencies were observed from responses recorded over the cervical dorsal columns during neurologic surgery. A latency difference of 1.5 msec was observed between the early response and the responses recorded from the junction of medial lemniscus and nucleus ventralis posterior lateralis of the thalamus during human stereotaxic surgery. Cervical cord transections and transection at the midpontine levels of the monkey showed that the evoked potential was due to generators between these levels. Depth recording of the monkey indicate that the early evoked potential originates in the region of dorsal column nuclei, while the later components are secondary to generators in cerebral cortex.

Animals↗
PubMed1978

Spinal evoked potentials in the primate: neural substrate.

Summated responses evoked by peripheral nerve stimulation were recorded from electrodes located in the epidural and subdural spaces anterior and posterior to the monkey spinal cord. Segmental microsurgical resection of the dorsal columns both at the thoracic and cervical levels resulted in total obliteration of the response recorded rostral to these lesions. Isolated segmental dorsal column preservation did not significantly alter response latency or wave form recorded at the rostral electrodes. Bilateral cervical dorsolateral column resection also resulted in no discernible alterations of these responses. These data indicate that spinal evoked potentials recorded from levels rostral to their root entry zones arise almost exclusively from the dorsal columns.

Animals↗
PubMed1977

The effect of cerebellar stimulation on focal seizure activity and spasticity in monkeys.

Experiments were carried out in awake, unmedicated monkeys to determine the effect of application of current to the cerebellar hemispheres on electrically induced focal motor seizures and surgically induced spasticity. Application of current at various frequencies and pulse amplitudes did not significantly alter focal motor seizures but did significantly reduce spasticity. Analysis of evoked potential recordings carried out during various experimental procedures suggests that application of current to the cerebellar hemispheres may reduce cortical neuronal responsiveness.

Animals↗
PubMed1976

Quantification of computer analyzed serial EEGs from stroke patients.

While considerable studies have been conducted by others in automation of the EEG, this method does appear to hold promise for quantitative evaluation and automation of the EEG in the CVA patients or those with similar neurologic deficits. Patients were followed up to 1 year post-ictus. The computerized evaluation of serial records in the CVA patients showed trends which were similar to the percent disability of the patients who were graded neurologically. The patients included in the study were those with middle cerebral artery, carotid and vertebro-basilar defects. A substantial increase in the low frequency activity with a concomitant decrease in high frequency activity was observed in the CVA patients. The results observed in these patient examples demonstrate the utility and efficacy of one method of automated analysis of serial EEGs. The parameters defined by this study have proven to be consistent and effective measures. Since these parameters are objective, they are not affected by patient histories and hence, can be utilized to track the ongoing EEG activity and the accompanying clinical state regardless of the disease entity or the course of therapy pursued. The addition of automated objective quantitative measures to EEG analysis provides a dimension not currently available to the clinician.

Aged↗