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Biomedical subjects

S J Larson

Publications and source records attributed to S J Larson.

At least 55 records · Page 3Linked to original sources
PubMed1984

Electrophysiological effects of lumbar dorsal root stimulation.

Electrical stimulation was applied to the L-5 and L-6 dorsal root ganglia of 14 monkeys with concurrent monitoring of cortical and intralaminar thalamic evoked potentials. Both responses were decreased by root stimulation, although cortical suppression required current levels 50 to 100% higher. The evoked potentials remained suppressed for periods of up to 60 minutes after 10- to 15-minute stimulation of the lumbar root electrodes. There was no increase in the duration of transmission block with longer stimulation periods. These results and available clinical data suggest that a local conduction block may be responsible for the pain relief produced by peripheral electrical stimulation. Further studies to identify more precisely the neural systems affected are required.

Afferent Pathways↗
PubMed1984

Influence of stimulus location and limb position on motor responses in the comatose patient.

Motor responses to standardized stimuli were evaluated in 18 comatose patients with abnormal motor reactions. Painful stimuli were applied to three areas: the supraorbital, sternal, and medial aspects of the arm. Stimulations were carried out with the upper limbs first flexed and then extended. The initial position of the arm significantly influenced the posturing pattern. With the arm initially flexed there was a significantly higher percentage of abnormal flexor reactions, and the opposite occurred with the arm initially extended. Supraorbital stimulation yielded a significantly higher number of extensor responses. Arm stimulation, instead, caused a higher percentage of abnormal flexor reactions. When painful stimulation was applied to an arm initially flexed, the percentage of extensor responses was extremely low. Conversely, supraorbital stimulation with the arms extended yielded the highest percentage of extensor responses. The study shows that, within the frame of abnormal motor responses, the same patient can exhibit different reactions according to the site of stimulation and initial position of the upper extremities. These patterns are fairly constant and should be borne in mind in the evaluation of comatose patients.

Adult↗
PubMed1984

The biomechanics of spinal injuries.

This manuscript is directed to review the epidemiology of spinal trauma, the anatomy of the vertebral column, spinal ligaments, muscles, motion of the spine and spinal cord. Because little information is available on the material properties of ligaments and the components of the vertebral column, this material is also included. A review of the experimental spinal cord injury models is given because of the concerted interest in this area today. Laboratory studies conducted in animals to develop typical spinal cord injury models and the corresponding alterations in perfusion and metabolic pathways, forces, and changes in the evoked potentials are discussed. Light and electron microscopy evaluations of the spinal cord are also treated. Clinical classifications of spinal injuries, pathology, and typical examples of upper cervical injuries, atlanto-axial disc locations and fractures, lower cervical spine injuries, injuries to thoracolumbar column with mathematical models, and typical force levels are given. The final section, investigation examples, provides a review of typical spinal injuries associated with sports injuries, motorcycle helmets, industrial helmets, and swimming pools investigated in our laboratories and by those of others. With lumped parameter mathematical model which predicts cervical compression, force, the various energies encountered in a one-dimensional impact is given. Typical examples of studies conducted on football helmets, motorcycle helmets, and industrial helmets are also included. Because of the importance of crash dummies used in the analysis of spinal injuries, a separate appendix is included, as well as an appendix reviewing motorcycle standards which are often dispersed throughout the literature. Considerable emphasis is placed upon actual experimental values of force and energy measured in the living animal and the most recent studies conducted in the fresh human cadaver to delineate the biomechanical mechanisms of spinal injury.

Accidents, Traffic↗
PubMed1983

Compression injuries of the cervical spine: a biomechanical analysis.

Three intact cadavers and 10 isolated cervical spinal columns underwent compression, with forces directed vertically, forward, or rearward. Failure modes were often different than force directions. The loads required to produce bony injury or ligamentous disruption ranged from 645 to 7439 N. Flexion and extension injuries were produced at approximately 50% of the loads required for axial compression failures. The direction of force delivery correlated only partially with the resulting pathological condition. Clinical decisions based on retrospective analysis of roentgenograms may not account for the variability of forces and the prominence of ligament injuries seen in spinal trauma. Some of the difficulties encountered in biomechanical analyses of spinal trauma are discussed.

Accidents, Traffic↗
PubMed1983

Distraction rod stabilization in the treatment of metastatic carcinoma.

Stabilization of the spinal column with Harrington distraction rods and acrylic fusion was the primary form of treatment in a select group of patients with metastatic carcinoma of the spinal column. Clinical criteria included patients in poor general medical condition with intractable pain originating from metastatic tumor involvement in the ventral components of the thoracic or upper lumbar spinal column and minimal evidence or absence of spinal cord compression. After stabilization, pain relief was almost total and sustained, and neurological status generally remained unchanged from preoperative findings without any evidence of improvement of preexisting abnormalities or occasions of rapid neurological deterioration. This form of spinal stabilization may offer significant relief of debilitating pain, lessen the risk of pathological fracture-dislocation of the thoracic or upper lumbar vertebral column, and reduction in the local compressive effects on the spinal cord caused by ventrally situated metastatic tumor.

Aged↗
PubMed1983

Somatosensory evoked potentials in lumbar stenosis.

The present findings suggest that, in patients with similar symptoms and findings, both physical and roentgenographic, the radiculopathy in those whose evoked potentials became abnormal after walking or change in posture had a mechanical cause. Consequently, operation designed to correct a mechanical problem was associated with a better result than in those patients in whom the evoked potentials were unaffected by these maneuvers. The recording of somatosensory evoked potentials is a noninvasive, painless, safe and relatively inexpensive procedure which appears to be a useful adjunct in the diagnosis and treatment of patients with lumbar stenosis and may help differentiate neurogenic from vascular claudication when these conditions cannot be clearly distinguished clinically.

Evoked Potentials, Somatosensory↗
PubMed1982

Cerebello-pallido-thalamic connections in man.

The brains of 5 patients who died at varying intervals following stereotactic pallidotomy or thalamotomy were examined using the Marchi stain for degenerating myelin. In 2 patients, the lesion was directed at the globus pallidus; in 2 the target was nucleus ventralis lateralis, and in 1 the target was n. ventralis posterior medialis. The observations indicated that the globus pallidus is reciprocally connected with n. ventralis lateralis, while the cerebellum is reciprocally connected with n. ventralis intermedius. Degenerating fibers from the medial lemniscus end within n. ventralis posterior, none reaching n. ventralis intermedius. On the basis of cytoarchitecture and subcortical connections, n. ventralis lateralis, n. ventralis intermedius, and n. ventralis posterior appear as distinct entities. However, each nucleus projects to both sensory and motor cortex, suggesting a functional unity.

Afferent Pathways↗
PubMed1982

Effects of vertebral column distraction in the monkey.

Experiments were performed to assess the effects of vertebral column distraction on evoked potential responses from multiple recording sites along the conducting pathway in the monkey, and on concurrent blood flows, measured with the radioactive microsphere technique, along the axis of the central nervous system. Linear distractive loads were applied until the amplitude of the evoked response was significantly reduced. In four monkeys, the loads (100 to 150 lb) were sustained, whereas in two monkeys the forces (80 to 110 lb) were relaxed. The earliest response changes were most marked in recordings dependent upon the integrity of the upper cervical dorsal columns or brain stem-lemniscal pathway. The responses returned to control levels with load relaxation, but maintenance of the tractive load produced generalized and progressive response attenuation. At selected periods of significant changes in the evoked potential response, blood flow remained stable except for the late onset of regional ischemia in the middle cervical through upper thoracic spinal cord levels in the animals undergoing sustained loads. These findings indicate that brain-stem or spinal cord dysfunction occurring with both acute and gradual elongation of the spinal canal are the result of excess tensile stress acting on fiber tracts, and the delayed onset of spinal cord ischemia is the probable result of a similar mechanical process acting upon intrinsic spinal cord blood vessels.

Animals↗
PubMed1982

Management of odontoid fractures.

Fifty-one adults with odontoid fractures were treated between 1966 and 1979. Approximately 50% had additional trauma; over half of the patients were younger than 40 years old. Three patients presented with myelopathy: 1 was complete at C-2 and the others recovered. Cervical roentgenograms were initially considered normal in 4 patients. The fracture was through the base of the odontoid process (Type 2) in 49 patients and was into the body of C-2 (Type 3) in 2 patients. Thirty-four patients underwent early posterior cervical fusion, whereas the others were treated initially with external immobilization. Only the 2 patients with Type 3 fractures healed in Minerva casts. All 15 Type 2 fractures initially treated conservatively failed to heal and were fused. There were no age, sex, or radiological characteristics (other than fracture location) peculiar to the nonunion group. Two patients died after operation, and there was 1 minor infection in an iliac crest donor site. All patients who were operated upon demonstrated evidence of fusion within 6 weeks after operation; 16 demonstrated healing of the fracture at 6 months. After follow-up ranging from 16 months to 15 years, 7 patients complain of neck pain, of whom 6 do not require regular analgesics. Of 40 patients tested, 7 have evidence of decreased range of motion in the neck, of whom 6 have loss of less than 15% of normal motion. Traction followed by posterior cervical fusion is effective treatment for Type 2 odontoid fractures. The surgical and long term morbidity is low, and satisfactory fusion can be expected.

Adolescent↗
PubMed1981

Experimental electrical injury studies.

Voltages from 10 to 14,000 volts demonstrated currents up to 70 amperes with resistances of approximately 200 ohms in studies in hogs. Below 1,000 volts, a current reduction is observed following arcing and skin necrosis. At the higher voltages, this phenomenon was not observed. The energy required for tissue damage was dependent upon the voltage and time of application. The tissue electrode resistance with stainless steel disc was proportional to the diameter. Skin buring commenced at the periphery of the electrodes and moved inwards. For application of currents between the hindlimbs of the hog, the current per tissue cross-section was greatest in artery and nerve, followed by muscle, fat, bone marrow, and bone cortex.

Animals↗