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Biomedical subjects

R W Shields

Publications and source records attributed to R W Shields.

At least 19 recordsLinked to original sources
PubMed2000

Strength training can improve steadiness in persons with essential tremor.

We evaluated the effect of a strength-training program on the ability of persons with essential tremor to exert steady forces with the index finger. Thirteen subjects with a diagnosis of essential tremor were assigned to three different groups: one group trained with heavy loads, one with light loads, and one did not perform any training. Subjects attempted to generate steady contractions during both postural and constant-force tasks. Steadiness was quantified by the root mean square amplitude of acceleration during postural tasks and the standard deviation and coefficient of variation of force during the constant-force tasks. Subjects who performed the training program with heavy loads experienced an increase in steadiness around the target force during the constant-force tasks. Subjects in the other two groups did not exhibit any changes. These findings suggest that strength training can decrease the magnitude of tremor. However, we did not observe any associated improvements in functional abilities.

Adult↗
PubMed1999

Vagal stimulation for reciprocal coupling between glottic and upper esophageal sphincter activities in the canine.

Glottic adduction couples with relaxation of the tonically contracted upper esophageal sphincter (UES) to constitute the end point of pharyngeal swallowing. Together with deglutitive laryngeal elevation, this reciprocal relationship contributes to protecting the lungs from aspiration. Degrees of uncoordination between glottic and upper esophageal sphincters can be seen under diverse circumstances of neurologic damage such as stroke, gastroesophageal reflux, and in the growing elderly population presenting with weaker musculature. We hypothesized that reciprocal coupling between glottic closure and UES relaxation may be artificially reestablished through vagal stimulation if the appropriate neural centers and their leading pathways remain capable of exciting a critical number of motor units. Orderly recruitment of the vagus nerve was produced in three dogs with a circuit superimposing 600-Hz, 3800-0-microA blocking over 10-70-Hz, 0-2300-microA stimulating currents. Amplitudes of motor unit or compound muscle action potentials were recorded from the thyroarytenoideus and cricopharyngeus via surface electromyographic electrodes. Stimulation was accompanied by a drop in UES intraluminal pressure. The reciprocal relationship between the two muscles could be time locked within certain stimulus parameters. We submit that electronic coupling between the glottic and UESs may show promise in preventing aspiration under selected circumstances.

Action Potentials↗
PubMed1997

Artificial control of glottic adduction for aspiration by orderly recruitment in the canine.

Laryngeal adduction for swallowing chiefly involves contraction of the thyroarytenoid and lateral cricoarytenoid muscles to seal the glottic chink. Vocal cord elongation supplements closure through cricoarytenoid activation. Relaxation of the posterior cricoarytenoid muscle is also involved in the swallowing process. Recent interest has focused on stimulating the laryngeal nerves to protect the lower airway from conditions where normal muscular coordination may be disrupted (e.g., in aspiration following stroke). Unfortunately, electrical stimulation results in a generalized contraction of all the dependent intrinsic laryngeal muscles because the larger, more excitable axons fire before their smaller counterparts can be activated. In the physiological state, however, the smaller fibers are recruited first. The current study focuses on electronic manipulation of force in the glottic muscles involved in deglutition. We used a stimulator that could selectively activate the intrinsic laryngeal muscles based on their specific motor unit architectures. In 5 dogs, the circuit recruited the axons in the recurrent and superior laryngeal nerves from small to large. The muscles were identified according to the differential recruitment rates of their compound muscle action potentials as they appeared on the graph. The smaller axons in the thyroarytenoid recruited faster than the large ones found in the lateral cricoarytenoid muscles, with intermediate figures observed with the cricothyroid. The posterior cricoarytenoid presented with the slowest recruitment rates, as expected from this muscle's highest contingent of larger motor units. Latencies between the onsets of stimulations and muscle saturations also appeared stable. This approach to manipulating glottic force saves energy because it allows stimulating the adductory muscles with minimal interference from their abductor antagonist.

Action Potentials↗
PubMed1996

American Association of Electrodiagnostic Medicine guidelines for outcome studies in electrodiagnostic medicine.

Based on a review of the literature and the clinical research experience of the authors and reviewers, the AAEM proposes 17 criteria which should be used to construct and evaluate diagnostic and/or therapeutic outcome studies for patients with symptoms and signs of neuromuscular diseases. Neuromuscular diseases are defined as diseases that cause pathology and/or dysfunction of the sensory, motor, and/or autonomic nerve offers and/or muscles.

Association↗
PubMed1996

Contraction patterns of intrinsic laryngeal muscles induced by orderly recruitment in the canine.

The specific performance of intrinsic laryngeal muscles has been difficult to evaluate, especially in living subjects. To reproduce natural contractions, we artificially induced orderly recruitment of their innervating axons according to the size principle. In 5 dogs, both recurrent laryngeal nerves (RLNs) were stimulated with 50 through 10 Hz, 300 to 1000 microA currents while 600 Hz, 1000 to 0 microA decreasing blocking currents were administered. Surface electromyography electrodes placed on the thyroarytenoid, posterior cricoarytenoid, and lateral cricoarytenoid muscles were used to determine the amplitudes (in mA) of compound muscle action potentials. There was a highly statistically significant difference (P<.004) between the thyroarytenoideus which had the fastest rate of recruitment (8.38%), and posterior cricoarytenoideus, which had the slowest (4.81%). There was an intermediate recruitment rate (6.72%) of the lateral cricoarytenoideus, a divergence attributed to a more equal distribution in fast and slow types of myofibers and a smaller sample. We submit that RLN axons can be recruited in an orderly manner according to their sizes and that the rates are unique to the muscle classes they innervate. The parameters defining these contraction patterns may offer key information for laryngeal pacing.

Animals↗
PubMed1993

Functional anatomy of the autonomic nervous system.

The autonomic nervous system (ANS) via its sympathetic and parasympathetic divisions influences the function of nearly all organ systems. Via autonomic reflexes, the ANS is responsible for maintaining homeostasis of the internal environment. This is achieved by a rather complex integration of autonomic sensory information, somatic sensory information, and descending influences from higher central nervous system centers.

Autonomic Nervous System↗
PubMed1991

Mononeuropathy in sickle cell anemia: anatomical and pathophysiological basis for its rarity.

Peripheral neuropathy is a rare complication of sickle cell disease. We report a young black woman with sickle cell anemia who developed a proximal median mononeuropathy in the setting of sickle cell crisis. The clinical and electrodiagnostic features are consistent with an ischemic mechanism from the sickling process. The pathophysiological basis for the rarity of this complication may be related to the rich anastomotic microvasculature of peripheral nerve and the unique large size of the capillaries of this vascular network.

Adult↗
PubMed1987

Vascular insufficiency in Okihiro's syndrome secondary to hypothenar hammer syndrome.

The presence of Okihiro's syndrome (congenital thenar hypoplasia and Duane's anomaly) in a patient became clinically significant when a hypothenar hammer syndrome developed. The ulnar artery occlusion resulted in a compromise of the hand's vascular supply because of a congenital hypoplastic radial artery. Resection of the thrombosed ulnar artery and insertion of an interposition vein graft restored circulation to the hand. Anatomic features in this case include a hypoplastic radial artery and double motor branch of the median nerve. Clinicians should consider Okihiro's syndrome in the differential diagnosis of thenar muscle atrophy since there are genetic, diagnostic, and clinical implications.

Adult↗
PubMed1987

The diagnosis and management of cerebral embolism and haemorrhagic infarction with sequential computerized cranial tomography.

Haemorrhagic infarction is typically not present immediately after cerebral embolism. Spontaneous haemorrhagic transformation evolves over several days. As a consequence, delayed CT scans are essential to exclude haemorrhagic infarction before initiating anticoagulant therapy. Sequential CT scanning can also help in the diagnosis of cerebral embolism in patients with stroke of unknown cause. In such cases the detection of haemorrhagic infarction on a delayed scan suggest an embolic mechanism. The evolution of haemorrhagic infarction on sequential CT scans graphically demonstrates the dynamic nature of this lesion and thereby indicates why serious brain haemorrhage may result from anticoagulation immediately after cerebral embolism.

Aged↗
PubMed1987

Single-fiber electromyography is a sensitive indicator of axonal degeneration in diabetes.

Axonal degeneration with reinnervation was assessed in diabetic subjects with single-fiber electromyography (SF-EMG). SF-EMG was performed on 18 control subjects, 20 diabetic control subjects without clinical or electromyographic evidence of polyneuropathy, and 30 diabetic subjects with clinical and electromyographic features of polyneuropathy. In the diabetic controls and diabetic neuropathy subjects, fiber density and jitter were increased indicating axonal degeneration with reinnervation. These findings confirm that axonal degeneration is a principal pathologic mechanism in diabetic polyneuropathy and that axonal degeneration commonly occurs in asymptomatic diabetic subjects. SF-EMG is thus a sensitive method for assessing axonal degeneration in diabetic subjects.

Adult↗
PubMed1986

Compartment syndromes and compression neuropathies in coma.

Eight patients are reported who developed peripheral nerve injuries due to limb compression during unattended coma. In each patient, the site of the peripheral nerve lesion or the unique combination of peripheral nerve lesions and swollen limbs, pressure blisters, or myoglobinuria indicated that compartment syndromes caused the nerve injury. The peripheral nerve injuries were characterized by severe axonal loss with persistent and often disabling sequelae.

Adult↗
PubMed1986

Median palmar digital neuropathy in a cheerleader.

Median palmar digital neuropathy developed in a 16-year-old girl as a result of chronic trauma to the palm during cheerleading activities. The clinical findings on examination, which included paresthesias in the distribution of a palmar digital nerve and exacerbation of symptoms with compression of the palm, were consistent with this diagnosis. Nerve conduction studies documented a lesion of the median palmar digital nerve. Avoidance of cheerleading activities resulted in nearly total resolution of the symptoms. Awareness of this entity and the value of nerve conduction studies in establishing the diagnosis may avoid confusion and facilitate correct diagnosis and management.

Adolescent↗
PubMed1984

Single fiber electromyography in the differential diagnosis of myopathic limb girdle syndromes and chronic spinal muscular atrophy.

Single fiber electromyography ( SFEMG ) of the extensor digitorum communis muscle was performed on 20 patients with either myopathic limb girdle syndromes ( LGS ) or chronic spinal muscular atrophy ( CSMA ) to assess its value in the differential diagnosis of these disorders. Neurologic examinations (muscle biopsies, standard electromyography, or both) were reviewed in 16 patients and resulted in diagnosing LGS in 11 patients and CSMA in 5 patients. In four patients, discordance between EMG and biopsy, or mixed features of myopathy and neuropathy in either test, resulted in an indeterminate diagnosis. Two groups were discerned from SFEMG , one with higher fiber density, jitter, and percentage of abnormal pairs consistent with neuropathy and another with lower values consistent with myopathy. In all 16 patients, SFEMG confirmed the initial diagnosis, and in the four patients with indeterminate diagnoses, SFEMG suggested diagnoses of LGS in two patients and CSMA in two patients. Single fiber electromyography may be a useful diagnostic aid in the differential diagnosis of myopathic LGS and CSMA .

Adolescent↗
PubMed1984

The effects of chronic muscular activity on age-related changes in single fiber electromyography.

Single fiber electromyography ( SFEMG ) of the extensor digitorum communis (EDC) muscle and nerve conduction studies were performed on healthy, active elderly men (66-77 years old) to assess age-related changes in neuromuscular physiology and the effect of long-term increased muscular activity on these changes. The following two groups were studied: a control group and a group composed of men with occupationally greater usage of hand extensors. Fiber density and mean jitter were essentially the same in both groups; however, in the hand-user group there was greater variability in mean jitter and a significant increase in the prevalence of potential pairs with increased jitter or blocking. In both groups, slower nerve conduction velocities and lower amplitudes of sensory and motor evoked potentials tended to correlate with increased jitter and fiber density. These electrophysiological changes in healthy aged men are consistent with an extremely mild process of nerve terminal denervation and reinnervation. Although long-term increased synaptic activity did not greatly alter the rate or extent of this process, it did produce a higher incidence of abnormal potential pairs and greater variability in mean jitter.

Aged↗
PubMedDate not supplied

Alcoholic polyneuropathy.

Alcoholic polyneuropathy is a common disorder, characterized by nonspecific clinical, electromyographic, and pathologic features. Nerve conduction studies and needle electromyography disclose findings consistent with a generalized, sensorimotor, axonal degenerative, polyneuropathy. Alcoholic polyneuropathy may be suspected when such findings occur in the setting of long-standing alcoholism and malnutrition. The lack of specific diagnostic criteria for alcoholic polyneuropathy requires that other potential etiologies be excluded before that diagnosis is made. The institution of a nutritionally-balanced diet constitutes the principal therapy for alcoholic polyneuropathy, however, significant improvement following such therapy is not frequently seen.

Alcoholism↗