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Biomedical subjects

S Satya-Murti

Publications and source records attributed to S Satya-Murti.

33 records · Page 2Linked to original sources
PubMed1980

Brainstem auditory evoked potentials: a comparison of two high-frequency filter settings.

Filter bandpass characteristics are important elements in all modalities of evoked potential recordings. We studied the brainstem auditory evoked potentials by changing the bandpass of the recording system between 150 to 1500 Hz and 150 to 3000 Hz. The 150- to 1500-Hz bandpass prolonged the absolute latencies of the various waves, whereas the interpeak latencies (I to III, IIII to V, III to IV/V, I to V, or I to IV/V) were not significantly altered. The 150- to 1500-Hz filter reduced notched or multipeaked wave forms by decreasing the raw high-frequency input activity.

Adult↗
PubMed1979

Abnormal auditory evoked potentials in hereditary motor-sensory neuropathy.

From a kinship with a dominantly inherited motor-sensory neuropathy, we studied 2 brothers with brainstem auditory evoked potentials and behavioral audiometric tests. They had abnormal prolongation of I-III interpeak intervals. Wave V was poorly developed. Conventional audiometric tests did not reveal a peripheral hearing loss. It is probable that their auditory nerves and spiral ganglia are undergoing a pathophysiological process analogous to that of their peripheral nerves.

Adolescent↗
PubMed1979

Isaacs syndrome with laryngeal involvement: an unusual presentation of myokymia.

A woman with widespread myokymia presented initially at age 19 with hoarseness and mild dyspnea on exertion. The diagnosis of Isaacs syndrome was suggested by the clinical findings of widespread continuous muscle activity and depressed tendon reflexes, although she lacked the usually prominent increased muscle tone. The diagnosis was confirmed by the electromyographic demonstration of continuous spontaneous muscle action potentials that were abolished by neuromuscular blockade but not by local nerve blockade. Pulmonary function tests were consistent with fixed extrathoracic obstruction. The vocal cords were closely approximated. Electromyographic studies of the laryngeal muscles under general anesthesia revealed continuous muscle activity, which accounted for the hoarseness and much of the exertional dyspnea. The patient responded well to treatment with phenytoin and carbamazepine. This unusual syndrome should be considered in the differential diagnosis of patients with respiratory complaints and muscle fasciculations, even though they have normal muscle tone.

Action Potentials↗
PubMed1978

Benign cerebellar hemorrhages.

Two patients with cerebellar hemorrhage and a benign outcome stress the potential for spontaneous resolution and clinical recovery in some cases of this disorder. In each patient, resolution of the hemorrhage was noted on the computed tomographic scan. Computed tomography may detect a cerebellar hemorrhage even though on clinical grounds a brainstem localization is favored.

Aged↗
PubMed1977

The declining electrical response of muscle to repetitive nerve stimulation in myotonia.

The electrical response of muscle to repetitive nerve stimulation was studied in patients with various myotonic disorders. A decrementing response was common but not invariable finding, and was unrelated to the severity or diagnosis. The decrement either continued throughout the period of stimulation or "leveled off", sometimes being followed by an increment. If it occurred at low rates of stimulation, a greater decrement occurred at higher rates, usually after a shorter latent period. It was not related consistently to the presence of weakness, but in patients with myotonia congenita it was more conspicuous and elicited by lower rates of stimulation when transient weakness was a feature of the history.

Adolescent↗
PubMed1976

Hypothenar Dimpling. A peripheral equivalent of Hemifacial Spasm?

In two patients, the skin over both hypothenar eminences underwent intermittent, spontaneous, irregular, dimpling contractions. The dimpling was benign, and was the result of spontaneous discharge of motor units in the palmaris brevis muscle. Electrophysiological investigations localized the site of origin of the discharge to the ulnar nerve, possibly at the wrist, but there was no clinical or physiological evidence of neuropathy or of nerve compression. In many respects, the clinical and electrophysiological features of hypothenar dimpling resemble hemifacial spasm.

Aged↗
PubMedDate not supplied

Critical reexamination of the thymus immunization model of myasthenia gravis.

Previous studies have described an experimental model of myasthenia gravis (MG) produced by immunizing animals with thymus extracts. In view of the hypothesis that the autoimmune process in MG may be initiated within the thymus itself, we have reexamined this model using presently available methods to evaluate its resemblance to MG. We immunized Lewis rats with extracts of rat thymus in Freund's adjuvant, as originally described by G. Goldstein. Five procedures were used to test for myasthenic characteristics: (1) repetitive nerve stimulation; (2) recording of miniature endplate potentials; (3) assays of anti-ACh receptor antibodies in serum; (4) determination of ACh receptors at neuromuscular junctions by [125I] alpha-bungarotoxin binding; and (5) evaluation of the histology of the thymus gland. Our results showed that the thymus-immunized animals did not demonstrate abnormalities in any of these parameters. We conclude that immunization of rats with thymus extracts, as described, failed to produce a myasthenia-like condition.

Animals↗
PubMedDate not supplied

Human middle-latency auditory evoked potentials: vertex and temporal components.

We recorded middle-latency (20-70 msec) auditory evoked potentials (MLAEPs) to monaural and binaural clicks in 30 normal adults (ages 20-49 years) at 32 scalp locations all referred to a balanced non-cephalic reference. Our goal was to define the MLAEP components that were present at comparable latencies and comparable locations across the subject population. Group and individual data were evaluated both as topographic maps and as MLAEPs at selected electrode locations. Three major components occurred between 20 and 70 msec, two well-known peaks centered at the vertex, and one previously undefined peak focused over the posterior temporal area. Pa is a 29 msec positive peak centered at the vertex and present with both monaural and binaural stimulation. Pb is a 53 msec positive peak also centered at the vertex but seen consistently only with binaural and right ear stimulation. TP41 is a 41 msec positive peak focused over both temporal areas. TP41 has not been identified in previous MLAEP studies that concentrated on central scalp locations and/or used active reference electrode sites such as ears or mastoids. Available topographic, intracranial, pharmacologic, and lesion studies indicate that Pa, Pb and TP41 are of neural origin. Whether Pa and/or Pb are produced in Heschl's gyrus, primary auditory cortex, remains unclear. TP41 is probably produced by auditory cortex on the posterior lateral surface of the temporal lobe. It should prove of considerable value in experimental and clinical evaluation of higher level auditory function in particular and of cortical function in general.

Adult↗
PubMedDate not supplied

Psychoacoustic and electrophysiologic effects of partial eighth nerve damage.

The authors present psychoacoustic and electrophysiologic data concerning a patient with partial damage to the auditory nerve, presumably from a dilated arterial vessel. The lesion was described and documented during neurosurgery for vestibular nerve decompression. Pure tone thresholds, psychoacoustical tuning curves, speech reception ability for spondaic words, maximum word recognition performance for monosyllabic NU-6 word lists, and performance on the synthetic sentence identification test in the ipsilateral and contralateral competing message modalities were normal. Findings consistent with eighth nerve dysfunction, absent contralateral acoustic reflexes, absent or unrecognizable early evoked potentials occurring in the first 10 msec, brainstem auditory evoked potentials (BAEPs), and slight rollover of the performance intensity function for monosyllabic words were obtained on the involved side. In spite of the grossly abnormal BAEPs, two late, presumably cortical, auditory evoked potential components, which occur in the 60 to 250-msec range--vertex potential and T complex--were present and normal. The findings indicate that the perceptual processes needed for speech reception and recognition and for the appearance of later, presumably cortical-evoked potentials can be preserved despite partial damage to the auditory nerve.

Adult↗