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Biomedical subjects

C M Epstein

Publications and source records attributed to C M Epstein.

At least 55 records · Page 3Linked to original sources
PubMed1991

Effect of head extension on equilibrium in normal subjects.

A dynamic posturography system was used to test the effect of 55 degrees head extension on postural sway in 20 normal subjects. There was a highly significant increase in sway with head extension under two conditions; in both, the support surface moves proportionally to body sway angle (sway-referenced feedback). The largest increase in sway occurred when the eyes were closed and the support surface was sway-referenced. This latter condition removes vision, reduces the effectiveness of ankle proprioception, and forces the subject to depend mostly on vestibular information for equilibrium. We suggest that head extension increases sway because the utricular otoliths are put into a disadvantageous position. This may be another example of the role of utricular input in the control of balance.

Adult↗
PubMed1991

Cervical magnetic stimulation: the role of the neural foramen.

Magnetic stimulation of cervical nerve roots is a promising new technique, limited in part by uncertainty about the site of nerve depolarization. We used a modified "butterfly" stimulus coil with an easily defined excitation field to activate the C-8/T-1 nerve roots, recording over abductor digiti minimi. Locating both the lowest threshold for stimulation and the points of maximum stimulation, we determined the optimum rostral-caudal position and orientation for the stimulus coil over the posterior neck and upper trunk. The most favorable positions corresponded to the C-8/T-1 neural foramina, and the most favorable orientations to the roots within them. Additional measurements of depth and electric field suggested that the stimuli used should have been insufficient to activate nervous tissue in a homogeneous medium. A simple model indicates that the induced current is intensified where it passes through a bony foramen and explains preferential excitation of the nerve root at this site.

Electrophysiology↗
PubMed1991

Enhancement of posturography testing with head tilt and energy measurements.

We have attempted to increase the sensitivity of dynamic posturography testing by adding head extension and sway energy measurement to the standard Equitest protocol. Both procedures were applied to 121 patients and to 89 normal subjects. A portion of the standard protocol was repeated with the patient's head extended 55 degrees. Head extension significantly increases the number of "falls" or losses of balance experienced by normal subjects 50 years or older. Using the formula, Energy = Force x Distance, and appropriate corrections for platform tilt and body weight, any previously recorded test can be analyzed with computer programming to give energy values in joules per kilogram. Adding the two criteria of head extension and sway energy to the standard protocol increased the percentage of patients classified as abnormal from 48 to 68 percent. The two added criteria are useful in separating symptomatic from asymptomatic subjects and patients.

Adult↗
PubMed1990

Localizing the site of magnetic brain stimulation in humans.

Magnetic stimulation of the human brain is performed in clinical and research settings, but the site of activation has not been clearly localized in humans or other species. We used a set of magnetic stimulus coils with different field profiles to isolate movement of single digits at motor threshold and to calculate corresponding electric field strengths at various distances beneath the scalp. Two coils could produce the same electric field intensity at only 1 point. Thus, we could estimate the depth of stimulation by finding the intersection of the electric field plots, which were then superimposed on MRIs of the underlying brain. In each of 3 subjects the field plots intersected at the crown of a gyrus, in the region of the central sulcus, an near the level of the gray-white junction. This position and the electric field orientation support localization to layer VI of cerebral cortex.

Adult↗
PubMed1989

EEG mean frequencies are sensitive indices of phenylalanine effects on normal brain.

We previously reported that changes in plasma phenylalanine (PHE) concentrations of 1000 microM or more adversely affected cognitive function and reduced mean frequency of the EEG power spectrum. In the present study, we characterized EEG effects of changes in plasma PHE from physiological to supraphysiological concentrations. Subjects were mentally normal children and adult volunteers with 3 different genotypes for phenylalanine hydroxylase (PHY): homozygous deficient, heterozygous, and homozygous normal. Double-blinded crossover studies were performed at equilibrium during PHE restriction and supplementation. The mean frequency of the power spectrum and the mean across a set of alpha-theta factors showed highly significant, reversible, generalized EEG slowing during PHE supplementation in subjects homozygous for PHY deficiency. Smaller but significant changes in EEG mean frequencies occurred in the heterozygous and normal subjects. Spectral profiles of EEG change were similar in both groups; the mean alpha-theta was more sensitive in the second group. Demonstration of EEG changes with PHE supplementation in normal individuals has important dietary implications.

Adult↗
PubMed1988

Familial mitochondrial encephalomyopathy (MERRF): genetic, pathophysiological, and biochemical characterization of a mitochondrial DNA disease.

A large MERRF pedigree permitted the direct testing of the predictions for a mitochondrial DNA (mtDNA) mutation. A mtDNA mutation was demonstrated by proving maternal inheritance and by identifying specific deficiencies in muscle energetics and mitochondrial respiratory complexes I and IV. mtDNA heteroplasmy (a mixture of mutant and wild-type mtDNAs) was demonstrated by showing variation in the mitochondrial energetic capacity between family members. The phenotypic consequences of differential tissue-specific reliance on mitochondrial ATP was shown by correlating individual respiratory deficiency with the nature and severity of patients' clinical manifestations. The observed spectrum of clinical manifestations resulting from this heteroplasmic mtDNA mutation implies that mtDNA disease may be much more prevalent than previously anticipated.

Calorimetry, Indirect↗
PubMed1988

Principles of signal analysis and averaging.

Averaging is the primary method for detecting small evoked potentials in the midst of surrounding electrical noise. Not all types of noise can be removed by averaging, however. The condition of the patient, electrodes, amplifiers, and filters are equally important for successful recording.

Amplifiers, Electronic↗
PubMed1988

The use of brain stem auditory evoked potentials in the evaluation of the central nervous system.

Brain stem auditory evoked potentials (BAEPs) are sensitive to anatomic disturbances of the brain stem auditory pathways, especially those caused by disruption of myelin. They are influenced by temperature but are virtually unaffected by level of consciousness, drugs, and metabolic disequilibrium. These properties make BAEPs useful in evaluating many posterior fossa disorders.

Acoustic Stimulation↗
PubMed1985

Maternally inherited mitochondrial myopathy and myoclonic epilepsy.

A family is described with familial myoclonic epilepsy associated with mitochondrial myopathy. The disorder follows a maternal inheritance pattern consistent with a mitochondrial DNA (mtDNA) mutation. The large kindred permitted exclusion of autosomal dominant, recessive, and X-linked patterns of transmission. Several characteristics of the inheritance and variability of expression within the pedigree are consistent with recently acquired knowledge about the genetics of human mtDNA. The clinical spectrum of disease is compatible with a proportionality model of mutant and wild-type mtDNAs. Muscle biopsies of affected patients showed an increased number of abnormal muscle mitochondria. Serum levels of pyruvate or pyruvate and lactate were elevated. The most severely affected patient had constant myoclonic jerking, dementia, ataxia, spasticity, hearing loss, and hypoventilation. Cerebral dysfunction in patients with mild involvement was marked by prominent photic driving seen on electroencephalograms and high-amplitude visual and somatosensory evoked responses but no myoclonus, ataxia, or dementia. The individual clinical features of the disease worsen over time for all patients; however, mildly affected patients have not become moderately affected and moderately affected patients have not become severely affected.

Adult↗
PubMed1985

Interelectrode distance and amplitude of the scalp EEG.

The relationship between interelectrode distance and amplitude of the scalp EEG was investigated quantitatively, using differential recording arrays extending anteriorly from Oz and coronally from T3. Amplitude was taken as the square root of the power spectrum. For total signal amplitude and for individual frequency bands, measured data correspond well to an exponential function of the form Y = A(1 - e-BX). The inverse of the exponential coefficient B may be taken as a space constant, and the asymptote A as an estimate of absolute EEG amplitude. The concept of the space constant is consistent with current models of neuronal synchrony in the scalp EEG. The coefficients A and B may be useful indices in EEG analysis.

Adult↗
PubMed1985

Sequential quantitative EEG analysis in acute lymphocytic leukemia of children.

Potential brain toxicity is a major concern in the treatment of acute lymphocytic leukemia with cranial irradiation or intrathecal methotrexate. We used quantitative EEG analysis based on the Fourier transform to study 13 children at the time of diagnosis, after induction, and following consolidation which included extended intrathecal chemotherapy. None had detectable CNS infiltration by leukemia. Nonetheless, initial EEG frequencies were markedly depressed compared to expected values for age (p less than .001), and improved dramatically after induction (p less than .001). Following consolidation, EEG frequencies remained significantly lower than predicted from a control population (p less than .05). Quantitative EEG is a sensitive procedure that appears useful in assessing subtle neurologic effects of acute leukemia and its treatment.

Adolescent↗
PubMed1985

Histamine H2 antagonists and the nervous system.

In extensive clinical trials, both cimetidine and ranitidine appeared free of central nervous system side effects. The potential for neurologic complications became apparent only after these drugs had been subjected to the test of general use. The incidence of side effects is generally low, but in the elderly and in patients with renal or hepatic failure, both of these drugs can produce confusional states. Ranitidine may also cause severe headache.

Central Nervous System Diseases↗
PubMed1984

Quantitative EEG alterations after isovolemic-hemodilutional augmentation of cerebral perfusion in stroke patients.

Eleven patients with ischemic neurologic deficits in the middle cerebral arterial (MCA) territory and ipsilateral slowing on initial EEG underwent venesection and equal volume replacement with intravenous 5% human serum albumin. As the mean hematocrit was reduced by 19%, the mean cerebral blood flow (CBF) in the MCA territory of the affected and contralateral hemisphere determined by the 133Xenon inhalation technique increased 18 and 21%, respectively. Similarly, CBF in the contralateral occipital region increased 17%. The percentage total slow-wave EEG activity (fractional sum of theta and delta activity, 1.0 to 7.5 Hz) determined by fourier analysis was reduced significantly in the affected MCA territory and in the contralateral occipital region within 1 to 2 hours after isovolemic hemodilution. Using quantitative EEG analysis, rapid improvement in background EEG activity can be demonstrated following the diffuse elevation in CBF by hemodilution.

Brain↗
PubMed1984

EEG frequency analysis in metrizamide radiography.

Computerized frequency analysis was used to quantitate the EEG effects of intrathecal metrizamide in 22 patients undergoing radiographic procedures. In comparison to baseline recordings, no changes were found immediately after the procedure, but a significant (p less than 0.001) shift to lower frequencies was seen at 16 to 26 hours. Individually significant changes were infrequent with lumbar myelograms or low-dose cisternograms and were most prominent in patients who had the combination of high metrizamide dose, cervical level, and a complex procedure with prolonged supine positioning.

Brain Diseases↗
PubMed1984

Absence of seizures during induction of anesthesia with high-dose fentanyl.

Anesthesia was induced in six patients scheduled for elective aortocoronary bypass (ACB) surgery with intravenous fentanyl, either 50 (n = 2) or 150 micrograms/kg (n = 4) over 20 or 60 sec, respectively. Patients had been given their usual antianginal medications before surgery and were premedicated with morphine sulfate. Arterial plasma fentanyl levels were measured repetitively at frequent intervals, and eight leads of the cortical electroencephalogram (EEG) were recorded continuously. Peak plasma fentanyl concentrations exceeded 1750 ng/ml at the end of the injection of 150 micrograms/kg and then decreased by more than 75% within 3 min. In an additional two patients, incremental doses of fentanyl (25, 25, 50, 50 micrograms/kg; total 150 micrograms/Kg) maintained fentanyl concentrations between 30 and 650 ng/ml for the entire 15 min of the study. In all cases, diffuse slow-wave EEG activity, characteristic of fentanyl anesthesia, was seen. Motor activity, including wrist flexion and ocular movements, was observed during the onset of fentanyl-induced truncal rigidity, but no seizure-like activity was found in the EEG.

Aged↗