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Biomedical subjects

D Dumitru

Publications and source records attributed to D Dumitru.

At least 55 records · Page 3Linked to original sources
PubMed1992

The effect of different needle recording electrodes on somatosensory-evoked potentials and intertrial waveform variation.

This investigation examined the cortical somatosensory-evoked potentials (SEP) waveforms obtained from four sets of commercially available subdermal needle electrodes in 19 normal subjects. The composite materials of the four electrodes were stainless steel and a platinum/iridium alloy. Tibial nerve SEP peak latencies for P37 and N45 as well as P37/N45 amplitudes were recorded from each electrode pair in a random fashion. Using nonparametric analysis, no significant differences of waveform parameters were found between electrode pairs (P greater than 0.01). Correlation evaluation demonstrated values in excess of 0.92. Additionally, intertrial waveform analysis for each of the electrode pairs was performed. Again, nonparametric evaluation demonstrated no statistically significant waveform differences. Correlation coefficients were also highly correlative. Variable temperature response to prolonged tibial nerve stimulation was recorded that did not significantly effect the latencies or amplitudes of the cortical SEP responses. We conclude that within temperature ranges typically encountered in clinical practice, there is no statistically significant waveform differences recorded with commonly available subdermal needle electrodes. Additionally, although intertrial waveform variation may exist during SEP recordings, these differences do not reach statistically significant levels.

Adult↗
PubMed1992

Far-field potentials in muscle: a quantitative investigation.

Far-field potentials have been produced from muscle tissue and shown to arise from both the proximal and distal musculotendinous junctions after the activation of a small group of muscle fibers. This investigation demonstrated that the polarity of muscle far-field potentials is consistent with the predictions of the leading/trailing dipole model. Far-field potential polarity was dependent upon the active electrode's orientation with respect to the positive or negative aspect of the trailing dipole after extinction of the leading dipole at the musculotendinous junction. This study also quantitatively measured the duration and magnitude of the two far-field potentials generated in the human biceps muscle by both proximal and distal muscle stimulation. The muscle far-field potential resulting from distal muscle stimulation closest to the musculotendinous junction was consistently shorter in mean duration (5.2msec +/- 2.1) but larger in mean amplitude (22.3 microV +/- 12.9) compared with the second far-field potential mean duration (10.4msec +/- 3.9) and amplitude (10.0 microV +/- 3.7). The mean areas under the curve for these far-field potentials, however, were comparable at 48.0msec microV and 48.7msec microV. Proximal muscle stimulation resulted in similar findings for the first far-field potential's mean duration, amplitude, and area (6.0msec; 19.7 microV; 50.6msec microV, respectively) in relation to those of the second far-field potential (12.5msec; 9.1 microV 49.1msec microV). The differences in amplitude and duration of the two far-field potentials, with similar areas, are consistent with, and can be adequately explained by, temporal dispersion effects of the muscle fiber action potentials' propagation over distance.

Action Potentials↗
PubMed1991

AAEM Minimonograph #10: volume conduction.

A volume conductor is any medium with the capability of passively conducting a current between regions of potential difference. The monophasic positive intracellular action potential produces a monophasic negative extracellular waveform and a triphasic extracellular waveform in a poor and good volume conductor, respectively. The observed waveform characteristics are dependent upon both the recording electrode montage and the type of volume conductor surrounding the excitable tissue. The extracellular current flow associated with an action potential can be divided into two current sources flanking a central current sink. If a recording electrode is located over the negative current sink, a negative potential is observed. When the two current sources approach a recording electrode, a positive potential is recorded. If a positive deflection of the baseline is observed, one may conclude that the wave of depolarization under investigation did not originate under, but traveled toward, the recording location. Electric currents from external sources are free to propagate extraneurally as the body is a good volume conductor. Care must be taken to not activate nearby nerves and, subsequently, obtain a waveform contaminated with potentials from undesired sources. Additionally, electrical activity from neighboring muscles and nerves can summate in the volume conductor and yield responses capable of masking pathology. An understanding of the principles of volume conduction theory can help the electrodiagnostician avoid artifactual errors and erroneous conclusions.

Electric Conductivity↗
PubMed1991

Somatosensory evoked potentials of the medial and lateral plantar and calcaneal nerves.

The ideal electrodiagnostic procedure to assess possible plantar neuropathies continues to elude investigators. Motor studies are rarely abnormal, pure sensory studies may be difficult to obtain, needle electromyography can demonstrate membrane instability in normal feet. Mixed nerve plantar studies may be more diagnostically valuable than the other techniques but they also have shortcomings. In this report, a technique utilizing somatosensory evoked potentials to assess the medial and lateral plantar and calcaneal nerves is demonstrated. Normative data with respect to latencies, amplitudes, and side-to-side differences are presented. Two illustrative cases are also discussed in which the more standard techniques to evaluate plantar neuropathies fail to do so, but the SEP methodology suggests compromise of the intrinsic foot nerves.

Adult↗
PubMed1991

Far-field potentials in muscle.

Far-field potentials have been predicted by computer simulations as well as demonstrated in both animals and humans with respect to the peripheral and central nervous systems. Computer simulations have also predicted far-field potentials originating at the termination of muscle tissue. This investigation demonstrates the occurrence of 2 far-field potentials in the human biceps muscle resulting from action potential termination at the musculotendonous junctions. A monophasic potential is produced at both the muscle's origin and insertion, and the polarity is entirely dependent upon the recording montage. Sequential stimulation of the biceps muscle at 2.5-cm increments resulted in the 2 far-field potentials and their respective latencies changing proportional to the distance between the stimulus site and the 2 musculotendonous junctions. Various stimulation and recording montages are used to investigate the properties of these far-field potentials. The leading/trailing dipole model is utilized to explain the production and polarity of far-field potentials generated by muscle tissue.

Action Potentials↗
PubMed1991

Needle and surface electrode somatosensory evoked potential normative data: a comparison.

Subdermal needle electrodes are now used routinely to record cortical somatosensory evoked potentials (SEPs). Investigators may make assumptions that: (1) SEP normative data obtained with surface electrodes can be used to interpret needle recordings, and (2) there is an increased potential for local dermal infection with needle electrodes. This investigation compared the waveform parameters obtained with surface and needle electrodes after stimulation of the tibial nerve, sural nerve, and L5 dermatome in 20 subjects. No statistically significant difference was found in the P latency, N latency, or P/N amplitude of the needle recordings as compared to the surface recordings. Additionally, 20 subjects studied for one week after four hours of needle insertion did not show any evidence of dermal infection. This study objectively documents no statistically significant difference between needle and surface SEP recordings and substantiates the use of surface normative data for needle SEP investigations.

Adult↗
PubMed1991

Electrophysiologic investigation of mandibular nerve injury.

Isolated lesions of the mandibular branch of the trigeminal nerve have only rarely been reported. We report the occurrence of an isolated lesion of the mandibular nerve associated with a unilateral mandibular fracture, and its substantiation electrophysiologically. A 65-year-old man was involved in a motor vehicle accident resulting in multiple fractures, including a unilateral mandibular fracture and temporomandibular joint dislocation. No evidence of intracranial pathology by CT scan was noted and the neurologic examination was nonfocal except for dysfunction of the mandibular nerve ipsilateral to the fracture site. Bilateral facial nerve latency and blink reflexes were normal. EMG evaluation of the muscles of facial expression and mastication demonstrated denervation confined to the muscles innervated by the mandibular branch of the trigeminal nerve. In patients complaining of facial sensory dysfunction, malocclusion, or weakness of muscles of mastication after mandibular fracture, an electrophysiologic examination can assist in evaluating cranial nerve integrity.

Aged↗
PubMed1990

Electrophysiologic investigation of thallium poisoning.

Electrophysiologic findings in thallium intoxication are usually untimely, limited in extent, and often uninformative. This report documents serial conduction and electromyographic findings in a case of thallium poisoning, beginning 10 days after symptom onset and ending 24 months later. Initially, the plantar nerves in the foot demonstrated profound axonal loss while the sural and peroneal nerves were essentially normal. The latter two nerves subsequently underwent axonal loss. Two years were required for the sural and peroneal nerves to display recovery. At 24 months, the plantar nerves continue to remain absent. A primarily distal axonopathy, significantly worse in the lower than upper extremities and requiring more than 2 years for recovery, now documents what was previously speculated: the electrophysiologic course of thallium intoxication. Additionally, this case emphasizes the need to examine the plantar nerves of the foot to avoid missing distal axonopathies during the early course of the disease process. The clinical course and pathophysiology of thallium poisoning are also reviewed.

Axons↗
PubMed1990

Inclusion body myositis. An electrophysiologic study.

Inclusion body myositis is a rare and slowly progressive myositis associated with cytoplasmic inclusions and fibrillar nuclear material. These histopathologic findings are of unknown significance. The clinical presentation of IBM has marked similarities to that of chronic polymyositis with proximal greater than distal weakness and muscle wasting more pronounced in the lower than upper extremities. In contrast to polymyositis, however, relatively few individuals report neck flexor weakness or dysphagia. Corticosteroid treatment is usually ineffective. The clinical, histopathologic and electrophysiologic findings in a patient with IBM are presented. Of particular interest in this report is the detailed motor unit recruitment frequency data. A number of previous IBM reports fail to mention specific electrophysiologic data or present evidence suggestive of a possible combined neuropathic and myopathic disease. Recruitment intervals of 150 ms or greater in combination with decreased motor unit duration and amplitudes in the involved muscles imply a myopathic pathophysiology. These findings are discussed in relation to electrophysiologic data from previously reported cases.

Electromyography↗
PubMed1990

Posterior femoral cutaneous nerve conduction.

The posterior femoral cutaneous nerve is a sensory nerve comprised of fibers originating from the anterior and posterior divisions of the first three sacral segments. It exists the pelvis distal to the piriformis muscle and proceeds distally, superficial to and between the medial and lateral hamstring musculature. The nerve's major cutaneous distribution is the posterior aspect of the thigh and a variable area of the posterior calf. An electrophysiologic technique to assess the peripheral axons of the posterior femoral cutaneous nerve is described. A recording electrode is placed 6cm proximal to the midpopliteal fossa and the nerve is stimulated supramaximally 12cm proximally on a line between the active electrode and the ischial tuberosity. A ground electrode is placed just proximal to the active recording electrode. The lower extremities of 40 individuals with a mean age of 34 years (20 to 78 years) were examined. The mean peak latency of the response is 2.8 (2.3 to 3.4) msec +/- 0.2msec with a mean amplitude of 6.5 (4.1 to 12.0) microV +/- 1.5 microV. This technique may facilitate the proximal evaluation of lower extremity peripheral neuropathies, lesions of the posterior femoral cutaneous nerve, or the assessment of the peripheral nervous system in persons with lower extremity amputations.

Action Potentials↗
PubMed1989

Prevalence of anabolic steroid use by male and female adolescents.

This study was performed to determine the prevalence of anabolic steroid use among male and female high school students. A total of 1,010 questionnaires were distributed in five high schools in a relatively affluent school district (Group I, 510 surveys with a 92.4% response rate) and five high schools in a relatively less affluent school district (Group II, 500 surveys with an 86.0% response rate). Three percent of all high school students reported using anabolic steroids: 5.0% of males and 1.4% of females. Among Group I students, 5.9% of all athletes reported using anabolic steroids, whereas only 1.5% of all Group II athletes admitted using them. A 10.2% usage of anabolic steroids among Group I male athletes was observed, but only 2.8% of Group II male athletes reported their use. The median age for anabolic steroid consumption was 17 yr. The primary source of anabolic steroids was the black market (85.2%), while physicians directly supplied anabolic steroids to only 7.4% of the adolescents. It appears that within the high school adolescent population, Group I male athletes are the primary consumers of these drugs, with a reported 10.2% prevalence.

Adolescent↗
PubMed1989

The premotor potential.

A small waveform precedes the compound muscle action potential evoked from the thenar eminence with median nerve stimulation with high amplifier gains. This potential is believed to emanate from fibers destined to innervate the volar aspect of the first digit. It has been suggested recently that the source of the premotor potential is the palmar cutaneous branch of the median nerve. In this study, the palmar cutaneous branch of the median nerve was blocked at the wrist. A localized zone of anesthesia was observed over the proximal midpalm, not the thenar eminence, and the premotor response remained unchanged as did a midpalmar potential. The median nerve was then blocked at the base of the thenar eminence; only then did the premotor potential disappear. The palmar cutaneous branch of the median nerve innervates only a small portion of the medial aspect of the thenar eminence and does not produce the thenar premotor potential. Additionally, because of the close proximity of the main median nerve to its palmar cutaneous branch, volume conduction of stimuli and responses precludes an electrophysiologic technique which exclusively localizes the palmar cutaneous branch of the median nerve.

Action Potentials↗
PubMed1989

Postpartum idiopathic brachial neuritis.

We present a case of a woman who developed bilateral idiopathic brachial neuritis in the postpartum period following normal pregnancy and delivery. The diagnosis was substantiated with extensive electrophysiologic testing. Shoulder girdle pain and muscular dysfunction resolved slowly, and 12 months later the patient complained only of minimal shoulder discomfort.

Adult↗
PubMed1988

Anabolic steroid use by athletes. How serious are the health hazards?

Use of anabolic steroids is widespread in the athletic community, especially among power athletes, who have used them for about 30 years. Despite educational and preventive measures, steroid use has increased. Controversy continues regarding the enhancement of athletic performance and the incidence of major side effects. Some investigators have suggested that the hazards of anabolic steroids may be overstated in the diseased population and are minimal or absent in healthy subjects. Yet, many questions are unanswered. Current data do not link life-threatening side effects with intermittent use of anabolic steroids. However, many concerns remain. Dangerous situations include use of anabolic steroids by adolescents, preadolescents, and persons with liver or heart disease and use of oral compounds in high doses for long periods. A coordinated team approach (with representatives from sports, medicine, advertising, and the pharmaceutical industry) is needed to determine the real risks of anabolic steroids to athletes who are considering their use.

Anabolic Agents↗
PubMed1988

Axilla to elbow radial nerve conduction.

Numerous techniques that evaluate radial nerve conduction from the axilla or supraclavicular fossa to the elbow have been reported. A shortcoming of most protocols is determining the precise radial nerve length as it proceeds along the spiral groove. The present study dissected out and measured directly eight cadaver radial nerves from the axilla to the elbow. These values were compared with a new surface tape measurement technique from axilla to elbow across the bicep muscle, obstetrical calipers over this region, and a surface determination approximating the course of the radial nerve posteriorly in the spiral groove. The anterior surface tape-measuring procedure compared most favorably with the actual anatomic length. Nerve conduction velocities were then calculated in 20 volunteers using all 3 techniques and compared with the median nerve in the arm. The anterior and posterior tape measurements yielded a conduction velocity of 72.5 +/- 4.7 and 86.6 +/- 7.0 m/s, respectively, whereas the caliper resulted in 65.7 +/- 3.9 m/s. We conclude that proximal radial nerve length assessment employing an anterior tape measurement from axilla to elbow across the bicep musculature is precise and compares favorably with the actual anatomic length of the radial nerve.

Adult↗
PubMed1988

Practical instrumentation and common sources of error.

A thorough comprehension of electrodiagnostic equipment is essential to consistently obtain accurate and reproducible data. Unreliable waveform latencies or morphologies may result from inappropriate filter settings, sensitivity comparisons, sweep speeds, interelectrode separation, cathode/anode reversals and stimulus artifact. A low frequency filter with too high a frequency limit may decrease amplitude, shorten peak latency, decrease the negative spike duration, add a phase and increase total waveform duration. A high frequency filter with too low a cut-off may decrease amplitude and prolong onset and peak latencies. Increasing the amplifier's sensitivity may shorten the onset latency of a response. Sweep speeds that are too slow may omit phases, turns or entire potentials when using digital equipment. If the interelectrode separation is inadequate, waveform morphology and amplitude can be altered. Reversing cathode and anode placement affects latency and velocity determinations. Stimulus artifact may obscure a response and its reduction must be understood. Comparing latencies and amplitudes at different instrument settings is never appropriate and can lead to serious errors and misdiagnoses. A naive approach to instrumentation, therefore, is indefensible.

Electrodiagnosis↗
PubMed1988

Electrophysiologic evaluation of the facial nerve in Bell's palsy. A review.

Facial nerve paralysis is the most common mononeuropathy and idiopathic facial paralysis (Bell's palsy) the most common seventh nerve disease electromyographers may be asked to evaluate. The electrophysiologic method of choice to assess the facial nerve is side-to-side evoked amplitude comparison with the affected side expressed as a percentage of the nonaffected side. This examination should be performed on days 3, 5, 7, 9, 11 and 13 after onset of paralysis. If the percentage of surviving axons falls below 10% within the first 14 days, an incomplete recovery is suggested. Electromyography may assist in prognosticating a functional return, determining neural conduction across the site of injury and following reinervation in the recovery period. The persistence or early return of an absent R1 component of the blink reflex may qualitatively suggest a satisfactory functional outcome in facial paralysis. Supramaximally exciting the facial nerve at the stylomastoid foramen and comparing the clinical response on the affected and nonaffected side, maximum stimulation test, can also predict eventual seventh nerve return. Observing a minimal twitch, utilizing the nerve excitability test or measuring the facial nerve latency have yielded poor correlations with functional return and are of limited usefulness in the prognostication of acute facial palsies. Trigeminal somatosensory evoked potentials can be employed to evaluate the status of the trigeminal nerve as approximately 50% of patients with Bell's palsy also have lesions involving the fifth nerve. Side-to-side amplitude comparison and electromyography are the two most valuable electrophysiologic methods of assessing facial nerve functioning.

Action Potentials↗