Biomedical subjects

D Dumitru

Publications and source records attributed to D Dumitru.

At least 19 recordsLinked to original sources

PubMed2001

Digit distribution of proper digital nerve action potential.

Antidromic sensory nerve action potential testing is well characterized and commonly used to assess the sensory component of the upper limb median and ulnar nerves. The final terminal segments of these nerves are the proper digital nerves. Ring recording electrodes are commonly used to detect the proper digital nerves' antidromic responses. Attempts to record the separate contributions of individual digital nerves along the lateral aspects of each finger, using small surface electrodes, is shown to be unreliable for determining the integrity of a single terminal digital branch. We found between 50% to 77% of the stimulated terminal branch's response amplitude when recorded at electrodes positioned over the nonstimulated branch located 180 degrees from the activated terminal branch. Detecting a single terminal nerve response was achieved by using the fourth digit and the second digit with one of the second digit's branches neurophysiologically blocked by local anesthetic. The volume-conducted response from the opposite side of the finger resulted in this relatively large recorded response, which remains within the range of reference values precluding the simple use of antidromic techniques to assess injury to a single proper digital nerve. Techniques are proposed to avoid such pitfalls and to assess most accurately the desired response.

Action Potentials↗

PubMed2001

Prevalence of denervation in paraspinal and foot intrinsic musculature.

OBJECTIVE: The primary purpose of this investigation was to determine the prevalence of abnormal spontaneous activity (positive sharp waves (PSWs) and fibrillation potentials (FPs)) in selected lumbosacral paraspinal and foot intrinsic muscles in an asymptomatic healthy population. DESIGN: This was a prospective assessment of 50 individuals without history or physical findings suggestive of peripheral neuromuscular disease whereby a monopolar needle electrode was located in the unilateral L4 and L5 paraspinal as well as abductor hallucis and extensor digitorum brevis muscles. These muscles were extensively evaluated for the presence of PSWs, FPs, and fasciculation potentials. RESULTS: Ten subjects per decade from 20-59 yr and ten subjects from 60-80 yr comprised the 50 participants (28 women), resulting in a mean age of 45+/-15.9 (range, 20-76) yr. A single individual (prevalence, 2%) demonstrated fibrillation potentials in the extensor digitorum brevis, and FPs and PSWs were detected in two subjects' (4% prevalence) L4/L5 paraspinal muscles. Ninety-four percent of the subjects had fasciculation potentials in the abductor hallucis, whereas 60% had these waveforms in the extensor digitorum brevis. Only 6% of subjects had fasciculation potentials in the L4 but not L5 paraspinal muscles. All subjects demonstrated both prototypical and "atypical" appearing endplate spikes in all of the muscles examined. CONCLUSIONS: We failed to confirm the previously reported prevalence of FPs and PSWs in both the paraspinal and foot intrinsic musculature. Atypical appearing endplate spikes, however, display configurations similar to FPs and PSWs and were present in all subjects. Failure to pay close attention to the discharge rate and rhythm of endplate spikes can lead to misinterpreting these waveforms as FPs and PSWs. It is likely that the previously reported high prevalence of spontaneous activity in healthy persons resulted from not fully appreciating the similarity between innervated and denervated spontaneous single muscle fiber discharge configurations.

Action Potentials↗

PubMed2001

Isolated sural neuropathy presenting as lateral ankle pain.

A case of job-related, unilateral traumatic sural neuropathy causing severe lateral ankle pain and impaired work performance for a 26-yr-old female grocery clerk is reported. This diagnosis is made both clinically and electrophysiologically. We review the pertinent electrophysiologic features, anatomy, and clinical findings in our patient with an isolated sural neuropathy. A review of the literature demonstrates that trauma is the most common cause of this unusual isolated neuropathy. Despite its rare occurrence, it should be considered in patients who present with lateral ankle pain and concomitant loss of sensation in the sural nerve distribution. The establishment of a neuropathic origin assists with management strategies that will differ from the more common musculoskeletal causes of lateral ankle pain. After an appropriate diagnosis and treatment, an excellent outcome resulted for our patient.

Accidents, Occupational↗

PubMed2001

Carpal tunnel syndrome and the Riche-Cannieu anastomosis: electrophysiologic findings.

Two cases of carpal tunnel syndrome with Riche-Cannieu anomalies are reported. Despite complete absence of a median nerve evoked compound muscle action potential from the thenar eminence, these patients had significant preservation of function and minimal muscle atrophy. Activation of the ulnar nerve at both the wrist and elbow generated easily obtainable compound muscle action potentials from the thenar eminence with initial negative onset. This observed preservation of function and electrophysiologic responses are best explained by the presence of a Riche-Cannieu anastomosis innervating the thenar eminence through branches from ulnar nerve. To our knowledge there has not been a report of similar cases in patients with profound carpal tunnel syndrome and a Riche-Cannieu anomaly. We review the clinical findings, the electrodiagnostic data, and the impact of a Riche-Cannieu anastomosis on advanced carpal tunnel syndrome.

Adult↗

PubMed2000

Reply.

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Journal Article↗

PubMed2000

Hybrid fibrillation potentials and positive sharp waves.

Fibrillation potential configurations are characterized as initially positive triphasic waveforms, whereas positive sharp waves appear biphasic with an initial positive deflection. Careful observation of single muscle fiber discharges in denervated muscle, however, can reveal many different-appearing and stable firing waveforms that resemble a bifid positive sharp wave or some form of combined fibrillation potential and positive sharp wave. In this investigation, a number of atypical-appearing single muscle fiber discharges are hypothesized to arise from particular interactions between the muscle fiber and recording electrode. Single muscle fiber potentials are modeled as originating from a single denervated muscle fiber's former endplate and midfiber region as well as from the fiber's tendinous termination for both a compressed and sealed end effect. The modeled waveforms' appearance corresponds well to those obtained clinically and the necessary interpotential summated templates' temporal domains are feasible for action potential termination at the electrode with subsequent reinitiation beyond the proposed peri-electrode compressed region. It is hypothesized that the majority of hybrid waveforms are the result of a single muscle fiber action potential terminating at a recording electrode while also initiating a "skipped" activation of the muscle fiber past the electrode resulting in the summation of two distinct time-locked waveforms.

Action Potentials↗

PubMed2000

Physiologic basis of potentials recorded in electromyography.

The extracellularly recorded configuration of a single muscle fiber discharge is generally appreciated to be triphasic with an initially positive deflection. However, careful attention to waveform appearance during the electrodiagnostic medicine examination reveals that both innervated and denervated muscle waveforms may display a pantheon of configurations. Further, despite the fact that innervated and denervated single muscle fiber discharges arise from distinctly different intracellular action potential (IAP) configurations, their extracellularly recorded waveforms can appear quite similar, leading to potential misidentification and, hence, the possibility of an erroneous diagnostic conclusion. The least appreciated, but nevertheless critical, aspect of explanations for muscle waveform configurations is the relationship between the muscle fiber and recording electrode. Additionally, it is important to appreciate both the near-field and far-field aspects of single fiber and compound muscle action potentials. In this review, the leading/trailing dipole model is used to explain muscle waveform configurations in both innervated and denervated tissues.

Electromyography↗

PubMed2000

Configuration of normal and abnormal non-volitional single muscle fiber discharges.

OBJECTIVE: This investigation utilizes a single muscle fiber simulation to compare and contrast single muscle fiber waveform configurations arising from innervated and denervated tissue taking into account possible tissue-electrode interactions. METHODS: Intracellular action potentials (IAPs) from innervated and denervated muscle tissue are simulated. The extracellular waveform configurations as recorded from the fiber's midpoint (endplate in innervated tissue), halfway between the midpoint and fiber termination, as well as fiber termination for both innervated and denervated single muscle fibers are examined. Further, two types of muscle fiber terminations are assessed: (1) sealed end effect; and (2) compressed end effect. RESULTS: Irrespective of different types of IAPs, recordings from the fibers' middle, halfway between the midpoint and termination, as well as from the sealed end, revealed similar configurations. However, for the innervated fiber's compressed termination, a monophasic positive waveform was derived while the denervated fiber's compressed termination generated a prototypical positive sharp wave. CONCLUSIONS: It is hypothesized that the needle electrode can no longer be considered a passive recording device but may interact with the fiber so as to generate a sealed end or compressed end effect. Depending upon the type of needle-fiber interaction and the electrode's location with respect to the IAP's generation site, a limited number of potentials with specific configurations will be recorded for both innervated and denervated tissue. Further, depending upon the type of needle-tissue interaction, innervated muscle fibers can generate non-volitional waveforms with configurations similar to those recorded from denervated tissue. It is no longer sufficient to merely consider waveform configuration when attempting to define positive sharp waves and fibrillation potentials, but it is important now also to consider firing rate and rhythm.

Action Potentials↗

PubMed1999

Positive sharp wave and fibrillation potential modeling.

A finite muscle fiber simulation program which calculates the extracellular potential for any given intracellular action potential (IAP) was used to model a fibrillation potential and a positive sharp wave. This computer model employs the core conductor model assumptions for an active muscle fiber and allows two distinct types of end effects: a cut or a crush. A "cut end" is defined as a membrane segment with the termination of both active and passive ion channels. The "crush end" is simulated as a focal membrane segment which blocks action potential propagation, and is connected to a region of normal membrane on either side of it so that a normal transmembrane potential is maintained beyond the crush zone. A prototypical positive sharp wave of appropriate amplitude and duration could only be detected extracellularly by using an IAP of the configuration found in denervated rat muscle recorded from a muscle fiber terminating in a crush segment of membrane.

Action Potentials↗

PubMed1999

Motor unit action potential components and physiologic duration.

Motor unit action potentials (MUAPs) recorded from the same motor unit at two distances along the biceps brachii muscle with monopolar needle electrodes at high amplifier gains (20 microV/division) and averaged 2000-3000 times reveal total potential durations of 39.6 +/- 4.6 ms. In addition, the terminal segment for each of these two MUAPs contained a late far-field potential with a mean duration of 23.8 +/- 4.1 ms. Computer simulations of MUAPs suggest that this long-duration positive far-field mirrors the true morphology of the intracellular action potential (IAP), which is monophasic positive, possessing a terminal repolarization phase approaching 30 ms. This investigation suggests that the MUAP's physiologic duration is directly proportional to the muscle fiber length and the IAP's duration, which becomes manifest as a positive far-field potential when the IAP encounters the musculotendinous junction and slowly dissipates. The leading/trailing dipole model is used to explain qualitatively this study's quantitative clinical and computer simulation findings.

Action Potentials↗

PubMed1999

Motor unit action potential duration and muscle length.

Motor unit action potential (MUAP) components are investigated by means of single fiber computer simulations and clinical measurements. The single fiber simulations have essentially full bandwidth without noise, whereas the clinical measurements were made with a 3-10,000-Hz bandwidth utilizing approximately 1000 averages to reduce noise optimally. These parameters allow the recording of a MUAP's complete "physiologic" duration including its very slow onset and termination. The simulation results demonstrate a constant waveform onset regardless of the electrode's recording location along the fiber. A far-field potential is initiated when the action potential encounters the muscle fiber's termination. The simulated waveform's and clinically recorded MUAP's near-field component extends between the potential's onset and its corresponding far-field potential's onset. This near-field component's duration should vary with fiber length, and this prediction is clinically confirmed by measuring three different muscle lengths. The far-field potential reveals a constant duration, independent of fiber length, and appears to be associated with the muscle fiber's intracellular action potential duration. A more complete understanding of the components contributing to MUAP duration should provide a more fundamental basis for quantitative clinical MUAP duration measurements.

Action Potentials↗

PubMed1999

Intracellular contribution to extracellularly recorded waveforms: the 'membrane rent' hypothesis.

OBJECTIVE: This investigation uses simulation studies to account for single muscle fiber waveforms with complex configurations as arising from the simultaneous recording of a partial intracellular discharge and its associated extracellular manifestation by way of an electrode-induced 'rent' or tear in the sarcolemma. METHODS: Published material on intracellular action potentials from healthy and 7 day denervated rat skeletal muscle was used as the basis for calculations. A single muscle fiber computer simulation capable of formulating a cut or crush termination effect used the modeled action potentials to generate extracellular waveforms at different locations along the muscle fiber. These extracellular waveforms were then summated with a varied fraction of the intracellular action potential to yield a combined potential. These simulated waveforms were then compared to previously recorded single muscle fiber discharges in order to establish if a combined waveform could reproduce the clinically recorded potentials' configuration. RESULTS: It was not possible to simulate any of the previously detected innervated single muscle fiber discharges by combining the action potential's intracellular and extracellular configurations. However, 12 of the 14 clinically observed complex waveforms documented in denervated tissue could be simulated with morphologies similar to the clinical potentials. CONCLUSIONS: Presumed single muscle fiber discharges with complex configurations may result from the needle electrode simultaneously recording the action potential's intracellular and extracellular waveforms secondary to a 'rent' in the sarcolemma. This explanation may in part account for some of the complex appearing potentials detected in denervated tissue, but this 'rent' hypothesis is likely not the explanation for potentials observed in innervated muscle tissue. The apparent success of the 'rent' hypothesis in denervated tissue may be a result of the denervated action potential's unique morphology rather than an actual tear in the sarcolemma. Further investigations are necessary to determine if it is possible for a needle electromyographic electrode to actually record in part the intracellular action potential without disrupting the fiber.

Action Potentials↗

PubMed1999

Determinants of motor unit action potential duration.

OBJECTIVE: Motor unit action potential (MUAP) recordings are modeled by means of a single muscle fiber simulation program, to define two key subcomponents comprising the complete physiologic MUAP duration. A number of defining properties of these subcomponents are further developed. METHODS: A single muscle fiber simulation program is utilized with various muscle fiber lengths and conduction velocities to generate near-field and far-field waveforms. RESULTS: Two key subcomponents to the total physiologic single muscle fiber and hence MUAP duration are identified. One, defined as the near-field component, is directly dependent upon muscle fiber hemi-length. The other, defined as the far-field component, is independent of fiber length, but matches the internal action potential in duration. Both the near-field and far-field components are inversely dependent upon intracellular action potential conduction velocity. Additionally, temporal dispersion among the individual fibers contributing to a MUAP must be included in the overall MUAP duration calculation. CONCLUSIONS: It is hoped that this approach to MUAP duration may allow a more complete appreciation of the components contributing to the MUAP, than permitted by the empirically derived values for MUAP duration presently under clinical use.

Action Potentials↗

PubMed1998

Normal needle electromyographic insertional activity morphology: a clinical and simulation study.

Needle electromyographic insertional activity waveform morphology, and mechanisms of generation, have received little attention. This study analyzes the individual component waveforms that contribute to the burst of electrical activity known as insertional activity. One hundred monopolar needle insertions were slowly performed and high speed recorded to allow better separation of the contributing individual component waveforms. Analysis of the many waveforms recorded demonstrates several classes of potentials. All of these could be reconstructed by the summation of two basic or elementary waveform patterns: a biphasic initially negative spike with or without a "prepotential" similar to an end-plate spike, and the biphasic initially positive spike with a slowly declining negative phase, similar to a positive sharp wave, though shorter in duration. The relationship between these elementary waveforms and their hypothesized generator sources is discussed.

Action Potentials↗

PubMed1998

Single muscle fiber discharge transformations: fibrillation potential to positive sharp wave.

It is presently believed that a fibrillation potential (FP) can transform into a positive sharp wave (PSW) by displaying a number of individual transitional potentials with a high degree of morphological variation between different sets of independent transformations. Clinically obtained examples of FP-to-PSW transformations and a myotonic discharge transformation are simulated by a finite fiber computer model. The simulations demonstrate that the two clinical FP-to-PSW examples may well be the result of two independent muscle fibers synchronously firing for a short period of time such that their separate waveforms summate at the electrode to create a false impression of one potential changing into another through a specific series of transitional waveforms. The transition characterized by the myotonic discharge is substantiated through modeling to define the most reasonable transitional series of waveform morphologies for a single muscle fiber. The combination of clinical examples, histological needle electrode muscle penetration studies, and simulations of single muscle fiber discharge transitions support the hypothesis that a needle recording electrode is capable of inducing a variable degree of mechanical compression with a commensurate amount of action potential blockade. The degree of action potential blockade directly contributes to the clinically observed configuration for the single muscle fiber discharge in both innervated and denervated tissues.

Animals↗

PubMed1998

Endplate spike morphology: a clinical and simulation study.

OBJECTIVE: To describe the various morphologic appearances of endplate spikes, define the theoretical volume conduction basis of these waveforms' morphologies, and simulate "atypical" endplate spike waveforms documented by other investigators. DESIGN: Endplate spikes were recorded from the biceps brachii in healthy individuals using a monopolar needle electrode. The morphologies of these waveforms were compared with those obtained from a computer simulation. Previously documented endplate waveforms were simulated using two fundamental types of biphasic initially negative and positive waveform morphologies. SETTING: University clinic outpatient electrodiagnostic medicine facility. SUBJECTS: Five subjects without history or physical evidence of neuromuscular disease. MAIN OUTCOME MEASURES: Endplate potential morphologies were assessed with respect to overall waveform shape and number of phases. Computer-generated waveforms for individual endplate spike waveforms were qualitatively compared with those recorded from the subjects. RESULTS: Three fundamental waveforms were documented to arise from the endplate regions of all subjects and were successfully simulated: (1) biphasic initially negative potential from the endplate itself and up to 0.2mm from the endplate, (2) triphasic initially positive potential from within 0.2mm of the endplate up to 0.5mm from the musculotendinous junction, and (3) biphasic initially positive potential from the last 0.4mm of the fiber or from impulse blocking. Two biphasic endplate spike waveforms could be summated to generate all other endplate waveforms described in previously documented literature. CONCLUSION: The combination of clinical and simulation studies suggests that endplate spike potentials can have quite varied morphologies. Triphasic initially positive and biphasic initially positive endplate spikes may be mistaken for fibrillation potentials and positive sharp waves, respectively. The triphasic waveforms most likely arise from an action potential propagating past the recording electrode adjacent to the endplate, while the biphasic initially positive potential is simulated to arise from the needle electrode blocking action potential propagation.

Action Potentials↗

PubMed1998

Concentric needle recording characteristics related to depth of tissue penetration.

This study investigates the influence of tissue penetration depth as it relates to a concentric needle electrode, particularly delineating regions where the cannula potential predominates over the core potential. The regions of cannula predominance is studied by means of a standard and 20 times enlarged physical model of an electromyographic concentric needle electrode in a homogeneous volume conductor by delineating the zero isopotential which partitions where the core potential predominates versus where the cannula potential predominates. Clinical studies in muscle tissue are used to test and confirm results from the enlarged physical model. At shallow electrode insertions equivalent to 4 mm, the concentric needle model records a net negative potential, which is a region where the cannula predominates, from a distant positive dipole at the same depth compared with a net positive potential for penetration depths exceeding 4 mm. The clinical portion of this study verifies the bipolar nature of the concentric needle electrode in detecting motor unit action potentials (MUAPs) with primarily an initial positive onset irrespective of recording depth. Refinements to the conceptualization of the nature and detection of MUAPs are discussed which are consistent with all the findings of the clinical and model study.

Adult↗

PubMed1997

Concentric needle electrode duration measurement and uptake area.

Motor unit action potentials (MUAPs) were recorded with a standard concentric needle electrode inserted into the right biceps brachii muscle with different angular orientations of the beveled recording surface to the muscle fibers. Contrary to the predictions from computer simulations, the MUAP duration remained constant during needle rotation. This finding is used to reexamine the previous assumptions regarding the concentric needle's spatial uptake recording territory and the implications with respect to MUAP duration measurements.

Action Potentials↗