Biomedical subjects

D Dumitru

Publications and source records attributed to D Dumitru.

At least 19 recordsLinked to original sources

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

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↗

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↗

PubMed1997

Comparison of single-fiber and macro electrode recordings: relationship to motor unit action potential duration.

The factors contributing to the duration of a motor unit action potential (MUAP) are believed to be well known, with both manual measurements and computer simulations agreeing with respect to MUAP durations approaching 10 ms. In this investigation, it is clearly demonstrated that use of a wide-open amplifier bandpass combined with signal-to-noise ratio enhancement results in MUAP durations approaching 30 ms recorded with either a macro or single-fiber electrode. Why the clinically recorded MUAP duration differs significantly from these physiologic durations is discussed. A hypothesis is presented whereby the major contributing factor toward MUAP duration is the total time of action potential transmembrane current flow along the muscle fiber from end-plate zone to musculotendinous junction.

Action Potentials↗

PubMed1997

Concentric and single fiber electrode spatial recording characteristics.

A better appreciation of the specific spatial recording characteristics of the single fiber and concentric needle electrode can result in more accurate physiologic and theoretical interpretations of single fiber and quantitative motor unit action potential analysis. We demonstrate by physical modeling that the 90% and 99% amplitude sensitivity envelopes are not simple hemispherical shapes. The 90% sensitivity concentric electrode volume does not extend beyond the insulated portion of the 15 degree beveled surface between the core and cannula and extends only 280 microm perpendicularly from the center of the core's surface. The 99% envelope extends approximately 830 microm perpendicularly from the core's center. This is a much smaller volume of sensitivity than exists for a similarly modeled monopolar electrode. The 90% and 99% envelopes extend to 110 and 320 microm perpendicularly from the exposed single fiber core. Both the single fiber and concentric needle volumes of sensitivity have specific asymmetries described.

Animals↗

PubMed1997

Motor unit action potentials recorded with concentric electrodes: physiologic implications.

Computer simulations of concentric needle electrode recording characteristics assume a hemisphere spatial recording territory for the electrode's core with the cannula shielding electrical activity arising from those muscle fibers located behind the cannula with respect to the electrode's core. It is also believed that the motor unit action potential's (MUAP) duration is generated by the number of muscle fibers within the electrode's hemispherical recording territory. This presumption suggests that rotating the needle will necessarily alter the number of muscle fibers within the hemispherical recording territory and hence lead to an alteration in MUAP duration. Comparisons were performed for different needle orientations with documentation of no statistically significant alteration in MUAP duration. Additionally, referential recording montages with the concentric needle electrode revealed that the electrode's core records MUAPs with durations comparable to those detected by the cannula. These findings strongly suggest that the recording territory of the concentric needle electrode, with respect to MUAP duration, is not a hemisphere but a sphere encompassing most if not all of the MUAP's muscle fibers in a manner similar to that of a monopolar needle. These findings have significant implications regarding presently used MUAP simulation techniques and require a reconceptualization of how the concentric needle electrode records electrical activity within a volume conductor.

Action Potentials↗

PubMed1997

Concentric/monopolar needle electrode modeling: spatial recording territory and physiologic implications.

Scaled 20:1 physical models of monopolar and standard concentric needle electrodes are investigated with a constant current bipolar generator to determine the amplitude versus radial distance characteristics of these two electrodes. Each model is examined at three scaled and simulated tissue penetration depths (4, 10 and 20 mm) with measurements documented from 20 to 9000 microns radially in front and behind the models. The monopolar compared to concentric electrode has a smaller response to a standardized stimuli but a flatter response curve at distances of less than 1500 microns. The cannula of the concentric needle also has a flatter response than that of its core. When compared to a remote reference such as that at scaled depths of tissue penetration approximating 4 mm or less the cannula-to-remote reference potential exceeds the amplitude of the core-to-remote reference, recording a net negative potential at 6500 microns in front and 3500 microns behind the core. This study offers an explanation for the clinically observed larger magnitude potentials detected with monopolar compared to concentric electrodes resulting from a larger recording cross-sectional area with more fibers contributing to the potential even though the magnitude of potential at any one location is comparatively smaller in magnitude than that for the concentric electrode. Additionally, the physiologic duration of a motor unit is anticipated to be considerably longer than presently measured clinically with automated methods because of the electrodes' ability to detect such small signals from a large region of the volume conductor.

Action Potentials↗

PubMed1997

Near- and far-fields: source characteristics and the conducting medium in neurophysiology.

It is possible to appreciate the production of far-field potentials by considering constant current dipolar source voltage distributions in bounded volumes, especially when they are stretched in one direction, e.g., a cylinder. An essentially nondeclining voltage is detected when the recording electrodes are on opposite sides of, and relatively far from, the dipolar source. This voltage maintains its (a) latency, (b) amplitude, (c) morphology, and (d) polarity even if recordings are performed a whole body length away. These four criteria define far-field potentials. A propagating action potential (AP) can be conceptualized as a linear quadrupole or the summation of two dipoles "back-to-back" (+ - - +). The far-field components of the summated dipoles cancel resulting in the anticipated triphasic waveform for APs with only near-field characteristics, not meeting the first three criteria above. Far-field potentials can be transiently generated when any propagating AP constitutes a net "real" or "virtual" dipolar source. "Real" dipolar sources can occur if an AP encounters the termination of excitable tissue, an alteration in conduction velocity, curvature in excitable tissue resulting in a change in propagation direction, or an abrupt change in resistance of the excitable tissue. Virtual dipolar sources may be produced if an AP encounters a change in the size or shape of the extracellular medium or a transition in extracellular conductivity.

Action Potentials↗

PubMed1996

Single muscle fiber discharges (insertional activity, end-plate potentials, positive sharp waves, and fibrillation potentials): a unifying proposal.

The exact origin and precise morphologic explanation of positive sharp waves (PSWs) are presently lacking. Observing normal needle electromyographic insertional activity reveals two types of waveforms: (1) biphasic negative/positive spikes, and (2) positive spikes followed by a small negative phase. In the end-plate region, it is possible to occasionally observe a biphasic end-plate spike transform into a monophasic positive end-plate waveform. It is postulated that this waveform is simply a form of intracellular recording for the biphasic end-plate spike or a form of extracellularly recorded but blocked single muscle fiber discharge. Similarly, the observed monophasic positive insertional activity may be an intracellularly recorded single muscle fiber discharge or a blocked extracellular discharge originating about the needle electrode. Applying this reasoning to PSWs suggests that they may also be an intracellular recording of a fibrillation potential, or needle-induced extracellular blocked local single muscle fiber discharge. This unifying concept is applied to various clinical situations purported to demonstrate "different" types of PSWs.

Animals↗

PubMed1996

Dermatomal/segmental somatosensory evoked potential evaluation of L5/S1 unilateral/unilevel radiculopathies.

Dermatomal and segmental somatosensory evoked potentials (SEPs) have been reported to be of diagnostic utility in unilateral/unilevel L5 and S1 radiculopathies. This investigation employs history, physical examination, imaging studies, and electrodiagnostic medicine evaluations to clearly define unilateral/unilevel L5 or S1 nerve root compromise. Inclusion criteria require all of the preceding diagnostic methods to corroborate a specific nerve root lesion. Regression equation analysis for cortical P1 latencies evaluating age and height based on comparable patient and control reference populations reveals segmental and dermatomal sensitivities for L5 radiculopathies to be 70% and 50%, respectively, at 90% confidence intervals. Similar sensitivities are obtained for 2 standard deviation mean cortical P1 latencies. Side-to-side cortical P1 latency difference data reveal segmental and dermatomal sensitivities for S1 radiculopathies to be 50% and 10%, respectively, at two standard deviations. The clinical utility of both segmental and dermatomal SEPs are questionable in patients with known unilateral/unilevel L5 and S1 nerve root compromise.

Adult↗

PubMed1996

Monopolar needle electrode spatial recording characteristics.

The recording characteristics of the monopolar needle in three dimensions have not been well established. A simple spherical recording territory is commonly assumed with the very tip proposed to have a greater spatial recording sensitivity by some authors. We demonstrate by enlarged physical modeling in a homogeneous volume conductor that the recorded amplitude diminishes more gradually radially away from the conical surface than distally past the tip or proximal to the insulation edge. The sensitivity over the exposed metallic surface is found to be uniformly proportional to the area, which results in relatively less sensitivity at the tip than the middle and proximal portions of the conical recording surface. The overall spatial amplitude recording characteristics can be better described by an apple shape than a sphere, centered at the midportion of the exposed conical surface. A better appreciation of the actual spatial recording characteristics of the monopolar needle electrode can result in more accurate physiologic interpretations of quantitative motor unit analysis.

Electric Conductivity↗

PubMed1995

Median/ulnar premotor potential identification and localization.

A small negative waveform is known to precede the median and ulnar compound muscle action potentials when recorded with surface or concentric needle electrodes. This investigation documents that there are two distinct waveforms preceding the median compound muscle action potential (CMAP) depending upon the type of recording electrodes used (concentric needle versus surface) and their respective locations. The negative waveform originally described with a concentric needle electrode positioned within the substance of the distal thenar eminence and having a restricted zone of detection is referred to as the intramuscular nerve action potential (INAP). This potential is shown to be distinct from the premotor potential (the small negative waveform preceding surface recorded ulnar and median CMAPs). Detection of the median and ulnar premotor potentials at multiple locations about the hand with the same respective onset/peak latencies and amplitudes substantiates that this potential is a far-field potential. The median and ulnar premotor potentials most likely originate from a dipolar moment imbalance generated by digital sensory nerve action potentials as they cross the first and fifth metacarpophalangeal junctions, respectively. Applying far-field principles permits the documentation of additional far-field potentials as they are generated at the second through fourth metacarpophalangeal junctions following median nerve stimulation. Also, because the premotor potential is a far-field potential, caution must be exercised with respect to its diagnostic utility as joint position and other unknown factors may affect amplitude and onset/peak latency. The INAP following median nerve excitation, however, is documented to be a near-field potential distinct from the premotor potential arising from the recurrent branch of the median nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1994

The biphasic morphology of voluntary and spontaneous single muscle fiber action potentials.

The extracellular morphology of single muscle fiber action potentials (SMFAPs) is anticipated by volume conductor theory to be triphasic. Single muscle fiber action potentials recorded during single muscle fiber studies (500 Hz to 20 kHz) usually appear triphasic; however, when recorded with an open bandwidth (1 Hz to 20 kHz) they are found to be biphasic. Fibrillation potentials recorded with a single fiber electrode and open bandwidth have identical biphasic morphologies as volitional SMFAPs. Computer simulations suggest that the intracellular action potential models currently used to derive simulated extracellularly recorded SMFAPs must have the repolarization phase considerably prolonged to yield the clinically recorded potentials. This implies that either the models presently used require significant modification, or there is some distortion of the transmembrane source current induced in needle recording studies such that biphasic and not triphasic potentials are detected.

Action Potentials↗

PubMed1993

Far-field potentials.

Far-field potentials are produced by neural generators located at a distance from the recording electrodes. These potentials were initially characterized incorrectly as being of positive polarity, widespread distribution, and constant latency; however, recent advances have clearly demonstrated that far-field potentials may be either positive or negative depending upon the location of the electrodes with respect to the orientation of the dipole generator. Additionally, peak latencies in the far-field can vary with alterations in body position and the spatial distribution of far-field potentials, while widespread, is not uniform. Recent studies of far-field potentials suggest how such waveforms are produced when the symmetry of an action potential, as recorded by distant electrodes, is broken by such factors as differing conductivities of volume conductor compartments, direction of action potential propagation, size differentials in adjoining body segments, or the termination of action potential propagation in excitable tissue. Human, animal, and computer experiments support the preceding generalizations. These new explanations are directly applicable to such far-field potentials as the short latency somatosensory-evoked potential. Furthermore, since far-field potentials can also occur in muscle tissue, one should expect that these generalizations will hold with respect to electromyographic potentials.

Action Potentials↗

PubMed1993

Far-field potentials in cylindrical and rectangular volume conductors.

The occurrence of a transient dipole is one method of producing a far-field potential. This investigation qualitatively defines the characteristics of the near-field and far-field electrical potentials produced by a transient dipole in both cylindrical and rectangular volume conductors. Most body segments of electrophysiologic interest such as arms, legs, thorax, and neck are roughly cylindrical in shape. A centrally located dipole generator produces a nonzero equipotential region which is found to occur along the cylindrical wall at a distance from the dipole of approximately 1.4 times the cylinder's radius and 1.9 times the cylinder's radius for the center of the cylinder. This distance to the equi-potential zone along the surface wall expands but remains less than 3.0 times the cylindrical radius when the dipole is eccentrically placed. The magnitude of the equipotential region resulting from an asymmetrically placed dipole remains identical to that when the dipole is centrally located. This behavior is found to be very similar in rectangular shallow conducting volumes that model a longitudinal slice of the cylinder, thus allowing a simple experimental model of the cylinder to be utilized. Amplitudes of the equipotential region are inversely proportional to the cylindrical or rectangular volume's cross-sectional area at the location of dipolar imbalance. This study predicts that referential electrode montages, when placed at 3.0 times the radius or greater from a dipolar axially aligned far-field generator in cylindrical homogeneous volume conductors, will record only equipotential far-field effects.

Electromyography↗

PubMed1993

Anodal block V anodal stimulation. Fact or fiction.

Anodal block and stimulation are poorly documented electrophysiologic phenomenon. Median and superficial radial nerves are examined in a prospective study to explore the significance of anodal block in routine nerve conduction studies. In addition, the anode's ability to stimulate the peripheral nervous system is evaluated. A monopolar stimulation technique is employed to achieve pure anode-generated responses. Additionally, a similar monopolar cathode stimulation technique is utilized and found to be equivalent to the traditional bipolar cathode stimulation. Based on the findings in this investigation, anodal block does not appear to occur during routine nerve conduction studies; however, transposition of the anode and cathode is clinically significant because the increased distance between the cathode and recording electrode results in predictably prolonged latencies. With higher levels of stimulus intensity, sensory, motor and F wave responses are generated by anodal stimulation in all cases. The actual mechanism of anodal stimulation remains uncertain and requires further study. Predicated on the results of this investigation, it appears that anodal block is an unlikely occurrence during routine electrodiagnostic medicine evaluations.

Action Potentials↗

PubMed1993

Intercostal somatosensory-evoked potentials. A new technique.

Presently, there are few electrodiagnostic medicine techniques to evaluate lesions affecting the thoracic nerve roots or spinal cord. A new electrophysiologic technique to assess these structures, intercostal somatosensory-evoked potentials (SEPs), is described. Thirty neurologically normal subjects were used in this investigation to generate intercostal SEPs. Bilateral intercostal SEPs were easily elicited after stimulation of the third intercostal nerves just lateral to the sternum anteriorly. Intercostal SEPs were also easily elicited from the fifth, seventh and ninth intercostal nerves along the anterior axillary line bilaterally. Intercostal SEPs are not only easily and painlessly obtained, but are specific for individual spinal levels. This SEP method will provide the clinician with another neural stimulation procedure to assist in the diagnosis of both central and peripheral thoracic neural compromise.

Adult↗

PubMed1993

Segmental v dermatomal somatosensory-evoked potentials. Normal intertrial variation and side-to-side comparison.

Although segmental and dermatomal somatosensory evoked potentials have been used in the diagnosis of lumbosacral radiculopathy, the unilateral or bilateral normal intertrial variation of these responses has not been investigated. Furthermore, there exists little consensus on how many sequential trials for a single nerve or dermatome are optimal and how to use the data generated from these trials. Without investigation of these basic parameters, determination of what constitutes a normal somatosensory-evoked potential (SEP) is difficult. In 29 normal subjects, the ipsilateral intertrial variations, arithmetic mean side-to-side differences and maximum potential side-to-side differences with stimulation of the superficial peroneal sensory nerve, sural nerve and L5 and S1 dermatomes with respect to P1 and N1 latencies and peak-to-peak amplitudes were investigated. Considerable ipsilateral intertrial variation was observed and side-to-side comparisons revealed a further increase in this inherent variation regarding the above measured parameters. The maximum potential side-to-side differences were even more remarkable than the mean side-to-side differences. For these results and others presented, a method of evaluating SEP parameters whereby the arithmetic mean of two sequential trials for both latency and amplitude is presented that attempts to minimize the normal, inherent variation. We also suggest an additional parameter with which to evaluate SEPs: the maximum side-to-side latency difference. Only through the use of a consistent methodology can segmental or dermatomal SEPs be utilized in a reliable diagnostic manner.

Adult↗