Daniel Dumitru - Academia.edu (original) (raw)
Papers by Daniel Dumitru
American Journal of Physical Medicine Rehabilitation Association of Academic Physiatrists, 1988
Facial nerve paralysis is the most common mononeuropathy and idiopathic facial paralysis (Bell&am... more 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.
Electroencephalography and clinical neurophysiology, 1997
Computer simulations of concentric needle electrode recording characteristics assume a hemisphere... more 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 ...
Electroencephalography and clinical neurophysiology, 1998
This study investigates the influence of tissue penetration depth as it relates to a concentric n... more 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 bipola...
Electroencephalography and clinical neurophysiology, 1997
Scaled 20:1 physical models of monopolar and standard concentric needle electrodes are investigat... more 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 off...
Electroencephalography and clinical neurophysiology
Far-field potentials have been observed clinically and recognized as such for approximately 30 ye... more Far-field potentials have been observed clinically and recognized as such for approximately 30 years. Unfortunately a complete understanding of far-field potential generation is not yet at hand. An attractive model is the representation of an action potential by a quadrupole consisting of a leading and trailing dipole with respect to the direction of propagation. This investigation physically models an action potential by using a quadrupole constant current source and substantiates the concept that an action potential as modeled by two dipoles back-to-back is capable of producing far-field potentials in cylindrical volume conductors. The 4 postulated mechanisms of generating far-field potentials are validated, i.e., an action potential encountering (1) different size volume conductors, (2) the termination of excitable tissue, (3) a change in conducting medium conductivity, and (4) a bend in the nerve. A fifth postulated but previously not demonstrated method of far-field production,...
Muscle & Nerve, 2006
In this study we utilized a dual monopolar needle recording technique to assess propagated electr... more In this study we utilized a dual monopolar needle recording technique to assess propagated electromyographic insertional activity from the same single muscle fiber in order to characterize different categories of insertional activity. A total of six combinations of insertional activity were identified. Only two fundamental types of single muscle-fiber insertional discharge configurations were generated: biphasic initially-negative and monophasic positive. The propagated waveforms corresponding to these two insertional discharges were primarily triphasic initially-positive and, only rarely, monophasic positive. The monophasic positive insertional activity generated at the inserting electrode site is postulated to arise from a depolarization zone adjacent to a needle-induced peri-electrode membrane crush. The monophasic positive discharge was utilized as a model for positive sharp wave generation. It is postulated that the majority of positive sharp waves are initiated at the inserting electrode adjacent to a needleinduced zone of muscle membrane crush in contrast to the previous supposition that positive sharp waves are blocked fibrillation potentials.
Muscle & Nerve, 2001
Antidromic sensory nerve action potential testing is well characterized and commonly used to asse... more 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.
Muscle & Nerve, 1990
Electrophysiologic findings in thallium intoxication are usually untimely, limited in extent, and... more 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. Key words: thallium poisoning peripheral neuropathy heavy metal intoxication axonal neuropathy, human MUSCLE 81 NERVE 13:433-437 1990
Muscle & Nerve, 1999
Motor unit action potentials (MUAPs) recorded from the same motor unit at two distances along the... more 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.
Muscle & Nerve, 1988
Numerous techniques that evaluate radial nerve conduction from the axilla or supraclavicular foss... more 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.
Muscle & Nerve, 1992
Preliminary investigations of circular volume conductors suggested that farfield potential magnit... more Preliminary investigations of circular volume conductors suggested that farfield potential magnitude declines progressively slower with increasing radial distance from a current source and follows a cosine function with angular displacement of the recording electrode from the electrical generator's axis. Using circular volumes of 6 differing radii, the mathematical relationship between angle, radii, and far-field potential amplitude is determined. Previous theoretical relationships of amplitude versus dipolar spacing, current, and distance from a dipole generator in a bounded volume conducting medium are verified for the near-field. Far-field potentials in circular volumes are found to become constant at radii greater than 75% of the bounded volume's radius. Additionally, an adjoining volume conductor acts simply as a passive fluid-filled electrode (wick electrode) to the circular volume containing the generator until the intercompartmental opening to the circular volume exceeds 20% of its circumference. This finding was clinically supported by recording similar P9 somatosensory-evoked far-field potentials generated caudal to the foramen magnum from various portions of the cranium, whose connections to the torso, foramen magnum, and neck, average 6.2% and 17.8%, respectively. Finally, 3 circular volume conductors were connected in series by channels less than 20% of the volume conductor's circumference. Both adjoining circular volumes were equipotential to the far-field potential present at the boundary of the first circular volume containing the dipole generator. This observation supports the clinical finding of far-field potential transmission through multiple human bodies in conductive Contact. 0 Approximately 20 years have elapsed since farfield potentials were first described clinically in au-ditorys39 and somatosensory-evoked potentials.'.' Far-field potential observations in both somatosensory-evoked and peripheral nervous system investigations offer insight into far-field potential characteristics. Additionally, mathematical substantiation of far-field potential principles are provided through computer m~deling.'~ Investigators have confirmed many of the clinical
Muscle & Nerve, 1991
The ideal electrodiagnostic procedure to assess possible plantar neuropathies continues to elude ... more 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.
Muscle & Nerve, 2007
This investigation analyzes the temporal characteristics of maximal depolarization times for thre... more This investigation analyzes the temporal characteristics of maximal depolarization times for three waveforms: end-plate spikes, fibrillation potentials, and positive sharp waves (PSWs) to provide support for the electrode initiation hypothesis of PSW induction. The maximal depolarization times for PSWs are documented to comprise two distinct populations conforming to relatively short and comparatively longer maximal depolarization times. Those PSWs with short maximal depolarization times were found to be equivalent to end-plate spike maximal depolarization times, whereas those with longer times were comparable to fibrillation potentials. The PSW group with shorter maximal depolarization times was encountered more frequently. The combination of two distinct groups of PSWs with respective times comparable to end-plate spikes and fibrillation potentials supports the hypothesis that the majority of PSWs originate at the recording electrode during insertion, whereas a smaller population of PSWs arises as propagating fibrillation potentials that block at the recording electrode. Subcutaneous compared to intramuscular recordings from denervated muscle document that the recording electrode is necessary to both record and produce PSWs. Hence, this study confirms the proposed hypothesis that the majority of observed PSWs represent a suprathreshold single muscle-fiber discharge induced by, and originating in close proximity to, a perielectrode crushed membrane that then propagate away from the electrode; a smaller population of PSWs conform to that of a blocked fibrillation potential.
Muscle & Nerve, 1998
Needle electromyographic insertional activity waveform morphology, and mechanisms of generation, ... more 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.
Muscle & Nerve, 1998
It is presently believed that a fibrillation potential (FP) can transform into a positive sharp w... more 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.
Muscle & Nerve, 1999
A finite muscle fiber simulation program which calculates the extracellular potential for any giv... more 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.
Muscle & Nerve, 1997
A better appreciation of the specific spatial recording characteristics of the single fiber and c... more 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°beveled surface between the core and cannula and extends only 280 µm perpendicularly from the center of the core's surface. The 99% envelope extends approximately 830 µm 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 µm perpendicularly from the exposed single fiber core. Both the single fiber and concentric needle volumes of sensitivity have specific asymmetries described.
Muscle & Nerve, 1996
Dermatomal and segmental somatosensory evoked potentials (SEPs) have been reported to be of diagn... more 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.
Muscle & Nerve, 1993
The occurrence of a transient dipole is one method of producing a far-field potential. This inves... more 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 equipotential 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. 0
American Journal of Physical Medicine Rehabilitation Association of Academic Physiatrists, 1988
Facial nerve paralysis is the most common mononeuropathy and idiopathic facial paralysis (Bell&am... more 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.
Electroencephalography and clinical neurophysiology, 1997
Computer simulations of concentric needle electrode recording characteristics assume a hemisphere... more 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 ...
Electroencephalography and clinical neurophysiology, 1998
This study investigates the influence of tissue penetration depth as it relates to a concentric n... more 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 bipola...
Electroencephalography and clinical neurophysiology, 1997
Scaled 20:1 physical models of monopolar and standard concentric needle electrodes are investigat... more 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 off...
Electroencephalography and clinical neurophysiology
Far-field potentials have been observed clinically and recognized as such for approximately 30 ye... more Far-field potentials have been observed clinically and recognized as such for approximately 30 years. Unfortunately a complete understanding of far-field potential generation is not yet at hand. An attractive model is the representation of an action potential by a quadrupole consisting of a leading and trailing dipole with respect to the direction of propagation. This investigation physically models an action potential by using a quadrupole constant current source and substantiates the concept that an action potential as modeled by two dipoles back-to-back is capable of producing far-field potentials in cylindrical volume conductors. The 4 postulated mechanisms of generating far-field potentials are validated, i.e., an action potential encountering (1) different size volume conductors, (2) the termination of excitable tissue, (3) a change in conducting medium conductivity, and (4) a bend in the nerve. A fifth postulated but previously not demonstrated method of far-field production,...
Muscle & Nerve, 2006
In this study we utilized a dual monopolar needle recording technique to assess propagated electr... more In this study we utilized a dual monopolar needle recording technique to assess propagated electromyographic insertional activity from the same single muscle fiber in order to characterize different categories of insertional activity. A total of six combinations of insertional activity were identified. Only two fundamental types of single muscle-fiber insertional discharge configurations were generated: biphasic initially-negative and monophasic positive. The propagated waveforms corresponding to these two insertional discharges were primarily triphasic initially-positive and, only rarely, monophasic positive. The monophasic positive insertional activity generated at the inserting electrode site is postulated to arise from a depolarization zone adjacent to a needle-induced peri-electrode membrane crush. The monophasic positive discharge was utilized as a model for positive sharp wave generation. It is postulated that the majority of positive sharp waves are initiated at the inserting electrode adjacent to a needleinduced zone of muscle membrane crush in contrast to the previous supposition that positive sharp waves are blocked fibrillation potentials.
Muscle & Nerve, 2001
Antidromic sensory nerve action potential testing is well characterized and commonly used to asse... more 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.
Muscle & Nerve, 1990
Electrophysiologic findings in thallium intoxication are usually untimely, limited in extent, and... more 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. Key words: thallium poisoning peripheral neuropathy heavy metal intoxication axonal neuropathy, human MUSCLE 81 NERVE 13:433-437 1990
Muscle & Nerve, 1999
Motor unit action potentials (MUAPs) recorded from the same motor unit at two distances along the... more 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.
Muscle & Nerve, 1988
Numerous techniques that evaluate radial nerve conduction from the axilla or supraclavicular foss... more 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.
Muscle & Nerve, 1992
Preliminary investigations of circular volume conductors suggested that farfield potential magnit... more Preliminary investigations of circular volume conductors suggested that farfield potential magnitude declines progressively slower with increasing radial distance from a current source and follows a cosine function with angular displacement of the recording electrode from the electrical generator's axis. Using circular volumes of 6 differing radii, the mathematical relationship between angle, radii, and far-field potential amplitude is determined. Previous theoretical relationships of amplitude versus dipolar spacing, current, and distance from a dipole generator in a bounded volume conducting medium are verified for the near-field. Far-field potentials in circular volumes are found to become constant at radii greater than 75% of the bounded volume's radius. Additionally, an adjoining volume conductor acts simply as a passive fluid-filled electrode (wick electrode) to the circular volume containing the generator until the intercompartmental opening to the circular volume exceeds 20% of its circumference. This finding was clinically supported by recording similar P9 somatosensory-evoked far-field potentials generated caudal to the foramen magnum from various portions of the cranium, whose connections to the torso, foramen magnum, and neck, average 6.2% and 17.8%, respectively. Finally, 3 circular volume conductors were connected in series by channels less than 20% of the volume conductor's circumference. Both adjoining circular volumes were equipotential to the far-field potential present at the boundary of the first circular volume containing the dipole generator. This observation supports the clinical finding of far-field potential transmission through multiple human bodies in conductive Contact. 0 Approximately 20 years have elapsed since farfield potentials were first described clinically in au-ditorys39 and somatosensory-evoked potentials.'.' Far-field potential observations in both somatosensory-evoked and peripheral nervous system investigations offer insight into far-field potential characteristics. Additionally, mathematical substantiation of far-field potential principles are provided through computer m~deling.'~ Investigators have confirmed many of the clinical
Muscle & Nerve, 1991
The ideal electrodiagnostic procedure to assess possible plantar neuropathies continues to elude ... more 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.
Muscle & Nerve, 2007
This investigation analyzes the temporal characteristics of maximal depolarization times for thre... more This investigation analyzes the temporal characteristics of maximal depolarization times for three waveforms: end-plate spikes, fibrillation potentials, and positive sharp waves (PSWs) to provide support for the electrode initiation hypothesis of PSW induction. The maximal depolarization times for PSWs are documented to comprise two distinct populations conforming to relatively short and comparatively longer maximal depolarization times. Those PSWs with short maximal depolarization times were found to be equivalent to end-plate spike maximal depolarization times, whereas those with longer times were comparable to fibrillation potentials. The PSW group with shorter maximal depolarization times was encountered more frequently. The combination of two distinct groups of PSWs with respective times comparable to end-plate spikes and fibrillation potentials supports the hypothesis that the majority of PSWs originate at the recording electrode during insertion, whereas a smaller population of PSWs arises as propagating fibrillation potentials that block at the recording electrode. Subcutaneous compared to intramuscular recordings from denervated muscle document that the recording electrode is necessary to both record and produce PSWs. Hence, this study confirms the proposed hypothesis that the majority of observed PSWs represent a suprathreshold single muscle-fiber discharge induced by, and originating in close proximity to, a perielectrode crushed membrane that then propagate away from the electrode; a smaller population of PSWs conform to that of a blocked fibrillation potential.
Muscle & Nerve, 1998
Needle electromyographic insertional activity waveform morphology, and mechanisms of generation, ... more 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.
Muscle & Nerve, 1998
It is presently believed that a fibrillation potential (FP) can transform into a positive sharp w... more 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.
Muscle & Nerve, 1999
A finite muscle fiber simulation program which calculates the extracellular potential for any giv... more 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.
Muscle & Nerve, 1997
A better appreciation of the specific spatial recording characteristics of the single fiber and c... more 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°beveled surface between the core and cannula and extends only 280 µm perpendicularly from the center of the core's surface. The 99% envelope extends approximately 830 µm 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 µm perpendicularly from the exposed single fiber core. Both the single fiber and concentric needle volumes of sensitivity have specific asymmetries described.
Muscle & Nerve, 1996
Dermatomal and segmental somatosensory evoked potentials (SEPs) have been reported to be of diagn... more 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.
Muscle & Nerve, 1993
The occurrence of a transient dipole is one method of producing a far-field potential. This inves... more 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 equipotential 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. 0