Measurement of the electric field induced into inhomogeneous volume conductors by magnetic coils: application to human spinal neurogeometry

Maccabee, Paul J.; Amassian, Vahé E.; Eberle, L.; Rudell, Alan P.; Cracco, Roger Q.; Lai, Kailok; Somasundarum, M.

doi:10.1016/0168-5597(91)90076-a

Cited by 102 publications

(46 citation statements)

References 16 publications

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“…Moreover, in these studies, the round coil was physically reversed leading to the possibility of coil displacement and/or tilt. In addition, the Amassian et al (1989b) study elicited responses from the ulnar nerve at the elbow, where the nerve lies close to bone, which could concentrate the current locally as in the intervertebral neuroforamina (Maccabee et al 1991). Subsequently, using both a monophasic pulse to energize the figure-of-eight MC (phase two amplitude was 35 % that of phase one) and the current reversing device described above, we again failed to detect consistently a shift in motor unit latency at threshold (Maccabee et al 1990 b).…”

Section: Discussionmentioning

confidence: 99%

“…Some of the details have previously been described in Maccabee et al 1988Maccabee et al , 1991Maccabee, Erbele, Amassian, Cracco, Rudell & Jayachandra, 1990a. A time-varying magnetic field was generated by a Cadwell Laboratories (Kennewick, WA, USA) MES-10 stimulator using either a 9-4 cm (outside diameter) round MC which was covered by epoxy, or a figure-of-eight MC covered by black tape (each half coil 5 x 4-8 cm).…”

Section: Magnetic Coils and Stimulatormentioning

confidence: 99%

“…Measurements by both pairs of orthogonal electrodes were used to calculate magnitude (by Pythagorean theorem) and direction (by arctangent) of the electric field. These vector fields, illustrated as arrow diagrams in the cylindrical tank for different MCs and orientations, were previously illustrated in Maccabee et al 1991. Because a homogeneous (saline) volume conductor was used, the current density in A m-2 is directly proportional to the recorded electric field.…”

Section: Current Reversing and Phase-damping Devicementioning

confidence: 99%

“…2A) is designated E, Because of its potential importance in defining the site of excitation, the first spatial derivative of the induced electric fields in the Y-axis (dE,/dY; Fig. 2B) was also calculated (for the specific algorithm, see Maccabee et al 1991). These are illustrated both as topographical and contour maps ( Fig In-vitro studies Nerve preparation.…”

Section: Current Reversing and Phase-damping Devicementioning

confidence: 99%

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Magnetic coil stimulation of straight and bent amphibian and mammalian peripheral nerve in vitro: locus of excitation.

Maccabee

Amassian

Eberle

et al. 1993

The Journal of Physiology

289

156

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SUMMARY1. According to classical cable theory, a magnetic coil (MC) should excite a linear nerve fibre in a homogeneous medium at the negative-going first spatial derivative of the induced electric field. This prediction was tested by MC stimulation of mammalian phrenic and amphibian sciatic nerve and branches in vitro, immersed in Ringer solution within a trough, and identifying the sites of excitation by recording responses of similar latency to local electrical stimulation. Subsequently, the identified sites of excitation were compared with measurements of the induced electric field and its calculated first spatial derivative. A special hardware device was used to selectively reverse MC current direction and to generate predominantly monophasic-or polyphasic-induced pulse profiles whose initial phases were identical in polarity, shape and amplitude. When using the amphibian nerve preparation, a complication was excitation at low threshold points related to cut branches.2. Reversal of monophasic current resulted in latency shifts corresponding approximately to the distance between induced cathode and anode. The location of each site of excitation was at, or very near, the negative-going first spatial derivative peaks of the induced electric field measured parallel to the straight nerve. Significantly, excitation of the nerve did not occur at the peak of the induced electric field above the centre of the 'figure of eight' MC junction.3. A polyphasic pulse excited the nerve at both sites, by the negative-going first phase at one location, and approximately 150 ,ts later, by the reversed negativegoing second phase at the other location. Polyphasic and monophasic pulses elicited responses with similar latency when the induced current flowed towards the recording electrode.4. Straddling a nerve with non-conducting solid lucite cylinders created a localized spatial narrowing and increase in the induced electric field, resulting in a lowered threshold of excitation. The corresponding closer spacing between first spatial derivative peaks was exhibited by a significant reduction in latency shift when MC current direction was reversed.5. When a nerve is bent and the induced current is directed along the nerve towards the bend, the threshold of excitation is reduced there. Increasing the angle of the bend from 0 deg to more than 90 deg graded the decrease in threshold.MS 1133 P. J. MACCABEE AND OTHERS 6. In a straight nerve the threshold was lowest when current was directed towards the cut end.7. Optimal excitation at a low threshold point (created on the nerve by a pair of cylinders or a bend, and at a nerve ending) occurs near or within the peak of the induced electric field, rather than at its first derivative. When adjusting MC output intensity and moving the junction region of the MC in the long axis of the nerve 3 cm towards or away from a low threshold point, responses were elicited at nearly identical latency, implying a common site of excitation. Possibly, these observations relate to examples in the human where...

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Section: Discussionmentioning

confidence: 99%

Section: Magnetic Coils and Stimulatormentioning

confidence: 99%

Section: Current Reversing and Phase-damping Devicementioning

confidence: 99%

Section: Current Reversing and Phase-damping Devicementioning

confidence: 99%

See 2 more Smart Citations

Magnetic coil stimulation of straight and bent amphibian and mammalian peripheral nerve in vitro: locus of excitation.

Maccabee

Amassian

Eberle

et al. 1993

The Journal of Physiology

289

156

View full text Add to dashboard Cite

show abstract

“…15 As the stimulator switched the coil off when it became too warm, two magnetic coils were used alternately to apply the full amount of magnetic stimuli in all patients. While determining the intensity for the stimulation motor threshold, we also located the best position and marked it on the subject's back.…”

Section: Magnetic Stimulationmentioning

confidence: 99%

Lumbar repetitive magnetic stimulation reduces spastic tone increase of the lower limbs

Krause¹,

Edrich²,

Straube³

2004

Spinal Cord

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Study Design: Comparison of spinal lesion subjects and normal subjects. Objective: To investigate the effects of a paravertebral repetitive magnetic stimulation on spastic tone increase of the lower limbs. Setting: Munich, Germany. Methods: We compared the effects in 15 patients with different spinal lesions and in 16 healthy subjects. The spastic tone increase was evaluated clinically with the Ashworth scale and apparatively with the pendulum test, both at fixed times before and after stimulation. Unilateral stimulation was applied to the lumbar nerve roots L3 and L4 of the clinically more spastic leg. Results: The spastic tone decreased significantly in the interval between 4 and 24 h after stimulation. This effect was slightly more pronounced in the contralateral extremity. Furthermore, the stimulation motor threshold of the patients was significantly raised. Conclusion: Repetitive magnetic unilateral stimulation has a positive effect on spastic tone increase due to spinal lesions, causing a decrease that lasts for about 1 day not only on the ipsilateral but also on the contralateral side.

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Functional magnetic stimulation of the respiratory muscles in dogs

1998

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This study assessed the ability of functional magnetic stimulation (FMS) to activate the respiratory muscles in dogs. With the animal supine, FMS of the phrenic nerves using a high‐speed magnetic stimulator was performed by placing a round magnetic coil (MC) at the carotid triangle. Following hyperventilation‐induced apnea, changes in volume (ΔV) and airway pressure (ΔP) against an occluded airway were determined. FMS of the phrenic nerves produced substantial inspired function (ΔV = 373 ± 20.5 mL and ΔP = −20 ± 2.0 cm H2O). After bilateral phrenectomies, maximal inspired ΔV (219 ± 12.2 mL) and ΔP (−10 ± 1.0 cm H2O) were produced when the MC was placed near the C6–C7 spinous processes, while maximal expired ΔV (−199 ± 22.5 mL) and ΔP (11 ± 2.3 cm H2O) were produced following stimulation near the T9–T10 spinous processes. We conclude: (1) FMS of either the phrenic or upper intercostal nerves results in inspired volume production; (2) FMS of the lower intercostal nerves generates expired volume production; and (3) FMS of the respiratory muscles may be a useful noninvasive tool for artificial ventilation and assisted cough in patients with spinal cord injuries or other neurological disorders. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:1048–1057, 1998.

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Measurement of the electric field induced into inhomogeneous volume conductors by magnetic coils: application to human spinal neurogeometry

Cited by 102 publications

References 16 publications

Magnetic coil stimulation of straight and bent amphibian and mammalian peripheral nerve in vitro: locus of excitation.

Magnetic coil stimulation of straight and bent amphibian and mammalian peripheral nerve in vitro: locus of excitation.

Lumbar repetitive magnetic stimulation reduces spastic tone increase of the lower limbs

Functional magnetic stimulation of the respiratory muscles in dogs

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