In vitro magnetic stimulation of pig phrenic nerve with transverse and longitudinal induced electric fields: analysis of the stimulation site.

IEEE transactions on bio-medical engineering · 2009 · Unclear · Low evidence

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UnclearLow evidencePaper 2788

Study snapshot

PublicationIEEE transactions on bio-medical engineering · 2009

Study typein_vitro

Reported directionUnclear

Evidence ratingLow

Abstract

The induced electric field transverse to peripheral nerve trunks has been shown to lead to stimulation, contrary to predictions of the cable equation. Two possible mechanisms of activation have been documented in literature: the change in the transmembrane voltage due to an electric field transverse to the membrane of a cylindrical fiber and the transverse field projection on the undulating fiber path within the fascicle. To distinguish between these alternatives, an analysis of the stimulation site was performed in vitro along 15 phrenic nerves from pigs, with a 5-cm-diameter round coil. Stimulation with induced electric field having longitudinal and attenuated transverse components resulted in stimulation sites in the vicinity of the negative peak of the spatial derivative of the longitudinal electric field and threshold variations with coil positions along the nerve trunk. Stimulation with a transverse field yielded patterns of one, two, or three stimulation sites, scattered or uniformly distributed around the location of the two field maxima. A nerve structure analysis outlined the fiber undulation within the fascicle and a network of wavy fascicles. The presence of this network and the variations of the stimulation site, and of the threshold suggest that the path of the fiber has a major undulation due to the undulation of the fascicles within the nerve trunk, which may be responsible for the stimulation with an electric field transverse to the nerve trunk.

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AI evidence extraction

Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.

Study typein_vitro

Effect directionunclear

PopulationPig phrenic nerves (in vitro)

Sample size15

ExposureNot supplied

Evidence strengthLowConfidence: 74% · Peer reviewed: yes

Main findings

In vitro analysis of 15 pig phrenic nerves using a 5-cm-diameter round coil found that stimulation with induced electric fields having longitudinal and attenuated transverse components produced stimulation sites near the negative peak of the spatial derivative of the longitudinal electric field, with threshold variations depending on coil position. Stimulation with a transverse field produced one to three stimulation sites distributed around the two field maxima. Structural analysis described fiber undulation within fascicles and wavy fascicles, and the observed stimulation-site/threshold variations were suggested to be related to fascicle/fiber path undulation.

Outcomes measured

Peripheral nerve stimulation site location
Stimulation threshold variation with coil position
Patterns/number of stimulation sites under transverse vs longitudinal induced electric fields
Nerve/fascicle structure (fiber/fascicle undulation)

Limitations

In vitro preparation (pig phrenic nerves) may not generalize to in vivo or human nerve stimulation
Frequency and detailed exposure parameters of the stimulation waveform are not reported in the abstract
Mechanistic interpretation is suggestive rather than definitively demonstrated in the abstract

View raw extracted JSON

{
  "study_type": "in_vitro",
  "exposure": {
    "band": null,
    "source": "magnetic stimulation coil",
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": null
  },
  "population": "Pig phrenic nerves (in vitro)",
  "sample_size": 15,
  "outcomes": [
    "Peripheral nerve stimulation site location",
    "Stimulation threshold variation with coil position",
    "Patterns/number of stimulation sites under transverse vs longitudinal induced electric fields",
    "Nerve/fascicle structure (fiber/fascicle undulation)"
  ],
  "main_findings": "In vitro analysis of 15 pig phrenic nerves using a 5-cm-diameter round coil found that stimulation with induced electric fields having longitudinal and attenuated transverse components produced stimulation sites near the negative peak of the spatial derivative of the longitudinal electric field, with threshold variations depending on coil position. Stimulation with a transverse field produced one to three stimulation sites distributed around the two field maxima. Structural analysis described fiber undulation within fascicles and wavy fascicles, and the observed stimulation-site/threshold variations were suggested to be related to fascicle/fiber path undulation.",
  "effect_direction": "unclear",
  "limitations": [
    "In vitro preparation (pig phrenic nerves) may not generalize to in vivo or human nerve stimulation",
    "Frequency and detailed exposure parameters of the stimulation waveform are not reported in the abstract",
    "Mechanistic interpretation is suggestive rather than definitively demonstrated in the abstract"
  ],
  "evidence_strength": "low",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "magnetic stimulation",
    "induced electric field",
    "transverse electric field",
    "longitudinal electric field",
    "peripheral nerve stimulation",
    "phrenic nerve",
    "pig",
    "fascicle undulation",
    "stimulation site",
    "threshold"
  ],
  "suggested_hubs": [
    {
      "slug": "occupational-exposure",
      "weight": 0.2,
      "reason": "Study concerns magnetic stimulation-induced electric fields and peripheral nerve stimulation mechanisms, potentially relevant to exposure/stimulation contexts, but no explicit occupational setting is described."
    }
  ]
}

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AI-extracted fields are generated from the abstract and metadata and may be incomplete or incorrect. This material is for informational purposes and is not medical advice.

Identifiers and source

DOI: 10.1109/tbme.2008.2009929
PubMed: 19272863

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