Anterior magnetic phrenic nerve stimulation: laboratory and clinical evaluation

Intensive Care Med. 2000 Aug;26(8):1065-75. doi: 10.1007/s001340051319.


Objective: Anterior magnetic stimulation (aMS) of the phrenic nerves is a new method for the assessment of diaphragm contractility that might have particular applications for the clinical assessment of critically ill patients who are commonly supine.

Design: We compared aMS with existing techniques for measurement of diaphragm weakness and fatigue in 10 normal subjects, 27 ambulant patients with suspected diaphragm weakness and 10 critically ill patients.

Setting: Laboratory and intensive care unit of two university hospitals.

Results: Although aMS was not demonstrably supramaximal in normal subjects, the mean value of twitch transdiaphragmatic pressure (Tw Pdi) obtained at 100% of stimulator output, 23.7 cmH2O, did not differ significantly from that obtained with bilateral supramaximal electrical stimulation (ES), 24.9 cmH2O, or bilateral anterior magnetic phrenic nerve stimulation (BAMPS), 27.3 cmH2O. A fatiguing protocol produced a 20 % fall in aMS-Tw Pdi and a 19% fall in BAMPS-Tw Pdi; the fall in aMS-Tw Pdi correlated with the fall in BAMPS-Tw Pdi (r2 = 0.84, p = 0.03) indicating that aMS can detect diaphragm fatigue. In ambulant patients aMS agreed closely with existing measures of diaphragm strength. The maximal sniff Pdi correlated with both the aMS-Tw Pdi (r2 = 0.60, p < 0.0001) and the BAMPS-Tw Pdi (r2 = 0.65, p < 0.0001) and the aMS-Tw Pdi was a mean (SD) 2.2 (4.3) cmH2O less than BAMPS-Tw Pdi. In addition, aMS correctly identified diaphragm dysfunction in patients studied on the ICU.

Conclusions: We conclude that aMS is of clinical value for the investigation of suspected diaphragm weakness.

MeSH terms

  • Action Potentials
  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Analysis of Variance
  • Diaphragm / innervation*
  • Diaphragm / physiopathology
  • Electromagnetic Phenomena*
  • Female
  • Humans
  • Intensive Care Units
  • Male
  • Middle Aged
  • Neuromuscular Diseases / diagnosis*
  • Phrenic Nerve / physiopathology*
  • Reproducibility of Results
  • Respiration, Artificial
  • Respiratory Function Tests / instrumentation
  • Respiratory Function Tests / methods*
  • Safety
  • Sensitivity and Specificity
  • Supine Position