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Updated: Aug 7, 2026
Functional and Morphological Assessment of Diaphragm Innervation by Phrenic Motor Neurons
Published on: May 25, 2015
Anterior magnetic phrenic nerve stimulation: laboratory and clinical evaluation
1Respiratory Muscle Laboratory, Royal Brompton Hospital, London, UK. m.polkey@rbh.nthames.nhs.uk
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.
