Comparison between Transcutaneous Electrical Phrenic Nerve Stimulation and Cervical Magnetic Stimulation

Practical aspects. The practical aspects of ES and CMS are described in previous sections. In summary:

1. ES is the original method for generating an isolated contraction of the diaphragm, but for the operator is difficult to master.

2. CMS is easier and faster to apply, with a lower risk of false results due to technical problems. It is better tolerated by the subject. There is some cocontraction of the upper rib cage and neck muscles, stiffening the rib cage, so that Pdi may be greater than with ES.

Physiological aspects. The two techniques are comparable with respect to reproducibility (similar within-occasion and between-occasion coefficients of variation) (100, 107) and the time characteristics of the Pdi twitches are very close. When supramaximal bilateral ES and CMS are compared in the same subjects (107-109) Pdi,tw values measured during CMS appear consistently higher by approximately 20-25% than Pdi,tw measured during ES, the difference being accounted for by more negative Pes values.

Conclusion and perspectives. Cervical magnetic stimulation and ES do not provide the same physiological information, so that normal values for PNS-related pressures (see Applications and Perspectives) depend on the technique used. This also means that the results of CMS and ES may be affected differently in diseases affecting both diaphragm and rib cage muscles. The possibility of focused phrenic nerve magnetic stimulation in the neck with small figure-of-eight coils bilaterally (114, 115) will probably reconcile the physiological need for pure diaphragm contraction and the clinical need for simplicity. CMS and other techniques of magnetic stimulation of the phrenic nerve, being easier to use than ES, should then overcome the limitations of ES for large series, exercise, ICU, or intraoperative studies.

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