COMPARISON OF MAGNETIC AND ELECTRICAL PHRENIC-NERVE STIMULATION IN ASSESSMENT OF PHRENIC-NERVE CONDUCTION TIME

Cervical magnetic stimulation (CMS), a nonvolitional test of diaphragm function, is an easy means for measuring the latency of the diaphragm motor response to phrenic nerve stimulation, namely, phrenic nerve co nduction time (PNCT). In this application, CMS has some practical adva ntages over electrical stimulation of the phrenic nerve in the neck (E S). Although normal ES-PNCTs have been consistently reported between 7 and 8 ms, data are less homogeneous for CMS-PNCTs, with some reports suggesting lower values. This study systematically compares ES- and CM S-PNCTs for the same subjects. Surface recordings of diaphragmatic ele ctromyographic activity were obtained for seven healthy volunteers dur ing ES and CMS of varying intensities. On average, ES-PNCTs amounted t o 6.41 +/- 0.84 ms and were little influenced by stimulation intensity . With CMS, PNCTs were significantly lower (average difference 1.05 ms ), showing a marked increase as CMS intensity lessened. ES and CMS val ues became comparable for a CMS intensity 65% of the maximal possible intensity of 2.5 Tesla. These findings may be the result of phrenic ne rve depolarization occurring more distally than expected with CMS, whi ch may have clinical implications regarding the diagnosis and follow-u p of phrenic nerve lesions.