Position effect of trans-spinal magnetic stimulation on diaphragmatic motor evoked potential in healthy humans

The present study was designed to evaluate the rostrocaudal and lateral-midline effects of trans-spinal magnetic stimulation on diaphragmatic motor evoked potential by utilizing a figure-of-eight coil. The bilateral diaphragm electromyograms were recorded during trans-spinal magnetic stimulation from 60% to 100% of maximum output in 21 healthy subjects. The rostrocaudal effect of trans-spinal magnetic stimulation was evaluated by comparing diaphragmatic motor evoked potential when the coil was placed at the midline of the fifth (C5) and seventh (C7) cervical vertebrae and the second thoracic vertebra (T2). The diaphragmatic motor evoked potential was also examined during midline and lateral (± 15 mm) trans-spinal magnetic stimulation to examine the lateral-midline effect. The results demonstrated that the amplitude of diaphragmatic motor evoked potential was not significantly different in response to C5, C7, or T2 trans-spinal magnetic stimulation. In addition, the sensitivity of the left and right diaphragms to trans-spinal magnetic stimulation was different, as reflected by a greater amplitude of the right diaphragmatic motor evoked potential during midline trans-spinal magnetic stimulation. Moreover, although midline trans-spinal magnetic stimulation could induce coactivation of the bilateral diaphragm, lateral trans-spinal magnetic stimulation can induce a greater motor evoked potential in the ipsilateral than the contralateral diaphragm. Finally, there was no significant sex effect on the diaphragmatic motor evoked potential induced by trans-spinal magnetic stimulation. These results suggest that trans-spinal magnetic stimulation using a figure-of-eight coil is feasible to induce diaphragmatic motor evoked potential, and there is a lateral-midline effect of trans-spinal magnetic stimulation on the bilateral diaphragm.NEW & NOTEWORTHY The present study investigated position effect of trans-spinal magnetic stimulation using figure-of-eight coil on diaphragm in healthy humans. The result demonstrated that midline trans-spinal magnetic stimulation induces coactivation of bilateral diaphragm, whereas lateral trans-spinal magnetic stimulation induces greater motor evoked potentials in the ipsilateral than the contralateral diaphragm. These results suggest that trans-spinal magnetic stimulation is feasible to induce diaphragmatic motor evoked potential, and there is a lateral-midline effect of trans-spinal magnetic stimulation on diaphragm.