Trans-spinal magnetic stimulation induces co-activation of the diaphragm and biceps in healthy subjects.

The present study was designed to examine the effect of trans-spinal magnetic stimulation on bilateral respiratory and forelimb muscles in healthy subjects. Two wings of a figure-of-eight magnetic coil were placed on the dorsal vertebrae, from the fifth cervical to the second thoracic dorsal vertebra with a center at the seventh cervical vertebra. The surface electromyograms of bilateral diaphragm and biceps were recorded in response to trans-spinal magnetic stimulation with 20%-100% maximum output of the stimulatory device in male (n = 12) and female participants (n = 8). Trans-spinal magnetic stimulation can induce a co-activation of bilateral diaphragm and biceps when the stimulation intensity is above 60%. The onset latency was comparable between the left and right sides of the muscles, suggesting bilateral muscles could be simultaneously activated by trans-spinal magnetic stimulation. In addition, the intensity-response curve of the biceps was shifted upward compared with that of the diaphragm in males, indicating that the responsiveness of the biceps was greater than that of the diaphragm. This study demonstrated the feasibility of utilizing trans-spinal magnetic stimulation to co-activate the bilateral diaphragm and biceps. We proposed that this stimulatory configuration can be an efficient approach to activate both respiratory and forelimb muscles.

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.

Rostral-Caudal Effect of Cervical Magnetic Stimulation on the Diaphragm Motor Evoked Potential after Cervical Spinal Cord Contusion in the Rat.

The present study was designed to investigate the rostral-caudal effect of spinal magnetic stimulation on diaphragmatic motor-evoked potentials after cervical spinal cord injury. The diaphragm electromyogram was recorded in rats that received a laminectomy or a left midcervical contusion at the acute (1 day), subchronic (2 weeks), or chronic (8 weeks) injury stages. The center of a figure-eight coil was placed at 30 mm lateral to bregma on the left side, and the effect of magnetic stimulation was evaluated by stimulating the rostral, middle, and caudal cervical regions in spontaneously breathing rats. The results demonstrated that cervical magnetic stimulation induced intensity-dependent motor-evoked potentials in the bilateral diaphragm in both uninjured and contused rats; however, the left diaphragm exhibited a higher amplitude and earlier onset than the right diaphragm. Moreover, the intensity-response curve was shifted upward in the rostral-to-caudal direction of magnetic stimulation, suggesting that caudal cervical magnetic stimulation produced more robust diaphragmatic motor-evoked potentials compared with rostral cervical magnetic stimulation. Interestingly, the diaphragmatic motor-evoked potentials were similar between uninjured and contused rats during cervical magnetic stimulation despite weaker inspiratory diaphragmatic activity in contused rats. In addition, in contused animals but not uninjured animals, diaphragmatic motor-evoked potential amplitudes were greater at the chronic stage than during earlier injury stages. These results demonstrated that cervical magnetic stimulation can excite the residual phrenic motor circuit to activate the diaphragm in the presence of a significant lesion in the cervical spinal cord. These findings indicate that this non-invasive approach is effective for modulating diaphragmatic excitability after cervical spinal cord injury.