Respiration triggered trans-spinal magnetic stimulation in healthy subjects.

Respiratory muscle dysfunction is usually observed in several neurological and pulmonary disorders. Consequently, it is essential to develop a clinically applicable strategy aimed at enhancing diaphragm excitability. The main objective of this study is to establish a respiration triggered trans-spinal magnetic stimulation protocol, and compare diaphragmatic motor evoked potentials during expiration-inspiration vs. inspiration-expiration transition. Bilateral diaphragm electromyograms were monitored in response to trans-spinal magnetic stimulation triggered by respiratory signals detected by the respiratory belt attached on the chest in 11 males and 10 females. The results demonstrated that bilateral diaphragmatic motor evoked potentials induced by trans-spinal magnetic stimulation gradually increased with increasing stimulation intensity in both male and female subjects. The response of diaphragmatic motor evoked potentials was greater when the stimulation was applied during inspiration-expiration transition in males; however, the modulatory effect of respiratory phase transition during trans-spinal magnetic stimulation was not observed in females. These findings suggested that respiration triggered trans-spinal magnetic stimulation is a feasible and non-invasively approach for selectively activating spinal circuits at a specific time point of the respiratory cycle to effectively induce greater diaphragmatic motor evoked potentials.