Motor evoked potentials of the human diaphragm elicited through magnetic transcranial brain stimulation

Magnetic transcranial brain stimulation has been used for several years now to study the function and integrity of the corticospinal tracts. In this study magnetic transcranial motor cortex stimulation of the diaphragm was carried out in order to describe the characteristics of the recorded motor evoked potentials (MEPs) of this muscle in humans. The motor cortex was stimulated transcranially in 10 healthy subjects, followed by stimulation of the cervical roots so that central motor conduction time (CMCT) could be calculated. Diaphragm MEPs were recorded at deep inspriration. Normal values were found to be 16.21 +/- 0.33 msec for the MEP latency time, 3.52 +/- 2.40 mV for the MEP amplitude, and 8.39 +/- 0.41 msec. for the CMCT. This study confirms the direct projection from the motor cortex to the human diaphragm and the ability of cortical magnetic stimuli to evoke more descending volleys along the corticospinal pathways. This technique can offer useful additional information about the function and integrity of central motor conduction properties of respiratory muscles in humans with various neurological and respiratory disorders.