The cerebral hemodynamics of repetitive transcranial magnetic stimulation

Repetitive transcranial magnetic stimulation (rTMS) has been shown to be effective in the treatment of affective disorders. However, only little is known about hemodynamic physiological and safety aspects of this method. We studied the cerebral hemodynamics as measured by transcranial Doppler sonography in 20 healthy subjects during different rTMS procedures. Mean cerebral blood flow velocity (CBFV), pulsatility index (PI), and oxygen consumption were recorded continuously and averaged directly after the rTMS procedure. RTMS did not influence blood pressure, pulse rate, or blood oxygenation. There was a maximal increase of CBFV in the middle cererbal artery (MCA) of 3.6% and 5.6% during 10 Hz and 20 Hz stimulation, respectively. This increase was only seen on the stimulated left hemisphere. The PI remained unchanged during the whole procedure. It is likely that the increase of CBFV is due to dilatation of the small resistance vessels rather than due to vasoconstriction of the MCA. In terms of cerebral hemodynamics, rTMS is a safe and well-tolerated technique with a lower increase of CBFV than that seen in electroconvulsive therapy.