Effects of vagal electrical stimulation on the heart rate power spectra in humans

Electrical stimulation of the left vagus nerve through an implanted pacemaker for treating patients with intractable epileptic seizures offers a unique opportunity to examine the effects of vagal electrical stimulation on the heart rate power spectra. The authors studied eight patients before surgical implantation and at 2 weeks and 1 year after the stimulator was turned on. In four patients the stimulator was set to 2 Hz, 0.1 mA. For others the stimulation parameters were 30 Hz and 1.0 mA. The heart rate power spectra (PS/HRV) were computed for all patients. The sympathovagal balance was expressed as the ratio of low frequency to high frequency areas (LF:HF area) in the PS/HRV. In the low stimulation group the heart rate and its power spectral parameters did not change significantly. In the high stimulation group there was a significant decrease in the LF:HF area. The results suggest that electrical stimulation of the vagus nerve produces enhanced and sustained vagotonic effects on the sinus node activity which is maintained for at least 1 year after the implantation of the pacemaker