Effect of Vagal Nerve Electrostimulation on the Power Spectrum of Heart Rate Variability in Man

Abstract

The power spectrum of heart rate variability contains low frequency (LF = 0.08-0.12 Hz) and high frequency (HF = 0.18-0.30 Hz) components said to represent neurocardiac rhythms. To verify whether such a relationship exists we report a unique study where the heart rate autospectrum was determined in a 28-year-old epileptic male patient with an implanted vagal electrical stimulator. The stimulator was activated at 20 Hz, 300 microseconds pulse, and 1.25 V. Continuous ECG and respiratory waveform records were obtained over 45 minutes every 8 hours (7-8 AM; 3-4 PM; 11-12 PM) with the stimulator ON, then 24 hours OFF and then 24 hours ON again. The overall LF:HF peak ratio increased from 0.64 to 1.99 (P less than 0.001) after the stimulator was turned OFF. There was a dramatic increase in the LF peak power (greater than 60%) and a corresponding decrease in the HF peak power (greater than 65%) when the stimulator was turned OFF. These values were reversed when the stimulator was turned ON again. In the early morning and late evening hours, there was a significant rightward shift in the LF peak power frequency (average 0.057 to 0.075 Hz) whenever the stimulator was ON. Otherwise, there were no significant circadian variations in any of the autospectral components. The results demonstrate an unequivocal relationship between selective vagal nerve electrostimulation and alterations in the heart rate autospectrum.

Effect of Constant and Intermittent Vagal Stimulation on the Heart Rate and Heart Rate Variability in Rabbits.

“…These results suggest that the HF component in HRV may not reflect the intensity of VS or probably vagal tone, irrespective of the presence of an intact or denervated autonomic nerve system. In contrast, Kamath et al [10] have reported that continuous VS for more than several hours increased HF power, but did not prolong the RR interval in only one patient with intractable epilepsy. The observed discrepancy may be attributable to setting, including anesthesia, denervation or stimulation protocol.…”

Pre-ictal heart rate variability assessment of epileptic seizures by means of linear and non-linear analyses

“…This dysfunction results in higher morbidity and mortality in patients with epilepsy than in those without epilepsy (17). Frequency-domain analysis of heart rate variability (HRV) is a sophisticated and noninvasive tool for detecting autonomic regulation of the heart (11,14,(18)(19)(20)(21)(22)(23)(24).…”

Increased vagal tone accounts for the observed immune paralysis in patients with traumatic brain injury

“…A unique in vivo experiment that illustrates this balance was conducted in patients with an implanted electrical vagus nerve stimulator for the treatment of epilepsy. 28 In these subjects, HF power and HF/LF ratio were greatly increased when the stimulator was activated, illustrating that these measures are reliable indicators of vagal activity in humans. Nevertheless, caution should be taken when evaluating these parameters because other workers have indicated that parasympathetic outflow and other factors such as baroreceptor activity also influence LF power, thus stating that LF power represents a combination of sympathetic and parasympathetic input.…”