Left vagus nerve stimulation with the neurocybernetic prosthesis has complex effects on heart rate and on its variability in humans

Purpose: The purpose of this study was to determine if stimulation of the l eft vagus nerve (LVNS) with the neurocybernetic prosthesis (NCP) in humans is, as claimed in the literature. without cardiac chronotropic actions. Met hods: We analyzed 228 h of ECG recorded from five subjects with intractable epilepsy who had not benefited front LVNS, for effects on instantaneous he art rate (IHR) and heart rate variability (HRV). Results: There were two main cardiac responses: (a) bradycardia. and (b) ta chycardia during the first half, followed by bradycardia during the second half of stimulation (biphasic response). Multiphasic responses characterize d by alternating bradycardia and tachycardia were rarely observed. HRV was either increased or decreased depending on the subject and on the stimulati on parameters. HRV as a function of HR also showed high interindividual var iability, and interestingly, in one case behaved paradoxically, increasing at higher and decreasing at lower heart rates. Conclusions: LVNS at high intensities has complex effects on IHR and HRV, w hich show large interindividual variability. These spectra of cardiac respo nses reflect the interplay of autonomic, visceral, and somatic sensory affe rences and the role of central structures in their integration. These findi ngs also point to the need for more comprehensive studies of cardiac functi on in humans implanted with the NCP, using sensitive methods for data proce ssing and analysis such as those developed for this study.