title: Left vagus nerve stimulation with the neurocybernetic prosthesis has complex effects on heart rate and on its variability in humans.
abstract: OBJECTIVE
  The purpose of this study was to determine if stimulation of the left vagus nerve (LVNS) with the neurocybernetic prosthesis (NCP) in humans is, as claimed in the literature, without cardiac chronotropic actions.
  
  
  METHODS
  We analyzed 228 h of ECG recorded from five subjects with intractable epilepsy who had not benefited from LVNS, for effects on instantaneous heart rate (IHR) and heart rate variability (HRV).
  
  
  RESULTS
  There were two main cardiac responses: (a) bradycardia, and (b) tachycardia during the first half, followed by bradycardia during the second half of stimulation (biphasic response). Multiphasic responses characterized by alternating bradycardia and tachycardia were rarely observed. HRV was either increased or decreased depending on the subject and on the stimulation parameters. HRV as a function of HR also showed high interindividual variability, 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, which show large interindividual variability. These spectra of cardiac responses reflect the interplay of autonomic, visceral, and somatic sensory afferences and the role of central structures in their integration. These findings also point to the need for more comprehensive studies of cardiac function in humans implanted with the NCP, using sensitive methods for data processing and analysis such as those developed for this study.
authors.affiliation: Flint Hills Scientific, L.L.C., Lawrence, Kansas, USA.
authors.forename: M G
authors.initials: MG
authors.lastname: Frei
authors.forename: I
authors.initials: I
authors.lastname: Osorio
mesh_terms: D000328:Adult; D003491:Cybernetics / Q000379:methods; D004599:Electric Stimulation Therapy / Q000379:methods*; D004562:Electrocardiography / Q000706:statistics & numerical data*; D004827:Epilepsy / Q000628:therapy*; D005260:Female; D006321:Heart / Q000294:innervation / Q000502:physiology; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic / Q000706:statistics & numerical data; D011300:Preoperative Care; D019736:Prostheses and Implants; D014630:Vagus Nerve / Q000502:physiology*