title: Effects of vagus nerve stimulation on respiration during sleep: a pilot study.
abstract: BACKGROUND
  Vagus nerve stimulation (VNS) is associated with respiratory effects such as hoarseness, dyspnea, and laryngeal irritation. The effects of VNS on sleep-related breathing in humans have not been reported previously.
  
  
  METHODS
  Four epilepsy patients underwent polysomnography (PSG) before and after 3 months of treatment with VNS. Two of the four patients also underwent follow-up PSG to assess the effects of changing stimulus parameters on sleep-related breathing.
  
  
  RESULTS
  All patients showed consistent sleep-related decreases in airflow and effort coinciding with VNS activation, although most events did not meet laboratory criteria for apneas or hypopneas. Apneas and hypopneas were more frequent during VNS activation than during nonactivation. Apnea-hypopnea index (AHI) for three subjects during VNS treatment PSG was <5 apneas and hypopneas/hour. In one patient with obstructive sleep apnea (OSA) before VNS treatment, AHI rose from 4 (pretreatment) to 11.3 (treatment). In this patient and in another patient without clinically significant OSA, lowering stimulus frequency, but not stimulus intensity, pulse width, or on-time, ameliorated VNS-related apneas and hypopneas.
  
  
  CONCLUSIONS
  VNS is associated with adverse changes in respiration during sleep. In patients without preexisting OSA, this VNS effect is probably not clinically significant. In patients with preexisting OSA, VNS should be administered with care. Lowering VNS stimulus frequency or prolonging off-time may prevent exacerbation of OSA.
authors.affiliation: Michael S. Aldrich Sleep Disorders Laboratory and the Epilepsy Program, Clinical Neurophysiology Section, Department of Neurology, University of Michigan Medical School, Ann Arbor, MI, USA. bmalow@umich.edu
authors.forename: B A
authors.initials: BA
authors.lastname: Malow
authors.forename: J
authors.initials: J
authors.lastname: Edwards
authors.forename: M
authors.initials: M
authors.lastname: Marzec
authors.forename: O
authors.initials: O
authors.lastname: Sagher
authors.forename: G
authors.initials: G
authors.lastname: Fromes
mesh_terms: D000328:Adult; D004558:Electric Stimulation; D004827:Epilepsy / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017286:Polysomnography; D012890:Sleep / Q000502:physiology*; D014630:Vagus Nerve / Q000503:physiopathology*