title: Effect of hypercapnia on sleep and breathing in unanesthetized cats.
abstract: OBJECTIVE
  In this study, we looked at the effect of hypercapnia on sleep architecture and breathing. We characterized the effect of hypercapnia on duration, frequency, and latency of NREM and REM sleep. We described state-specific patterns of breathing as well. This study is relevant to understand possible treatments for sleep disordered breathing.
  
  
  METHODS
  Four cats were studied during 3-hour sessions while breathing 0%, 2%, 4%, and 6% CO2 in room air. Each animal was studied 4 days per week for a period of 4 weeks. The animals breathed through a tube inserted into the trachea via a surgically created fistula. Respiration was measured using pneumotachography, and brain activity was recorded from implanted electrodes to discriminate states of sleep and wakefulness.
  
  
  RESULTS
  Two percent inspired CO2 increased sleep duration and decreased time awake. On the other hand, 6% CO2 induced a worsening of sleep parameters: the duration of wakefulness increased by 24.2%. As a response to hypercapnia, tidal volume (V(T)), minute ventilation (V(E)), and respiratory effort (V(T)/T(I)) increased proportionally in all states with increasing levels of CO2. With 6% CO2, breathing tended to become similar in all states of consciousness. All breathing parameters converged towards a common value independently of the states.
  
  
  CONCLUSIONS
  We conclude that a mild hypercapnic stimulus can stimulate both breathing and sleep, and it may be useful in treatment of sleep disordered breathing.
authors.affiliation: Texas Tech University Health Sciences Center School of Medicine, Department of Cell Physiology and Molecular Biophysics, Lubbock, TX, USA. jimmy.fraigne@ttuhsc.edu
authors.forename: Jimmy J
authors.initials: JJ
authors.lastname: Fraigne
authors.forename: Witali L
authors.initials: WL
authors.lastname: Dunin-Barkowski
authors.forename: John M
authors.initials: JM
authors.lastname: Orem
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000097:blood*; D002415:Cats; D002540:Cerebral Cortex / Q000502:physiology; D017286:Polysomnography; D012123:Pulmonary Ventilation / Q000502:physiology; D011930:Reaction Time / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D012890:Sleep / Q000502:physiology*; D012895:Sleep, REM / Q000502:physiology*; D014851:Wakefulness / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide