title: The effects of breath-holds and Muller manoeuvres on upper airway carbon dioxide concentration in humans.
abstract: BACKGROUND
  Obstructive sleep apnoea is caused by collapse of the upper airway. The presence of CO(2) in the upper airway lumen evokes a number of reflexes which favour upper airway re-opening, and we have proposed previously that CO(2) would build up in the upper airway following airway collapse and that this would contribute to reflex airway re-opening. However, it is not known if CO(2) can transfer from the alveoli to the anatomical dead space of the upper airway during apnoea.
  
  
  OBJECTIVE
  To determine if alveolar CO(2) can enter the upper airway during breath-holds and Muller manoeuvres.
  
  
  METHODS
  With local ethics committee approval, 6 male volunteers (aged 22-48 years), following a quiet inspiration, carried out breath-holds and Muller manoeuvres until breaking point. CO(2) was measured continuously in samples obtained from the hypopharynx using an infrared analyser with a sample rate of 50 ml/min. Muller manoeuvres (forced inspirations against a closed upper airway) mimic the respiratory efforts which occur during obstructive apnoeas.
  
  
  RESULTS
  In all cases, CO(2) increased progressively during apnoeas. There was a much larger increase in Muller manoeuvres (3.78 +/- 0.51%, mean +/- SEM at breaking point) compared to breath-holds.
  
  
  CONCLUSIONS
  These results show that upper airway CO(2) concentration rises substantially during apnoeas and suggest that transfer of CO(2) from the lungs to the upper airway may evoke a number of reflex effects which could affect breathing and upper airway re-opening during obstructive apnoeas.
authors.affiliation: Department of Anatomy, Royal College of Surgeons in Ireland, University College Dublin, Dublin, Ireland.
authors.forename: A
authors.initials: A
authors.lastname: Raza
authors.forename: T
authors.initials: T
authors.lastname: Farrell
authors.forename: K D
authors.initials: KD
authors.lastname: O'Halloran
authors.forename: A
authors.initials: A
authors.lastname: Bradford
mesh_terms: D000328:Adult; D002245:Carbon Dioxide / Q000378:metabolism*; D006801:Humans; D007013:Hypopharynx / Q000502:physiology; D008297:Male; D008875:Middle Aged; D012123:Pulmonary Ventilation / Q000502:physiology; D012119:Respiration; D012126:Respiratory Dead Space / Q000502:physiology; D020181:Sleep Apnea, Obstructive / Q000378:metabolism* / Q000503:physiopathology
chemical_list: D002245:Carbon Dioxide