title: Post-hyperventilation hypoxaemia is due to alteration of ventilation and perfusion matching.
abstract: OBJECTIVE
  The aim of this study was to investigate the mechanisms of post-hyperventilation hypoxia.
  
  
  METHODS
  Seven healthy male volunteers, aged 29.1 +/- 1.4 years, underwent two 10-min periods of voluntary hyperventilation to pulmonary end tidal CO2 values of 20 mmHg (severe hyperventilation), or 30 mmHg (moderate hyperventilation). Post-hyperventilation, the arterial oxygen saturation, VE and arterial blood gas values were measured. Sleep was excluded by EEG monitoring.
  
  
  RESULTS
  Maximal hypoxaemia occurred in proportion to severity of hyperventilation; at approximately 5 min post-hyperventilation Pao2 fell to 64 +/- 7 mmHg (severe hyperventilation) and 72 +/- 6 mmHg (moderate hyperventilation) from 97 +/- 3 mmHg at baseline. Hypoxaemia persisted beyond the time of normalization of Paco2 and HCO3. On another occasion, a N2 washout test was performed after severe hyperventilation, which excluded bronchoconstriction.
  
  
  CONCLUSIONS
  Relative hypoventilation may partly explain post-hyperventilation hypoxaemia, but by excluding bronchoconstriction and periodic breathing, we have demonstrated that most of the hypoxaemia must have been due to alteration of pulmonary blood flow distribution causing a fall in V/Q ratio.
authors.affiliation: Department of Critical Care, Manly Hospital, Manly, New South Wales, Australia.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Nolan
authors.forename: Manox
authors.initials: M
authors.lastname: Saxena
authors.forename: Keith R
authors.initials: KR
authors.lastname: Burgess
authors.forename: Rein
authors.initials: R
authors.lastname: Simmel
authors.forename: Stanley
authors.initials: S
authors.lastname: Braude
mesh_terms: D000328:Adult; D001784:Blood Gas Analysis; D002153:Calorimetry, Indirect; D006801:Humans; D006985:Hyperventilation / Q000503:physiopathology*; D000860:Hypoxia / Q000209:etiology / Q000503:physiopathology*; D008297:Male; D011652:Pulmonary Circulation / Q000502:physiology; D014692:Ventilation-Perfusion Ratio / Q000502:physiology*