title: The effect of hypoxia on intra-ocular, mean arterial, retinal venous and ocular perfusion pressures.
abstract: BACKGROUND
  High altitude hypoxia is linked to decreased blood oxygen saturation with a related increase of Endothelin-1 (ET-1) blood plasma levels. As a consequence of such elevated ET-1 levels, alterations of retinal venous and ocular perfusion pressures are suspected.
  
  
  OBJECTIVE
  To measure the effect of hypoxia on intra-ocular pressure, mean arterial pressure, retinal venous pressure and to calculate ocular perfusion pressure.
  
  
  METHODS
  An experimental, prospective cohort study with 33 healthy subjects was conducted in which the subjects were confronted with long-term (days) environmental hypoxia at high altitudes. Mean arterial pressure, arterial blood oxygen saturation, intra-ocular pressure, retinal venous and ocular perfusion pressure were measured at 300 m/1'000 ft (baseline), 4200 m/13'800 ft and 6000 m/19'700 ft above sea level.
  
  
  RESULTS
  Arterial oxygen saturation (-13.06% ± 4.69, p = < 0.001; -23.46% ± 5.7,p = < 0.001), retinal venous pressure (+7.16 m Hg±8.2, p = < 0.001;+9.9 mm Hg±8.5, p = < 0.001) and ocular perfusion pressure (-8.49 mm Hg±10.6, p = < 0.001; -6.02 mm hg±11.2, p = 0.006) changed significantly from baseline at both high altitude of 4200 and 6000 m. Intra-ocular pressure did not change significantly at all altitudes (+1.16 mm Hg±4.5, p = 0.227; +0.84 mm Hg±4.8, p = 0.286) and mean arterial pressure changed significantly only at an altitude of 6000 m (+3,8 mm Hg±21.1, p = 0.005) from baseline.
  
  
  CONCLUSIONS
  As hypoxia increases with higher altitude, arterial oxygen saturation and ocular perfusion pressure decreased, retinal venous pressure increased, intra-ocular pressure remains stable and mean arterial pressure was elevated only at 6000 m.
authors.affiliation: University of Basel, Department of Ophthalmology, Basel, Switzerland.|SALUS University, Philadelphia, PA, USA.|Eyeness AG, Hirschengraben, Bern, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Baertschi
authors.affiliation: SALUS University, Philadelphia, PA, USA.
authors.forename: P
authors.initials: P
authors.lastname: Dayhaw-Barker
authors.affiliation: University of Basel, Department of Ophthalmology, Basel, Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Flammer
mesh_terms: D000328:Adult; D062186:Arterial Pressure / Q000502:physiology*; D015687:Cell Hypoxia; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D010100:Oxygen / Q000097:blood*; D010477:Perfusion; D011446:Prospective Studies; D012169:Retinal Vein / Q000503:physiopathology*
chemical_list: D010100:Oxygen
keywords: Endothelin; Hypoxia; Ophthalmo-Dynamometry; high altitudes; hypobaric; intra-ocular pressure; mean arterial pressure; ocular perfusion pressure; retinal venous pressure