title: Retinal vessel regulation at high altitudes1.
abstract: OBJECTIVE
  To measure static and dynamic changes of retinal vessels in response to normobaric hypoxia (NH, study A) and hypobaric hypoxia (HH, study B).
  
  
  METHODS
  Study A included 10 healthy individuals exposed to a simulated altitude of 5500 meters in a NH chamber; study B included 17 individuals studied after ascent to 3000-meter altitude. Retinal vessel diameter, response to flicker light, retinal oxygen saturation and retinal venous pressure were measured at baseline, under the corresponding hypoxia condition. The effects of macitentan, an endothelin receptor antagonist, were examined in study B.
  
  
  RESULTS
  The mean age of participants was 34.6±9.3 years in study A and 36.7±10.8 years in study B. Retinal arterial and venous diameter increased, arterial and venous response to flicker light decreased, while retinal oxygen saturation remained stable under both experimental conditions. Retinal venous pressure increased in six individuals after ascent to 3000 meters and normalized after macitentan treatment. The occurrence of acute mountain sickness (AMS) correlated only with the decrease of arterial constriction after ascent to 3000 meters.
  
  
  CONCLUSIONS
  Retinal arterial and venous vessels react to NH and HH with a diameter increase and an impaired response to flicker light. Macitentan was capable to normalize the increased retinal venous pressure observed at high altitudes.
authors.affiliation: Department of Internal Medicine III, Jena University Hospital, Jena, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Neumann
authors.affiliation: Department of Ophthalmology, University of Basel, Switzerland.|Eyeness AG, Bern, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Baertschi
authors.affiliation: IMEDOS Systems UG, Jena, Germany.
authors.forename: Walthard
authors.initials: W
authors.lastname: Vilser
authors.affiliation: Klinik Buchinger Wilhelmi, Überlingen, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Drinda
authors.affiliation: Department of Internal Medicine I, Jena University Hospital, Jena, Germany.
authors.forename: Marcus
authors.initials: M
authors.lastname: Franz
authors.affiliation: Klinik Buchinger Wilhelmi, Überlingen, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Brückmann
authors.affiliation: Department of Internal Medicine III, Jena University Hospital, Jena, Germany.
authors.forename: Gunter
authors.initials: G
authors.lastname: Wolf
authors.affiliation: University Hospital Düsseldorf, Heinrich-Heine-University Düsseldorf, Medical Faculty, Division of Cardiology, Pulmonology and Vascular Medicine, Düsseldorf, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Jung
mesh_terms: D000328:Adult; D000368:Aged; D000531:Altitude; D015687:Cell Hypoxia / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012171:Retinal Vessels / Q000002:abnormalities* / Q000473:pathology; D055815:Young Adult
keywords: Digital vessel analysis; high altitude; hypoxia; macitentan; retinal; retinal venous pressure