title: Acute normobaric hyperoxia transiently attenuates plasma erythropoietin concentration in healthy males: evidence against the 'normobaric oxygen paradox' theory.
abstract: OBJECTIVE
  The purpose of the present study was to evaluate the 'normobaric oxygen paradox' theory by investigating the effect of a 2-h normobaric O(2) exposure on the concentration of plasma erythropoietin (EPO).
  
  
  METHODS
  Ten healthy males were studied twice in a single-blinded counterbalanced crossover study protocol. On one occasion they breathed air (NOR) and on the other 100% normobaric O(2) (HYPER). Blood samples were collected Pre, Mid and Post exposure; and thereafter, 3, 5, 8, 24, 32, 48, 72 and 96 h, and 1 and 2 weeks after the exposure to determine EPO concentration.
  
  
  RESULTS
  The concentration of plasma erythropoietin increased markedly 8 and 32 h after the NOR exposure (approx. 58% and approx. 52%, respectively, P ≤ 0.05) as a consequence of its natural diurnal variation. Conversely, the O(2) breathing was followed by approx. 36% decrement of EPO 3 h after the exposure (P ≤ 0.05). Moreover, EPO concentration was significantly lower in HYPER than in the NOR condition 3, 5 and 8 h after the breathing intervention (P ≤ 0.05).
  
  
  CONCLUSIONS
  In contrast to the 'normobaric oxygen paradox' theory, the present results indicate that a short period of normobaric O(2) breathing does not increase the EPO concentration in aerobically fit healthy males. Increased O(2) tension suppresses the EPO concentration 3 and 5 h after the exposure; thereafter EPO seems to change in a manner consistent with natural diurnal variation.
authors.affiliation: Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia. mkeram@phed.uoa.gr  
authors.forename: M E
authors.initials: ME
authors.lastname: Keramidas
authors.forename: S N
authors.initials: SN
authors.lastname: Kounalakis
authors.forename: T
authors.initials: T
authors.lastname: Debevec
authors.forename: B
authors.initials: B
authors.lastname: Norman
authors.forename: T
authors.initials: T
authors.lastname: Gustafsson
authors.forename: O
authors.initials: O
authors.lastname: Eiken
authors.forename: I B
authors.initials: IB
authors.lastname: Mekjavic
mesh_terms: D000328:Adult; D018592:Cross-Over Studies; D004921:Erythropoietin / Q000097:blood*; D006801:Humans; D018496:Hyperoxia / Q000097:blood*; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D016037:Single-Blind Method; D055815:Young Adult
chemical_list: D004921:Erythropoietin; D010100:Oxygen