title: Influence of hyperoxia and physical exercise on *OH-radical stress in humans as measured by dihydroxylated benzoates (DHB) in urine.
abstract: BACKGROUND
  Hyperoxia and physical exercise are known to produce reactive oxygen species (ROS), and the *OH radical is the most aggressive among them. However, knowledge is limited about *OH stress during physical work under hyperoxic conditions.
  
  
  METHODS
  This study monitored *OH stress in human volunteers before and after a total of 135 exposures to ambient air (control), different levels of hyperoxia at rest and challenging open-water closed-circuit dives by measurement of dihydroxylated benzoates (DHB) with HPLC by electrochemical detection in urine.
  
  
  RESULTS
  Changes in DHB in urine after control were only 3.43 +/- 4.8% (n = 9). After exposures to 100 kPa oxygen (O2) for 110 minutes DHB revealed increases in urine of 23.14 +/- 5.12% (n = 9); exposures to 240 kPa O2 for 90 minutes increases of 22.38 +/- 8.91% (n = 8); and 280 kPa 02 for 30 minutes of 21.92 +/- 10.76% (n = 17). Closed-circuit dives in open water (45-54 minutes of 125-160 kPa O2) revealed DHB increases of 66.34 +/- 25.73% (n = 92). All results differed significantly from control (p < 0.001). The closed-circuit dives also differed significantly from all exposures to hyperoxia without exercise (p < 0.001). Standardization of "oxygen burden" during each exposure (pO2 x exposure time x VO2) allowed for comparison of different exposures vs. DHB changes and revealed goodness of linear fit of r2 = 0.432 (p < 0.0001).
  
  
  CONCLUSIONS
  Increases in urine DHB after exposures to different levels of hyperoxia at rest and during exercise are consistent with *OH stress that is greater during exercise than at rest, although other interpretations are possible. Standardization of the individual "oxygen burden" for a given exposure may become useful in future for the estimation of *OH stress.
authors.affiliation: Section for Maritime Medicine of the Christian-Albrechts-University, German Naval Medical Institute, Kiel-Kronshagen, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Kähler
authors.forename: I
authors.initials: I
authors.lastname: Koch
authors.forename: C
authors.initials: C
authors.lastname: Wohlrab
authors.forename: J
authors.initials: J
authors.lastname: Kowalski
authors.forename: J
authors.initials: J
authors.lastname: Witte
authors.forename: A
authors.initials: A
authors.lastname: Koch
mesh_terms: D000328:Adult; D004242:Diving / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D062385:Hydroxybenzoates / Q000652:urine*; D017665:Hydroxyl Radical / Q000378:metabolism*; D006900:Hydroxylation; D006931:Hyperbaric Oxygenation / Q000379:methods; D018496:Hyperoxia / Q000652:urine*; D018384:Oxidative Stress; D010101:Oxygen Consumption; D055815:Young Adult
chemical_list: D062385:Hydroxybenzoates; D017665:Hydroxyl Radical