title: Physical exercise might influence the risk of oxygen-induced acute neurotoxicity.
abstract: OBJECTIVE
  Hyperoxia can induce acute neurotoxicity with generalized seizures. Hyperoxia-induced reduction in cerebral blood flow velocity (CBFV) might be protective. It is unclear whether dynamic exercise during hyperoxia can overcome CBFV-reduction and thus possibly increase the risk of neurotoxicity.
  
  
  METHODS
  We studied CBFV with both-sided transcranial Doppler with fixed transducer-position and heart rate under increasing hyperoxic conditions in nine professional military oxygen divers. The divers performed dynamic exercise on a bicycle-ergometer in a hyperbaric chamber (ergometries I-III, 21kPa, 100kPa, 150kPa pO2), with continuous blood pressure (ergometries I, II), end-tidal CO2 (PetCO2; ergometry I) being measured.
  
  
  RESULTS
  Systolic (CBFVsyst) and diastolic CBFV (CBFVdiast) readings at rest decreased with increasing pO2. During exercise, CBFVsyst and CBFVdiast significantly increased in parallel with increasing pO2, despite reduced flow velocities at rest.
  CBFVsyst increased from 65.0 +/- 11.3 cm/second at rest to 80.2 +/- 23.4cm/s during maximum workload (n.s.), diastolic from 14.5 +/- 4.1 cm/second to 15.6 +/- 7.5 cm/s (n.s.). PetCO2 increased from 43.4 +/- 7.8mmHg to 50.0 +/- 7.5mmHg.
  CBFVsyst increased from 58.2 +/- 16.5 cm/second to 99.7 +/- 17.0 cm/s (p<0.001), diastolic from 14.0 +/- 10.7 cm/second to 29.4 +/- 11.1 cm/second (p<0.01).
  CBFVsyst increased from 54.4 +/-15.0cm/second to 109.4 +/- 22.3cm/s (p<0.001), diastolic from 14.7 +/- 10.4 cm/second to 35.5 +/- 9.3 cm/second (p<0.01).
  
  
  CONCLUSIONS
  Physical exercise overrules the decrease in CBFV during hyperoxia and leads to even higher CBFV-increases with increasing pO2. A tendency towards CO2 retainment with elevated PetCOz may be causative and thus heighten the risk of oxygen-induced neurotoxicity.
authors.affiliation: SGerman Naval Medical Institute - Section for Maritime Medicine, Christian-Albrechts-University of Kiel, Germany. a.koch@iem.uni-kiel.de
authors.forename: A E
authors.initials: AE
authors.lastname: Koch
authors.forename: I
authors.initials: I
authors.lastname: Koch
authors.forename: J
authors.initials: J
authors.lastname: Kowalski
authors.forename: J D
authors.initials: JD
authors.lastname: Schipke
authors.forename: B E
authors.initials: BE
authors.lastname: Winkler
authors.forename: G
authors.initials: G
authors.lastname: Deuschl
authors.forename: J
authors.initials: J
authors.lastname: Meyne
authors.forename: W
authors.initials: W
authors.lastname: Kähler
mesh_terms: D000328:Adult; D001273:Atmosphere Exposure Chambers; D001783:Blood Flow Velocity / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D002245:Carbon Dioxide / Q000097:blood*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003971:Diastole / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000379:methods; D005858:Germany; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D006931:Hyperbaric Oxygenation / Q000295:instrumentation; D018496:Hyperoxia / Q000097:blood / Q000503:physiopathology*; D008889:Military Personnel; D012640:Seizures / Q000209:etiology; D013599:Systole / Q000502:physiology; D017585:Ultrasonography, Doppler, Transcranial / Q000379:methods
chemical_list: D002245:Carbon Dioxide