title: Exercise limb blood flow response to acute and chronic hypoxia in Danish lowlanders and Aymara natives.
abstract: OBJECTIVE
  The femoral artery blood flow response to submaximal, one-legged, dynamic, knee-extensor exercise was determined in acute and chronic hypoxia to investigate the hypotheses that with adaptation to chronic hypoxia blood haemoglobin increases, allowing preservation of blood flow as in normoxia.
  
  
  METHODS
  Sixteen Danish lowlanders participated, in groups of six to eight, in the experiments at sea level normoxia (FiO2 congruent with 0.21) and acute hypoxia (FiO2 congruent with 0.11), and chronic hypoxia after approximately 7 and 9-10 weeks at approximately 5260 m altitude breathing ambient air (FiO2 congruent with 0.21) or a hyperoxic gas (FiO2 congruent with 0.55). The response was compared with that in six Aymara natives.
  
  
  RESULTS
  The haemoglobin and haematocrit increased (P < 0.003) in the lowlanders at altitude vs. at sea level by approximately 39 and 27% respectively; i.e. to a similar (P = ns) level as in the natives. At rest, blood flow was the same (P = ns) in the lowlanders at sea level and altitude, as in the natives at altitude. During the onset of and incremental exercise, blood flow was the same (P = ns) in the lowlanders at sea level and altitude, as in the natives at altitude. Acute hypoxia increased (P < 0.05) blood flow by approximately 55% during exercise in the lowlanders at sea level. Acute hyperoxia decreased (P < 0.05) blood flow by approximately 22-29% during exercise in the lowlanders and natives at altitude.
  
  
  CONCLUSIONS
  In chronic hypoxia, blood haemoglobin increases, allowing normalization of the elevated exercise blood flow response in acute hypoxia, and preservation of the kinetics and steady-state exercise blood flow as in normoxia, being similar as in the natives at altitude.
authors.affiliation: The Copenhagen Muscle Research Centre, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark. goranradegran@hotmail.com
authors.forename: G
authors.initials: G
authors.lastname: Rådegran
mesh_terms: D000531:Altitude; D001838:Bolivia; D002908:Chronic Disease; D003718:Denmark; D015444:Exercise / Q000502:physiology*; D005260:Female; D005263:Femoral Artery / Q000502:physiology*; D006454:Hemoglobins; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D007866:Leg / Q000098:blood supply*; D008297:Male; D044382:Population Groups
chemical_list: D006454:Hemoglobins