title: Peripheral arterial vascular function at altitude: sea-level natives versus Himalayan high-altitude natives.
abstract: OBJECTIVE
  Regulation of the vascular system may limit physical performance and contribute to adaptation to high altitude. We evaluated vascular function in 10 Himalayan high-altitude natives and 10 recently acclimatized sea-level natives at an altitude of 5,050 m.
  
  
  METHODS
  We registered electrocardiogram, blood flow velocity in the common femoral artery, and blood pressure in the radial artery using non-invasive methods under baseline conditions, and during maximal vasodilation after 2 min leg occlusion. Vascular mechanics were characterized by estimating pulse wave velocity and input impedance.
  
  
  RESULTS
  Pulse wave velocity and parameters of input impedance did not differ between groups under baseline conditions. In the post-ischemic period, the ratio between maximal hyperemic and baseline blood flow velocity was significantly higher in the high-altitude than in the sea-level natives (5.7 +/- 2.5 versus 3.8 +/- 1.2, P < 0.05). The leg vascular resistance decreased in the post-occlusive period without differences between groups. Characteristic impedance decreased in the post-ischemic period by about one third of the baseline level without differences between groups. The post-ischemic decrease of input impedance modulus was more marked in the high-altitude than in the sea-level natives at low frequencies (28 +/- 12 versus 6.4 +/- 20% at 2 Hz, P < 0.01).
  
  
  CONCLUSIONS
  Our results demonstrate a superior ability to increase blood flow velocity as a response to muscular ischemia in high-altitude natives compared to sea-level natives. This phenomenon may be associated with a more effective coupling between blood pressure and blood flow which is probably caused by differences in conduit vessel function.
authors.affiliation: Department of Anesthesiology, University Medical Centre Regensburg, University of Regensburg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Schneider
authors.forename: R E
authors.initials: RE
authors.lastname: Greene
authors.forename: C
authors.initials: C
authors.lastname: Keyl
authors.forename: G
authors.initials: G
authors.lastname: Bandinelli
authors.forename: C
authors.initials: C
authors.lastname: Passino
authors.forename: G
authors.initials: G
authors.lastname: Spadacini
authors.forename: M
authors.initials: M
authors.lastname: Bonfichi
authors.forename: L
authors.initials: L
authors.lastname: Arcaini
authors.forename: L
authors.initials: L
authors.lastname: Malcovati
authors.forename: A
authors.initials: A
authors.lastname: Boiardi
authors.forename: P
authors.initials: P
authors.lastname: Feil
authors.forename: L
authors.initials: L
authors.lastname: Bernardi
mesh_terms: D000293:Adolescent; D000328:Adult; D000531:Altitude; D001158:Arteries / Q000502:physiology*; D001783:Blood Flow Velocity; D001794:Blood Pressure; D017097:Electric Impedance; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged