title: Retrograde blood flow in the inactive limb is enhanced during constant-load leg cycling in hypoxia.
abstract: OBJECTIVE
  This study aimed to elucidate the effects of hypoxia on the pattern of oscillatory blood flow in the inactive limb during constant-load dynamic exercise. We hypothesised that retrograde blood flow in the brachial artery of the inactive limb would increase during constant-load leg cycling under hypoxic conditions.
  
  
  METHODS
  Three maximal exercise tests were conducted in eight healthy males on a semi-recumbent cycle ergometer while the subjects breathed a normoxic [inspired oxygen fraction (FIO2) = 0.209] or two hypoxic gas mixtures (FIO2 = 0.155 and 0.120). Subjects then performed submaximal exercise at the same relative exercise intensity of 60 % peak oxygen uptake under normoxic or the two hypoxic conditions for 30 min. Brachial artery blood velocity and diameter were recorded simultaneously during submaximal exercise using Doppler ultrasonography.
  
  
  RESULTS
  Antegrade blood flow gradually increased during exercise, with no significant differences among the three trials. Retrograde blood flow showed a biphasic response, with an initial increase followed by a gradual decrease during normoxic exercise. In contrast, retrograde blood flow significantly increased during moderate and severe hypoxic exercise, and remained elevated above normoxic conditions during exercise. At 30 min of exercise, the magnitude of the change in retrograde blood flow during exercise was greater as the level of hypoxia increased (normoxia: -18.7 ± 23.5 ml min(-1); moderate hypoxia: -39.3 ± 21.4 ml min(-1); severe hypoxia: -64.0 ± 36.3 ml min(-1)).
  
  
  CONCLUSIONS
  These results indicate that moderate and severe hypoxia augment retrograde blood flow in the inactive limb during constant-load dynamic leg exercise.
authors.affiliation: Second Division of Physical Therapy, Department of Physical Therapy, School of Health Sciences, Sapporo Medical University, South1, West17, Chuo-ku, Sapporo, 060-8556, Japan, e.iwamoto@sapmed.ac.jp.
authors.forename: Erika
authors.initials: E
authors.lastname: Iwamoto
authors.forename: Keisho
authors.initials: K
authors.lastname: Katayama
authors.forename: Shin
authors.initials: S
authors.lastname: Yamashita
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Oshida
authors.forename: Koji
authors.initials: K
authors.lastname: Ishida
mesh_terms: D000328:Adult; D001916:Brachial Artery / Q000502:physiology*; D015444:Exercise; D006439:Hemodynamics; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D007866:Leg / Q000098:blood supply / Q000502:physiology*; D008297:Male; D009068:Movement; D010101:Oxygen Consumption; D012039:Regional Blood Flow