title: Regulation of human skeletal muscle perfusion and its heterogeneity during exercise in moderate hypoxia.
abstract: Although many effects of both acute and chronic hypoxia on the circulation are well characterized, the distribution and regulation of blood flow (BF) heterogeneity in skeletal muscle during systemic hypoxia is not well understood in humans. We measured muscle BF within the thigh muscles of nine healthy young men using positron emission tomography during one-leg dynamic knee extension exercise in normoxia and moderate physiological systemic hypoxia (14% O(2) corresponding to approximately 3,400 m of altitude) without and with local adenosine receptor inhibition with femoral artery infusion of aminophylline. Systemic hypoxia reduced oxygen extraction of the limb but increased muscle BF, and this flow increment was confined solely to the exercising quadriceps femoris muscle. Exercising muscle BF heterogeneity was reduced from rest (P = 0.055) but was not affected by hypoxia. Adenosine receptor inhibition had no effect on capillary BF during exercise in either normoxia or hypoxia. Finally, one-leg exercise increased muscle BF heterogeneity both in the resting posterior hamstring part of the exercising leg and in the resting contralateral leg, whereas mean BF was unchanged. In conclusion, the results show that increased BF during one-leg exercise in moderate hypoxia is confined only to the contracting muscles, and the working muscle hyperemia appears not to be directly mediated by adenosine. Increased flow heterogeneity in noncontracting muscles likely reflects sympathetic nervous constraints to curtail BF increments in areas other than working skeletal muscles, but this effect is not potentiated in moderate systemic hypoxia during small muscle mass exercise.
authors.affiliation: Turku PET Centre, Turku University Hospital, University of Turku, Turku, Finland. ilkka.heinonen@tyks.fi
authors.forename: Ilkka H
authors.initials: IH
authors.lastname: Heinonen
authors.forename: Jukka
authors.initials: J
authors.lastname: Kemppainen
authors.forename: Kimmo
authors.initials: K
authors.lastname: Kaskinoro
authors.forename: Juha E
authors.initials: JE
authors.lastname: Peltonen
authors.forename: Ronald
authors.initials: R
authors.lastname: Borra
authors.forename: Markus
authors.initials: M
authors.lastname: Lindroos
authors.forename: Vesa
authors.initials: V
authors.lastname: Oikonen
authors.forename: Pirjo
authors.initials: P
authors.lastname: Nuutila
authors.forename: Juhani
authors.initials: J
authors.lastname: Knuuti
authors.forename: Robert
authors.initials: R
authors.lastname: Boushel
authors.forename: Kari K
authors.initials: KK
authors.lastname: Kalliokoski
mesh_terms: D000241:Adenosine / Q000494:pharmacology; D000328:Adult; D000531:Altitude; D002196:Capillaries / Q000503:physiopathology; D015444:Exercise / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D006940:Hyperemia / Q000000981:diagnostic imaging; D000860:Hypoxia / Q000000981:diagnostic imaging / Q000503:physiopathology*; D007866:Leg / Q000098:blood supply / Q000502:physiology / Q000503:physiopathology; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000000981:diagnostic imaging / Q000502:physiology*; D010100:Oxygen / Q000097:blood; D010477:Perfusion; D052097:Quadriceps Muscle / Q000098:blood supply* / Q000503:physiopathology; D011877:Radionuclide Imaging; D018047:Receptors, Purinergic P1 / Q000378:metabolism; D012146:Rest / Q000502:physiology; D013564:Sympathetic Nervous System / Q000502:physiology / Q000503:physiopathology
chemical_list: D018047:Receptors, Purinergic P1; D000241:Adenosine; D010100:Oxygen