title: Vascular conductance and muscle blood flow during exercise are altered by inspired oxygen fraction and arterial perfusion pressure.
abstract: We tested the hypothesis during the combined challenges of altered inspired O2fraction (FIO2) and posture changes at lower power output regardless of body position that the vascular conductance (VC) recruitment to the exercising muscle would not limit muscle perfusion and estimated O2delivery (DO2est). However, in head-down tilt at the higher power output exercise in hypoxia, the recruitment of VC would have a functional limitation which would restrict muscle blood flow (MBF) leading to a limitation in DO2estwith consequent increases in metabolic stress. Ten healthy volunteers repeated plantar flexion contractions at 20% (low power output = LPO) and 30% (higher power output = HPO) of their maximal voluntary contraction in horizontal (HOR), 35° head-down-tilt (HDT) and 45° head-up-tilt (HUT). Popliteal diameter and muscle blood flow velocity were measured by ultrasound determining MBF. VC was estimated by dividing MBF flow by MPP, and DO2estwas estimated by MBF times saturation. LPOHUTin hypoxia was associated with no changes in VC and MBF leading to reduced DO2estIn LPOHDTunder hypoxia, despite no apparent functional limitation in the VC recruitment, rise in MBF to maintain DO2estwas associated with marked increase in muscle electromyographic activity, indicating greater metabolic stress. In HPOHDTunder hypoxia, a functional limitation for the recruitment of VC constrained MBF and DO2estElevated muscle electromyographic signal in HPOHDTunder hypoxia was consistent with challenged aerobic metabolisms which contributed to a greater increase in the relative stress of the exercise challenge and advance the onset of muscle fatigue.
authors.affiliation: Division of Natural Sciences, Faculty of Health Sciences, Franklin Pierce University, Rindge, New Hampshire villarr@franklinpierce.edu.|Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada.|Coordenação de Aperfeiçoamento de Pessoal de Nivel Superior (CAPES), Brasilia DF, Brazil.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Villar
authors.affiliation: Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada.|Schlegel-University of Waterloo Research Institute for Aging, Waterloo, Ontario, Canada.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Hughson
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D004576:Electromyography; D015444:Exercise / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000098:blood supply*; D011187:Posture / Q000502:physiology; D012039:Regional Blood Flow / Q000502:physiology*; D055815:Young Adult
keywords: Doppler ultrasound; electromyography; hypoxia; maximal vasodilatory capacity; oxygen delivery