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Related Experiment Videos

Leg vasoconstriction during dynamic exercise with reduced cardiac output.

J A Pawelczyk1, B Hanel, R A Pawelczyk

  • 1Department of Anesthesia, Rigshospitalet, Copenhagen, Denmark.

Journal of Applied Physiology (Bethesda, Md. : 1985)
|November 1, 1992
PubMed
Summary

Beta-1 adrenergic blockade during dynamic exercise reduces cardiac output and constricts active skeletal muscle vasculature. This response is linked to increased sympathetic activity, impacting blood flow during exercise.

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Area of Science:

  • Cardiovascular Physiology
  • Exercise Physiology
  • Skeletal Muscle Metabolism

Background:

  • Dynamic exercise typically increases cardiac output to meet skeletal muscle oxygen demands.
  • The role of cardiac output reduction in skeletal muscle vasoconstriction during exercise is not fully understood.
  • Adrenergic signaling plays a crucial role in regulating vascular tone during physical activity.

Purpose of the Study:

  • To investigate if reduced cardiac output during dynamic exercise leads to vasoconstriction in active skeletal muscle vasculature.
  • To assess the impact of cardioselective (beta 1) adrenergic blockade on exercise hemodynamics and leg vascular conductance.
  • To evaluate regional sympathetic nervous system activity during exercise under beta 1-blockade.

Main Methods:

Related Experiment Videos

  • Nine subjects performed graded cycling exercise (40-84% maximal oxygen uptake) under control and beta 1-adrenergic blockade (metoprolol) conditions.
  • Cardiac output and leg blood flow were measured using indocyanine green dye dilution.
  • Systemic and leg vascular conductance were calculated, and leg norepinephrine spillover was assessed as an index of sympathetic activity.

    • Main Results:

    • Beta 1-blockade significantly reduced heart rate and cardiac output during exercise.
    • At maximal exercise intensity, beta 1-blockade decreased leg blood flow and leg vascular conductance.
    • Leg norepinephrine spillover increased significantly during exercise with beta 1-blockade, indicating heightened sympathetic drive.

    Conclusions:

    • A reduction in cardiac output during dynamic exercise, induced by beta 1-blockade, is associated with vasoconstriction of active skeletal muscle vasculature.
    • This vasoconstriction may be mediated or exacerbated by increased sympathetic nervous system activity.
    • These findings highlight the interplay between cardiac output, sympathetic activity, and skeletal muscle blood flow regulation during exercise.