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Autonomic and vascular responses to reduced limb perfusion
Joseph C Daley1, Mazhar H Khan, Cynthia S Hogeman
1Div. of Cardiology, MC H047, The Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, P.O. Box 850, Hershey, PA 17033, USA.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|July 2, 2003
Summary
Positive pressure exercise enhances muscle sympathetic nerve activity (MSNA) and mean arterial blood pressure (MAP). At +50 mmHg, increased MSNA prevents restoration of forearm blood flow, suggesting active vasoconstriction.
Area of Science:
- Physiology
- Exercise Science
- Autonomic Nervous System
Background:
- Hemodynamic responses to exercise are crucial for understanding muscle function.
- The role of the muscle reflex in modulating blood flow during exercise requires further investigation.
Purpose of the Study:
- To investigate hemodynamic and autonomic responses to graded muscle reflex engagement during rhythmic handgrip exercise.
- To determine the effects of positive pressure on muscle sympathetic nerve activity (MSNA) and forearm blood flow.
Main Methods:
- Seven healthy volunteers performed rhythmic handgrip exercise at 40% maximal voluntary contraction (MVC).
- Positive pressure (10-50 mmHg) was applied incrementally during exercise.
- Measurements included MSNA, mean arterial blood pressure (MAP), forearm blood flow velocity, and venous blood markers.
Main Results:
- Ischemic exercise with positive pressure increased MSNA and MAP, particularly at +40 and +50 mmHg.
- Positive pressure initially decreased forearm perfusion pressure and flow velocity.
- Blood flow was restored at +10 to +40 mmHg but not at +50 mmHg, coinciding with heightened MSNA.
Conclusions:
- Muscle reflex engagement, indicated by increased MSNA, plays a significant role in regulating blood flow during exercise under positive pressure.
- At high positive pressures (+50 mmHg), active vasoconstriction within the muscle may limit blood flow restoration despite elevated perfusion pressure.