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Limb neurovascular control during altered otolithic input in humans
Kevin D Monahan1, Chester A Ray
1Department of Medicine (Cardiology), General Clinical Research Center, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA.
The Journal of Physiology
|January 5, 2002
Summary
Head-down rotation increases sympathetic nerve activity in both arms and legs, causing vasoconstriction in the calf and forearm. However, arterial blood pressure remains stable, suggesting compensatory vasodilation elsewhere.
Area of Science:
- Human physiology
- Autonomic nervous system research
- Vestibular system function
Background:
- Head-down rotation (HDR) activates the vestibulosympathetic reflex, increasing leg muscle sympathetic nerve activity (MSNA) and calf vasoconstriction without altering cardiac output or arterial blood pressure.
- Animal studies suggested differential control of arm and leg MSNA might explain the lack of blood pressure change during HDR.
Purpose of the Study:
- To investigate whether differential control of arm and leg MSNA explains the absence of arterial blood pressure changes during head-down rotation in humans.
Main Methods:
- Fifteen healthy subjects underwent head-down rotation.
- Measurements included heart rate, arterial blood pressure, forearm and calf blood flow, and simultaneous recordings of arm and leg MSNA in five subjects.
Main Results:
- HDR increased both leg and arm MSNA similarly.
- Calf vasoconstriction was approximately 60% greater than forearm vasoconstriction.
- Calf and forearm vascular conductance decreased, while vascular resistance increased, with no change in arterial blood pressure or heart rate.
Conclusions:
- Human responses to HDR do not show differential control of arm and leg MSNA.
- Greater vasoconstriction in the calf compared to the forearm occurs during HDR.
- Compensatory vasodilation in other vascular beds likely prevents an increase in arterial blood pressure during HDR.