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Venomotor responses during central and local hypoxia
1Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle 98195.
The American Journal of Physiology
|October 1, 1988
Summary
Hypoxemia, or low oxygen levels, does not block sympathetic venoconstriction during cold-induced spinal reflexes or moderate exercise. This indicates the sympathetic nervous system remains functional under hypoxic conditions.
Area of Science:
- Physiology
- Cardiovascular System
- Neuroscience
Background:
- Sympathetic neuroeffector mechanisms regulate vascular tone.
- Hypoxemia can potentially impair autonomic nervous system function.
- Venomotor responses are a key indicator of sympathetic activity.
Purpose of the Study:
- To investigate the impact of moderate to severe hypoxemia on sympathetic venoconstriction.
- To determine if hypoxemia affects venoconstriction induced by spinal reflexes (cold) or central command (exercise).
Main Methods:
- Venomotor responses were measured via forearm venous pressure changes in 10 healthy men.
- Two experiments were conducted: cold-induced reflex venoconstriction and exercise-induced venoconstriction.
- Subjects experienced varying levels of normoxia and hypoxemia, with controlled oxygen tensions in the arm and body.
Main Results:
- Large reflex venoconstrictions persisted during both mild (10.3% O2) and severe (7.7% O2) hypoxemia.
- Strong venoconstrictor responses to moderate exercise were maintained during both local and central hypoxemia.
- Hypoxemia did not appear to block sympathetic venoconstriction pre- or postjunctionally.
Conclusions:
- Moderate to severe hypoxemia does not inhibit sympathetic venoconstriction originating from spinal reflexes.
- Exercise-induced sympathetic venoconstriction is also preserved during hypoxemia.
- These findings suggest preserved sympathetic nervous system function during hypoxic conditions.