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Human sympathetic nerve activity to glabrous skin does not increase during simulated diving
1Department of Neurology, University Hospital, Uppsala, Sweden.
Acta Physiologica Scandinavica
|November 1, 1994
Summary
Simulated diving initially increases sympathetic nerve activity (SNA) causing skin vasoconstriction, but then inhibits skin nerve sympathetic activity (SSA) upon facial immersion. This contrasts with muscle sympathetic outflow, highlighting diverse autonomic regulation.
Area of Science:
- Human physiology
- Autonomic nervous system
- Cardiovascular regulation
Background:
- Simulated diving in humans causes increased sympathetic outflow to muscles, leading to vasoconstriction.
- Previous studies showed unexpected reductions in skin nerve sympathetic activity (SSA) during diving.
- Cutaneous vasoconstriction is observed during simulated diving, but the underlying sympathetic response is debated.
Purpose of the Study:
- To investigate the effect of simulated diving on skin nerve sympathetic activity (SSA) in humans.
- To clarify the role of SSA in mediating skin vasoconstriction during the diving reflex.
- To compare sympathetic responses in skin versus muscle during simulated diving.
Main Methods:
- Microneurography recorded SSA in the median nerve of 13 healthy volunteers.
- Simulated diving involved facial immersion in water.
- Skin blood flow in the hand and finger was monitored concurrently.
Main Results:
- SSA increased before facial immersion, accompanied by skin vasoconstriction.
- Upon facial immersion, SSA significantly decreased, indicating inhibition.
- Mental arithmetic during diving elicited strong SSA bursts, similar to mental stress responses.
Conclusions:
- Simulated diving primarily inhibits SSA, contrasting with increased muscle sympathetic outflow.
- Pre-dive SSA increase is likely a stress response, not the direct diving reflex.
- Divergent sympathetic regulation of skin and muscle highlights organ-specific autonomic control.