The function of the autonomic nervous system during spaceflight

Area of Science:

• Cardiovascular Physiology
• Neuroscience
• Space Medicine

Background:

• Autonomic nervous system (ANS) activity in space is poorly understood, with conflicting theories on sympathetic activation and vasorelaxation.
• Decades of research have yet to provide a definitive understanding of ANS function during spaceflight.

Purpose of the Study:

• To review in-flight autonomic and hemodynamic data to resolve discrepancies in understanding ANS activity during spaceflight.
• To highlight findings from the NASA NEUROLAB mission, a comprehensive assessment of autonomic function in microgravity.

Main Methods:

• Review of in-flight autonomic and hemodynamic data.
• Analysis of data from the NASA NEUROLAB mission.
• Presentation of mechanisms altering autonomic activity, including hypovolemia, cardiovascular deconditioning, and altered central processing.

Main Results:

• NEUROLAB experiments showed increased sympathetic activity and impaired vagal baroreflex function during short-duration spaceflight.
• Subsequent studies confirm increased sympathetic activity in space compared to the supine position on Earth.
• Disparate theories on vasorelaxation and vagal activity reflect different pre-flight postural controls.

Conclusions:

• Spaceflight presents a minor autonomic challenge, less than upright posture on Earth.
• In-flight countermeasures like exercise and short-arm centrifugation are effective.
• Neurohumoral mechanisms remain intact, ensuring stable cardiovascular function during long-duration spaceflight.