Respiratory modulation of human autonomic function: long-term neuroplasticity in space

Area of Science:

• Cardiovascular physiology
• Neuroscience
• Space medicine

Background:

• Orthostatic intolerance is a common issue for astronauts returning from space.
• Autonomic nervous system (ANS) dysfunction may contribute to postflight orthostatic intolerance.
• Understanding ANS changes during spaceflight is crucial for astronaut health.

Purpose of the Study:

• To investigate autonomic nervous system (ANS) changes in astronauts during and after space shuttle missions.
• To identify specific autonomic alterations that may lead to postflight orthostatic intolerance.
• To assess the neuroplasticity of sympathetic and vagal responses to breathing challenges in microgravity.

Main Methods:

• Studied six healthy astronauts before, during (early and late mission), and after the Neurolab Space Shuttle mission.
• Utilized controlled breathing and apnea protocols to perturb autonomic function.
• Measured electrocardiogram, arterial pressure, respiratory gases, tidal volume, and peroneal nerve muscle sympathetic activity.

Main Results:

• Arterial pressure showed a biphasic response in space (fall then rise) and returned to preflight levels post-flight.
• Vagal baroreflex gain and fluctuations initially increased then decreased in space, returning to baseline.
• Sympathetic burst frequencies increased in space and on landing day, with diminished modulation capacity during apnea.

Conclusions:

• Spaceflight induces significant, long-lasting neuroplastic changes in both sympathetic and vagal motoneurone responsiveness.
• These reciprocal changes in autonomic control may underlie postflight orthostatic intolerance.
• Astronaut ANS function is profoundly affected by microgravity exposure, requiring further investigation.