Muscle sympathetic outflow during horizontal linear acceleration in humans

Area of Science:

• Physiology
• Neuroscience
• Cardiovascular Research

Background:

• Muscle sympathetic nerve activity (MSNA) is crucial for regulating cardiovascular function and blood pressure.
• The vestibular system's role in sympathetic regulation is not fully understood, particularly its response to dynamic linear acceleration.

Purpose of the Study:

• To investigate the impact of linear acceleration on MSNA in healthy human subjects.
• To determine if vestibular stimulation via linear acceleration influences sympathetic nerve outflow.

Main Methods:

• Sixteen healthy men underwent testing in a linear accelerator, experiencing sinusoidal linear acceleration.
• Measurements included MSNA, electrocardiogram, blood pressure, and thoracic impedance.
• Acceleration was applied in anteroposterior (Gx) and lateral (Gy) directions at peak values of +/-0.10, +/-0.15, and +/-0.20 G.

Main Results:

• A significant decrease in both total activity and burst rate of MSNA was observed during forward, backward, left, and right linear accelerations.
• At peak +/-0.20 G acceleration, MSNA total activity reduced to approximately 50-70% of baseline levels across directions.
• The inhibition of MSNA was evident across all tested directions and magnitudes of linear acceleration.

Conclusions:

• Dynamic stimulation of otolith organs by linear acceleration in horizontal directions inhibits MSNA in humans.
• This inhibition likely facilitates rapid blood redistribution to muscles during passive postural reflexes.
• The findings support a significant role for the vestibular system in the sympathetic regulation of cardiovascular function.