Respiratory effects of transient axial acceleration

Area of Science:

• Physiology
• Biophysics

Background:

• Gravity influences respiration, with upright posture typically having an inspiratory effect.
• Previous research suggests transient upward acceleration may have an expiratory effect.

Purpose of the Study:

• To investigate the respiratory effects of transient axial accelerations.
• To differentiate between initial mechanical effects and subsequent reflex responses on airflow.

Main Methods:

• Measured axial acceleration, transrespiratory pressure, and airflow in five subjects undergoing platform drops or lifts.
• Utilized a computational model of a passive respiratory system to simulate experimental findings.

Main Results:

• For the initial 100 ms, upward acceleration decreased mouth pressure and inspiratory flow; downward acceleration had the opposite effect.
• After 100 ms, respiratory airflow became highly variable and independent of acceleration.
• Electromyograms revealed muscle activity starting 40-125 ms post-acceleration, indicating reflex responses.

Conclusions:

• Transient upward axial acceleration induces inspiratory airflow, and downward acceleration induces expiratory airflow in relaxed subjects.
• Reflex activation of respiratory muscles significantly influences airflow after the initial 100 ms, overriding mechanical effects.