Rapid decompression to 50,000 feet: effect on heart rate response.

Area of Science:

• Aerospace Medicine
• Cardiovascular Physiology
• Environmental Physiology

Background:

• Molecular Sieve Oxygen Generation Systems (MSOGS) are crucial for military aircraft oxygen supply.
• Rapid decompression (RD) in aircraft presents a critical physiological challenge.
• Understanding the effects of MSOGS gas during RD is vital for aircrew safety.

Purpose of the Study:

• To investigate the heart rate (HR) response to positive pressure breathing (PPB) during and after rapid decompression (RD).
• To evaluate the physiological effects of breathing simulated MSOGS product gas under hypobaric conditions.
• To differentiate the impacts of hypoxia, anxiety, and PPB on HR during simulated RD.

Main Methods:

• Ten subjects were exposed to RD from 6,096 m to 15,239 m in a hypobaric chamber.
• Subjects breathed either Aviators' Breathing Oxygen (ABO, 99.5% O2) or 93% O2 at different regulator settings.
• Interbeat (R-R) intervals were recorded to assess heart rate and variability.
• Additional experiments isolated the effects of hypoxia, anxiety, and PPB.

Main Results:

• Most subjects exhibited increased HR and reduced HR variability immediately after decompression and onset of PPB.
• HR variability increased as HR declined during continued exposure.
• No consistent HR changes were attributed to the mild hypoxia from breathing 93% O2 compared to ABO.
• Anxiety appeared to be the most significant factor influencing HR changes post-RD.

Conclusions:

• Anxiety, rather than mild hypoxia, is a primary driver of cardiovascular response during simulated MSOGS use after RD.
• Positive pressure breathing during RD significantly alters heart rate and variability.
• Further research should focus on mitigating anxiety-induced physiological effects in aircrew exposed to RD scenarios.