An abrupt zero-preoxygenation altitude threshold for decompression sickness symptoms

Area of Science:

• Aerospace Medicine
• Physiology
• Environmental Health

Background:

• Decompression sickness (DCS) symptom thresholds vary widely, from 18,000 to over 25,000 ft.
• Precise DCS threshold determination is crucial for aerospace operational safety and efficiency.

Purpose of the Study:

• To establish a more accurate altitude threshold for the onset of DCS symptoms.
• To evaluate the relationship between simulated altitude exposure and DCS incidence.

Main Methods:

• 124 male subjects were exposed to simulated altitudes ranging from 11,500 ft to 25,000 ft for 4-8 hours, breathing 100% oxygen.
• Monitoring included precordial venous gas emboli (VGE) and DCS symptoms.
• Probit analysis was used to estimate the risk of DCS and VGE at different altitudes.

Main Results:

• Venous gas emboli (VGE) were detected starting at 15,000 ft, with incidence increasing significantly at higher altitudes.
• A 5% incidence of DCS symptoms was observed at 21,200 ft.
• DCS incidence sharply rose to 55% at 22,500 ft.

Conclusions:

• The study concluded a 5% DCS symptom threshold at 20,500 ft under the tested conditions.
• The rapid increase in DCS symptoms above 21,200 ft necessitates a review of current USAF and FAA altitude exposure guidelines.