The effect of staged decompression while breathing 100% oxygen on altitude decompression sickness

Area of Science:

• Aerospace Medicine
• Physiological Adaptations to Spaceflight
• Decompression Physiology

Background:

• Space Shuttle extravehicular activity (EVA) requires significant pressure reduction from 14.7 psia to 4.3 psia.
• Current EVA protocols use a 12-36 hour staged decompression (SD) at 10.2 psia with an oxygen-enriched gas for denitrogenation.
• Denitrogenation is crucial for preventing decompression sickness (DCS) during EVA.

Purpose of the Study:

• To identify the maximum altitude for effective staged decompression using 100% oxygen (SD100).
• To assess DCS risk after decompression to 4.5 psia (29,500 ft) following SD100.
• To evaluate the efficacy of SD100 in preventing DCS symptoms.

Main Methods:

• 30 male subjects underwent 11 conditions, including exposures to 29,500 ft for 4 hours with mild exercise.
• Subjects received 15 minutes of ground-level (GL) preoxygenation plus 60 or 120 minutes of SD100 at altitudes from 8,000 to 18,000 ft.
• Venous gas emboli (VGE) were monitored using echo-imaging; control exposures used GL preoxygenation.

Main Results:

• One case of DCS occurred during SD100 at 18,000 ft; no DCS occurred at lower staging altitudes.
• Higher VGE levels were detected during SD100 at 18,000 ft compared to lower altitudes.
• SD100 at altitudes 16,000 ft and below did not result in increased DCS risk.

Conclusions:

• Staged decompression at 16,000 ft and below provides decompression risk similar to ground-level preoxygenation.
• SD100 at altitudes up to 16,000 ft is effective in preventing DCS for subsequent decompression to 29,500 ft.
• The findings support optimizing pre-EVA denitrogenation protocols for astronaut safety.