Decompression sickness risk at 6553 m breathing two gas mixtures

Area of Science:

• Aerospace Medicine
• Physiology
• Hypobaric Medicine

Background:

• Decompression sickness (DCS) risk escalates above 6248 m, especially with higher inert gas fractions.
• Modern aircrew may face higher cabin altitudes using molecular sieve oxygen concentrator (MSOC) product gas with variable oxygen concentrations.
• This study investigates DCS risk under simulated MSOC gas conditions at 6553 m.

Purpose of the Study:

• To assess the risk of decompression sickness (DCS) at a cabin altitude of 6553 m (21,500 ft).
• To evaluate DCS risk associated with breathing two different simulated molecular sieve oxygen concentrator (MSOC) product gas mixtures.
• To determine the impact of varying oxygen, nitrogen, and argon concentrations on DCS incidence and venous gas emboli (VGE) load.

Main Methods:

• Ten subjects underwent two 4-hour exposures in a hypobaric chamber at 6553 m.
• Breathing gas mixtures were either 75% O2:21% N2:4% Ar or 56% O2:42% N2:2% Ar.
• Venous gas emboli (VGE) load was monitored using echocardiography, with subjects performing simulated aircrew activities.

Main Results:

• Decompression sickness (DCS) occurred in 25% of exposures, with the earliest onset at 90 minutes.
• All DCS cases were minor limb bends, resolving with recompression.
• Venous gas emboli (VGE) were present in 85% of exposures; lower oxygen (56%) significantly reduced VGE latency compared to higher oxygen (75%).

Conclusions:

• The estimated risk of DCS at 6553 m is 5% by 90 minutes and 20% by 3 hours.
• Venous gas emboli (VGE) latency serves as a reliable surrogate for DCS protection.
• Improved MSOC performance, yielding higher oxygen concentrations, is crucial for protecting aircrew at high cabin altitudes.