Hyperoxic Effects on Decompression Strain During Alternating High and Moderate Altitude Exposures

Area of Science:

• Aerospace Medicine
• Physiology
• Environmental Medicine

Background:

• High-altitude fighter aircraft sorties are interrupted by refueling at lower altitudes.
• Normoxic conditions during altitude excursions may increase venous gas emboli (VGE) at high cabin altitudes.

Purpose of the Study:

• To investigate the effect of hyperoxia on VGE and decompression sickness (DCS) during alternating high and moderate altitude exposure.

Main Methods:

• 13 healthy men were exposed to three altitude conditions in a chamber: continuous high altitude breathing normoxic gas (H-NOR), continuous high altitude breathing hyperoxic gas (H-HYP), and alternating high and moderate altitude breathing hyperoxic gas (ALT-HYP).
• Venous gas emboli (VGE) were assessed using cardiac ultrasound, and decompression sickness (DCS) symptoms were rated.

Main Results:

• Decompression sickness (DCS) occurred in 6 of 39 exposures across all conditions.
• Venous gas emboli (VGE) prevalence was similar between normoxic and hyperoxic high-altitude exposures.
• Following an excursion to moderate altitude, VGE scores were lower in the alternating hyperoxic condition (ALT-HYP) compared to continuous high-altitude exposures.

Conclusions:

• Hyperoxic excursions to moderate altitudes reduce VGE occurrence by enhancing diffusive gas exchange.
• Despite VGE reduction, alternating altitude exposures did not eliminate the risk of decompression sickness (DCS).