Oxygen above the clouds
A study explored whether providing supplementary oxygen during high-altitude flights could protect passengers, while also assessing its potential risk of brain damage.
Loss of cabin pressure at high altitudes can be fatal, as demonstrated by the death of golf star Payne Stewart in 1999 and the Helios Airways Flight crash in Greece in 2005, which claimed 121 lives. Oxygen masks play a critical role in such emergencies by supplying the body with oxygen, helping prevent loss of consciousness and save lives. However, there is growing concern prolonged exposure to high levels of oxygen such as that experienced by military pilots, may pose a risk to brain health. To investigate this, a study simulated these flight conditions using terraXcube.
Commercial aircraft use artificially regulated air pressure, for aircraft without pressurized cabins, additional oxygen is recommended or even mandatory above a certain altitude. This is because the higher you fly, the “thinner” the air becomes meaning the body receives less oxygen. But to what extent does artificial oxygen supply affect our brains, blood, and concentration? The Hypoxiflight study took place in terraXcube, Eurac Research's center for extreme climate simulation and examined just this. With researchers recreating realistic flight conditions for non-commercial pilots and passengers under strictly controlled, standardized conditions.
High-altitude flights in the lab
The simulation took place in terraXcube, Eurac Research’s state-of-the-art climate simulator where environmental conditions such as cold, wind, and high altitudes can be realistically simulated. Twelve healthy volunteers with an average age of 36 were medically examined before being subjected to three hours of “flying” at altitudes between 2,500 and 4,500 meters. For each flight, different amounts of additional oxygen were supplied via a Venturi mask. The concentration of oxygen inhaled gradually increased from 35 percent to 50 and 60 percent and finally to 100 percent. Venturi masks are used in clinical care as they enable the precise adjustment of oxygen content in the air we breathe, regardless of how quickly or deeply the person being tested breathes, making them ideal for controlled studies, where even the smallest physiological changes need to be measured reliably. The research team wanted to know whether breathing oxygen-rich air at these altitudes lead to oxidative stress: a condition in which more free radicals are produced in the body than can be neutralized? The reason – free radicals can damage cells, especially in the brain. In order to obtain the most accurate data possible, the participants were “wired up” and comprehensively monitored. A thin arterial catheter was inserted into each participant allowing blood pressure and oxygen levels in the blood to be measured continuously. In addition, the research team took blood samples at regular intervals to analyze two typical markers of oxidative stress: malondialdehyde-modified LDL (M-LDL), an oxidized fat molecule in the blood, and glutathione peroxidase 1 (GPX1), an enzyme produced by the body that keeps harmful oxidative processes in check. At the same time, psychological tests were carried out to check concentration and responsiveness under simulated flight conditions.
No oxidative stress – despite high oxygen levels
The study focused on the question of whether the administration of additional oxygen under flight conditions increased oxidative stress in the body. The evaluation of the blood samples showed that despite significantly increased oxygen levels in the arterial blood, no significant changes were found in either of the two stress markers examined. Individual participants showed slightly elevated or reduced values, but without any noticeable or worrying deviations. Nevertheless, one interesting observation was made: the GPX1 value tended to rise slightly more in the slightly elder subjects. Further studies are needed to determine whether this is significant.
Real incidents – the danger of pressure loss in flight
Two tragic plane crashes dramatically demonstrated how life-threatening pressure loss at high altitudes can be – especially when the oxygen supply fails. In 1999, the Learjet of US golf pro Payne Stewart lost cabin pressure shortly after takeoff. The crew and passengers are believed to have lost consciousness within minutes. The jet flew unpiloted through US airspace for several hours until it ran out of fuel and crashed – no one on board survived. Just a few years later, in 2005, a similar incident occurred on board Helios Airways Flight 522, a Boeing 737-300. Due to an incorrectly set pressure system, the oxygen supply failed. The aircraft continued to fly in autopilot mode until it crashed near Athens. All 121 people on board were killed. The accident is considered one of the most serious caused by hypoxic unconsciousness in civil aviation.
What does this mean for pilots?
“The result is reassuring – and, above all, relevant in terms of current practices,” emphasizes study leader Nikolaus Netzer. “Supplementary oxygen levels of up to 60 percent – the amount commonly used in civil aviation – are physiologically harmless for pilots and for passengers,” Netzer continues. “In emergency situations, especially drops in cabin pressure, oxygen masks can be lifesaving.” An interesting observation was that one participant panicked while wearing the mask, hyperventilated, and complained of dizziness. Reactions such as these, triggered by psychological stress, not by the additional oxygen, can be problematic in an emergency. This shows that breathing training and mental preparation for flight personnel and passengers could become just as important as technical equipment in the future.
The Hypoxiflight study confirms that additional oxygen on flights at high altitudes is not dangerous – it is sensible and safe and in line with the existing protective measures in civil aviation.
The study published in Biomolecules entitled “Oxidative Stress Reaction to Hypobaric–Hyperoxic Civilian Flight Conditions”: https://doi.org/10.3390/biom14040481
What happens when there is a drop in pressure in an aircraft?
- Technical safety:
Modern aircraft artificially maintain a safe level of cabin pressure. Several safety valves and structural protection mechanisms ensure that no uncontrolled stresses occur when there is a sudden loss of pressure.
- Automatic oxygen masks:
At an altitude of 4,200 meters, oxygen masks automatically drop from the cabin ceiling. They supply passengers with oxygen for about 15 minutes – enough time to descend to a safe altitude. The cockpit crew has access to longer oxygen reserves.
- Emergency descent:
In the event of a loss of pressure, pilots immediately initiate a rapid descent – typically below an altitude of 3,000 meters. At this altitude, no additional oxygen supply is necessary. In some aircraft models, this descent is semi-automated via special safety systems.
- Passenger behavior:
After a loss of pressure, every second counts: studies show that cognitive function can decline within seconds of cabin pressure loss at cruising altitude. Within 30 seconds, many passengers are no longer able to perform simple tasks correctly, such as putting on a mask. Therefore, in an emergency, passengers should put on their masks immediately and only then help others.
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