July 5, 2007 -- A new study suggests that the level of passenger discomfort onboard airplanes increases with increasing altitude, and it may be tied to a drop in oxygen levels in the blood.
Researchers found discomfort peaked at a 4.4 percentage point drop in the
oxygen saturation of the blood at 8,000 feet above sea level. But that
discomfort improved at slightly lower elevations, such as 6,000 feet.
Although airplane cabins are pressurized to protect passengers from the low barometric pressures at flight altitudes, researchers say sea-level air pressure of 760 mmHg is not maintained. Instead, aircraft are designed to maintain cabin pressure at no lower than 565 mmHg, which is equivalent to an altitude of 8,000 feet.
Sustained exposure to such an environment may lead to symptoms similar to those found in acute mountain sickness, such as headache, nausea, vomiting, and problems sleeping, which may explain why long flights can be challenging physically as well as mentally.
Why Long Flights Are Uncomfortable
In the study, published in the New England Journal of Medicine, researchers at Boeing Commercial Airplanes simulated conditions on board a 20-hour commercial flight in a group of about 500 volunteers.
They found that the average oxygen saturation in the blood decreased with increasing altitude, peaking at a 4.4 percentage point decrease at 8,000 feet above sea level.
Participants reported more discomfort at altitudes of 7,000 and 8,000 feet than at all other lower altitudes combined, and those differences became apparent after three to nine hours of exposure to decreased cabin pressures.
The study also showed that people under age 60 were more likely to complain of discomfort at higher altitudes and men were more likely than women to suffer discomfort.