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Uncomfortable in Airplanes
Abstract and Commentary
By Philip Fischer, MD, DTM&H
Dr. Fischer is Professor of Pediatrics, Division of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN
Dr. Fischer reports no financial relationship relevant to this field of study.
Synopsis: Seven percent of long-haul air travelers have symptoms compatible with acute mountain sickness, and others have significant atmospheric pressure-related discomfort. Mild decreases in oxygen saturation relate to some of the discomfort.
Source: Muhm JM, et al. Effect of aircraft-cabin altitude on passenger discomfort. N Engl J Med 2007;357:18-27.
Acute mountain sickness occurs in travelers to high altitudes and consists of symptoms such as headache, nausea, malaise, loss of appetite, and poor sleep. The incidence of acute mountain sickness increases with rapid ascent. At higher altitudes, the severity of symptoms seems to relate with decreased oxygen saturations in a low-pressure, low-oxygen atmospheric environment.
Some travelers experience symptoms similar to those of acute mountain sickness during long commercial air flights, even though the aircraft cabins are pressurized to approximate altitudes of no more than 8,000 feet. A collaborative group of researchers, including some at the Boeing Company, studied the effects of barometric pressure on discomfort during simulated 20-hour flights.
A total of 502 adult subjects who had not experienced significant recent altitude or air travel exposures during the preceding month participated in the study. A hypobaric chamber simulated conditions during a 20-hour commercial flight (with meals, movies, and seating typical of an air trip). Some participants were randomly assigned to an exercise protocol, with 10 minutes of walking each hour during the first 9 "flight" hours. Symptoms were assessed using the Environmental Symptoms Questionnaire IV, one of the standard measures of acute mountain sickness.
Oxygen saturations decreased with increasing simulated altitude with a 4.4% drop in the group simulating 8,000 feet altitude. Seven percent of subjects qualified for a diagnosis of acute mountain sickness, and this incidence did not vary between altitude groups (4,000, 6,000, 7,000, and 8,000 feet). Malaise, muscle discomfort, and fatigue were more common at 8,000 feet than at other simulated altitudes. Discomfort was inversely related to oxygen saturation. Women were more likely than men to report discomfort, and older individuals were least likely to report discomfort. Exercise was associated with a reduced prevalence of muscle discomfort, but it did not affect other symptomatic outcomes.
There are many mechanisms by which people feel uncomfortable during long air flights. The Boeing study summarized here suggests that acute "mountain" sickness might indeed be a source of discomfort on airline flights.
Acute mountain sickness occurs largely at very high altitudes. But, more than 20% of travelers are reported to have symptoms of this condition even at lower elevations (6,500 feet).1 The data summarized here indicate that identical symptoms can develop with prolonged air travel, at least in a simulated setting. As at altitude, symptoms in aircraft are linked to oxygen desaturations occurring over time. It is likely that the physiology of acute mountain sickness combines both hypoxia and gradual pressure-related fluid shifts, Similar changes could take place in aircraft, as well as on the ground, at simulated altitudes.
Muscular discomfort was much more prevalent at 8,000 feet altitude (10%-15% at various times in the simulated flight) than at lower altitudes (4% - 6% at 7,000 feet). Maintaining a cabin "altitude" of 6,000 feet during long flights could greatly facilitate passenger comfort. Since walking periodically during the flight decreased the risk of muscle discomfort by more than half, it could be suggested that travelers prone to discomfort during long flights get up and move about the cabin regularly.
Even without acute mountain sickness and hypoxia-related myalgia, many passengers are uncomfortable during long commercial air flights. Deep vein thrombosis is an uncomfortable and dangerous risk for travelers. Passengers with risk factors for deep vein thrombosis (previous thromboembolism, malignancy, recent surgery, obesity, a Factor V Leiden heterozygote or homozygote, pregnancy or recently post-partum) traveling in aircraft for more than 6 hours should move their legs regularly, use compression stockings, and possibly consider prophylactic use of low molecular weight heparin.2, 3
Pressure changes in aircraft also hinder Eustachian tube function and cause ear pain. Up to 9% of adults 4,5 and 14% of children6 are bothered by earaches during times of changing cabin pressure. Prophylactic pseudoephedrine is effective in adults with a history of air travel-associated ear pain (120 mg orally 30 minutes prior to take-off)5,7 but is ineffective in children.6
Intestinal gas expands approximately 35% when transitioning from sea level to the 8,000 foot "altitude" of a pressured airplane cabin. Nausea and discomfort result. Meals containing high levels of fiber slow gastric emptying by 33% at altitude and further aggravate symptoms.4
There are, therefore, many reasons long-haul travelers can feel physically uncomfortable in airplanes. What's an airline to do? Perhaps adjusting cabin pressure to the equivalent of 6,000 feet (rather than 8,000 feet) would help. What's a traveler to do? Move about the cabin when possible. Exercise leg muscles, even when seated. Use compression stockings if there is a pre-existing personal risk for thromboembolism. Adults with a history of air-travel-associated earache can consider pre-flight use of pseudoephedrine. And, travelers with past feelings of bloating and dyspepsia during flight should choose low fiber meals just prior to and during the flight.