Air sickness link to cabin pressure

Air passengers may experience symptoms of altitude sickness while flying and cabin pressures should be increased, scientists said.

The study found that maintaining a cabin altitude of 6,000ft or lower on long-duration commercial flights would reduce the discomfort among passengers.

Researchers found that an ascent from ground level to 8,000ft by healthy unacclimatised adults lowered the oxygen levels in their arteries by around 4% and led to increased discomfort after three to nine hours.

The pressure at 8,000ft (565 mm Hg) is equivalent to the lowest currently found on commercial aircraft at their maximum operating altitude.

The scientists said the discomfort felt by participants in the study cannot be explained by other flight-related factors, such as jet lag, dehydration or prolonged sitting, which are commonly thought to cause symptoms in commercial airline passengers. They also noted that exercise may not help as it reduces arterial oxygenation further.

The level of oxygen saturation at pressures found at 7,000ft to 8,000ft "played an important role in the development of discomfort", the researchers said.

The design of aeroplanes currently allows the cabin pressure to drop from that at sea-level (760 mm Hg) to 565 mm Hg, equivalent to an altitude of 8,000ft.

Higher levels of pressurisation would reduce the energy available for other aircraft systems, cut the operational lifetime of aluminium airframes, necessitate increased structural weight, and lead to decreased fuel efficiency, the scientists said.

The study, by Dr Michael Muhm and colleagues, found that discomfort caused by the higher altitudes was least frequent in older people. It also found that its onset was in the range of six to 10 hours, the same time range associated with acute mountain sickness, and that men were less likely than women to report discomfort.

Dr Muhm and his colleagues are from the Seattle-based Boeing Company and the study was carried out with the Centre for Aerospace and Hyperbaric Medicine at Oklahoma State University for Health Sciences, Tulsa.

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