Description
Modern jet aircraft, including the supersonics, maintain cabin pressure equivalent to 5,000 and 8,000 feet. At such altitudes, free air in body cavities tends to expand by about 25 percent and may aggravate certain medical conditions. The occasional loss of cabin pressure and the fact that some airplanes are unpressurized can present problems.
During a sudden increase in ambient pressure, gas must move from the nasopharynx into the middle ear to maintain equal pressure on both sides of the tympanic membrane. If the eustachian tube is not functioning properly, as in upper respiratory tract infections or allergy, the pressure in the middle ear is lower than the ambient pressure. The relative negative pressure in the middle ear results in retraction of the tympanic membrane and a transudate of blood from the vessels in the lamina propria of the mucous membrane forms in the middle ear.
If the difference in pressure becomes great, ecchymosis and subepithelial hematoma may develop in the mucous membrane of the middle ear and in the tympanic membrane.
Very severe pressure differentials cause bleeding into the middle ear and rupture of the tympanic membrane. A perilymph fistula through the oval or round window may occur.
Pressure differentials between the middle ear and ambient pressures usually produce severe pain and a conductive hearing loss.
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