The remarkable phenomenon of adaptation to environmental stress is exemplified by man's tolerance of rapid and extreme alterations in barometric pressure. If pressure per se is considered apart from the effect of gases in the viscera, in aural and sinal spaces and in solution in tissues, then variations in pressure in the range of 0.11 atmosphere (50,000 feet [15,000 meters] altitude) to 16.1 atmospheres (500 feet [150 meters] diving depth) are without physiologic effect.
When the body is subjected to increased pressure, every air space, from the smallest and most inaccessible ethmoid cell to the air cells in the mastoid process, receives air provided that the passages to these spaces are unobstructed. The ingress of air to the aural spaces must be consciously brought about by various maneuvers, such as swallowing, yawning and using the Valsalva maneuver, which relax tension on the normally closed "flutter valve" of the eustachian
BEHNKE CAR. PHYSIOLOGIC EFFECT OF PRESSURE CHANGES WITH REFERENCE TO OTOLARYNGOLOGY. Arch Otolaryngol. 1945;42(2):110–116. doi:10.1001/archotol.1945.00680040146003
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