[Medical Q&A] Why do we feel discomfort in our ears during hyperbaric oxygen therapy?

Author: Liu Bo China Rehabilitation Research Center

Reviewer: Du Juan, deputy chief physician, China Rehabilitation Research Center

As the application of hyperbaric oxygen therapy becomes more and more widespread, many people have received hyperbaric oxygen therapy. During hyperbaric oxygen therapy, as the pressure in the cabin changes, most people in the cabin will feel discomfort in their ears, such as stuffy ears and hearing loss, just like flying or diving. The problem is mainly caused by the middle ear.

The middle ear has a cavity called the tympanic cavity, which is covered by the eardrum. The front wall is connected to the nasopharynx through the Eustachian tube. The total length of the Eustachian tube in an adult is about 35 mm. One end of the Eustachian tube is in the tympanic cavity and the other end is in the nasopharynx. The middle ear tympanic cavity has an opening in the nasopharynx, like a "valve". It is usually closed and only opens when we make certain oral and maxillary movements. Air takes this opportunity to enter the middle ear tympanic cavity to balance the pressure inside and outside the eardrum.

If the Eustachian tube cannot be opened in time to allow gas to enter the tympanic cavity through the Eustachian tube during pressurization, the pressure in the tympanic cavity will be lower than the pressure of the external auditory canal outside the tympanic membrane, and the tympanic membrane will be pressed inward, causing the tympanic membrane to collapse, causing stuffy ears and ear pain. When the pressure in the hyperbaric oxygen chamber increases, the hollow organs in our body can adjust the pressure to the same as the external pressure through breathing movements, but the middle ear tympanic cavity cannot do this, and the Eustachian tube must be used to adjust the internal and external pressure balance. When the pressure difference between the inside and outside of the tympanic membrane is between 10 and 30 mmHg, the tympanic membrane will collapse, and people will feel stuffy ears and hearing loss. When the pressure difference reaches 60 mmHg, the mucous membrane of the tympanic membrane and tympanic cavity will become congested, and ear pain will be felt. When the pressure reaches 100 mmHg, the tympanic membrane will be widely congested, and there will be exudation in the tympanic cavity. People will feel blocked ears, tinnitus, and severe ear pain. When the pressure exceeds 120 mmHg, the tympanic membrane may rupture, which is the middle ear barotrauma.