Gas Supply, Demand and Middle Ear Gas Balance: Specific Aim 3a Part ii

Study Summary

The middle ear is an airspace located behind the eardrum that consists of two connecting compartments. The compartment directly behind the eardrum is called the tympanum and contains the three small bones of the middle ear, the hammer, anvil and stapes, that function to transfer eardrum movements to the inner ear so that you can hear. Behind the tympanum is the mastoid cavity which is a larger airspace subdivided into small air cells of unknown function. For normal hearing, it is important that the air pressure in the middle ear is similar to that of the environment so that the eardrum can move freely in response to sounds. The air pressure of the environment is not constant and is affected by changes in weather conditions (high and low pressure systems that move through the area) and by changes in elevation above sea level (the fullness in your ears that can be noticed when you ride in an elevator or in an airplane). The air pressure in the middle ear also changes because middle ear gas is constantly leaking from that airspace to the blood that flows through the walls of the middle ear. These effects (changing environmental air pressures and changing middle ear air pressure) are independent and cause the middle ear and environmental pressures to be different from each other. Periodically and during swallowing or yawning, any existing difference between middle ear and environmental air pressure is reset to zero by the opening of a biological tube (the Eustachian tube) that connects the middle ear to the back of the nose. This allows gas flow between the middle ear and the environment which increases or decreases middle ear pressure to the level in the environment at that time. Most people cannot open their Eustachian tubes at will and the number of automatic openings varies from infrequent to often in a population. Whether or not a person's usual frequency of Eustachian openings is good enough to keep the middle ear pressure the same as environmental levels depends