Almost every acute ear infection is followed by days or weeks of OME. In addition, many people develop OME without first having acute inflammation. OME is caused when the Eustachian tube, a narrow channel that connects the inside of the ear to the back of the throat, becomes blocked. This tube is a drainage conduit to prevent the build-up of secretions that are normally made in the middle ear. These secretions drain down the tube and are swallowed. The tube also functions to keep the air space in the middle ear at the same pressure as the air around us. In this way, the eardrum can move freely, and our hearing is most effective. When all is well, the tube is collapsed most of the time in order to protect the middle ear from the many organisms that live in the nose and mouth. Only upon swallowing does a tiny muscle open it briefly to equalize the pressures and drain the ear secretions. If any bacteria make it into the ear, the drainage mechanism, helped by little hair cells, should flush it out. When the Eustachian tube is partially blocked, fluid accumulates in the middle ear. Bacteria already there are trapped and begin to multiply. Respiratory infections, irritants (especially cigarette smoke), and allergies can all inflame the lining of the tube, producing swelling and increased secretions. They can also cause enlargement of the adenoid glands near the opening of the tube, blocking flow at the outlet. Sudden increases in air pressure (during descent in an airplane or on a mountain road) can squeeze the floppy tube closed and create a relative vacuum in the ear. Drinking while lying on one's back can close the slit-like tube opening. Although a myriad of factors can lead to a blocked tube, getting water in a baby's ears will not. The last two decades of the 20th century saw a dramatic rise in OME, largely due to increased pollution and increased use of early childhood day care (where children are exposed to many respiratory infections). OME is most common in winter or early spring, but can occur at any time of year. It occurs most often in children under 2 years old, but it can affect people of any age. Small children get more OME than older children or adults for several reasons: The tube is shorter, more horizontal, and straighter (quick and easy trip for the bacteria). The tube is floppier, with a tinier opening (easier to block). And young children get more colds (it takes time for the immune system to be able to recognize and ward off cold viruses). It used to be thought that the longer the fluid was present, the thicker it became. Thus, the term "glue ear" became synonymous with chronic OME. It is now thought that the thickness of the fluid relates more with the particular ear than with how long the fluid is present.
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