While the variance among individuals and age groups in tympanum volume (V tym) is low (V tym ≈ 1 ml), that of the mastoid (V mas) is large (V mas ≈ 0–15 ml) due to contributions of age, gender, and disease history effects ( 37, 46). The ME consists of two functionally discrete but continuous air spaces: the anterior tympanum, which contains the ossicles, ligaments, and muscles of the sound transducer mechanism and the posterior mastoid cavity, which is subdivided into numerous intercommunicating air cells ( 5). Because the ME is usually a closed, relatively noncollapsible, temperature-stable, mucosal-lined bony cavity, its pressure is a direct function of the contained gas volume, and gas transfers to or from the ME change its pressure. Normally, the pressure of the fluid-free ME is near ambient (Pam) (P ME ≈ Pam ≈ P Cabin), which ensures free vibration of the TM and efficient transduction of sound energy to the inner ear. Our goal is to clarify the buffering mechanisms that protect the ME from barotrauma during pressurized flight.īarotrauma is caused by an inability to maintain near pressure equivalence between the ME (P ME) and airplane cabin (P Cabin) as the latter is changed rapidly during ascent and descent. Here, we approach the pathogenesis of ME barotrauma from the perspective of basic physiology using both descriptive and mathematical formats. The inadequacy of this approach was recently highlighted in a study by Sade and colleagues ( 48) who reported disease-free flights for children and adults with presumably poor ET function. Moreover, most publications and reviews that specifically focused on ME barotrauma during flight lack empirical data and described disease pathogenesis using broad generalizations ( 2, 6, 33, 45) with a primary focus on the function of the eustachian tube (ET). Previous studies describing the pathogenesis of ME barotrauma were done on divers or on patients being treated in hyperbaric O 2 chambers ( 3, 25, 32, 41), situations that do not share the physiological conditions experienced during pressurized flight. Sequelae of barotrauma can include dizziness, tinnitus, and deafness ( 16, 45). Baromyringitis is structural damage to the tympanic membrane (TM) with severe pain caused by large pressure differences between ME and cabin. Barotitis media is ME mucosal (MEM) inflammation, hemorrhage, and leakage of transudate into the ME precipitated by moderate ME underpressures relative to the surrounding MEM. Two primary expressions of barotrauma can be distinguished based on signs and pathophysiology: barotitis media and baromyringitis. Middle ear (ME) barotrauma, the most common medical disorder associated with modern air travel, affects an estimated 5% of adult and 25% of child passengers ( 49). These buffering systems can explain why some children and adults with poor eustachian tube function do not experience middle ear barotrauma. Also, the specific type of functional deficit is important since ears with a completely obstructed eustachian tube can be less susceptible to barotrauma than those with a eustachian tube that passively opens but fails to dilate in response to muscle activity. These include the relative difference between destination and departure elevations and the ratio of maximum tympanic membrane volume displacement to middle ear volume, where greater absolute values require lesser efficiencies for disease-free flight. The results document buffering mechanisms that decrease the requisite efficiency of active, muscle-assisted eustachian tube opening for disease-free flight. Here we describe a mathematical model of middle ear pressure regulation and simulate the pressure response to the changes in cabin pressure experienced over typical flights. Previous reports emphasized the important role of poor eustachian tube function in disease pathogenesis but paid little attention to other moderating factors. Middle ear barotrauma during flight is a painful disorder experienced by passengers who cannot properly regulate their middle ear pressure in response to the changing cabin pressures during ascent and descent.
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