ACOUSTIC TRAUMA

physiological changes in the body caused by sound waves. Sound waves cause variations in pressure, the intensity of which depends upon the range of oscillation, the force exerting the sound, and the distribution of waves. Excessive noise exposures can cause hearing loss and produce physical damage to the components of the ear. The ability to interpret sounds can decrease as a result of continuous exposures to sound waves of sufficient intensity and duration. Hearing loss can be caused by damage to the middle ear, tympanic membrane (eardrum), and inner ear. The hair cells that line the inner ear and take part in the process of hearing can be irreversibly damaged by excessive noise levels. Intense sound blasts can rupture the tympanic membrane and dislocate or fracture the small bones of the middle ear. Hearing loss that comes from middle-ear damage can sometimes be corrected. A ruptured membrane usually heals in time, restoring most of the hearing loss. The small bones of the ear may be repaired or replaced by surgery. Pain felt in the ears from sound waves serves as a warning that the threshold for damage has been reached. Nonauditory effects of acoustic energy can also occur; most of these can be prevented by use of ear protection devices. The body's equilibrium is partially controlled by the vestibular system in the ears; high-level noise may cause disorientation, motion sickness, and dizziness. Noise does not usually affect the speed at which work is performed; it may increase the number of errors, however. More constant noises of moderate to high levels cause stress, fatigue, and irritability.