Two major types of deafness are conduction deafness and nerve deafness. In conduction deafness, the ossicles tend to fuse together, restricting their ability to magnify sound waves. Conduction deafness can be caused by a congenital defect, particularly when a pregnant woman contracts German measles (rubella) during the first trimester of pregnancy. (For this reason, every female should be immunized against rubella before the childbearing years.) Conduction deafness can also be due to repeated infections or otosclerosis. With otosclerosis (o"to-skle-ro'sis), the normal bone of the middle ear is replaced by vascular spongy bone.
Nerve deafness most often occurs when cilia on the receptors within the cochlea have worn away. Since this may happen with normal aging, older people are more likely to have trouble hearing. However, studies also suggest that age-associated hearing loss can be prevented if ears are protected from loud noises, starting even during infancy. Hospitals are now aware of the problem and ate taking steps to ensure that neonatal intensive care units and nurseries are as quiet as possible.
In today's society, exposure to the noises is common. Noise is measured in decibels, and any noise above 80 decibels could damage the hair cells of the organ of Corti. Since even listening to city traffic for extended periods can damage hearing, frequent attendance at rock concerts and constant loud music from a stereo are obviously dangerous. Noisy indoor or outdoor equipment, such as a rug-cleaning machine or a chain saw, are also troublesome. Even motorcycles and recreational vehicles, such as snowmobiles and motocross bikes, can contribute to a gradual hearing loss. Exposure to intense sounds of short duration, such as a burst of gunfire, can result in an immediate hearing loss. Since the butt of a rifle offers some protection, hunters may have a significant hearing reduction in the ear opposite the shoulder on which they carry their gun.
The first hint of a problem could be temporary hearing loss, a "full" feeling in the ears, muffled hearing, or tinnitus (ringing in the ears). Tfyou have any of these symptoms, modify your listening habits immediately to prevent further damage. If exposure to noise is unavoidable, use specially designect • noise-reduction earmuffs or purchase earplugs made from a compressible, spongelike material at a drugstore or sporting goods store. These earplugs are not the same as those worn for swimming, and they should not be used interchangeably.
Finally, people need to be aware that some medicines are ototoxic (damaging to any of the elements of hearing or balance). Anticancer drugs-most notably, cisplatin-and certain antibiotics (for example, streptomycin, kanamycin, and gentamicin) make ears especially susceptible to a hearing loss. Anyone taking such medications should protect ears from any loud noises.
Cochlear implants that directly stimulate the auditory nerve are available for persons with nerve deafness. However, they are costly, and people wearing these electronic devices report that the speech tl1ey hear is like that of a robot.
