Bone-conducted sound: physiological and clinical aspects.
OBJECTIVE
The fact that vibration of the skull causes a hearing sensation has been known since the 19th century. This mode of hearing was termed hearing by bone conduction. Although there has been more than a century of research on hearing by bone conduction, its physiology is not completely understood. Lately, new insights into the physiology of hearing by bone conduction have been reported. Knowledge of the physiology, clinical aspects, and limitations of bone conduction sound is important for clinicians dealing with hearing loss and is the purpose of this review.


METHODS
The data were compiled from the published literature in the areas of clinical bone conduction hearing, bone conduction hearing aids, basic research on bone conduction physiology, and recent research on bone conduction hearing from our laboratory.


CONCLUSIONS
Five factors contributing to bone conduction hearing have been identified: 1) sound radiated into the external ear canal, 2) middle ear ossicle inertia, 3) inertia of the cochlear fluids, 4) compression of the cochlear walls, and 5) pressure transmission from the cerebrospinal fluid. Of these five, inertia of the cochlear fluid seems most important. Bone conduction sound is believed to reflect the true cochlear function; however, certain conditions such as middle ear diseases can affect bone conduction sensitivity, but less than for air conduction. The bone conduction route can also be used for hearing aids; since the bone conduction route is less efficient than the air conduction route, bone conduction hearing aids are primarily used for hearing losses where air conduction hearing aids are contraindicated.
Stenfelt
Stefan
S
Department of Otolaryngology-Head and Neck Surgery, Stanford University Medical Center, Stanford, California 94305-5739, USA.
Goode
Richard L
RL
D001489:Basilar Membrane / Q000503:physiopathology; D001844:Bone Conduction / Q000502:physiology*; D002555:Cerebrospinal Fluid / Q000502:physiology; D003051:Cochlea / Q000503:physiopathology; D004427:Ear Diseases / Q000175:diagnosis / Q000503:physiopathology; D004429:Ear Ossicles / Q000503:physiopathology; D004432:Ear, Middle / Q000503:physiopathology; D006310:Hearing Aids; D006801:Humans; D013701:Temporal Bone / Q000503:physiopathology