sounds to the brain. Hearing testscan
determine whether deafness is conduc-
tive or sensorineural.
The most common cause of conductive
deafness in adults is earwax. Otosclerosis
is a less common cause and is usually
treated by an operation called stapedec-
tomy, in which the stapes(a small bone
in the middle ear) is replaced with an
artificial substitute. In a child, conductive
deafness usually results from otitis media
or glue ear. This condition may be treated
by surgery (seemyringotomy). In rare
cases, deafness results from a perfor-
ated eardrum (see eardrum, perforated).
Sensorineural deafness may be pre-
sent from birth. This type of deafness
may result from a birth injury or damage
resulting from maternal infection with
rubellaat an early stage of pregnancy.
Inner-ear damage may also occur soon
after birth as the result of severe jaun-
dice. Deafness at birth is incurable.
Many children who are born deaf can
learn to communicate effectively, often
by using sign language. Cochlear im-
plantsmay help those children born
profoundly deaf to learn speech.
In later life, sensorineural deafness can
be due to damage to the cochlea and/or
labyrinth. It may result from prolonged
exposure to loud noise, to Ménière’s
disease, to certain drugs, or to some viral
infections. The cochlea and labyrinth
also degenerate naturally with old age,
resulting in presbyacusis. Sensorineural
deafness due to damage to the acoustic
nerve may be the result of an acoustic
neuroma. Deafness may be accompan-
ied by tinnitusand vertigo. Sometimes it
can lead to depression.
People with sensorineural deafness
usually need hearing-aidsto increase
the volume of sound reaching the inner
ear. Lip-readingis invaluable for deaf
people. Other aids, such as an amplifier
for the earpiece of a telephone, are
available. (See also ear; hearing.)
deathPermanent cessation of all vital
functions. The classic indicators of death
are the permanent cessation of heart
and lung function, and, in almost all
cases, these remain the criteria by
which death is certified. Brain deathis
the irreversible cessation of all functions
of the entire brain, including the brain-
stem. The diagnosis of death under
normal circumstances, when the indivi-
dual is not on a ventilator, is based on
the absence of breathing, absence of
heartbeat, and on the pupils being fixed
wide open and unresponsive to light.
When an individual is on a ventilator,
the criteria for diagnosing brain death
are based on clear evidence of irre-
versible damage to the brain; persistent
deep coma; no attempts at breathing
when the patient is taken off the venti-
lator; and lack of brainstem function.
(See also death, sudden; mortality.)
death rateSee mortality.
death, suddenUnexpected death in a
person who previously seemed to be
healthy. The most common cause in
adults is cardiac arrest. Cardiomyopathy
may cause sudden death at any age,
and its presence may have been unsus-
pected. Sudden death may also occur
as a result of strokeor in people with
unsuspected myocarditis, or pneumonia.
Less common causes of a sudden death
include anaphylactic shock, a severe
attack of asthma, and suicide.
In infants, death without warning is
called sudden infant death syndrome
(SIDS) or cot death. Cases of sudden
death at any age must be reported to
the coroner, who decides whether there
should be an autopsy.
death, sudden infant See sudden infant
death syndrome (SIDS).
debilityGeneralized weakness and lack
of energy. It may be due to a physical
disorder (such as anaemia) or a psycho-
logical disorder (such as depression).
debridementSurgical removal of for-
eign material and/or dead, damaged, or
infected tissue from a wound or burn in
order to expose healthy tissue. Such
treatment promotes the healthy healing
of badly damaged skin, muscle, and
other tissues in the body.
decalcification, dentalThe dissolving
of minerals in a tooth. Dental decalcifi-
cation is the first stage of tooth decay. It
is caused by the bacteria in plaqueact-
ing on refined carbohydrates (mainly
sugar) in food to produce acid, which
leads to changes on the surface of the
tooth. If the decalcification penetratesDEATH DECALCIFICATION, DENTAL
D