I
DOWN’S SYNDROME
Doppler ultrasonography
A type of
ultrasound scanning
in w hich
shifts in the frequency of ultrasonic
waves are used to measure the velocity
of moving structures. An emitter sends
out pulses of ultrasound
(inaudible,
high-frequency sound)
of a specific
frequency. W hen the pulses bounce off
a moving object (for example, blood
flowing through a blood vessel), the
frequency of the echoes is changed
from that of the emitted sound. A sen-
sor is able to
detect the frequency
changes and converts the data into use-
ful information
(about how fast the
blood flows, for example).
Doppler ultrasonography is widely
used to detect narrowing of arteries in
the neck due to
atherosclerosis
(accu-
mulation of fatty deposits on the artery
walls) and to detect blood clots in veins
(as occurs in
deep vein thrombosis
) .
In
addition,
Doppler
ultrasound
tech-
niques are used to monitor the fetal
heartbeat, to detect air bubbles during
dialysis
and in
heart-lung machines,
and
to measure blood pressure. (See also
Doppler echocardiography
. )
Dorfman-Chanarin syndrome
A very rare, autosomal recessive
genetic
disorder
affecting fat metabolism (see
lipidosis
) .
The disease is
congenital
(pre-
sent from birth). It is characterized by
ichthyosis
(thickened, scaly skin);
myo-
pathy
(degeneration of muscle), and
sometimes also defects in vision and in
hearing.
Blood tests
show
abnormal
white
blood cells
containing vacuoles
(tiny spaces) filled with fat.
dorsal
Relating to the back, located on or near
the back, or describing the uppermost
part of a body structure when a person
is lying face-down. For example, dor-
salgia describes pain in the back, and
the dorsal part of the hand is the back
of the hand. In human anatomy, the
term dorsal means the same as posteri-
or. The opposite of dorsal is
ventral
(meaning anterior or front).
dose
A term used to refer to the amount
of a drug to be taken at a particular
time, or to the amount of radiation to
w hich an individual is exposed during
a session of
radiotherapy
.
Drug dose
may
be
expressed
in terms
of the
weight of the active substance, the vol-
ume of liquid to be taken, or its effects
on body tissues. The amount of radia-
tion that is absorbed by body tissues
during
a session of radiotherapy is
expressed in units called millisieverts
(see
radiation units
).
dosulepin
A tricyclic
antidepressant drug
used in
the treatment of
depression
.
The drug
has a sedative action and is particularly
useful in cases of depression accom-
panied by
anxiety
or
insomnia
.
Possible
adverse effects include blurred vision,
dizziness, flushing, and rash.
dothiepin
The former name for
dosulepin
.
double-blind
A type of
controlled trial
that tests the
effectiveness of a particular treatment
or compares the benefits of different
treatments. In double-blind trials, neither
the patients undergoing the treatments
nor the doctors w ho are assessing them
know w hich of the patients are receiv-
ing w hich treatment. This eliminates
any expectations about w hich treat-
ment w ill be most effective.
double contrast enema
Radiologic investigation (see
radiology
)
of the
intestine
(the main part of the
digestive tract). A
contrast medium
(a
substance opaque to
X-rays
)
is intro-
duced into the passage or cavity to be
examined. The area is then distended
(widened) by the introduction of air. A
thin coating of the contrast medium is
left on the walls of the intestine. As a
result,
the
area to be
examined is
shown in outline on X-ray images. (See
also
barium X-ray examinations
. )
double vision
Also known as diplopia, double vision
is a condition in w hich a person sees
two visual images of a single object
instead of only one image. The two
images are separate, but each of them is
quite clearly focused.
CAUSES
It is usually a symptom of a squint,
especially of paralytic squint, in w hich
paralysis of one or more of the eye
muscles impairs eye movement. Other
causes include a tumour in the eyelid
or a tumour or blood clot behind the
eye. Double vision can also occur in
exophthalmos
,
when the eyeballs pro-
trude as the result of an underlying
hormonal disorder.
TREATMENT
Double vision needs immediate investi-
gation. The treatment depends on the
underlying cause.
A
chromosomal abnormality
that results
in a variable degree of
learning difficulty
and a characteristic physical appearance
in affected individuals.
CAUSES
People with Down’s syndrome have an
extra
chromosome
(47 instead of the
normal 46). Affected individuals have
three copies of chromosome number
21
instead of two; for this reason, the
disorder is also called trisomy 21. In
most cases, it is the result of a sperm or
egg being formed w ith an extra chro-
mosome
21
, due to the failure of the
chromosome
2
1
pair to part and enter
separate cells during
meiosis
.
If one of
these abnormal egg or sperm cells takes
part in fertilization, the baby w ill also
have the extra chromosome. This type
of abnormality is more likely if the
mother is aged over 3 5.
A less common cause is a chromoso-
mal abnormality called a
translocation
,
in w hich part of one parent’s own
Down's syndrome child using sign language
There is a greater than normal risk of congenital
deafness in Down’s babies. Typical features of the
condition include upward sloping eyes that are
covered at the corners, small facial features, and a
large tongue that tends to stick out.
douche
The introduction of water and/or a
cleansing agent into the vagina using a
bag and tubing with a nozzle. Douch-
ing is unnecessary for hygiene and is
ineffective
contraception
.
It may cause
infection or spread existing infection
into the uterus or fallopian tubes.
Down's syndrome
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