Webster's New World Medical Dictionary

SPECT scan
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sphingolipidosis
One of a group of hereditary
diseases that involve overproduction or accumula-
tion of fatty substances called sphingolipids in the
brain and nervous system. See also 
Anderson-Fabry
disease; Gaucher disease; GM1-gangliosidosis,
histiocytosis, lipid; Krabbe disease; leukodystro-
phy; Tay-Sachs disease; Sandhoff disease.
sphingomyelinosis
See 
histiocytosis, lipid.
sphygmomanometer
Blood pressure cuff, an
instrument for measuring blood pressure, particu-
larly in arteries. Digital and manual models are
available. The two basic types of manual sphygmo-
manometers are the mercury column and the gauge
with a dial face. The manual sphygmomanometer in
most frequent use today consists of a gauge attached
to a rubber cuff that is wrapped around the upper
arm and is inflated to constrict the arteries. A blood
pressure reading consists of two numbers: systolic
and diastolic. Systolic refers to systole, the phase
when the heart pumps blood out into the aorta.
Diastolic refers to diastole, the resting period when
the heart refills with blood. At each heartbeat, the
blood pressure is raised to the systolic level, and,
between beats, it drops to the diastolic level. With the
cuff inflated with air, a stethoscope is placed over an
artery (the brachial artery) in the crook of the arm.
As the air in the cuff is released, the pressure reading
when the first sound is heard through the stethoscope
marks the systolic pressure. As the release of air from
the cuff continues, a point is reached when the sound
diminishes and then is no longer heard. The pressure
at which the last sound is heard marks the diastolic
pressure. The blood pressure reading might show the
systolic and diastolic pressures to be, for example,
120 and 78mm of mercury (Hg), respectively. This is
usually written 120/78 and said to be “120 over 78.”
Blood pressure readings vary depending on age and
many other factors. Children and adults with smaller-
or larger-than-average-sized arms may need special-
sized pressure cuffs. See also 
blood pressure; hyper-
tension; hypotension.
spider bite
A bite from a spider. Bites from most
spiders are irritating but not poisonous. Localized
reddening and swelling are not unusual and should
pass within a few days. A few spiders are poisonous,
notably the black widow and brown recluse (brown
fiddler) in the US. Bites from these spiders require
emergency treatment, especially for children.