Webster's New World Medical Dictionary

volume, stroke
See 
stroke volume.
voluntary
Done in accordance with the con-
scious will of the individual. The opposite of volun-
tary is involuntary. The terms voluntary and
involuntary apply to the human nervous system and
its control over muscles. The nervous system is
divided into two parts: somatic and autonomic. The
somatic nervous system operates the skeletal mus-
cles, which are under voluntary control. The auto-
nomic (automatic, or visceral) nervous system
regulates individual organ function and is involun-
tary. For example, opening the mouth is voluntary,
and blushing and the beating of the heart are invol-
untary. See also 
autonomic nervous system.
volvulus
Abnormal twisting of a portion of the
gastrointestinal tract, usually the intestine, which
can impair blood flow. Volvulus can lead to gan-
grene and death of the involved segment of the 
gastrointestinal tract, intestinal obstruction, perfo-
ration of the intestine, and peritonitis. The stomach,
small intestine, cecum, and sigmoid colon are all
subject to volvulus. Malrotation of the bowel during
fetal development can predispose one to a volvulus,
which often has a sudden onset. The symptoms and
signs of a volvulus may include abdominal pain,
nausea, vomiting, and blood in the stool. The treat-
ment is surgery to free the obstruction and ensure
normal blood flow to the bowel. Volvulus is a surgi-
cal emergency.
vomit 1
Matter from the stomach that is ejected in
tandem with symptoms of nausea. When vomit is
reddish or coffee-ground colored, it indicates seri-
ous internal bleeding. Also known as vomitus.
2
To
expel vomit. Also known as emesis.
vomiting in pregnancy, excess
See 
hypereme-
sis gravidarum.