Encyclopedia of Health and Medicine

106 The Cardiovascular System
soy and cardiovascular health Soy protein
appears to help lower cholesterol blood levels,
particularly low-density lipoprotein cholesterol
(LDL-C). The American Health Association recommends
replacing animal protein with soy protein
as part of a balanced, low-fat diet. People who
consume 25 to 50 grams of soy protein daily can
lower their LDL-C levels by as much as 8 percent.
In combination with other cholesterol-lowering
approaches such as increased daily exercise, soy in
the diet contributes to a heart-healthy lifestyle.
Soy protein contains isoflavones—notably genistein,
daidzein, and glycetein—that help to reduce
the formation of ATHEROSCLEROTIC PLAQUE, thus
lowering the risk for ATHEROSCLEROSIS and related
conditions such as CORONARY ARTERY DISEASE (CAD).
Soy protein is also high in fiber, helping absorb
dietary cholesterol and fats in the intestinal tract
to reduce the amount that enters the blood circulation.
DIETARY SOURCES OF SOY PROTEIN
soy cheese
soy flour
soybeans (boiled or roasted)
soy milk
textured vegetable protein (TVP) products tofu
See also CARDIOVASCULAR DISEASE PREVENTION; DIET
AND CARDIOVASCULAR HEALTH; HORMONE-DRIVEN CAN-
CERS; LIFESTYLE AND CARDIOVASCULAR HEALTH.
stent A tiny, springlike device inserted into an
ARTERY to help maintain the artery’s patency after
ANGIOPLASTY (a CARDIAC CATHETERIZATION procedure to
clear or compress ATHEROSCLEROTIC PLAQUE from the
inner walls of an artery). The stent holds pressure
against the artery’s inner wall, maintaining compression
of the plaque as well as making it difficult
for the artery to constrict. Cardiologists use stents
primarily in the CORONARY ARTERIES though may also
use them in carotid ENDARTERECTOMY and peripheral
artery angioplasty. An anticoagulant medication
coats some stents, called DRUG-emitting, to discourage
clot formation. Stents can extend the effectiveness
of angioplasty by months to a year or more.
Angioplasty with stent placement can delay the
need for CORONARY ARTERY BYPASS GRAFT (CABG) or
provide an acceptable alternative for people with
less severe occlusions. Most stents require replacement
every three to five years.
See also ANTICOAGULATION THERAPY; BLOOD; MED-
ICATIONS TO TREAT CARDIOVASCULAR DISEASE.
stethoscope An instrument the doctor uses to
listen to sounds within the body. The cardiologist
uses a stethoscope to listen to the function of the
valves in the HEART, to the HEART RATE, to the flow
of BLOOD through the chambers of the heart, and
for abnormal sounds, such as a pericardial rub or a
HEART MURMUR, that can indicate cardiovascular
disorders. The French physician René Laënnec
(1781–1821) invented the stethoscope and introduced
the first practical model, a simple tube with
a flare at one end and a small opening that served
as an earpiece at the other end, in 1816. The
instrument evolved over the next 100 years into
the familiar style in use today, a flexible “Y” of
tubing with dual earpieces and a combination bell
and diaphragm with a lever to switch between
them. The bell picks up low-pitched tones and the
diaphragm picks up high-pitched tones.
See also AUSCULTATION.
stress test A diagnostic procedure to evaluate
the cardiovascular system’s ability to meet the
body’s increased oxygen needs during physical
exercise. The most common procedure is the exercise
stress test, in which the person walks on a
treadmill or rides a stationary bicycle at an escalating
pace. A continuous ELECTROCARDIOGRAM (ECG)
monitors the heart’s response. Variations of the
stress test include the ECHOCARDIOGRAM stress test,
in which the cardiologist uses ULTRASOUND to visualize
the heart’s functions during exercise, and the
pharmacological stress test, in which the cardiologist
administers a DRUG such as dipyridamole that
causes a cardiovascular response that simulates
the effects of exercise. A stress test helps determine
the extent of cardiovascular impairment
present as a result of conditions such as CORONARY
ARTERY DISEASE (CAD) and HEART FAILURE. A stress
test does not require preparation or recovery, and
takes 20 to 40 minutes to complete. There is a
very slight risk that a stress test may trigger a
HEART ATTACK, to which the facility and its staff are
prepared to respond if necessary.
See also HEART; MYOCARDIAL PERFUSION IMAGING;
OXYGEN–CARBON DIOXIDE EXCHANGE.