system must perfuse with blood. Excessive body
fat may compress the neck, causing OBSTRUCTIVE
SLEEP APNEA(episodes during sleep in which the
person stops BREATHING). Obstructive sleep apnea
prevents adequate air flow to the LUNGS, reducing
oxygenation of the blood and causing ischemic
episodes in which the heart does not receive
enough oxygen, which results in ARRHYTHMIA.
Excessive body fat may also compress the heart
itself, further increasing the forces against which it
must work to pump blood. All of these factors
conspire to raise blood pressure and increase HEART
RATEin an attempt to help the heart, which, if
allowed to progress unchecked, are likely to result
in HEART FAILURE.
Metabolically, obesity triggers INSULINdysfunc-
tion. Because insulin plays a key role in cholesterol
synthesis in the LIVER, hyperlipidemia is likely.
Hyperlipidemia contributes to CORONARY ARTERY DIS-
EASE(CAD) and PERIPHERAL VASCULAR DISEASE(PVD). A
more significant health concern is the evolution
from insulin resistance to diabetes. Diabetes
increases cardiovascular disease risk substantially,
as it is itself an independent risk factor for, as well as
a leading cause of, cardiovascular disease.
When obesity declines even modestly, cardio-
vascular risk drops and cardiovascular health
improves. As little as a 10-pound weight loss can
drop systolic blood pressure by 10 millimeters of
mercury (mm Hg). With sustained weight loss,
many cardiovascular symptoms retreat and risk
continues to fall.
See also BODY FAT PERCENTAGE; CARDIOVASCULAR
DISEASE PREVENTION; EATING HABITS; DIET AND HEALTH;
EXERCISE AND HEALTH; LIFESTYLE AND CARDIOVASCULAR
HEALTH; OBESITY AND DIABETES; WEIGHT LOSS AND
WEIGHT MANAGEMENT.
omega fatty acids and cardiovascular health
Omega fatty acids are dietary substances that
increase high-density lipoprotein cholesterol
(HDL-C) and decrease low-density lipoprotein
cholesterol (LDL-C). Omega fatty acids also reduce
the likelihood of ARRHYTHMIAand may help lower
BLOOD PRESSURE. The omega fatty acids that appear
most beneficial are eicosapentaenoic acid (EPA)
and docosahexaenoic acid (DHA). Researchers do
not know how omega fatty acids affect cardiovas-
cular health though believe they reduceINFLAMMA-
TIONand the blood’s clotting tendencies. These
effects slow ATHEROSCLEROTIC PLAQUEaccumulation
and infiltration into the arterial intima, the inner-
most layer of the arterial wall.
The most abundant dietary sources of omega
fatty acids are cold-water fish such as mackerel,
tuna, and salmon. Health experts recommend eat-
ing at least two servings a week of these fish,
which contain high levels of EPA and DHA, or
taking supplements that provide 1 to 1.5 grams of
EPA and DHA. People who have high levels of
triglycerides may need to take higher doses. How-
ever, doses higher than 3 grams may cause exces-
sive bleeding. Flaxseed and flaxseed oil, canola oil,
soybeans and soybean foods such as tofu, and
walnuts are good dietary sources of alpha-
linolenic acid (LNA), from which the body can
metabolize omega fatty acids.
An unresolved concern remains that of mer-
cury contamination in cold-water fish. Mercury
poisoning is particularly harmful to a developing
FETUSand raises the risk for certain kinds of CANCER
in adults. The US Environmental Protection
Agency (EPA) routinely samples and reports mer-
cury levels in different species of fish and issues
advisories for those that exceed established safety
levels. People who are concerned about mercury
contamination can obtain omega fatty acids
through dietary supplements, which appear
equally effective.
See alsoCARDIOVASCULAR DISEASE PREVENTION; DIET
AND CARDIOVASCULAR HEALTH; DIET AND HEALTH; NUTRI-
TIONAL NEEDS; NUTRITIONAL SUPPLEMENTS.open heart surgery AnyOPERATIONin which the
surgeon opens the chest to expose the HEART.
Open heart surgery is the most common method
for CORONARY ARTERY BYPASS GRAFT(CABG), valvulo-
plasty and heart valve replacement, reconstructive
operations to correct congenital heart malforma-
tions, and HEART TRANSPLANTATION. In the United
States, surgeons perform about 750,000 open
heart surgery operations each year, about 600,000
of which are CABG. Open heart surgery requires
general ANESTHESIAand a hospital stay of 3 to 10
days, depending on the operation. Though most
open heart operations also employ CARDIOPUL-
MONARY BYPASS, in which a machine takes over the
role of oxygenating and pumping the BLOODso the90 The Cardiovascular System