Heart disease in tHe fire service - West Valley City Firefighters, IAFF ...

BLOOD PRESSURE (hg)
Blood pressure refers to the pressure
within arteries generated by the heart’s
pumping. Blood pressure is reported in
millimeters (mm) of mercury. For
example, a pressure of 20 mm means that
a column of liquid mercury (Hg) would
be elevated 20 mm against gravity. For
clinical purposes, two values of blood
pressure are measured and recorded
together, such as 110/70. The first
number, the systolic pressure, is a
measurement of the peak pressure in the
arteries that occurs after the left ventricle
contracts to sends blood into the aorta
and rest of the body. The second number,
the diastolic pressure, is the resting
pressure of the arteries.
Blood pressure is determined by
multiple variables, such as the volume of
blood in the vascular system, force from
the left ventricle contraction, and the
diameter of arteries, which can be
controlled by contraction of muscles in
the arterial walls. The body has
homeostatic mechanisms to control the
effective circulating volume of fluid by
altering the rate of blood filtration and
excretion of fluid in the kidneys, and
secretes hormones that can alter dilation
of blood vessels and change the force of
heart contractions.
A DYNAMIC SYSTEM
The circulatory system has homeostatic
mechanisms in place to respond to
conditions requiring increased work to
keep the tissues of the body supplied with
oxygen. This can include, but is not
limited to increased physical exertion,
strong emotions, pain and illness. The
heart can respond to signals from the
nervous system and chemical messengers
like epinephrine to change the rate of
contraction, force of contraction or
amount of blood pumped out of the left
ventricle with each contraction. Similarly,
the arteries and veins can change
diameter that can alter blood pressure. If
arteries decrease in diameter, the blood
pressure will increase and conversely, if
the diameter of arteries is increased,
blood pressure will fall. Additionally,
medications can interact with this system.
CONCLUSION
The circulatory system is composed of
the heart and associated vessels that
transport blood, which carries oxygen
and essential materials throughout the
body. These components form a dynamic
system that can respond to multiple
demands on the body by altering
variables like heart rate, blood pressure,
effective circulating volume of blood and
myocardial contractility. The brain and
other vital organs depend on the proper
function of the circulatory system for
survival, making circulatory health
critically important. n
i
, ii , iii , iv From The Merck Manual Home Health Handbook, edited by Robert Porter. Copyright 2010-2011 by Merck Sharp & Dohme Corp., a subsidiary of Merck &
Co., Inc., Whitehouse Station, NJ. Available at: http://www.merckmanuals.com/home/index.html. Accessed (3/31/12).
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