Encyclopedia of Health and Medicine

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blood pressure The force BLOOD exerts against
the walls of the arteries as it travels through them,
as a combination of resistance and the HEART’s
pumping effort. A sphygmomanometer is the
device that measures blood pressure, reported in
millimeters of mercury (mm Hg). A typical blood
pressure reading reports the pressure at the peak
(systole, at ventricular contraction) and trough
(diastole, at ventricular filling) of the CARDIAC
CYCLE. The first number in a blood pressure reading
is the systolic measure and the second number
is the diastolic measure. These measures are independently
important as well as significant in combination.
Blood pressure is among the vital signs
health-care providers measure to assess general
health status.
Several mechanisms within the body, including
neurologic actions in the brainstem and hormonal
actions initiated in the KIDNEYS, regulate blood
pressure. Clusters of specialized NERVE cells in the
heart and major arteries, called baroreflex sensors,
continuously send biochemical signals to the regulatory
mechanisms. These mechanisms are redundant—that
is, they overlap one another to respond
to physiologic changes such as fluid volume and
oxygen demand. These mechanisms increase
blood pressure by constricting arteries and arterioles,
raising the resistance blood encounters as it
flows through these blood vessels, and correspondingly
increasing the rate and force of the
heart’s contractions. They decrease blood pressure
through reverse actions, dilating arteries and arterioles
and decreasing the heart’s pumping force.
Blood pressure typically increases with exercise or
stress, reflecting increased METABOLISM. Higher
blood pressure pushes oxygen and NUTRIENTS more
rapidly into the CAPILLARY BEDS, speeding the rate
at which these substances reach cells.
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Blood pressure that is higher than is optimal for
cardiovascular health is HYPERTENSION; blood pressure
that is too low to adequately circulate blood
is HYPOTENSION. Most hypotension occurs as a SIDE
EFFECT of medications or neurologic conditions,
although some degree of hypotension is common
with cardiovascular slowing in aging. Researchers
believe age-related hypotension reflects disturbances
of the baroreflexes. Cardiologists may prescribe
medications to constrict the arteries and
intensify the heart’s contractions when hypotension
causes symptoms such as mental confusion or
SYNCOPE (fainting).
BLOOD PRESSURE VALUES
Classification Systolic Diastolic
healthy below 120 mm Hg below 80 mm Hg
prehypertension 120–139 mm Hg 80–89 mm Hg
stage 1 140–159 mm Hg 90–99 mm Hg
hypertension
stage 2 160 mm Hg and 100 mm Hg and
hypertension above above
Hypertension poses a significant threat to cardiovascular
health, raising the risk for HEART ATTACK,
RENAL FAILURE, and STROKE. Researchers do not fully
understand how hypertension develops, though
they do know the contributing factors the development
of it (salt intake, physical inactivity, OBESITY,
and DIABETES) as well as how to influence blood
pressure regulatory mechanisms to bring it under
control in most situations. Hypertension exists
when either systolic or diastolic pressure is elevated.
Health conditions that contribute to hypertension
include
• arteriosclerosis, atherosclerotic disease, and cigarette
smoking, each of which stiffens the arteries
and narrows the arterioles