Blood Pressure is a pressure of circulating blood against
the walls of the arteries. Blood pressure is an important
diagnostic index. This is because the heart can pump into
the large arteries a greater volume of blood than can be
absorbed by the tiny arterioles and capillaries, the resulting
back pressure is exerted against the arteries. Any condition
that dilates or contracts the blood vessels or affects their
elasticity of the blood vessels then it affects the blood
pressure. In a healthy animal the blood pressure normal
for its species is maintained within a certain average range
with great constancy. Controlled by both cerebrospinal and
sympathetic nerve centres, the complex nervous mechanisms
that balance and coordinate the activity of the heart and
arterial muscles permit great local variation in the rate
of blood flow without disturbing the general blood pressure.
Blood pressure is read at two points: the high point at
which the heart contracts to empty its blood into the circulation,
called systole; and the low point at which the heart relaxes
to fill with blood returned by the circulation, called diastole.
Pressure is always measured in millimetres (mm) of mercury
by an instrument called a sphygmomanometer which consisting
of an inflatable rubber cuff connected to a pressure-detecting
device with a dial. The cuff is wrapped around the upper
left arm and inflated by squeezing a rubber bulb connected
to it by a tube. Meanwhile, the doctor making the examination
listens to a stethoscope applied to an artery in the lower
arm. When the cuff expands then it gradually compresses
the artery. The point at which the cuff stops the circulation
and at which no pulsations can be heard is read as the systolic
pressure. A spurting sound can then be heard as the heart
contraction forces blood through the artery. The cuff is
then allowed gradually to deflate further until the blood
is flowing smoothly again. A reading at this point shows
the diastolic pressure that occurs during relaxation of
the heart. During a single cardiac cycle or heartbeat the
blood pressure varies from maximum during systole to minimum
during diastole. Usually both measurements are given as
a ratio expression of the highest over the lowest.
In healthy people the blood pressure varies from about
80/45 in infants, to about 120/80 at age 30, to about 140/85
at age 40 and over. This increase occurs when the arteries
lose the elasticity which in younger people used to absorbs
the shock of heart contractions. Blood pressure varies between
individuals and in the same individual at different times.
It is generally higher in men than in women and children
it is lowest during sleep, and is influenced by a wide range
Many healthy people have habitual systolic pressures of
from about 95 to 115 not associated with symptoms or disease.
Abnormally high blood pressure, or hypertension, is considered
a contributory cause of arteriosclerosis. Poisons generated
within the body cause extreme hypertension in various disorders.
Abnormally low pressure also called hypotension, is observed
in infectious and wasting diseases. A systolic pressure
of much lower than 80 is usually associated with shock.
In the case that you have a doubt
on a something listed here or want to know something that
has not been mentioned please use our Reference