1-20. BLOOD PRESSURE
a. Blood pressure is defined as the pressure exerted by the blood on the walls of
the blood vessels. When speaking of blood pressure, it is the arterial blood pressure
that we are concerned with. When taking a patient's blood pressure with a
sphygmomanometer and stethoscope, it is the arterial blood pressure that is being
b. Blood pressure is registered by two numbers that represent the pressures
exerted during contraction and relaxation of the heart.
(1) Systolic pressure is the maximum pressure occurring during systole, or
contraction, of the ventricles. It is the higher of the two numbers. Normal systolic
pressure for the average resting adult is between 100-150 mmHg.
(2) Diastolic pressure is the pressure occurring during diastole, the period of
relaxation and filling of the ventricles. This is the lowest pressure. Normal diastolic
pressure for the average resting adult is between 60-90 mmHg.
c. Blood pressure is best measured over a large artery. The most commonly
used is the brachial artery. The cuff is wrapped around the upper arm and auscultation
is done over the brachial artery in the antecubital space.
(1) With extremely obese patients, the application of the cuff around the
forearm and auscultation over the radial artery may give a truer measurement of blood
(2) Blood pressure may also be taken in the leg by wrapping the cuff around
the thigh and auscultating the popliteal artery behind the knee.
(3) An accurate blood pressure reading depends upon the width of the cuff
in relation to the diameter of the limb used. If the cuff is too large for the limb, as in a
child, the reading obtained could be significantly lower than the true pressure. If the cuff
is too small for the limb, as in an obese person, the reading obtained may be higher
than the true pressure.
d. Blood pressure depends upon the force of the heartbeat, the volume of blood
in the circulatory system, and the resistance within the blood vessels. Other factors that
affect blood pressure are:
Pain. Moderate to severe pain will increase blood pressure.
Emotions. Fear, anger, anxiety, or excitement will increase blood