1-20
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 measured.
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 pressure.
(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:
(1) Pain. Moderate to severe pain will increase blood pressure.
(2) Emotions. Fear, anger, anxiety, or excitement will increase blood pressure.
(3) Disease. Disease conditions may cause abnormal increase or decrease of blood pressure.
e. In patients with hypertension or other cardiovascular disease, it is best to measure blood pressure in both the right and left arms. There should be no more than 5 mmHg difference between the two readings. A greater difference is indicative of vascular disease.
f. The physician may order blood pressure checks to be done with the patient lying down, sitting, and standing. The corresponding rise or fall in pressure with the change of position may give the physician valuable information about the nature of the cardiovascular disease.
g. Pulse pressure is the difference between the systolic and diastolic pressures. Normal range for pulse pressure should be 30-50 mmHg, with 40 mmHg the average.
(1) A decreased pulse pressure (less than 30 mmHg) is related to factors that cause an increase in the diastolic blood pressure, a decrease in systolic blood pressure, or a combination of both. Causes of decreased pulse pressure included peripheral vasoconstriction, aortic valve stenosis, mitral valve insufficiency, or decreased stroke volume due to heart failure or hypovolemia.
(2) An increased pulse pressure (greater than 50 mmHg) is related to factors that cause a decrease in the diastolic blood pressure, an increase in systolic blood pressure, or both. Causes of increased pulse pressure include hypertension, circulatory overload, arrhythmias, increased stroke volume caused by anxiety or exercise, or decreased distensibility of the arteries as seen in arteriosclerosis and aging.
