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5-1. WHAT IS BLOOD PRESSURE?

Blood pressure refers to the force (pressure) with which the blood presses against the walls of the blood vessel. All blood vessels--large or small, artery or vein--have blood pressure. However, the term blood pressure normally refers to the blood pressure of a major artery. Unlike the other vital signs discussed previously, it takes two numbers--the systolic pressure and the diastolic pressure--to describe this vital sign. Blood pressure is normally measured in millimeters of mercury (mm Hg). "Millimeters of mercury" is a standard unit for measuring pressure. It refers to how high a force (pressure) would cause a column of mercury (chemical symbol Hg) to rise in a tube. Figure 5-1 gives the general idea. The greater the pressure, the more mercury is forced up the tube.

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Figure 5-1. "Millimeters of mercury" as a measure of pressure.

 

5-2. WHAT ARE SYSTOLIC AND DIASTOLIC PRESSURES?

Basically, the systolic pressure is the greatest pressure that the blood exerts against the walls of the blood vessel while the diastolic is the lowest pressure that the blood exerts against the walls of the vessel. A person's blood pressure depends upon the force of the heart's pumping action, the degree to which the blood vessel will stretch, and the amount of blood in the blood vessel.

a. Systolic. The arteries are under the greatest pressure when the heart pumps blood into them. The extra blood that is forced into the arteries make them stretch.

(1) In a normal adult male, the systolic pressure should be between 100 and 140 mm Hg, inclusive. (Inclusive simply means to include the ends of the range. Systolic pressures of 100 and of 140 are within normal range.)

(2) In a normal adult female, the systolic pressure should be between 90 and 130 mm Hg, inclusive.

b. Diastolic. The arteries are under the least pressure from the blood when the heart is at rest (between pumps or beats) and the arteries have returned to their normal size.

(1) In a normal adult male, the diastolic pressure should be between 60 and 90 mm Hg, inclusive.

(2) In a normal adult female, the diastolic pressure should be between 50 and 80 mm Hg, inclusive.

5-3. WHAT FACTS AFFECT A PERSON'S BLOOD PRESSURE?

There are several factors that can affect a patient's blood pressure. Some are only temporary; others are long-term effects. A condition in which the blood pressure is considerably above normal is called "hypertension." If the blood pressure is too low, it is called "hypotension."

a. Condition of Cardiovascular System. A primary factor influencing a patient's blood pressure is the condition of his cardiovascular system (heart and blood vessels).

(1) If a patient's heart is not pumping blood with enough force, his blood pressure will be low. This will decrease the rate that blood is circulated throughout the body. Slow blood circulation may result in certain parts of the body (especially the brain) not receiving enough oxygen since oxygen is carried by the blood.

(2) If a patient's heart is pumping with too much force, his blood pressure will be high. If an artery has a weak spot, the force of the systolic pressure may be enough to rupture the artery and allow blood to escape.

(3) If a patient's arteries loose part of their elasticity, such as in patients who have arteriosclerosis (hardening of the arteries), the patient's blood pressure will be higher, since the artery walls stretch less and cannot relieve as much pressure.

b. Age. A person's blood pressure readings tend to increase as he grows older.

c. Gender. As indicated in paragraph 5-2, men tend to have higher blood pressure than women of the same age.

d. Physical Fitness. People who are physically fit tend to have more normal blood pressure than people who are "out of shape."

e. Obesity. People who are very overweight usually have higher blood pressure than they would if their weight were closer to their ideal weight.

f. Pain. Pain is a type of body defense that lets the brain know that something is wrong. The brain may respond to pain by increasing the rate and strength of heartbeats. The increased rate increases the amount of oxygen available to the muscles for producing energy. It also results in an increased blood pressure.

g. Emotion. Fear, worry, excitement, and similar emotions can result in a higher blood pressure. The brain may react to these emotions in basically the same way that it reacts to pain.

h. Gravity. If a person is standing, the blood pressure of the arteries in the lower part of the body will be greater than the pressure in the upper part of the body.

i. Exercise. A person's blood pressure is greater during and just after exercising because the heart beats faster in order to supply additional oxygen to the muscles.

j. Disease. Almost any disorder that affects the arteries or the renal (kidney) system will result in a higher blood pressure. Diseases that weaken the heart will usually result in a lower blood pressure.

k. Drugs. Drugs designed to strengthen the actions of the heart, such as digitalis, will cause the patient's blood pressure to rise. Drugs that cause the arteries to become smaller in diameter (called vasoconstrictors) will also cause the patient's blood pressure to rise. Drugs that cause the patient's arteries to become larger in diameter (called vasodilators) will decrease blood pressure.

l. Eating. A person's blood pressure is usually elevated (increased) while he is eating and for a while after he finishes the meal.

m. Bleeding. Serious bleeding (hemorrhaging) reduces the amount of blood in the body's circulatory system and thus reduces blood pressure.

David L. Heiserman, Editor

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Revised: June 06, 2015