Structure and Functions (Magill’s Medical Guide, Sixth Edition)
When the left ventricle of the heart beats, it pumps 5 liters of blood per minute to the aorta, through the arteries, and into the arterioles. As these blood vessels decrease in diameter, they create resistance to blood flow and the pressure of the blood against their walls increases. This blood pressure is expressed as two numbers measured in millimeters of mercury (mmHg) by a sphygmomanometer. The first number, called the systolic pressure, is the maximum pressure that occurs when the heart contracts and the ventricle is emptying its blood. The second number, called the diastolic pressure, is the minimum pressure that occurs when the heart relaxes and the ventricle is filling with blood before the next contraction.
Blood pressure depends on the strength of the heart muscle, the volume and thickness of blood being pumped, and the diameter and flexibility of the blood vessels, all of which may vary with age, health, and physical condition. Blood pressure is also affected by activity, diet, hydration (including caffeine and alcohol), emotional stress, physical pain, tobacco use, weight (including pregnancy), abrupt changes in body position, and medication.
Blood pressure is a commonly measured indicator of the body’s state of health, along with body temperature, pulse rate (number of heartbeats per minute), and respiratory rate (number of breaths per minute). It can be measured noninvasively using a...
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Disorders and Diseases (Magill’s Medical Guide, Sixth Edition)
The average blood pressure for healthy adults is 120 over 80 mmHg (written as 120/80). A systolic pressure of 120-139 mmHg or a diastolic pressure of 80 to 89 mmHg is considered to be slightly elevated, a condition called prehypertension. A systolic pressure of at least 140 mmHg or a diastolic pressure of at least 90 mmHg is considered to be elevated, a condition called hypertension. In most cases, hypertension has no known direct medical cause; however, in some cases, it is secondary to other health conditions such as kidney disease. Four groups of people are predisposed to hypertension: obese people, elderly people, people with diabetes, and African Americans. Chronic hypertension is a risk factor for heart attack, stroke, and aortic aneurysm.
The goal of hypertension treatment is to get the resting blood pressure below 140/90. In some cases, this may be accomplished solely with lifestyle changes, which should be tried before drug therapy is begun. These lifestyle changes include discontinuing alcohol consumption and tobacco use, reducing dietary salt and sugar intake, eating foods low in saturated fat, performing regular low-intensity exercise such as walking, and getting sufficient sleep and stress relief. When these changes alone are insufficient, one or more medications may be prescribed, such as diuretics, beta-blockers, calcium-channel blockers, or angiotensin-converting enzyme (ACE) inhibitors.
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
Direct measurement of arterial blood pressure was first reported by Reverend Stephen Hales in 1733. He inserted a glass tube in a horse’s artery and found that the column of blood rose to a vertical height of more than 8 feet. Pressures were later measured with columns of water and saline, but they still required an unwieldy length of tube. Eventually, a mercury column was used because mercury is more than thirteen times as dense as water and the column length was more manageable. Sphygmomanometers today no longer use mercury, but the standard unit of mmHg remains.
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Fortmann, Stephen P., and Prudence E. Breitrose. The Blood Pressure Book: How to Get It Down and Keep It Down. 3d ed. Boulder, Colo.: Bull, 2006.
Kowalski, Robert E. The Blood Pressure Cure: Eight Weeks to Lower Blood Pressure Without Prescription Drugs. Hoboken, N.J.: John Wiley & Sons, 2008.
Rubin, Alan L. High Blood Pressure for Dummies. 2d ed. Hoboken, N.J.: John Wiley & Sons, 2007.
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Blood Pressure (Encyclopedia of Nursing & Allied Health)
Blood pressure is the pressure of the blood against the blood vessel walls as blood flows through the vessels.
The heart beats about 60 to 70 times a minute. With each beat as the heart contracts, a surge of blood is pumped from the heart into the arteries. The pressure in the artery walls during this surge is measured as the systolic blood pressure (a higher number). Between beats, the heart is relaxed and there is much less pressure on the artery walls. This is measured as the diastolic blood pressure (a lower number). Blood pressure is given as two numbers written as 120/80 mm Hg and is measured with a device called a sphygmomanometer in millimeters (mm) of mercury (Hg). The pressure depends on the amount of blood pumped through the heart in addition to the resistance and elasticity of the blood vessels to the amount of blood flowing.
Blood pressure is necessary to sustain life. It continuously forces blood carrying oxygen and nutrients from the heart to the organs and tissues of the body. Blood pressure levels can go up or down in the course of a day depending on activity and stress levels, medications, or diet.
A person's blood pressure is determined by the contraction of the heart's ventricles, which pump blood into the aorta and subsequently throughout the body. The normal adult blood pressure has a systolic number of 120 and a diastolic number of 80. Systolic pressure is taken when the heart contracts; diastolic pressure is taken when the heart is relaxed.
Normally, about 5.5 quarts (5.25 liters) of blood goes through the heart and blood vessels each minute, an amount called cardiac output. The body is dependent on its volume of blood to maintain blood pressure. If a person experiences heavy blood loss, blood pressure will plunge. Similarly, an increase in blood volume, in cases like water retention, will cause blood pressure to rise.
The brain's medulla contains a cluster of nerves, called the cardiovascular center, that control heart rate, the contraction of the ventricles, and blood vessel diameter. Sensory receptors monitor the stretching of blood vessel walls. During exercise, the heart rate rises and the ventricles contract more forcefully. The cardiovascular center then monitors the dilation (expansion) or constriction of peripheral blood vessels. For example, the blood vessels to organs directly involved the exercise will expand. Blood flow to skeletal muscles may increase by a factor of 10 and that to the heart and skin can triple. Simultaneously, constriction will occur in the blood vessels of the digestive system.
The sensory receptors in the walls of blood vessels continually monitor blood pressure. When the receptors
|Classification of blood pressure (BP)|
|SOURCE: Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure.|
|Category||Range (mm Hg)||Recommendation|
|Normal BP||Systolic <140; diastolic <85||Recheck in 2 years|
|High-normal BP||Diastolic 859||Recheck in 1 year|
|Mild hypertension||Diastolic 9004||Confirm within 2 months|
|Moderate hypertension||Diastolic 10514||Evaluate within 1 month|
|Severe hypertension||Diastolic [.greaterequal] 115||Evaluate immediately or within 1 week|
|Borderline isolated systolic hypertension||Systolic 14059; diastolic <90||Confirm within 2 months|
|Isolated systolic hypertension||Systolic [.greaterequal] 160; diastolic <90||Confirm within 2 months|
detect an increase in aortic pressure, for example, the cardiovascular center directs the lowering of the heart rate and the stretching of blood vessels, which decreases the blood pressure. A decrease in blood pressure causes an increased heart rate and vasoconstriction.
As people age, the blood vessels become less flexible and the heart muscle is less strong, resulting in a smaller output and lower maximum heart rate. Systolic pressure tends to rise as a person ages. Coronary artery disease, which causes the blood vessels in the heart to receive inadequate oxygenation, can cause chest pain or heart attack. Atherosclerosis (clogging of the arteries) can also cause an increase in blood pressure.
Role in human health
The Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC) develops high blood pressure prevention and control recommendations for healthcare providers. According to the JNC, optimal blood pressure (BP) measurement is a systolic blood pressure (SBP) of 120mm Hg or less and a diastolic blood pressure (DBP) of 80mm Hg or less. Blood pressure is still considered normal at levels of 130mm Hg SBP or less and 85mm Hg DBP or less.
Periodic blood pressure measurement is recommended every one to two years for adults with normal blood pressure. A healthcare provider should determine the frequency of blood pressure measurement based on each patient's individual risk factors for high blood pressure. Individual risk factors that contribute to high blood pressure, such as diabetes, a family history of high blood pressure, a diet high in fat and cholesterol, being African-American, elderly, overweight, a smoker, or heavy drinker, are important to consider when advising patients on the frequency of periodic blood pressure measurement. Prevention and management of high blood pressure requires not only active participation by the patient but also education and support from health care providers. Patient education is a shared responsibility among physicians, nurses, dietitians, and allied health professionals. While patient education is time-consuming, it is very important to the process of maintaining health and preventing disease.
Common diseases and disorders
High blood pressure, also called hypertension, is a cardiovascular disease affecting nearly 50 million Americans. The higher than normal pressure pushes blood against the artery walls causing the heart to work harder in order to pump blood to the body. The JNC defines high blood pressure as a systolic blood pressure (SBP) of 140mm Hg or greater, a diastolic blood pressure (DBP) of 90mm Hg or greater, or taking high blood pressure (antihypertensive) medications.
High blood pressure often has no warning signs or symptoms. So, if it is not identified or treated, high blood pressure can damage the arteries and organs causing serious medical problems over time. If not properly managed, high blood pressure can increase the risk of developing, among other problems, the following:
- Atherosclerosis, also called "hardening of the arteries"igh blood pressure can cause atherosclerosis or a thickening and narrowing of the blood vessel walls. This can slow or prevent blood flow through the arteries and may lead to heart attack or stroke.
- Strokeigh blood pressure can cause the arteries to narrow and lead to a stroke if a blood clot blocks one of the narrowed arteries (thrombolytic stroke) or if a weakened blood vessel in the brain ruptures (hemorrhagic stroke).
- Coronary heart diseaseigh blood pressure can cause the coronary arteries to narrow and harden. The coronary arteries carry oxygen to the heart muscle so it can function to pump blood to the body. If blood cannot flow properly through the coronary arteries to the heart, the heart cannot get enough oxygen. This can cause chest pain (angina). If the blood flow to the heart muscle is blocked, it can cause a heart attack. Heart disease is the leading cause of death in the United States.
- Congestive heart failurever years, uncontrolled high blood pressure can cause the heart muscle to compensate by becoming larger (dilatation) to allow more blood to fill it, by thickening the heart muscle (hyper- trophy) to pump more forcefully, or by beating faster to increase circulation. According to the National Institutes of Health, uncontrolled high blood pressure increases the risk of heart failure by 200%, compared with those who do not have high blood pressure.
- Kidney failurever years, high blood pressure can damage the blood vessels of the kidney. The damage may cause the kidneys to no longer filter waste from the blood adequately, which could require dialysis treatment or possibly a kidney transplant.
The cause of high blood pressure is usually unknown, in which case it is called primary or essential hypertension. This cannot be cured. However, it can be easily diagnosed and, in most cases, controlled with lifestyle modifications and/or medications.
Some of the lifestyle modifications for high blood pressure prevention and management include:
- Weight loss if the patient is overweight. As weight increases, blood pressure rises.
- Cutting down on alcohol, no more than one drink per day for women and no more than two drinks per day for men.
- Decreasing salt and sodium, saturated fat, and cholesterol.
- Increasing physical activity, especially aerobic activity 30 to 45 minutes on most days.
- Stopping smoking.
High blood pressure medications work in various ways. They can affect the force of the heartbeat, the blood vessels, and the amount of fluid in the body. Some of the different types of medications prescribed to treat high blood pressure are:
- Diuretics, also called "water pills," decrease the amount of fluid in the body by flushing excess water and sodium from the body through the urine.
- Beta blockers make the heart beat less often and with less force by reducing nerve impulses to the heart and blood vessels.
- Calcium channel blockers relax the blood vessels by preventing calcium from entering the muscle cells of the heart.
- Alpha blockers relax the blood vessels by way of the nervous system. They decrease renin secretion, which is involved in angiotensin II formation.
- Vasodilators widen blood vessels by relaxing the muscle in the vessel walls.
- Angiotensin converting enzyme (ACE) inhibitors relax the blood vessels by preventing angiotensin II from being formed.
High blood pressure can sometimes be traced to a cause such as an adrenal gland tumor, kidney disease, hormone abnormalities, birth control pills, or pregnancy. This is called secondary hypertension and can usually be cured if the cause disappears or is corrected.
Angiotensin converting enzyme (ACE) inhibitor drug used to decrease pressure inside blood vessels.
Artery blood vessel that carries blood from the heart to the body.
Beta blocker drug used to slow heart rate and reduce pressure inside blood vessels.
Calcium channel blocker drug used to relax blood vessels and the heart muscle.
Cardiovascularhe heart and blood vessels.
Congestive heart failure cardiovascular dis- ease that involves the heart muscle's diminished or loss of pumping ability, generally causes fluid that cannot be completely ejected from the heart to back up in the lungs.
Diastolic blood pressurehe lower number of a blood pressure measurement or the pressure when the heart is at rest.
Diuretic drug that eliminates excess fluid in the body.
Fatne of the nutrients that supply calories to the body.
Hypertensionigh blood pressure.
Hypertrophynlargement of tissue or an organ.
Millimeter (mm) unit of measurement equal to one-thousandth of a meter.
Risk factorsehaviors, traits, or conditions in a person that are associated with an increased chance (risk) of disease.
Signn objective observation of an illness.
Sphygmomanometer manual device used to measure blood pressure.
Symptomny indication of disease noticed or felt by a patient.
Systolic blood pressurehe higher number of a blood pressure measurement or the pressure when the heart is contracting.
Report of the United States Preventive Services Task Force. Guide to Clinical Preventive Services. International Medical Publishing, 1996.
Tortora, Gerard, and Sandra Grabowski. Principles of Anatomy and Physiology. 8th ed. New York: John Wiley and Sons, 1996.
American College of Cardiology. Heart House. 9111 Old Georgetown Rd., Bethesda, MD 20814-1699. (800) 253-4636. <<a href="http://www.acc.org">http://www.acc.org>.
American Heart Association. National Center. 7272 Greenville Ave., Dallas, TX 75231. (800) AHA-USA1. <<a href="http://www.americanheart.org">http://www.americanheart.org>.
American Society of Hypertension. 515 Madison Ave., Ste. 1212, New York, NY 10022. (212) 644-0650. <<a href="http://www.ash-us.org">http://www.ash-us.org>.
National Heart, Lung, and Blood Institute. Information Center. PO Box 30105, Bethesda, MD 20824-0105. (800) 575-WELL. <<a href="http://www.nhlbi.nih.gov">http://www.nhlbi.nih.gov>.
National High Blood Pressure Education Program. NHLBI Health Information Center. PO Box 30105, Bethesda, Maryland 20824-0105. (301) 592-8573.
National Heart, Lung, and Blood Institute. Healthy Heart Handbook for Women. 1997. <<a href="http://www.nhlbi.nih.gov">http://www.nhlbi.nih.gov>.
The Sixth Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. Pub No. 98-4080. November 1997.
Deborah Eileen Parker, R.N.
Blood Pressure (Encyclopedia of Public Health)
Blood pressure is a physiological variableike body temperature, respiratory rate, or heart rate. Blood pressure is not constant throughout the day; each time the heart squeezes and relaxes, there is a new blood pressure. It increases before awakening and declines with sleep. The level of blood pressure is regulated by the kidneys, brain, heart, endocrine glands, and blood vessels. In the United States, the actual level of blood pressure gradually increases from birth to adulthood. Due to difference in diet and activity levels in nonindustrialized countries, however, blood pressure does not increase beyond the age of eighteen.
Whereas temperature is measured with a thermometer, blood pressure is measured with a sphygmomanometer, preferably a mercury sphygmo-manometer, though aneroid and electronic devices are sometimes used.
Blood pressure should be measured after a five-minute period of rest, with the back supported and the legs uncrossed. Constrictive clothing should be removed from around the upper arm, which must be resting on a table at heart level. The blood pressure cuff is evenly and snugly applied around the upper arm above the elbow, and a stethoscope is placed over the crease of the elbow. The cuff is inflated to 15 millimeters of mercury (mmHg) above the point where radial artery pulse (the artery above the thumb at the wrist) disappears. The pressure in the cuff is then slowly released at 2 mmHg per second. The first of two consecutive sounds as cuff pressure decreases is called the systolic blood pressurehe pressure to open the artery occluded with the cuff. The diastolic blood pressure is recorded at the absence of sounds with continued deflation of the blood pressure cuff. Blood pressure is generally recorded to the nearest 2 mmHg. For example, a blood pressure of 142/86 mmHg indicates a systolic blood pressure of 142 mmHg and a diastolic blood pressure of 86 mmHg. Pain and emotional disturbance, as well as caffeine, tobacco, and alcohol, can elevate systolic blood pressure.
An abnormal blood pressure requires confirmation on two subsequent days. An optimal blood pressure is less than 120/80 mmHg. High blood pressure, or hypertension, is defined as either a systolic blood pressure greater than 140 mmHg or a diastolic blood pressure greater than 90 mmHg. Systolic blood pressure is a more powerful predictor of cardiovascular events than diastolic blood pressure. With increasing age, the diastolic blood pressure may actually decrease while systolic blood pressure increases; this indicates increased stiffening of the arteries throughout the body.
Hypertension is not a nervous disorder or an anxiety state, but rather a disease of the blood vessels that increases blood vessel constriction of the small arteries. It particularly damages the blood vessels inside the brain, heart, kidneys, eyes, and the largest artery, the aorta. Damaged arteries may rupture, thicken, or harden and narrowesulting in strokes, heart attacks, kidney failure, visual impairment, or tearing or rupture of the aorta. Also, the left heart chamber thickens as a consequence of increased blood pressure. When the heart can no longer thicken or enlarge to overcome the increased pressure in the blood vessels, the squeezing function of the heart decreases, resulting in congestive heart failure.
CAUSES OF HYPERTENSION
Fifty million Americans (about one-fifth of the U.S. population) have hypertension (see Figure 1). Over 90 percent of the causes of hypertension remain unknown. Four groups are predisposed to developing hypertension: the obese, the elderly, diabetics, and African Americans. Certain drugs are known to elevate blood pressure, including most arthritis medications (except acetaminophen and aspirin), many cold remedies, nose sprays, weight-reducing pills, and alcohol. Increased heart rate, anemia, excessive thyroid hormone, or stiff
(nondistendible) arteries can increase systolic blood pressure. Blocked arteries to the kidney, kidney failure, and decreased production of thyroid hormone are common causes of hypertension. Other rare causes include tumors of the adrenal gland.
TREATMENT OF HYPERTENSION
Nondrug treatment of hypertension should include weight loss, salt restriction, smoking cessation, and alcohol restriction. A reduced saturatedand total-fat diet that is rich in fruits, vegetables, and low-fat dairy products lowers blood pressure in some individuals, avoiding the need for drug treatment. The treatment goal for uncomplicated hypertensives is below 140/90 mmHg. To achieve that goal consistently, most individuals will need to be treated with more than one drug. Treatment has been proven to decrease heart attacks, strokes, and heart failure, and is usually required throughout life.
L. MICHAEL PRISANT
(SEE ALSO: Atherosclerosis; Cardiovascular Diseases; Coronary Artery Disease; Foods and Diets; Lifestyle; Nutrition)
"The Sixth Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure." (1997). Arch Intern Med 157:2413446.