Blood pressure is the pressure of the blood against the blood vessel walls as blood flows through the vessels.
Description
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.
Function
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
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"—High 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.
Stroke—High 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 disease—High 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 failure—Over 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 failure—Over 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.
Lifestyle modifications
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.
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.
Angiotensin converting enzyme (ACE) inhibitor—A drug used to decrease pressure inside blood vessels.
Artery—A blood vessel that carries blood from the heart to the body.
Beta blocker—A drug used to slow heart rate and reduce pressure inside blood vessels.
Calcium channel blocker—A drug used to relax blood vessels and the heart muscle.
Cardiovascular—The heart and blood vessels.
Congestive heart failure—A 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 pressure—The lower number of a blood pressure measurement or the pressure when the heart is at rest.
Diuretic—A drug that eliminates excess fluid in the body.
Fat—One of the nutrients that supply calories to the body.
Hypertension—High blood pressure.
Hypertrophy—Enlargement of tissue or an organ.
Millimeter (mm)—A unit of measurement equal to one-thousandth of a meter.
Risk factors—Behaviors, traits, or conditions in a person that are associated with an increased chance (risk) of disease.
Sign—An objective observation of an illness.
Sphygmomanometer—A manual device used to measure blood pressure.
Symptom—Any indication of disease noticed or felt by a patient.
Systolic blood pressure—The higher number of a blood pressure measurement or the pressure when the heart is contracting.
BOOKS
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.
ORGANIZATIONS
American College of Cardiology. Heart House. 9111 Old Georgetown Rd., Bethesda, MD 20814-1699. (800) 253-4636. <http://www.acc.org>.
American Heart Association. National Center. 7272 Greenville Ave., Dallas, TX 75231. (800) AHA-USA1. <http://www.americanheart.org>.
American Society of Hypertension. 515 Madison Ave., Ste. 1212, New York, NY 10022. (212) 644-0650. <http://www.ash-us.org>.
National Heart, Lung, and Blood Institute. Information Center. PO Box 30105, Bethesda, MD 20824-0105. (800) 575-WELL. <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.
OTHER
National Heart, Lung, and Blood Institute. Healthy Heart Handbook for Women. 1997. <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.
