What is high blood pressure?

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Created on Thursday, 05 July 2012 00:00

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What is high blood pressure?

High blood pressure (HBP) or hypertension means high pressure (tension) in the arteries. Arteries are vessels that carry blood from the pumping heart to all the tissues and organs of the body. High blood pressure does not mean excessive emotional tension, although emotional tension and stress can temporarily increase blood pressure. Normal blood pressure is below 120/80; blood pressure between 120/80 and 139/89 is called "pre-hypertension", and a blood pressure of 140/90 or above is considered high.

The top number, the systolic blood pressure, corresponds to the pressure in the arteries as the heart contracts and pumps blood forward into the arteries. The bottom number, the diastolic pressure, represents the pressure in the arteries as the heart relaxes after the contraction. The diastolic pressure reflects the lowest pressure to which the arteries are exposed.

An elevation of the systolic and/or diastolic blood pressure increases the risk of developing heart (cardiac) disease, kidney (renal) disease, hardening of the arteries (atherosclerosis or arteriosclerosis), eye damage, and stroke (brain damage). These complications of hypertension are often referred to as end-organ damage because damage to these organs is the end result of chronic (long duration) high blood pressure. For that reason, the diagnosis of high blood pressure is important so efforts can be made to normalize blood pressure and prevent complications.

It was previously thought that rises in diastolic blood pressure were a more important risk factor than systolic elevations, but it is now known that in people 50 years or older systolic hypertension represents a greater risk.

The American Heart Association estimates high blood pressure affects approximately one in three adults in the United States -- 73 million people. High blood pressure is also estimated to affect about two million American teens and children, and the Journal of the American Medical Association reports that many are underdiagnosed. Hypertension is clearly a major public health problem.

How is the blood pressure measured?

The blood pressure usually is measured with a small, portable instrument called a blood pressure cuff (sphygmomanometer). (Sphygmo is Greek for pulse, and a manometer measures pressure.) The blood pressure cuff consists of an air pump, a pressure gauge, and a rubber cuff. The instrument measures the blood pressure in units called millimeters of mercury (mm Hg).

The cuff is placed around the upper arm and inflated with an air pump to a pressure that blocks the flow of blood in the main artery (brachial artery) that travels through the arm. The arm is then extended at the side of the body at the level of the heart, and the pressure of the cuff on the arm and artery is gradually released. As the pressure in the cuff decreases, a health practitioner listens with a stethoscope over the artery at the front of the elbow. The pressure at which the practitioner first hears a pulsation from the artery is the systolic pressure (the top number). As the cuff pressure decreases further, the pressure at which the pulsation finally stops is the diastolic pressure (the bottom number). Measurement of blood pressure can also be done with electronic machines that automatically inflate the cuff and recognize the changes in pulsations.

How is high blood pressure defined?

Blood pressure can be affected by several factors, so it is important to standardize the environment when blood pressure is measured. For at least one hour before blood pressure is taken, avoid eating, strenuous exercise (which can lower blood pressure), smoking, and caffeine intake. Other stresses may alter the blood pressure and need to be considered when blood pressure is measured.

Even though most insurance companies consider high blood pressure to be 140/90 and higher for the general population, these levels may not be appropriate cut-offs for all individuals. Many experts in the field of hypertension view blood pressure levels as a range, from lower levels to higher levels. Such a range implies there are no clear or precise cut-off values to separate normal blood pressure from high blood pressure. Individuals with so-called pre-hypertension (defined as a blood pressure between 120/80 and 139/89) may benefit from lowering of blood pressure with lifestyle modification and possibly medication, especially if there are other risk factors for end-organ damage such as diabetes or kidney disease (lifestyle changes are discussed below).

For some people, blood pressure readings lower than 140/90 may be a more appropriate normal cut-off level. For example, in certain situations, such as in patients with long duration (chronic) kidney diseases that spill (lose) protein into the urine (proteinuria), the blood pressure is ideally kept at 130/80, or even lower. The purpose of reducing the blood pressure to this level in these patients is to slow the progression of kidney damage. Patients with diabetes (diabetes mellitus) may also benefit from blood pressure that is maintained at a level lower than 130/80. In addition, African Americans, who have an increased risk for developing the complications of hypertension, may decrease this risk by reducing their systolic blood pressure to less than 135 and their diastolic blood pressure to 80 or less.

In line with the thinking that the risk of end-organ damage from high blood pressure represents a continuum, statistical analysis reveals that beginning at a blood pressure of 115/75 the risk of cardiovascular disease doubles with each increase in blood pressure of 20/10. This type of analysis has led to an ongoing "rethinking" in regard to who should be treated for hypertension, and what the goals of treatment should be.

What are the signs and symptoms of high blood pressure?

Uncomplicated high blood pressure usually occurs without any symptoms (silently) and so hypertension has been labeled "the silent killer." It is called this because the disease can progress to finally develop any one or more of the several potentially fatal complications such as heart attacks or strokes. Uncomplicated hypertension may be present and remain unnoticed for many years, or even decades. This happens because there are no symptoms, and those affected fail to undergo periodic blood pressure screening.

Some people with uncomplicated hypertension, however, may experience symptoms such as headache, dizziness, shortness of breath, and blurred vision usually with blood pressure that is very high. The presence of symptoms can be a good thing in that they can prompt people to consult a doctor for treatment and make them more compliant in taking their medications. Often, however, a person's first contact with a physician may be after significant damage to the body has occurred. In many cases, a person visits or is brought to the doctor or an emergency department with a heart attack, stroke, kidney failure, or impaired vision (due to damage to the back part of the retina). Greater public awareness and frequent blood pressure screening may help to identify patients with undiagnosed high blood pressure before significant complications have developed.

About one out of every 100 (1%) people with hypertension is diagnosed with severe high blood pressure (accelerated or malignant hypertension) at their first visit to the doctor. In these patients, the diastolic blood pressure (see the following section) exceeds 140 mm Hg! Affected persons often experience severe headache, nausea, visual symptoms, dizziness, and sometimes kidney failure. Malignant hypertension is a medical emergency and requires urgent treatment to prevent a stroke (brain damage).

What are the different types of high blood pressure?

In addition to the most common type of hypertension in which both systolic and diastolic pressures are elevated, there are three additional types of high blood pressure (hypertension): isolated systolic high blood pressure, white coat high blood pressure, and borderline high blood pressure.

Isolated systolic high blood pressure

Remember that the systolic blood pressure is the top number in the blood pressure reading and represents the pressure in the arteries as the heart contracts and pumps blood into the arteries. A systolic blood pressure that is persistently higher than 140 mm Hg is usually considered elevated.

Isolated systolic hypertension is defined as a systolic pressure that is above 140 mm Hg with a diastolic pressure that is below 90. This disorder primarily affects older people and is characterized by an increased (wide) pulse pressure. The pulse pressure is the difference between the systolic and diastolic blood pressures. An elevation of the systolic pressure without an elevation of the diastolic pressure, as in isolated systolic hypertension, therefore increases the pulse pressure. Stiffening of the arteries contributes to this widening of the pulse pressure.

Once considered to be harmless, a high pulse pressure is now considered an important precursor or indicator of health problems and potential end-organ damage. Isolated systolic hypertension is associated with a two to four times increased future risk of an enlarged heart, a heart attack (myocardial infarction), a stroke (brain damage), and death from heart disease or a stroke. Clinical studies in patients with isolated systolic hypertension have indicated that a reduction in systolic blood pressure by at least 20 mm to a level below 160 mm Hg reduces these increased risks.

What causes high blood pressure?

Two forms of high blood pressure have been described -- essential (or primary) hypertension and secondary hypertension. Essential hypertension is a far more common condition and accounts for 95% of hypertension. The cause of essential hypertension is multifactorial, that is, there are several factors whose combined effects produce hypertension. In secondary hypertension, which accounts for 5% of hypertension, the high blood pressure is secondary to (caused by) a specific abnormality in one of the organs or systems of the body. (Secondary hypertension is discussed further in a separate section later.)

Essential hypertension affects approximately 72 million Americans, yet its basic causes or underlying defects are not always known. Nevertheless, certain associations have been recognized in people with essential hypertension. For example, essential hypertension develops only in groups or societies that have a fairly high intake of salt, exceeding 5.8 grams daily. Salt intake may be a particularly important factor in relation to essential hypertension in several situations, and excess salt may be involved in the hypertension that is associated with advancing age, African American background, obesity, hereditary (genetic) susceptibility, and kidney failure (renal insufficiency). The Institute of Medicine of the National Academies recommends healthy 19 to 50-year-old adults consume only 3.8 grams of salt to replace the average amount lost daily through perspiration and to achieve a diet that provides sufficient amounts of other essential nutrients.

Genetic factors are thought to play a prominent role in the development of essential hypertension. However, the genes for hypertension have not yet been identified. (Genes are tiny portions of chromosomes that produce the proteins that determine the characteristics of individuals.) The current research in this area is focused on the genetic factors that affect the renin-angiotensin-aldosterone system. This system helps to regulate blood pressure by controlling salt balance and the tone (state of elasticity) of the arteries.

Approximately 30% of cases of essential hypertension are attributable to genetic factors. For example, in the United States, the incidence of high blood pressure is greater among African Americans than among Caucasians or Asians. Also, in individuals who have one or two parents with hypertension, high blood pressure is twice as common as in the general population. Rarely, certain unusual genetic disorders affecting the hormones of the adrenal glands may lead to hypertension. (These identified genetic disorders are considered secondary hypertension.)

The vast majority of patients with essential hypertension have in common a particular abnormality of the arteries: an increased resistance (stiffness or lack of elasticity) in the tiny arteries that are most distant from the heart (peripheral arteries or arterioles). The arterioles supply oxygen-containing blood and nutrients to all of the tissues of the body. The arterioles are connected by capillaries in the tissues to the veins (the venous system), which returns the blood to the heart and lungs. Just what makes the peripheral arteries become stiff is not known. Yet, this increased peripheral arteriolar stiffness is present in those individuals whose essential hypertension is associated with genetic factors, obesity, lack of exercise, overuse of salt, and aging. Inflammation also may play a role in hypertension since a predictor of the development of hypertension is the presence of an elevated C reactive protein level (a blood test marker of inflammation) in some individuals.

Exercise

A regular exercise program may help lower blood pressure over the long term. Activities such as jogging, bicycle riding, power walking, or swimming for 30 to 45 minutes daily may lower blood pressure by as much as 5 to15 mm Hg. There also appears to be a relationship between the amount of exercise and the degree to which the blood pressure is lowered. So the more you exercise (up to a point), the more you lower the blood pressure. This beneficial response occurs only with aerobic (vigorous and sustained) exercise programs. Any exercise program must be recommended or approved by a physician.

How is high blood pressure treated?

Goals of treatment

High blood pressure is usually present for years before its complications develop. Ideally, hypertension is treated early, before it damages critical organs in the body. Increased public awareness and screening programs to detect early, uncomplicated hypertension are keys to successful treatment. Successful early treatment of high blood pressure can significantly decrease the risk of stroke, heart attack, and kidney failure.

The goal for patients with combined systolic and diastolic hypertension is to attain a blood pressure of 140/85 mm Hg. Bringing the blood pressure down even lower may be desirable in African American patients, and patients with diabetes or chronic kidney disease. Although life style changes in pre-hypertensive patients are appropriate, it is not well established that treatment with medication of patients with pre-hypertension is beneficial.

Treatment with combinations of drugs for high blood pressure

The use of combination drug therapy for hypertension is common. At times, using smaller amounts of one or more drugs in combination can minimize side effects while maximizing the anti-hypertensive effect. For example, diuretics, which also can be used alone, are more often used in a low dose in combination with another class of anti-hypertensive medications. This way, the diuretic has fewer side effects while improving the blood pressure - lowering effect of the other drug. Diuretics also are added to other anti-hypertensive medications when a patient with hypertension also has fluid retention and swelling (edema).

ACE inhibitors or angiotensin receptor blockers may be useful in combination with most other anti-hypertensive medications. These kinds of drugs have additive effects in treating patients with cardiomyopathies and proteinuria. Another useful combination is that of a beta-blocker with an alpha-blocker in patients with high blood pressure and enlargement of the prostate gland in order to treat both conditions simultaneously. Caution is necessary when combining two drugs that both lower the heart rate. For example, patients receiving a combination of a beta-blocker to a non-dihydropyridine calcium channel blocker [for example, diltiazem (Cardizem, Dilacor, Tiazac) or verapamil (Calan, Verelan, Isoptin, Covera-HS)] need to be monitored carefully to avoid an excessively slow heart rate (bradycardia). Combining alpha and beta-blockers such as carvedilol (Coreg) and labetalol (Normodyne, Trandate) is useful for cardiomyopathies and for hypertension patients.

Starting treatment for high blood pressure

Blood pressure persistently higher than 140/ 90 mm Hg usually is treated with lifestyle modifications and medication. More aggressive treatment may be recommended in certain circumstances if the diastolic pressure remains at a borderline level (usually less than 90 mm Hg, yet persistently above 85). These circumstances include borderline diastolic pressures in association with end-organ damage, systolic hypertension, or factors that increase the risk of cardiovascular disease, such as age over 65 years, African American descent, smoking, hyperlipemia (elevated blood fats), or diabetes.

Any one of several classes of medications may be started, except the alpha-blocker medications, which are used only in combination with another anti-hypertensive medication in specific medical situations. (See the next section for a more detailed discussion of each of the several classes of anti-hypertensive medications.)

In some situations, certain classes of anti-hypertensive drugs are preferable to others as the first line (preferred first choice) drugs. Angiotensin converting enzyme (ACE) inhibitors or angiotensin receptor blocking (ARB) drugs are the drugs of choice in patients with heart failure, chronic kidney failure (in diabetics or non-diabetics), or heart attack (myocardial infarction) that weakens the heart muscle (systolic dysfunction). Also, beta-blockers are sometimes the preferred treatment in hypertensive patients with a resting tachycardia (racing heart beat when resting) or an acute (rapid onset) heart attack.

Patients with hypertension may sometimes have a co-existing, second medical condition. In such cases, a particular class of anti-hypertensive medication or combination of drugs may be chosen as the first line approach. The idea in these cases is to control the hypertension while also benefiting the second condition. For example, beta-blockers may treat chronic anxiety or migraine headache as well as hypertension. Also, the combination of an ACE inhibitor and an ARB drug can be used to treat certain diseases of the heart muscle (cardiomyopathies) and certain kidney diseases where reduction in proteinuria would be beneficial.

In other situations, certain classes of anti-hypertensive medications should not be used. Dihydropyridine calcium channel blockers used alone may cause problems for patients with chronic renal disease by increasing proteinuria. However, an ACE inhibitor will blunt this effect. The non-dihydropyridine type of calcium channel blockers should not be used in patients with heart failure. However, these drugs may be beneficial in treating certain arrhythmias. Some drugs, such as minoxidil, may be relegated to second or third line choices for treatment. Clonidine is an excellent drug but has side effects such as fatigue, sleepiness, and dry month making it a second or third line choice. See the section below on pregnancy for the anti-hypertensive drugs that are used in pregnant women.

Which lifestyle modifications are beneficial in treating high blood pressure?

Lifestyle modifications refer to certain specific recommendations for changes in habits, diet and exercise. These modifications can lower the blood pressure as well as improve a patient's response to blood pressure medications.

Alcohol

People who drink alcohol excessively (over two drinks per day*) have a one and a half to two times increase in the prevalence of hypertension. The association between alcohol and high blood pressure is particularly noticeable when alcohol intake exceeds five drinks per day. The connection is a dose-related phenomenon. In other words, the more alcohol consumed, the stronger is the link with hypertension.

*The National Institute on Alcohol Abuse and Alcoholism considers a standard drink to be 12 ounces of beer, 5 ounces of wine, or 1.5 ounces of 80-proof distilled spirits. Each contains roughly the same amount of absolute alcohol- approximately one-half ounce or 12 grams.

Smoking

Although smoking increases the risk of vascular complications (for example, heart disease and stroke) in people who already have hypertension, it is not associated with an increase in the development of hypertension. But cigarette smoking can repeatedly produce an immediate, temporary rise in the blood pressure of 5 to10 mm Hg. Steady smokers however, may have a lower blood pressure than nonsmokers. The reason for this is that nicotine in cigarettes causes a decrease in appetite, which leads to weight loss. This, in turn, lowers blood pressure.

Renal (kidney) hypertension

Diseases of the kidneys can cause secondary hypertension. This type of secondary hypertension is called renal hypertension because it is caused by a problem in the kidneys. One important cause of renal hypertension is narrowing (stenosis) of the artery that supplies blood to the kidneys (renal artery). In younger individuals, usually women, the narrowing is caused by a thickening of the muscular wall of the arteries going to the kidney (fibromuscular hyperplasia). In older individuals, the narrowing generally is due to hard, fat-containing (atherosclerotic) plaques that are blocking the renal artery.

How does narrowing of the renal artery cause hypertension? First, the narrowed renal artery impairs the circulation of blood to the affected kidney. This deprivation of blood then stimulates the kidney to produce the hormones, renin and angiotensin. These hormones, along with aldosterone from the adrenal gland, cause a constriction and increased stiffness (resistance) in the peripheral arteries throughout the body, which results in high blood pressure.

Renal hypertension is usually first suspected when high blood pressure is found in a young individual or a new onset of high blood pressure is discovered in an older person. Screening for renal artery narrowing then may include renal isotope (radioactive) imaging, ultrasonographic (sound wave) imaging, or magnetic resonance imaging (MRI) of the renal arteries. The purpose of these tests is to determine whether there is a restricted blood flow to the kidney and whether angioplasty (removal of the restriction in the renal arteries) is likely to be beneficial. However, if the ultrasonic assessment indicates a high resistive index within the kidney (high resistance to blood flow), angioplasty may not improve the blood pressure because chronic damage in the kidney from long-standing hypertension already exists. If any of these tests are abnormal or the doctor's suspicion of renal artery narrowing is high enough, renal angiography (an X-ray study in which dye is injected into the renal artery) is done. Angiography is the ultimate test to actually visualize the narrowed renal artery.

A narrowing of the renal artery may be treated by balloon angioplasty. In this procedure, the physician threads a long narrow tube (catheter) into the renal artery. Once the catheter is there, the renal artery is widened by inflating a balloon at the end of the catheter and placing a permanent stent (a device that stretches the narrowing) in the artery at the site of the narrowing. This procedure usually results in an improved blood flow to the kidneys and lower blood pressure. Moreover, the procedure also preserves the function of the kidney that was partially deprived of its normal blood supply. Only rarely is surgery needed these days to open up the narrowing of the renal artery.

Any of the other types of chronic kidney disease that reduce the function of the kidneys can also cause hypertension due to hormonal disturbances and/or retention of salt.

It is important to remember that not only can kidney disease cause hypertension, but hypertension can also cause kidney disease. Therefore, all patients with high blood pressure should be evaluated for the presence of kidney disease so they can be treated appropriately.

Cholesterol Levels Vary Widely by Country: Study

MONDAY, April 9 (HealthDay News) -- People's average cholesterol levels seem to rise and fall along with their countries' economies and ease of access to quality health care, according to a new study.

Researchers examined data from thousands of patients with a history of high cholesterol (more than 200 milligrams per deciliter) in 36 countries, including the United States.

The analysis revealed that countries with higher overall income levels, lower out-of-pocket health care costs, and high-performing and efficient health systems tend to have lower rates of high cholesterol among people who'd had a history of high cholesterol.

For patients with no history of high cholesterol, there was no association between a country's economy and health care system and the risk of high cholesterol.

Among the specific findings:

Rates of total high cholesterol varied widely, ranging from 73 percent in Bulgaria to 24 percent in Finland.

Rates of elevated cholesterol levels in patients were particularly high in the following Eastern European countries: Bulgaria, Lithuania, Romania, Ukraine, Hungary and Russia. These countries also scored relatively low in terms of their economies and health systems.

The United States' rate of people with elevated cholesterol levels was similar to that of other developed countries -- such as Australia, Canada, Finland, Israel and the United Kingdom -- but U.S. spending on health care was considerably higher than other developed countries.

The study appears April 9 in the journal Circulation.

The optimum management of heart disease is difficult, and differences in rates of high cholesterol between nations "may be due to differences in clinical guidelines, as well as whether and the extent to which guidelines are followed and specific initiatives are effectively implemented," lead author Elizabeth Magnuson, director of the Health Economics and Technology Assessment at Saint Luke's Mid America Heart Institute in Kansas City, Mo., said in a journal news release.

She added that the association between high out-of-pocket health care costs for patients and their higher cholesterol levels "may reflect an inability or unwillingness" among these patients to take the medicines they've been prescribed. However, "the recent availability of generic cholesterol-lowering therapy should make out-of-pocket expense less of a barrier," Magnuson noted.

Source:medicinenet.com