| Friday, March 9, 2007 |
| High Blood Pressure (Hypertension) |
What is high blood pressure?
High blood pressure or hypertension means high pressure (tension) in the arteries. The arteries are the vessels that carry blood from the pumping heart to all of the tissues and organs of the body. High blood pressure does not mean excessive emotional tension, although emotional tension and stress can temporarily increase the 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 blood pressure. The systolic blood pressure, which is the top number, represents the pressure in the arteries as the heart contracts and pumps blood into the arteries. The diastolic pressure, which is the bottom number, represents the pressure in the arteries as the heart relaxes after the contraction. The diastolic pressure, therefore, reflects the minimum 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. Accordingly, the diagnosis of high blood pressure in an individual is important so that efforts can be made to normalize the blood pressure and, thereby, prevent the complications. Since hypertension affects approximately 1 in 4 adults in the United States, it is clearly a major public health problem.
Whereas it was previously thought that diastolic blood pressure elevations were a more important risk factor than systolic elevations, it is now known that for individuals older than 50 years of age systolic hypertension represents a greater risk.
How is the blood pressure measured?
The blood pressure usually is measured with a small, portable instrument called a blood pressure cuff (sphygmomanometer). (Sphygmo in Greek means 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 the air pump to a pressure that blocks the flow of blood in the main artery (brachial artery) that travels through the arm. With the arm extended at the side of the body at the level of the heart, the pressure of the cuff on the arm and artery is gradually released. As the pressure in the cuff decreases, the 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 over the artery is the systolic pressure. As the cuff pressure decreases further, the pressure at which the pulsation finally stops is the diastolic pressure.
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 below.)
Essential hypertension affects approximately 75 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. In fact, salt intake may be a particularly important factor in relation to essential hypertension in several situations. Thus, 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).
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 actually considered secondary hypertension.)
The vast majority of patients with essential hypertension have in common a particular abnormality of the arteries. That is, they have 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 venous system (or the veins), 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.
What do patients feel with high blood pressure?
Uncomplicated high blood pressure usually occurs without any symptoms. Therefore, hypertension has been labeled "the silent killer." In other words, the disease can progress without symptoms (silently) to finally develop any one or more of the several potentially fatal complications of hypertension such as heart attacks or strokes. As a matter of fact, uncomplicated hypertension may be present and remain unnoticed for many years, or even decades. This happens when 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. 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. Not infrequently, however, a person's first contact with a physician may be after significant damage to the end-organs has occurred. In many cases, a person visits or is brought to the doctor or an emergency room 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 (the minimum pressure) 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).
How is end-organ damage assessed in the patient with high blood pressure?
As already mentioned, chronic high blood pressure can lead to an enlarged heart, kidney failure, brain or neurological damage, and changes in the retina at the back of the eyes. Examination of the eyes in patients with severe hypertension may reveal damage--narrowing of the small arteries, small hemorrhages (leaking of blood) in the retina, and swelling of the eye nerve. From the amount of damage. The doctor can gauge the severity of the hypertension.
As noted previously, people with high blood pressure have an increased stiffness, or resistance, in the peripheral arteries throughout the tissues of the body. This increased resistance causes the heart muscle to work harder to pump the blood through these blood vessels. The increased workload can put a strain on the heart, which can lead to heart abnormalities that are usually first seen as enlarged heart muscle. Enlargement of the heart can be evaluated by chest x-ray, electrocardiogram, and most accurately by echocardiography (an ultrasound examination of the heart). Echocardiography is especially useful in determining the thickness (enlargement) of the left side (the main pumping side) of the heart. Heart enlargement may be a forerunner of heart failure, coronary (heart) artery disease, and abnormal heart rate or rhythms (cardiac arrhythmias). Proper treatment of the high blood pressure and its complications can reverse some of these heart abnormalities.
Blood and urine tests may be helpful in detecting kidney abnormalities in people with high blood pressure. (Remember that kidney damage can be the cause or the result of hypertension.) Measuring the serum creatinine in a blood test can assess how well the kidneys are functioning. An abnormal (elevated) level of serum creatinine indicates damage to the kidney. In addition, the presence of protein in the urine (proteinuria) may reflect chronic kidney damage from hypertension, even if the kidney function (as represented by the blood creatinine level) is normal. In fact, protein in the urine alone signals the risk of deterioration in kidney function if the blood pressure is not controlled. Even small amounts of protein (microalbuminuria) may be a signal of impending kidney failure and other vascular complications from uncontrolled hypertension. African American patients with poorly controlled hypertension are at a higher risk than Caucasians for most end-organ damage and particularly kidney damage.
Uncontrolled hypertension can cause strokes, which can lead to brain or neurological damage. The strokes are usually due to a hemorrhage (leaking blood) or a blood clot (thrombosis) of the blood vessels that supply blood to the brain. The patient's symptoms and signs (findings on physical examination) are evaluated to assess the neurological damage. A stroke can cause weakness, tingling, or paralysis of the arms or legs and difficulties with speech or vision. Multiple small strokes can lead to dementia (impaired intellectual capacity). The best prevention for this complication of hypertension or, for that matter, for any of the complications, is control of the blood pressure. Recent studies have also suggested the angiotensin receptor blocking drugs may offer an additional protective effect against strokes above and beyond control of blood pressure.
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 the alcohol intake exceeds 5 drinks per day. Moreover, the connection is a dose-related phenomenon. In other words, the more alcohol that is consumed, the stronger is the link with hypertension.
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. Nevertheless, smoking a cigarette can repeatedly produce an immediate, temporary rise in the blood pressure of 5 to10 mm Hg. Steady smokers however, actually may have a lower blood pressure than nonsmokers. The reason for this is that the nicotine in the cigarettes causes a decrease in appetite, which leads to weight loss. This, in turn, lowers the blood pressure.
In one study, the caffeine consumed in 5 cups of coffee daily caused a mild increase in blood pressure in elderly people who already had hypertension, but not in those who had normal blood pressures. What's more, the combination of smoking and drinking coffee in persons with high blood pressure may increase the blood pressure more than coffee alone. Limiting caffeine intake and cigarette smoking in hypertensive individuals, therefore, may be of some benefit in controlling their high blood pressure.
Salt
The American Heart Association recommends that the consumption of dietary salt be less than 6 grams of salt per day in the general population and a lower level (for example, less than 4 grams) for people with hypertension. To achieve a diet containing less than 4 grams of salt, a person should not add salt to their food or cooking. Also, the amount of natural salt in the diet can be reasonably estimated from the labeling information provided with most purchased foods.
Obesity is common among hypertensive patients, and its prevalence increases with age. In fact, obesity may be what determines the increased incidence of high blood pressure with age. Obesity can contribute to hypertension in several possible ways. For one thing, obesity leads to a greater output of blood because the heart has to pump out more blood to supply the excess tissue. The increased cardiac output then can raise the blood pressure. For another thing, obese hypertensive individuals have a greater stiffness (resistance) in their peripheral arteries throughout the body. In addition, insulin resistance and the metabolic syndrome described previously occur more frequently in the obese. Finally, obesity may be associated with a tendency for the kidneys to retain salt. Weight loss may help reverse problems related to obesity while also lowering the blood pressure. It has been estimated that the blood pressure can be decreased 0.32 mm Hg for every 1 kg (2.2 pounds) of weight lost down to ideal body weight for the individual.
Some obese people, especially if they are very obese, have a syndrome called sleep apnea. This syndrome is characterized by the periodic interruption of normal breathing during sleep. Sleep apnea may contribute to the development of hypertension in this subgroup of obese individuals. This happens because the repeated episodes of apnea cause a lack of oxygen (hypoxia). The hypoxia then causes the adrenal gland to release adrenalin and related substances. Finally, the adrenalin and related substances cause a rise in the blood pressure.
Exercise
A regular exercise program may help lower blood pressure over the long term. For example, activities such as jogging, bicycle riding, or swimming for 30 to 45 minutes daily may ultimately lower blood pressure by as much as 5 to15 mm Hg. Moreover, there appears to be a relationship between the amount of exercise and the degree to which the blood pressure is lowered. Thus, the more you exercise (up to a point), the more you lower the blood pressure. The beneficial response of the blood pressure to exercise occurs only with aerobic (vigorous and sustained) exercise programs. Therefore, any exercise program must be recommended or approved by an individual's physician
How is high blood pressure treated?
Goals of treatment
Keep in mind that high blood pressure is usually present for many years before its complications develop. The idea, therefore, is to treat hypertension early, before it damages critical organs in the body. Accordingly, increased public awareness and screening programs to detect early, uncomplicated hypertension are the keys to successful treatment. The point is that by treating high blood pressure successfully early enough, you 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, as mentioned earlier, may be desirable in African American patients, and patients with diabetes or chronic kidney disease. Although life style changes in pre-hypertensive patients is appropriate, it is not well established that treatment with medication of patients with pre-hypertension is beneficial.
Starting treatment for high blood pressure
Blood pressure that is persistently higher than 140/ 90 mm Hg usually is treated with lifestyle modifications and medication. If the diastolic pressure remains at a borderline level (usually under 90 mm Hg, yet persistently above 85), however, more aggressive treatment also may be started in certain circumstances. 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 decent, smoking, hyperlipemia (elevated blood fats), or diabetes.
Any one of the several classes of medications may be started, except the alpha-blocker medications. The alpha-blockers 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 particular situations, certain classes of anti-hypertensive drugs are preferable to others as the first line (choice) drugs. For example, 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, current) heart attack.
Furthermore, 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 (initial) 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 the hypertension. Also, the combination of an ACE inhibitor and an ARB drug can be used to treat certain diseases of the heart muscle (called cardiomyopathies) and certain kidney diseases where reduction in proteinuria would be beneficial.
In some other situations, certain classes of anti-hypertensive medications should not be used (are contraindicated). Dihydropyridine calcium channel blockers used alone may cause problems for patients with chronic renal disease by tending to increase proteinuria. However, an ACE inhibitor will blunt this effect. Furthermore, the non-dihydropyridine type of calcium channel blockers should not be used in patients with heart failure or certain abnormal heart rates or rhythms (arrhythmias). On the other hand, these drugs may be beneficial in treating certain other arrhythmias. Also, some drugs, such as minoxidil, since it is so powerful, usually are 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 that make it a second or third line choice. That is, it is used only after all of the first and second line drugs have been tried without success. Finally, see the section below on pregnancy for the anti-hypertensive drugs that are appropriate or inappropriate for use in pregnant women.
Treatment with combinations of drugs for high blood pressure
The use of combination drug therapy for hypertension is not uncommon. At times, using smaller amounts of one or more agents 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. In this way, the diuretic has fewer side effects while it improves 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).
The ACE inhibitors or angiotensin receptor blockers may be useful in combination with most other anti-hypertensive medications. ACE inhibitors and angiotensin receptor blockers 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, however, when combining two drugs that both lower the heart rate. For example, adding a beta-blocker to a non-dihydropyridine calcium channel blocker (e.g., diltiazem or verapamil) warrants caution. Patients receiving a combination of these two classes of drugs need to be monitored carefully to avoid an excessively slow heart rate (bradycardia). Combining alpha and beta-blockers may be beneficial for cardiomyopathies and hypertension. Carvedilol (Coreg) is useful for cardiomyopathies and labetalol for hypertension patients.
Emergency treatment of high blood pressure
In a hospital setting, injectable drugs may be used for the emergency treatment of hypertension. The most commonly used agents in this situation are sodium nitroprusside (Nipride) and labetalol (Normodyne). As already mentioned, emergency medical therapy may be needed for patients with severe (malignant) hypertension. In addition, emergency treatment of hypertension may be necessary in patients with short duration (acute) congestive heart failure, dissecting aneurysm (dilation or widening) of the aorta, stroke, and toxemia of pregnancy (see below).
Treatment during pregnancy
Women with hypertension may become pregnant. These patients have an increased risk of developing preeclampsia or eclampsia (toxemia) of pregnancy. These conditions usually develop during the last three months (trimester) of pregnancy. In preeclampsia, which can occur with or without pre-existing hypertension, affected women have hypertension, protein loss in the urine (proteinuria), and swelling (edema). In eclampsia (toxemia), convulsions also occur and the hypertension may require prompt treatment. The foremost goal of treating the high blood pressure in toxemia is to keep the diastolic pressure below 105 mm Hg in order to prevent a brain hemorrhage in the mother.
Hypertension that develops before the 20th week of pregnancy almost always is due to pre-existing hypertension and not toxemia. High blood pressure that occurs only during pregnancy, called gestational hypertension, may start late in the pregnancy. These women, however, do not have proteinuria, edema, or convulsions. Furthermore, gestational hypertension appears to have no ill effects on the mother or the fetus. This form of hypertension resolves shortly after delivery, although it may recur with subsequent pregnancies.
The use of medications for hypertension during pregnancy is controversial. The key question is, "At what level should the blood pressure be maintained?" For one thing, the risk of untreated mild to moderate hypertension to the fetus or mother during the relatively brief period of pregnancy probably is not very large. Furthermore, lowering the blood pressure too much can interfere with the flow of blood to the placenta and thereby impair fetal growth. So, some sort of a compromise must be met. Accordingly, not all mild or moderate hypertension during pregnancy needs to be treated with medication. If it is treated, however, the blood pressure should be reduced slowly and not to very low levels, perhaps not below 140/80.
The anti-hypertensive agents used during pregnancy need to be safe for normal fetal development. The beta-blockers, hydralazine (an old vasodilator), labetalol, alpha methyldopa (Aldomet), and more recently, the calcium channel blockers have been advocated as suitable medications for hypertension during pregnancy. Certain other anti-hypertensive medications, however, are not recommended (they are contraindicated) during pregnancy. These include the ACE inhibitors, the ARB drugs, and probably the diuretics. ACE inhibitors may aggravate a diminished blood supply to the uterus (uterine ischemia) and cause kidney dysfunction in the fetus. The ARB drugs may even lead to death of the fetus. Diuretics can cause depletion of the blood volume and so impair placental blood flow and fetal growth.
Which medications are used to treat high blood pressure?
Angiotensin converting enzyme inhibitors (ACE Inhibitors) and angiotensin receptor blockers
The angiotensin converting enzyme (ACE) inhibitors and the angiotensin receptor blocker (ARB) drugs both affect the renin-angiotensin hormonal system, which, as mentioned previously, helps regulate the blood pressure. The ACE inhibitors work by blocking (inhibiting) an enzyme that converts the inactive form of angiotensin in the blood to its active form. The active form of angiotensin constricts or narrows the arteries, but the inactive form cannot. With an ACE inhibitor as a single drug treatment (monotherapy), 50 to 60 percent of Caucasians usually achieve good blood pressure control. African American patients may also respond, but they require higher doses and frequently do best when an ACE inhibitor is combined with a diuretic. (Diuretics are discussed below.)
As an added benefit, ACE inhibitors may reduce an enlarged heart (left ventricular hypertrophy) in patients with hypertension. These drugs also appear to slow the deterioration of kidney function in patients with hypertension and protein in the urine (proteinuria). Moreover, they have been particularly useful in slowing the progression of kidney dysfunction in hypertensive patients with kidney disease resulting from Type 1 diabetes (insulin-dependent). Accordingly, ACE inhibitors usually are the first line drugs of choice to treat high blood pressure in cases that also involve congestive heart failure, chronic kidney failure in both diabetics and non-diabetics, and heart attack (myocardial infarction) that weakens the heart muscle (systolic dysfunction). ARB drugs are currently recommended for first line renal protection in diabetic nephropathy (kidney disease).
Patients who are treated with ACE inhibitors who also have kidney disease should be monitored for further deterioration in kidney function and high serum potassium. In fact, these drugs may be used to reduce the loss of potassium in people who are being treated with diuretics that tend to cause patients to lose potassium. ACE inhibitors have few side effects. One bothersome side effect, however, is a chronic cough. The ACE inhibitors include enalapril (Vasotec), captopril (Capoten), lisinopril (Zestril and Prinivil), benazepril (Lotensin), quinapril (Accupril), perindopril (Aceon), ramipril (Altace), trandolapril (Mavik), fosinopril (Monopril), and moexipril (Univasc ).
For patients who develop a chronic cough on an ACE inhibitor, an ARB drug is a good substitute. ARB drugs work by blocking the angiotensin receptor (binder) on the arteries to which activated angiotensin must bind to have its effects. As a result, the angiotensin is not able to work on the artery. (Recall that angiotensin is a hormone that constricts the arteries.) The ARB drugs appear to have many of the same advantages as the ACE inhibitors but without the associated cough. Accordingly, they are also suitable as first line agents to treat hypertension. ARB drugs include losartan (Cozaar), irbesartan (Avapro), valsartan (Diovan), candesartan (Atacand), olmesartan (Benicar), telmisartan (Micardis), and eprosartan (Teveten).
In patients who have hypertension in addition to certain second diseases, a combination of an ACE inhibitor and an ARB drug may be effective in controlling the hypertension and also benefiting the second disease. For example, while treating hypertension, this combination of drugs can reduce the loss of protein in the urine (proteinuria) in certain kidney diseases and perhaps help strengthen the heart muscle in certain diseases of the heart muscle (cardiomyopathies). Note that both the ACE inhibitors and the ARB drugs are not to be used (are contraindicated) in pregnant women. (See the section above on pregnancy.)
Beta-blockers
The sympathetic nervous system is a part of the nervous system that helps to regulate certain involuntary (autonomic) functions in the body such as the function of the heart and blood vessels. The nerves of the sympathetic nervous system extend throughout the body and exert their effects by releasing chemicals that travel to nearby cells in the body, for example, muscle cells. The released chemicals bind to receptors (molecules) on the surface of the nearby cells and stimulate or inhibit the function of the cells. In the heart and blood vessels, the receptors for the sympathetic nervous system that are most important are the beta receptors. When stimulated, beta-receptors in the heart increase the heart rate and the strength of heart contractions (pumping action). Beta-blocking drugs acting on the heart, therefore, slow the heart rate and reduce the force of the heart’s contraction.
Stimulation of beta-receptors in the smooth muscle of the peripheral arteries and in the airways of the lung causes these muscles to relax. Accordingly, beta-blockers cause contraction of the smooth muscle of the peripheral arteries and thereby decrease the blood flow to the tissues throughout the body. As a result, the patient may experience, for example, coolness in the hands and feet. Likewise, in response to the beta-blockers, the airways are squeezed (constricted) by the contracting smooth muscle. This squeezing (impingement) on the airway causes wheezing, especially in individuals with a tendency for asthma. In short, beta-blockers reduce both the force of the heart's pumping action and the blood pressure that the heart generates in the arteries.
Beta-blockers remain useful medications in treating hypertension, especially in patients with a fast heartbeat while resting (tachycardia), cardiac chest pain (angina), or a recent heart attack (myocardial infarction). For example, beta-blockers appear to improve long-term survival when given to patients who have had a heart attack. Whether beta-blockers can prevent heart problems (are cardio-protective) in patients with hypertension any more than other anti-hypertensive medications, however, is uncertain. Beta-blockers may be considered for treatment of hypertension because they also may treat co-existing medical problems. For example, beta-blockers can help treat chronic anxiety or migraine headaches in people with hypertension. The common side effects of these drugs include depression, fatigue, nightmares, sexual impotence in males, and increased wheezing in people with asthma. The beta-blockers include atenolol (Tenormin), propranolol (Inderal), metoprolol (Toprol), nadolol (Corgard), betaxolol (Kerlone), acebutolol (Sectral), pindolol (Visken), and bisoprolol (Zebeta).
Diuretics
Diuretics are among the oldest known medications for treating hypertension. They work in the tiny tubes (tubules) of the kidneys to remove salt from the body. Water (fluid) also may be removed along with the salt. Diuretics may be used as single drug treatment (monotherapy) for hypertension. More frequently, however, low doses of diuretics are used in combination with other anti-hypertensive medications to enhance the effect of the other medications.
The diuretic hydrochlorothiazide (Hydrodiuril) works in the far end (distal) part of the kidney tubules to increase the amount of salt that is removed from the body in the urine. In a low dose of 12.5 to 25 mg per day, this diuretic may improve the blood pressure-lowering effects of other anti-hypertensive drugs. The idea is to treat the hypertension without causing the adverse effects that are sometimes seen with the higher doses of hydrochlorothiazide. These side effects include potassium depletion and elevated levels of triglyceride (fat), uric acid, and glucose (sugar) in the blood.
Occasionally, when salt retention causing accumulation of water and swelling (edema) is a major problem, the more potent, so-called, loop diuretics may be used in combination with other anti-hypertensive medications. (The loop diuretics are so called because they work in the loop segment of the kidney tubules to eliminate salt.) The most commonly used diuretics to treat hypertension include hydrochlorothiazide (Hydrodiuril), the loop diuretics furosemide (Lasix) and torsemide (Demadex), the combination of triamterene and hydrochlorothiazide (Dyazide), and metolazone (Zaroxolyn). For those individuals who are allergic to sulfa drugs, ethacrynic acid, a loop diuretic, is a good option. Note that diuretics probably should not be used in pregnant women.
Calcium channel blockers (CCBs)
Calcium channel blockers inhibit the movement of calcium into the muscle cells of the heart and arteries. The calcium is needed for these muscles to contract. These drugs, therefore, lower blood pressure by decreasing the force of the heart's pumping action (cardiac contraction) and relaxing the muscle cells in the walls of the arteries.
Three major types of calcium channel blockers are used. One type is the dihydropyridines, which do not slow the heart rate or cause other abnormal heart rates or rhythms (cardiac arrhythmias). These drugs include amlodipine (Norvasc), sustained release nifedipine (Procardia XL, Adalat CC), felodipine (Plendil), and nisoldipine (Sular).
The other two types of calcium channel blockers are referred to as the non-dihydropyridine agents. One type is verapamil (Calan, Covera, Isoptin, Verelan) and the other is diltiazem (Cardizem, Tiazac, Dilacor, and Diltia). Both the dihydropyridines and the non-dihydropyridines are very useful when used alone or in combination with other anti-hypertensive agents. The non-dihydropyridines, however, are not recommended (contraindicated) in congestive heart failure or with certain arrhythmias. Sometimes, however, these same dihydropyridines are useful in preventing certain other arrhythmias.
Many of the calcium channel blockers come in a short-acting form and a long-acting (sustained release) form. The short-acting forms of the calcium channel blockers, however, may have adverse long-term consequences, such as strokes or heart attacks. These effects are presumably due to the wide fluctuations in the blood pressure and heart rate that occur during treatment. The fluctuations result from the rapid onset and short duration of the short-acting compounds. When the calcium channel blockers are used in sustained release preparations, however, less fluctuation occurs. Accordingly, the sustained release forms of calcium channel blockers are probably safer for long-term use. The main side effects of these drugs include constipation, swelling (edema), and a slow heart rate (only with the non-dihydropyridine types).
Alpha-blockers
Alpha-blockers lower blood pressure by blocking alpha-receptors in the smooth muscle of peripheral arteries throughout the tissues of the body. The alpha-receptors are part of the sympathetic nervous system, as are the beta-receptors. The alpha-receptors, however, serve to narrow (constrict) the peripheral arteries. Accordingly, the alpha-blockers cause the peripheral arteries to widen (dilate) and thereby lower the blood pressure.
Recent evidence, however, suggests that using alpha-blockers alone as a first line drug choice for hypertension may actually increase the risk of heart-related problems, such as heart attacks or strokes. Alpha-blockers, therefore, should not be used as an initial drug choice for the treatment of high blood pressure. Examples of alpha-blockers include terazosin (Hytrin) and doxazosin (Cardura).
Alpha-blockers are particularly useful in patients with enlargement of the prostate gland (which usually occurs in older men) because these drugs reduce the problems associated with urinating. Alpha-blockers alone, however, have a relatively small blood pressure-lowering effect. Accordingly, when hypertension coexists with prostatic enlargement, another anti-hypertensive medication should be used together with an alpha-blocker. For example, tamsulosin (Flomax) or alfuzosin (Uroxatral) are alpha-blockers that work well in combination with other anti-hypertensive medications.
Clonidine
Clonidine (Catapres) is an antihypertensive drug that works centrally. That is, it works in a control center for the sympathetic nervous system in the brain. The drug is referred to as a central alpha agonist because it stimulates alpha-receptors in the brain. The result of this central stimulation, however, is to decrease the sympathetic nervous system outflow and to decrease the stiffness (resistance) of the peripheral arteries. Clonidine lowers the blood pressure, therefore, by relaxing (dilating or widening) the peripheral arteries throughout the body. This drug is useful as a second or third line drug choice for lowering blood pressure when other anti-hypertensive medications have failed. It also may be useful on an as-needed basis to control or smooth out fluctuations in the blood pressure. This drug tends to cause dryness of the mouth and fatigue so that some patients do not tolerate it. Clonidine comes in an oral form or as a sustained release skin patch. For more information, please see the drug monograph on Clonidine.
Minoxidil
Minoxidil is the most potent of the drugs that lower blood pressure by dilating the peripheral arteries. This drug, however, does not work through the peripheral sympathetic nervous system, as do the alpha and beta-blocker drugs, or through the control center in the brain, as does clonidine. Rather, it is a muscle relaxant that works directly on the smooth muscle of the peripheral arteries throughout the body. Minoxidil is used for patients who have not responded to any other medications. It must be combined with a beta-blocker or clonidine to prevent an increase in the heart rate and with a diuretic to prevent retention of fluid (swelling). Minoxidil may also increase hair growth. For more information, please see the drug monograph on Minoxidil.
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Source: http://www.medicinenet.com/high_blood_pressure/article.htm#toc1bp |
posted by Eko Priyanto @ 5:31 PM   |
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