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hypertension

[hahy-per-ten-shuhn]

hypertension or high blood pressure, elevated blood pressure resulting from an increase in the amount of blood pumped by the heart or from increased resistance to the flow of blood through the small arterial blood vessels (arterioles). Hypertension is generally defined as a blood pressure reading greater than 140 over 90; presssures of 120-139 over 80-89 are now considered prehypertension. When the cause is unknown, the hypertension is called primary, or essential, hypertension. When a cause can be identified (e.g., a disorder of the adrenal glands, kidneys, or arteries), the condition is known as secondary hypertension. Factors such as heredity, obesity, smoking, and emotional stress are thought to play a role; the usual immediate cause is an imbalance in the body's vasoconstriction/fluid retention systems, often involving a decrease in the kidney's secretion of the regulatory hormone, renin.

Known as the "silent killer," hypertension often produces few overt symptoms; it may, however, result in damage to the heart, eyes, kidneys, or brain and ultimately lead to congestive heart failure, heart attack (see infarction), kidney failure, or stroke. African Americans and women are the most affected. Treatment of hypertension includes diets to reduce weight and salt and alcohol intake, increased exercise, quitting smoking, and various drugs, such as diuretics, ACE inhibitors, beta-blockers, calcium-channel blockers or angiotensin-receptor blockers, as well as biofeedback. Many patients require a combination of drugs to control their blood pressure. Treatment for persons with prehypertension includes dietary and other lifestyle changes. Recent research has questioned the importance of dietary salt as a major contributor to hypertension; some studies point to low calcium intake as a cause.

Signs and symptoms

Hypertension is usually found incidentally by healthcare professionals measuring blood pressure during a routine checkup. In isolation, it usually produces no symptoms although some people report headaches, fatigue, dizziness, blurred vision, facial flushing, transient insomnia or difficulty sleeping due to feeling hot or flushed, and tinnitus during beginning onset or before hypertension diagnosis.

Hypertension is often confused with mental tension, stress and anxiety. While chronic anxiety and/or irritability is associated with poor outcomes in people with hypertension, it alone does not cause it. Accelerated hypertension is associated with somnolence, confusion, visual disturbances, and nausea and vomiting (hypertensive encephalopathy).

Hypertension is rarely severe enough to cause symptoms. These typically only surface with a systolic blood pressure over 240 mmHg and/or a diastolic blood pressure over 120 mmHg. These pressures without signs of end-organ damage (such as renal failure) are termed "accelerated" hypertension. When end-organ damage is possible or already ongoing, but in absence of raised intracranial pressure, it is called hypertensive emergency. Hypertension under this circumstance needs to be controlled, but prolonged hospitalization is not necessarily required. When hypertension causes increased intracranial pressure, it is called malignant hypertension. Increased intracranial pressure causes papilledema, which is visible on ophthalmoscopic examination of the retina.

Causes

Although no specific medical cause can be determined in essential hypertension, it often has several contributing factors. These include obesity, salt sensitivity, renin homeostasis, insulin resistance, genetics, and age.

Obesity

The risk of hypertension is 5 times higher in the obese as compared to those of normal weight and up to two-thirds of cases can be attributed to excess weight. More than 85% of cases occur in those with a BMI>25.

Sodium sensitivity

Sodium is an environmental factor that has received the greatest attention. Approximately one third of the essential hypertensive population is responsive to sodium intake. This is due to the fact that increasing amounts of salt in a person's bloodstream causes cells to release water (due to osmotic pressure) to equilibrate concentration gradient of salt between the cells and the bloodstream; increasing the pressure on the blood vessel walls.

Role of renin

Renin is an enzyme secreted by the juxtaglomerular apparatus of the kidney and linked with aldosterone in a negative feedback loop. The range of renin activity observed in hypertensive subjects tends to be broader than in normotensive individuals. In consequence, some hypertensive patients have been defined as having low-renin and others as having essential hypertension. Low-renin hypertension is more common in African Americans than white Americans, and may explain why African Americans tend to respond better to diuretic therapy than drugs that interfere with the renin-angiotensin system.

High Renin levels predispose to Hypertension: Increased Renin → Increased Angiotensin II → Increased Vasoconstriction, Thirst/ADH and Aldosterone → Increased Sodium Resorption in the Kidneys (DCT and CD) → Increased Blood Pressure. Some authorities claim that potassium might both prevent and treat hypertension.

Insulin resistance

Insulin is a polypeptide hormone secreted by cells in the islets of langerhans, which are contained throughout the pancreas. Its main purpose is to regulate the levels of glucose in the body antagonistically with glucagon through negative feedback loops. Insulin also exhibits vasodilatory properties. In normotensive individuals, insulin may stimulate sympathetic activity without elevating mean arterial pressure. However, in more extreme conditions such as that of the metabolic syndrome, the increased sympathetic neural activity may over-ride the vasodilatory effects of insulin. Insulin resistance and/or hyperinsulinemia have been suggested as being responsible for the increased arterial pressure in some patients with hypertension. This feature is now widely recognized as part of syndrome X, or the metabolic syndrome.

Sleep apnea

Sleep apnea is a common, under-recognized cause of hypertension. It is often best treated with nocturnal nasal continuous positive airway pressure, but other approaches include the Mandibular advancement splint (MAS), UPPP, tonsilectomy, adenoidectomy, sinus surgery, or weight loss.

Genetics

Hypertension is one of the most common complex disorders, with genetic heritability averaging 30%. Data supporting this view emerge from animal studies as well as in population studies in humans. Most of these studies support the concept that the inheritance is probably multifactorial or that a number of different genetic defects each have an elevated blood pressure as one of their phenotypic expressions.

More than 50 genes have been examined in association studies with hypertension, and the number is constantly growing.

Age

Over time, the number of collagen fibers in artery and arteriole walls increases, making blood vessels stiffer. With the reduced elasticity comes a smaller cross-sectional area in systole, and so a raised mean arterial blood pressure.

Liquorice

Consumption of liquorice (which can be of potent strength in liquorice candy) can lead to a surge in blood pressure. People with hypertension or history of cardio-vascular disease should avoid liquorice raising their blood pressure to risky levels. Frequently, if liquorice is the cause of the high blood pressure, a low blood level of potassium will also be present.

Liquorice extracts are present in many medicines (for example cough syrups, throat lozenges and peptic ulcer treatments).

Secondary hypertension

Only in a small minority of patients with elevated arterial pressure can a specific cause be identified. In 90 percent to 95 percent of high blood pressure cases, the American Heart Association says there's no identifiable cause. These individuals will probably have an endocrine or renal defect that, if corrected, could bring blood pressure back to normal values.

Renal hypertension

Hypertension produced by diseases of the kidney. This includes diseases such as polycystic kidney disease or chronic glomerulonephritis. Hypertension can also be produced by diseases of the renal arteries supplying the kidney. This is known as renovascular hypertension; it is thought that decreased perfusion of renal tissue due to stenosis of a main or branch renal artery activates the renin-angiotensin system.

Adrenal hypertension

Hypertension is a feature of a variety of adrenal cortical abnormalities. In primary aldosteronism there is a clear relationship between the aldosterone-induced sodium retention and the hypertension.

Cushing's syndrome

Both adrenal glands can overproduce the hormone cortisol or it can arise in a benign or malignant tumor. Hypertension results from the interplay of several pathophysiological mechanisms regulating plasma volume, peripheral vascular resistance and cardiac output, all of which may be increased. More than 80% of patients with Cushing's syndrome have hypertension.

In patients with pheochromocytoma increased secretion of catecholamines such as epinephrine and norepinephrine by a tumor (most often located in the adrenal medulla) causes excessive stimulation of adrenergic receptors, which results in peripheral vasoconstriction and cardiac stimulation. This diagnosis is confirmed by demonstrating increased urinary excretion of epinephrine and norepinephrine and/or their metabolites (vanillylmandelic acid).

Genetic

Hypertension can be caused by mutations in single genes, inherited on a mendelian basis.

Coarctation of the aorta

The congenital abnormality aortic coarctation can result in hypertension.

Drugs

Certain medications, especially NSAIDS (Motrin/Ibuprofen) and steroids can cause hypertension. Licorice (Glycyrrhiza glabra) inhibits the 11-hydroxysteroid hydrogenase enzyme (catalyzes the reaction of cortisol to cortison) which allows cortisol to stimulate the Mineralocorticoid Receptor (MR) which will lead to effects similar to hyperaldosteronism, which itself is a cause of hypertension.

Rebound hypertension

High blood pressure that is associated with the sudden withdrawal of various antihypertensive medications. The increases in blood pressure may result in blood pressures greater than when the medication was initiated. Depending on the severity of the increase in blood pressure, rebound hypertension may result in a hypertensive emergency. Rebound hypertension is avoided by gradually reducing the dose (also known as "dose tapering"), thereby giving the body enough time to adjust to reduction in dose.

Medications commonly associated with rebound hypertension include centrally-acting antihypertensive agents, such as clonidine and beta-blockers.

Pregnancy

Although few women of childbearing age have high blood pressure, up to 10% develop hypertension of pregnancy. While generally benign, it may herald three complications of pregnancy: pre-eclampsia, HELLP syndrome and eclampsia. Follow-up and control with medication is therefore often necessary.

Children and adolescents

As with adults, blood pressure is a variable parameter in children. It varies between individuals and within individuals from day to day and at various times of the day. The epidemic of childhood obesity, the risk of developing left ventricular hypertrophy, and evidence of the early development of atherosclerosis in children would make the detection of and intervention in childhood hypertension important to reduce long-term health risks; however, supporting data are lacking. Most childhood hypertension, particularly in preadolescents, is secondary to an underlying disorder. Renal parenchymal disease is the most common (60 to 70%) cause of hypertension. Adolescents usually have primary or essential hypertension, making up 85 to 95% of cases.

Pathophysiology

Most of the secondary mechanisms associated with hypertension are generally fully understood, and are outlined at secondary hypertension. However, those associated with essential (primary) hypertension are far less understood. What is known is that cardiac output is raised early in the disease course, with total peripheral resistance (TPR) normal; over time cardiac output drops to normal levels but TPR is increased. Three theories have been proposed to explain this:

Inability of the kidneys to excrete sodium, resulting in natriuretic factors such as Atrial Natriuretic Factor being secreted to promote salt excretion with the side-effect of raising total peripheral resistance.
An overactive renin / angiotensin system leads to vasoconstriction and retention of sodium and water. The increase in blood volume leads to hypertension.
An overactive sympathetic nervous system, leading to increased stress responses.

It is also known that hypertension is highly heritable and polygenic (caused by more than one gene) and a few candidate genes have been postulated in the etiology of this condition.

Diagnosis

Measuring blood pressure

Diagnosis of hypertension is generally on the basis of a persistently high blood pressure. Usually this requires three separate measurements at least one week apart. Exceptionally, if the elevation is extreme, or end-organ damage is present then the diagnosis may be applied and treatment commenced immediately.

Obtaining reliable blood pressure measurements relies on following several rules and understanding the many factors that influence blood pressure reading.

For instance, measurements in control of hypertension should be at least 1 hour after caffeine, 30 minutes after smoking or strenuous exercise and without any stress. Cuff size is also important. The bladder should encircle and cover two-thirds of the length of the (upper) arm. The patient should be sitting upright in a chair with both feet flat on the floor for a minimum of five minutes prior to taking a reading. The patient should not be on any adrenergic stimulants, such as those found in many cold medications.

When taking manual measurements, the person taking the measurement should be careful to inflate the cuff suitably above anticipated systolic pressure. The person should inflate the cuff to 200 mmHg and then slowly release the air while palpating the radial pulse. After one minute, the cuff should be reinflated to 30 mmHg higher than the pressure at which the radial pulse was no longer palpable. A stethoscope should be placed lightly over the brachial artery. The cuff should be at the level of the heart and the cuff should be deflated at a rate of 2 to 3 mmHg/s. Systolic pressure is the pressure reading at the onset of the sounds described by Korotkoff (Phase one). Diastolic pressure is then recorded as the pressure at which the sounds disappear (K5) or sometimes the K4 point, where the sound is abruptly muffled. Two measurements should be made at least 5 minutes apart, and, if there is a discrepancy of more than 5 mmHg, a third reading should be done. The readings should then be averaged. An initial measurement should include both arms. In elderly patients who particularly when treated may show orthostatic hypotension, measuring lying sitting and standing BP may be useful. The BP should at some time have been measured in each arm, and the higher pressure arm preferred for subsequent measurements.

BP varies with time of day, as may the effectiveness of treatment, and archetypes used to record the data should include the time taken. Analysis of this is rare at present.

Automated machines are commonly used and reduce the variability in manually collected readings . Routine measurements done in medical offices of patients with known hypertension may incorrectly diagnose 20% of patients with uncontrolled hypertension

Home blood pressure monitoring can provide a measurement of a person's blood pressure at different times throughout the day and in different environments, such as at home and at work. Home monitoring may assist in the diagnosis of high or low blood pressure. It may also be used to monitor the effects of medication or lifestyle changes taken to lower or regulate blood pressure levels.

Home monitoring of blood pressure can also assist in the diagnosis of white coat hypertension. The American Heart Association states, "You may have what's called 'white coat hypertension'; that means your blood pressure goes up when you're at the doctor's office. Monitoring at home will help you measure your true blood pressure and can provide your doctor with a log of blood pressure measurements over time. This is helpful in diagnosing and preventing potential health problems."

Some home blood pressure monitoring devices also make use of blood pressure charting software. These charting methods provide printouts for the patient's physician and reminders to take a blood pressure reading. However, a simple and cheap way is simply to manually record values with pen and paper, which can then be inspected by a doctor.

Systolic hypertension is defined as an elevated systolic blood pressure. If systolic blood pressure is elevated with a normal diastolic blood pressure, it is called isolated systolic hypertension. Systolic hypertension may be due to reduced compliance of the aorta with increasing age.

Distinguishing primary vs. secondary hypertension

Once the diagnosis of hypertension has been made it is important to attempt to exclude or identify reversible (secondary) causes.

Over 91% of adult hypertension has no clear cause and is therefore called essential/primary hypertension. Often, it is part of the metabolic "syndrome X" in patients with insulin resistance: it occurs in combination with diabetes mellitus (type 2), combined hyperlipidemia and central obesity.
Secondary hypertension is more common in preadolescent children, with most cases caused by renal disease. Primary or essential hypertension is more common in adolescents and has multiple risk factors, including obesity and a family history of hypertension.

Investigations commonly performed in newly diagnosed hypertension

Tests are undertaken to identify possible causes of secondary hypertension, and seek evidence for end-organ damage to the heart itself or the eyes (retina) and kidneys. Diabetes and raised cholesterol levels being additional risk factors for the development of cardiovascular disease are also tested for as they will also require management.

Blood tests commonly performed include:

Creatinine (renal function) - to identify both underlying renal disease as a cause of hypertension and conversely hypertension causing onset of kidney damage. Also a baseline for later monitoring the possible side-effects of certain antihypertensive drugs.
Electrolytes (sodium, potassium)
Glucose - to identify diabetes mellitus
Cholesterol

Additional tests often include:

Testing of urine samples for proteinuria - again to pick up underlying kidney disease or evidence of hypertensive renal damage.
Electrocardiogram (EKG/ECG) - for evidence of the heart being under strain from working against a high blood pressure. Also may show resulting thickening of the heart muscle (left ventricular hypertrophy) or of the occurrence of previous silent cardiac disease (either subtle electrical conduction disruption or even a myocardial infarction).
Chest X-ray - again for signs of cardiac enlargement or evidence of cardiac failure.

Prevention

Testing of urine sample should also include periodic tests for microalbuminuria as hypertension is the number one cause of renal damage, especially if there is co-existing diabetes. Early detection at the microalbumin level can result in reversing renal damage using suitable drugs.

Treatment

Lifestyle modification (nonpharmacologic treatment)

Weight reduction and regular aerobic exercise (e.g., jogging) are recommended as the first steps in treating mild to moderate hypertension. Regular mild exercise improves blood flow and helps to reduce resting heart rate and blood pressure. These steps are highly effective in reducing blood pressure, although drug therapy is still necessary for many patients with moderate or severe hypertension to bring their blood pressure down to a safe level.

Reducing dietary sugar intake

Reducing sodium (salt) in the diet is proven very effective: it decreases blood pressure in about 60 percent of people (see above). Many people choose to use a salt substitute to reduce their salt intake.

Additional dietary changes beneficial to reducing blood pressure includes the DASH diet (dietary approaches to stop hypertension), which is rich in fruits and vegetables and low fat or fat-free dairy foods. This diet is shown effective based on research sponsored by the US National Institutes of Health. In addition, an increase in daily calcium intake has the benefit of increasing dietary potassium, which theoretically can offset the effect of sodium and act on the kidney to decrease blood pressure. This has also been shown to be highly effective in reducing blood pressure.

Discontinuing tobacco use and alcohol consumption has been shown to lower blood pressure. The exact mechanisms are not fully understood, but blood pressure (especially systolic) always transiently increases following alcohol and/or nicotine consumption. Besides, abstention from cigarette smoking is important for people with hypertension because it reduces the risk of many dangerous outcomes of hypertension, such as stroke and heart attack. Note that coffee drinking (caffeine ingestion) also increases blood pressure transiently, but does not produce chronic hypertension.

Reducing stress, for example with relaxation therapy, such as meditation and other mindbody relaxation techniques, by reducing environmental stress such as high sound levels and over-illumination can be an additional method of ameliorating hypertension. Jacobson's Progressive Muscle Relaxation and biofeedback are also used , particularly, device-guided paced breathing , although meta-analysis suggests it is not effective unless combined with other relaxation techniques.

Medications

Unless hypertension is severe, lifestyle changes such as those discussed in the preceding section are strongly recommended before initiation of drug therapy. Adoption of the DASH diet is one example of lifestyle change repeatedly shown to effectively lower mildly-elevated blood pressure. If hypertension is high enough to justify immediate use of medications, lifestyle changes are initiated concomitantly.

There are many classes of medications for treating hypertension, together called antihypertensives, which — by varying means — act by lowering blood pressure. Evidence suggests that reduction of the blood pressure by 5-6 mmHg can decrease the risk of stroke by 40%, of coronary heart disease by 15-20%, and reduces the likelihood of dementia, heart failure, and mortality from vascular disease.

The aim of treatment should be blood pressure control to <140/90 mmHg for most patients, and lower in certain contexts such as diabetes or kidney disease (some medical professionals recommend keeping levels below 120/80 mmHg). Each added drug may reduce the systolic blood pressure by 5-10 mmHg, so often multiple drugs are necessary to achieve blood pressure control.

Commonly used drugs include:

ACE inhibitors such as creatine captopril, enalapril, fosinopril (Monopril), lisinopril (Zestril), quinapril, ramipril (Altace)
Angiotensin II receptor antagonists: eg, telmisartan (Micardis, Pritor), irbesartan (Avapro), losartan (Cozaar), valsartan (Diovan), candesartan (Amias)
Alpha blockers such as prazosin, or terazosin. Doxazosin has been shown to increase risk of heart failure, and to be less effective than a simple diuretic, so is not recommended.
Beta blockers such as atenolol, labetalol, metoprolol (Lopressor, Toprol-XL), propranolol.
Calcium channel blockers such as nifedipine (Adalat) amlodipine (Norvasc), diltiazem, verapamil
Direct renin inhibitors such as aliskiren (Tekturna)
Diuretics: eg, bendroflumethiazide, chlortalidone, hydrochlorothiazide (also called HCTZ)
Combination products (which usually contain HCTZ and one other drug)

Choice of initial medication

Unless the blood pressure is severely elevated, consensus guidelines call for medically-supervised lifestyle changes and observation before recommending initiation of drug therapy. All drug treatments have side effects, and while the evidence of benefit at higher blood pressures is overwhelming, drug trials to lower moderately-elevated blood pressure have failed to reduce overall death rates.

If lifestyle changes are ineffective or the presenting blood pressure is critical, then drug therapy is initiated, often requiring more than one agent to effective lower hypertension. Which type of many medications should be used initially for hypertension has been the subject of several large studies and various national guidelines.

The ALLHAT study showed better cost-effectiveness and slightly better outcomes for the thiazide diuretic chlortalidone compared with a calcium channel blocker and an ACE inhibitor in a 33,357-member ethnically mixed study group. The 1993 consensus recommendation for use of thiazide diuretics as initial treatment stems in part from the ALLHAT study results, which concluded in 2002 that "Thiazide-type diuretics are superior in preventing 1 or more major forms of CVD and are less expensive. They should be preferred for first-step antihypertensive therapy."

A subsequent smaller study (ANBP2) did not show the slight advantages in thiazide diuretic outcomes observed in the ALLHAT study, and actually showed slightly better outcomes for ACE-inhibitors in older white male patients.

Thiazide diuretics are effective, recommended as the best first-line drug for hypertension by many experts, and much more affordable than other therapies, yet they are not prescribed as often as some newer drugs. Arguably, this is partly because they are off-patent, less profitable, and thus rarely promoted by the drug industry.

The consensus recommendations of thiazide diuretics as first-line therapy for hypertension stand against a the backdrop that all blood pressure treatments have side-effects. Potentially serious side effects of the thiazide diuretics include hypercholesterinemia, and impaired glucose tolerance with consequent increased risk of developing Diabetes mellitus type 2. The thiazide diuretics also deplete circulating potassium unless combined with a potassium-sparing diuretic or supplemental potassium. On this basis, the consensus recommendations to prefer use of thiazides as first line treatment for essential hypertension have been repeatedly and strongly questioned. However as the Merck Manual of Geriatrics notes, "thiazide-type diuretics are especially safe and effective in the elderly.

Advice in the United Kingdom

The risk of beta-blockers provoking type 2 diabetes led to their downgrading to fourth-line therapy in the United Kingdom in June 2006, in the revised national guidelines.

Advice in the United States

The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7) in the United States recommends starting with a thiazide diuretic if single therapy is being initiated and another medication is not indicated.

Prognosis

Complications

While elevated blood pressure alone is not an illness, it often requires treatment due to its short- and long-term effects on many organs. The risk is increased for:

Cerebrovascular accident (CVAs or strokes)
Myocardial infarction (heart attack)
Hypertensive cardiomyopathy (heart failure due to chronically high blood pressure)
Hypertensive retinopathy - damage to the retina
Hypertensive nephropathy - chronic renal failure due to chronically high blood pressure
Hypertensive encephalopathy - confusion, headache , convulsion due to vasogenic edema in brain due to high blood pressure.

Epidemiology

The level of blood pressure regarded as deleterious has been revised down during years of epidemiological studies. A widely quoted and important series of such studies is the Framingham Heart Study carried out in an American town: Framingham, Massachusetts. The results from Framingham and of similar work in Busselton, Western Australia have been widely applied. To the extent that people are similar this seems reasonable, but there are known to be genetic variations in the most effective drugs for particular sub-populations. Recently (2004), the Framingham figures have been found to overestimate risks for the UK population considerably. The reasons are unclear. Nevertheless the Framingham work has been an important element of UK health policy.

History

Sushruta (6th century BCE) explained hypertension in a manner which matches the modern symptoms of the disease.

References

External links

High Blood Pressure from the Heart and Stroke Foundation of Canada
High Blood Pressure from MedlinePlus
A guide to lowering high blood pressure from the National Heart, Lung, and Blood Institute
The DASH diet from the National Heart, Lung, and Blood Institute
High Blood Pressure (from the American Heart Association)