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Hypertension (High Blood Pressure) Print E-mail

Dr. Kennedy Hypertension, commonly referred to as "high blood pressure," is a condition in which the blood pressure is chronically elevated. The word "hypertension" without a qualifier normally refers to arterial hypertension, the pressure measured in the arteries. Hypertension is classified as either essential (primary) or secondary. Essential hypertension indicates that no specific medical cause can be found. Secondary hypertension indicates that the elevated blood pressure is a result of another condition, e.g. kidney disease or tumors (pheochromocytoma and paraganglioma). Persistent hypertension is one of the risk factors for strokes, heart attacks, heart failure and arterial aneurysm, and is a major cause of chronic renal failure. Even moderate elevation of arterial blood pressure leads to shortened life expectancy. At severely high pressures, defined as mean arterial pressures 50% or more above average, a person can expect to live no more than a few years unless appropriately treated.

In thinking about hypertension, it is important to realize that it may be caused by metabolic conditions or by mechanical circumstances, or both. With age the arterial system becomes less elastic and therefore does not stretch, expand and then relax with each heart beat cycle. One could compare it with a car in which the shock absorbers have worn out and do not absorb the shock of a bumpy road. The youthful aterial system is an elastic shock absorber. Therefore, there is a normal elevation of blood pressure with the aging vascular system. Whether or not this calls for treatment is a matter of how elevated blood pressure becomes.

Hypertension is considered to be present when a person's systolic blood pressure is consistently 140 mm Hg or greater, and/or diastolic blood pressure is consistently 90 mm Hg or greater. If only the systolic reading is elevated, this is referred to as systolic hypertension and is dealt with separately in another article. Hypertension is labeled resistant hypertension if a person’s blood pressure remains above their target blood pressure despite taking three or more medications to lower it.

In 2003, the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure defined blood pressure 120/80 mm Hg to 139/89 mm Hg as "prehypertension." Prehypertension is not a disease category. Rather it is a designation chosen to identify people at high risk of developing hypertension. In patients with diabetes mellitus or kidney disease studies have shown that blood pressure over 130/80 mm Hg should be considered high and should be treated.

Signs and Symptoms

Hypertension is usually found incidentally by health care professionals during a routine checkup. The only test for hypertension is a blood pressure measurement. Hypertension in isolation usually produces no symptoms ("silent hypertension") 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 initial onset and prior to hypertension diagnosis. Malignant hypertension (aka accelerated hypertension) is distinct as a late phase in the condition, and may present with headaches, blurred vision and kidney damage. 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, nausea and vomiting and when it reaches this level it is known as hypertensive encephalopathy.

Contributing Factors of Essential Hypertension

Although no specific medical cause can be determined in essential hypertension, the most common form has several contributing factors. These include licorice, salt sensitivity, renin homeostasis, insulin resistance, genetics, sleep apnea, and age. These are discussed below.

Liquorice

Consumption of liquorice can lead to a surge in blood pressure. People with hypertension or history of cardiovascular 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).

Sodium Sensitivity

Sodium is an environmental factor that has received the most attention. Approximately one third of the essential hypertensive population is responsive to sodium intake, that is to say their already existing hypertension is made worse by sodium ingestion. 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. This increases the total blood volume and thus increases the pressure on the blood vessel walls. The kidneys are responsible for regulating salt and water levels in the body. When salt and water levels increase around cells, the excess is drawn into the blood, which is filtered by the kidneys. The kidneys remove excess salt and water from the blood, both of which are excreted as urine. When the kidneys do not work well, fluid builds up around cells and in the blood. The heart is the pump that pushes the blood around. If there is more fluid in the blood, the heart has to work harder and the blood pressure goes up because there is more pressure on the walls of the blood vessels. The heart can get weaker or even worn out from the extra work. Salt has been blamed in the past as causing high blood pressure, however new research suggests that too little calcium or potassium also has an impact on blood pressure.

Renin

High Renin levels predispose to hypertension, Increased Renin leads to increased production of Angiotensin II which in turn causes vasoconstriction, thirst/ADH and aldosterone increasing sodium resorption in the Kidneys and finally increased blood pressure. Some authorities believe that potassium might both prevent and treat hypertension. Salt avoidance may assist in lowering blood pressure in two ways: by replacing highly processed (salted foods) with natural foods which contain higher levels of potassium, and by reducing salt intake.

Insulin Resistance

Insulin regulates blood sugar levels, and 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 (aka the metabolic syndrome). A better name for it is sustained hyperinsulinemia.

Sleep Apnea

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

Genetics

Hypertension is one of the most common complex disorders, with genetic inheritability averaging thought to account for around 30% of cases. Data supporting this view emerge from animal studies as well as in population studies in humans. Most of these studies support the concept that inheritance is probably multi-factorial 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 of hypertension, and the number is 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 an elevated arterial blood pressure. If this is the only factor, it leads to systolic hypertension.

Causes of Temporary, Non-pathogenic Hypertension

There are some anecdotal or transient causes of high blood pressure such as extreme exercise and emotional excitement. These are not to be confused with the disease called hypertension in which there is an intrinsic physiopathological mechanism as described below.

Etiology of Secondary Hypertension

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

Renal Hypertension

This category includes diseases such as polycystic kidney disease or chronic glomerulonephritis. Hypertension can also be produced by diseases of the renal arteries supplying the kidney which 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 hypertension. Cushing's syndrome (hypersecretion of cortisol) overproduction the hormone cortisol can have no obvious cause 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 (usually 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).

Drugs Induced Hypertension

Certain medications, especially NSAIDS (Motrin/Ibuprofen) and steroids can cause hypertension. Licorice inhibits the 11-hydroxysteroid hydrogenase enzyme (which catalyzes the conversion of cortisol to cortisone) which allows cortisol to build up and stimulate the Mineralocorticoid Receptors which will lead to effects similar to hyperaldosteronism, which itself is a cause of hypertension.

Rebound Hypertension

High blood pressure can be associated with the sudden withdrawal of various anti-hypertensive medications. The increases in blood pressure may result in blood pressures greater than when the medication was initiated and can result in a hypertensive emergency. Rebound hypertension is avoided by gradually reducing the dose, thereby giving the body enough time to adjust to the reduction in dose. Medications commonly associated with rebound hypertension include centrally-acting anti-hypertensive agents, such as clonidine and beta-blockers.

Hypertensive Emergency

Hypertension is rarely severe enough to cause symptoms. These typically only surface with a systolic blood pressure over 240 mm Hg and/or a diastolic blood pressure over 120 mm Hg. 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 the 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.

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)
  • Encephalopathy - confusion, headache , convulsion due to vasogenic edema in brain due to high blood pressure.
  • Cardiomyopathy (heart failure due to chronically high blood pressure)
  • Retinopathy - damage to the retina
  • Nephropathy - chronic renal failure due to chronically high blood pressure

Hypertension in Blacks

As of March 18 2008, statistics show, Blacks in Africa and in America have the highest prevalence of hypertension worldwide. At the same level of BP in Caucasians, blacks have a more severe organ complication and accelerated course of hypertension-induced organ damage. This includes greater severity and prevalence of end stage renal disease (ESRD) requiring dialysis or transplantation, hypertensive retinopathy, systolic dysfunction and hypertensive heart failure (HHF) and sudden cardiac deaths due to hypertensive acute pulmonary edema with arrhythmias. The geometric effects of hypertension on the heart of blacks are severe, but concentric hypertrophy is commonest at the early stages. African hypertensives present late and have valvar regurgitations and greater left ventricular enlargement. There is evidence of genetic polymorphisms of adrenergic receptors and Gq which predispose Africans to more severe complications. Blacks require 2 or more drugs to control their blood pressure, the most effective drugs often being expensive. The combination of an angiotensin converting enzyme inhibitor - thiazide diuretic and alpha blocker (prazosin or methyldopa) seem to be very effective to treat severe hypertension,and hypertensive crises rapidly, safely and effectively in Africans.

Hypertension of 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.

Hypertension in 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 detection and intervention in childhood hypertension important to reducing 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. Affected adolescents usually have primary or essential hypertension, making up 85 to 95% of cases.

Diagnosis

Blood Pressure Measurement

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. 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 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 some cold medications. 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 mm Hg and then slowly release the air while palpating the radial pulse. After one minute, the cuff should be reinflated to 30 mm Hg 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. 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 mm Hg, 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. Studies have shown that 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 (elevation of blood pressure from the anxiety of being examined). Those using home blood pressure monitoring devices are increasingly also making use of blood pressure charting software. These charting methods provide printouts for the patient's physician and reminders to take a blood pressure reading.

Distinguishing Primary vs. Secondary Hypertension

Once the diagnosis of hypertension has been made it is important 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 which occurs in type 2 diabetes, 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.

Diagnostic Tests

Blood tests commonly performed include:

Creatinine to identify both underlying renal disease as a cause of hypertension and conversely hypertension as the cause of kidney damage. Also a baseline for later monitoring the possible side-effects of certain antihypertensive drugs which may damage the kidneys.
Electrolytes (sodium, potassium)
Glucose - to identify diabetes mellitus
Cholesterol
Urine protein
Electrocardiogram for evidence of the heart being under strain working against 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 for signs of cardiac enlargement or evidence of cardiac failure.

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.

Treatment

Lifestyle modification involves weight reduction and regular aerobic exercise (e.g., cycling) and 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.

Reduced sodium (salt) diet is proven very effective. It decreases blood pressure in about 60% of people. Many people choose to use a salt substitute to reduce their salt intake.

Additional dietary changes beneficial to reducing blood pressure include 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 National Institutes of Health sponsored research.

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. Blood pressure (especially systolic) always transiently increases following alcohol and/or nicotine consumption. Abstention from cigarette smoking is important to reduce the risk of many dangerous outcomes of hypertension, such as stroke and heart attack.

Relaxation therapy, such as meditation, that reduces environmental stress, reducing high sound levels and over-illumination can lessen hypertension.

Medications: unless hypertension is severe, lifestyle changes such as those discussed in the preceding section are recommended before initiation of drug therapy. Adoption of the DASH diet is an 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 act by lowering blood pressure. Evidence suggests that reduction of the blood pressure by 5-6 mm Hg 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 less than 140/90 mm Hg for most patients, and lower in certain conditions such as diabetes or kidney disease (some medical professionals recommend keeping levels below 120/80 mm Hg). Each added drug may reduce the systolic blood pressure by 5-10 mm Hg, 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 doxazosin, prazosin, or terazosin
  • Beta blockers such as atenolol, labetalol, metoprolol (Lopressor, Toprol-XL), propranolol.
  • Calcium channel blockers such as nifedipine (Adalat)[24] 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)


The information in this article is not meant to be medical advice.�Treatment for a medical condition should come at the recommendation of your personal physician.

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