Arterial hypertension, or high blood pressure is a medical condition where the blood pressure is chronically elevated. Persistent hypertension is one of the risk factors for strokes, heart attacks and heart failure, and is a leading cause of chronic renal failure.

Definition

Blood pressure is a continuous variable, and risks of various adverse outcomes rise with it. Hypertension is usually diagnosed on finding blood pressure above 140/90 mmHg measured on both arms on three occasions over a few weeks. (Also see urgency below). In patients with diabetes mellitus studies have shown that blood pressure over 130/80 mmHg should be considered a risk factor and may warrant treatment. Recently there have been calls to define blood pressure over 120/80 mmHg as "pre-hypertension", even in non-diabetic populations.

Signs and symptoms

Hypertension

Hypertension is usually found incidentally - "case finding" by healthcare professionals. It normally produces no symptoms.

Malignant hypertension (or accelerated hypertension) is distinct as a late phase in the condition, and may present with headaches, blurred vision and end-organ damage.

It is recognised that stressful situations can increase the blood pressure; if a normally normotensive patient has a high blood pressure only when being reviewed by a health care professional, this is colloquially termed white coat hypertension. Since most of what we know of hypertension and its outcome with or without modification is based on large series of readings in doctors' offices and clinics (eg Framingham) it is difficult to be sure of the significance of white-coat hypertension. Ambulatory monitoring may help determine whether traffic and ticket inspectors produce similar sustained rises.

Hypertension is often confused with mental tension, stress and anxiety. While chronic anxiety is associated with poor outcomes in people with hypertension, it alone does not cause it.

Emergencies

Hypertension is rarely severe enough to cause symptoms. These 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 present, but in absence of raised intracranial pressure, it is called hypertensive urgency. Hypertension under this circumstance needs to be controlled, but hospitalization is not 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)
• 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

Pregnancy

See the main article: 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.

Diagnosis

The diagnosis of hypertension is by definition made by three separate measurements at least one week apart. Two caveats to this criteria is it must be in the presence mild elevations and in the absence of end organ damage. If either are not met, the diagnosis may be made without repeat measurements in some cases.

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

For instance, measurements should be at least 1 hour after caffeine, 30 minutes after smoking 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 for a minimum of five minutes. 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 at least 30 mmHg greater than systolic pressure. A stethoscope should be placed lightly over the brachial artery. The arm should be at the level of the heart and the cuff should be deflated at a rate of 2-3 mmHg/sec. Systolic pressure is the pressure reading at the onset of sounds. Diastolic pressure is then defined as the pressure at which the sounds disappear. 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. Also, in elderly patients, it is recommended to measure pressures in multiple postures as they are at risk for orthostatic hypotension.

Once the diagnosis of hypertension has been made it is important to attempt to identify reversible (secondary) causes. In the adult population over 90% of all hypertension has no known 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. However, in the pediatric population the opposite is true, most cases have a secondary cause and these should be pursued more aggresively.

Important causes of secondary hypertension are:

• Heavy alcohol use
• Renal artery stenosis
• Obstructive sleep apnea
• Pheochromocytoma
• Hyperaldosteronism (Conn's syndrome)
• Cushing's disease
• Steroid use
• Coarcation of the aorta
• Chronic renal failure
• Scleroderma renal crisis
• Hyperparathyroidism
• Liquorice (when consumed in excessive amounts)

Blood tests commonly performed in a newly diagnosed hypertension patient are:

• Creatinine (renal function)
• Electrolytes (sodium, potassium)
• Glucose (to identify diabetes mellitus)
• Cholesterol

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

Doctors recommend weight loss and regular exercise, as well as discontinuing smoking, as the first steps in treating mild to moderate hypertension. These steps are highly effective in reducing blood pressure. Unfortunately these actions are easier to suggest than to achieve and most patients with moderate or severe hypertension end up requiring indefinite drug therapy to bring their blood pressure down to a safe level.

Mild hypertension is usually treated by diet, exercise and improved physical fitness. A diet rich in fruits and vegetables and fat-free dairy foods and low in fat and sodium lowers blood pressure in people with hypertension. Dietary sodium (salt) causes hypertension in some people and reducing salt intake decreases blood pressure in a third of people. Regular mild exercise improves blood flow, and helps to lower blood pressure.

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 10 mmHg can decrease the risk for complications by about 25%.

Which type of medication to use initially for hypertension has been the subject of several large studies. The JNC7 (The Seventh Report of the Joint National Committee on Prevention of Detection, Evaluation and Treatment of High Blood Pressure) recommends starting with a thiazide diuretic if single therapy is being initiated and a another medication is not indicated. This is based on a slightly better outcome for chlorothiazide in the ALLHAT study versus other anti-hypertensives and because thiazide diuretics are relatively cheap. Another large study (ANBP2) published after the JNC7 did not show this small difference in outcome and actually showed a slightly better outcome for ACE-inhibitors. The bottom line is this - the fundamental goal of treatment should be blood pressure control and in reality all three classes of medications are very effective.

References

• Chobanian AV et al. The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: the JNC 7 report. JAMA. 2003 May 21;289(19):2560-72. PMID 12748199 fulltext (http://jama.ama-assn.org/cgi/content/full/289.19.2560v1)