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.
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 'Hypertensive urgencies and emergencies' below). Recently, the JNC VII(The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure)has defined blood pressure over 120/80 mmHg and below 140/90 mmHg as "pre-hypertension". "Prehypertension is not a disease category. Rather,it is a designation chosen to identify individuals at high risk of developing hypertension(JNC VII)." Normal blood pressure is 120/80 mmHg.
In patients with diabetes mellitus or kidney disease studies have shown that blood pressure over 130/80 mmHg should be considered a risk factor and may warrant treatment.
- Age. Over time, the number of collagen fibres 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.
- High salt intake
- Sedentary lifestyle
- Alcohol abuse
- High levels of saturated fat in the diet
Obesity. In obese subjects, losing a pound in weight generally reduces blood pressure by 1mmHg.
- Low birth-weight
- Diabetes mellitus
- Various genetic causes
The mechanisms behind the factors associated with inessential hypertension are generally fully understood, and are outlined below. However, those associated with essential hypertension are far less understood. What is known is that cardiac output is raised early in the disease course, with total peripheral resistance 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 factor (note: the existence of this substance is theoretical) being secreted to promote salt excretion with the side-effect of raising total peripheral resistance.
- An overactive renin / angiotension 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.
- Pregnancy: unclear.
- Kidney disease / renal artery stenosis: the normal physiological response to low blood pressure in the renal arteries is to increase cardiac output to maintain the pressure needed for glomerular filtration. Here, however, increased CO can't solve the structural problems causing renal artery hypotension, with the result that CO remains chronically elevated.
- Cancers: tumours in the kidney can operate in the same way as kidney disease. More commonly, however, tumours cause inessential hypertension by ectopic secretion of hormones involved in normal physiological control of blood pressure.
- Drugs: anything with an adrenergic effect causes vasoconstriction at sites with alpha-adrenoceptors, increasing total peripheral resistance.
- Malformed aorta, slow pulse: these cause reduced blood flow to the renal arteries, with physiological responses as already outlined.
- Anemia: unclear.
- Fever: unclear.
- Aortic valve disease: unclear.
Signs and symptoms
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.
Hypertensive urgencies and 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.
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:
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.
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:
Blood tests commonly performed in a newly diagnosed hypertension patient are:
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.
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 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.
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.
- 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
Last updated: 10-23-2005 20:41:32