Hypertension

Table of Contents

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Hypertension or high blood pressure is a medical condition wherein the blood pressure is chronically elevated. While it is formally called arterial hypertension, the word "hypertension" without a qualifier usually refers to arterial hypertension. Persistent hypertension is one of the risk factors for strokes, heart attacks, heart failure and arterial aneurysm, and is a leading cause of chronic renal failure.

Definition

Hypertension is usually diagnosed on finding blood pressure of 140/90 mmHg or above, measured on both arms. Because blood pressure readings in many individuals are highly variable — especially in the office setting — the diagnosis of hypertension should be made only after noting a mean elevation on two or more readings on two or more office visits, unless the elevations are severe or associated with compelling indications such as diabetes mellitus, chronic kidney disease, heart failure, post-myocardial infarction, stroke, and high coronary disease risk. Recently, the JNC 7 (The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure)[1] has defined blood pressure 120/80 mmHg to 139/89 mmHg as "prehypertension." Prehypertension is not a disease category; rather, it is a designation chosen to identify individuals at high risk of developing hypertension. 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.

Etiology

Essential hypertension

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. High salt intake Sedentary lifestyle Tobacco smoking Alcohol abuse High levels of saturated fat in the diet Obesity - In obese subjects, losing a kilogram of mass generally reduces blood pressure by 2 mmHg. Stress Low birth-weight Diabetes mellitus Various genetic causes

Secondary hypertension

• Main article: Secondary hypertension

While most forms of hypertension have no known underlying cause (and are thus known as "essential hypertension" or "primary hypertension"), in about 5% of the cases, there is a known cause, and thus the hypertension is secondary hypertension.

Pathophysiology

The mechanisms behind the factors associated with inessential hypertension are generally fully understood, and are outlined at secondary hypertension. 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.

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 healthcare professional, this is colloquially termed white coat effect. 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 (e.g., Framingham), it is difficult to be sure that white-coat hypertension is not significant. 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 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.

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

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

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 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 suitably above anticipated systolic pressure. 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.

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 90% 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. In hypertensive children most cases are secondary hypertension, and the cause should be pursued diligently.

Blood tests commonly performed in a newly diagnosed hypertension patient

• 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

Lifestyle modification

Doctors recommend weight loss and regular exercise as the first steps in treating mild to moderate hypertension. These steps are highly effective in reducing blood pressure, but 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. Discontinuing smoking does not directly reduce blood pressure, but is very important for people with hypertension because it reduces the risk of many dangerous outcomes of hypertension, such as stroke and heart attack. 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.

Medications

See main article: Antihypertensives 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 recommends starting with a thiazide diuretic if single therapy is being initiated and another medication is not indicated. This is based on a slightly better outcome for chlortalidone in the ALLHAT study versus other anti-hypertensives and because thiazide diuretics are relatively cheap. A subsequent smaller study (ANBP2) published after the JNC7 did not show this small difference in outcome and actually showed a slightly better outcome for ACE-inhibitors in older male patients. Despite thiazides being cheap, effective, and recommended as the best first-line drug for hypertension by many experts, they are not prescribed as often as some newer drugs. Arguably, this is because they are off-patent and thus rarely promoted by the drug industry. Physicians may start with non-thiazide antihypertensive medications if there is a compelling reason to do so. An example is the use of ACE-inhibitors in diabetic patients who have evidence of kidney disease, as they have been shown to both reduce blood pressure and slow the progression of diabetic nephropathy. In patients with coronary artery disease or a history of a heart attack, beta blockers and ACE-inhibitors both lower blood pressure and protect heart muscle over a lifetime, leading to reduced mortality. Commonly used drugs include: Beta blockers: eg, metoprolol (Lopressor®), atenolol, labetalol, carvedilol (Coreg®) ACE inhibitors: eg, lisinopril (Zestril®), quinapril, fosinopril (Monopril®), captopril, enalapril Angiotensin receptor blockers (ARBs): eg, losartan (Cozaar®), valsartan (Diovan®), irbesartan (Avapro®) Calcium channel blockers: e.g. amlodipine (Norvasc®), verapamil Diuretics: eg, chlortalidone, hydrochlorothiazide (also called HCTZ) Combination products (which usually contain HCTZ and one other drug) The aim of treatment should be blood pressure control (<140/90 mmHg for most patients, and lower in certain contexts such as diabetes or kidney disease). Each added drug may reduce the systolic blood pressure by 5-10 mmHg, so often multiple drugs are necessary to achieve blood pressure control.

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