Hypertension (High Blood Pressure)

What is it?

Hypertension is persistently high pressure in the arteries that can, over time, cause damage to organs such as the kidneys, brain, eyes, and heart. Arterial blood pressure, the amount of force blood exerts on the walls of the arteries, depends on the force and rate that the heart contracts as it pumps oxygenated blood from the left ventricle (compartment) of the heart into the arteries and the resistance to that flow. The amount of resistance depends on the elasticity and diameter of the smaller blood vessels and how much blood is flowing through them.

Blood pressure is dynamic; it rises and falls depending on a person’s level of activity, the time of day, and physical and emotional stresses. It is largely regulated by the autonomic nervous system changing the rate that the heart beats and the diameter of small blood vessels. Hormones like adrenaline produced by the adrenal glands and angiotensin II produced by the kidneys also constrict small blood vessels. Another hormone produced by the adrenal glands, aldosterone, alters blood pressure by affecting the amount of sodium, potassium and fluids excreted by the kidneys. When one or more of these regulating processes is not able to respond appropriately, blood pressure may become persistently high.

Two pressures are recorded when blood pressure is measured. Systolic pressure is the peak force on the blood vessel walls when the heart is contracting, and diastolic pressure is the pressure present when the heart is relaxing between beats. Both pressures are measured in millimetres of mercury (mm Hg) and are expressed as systolic over diastolic pressure. For instance, a blood pressure of 120/80 mm Hg corresponds to a systolic pressure of 120 and a diastolic pressure of 80 and would be spoken of as 120 over 80.

Usually diastolic pressure mirrors systolic pressure, but as people get older the diastolic changes less than systolic pressure and hypertension due to high systolic pressure (called isolated systolic hypertension) becomes more common. In general, the higher the blood pressure and the longer the period of high pressure, the greater the likelihood of damage.

Blood pressures in adults are generally classified as follows:

  • Normal blood pressure - a systolic of less than 120 and a diastolic of less than 80 mm Hg (or 90 mm Hg in the elderly).
  • Mild hypertension - a systolic pressure of 120-139 and/or a diastolic of 80-89 mm Hg. This usually responds to lifestyle changes like reducing salt intake and taking more exercise.
  • Moderate hypertension- a systolic of 140-179 and/or a diastolic of 90-109 mm Hg. A number of measurements are likely to be made to confirm these values which usually require drug treatment in addition to lifestyle changes.
  • Severe hypertension - a systolic over 180 and/or a diastolic over 110 mm Hg. This will almost certainly require referral to a specialist for urgent investigation and treatment.

Blood pressure in children is assessed differently than in adults, and is compared with the 95th percentile values in children of the same age, height and sex.

Signs and Symptoms

Occasionally high blood pressure causes headaches, but in most cases there are no symptoms until it begins to damage body organs. For this reason hypertension is sometimes referred to as the “silent killer,” quietly increasing the risk of developing stroke, heart disease, heart attack, kidney damage, and blindness. Very high blood pressure may cause breathlessness, blurred or double vision and nose bleeds as well as a persistent headache.

Because hypertension is both a quiet and a common condition, blood pressure is often measured each time a patient sees their doctor. Nearly a third of UK residents with high blood pressure do not know about it and are not being treated.

 

Causes

Essential hypertension
In most cases the cause of hypertension is not known. This form of high blood pressure is called essential or primary hypertension. It can affect anyone, but is found more frequently in men and more often in people of African-Caribbean origin and in South Asians who live in the UK than in the rest of the UK population. It becomes more common in everyone with increasing age and it tends to run in families.

Although it may not be possible to identify the cause, there are several things that are known to increase the risk of developing hypertension and to make it worse it when it is present. These include:

  • Obesity
  • A lifestyle with little exercise
  • Smoking
  • Excessive use of alcohol
  • Excessive dietary salt (sodium)
  • Stress

Secondary hypertension
Hypertension may also be due to identifiable causes. This form of high blood pressure is called secondary hypertension. It is important to identify these conditions as they may be treatable, allowing the blood pressure to return to normal or near normal levels. These causes include:

  • Kidney disease or damage – this decreases the removal of salts and fluids from the body and increases blood volume and pressure. Since hypertension can also cause kidney damage, the problem can get progressively worse if left untreated.
  • Narrowing of the arteries supplying the kidneys by atheroma (atherosclerosis)
  • Diabetes – over time this condition can damage the kidneys and the blood vessels.
  • Cushing’s syndrome – a disease with increased production of the hormone cortisol by the adrenal gland.
  • Hyperaldosteronism (Conn's syndrome) – a condition with overproduction of aldosterone, a hormone that helps regulate the removal of sodium by the kidneys; it may be due to an adrenal gland tumour which is usually benign.
  • Phaeochromocytoma – a rare and usually benign tumour of the adrenal gland that produces excessive amounts of adrenaline, a hormone that the body uses to help it respond to stress; affected patients often have episodes of severe hypertension.
  • Thyroid disease – both excessive and deficient thyroid hormone production can cause increased blood pressure
  • Primary hyperparathyroidism – increased activity of parathyroid gland tissue increases plasma calcium which can be associated with hypertension.
  • Pregnancy – hypertension may develop at any time during a woman’s pregnancy but is most common in the last three months, when it can cause pre-eclampsia, a condition when blood pressure is increased and fluids are retained.
  • Oral contraceptives (rarely)
  • Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen
  • Recreational drugs such as cocaine and the amphetamines
Tests

The goals of testing are to detect high blood pressure, to confirm that it is persistent over time, to find out whether it is being caused by an a treatable disease, to check the health of various body organs, to get baseline values prior to starting treatment, and to monitor blood pressure and organ health during treatment.

Laboratory Tests
Laboratory tests cannot diagnose hypertension, but are frequently requested to help evaluate and monitor organ function. Specific tests are sometimes requested to detect diseases that may be causing the high blood pressure or making it worse.

General tests that may be requested include:

  • Urinalysis including Urine Albumin to Creatinine Ration (ACR) - to help assess kidney function
  • Urea and Creatinine – to detect and monitor kidney disease or to monitor the effect of drug treatment on the kidneys
  • Electrolytes sodium and potassium - some high blood pressure treatments can cause high sodium and potassium loss
  • Fasting Glucose – to detect diabetes
  • Calcium – increased activity of the parathyroid glands produces an increase in serum calcium which can be associated with high blood pressure
  • Lipid Profile – to check levels of total cholesterol, HDL cholesterol, LDL cholesterol and triglycerides because persistent hypertension promotes hardening of the arteries (atherosclerosis)

Specific tests that may be requested because of the patient’s medical history, physical findings or general laboratory test results to help detect, diagnose, and monitor conditions causing secondary hypertension include:

  • Aldosterone and Renin – to help detect the overproduction of aldosterone by the adrenal glands (which may be due to a tumour)
  • Cortisol – to detect an overproduction of cortisol that may be due to Cushing’s syndrome
  • Catecholamines and methylated amines – adrenaline, noradrenaline and their metabolites and are used to help detect the presence of a phaeochromocytoma (a tumour of the adrenal gland) that can cause episodes of severe hypertension
  • Parathyroid hormone (PTH) – if calcium is found to be increased
  • TSH (Thyroid Stimulating Hormone) and free T4 – to detect and monitor thyroid dysfunction

Blood pressure measurements are usually performed after the patient has been sitting quietly for at least five minutes but may also be done in other postures, such as standing. If a patient has an elevated blood pressure, the pressure in the other arm may be measured to confirm the finding. Since blood pressure can and will vary, a diagnosis of hypertension is not made from a single measurement, but involves multiple measurements made at different times. It is not a single high reading that the doctor is interested in, but persistent high blood pressure.

The doctor may ask the patient to wear a device that monitors and records the blood pressure at regular intervals during the day to monitor it over time. This is especially helpful during the diagnostic process and can help rule out the high measurements that only occur when the patient is in the doctor’s surgery. This is known as the “white coat phenomenon,” which has been estimated to account for as much as 10-20% of suspected cases of hypertension. There are electronic blood pressure measuring devices that can be used in the home. These can be used effectively but should be checked at intervals against the findings at the doctor’s surgery to ensure accuracy.

These forms of blood pressure measurement are considered indirect. Very rarely, a direct measurement of blood pressure may be required. This can be obtained by inserting a catheter into an artery to measure the pressure inside the blood vessel.

As part of the diagnostic process and to help evaluate the status of vital organs, the doctor would normally carry out:

  • Eye examination – to look at the retina for changes in the appearance of the blood vessels (retinopathy)
  • Physical examination – to help evaluate the kidneys, to look for abdominal tenderness, to listen for bruits (the sound of blood flowing through a narrowed artery), to examine the thyroid gland in the throat for enlargement and to detect any other clinical signs present
Treatments

Lifestyle changes can help lower blood pressure and are advised for all patients. In those with mild hypertension (a systolic preassure of 120-139 and/or a diastolic of 80-89mm Hg), reaching and maintaining a healthy weight, exercising regularly, limiting dietary alcohol and salt, and stopping smoking can reduce blood pressure levels to normal and may be the only “treatment” required. The risks associated with gender, race and increasing age, however, do not disappear with lifestyle changes and, in most other patients, a treatment plan that includes medicines is necessary to control persistently high blood pressure.

There are several classes of drugs available to treat hypertension. Each class works differently, targeting a particular aspect of blood pressure regulation. Frequently, a patient will need to take a couple of different drugs together to achieve blood pressure control. Your doctor will work with you to select the combinations and dose that are right for you. Classes that are available include:

  • Diuretics – a commonly used group of drugs that increase the removal of salt and water by the kidneys. This reduces the volume of fluid in circulation and lowers the blood pressure.
  • Adrenergic blockers (alpha blockers, beta blockers, alpha-beta blockers) – work to reduce the nervous system’s rapid response to physical and emotional stress.
  • ACE (angiotensin-converting enzyme) inhibitors and ARBs (Antiotensin II receptor blockers) – help prevent the constriction of arterioles (small arteries) by blocking the formation and/or action of angiotensin II, an enzyme that the body produces to constrict blood vessels and increase blood pressure.
  • Calcium channel blockers – dilate arterioles by decreasing the amount of calcium that enters into the blood vessel walls and the heart muscle.
  • Vasodilators – work directly on blood vessels to relax the muscles that constrict and dilate the arteries.

If a condition causing secondary hypertension can be cured (for example, by removing an adrenal tumour) or controlled (for example, by treating diabetes or thyroid disease), then blood pressure levels may fall to normal or near normal. When a cure is not possible and control of the disease consists of minimising further damage (as may occur with kidney disease), then the hypertension will be controlled with a combination of medicines, and the patient will be monitored closely to help maintain organ function and reduce the likelihood of problems arising.

Any patient, asymptomatic or not, who has severe hypertension with a blood pressure over 180/110 mm Hg or who has hypertensive changes in the retina on eye examination must be treated urgently and may require admission to hospital.

In about 4% of first pregnancies mothers develop a combination of increased blood pressure and protein in the urine called pre-eclampsia. In the last three months of pregnancy about one in 50 develop full eclampsia with fits, fluid in the lungs, kidney failure and clotting problems. Women with pre-eclampsia require rest, close monitoring, and frequent visits to their doctor’s surgery or even admission to hospital. The only real solution for pre-eclampsia is delivery, but postponing delivery as long as possible allows the foetus more time to mature. This time delay must be balanced against the increasing danger of the development of full eclampsia that can be life-threatening for both baby and mother.