Hypertension is persistent abnormally high blood pressure. Blood pressure is the pressure of blood in your arteries.

The blood circulation is a closed system in which the pressure varies constantly. It rises to a peak, called the systolic pressure, at the height of the contraction of each heartbeat as the heart pumps blood out. Then it falls to a lower level, called the diastolic pressure, which it reaches just before each heartbeat. The diastolic pressure is the running pressure between beats.

In addition to the variations within the cycle, blood pressure varies constantly with the level of physical exertion, with anxiety, stress, emotional changes, and other factors. So single measurements are not particularly meaningful and the blood pressure should be checked under resting conditions, at different times. Blood pressure is measured in terms of millimetres of mercury (mmHg). Hypertension is usually defined as a sustained systolic blood pressure of 140 mmHg or more, or diastolic blood pressure of 90 mmHg or more, at rest.

Lifestyle changes, such as dietary control and increased exercise are important for everyone with raised blood pressure.

Drug treatment is usually recommended in cases of sustained systolic pressure of 160 mmHg or more and/or diastolic pressure 100 mmHg or more.

When blood pressure is between 140/90-160/100mmHg tablets may not be necessary providing that the lifestyle changes work and there are no risk factors for heart disease and stroke, such as high cholesterol, smoking or a previous stroke or heart attack.

Diastolic pressures of 90–109 mmHg are found in about 20 per cent of the middle-aged adult population. They are less common in younger people and more common in those who are older. Diastolic pressures of 110–129 mmHg are found in about 4% of the adult population.

Causes

The cause of hypertension in approximately 90% of cases is unknown, in such cases this is called essential hypertension. Essential hypertension is very common, and affects perhaps 20 per cent of the adult population. Lifestyle and genetic factors may contribute. It is slightly more common in men. Obese people or those who drink excessive amounts of alcohol are more likely to develop hypertension. Stress may contribute to the condition.

In a few of people, the underlying causes of the hypertension are known e.g. Cushing's syndrome, kidney disease or rarely, a tumour of the adrenaline-producing cells in the adrenal gland. Combined oral contraceptives may cause hypertension. In pregnant women, pre-eclampsia and eclampsia leads to raised blood pressure, which is potentially life- threatening.

A general rise in blood pressure is known to be damaging to arteries, and arterial damage can cause raised blood pressure. In this way a spiral, leading to higher pressure. Arterial damage affects the elasticity of arteries, which become stiff and rigid. It also promotes the arterial disease atherosclerosis, which can lead to narrowed arteries. The condition is most common in older people because the arteries become more rigid with age.

Treatment

The treatment of hypertension involves both a change in lifestyle and, if necessary, the prescription of drugs. In many cases of mild hypertension, a change in eating habits, regular exercise, a low fat diet, no smoking, and if necessary a reduction in salt intake and alcohol, will be sufficient to get the blood pressure down to normal.If these changes are not successful, then drug treatment is necessary.

Three main classes of drugs are used to treat hypertension:

• Diuretics act on the kidneys to cause them to pass more water and salt in the urine and reduce the volume of the blood, so bringing down the pressure.
• Beta- blockers interfere with the hormone and nervous control of the heart, slowing it and causing it to beat more slowly, so reducing the pressure.
• Vasodilators act on the arteries to widen them. This group contains drugs acting in quite different ways. They include the alpha- blockers, the calcium antagonists, and the ACE inhibitors.

If there is an underlying medical cause, such as a hormonal disorder, treatment of this disorder often results in blood pressure returning to a normal level.