Blood pressure is the term used to describe the pressure exerted on the arterial walls as blood flows through them. This pressure is at its highest when the heart contracts and pumps blood through the arteries and is called the systolic pressure.

Blood pressure is measured in millimetres of mercury (mm Hg) and a healthy systolic blood pressure reading is around 120 mm Hg. As the heart relaxes between two beats, the blood flows back through the veins into the heart and the pressure within the arteries falls. However, there is still some residual pressure in the arteries to prevent them from collapsing. This is called the diastolic pressure and it should measure around 80 mm Hg in a healthy individual.

Blood pressure fluctuates throughout the day, rising on physical exertion or during stressful moments for example, when the heart may pump harder. Age also influences blood pressure, as the walls of the blood vessels become hard and lose some of their elasticity as a person ages, leading to increases in systolic and diastolic blood pressure.

Some of the risk factors for high blood pressure include:

Essential hypertension

Some people have hypertension or high blood pressure with no known cause. This type of hypertension is called essential hypertension. In people with this condition, the smaller arteries of the body become narrower which means the heart has to pump harder to circulate blood to distant organs and limbs. This raises the blood pressure. Essential hypertension is also called primary hypertension and 5% of all cases of hypertension are essential hypertension.

Family history

Hypertension, especially essential hypertension often has a genetic basis and may run in families. People with first degree relatives who have the condition are at an increased risk of developing hypertension.

Diseases

Hypertension may be caused by other diseases such as kidney disease, Cushing's syndrome, Lupus, pheochromocytoma or adrenal tumors.

Drugs

Drugs may also cause hypertension. Some examples include pain relievers such as non-steroidal anti-inflammatory drugs (NSAIDs), corticosteroids, oral contraceptives, some antidepressant medications and drugs of abuse such as amphetamine, methamphetamine and cocaine.

Other factors

• Increasing age is a risk factor for hypertension
• People of African or Caribbean descent are at a greater risk of hypertension
• A high dietary salt or caffeine intake and a low intake of fresh fruits and vegetables increases the risk of hypertension
• Smokers and alcoholics are at a greater risk of hypertension
• Obesity, overweight and lack of physical exercise also increases the risk
• Stress and a "type A" personality raise the risk of developing high blood pressure