Basics of High Blood Pressure

High blood pressure (hypertension) is a risk factor that can increase your chance of developing heart disease, a stroke, and other serious conditions. As a rule, the higher the blood pressure, the greater the risk. Treatment includes a change in lifestyle risk factors where these can be improved. For example, losing weight if you are overweight, regular physical activity, a healthy diet, cutting back if you drink a lot of alcohol, stopping smoking, and a low salt and caffeine intake. If needed, medication can lower blood pressure.

What is blood pressure?

Blood pressure is the pressure of blood in your blood vessels (arteries). Blood pressure is measured in millimeters of mercury (mm Hg). Your blood pressure is recorded as two figures. For example, 150/95 mm Hg. This is said as 150 over 95.

• The top (first) number is the systolic pressure. This is the pressure in the arteries when the heart contracts.
• The bottom (second) number is the diastolic pressure. This is the pressure in the arteries when the heart rests between each heartbeat.

What is high blood pressure (hypertension)?

High blood pressure is a blood pressure that is 140/90 mm Hg or above each time it is taken at the GP surgery (or home or ambulatory readings always more than 135/85 mm Hg). That is, it is sustained at this level. High blood pressure can also be:

• Just a high systolic pressure – for example, 170/70 mm Hg.
• Just a high diastolic pressure – for example, 120/104 mm Hg.
• Or both – for example, 170/110 mm Hg.

However, it is not quite as simple as this. Depending on various factors, the level at which blood pressure is considered high enough to be treated with medication can vary from one person to another.

You have high blood pressure if you have several blood pressure readings that are high, and which are taken on different occasions, and when you are relaxed.

Observation period

If one reading is found to be high, it is usual for your doctor or nurse to advise a time of observation. This means several blood pressure checks at intervals over time. The length of the observation period varies depending on the initial reading, and if you have other health risk factors.

For example, say a first reading was mildly high at 145/89 mm Hg. If you are otherwise well, then a period of several weeks of observation may be advised. This may involve several blood pressure measurements over the next few weeks. You may be given a machine to monitor blood pressure while you are going about doing your everyday activities (ambulatory monitoring).
You may be given (or asked to buy) a machine to measure your blood pressure at home (home monitoring). One reason this may be advised is because some people become anxious in medical clinics. This can can cause the blood pressure to rise. (This is often called white coat hypertension.) Home or ambulatory monitoring of blood pressure may show that the blood pressure is normal when you are relaxed.

The observation period is also a good time to change any lifestyle factors that can reduce blood pressure (see below). If the blood pressure readings remain high after an observation period then medication may be advised, depending on your risk factors (see below).

However, if you have diabetes, or have recently had a heart attack or stroke, you may be advised to have blood pressure checks fairly often over the next week or so. Also, treatment with medication is usually considered at an earlier stage if the readings remain high.

What causes high blood pressure (hypertension)?

The cause is not known in most cases

This is called essential hypertension. The pressure in the blood vessels (arteries) depends on how hard the heart pumps, and how much resistance there is in the arteries. It is thought that slight narrowing of the arteries increases the resistance to blood flow, which increases the blood pressure. The cause of the slight narrowing of the arteries is not clear. Various factors probably contribute.

In some cases, high blood pressure is caused by other conditions

It is then called secondary hypertension. For example, certain kidney or hormone problems can cause high blood pressure.