Low blood pressure (hypotension)

Low blood pressure means a blood pressure lower than would normally be expected for a particular person – low enough to cause symptoms such as fainting. Although it’s usually good for health to have as low a blood pressure as possible, when blood pressure becomes too low it can cause a reduction in blood flow to vital organs around the body.  

About low blood pressure
Symptoms of low blood pressure
Causes of low blood pressure
Diagnosis of low blood pressure
Treatment of low blood pressure

About low blood pressure

Your blood pressure is a measure of the force that your blood puts on the walls of your arteries as it’s pumped around your body by your heart. Your body uses a number of different mechanisms to control your blood pressure and make sure it is maintained within a narrow range.

Blood pressure is expressed as two numbers, such as 120/80 mmHg (millimetres of mercury). These numbers show the maximum blood pressure when your heart contracts and the minimum pressure in between heart beats.
If your blood pressure is too high, you will be at greater risk of certain diseases, such as coronary heart disease and stroke. So it's normally good to have as low a blood pressure as possible, as this can reduce your chance of getting these conditions. The ideal blood pressure for adults is less than 120/80 mmHg.

However, if your blood pressure becomes lower than normal for you, the blood flow to some of your vital organs, like your brain and lungs, can be restricted. This leads to symptoms such as fainting.

There is no recognised threshold for low blood pressure. If the first number (your systolic blood pressure) is lower than 100, your doctor may consider it to be low. However a blood pressure lower than this may be completely normal for some people, whereas others may experience symptoms of low blood pressure at a much higher level. It also depends a lot on individual factors: blood pressure is lower in young women and especially in pregnant women. It’s therefore only considered to be a problem if you are having symptoms.

Symptoms of low blood pressure

If your blood pressure is naturally low, you are unlikely to have any symptoms and it’s not something you should be concerned about.

However, if your blood pressure becomes lower than normal for you, it can cause symptoms such as:
•    dizziness or light-headedness
•    fainting
•    shortness of breath
•    chest pain
•    cold feet and hands
•    palpitations (you can feel your heart beating more forcefully)

You may find you mainly get these symptoms when you stand up from a sitting or lying position, usually within the first few seconds or minutes. This is called postural (or orthostatic) hypotension. If you usually get symptoms after eating a large meal, it’s called postprandial hypotension.

If you have any of the symptoms of low blood pressure, you should see your GP.

Causes of low blood pressure

If your blood pressure has been described as low but you don’t have any symptoms, then there is unlikely to be any underlying problem, and this is a normal blood pressure for you.

Anyone can occasionally get a sudden drop in blood pressure that causes symptoms, such as fainting. A number of factors can cause this, such as standing for a long time in a hot environment, pain and strong emotions. These usually cause only a brief, temporary drop in blood pressure.

However, if you have low blood pressure that is regularly causing symptoms, it means the mechanisms that control blood pressure in your body are not working as they should be, causing your blood pressure to drop. If you have postural hypotension, your body doesn’t respond quickly enough when you stand up, causing blood to pool in your legs. Postprandial hypotension happens when blood flows to your digestive system after eating a meal – but your body doesn’t respond in the normal way to maintain blood pressure in the rest of your body.

Factors that can cause this include the following.

• Injury, burns and dehydration – these can all reduce the volume of blood in your body, leading to a drop in blood pressure.
• Heart conditions, such as heart failure, heart attack and arrhythmia, which can stop your heart pumping effectively.
• High blood pressure – people who have high blood pressure often find that their blood pressure is more likely to fluctuate from high to low. Taking medicines to treat high blood pressure (hypertension) – especially medicines called diuretics and alpha-    blockers – can sometimes reduce your blood pressure too much.
• Conditions involving your nervous system, such as Guillain-Barré syndrome, diabetes and Parkinson’s disease – these affect how well your body is able to respond to a change in posture.
• Age – postural hypotension is more likely as you get older.

Diagnosis of low blood pressure

Your GP will ask about your symptoms and when you usually get them, to try to find out what is causing your low blood pressure. He or she will examine you and may also ask you about your medical history.

Your GP will measure your blood pressure using a device called a sphygmomanometer. This is usually an automated, digital device, made up of a monitor attached to a cuff, which is wrapped around your upper arm. Your doctor will press a button to inflate the cuff, and it will automatically slowly deflate. A sensor in the cuff detects your blood pressure and the result is shown on the display screen.

If you have symptoms of postural hypotension your GP may also measure the change in your blood pressure as you stand up after lying or sitting down. He or she may also refer you for a tilt test. This happens in hospital and involves being slowly tilted upwards on a table as your blood pressure and heart rate and rhythm are monitored.

If you have symptoms of postprandial hypotension, your blood pressure will be measured before and after you have a big meal. You may also have other tests depending on what symptoms you have had and what your GP suspects may be causing your low blood pressure.

Treatment of low blood pressure

You are unlikely to need any treatment if your blood pressure is naturally low and you don’t have any symptoms.

If you are experiencing symptoms, your treatment will depend on the cause of your low blood pressure. For example, if you are taking medicines to treat high blood pressure and these are causing your blood pressure to drop too much, your doctor may switch you to a different type of medicine. Similarly, your GP will check you are receiving the right treatment for any other underlying conditions, such as diabetes or Parkinson’s disease. He or she may refer you to a specialist if necessary, particularly if you have symptoms such as fainting.

Self-help

There are several self-help measures that can help if you have postural or postprandial hypotension.

If you have postural hypotension, your GP may advise you to:

•    stand up slowly, especially when you first wake up
•    take care getting out of hot baths or showers
•    make sure you drink enough fluids and, if you drink alcohol, not to drink too much of it
•    wear compression stockings

Your GP may advise you to alter your diet so it includes more salt. However, don’t do this unless your GP advises you to as it needs to be done in a controlled way.

If you have postprandial hypotension, your doctor may advise you to:

•    eat small, regular meals with lower levels of carbohydrate, rather than large meals with lots of carbohydrate.
•    lie down after a meal.

These measures may not be suitable for everyone. Ask your doctor about what is right for you.

Medicines

Occasionally, your doctor may prescribe medicines if the self-help measures described are not stopping your symptoms of low blood pressure. These may include:

•    medicines to increase how much salt is in your body
•    medicines to make your veins constrict