Low Blood Pressure

Low blood pressure

What is blood pressure?

As the heart contracts it pushes blood into your arteries and this causes an increase in pressure. When your heart contracts, the pressure is at its highest in your arteries and this is known as systolic pressure. As your heart relaxes and refills with blood, the pressure in your arteries falls and this is known as diastolic pressure. When blood pressure is measured in your arm, both of these pressures are measured.

Your blood pressure varies by large amounts, depending on what you are doing. The lowest blood pressures occur when you are asleep or if you relax all your muscles. Standing up, exercising or anxiety all cause an increase in blood pressure. In a single day your blood pressure may vary by 30 to 40 mmHg systolic with similar proportionate changes in diastolic pressure. This is why when you have your blood pressure level assessed it is so important to have it measured under the same conditions every time.

Whether you have high blood pressure, or a normal blood pressure, it is important to realise that the higher your blood pressure, the higher your risk of heart disease or stroke. This means that all of us should be adopting a lifestyle that will help to lower our blood pressure whether we have high blood pressure or not.

The only way for you to know your blood pressure is to have it measured with an automatic digital home blood pressure monitor

Symptoms of low blood pressure

When blood pressure is too low, the first organ to malfunction is usually the brain. The brain malfunctions first because it is located at the top of the body and blood has to fight gravity to reach the brain. Consequently, most people with low blood pressure feel dizzy or light-headed when they stand, and some may even faint. People who faint fall to the floor, usually bringing the brain to the level of the heart. As a result, blood can flow to the brain without having to fight gravity, and blood flow to the brain increases, helping protect it from injury. However, if blood pressure is low enough, brain damage can still occur.

Low blood pressure occasionally causes shortness of breath or chest pain due to an inadequate blood supply to the heart muscle (angina).

All organs begin to malfunction if blood pressure becomes sufficiently low and remains low; this condition is called shock.

The disorder causing low blood pressure may produce many other symptoms, which are not due to low blood pressure itself. For example, an infection may produce a fever.

Some symptoms occur when the body’s compensatory mechanisms try to increase blood pressure that is low. For example, when arterioles constrict, blood flow to the skin, feet, and hands decreases. These areas may become cold and turn blue. When the heart beats more quickly and more forcefully, a person may feel palpitations (awareness of heartbeats).

What should I do if I think I have got low blood pressure?

The first thing to do is to have it measured either by your doctor or practice nurse, or get a machine to measure it yourself. It is important to measure your blood pressure not just when you are sitting, but also when you are lying down and standing up. If when you stand there is a large fall in blood pressure and you feel dizzy, you should then seek further advice.

If your systolic pressure is above 80mmHg with no drop when you stand up, and you feel quite well, then you are one of the few lucky people who naturally have very low blood pressure. For reasons that are not fully understand you are protected from the effects of salt and other factors that can cause raised blood pressure levels. On average, you will live longer than people with higher blood pressures.

Will I need any investigations?

Investigations are only conducted if you have symptoms that suggest a fall in blood pressure when you stand up, ie, dizziness or faintness. If you do have these symptoms or a fall in blood pressure when you stand then your doctor should conduct further tests or refer you to a specialist. This will mean having a tilt test where you will be strapped to a table and tilted, with careful measurements of heart rate and blood pressure taken. Hormone levels in your blood may also be measured to check that your adrenal glands and nerves are working normally.

How is low blood pressure treated?

This will very much depend on the cause. If you are well with no drop in blood pressure when standing then you should congratulate yourself – you do not need any treatment. However, if you do have symptoms then treatment will depend on the underlying cause. If you are taking blood pressure lowering drugs they may need to be changed, particularly if you are taking an alpha blocker such as doxazosin. You will need to discuss this with your doctor or practice nurse. Many people find that by getting up slowly their symptoms can be avoided.Failure of the adrenal glands can be treated by replacement of the missing hormones. If you have a disease of the nerves then this can be more difficult to treat, but you may respond to drugs that stimulate the nervous system. You may also find that wearing elastic stockings or an anti-gravity suit, or taking hormones that cause retention of salt and/or eating more salt can help. Talk to your doctor for more information.

Is low blood pressure associated with tiredness or depression?

Many years ago it was thought that blood pressures below a systolic of 90 mmHg could lead to tiredness and depression and many women were wrongly treated for low blood pressure with drugs that stimulate the nervous system. Large studies have now suggested that there is no relationship, provided there is no underlying cause for the low blood pressure.

What causes low blood pressure?

For a comprehensive information about the causes of low blood pressure visit this Blood Pressure web site.