Low Blood Pressure | Hypotension
Low blood pressure or hypotension is persistent abnormally low 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.
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.
Blood pressure varies between individuals and throughout the day. Blood pressure is normally above 90/60 mmHg. 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. Find out more about measuring your blood pressure
What are the symptoms of low blood presure?
Hypotension usually means blood pressure that is lower than 90/60mmHg (millimeters of mercury) or is low enough to cause symptoms. When the blood pressure is too low there is inadequate blood flow to the brain and other vital organs, light-headedness or fainting may occur.
A common type of hypotension is postural (also known as orthostatic) hypotension, in which suddenly standing leads to light-headedness and fainting.
Symptoms of low blood pressure
Symptoms of hypotension may include:
- General weakness
- Light-headedness and fainting
- Blurred vision
- Temporary loss of consciousness
Causes of Low Blood Pressure
- Adverse effect of certain drugs, including diuretics, anesthetics, nitrates, calcium blockers, certain types of antidepressant drugs and drugs for the treatment of high blood pressure
- Dehydration (Heavy sweating, loss of blood, severe diarrhoea
- Vasovagal attack (Fainting)
- Suddenly standing from lying or sitting position (postural, also known as orthostatic hypotension)
- Shock due to internal bleeding, severe infection or heart failure, heart attack or an irregular heartbeat
- Anaphylaxis (a severe allergic response)
- Diabetic neuropathy or peripheral neuropathies
- It can also be related to pregnancy
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 consider getting 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
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.
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.
Generally if you feel well then treatment is unnecessary. Checking whether you are drinking enough and are not dehydrated may be important.
If an underlying disorder, such as a heart condition is suspected then you may be advised to go to hospital for tests and treatment.
If your medication is suspected of causing hypotension the doctor will probably advise a change of drug or dosage.
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.