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
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 the Blood Pressure Association web site