What are the symptoms of low blood pressure?

Each time that you have your blood pressure measured, it is important that the test is carried out under similar conditions to ensure that the results are consistent. If you have a low blood pressure reading, your GP will first consider the everyday causes that might have affected it, before considering the possible underlying causes.

Many factors have a daily, or sometimes even hourly, effect on your heart and circulation. Below are things that could affect your blood pressure and, in some cases, may cause low blood pressure.

If your blood pressure is still considered low after taking into account everyday factors such as those listed above, there may be another cause. Some possibilities are explained below.

Some medication may cause hypotension as a side effect. This tends to be orthostatic, or postural hypotension (low blood pressure when you stand up or change position). Examples of medication that can cause hypotension include:

Your GP will discuss any possible side effects with you when prescribing medication. While you are taking medication, your blood pressure will be carefully monitored if you are considered to be at risk of hypotension.

If you have an acute (short-term) illness, your blood pressure will be measured regularly because it is a good indicator of the severity of your illness. A heart condition, such as heart failure or a heart attack, can also cause low blood pressure, as your heart may not be able to pump blood around your body.

Autonomic disorders affect your autonomic nervous system and they can cause hypotension. Your autonomic nervous system is part of your nervous system (the network of cells that carry information around your body). It controls the bodily functions that you do not actively think about, such as sweating, digestion and the beating of your heart.

The autonomic nervous system also controls the widening and narrowing of your blood vessels. If there is a problem with it, your blood vessels could remain too wide, causing low blood pressure. In particular, autonomic disorders tend to cause orthostatic hypotension.

Some examples of autonomic disorders are:

The adrenal glands are two small glands that are located just above your kidneys. They produce hormones that control your blood pressure and maintain the balance of salt and water in your body. One of the hormones they produce is called aldosterone, which is responsible for controlling the amount of salt in your body.

If your adrenal glands become damaged - for example through an infection or a tumour - the production of aldosterone may be reduced, resulting in a loss of salt from your body. This can cause dehydration which, in turn, leads to low blood pressure.

If a problem with your adrenal glands is diagnosed, it can be treated by increasing the amount of aldosterone in your body. This could also be a symptom of Addison’s disease (a condition in which the adrenal glands cannot produce enough of the hormones cortisol and aldosterone). Addison’s disease can also be treated with medication.

Low blood pressure can also be caused by serious injuries or burns, particularly if you have lost a lot of blood. This can mean that there is less blood being pumped around your body. Low blood pressure can also occur if you go into shock after having a serious injury.

Other kinds of shock are described below.

Septic shock and toxic shock syndrome are caused by bacterial infections. The bacteria attack the walls of the small blood vessels, causing them to leak fluid from the blood into the surrounding tissues. This causes a significant drop in blood pressure (severe hypotension).

Anaphylactic shock, or anaphylaxis, is caused by an allergic reaction to something - for example, a wasp sting or a peanut. During an allergic reaction, your body produces a large amount of a chemical called histamine, which causes your blood vessels to widen and leads to a sudden, severe drop in blood pressure.

A network of blood vessels carries the blood to and from the heart to the rest of the body, and if the volume of blood being pumped becomes low due to certain reasons, it causes hypotension resulting in a lack of adequate oxygen and nutrition. Even as the signs of low blood pressure are not always obvious, many otherwise healthy people can have hypotension because of this. There are several medical reasons that lead to low blood pressure including:

Fluctuations in blood pressure is not abnormal during pregnancies since the body's circulatory system undergoes expansion and there are changes to the production of certain hormones, and low blood pressure is common at this time. It returns to normal soon after delivery, but may require medical attention if it causes more severe symptoms.

A healthy heart is capable of offsetting any drop in blood pressure by pumping an additional amount once it receives a signal from the brain. Heart attacks, arterial blockage in the heart or heart valve concerns render the heart incapable of supplying a more constant blood flow and may cause low blood pressure.

The endocrine system affects several signalling mechanisms in a healthy body, and an imbalance in its production of hormones can cause a drop in blood pressure. Thyroid and insulin conditions are often cited as causes of low blood pressure.

A lack of nutrients such as vitamin B-12, iron, omega 2 &3 fatty acids and folate in the body results in a drop of production of red blood cells, affecting the blood's ability to carry sufficient oxygen. A low blood pressure diet is often prescribed to counter any symptoms and works effectively in a majority of cases.

The kidneys maintain a sufficient balance of nutrients and water to aid blood flow. However, kidney disease resulting in either dehydration or overhydration can lead to an imbalance of electrolytes and constriction of blood vessels causing impediment to blood flow.

A rare but recognized cause of low blood pressure is shock arising from severe infection and results from the infection entering the bloodstream.

A severe reaction to an allergen can also cause symptoms of low blood pressure by causing the heart to beat irregularly and impeding the flow of blood.

• Blurry vision.
• Confusion.
• Dizziness.
• Fainting (syncope)
• Lightheadedness.
• Nausea or vomiting.
• Sleepiness.
• Weakness.

There are several types of hypotension. Low blood pressure is categorized according to when it happens and what’s causing it.

Orthostatic hypotension (also known as postural hypotension) is the drop in blood pressure that occurs when you move from sitting or lying down to standing.

As your body adjusts to the position change, you may feel dizzy or lightheaded. This is what some people refer to as “seeing stars” when they get up.

Orthostatic hypotension is the most common form of low blood pressure. It can affect people of all ages, but it’s especially common in older adults. Aging and pregnancy can also cause an overall lowering of blood pressure.

Conditions affecting the autonomic nervous system, such as Parkinson’s disease and diabetes, can often lead to orthostatic hypotension. This form of low blood pressure affects 30 to 50 percent of people with Parkinson’s disease, and about 30 percent of people with diabetes.

Postprandial hypotension is a drop in blood pressure that occurs after eating. According to a 2010 review, low blood pressure after eating is more common in older adults and people with autonomic dysfunction.

Blood pressure is a balancing act between your nervous system and other bodily systems (like your hormones and organs). Neurally mediated hypotension happens when there is an abnormal reflex interaction between the heart and the brain.

Causes of neurally mediated hypotension include:

A severe drop in blood pressure can occur during shock. Shock can happen if you experience a serious injury or infection.

During shock, your organs do not get the blood and oxygen they need to function properly. Severe hypotension can be life threatening if not treated quickly.