Low blood pressure: Symptoms, diagnosis and treatment
What is low blood pressure?
Low blood pressure is also known as hypotension and is usually diagnosed with a blood pressure reading that is consistently lower than 90/60 mm/Hg.
Some people have naturally low blood pressure, which doesn’t cause any symptoms. However, if the blood pressure is too low, it can affect blood flow around the body making a person feel dizzy or unsteady.
Sudden drops in blood pressure most commonly occur in someone who's rising from a prone or sitting position to standing. This kind of low blood pressure is known as postural hypotension, orthostatic hypotension, or neurally mediated orthostatic hypotension.
Postural hypotension is considered a failure of the autonomic nervous system - the part of the nervous system that controls involuntary vital actions, such as heartbeat - to react appropriately to sudden changes. Normally, when you stand up, some blood pools in your lower extremities. Uncorrected, this would cause your blood pressure to fall. But your body normally compensates by sending messages to your heart to beat faster and to your blood vessels to constrict. This offsets the drop in blood pressure. If this does not happen, or happens too slowly, postural hypotension results.
The risk of both low and high blood pressure normally increases with age, due in part to normal changes during ageing. In addition, blood flow in the brain declines with age, often as a result of plaque build-up in blood vessels. An estimated 10 to 20% of people over age 65 have postural hypotension.
What causes low blood pressure?
The cause of low blood pressure isn't always clear. It may be associated with the following:
What causes a sudden drop in blood pressure?
Sudden drops in blood pressure can be life-threatening. Causes of this type of hypotension include:
- Loss of blood from bleeding
- Low body temperature
- High body temperature
- Heart muscle disease causing heart failure
- Sepsis, a severe blood infection
- Severe dehydration from vomiting, diarrhoea, or high temperature
- A reaction to medication or alcohol
- A severe allergic reaction, called anaphylaxis