Low Blood Pressure (Hypotension): What is It?

Postural hypotension vs vaso-vagal attacks

Low blood pressure (hypotension): How does it occur?

Low blood pressure (hypotension) can cause postural hypotension (giddiness when standing up suddenly). However, it can be relieved by sitting down or stooping down.

Low blood pressure (hypotension) can cause dizziness when standing up too fast (also known as postural hypotension).

You may sometimes experience dizzy spells when standing up too quickly (postural hypotension). However, that usually disappears after a few seconds, as soon as your body has adjusted to the changes in position and blood pressure, and when normal blood flow has been restored to your brain.

Postural hypotension is an abnormal fall in blood pressure within three minutes of standing upright from lying or sitting. This happens due to the pooling of blood in the legs as a result of gravity. For the elderly, such dizziness may potentially result in falls, and if serious, may lead to hospitalisation or even death. Getting up slowly may help to reduce the sudden drop in blood pressure.

Why do I feel faint when I see or hear something shocking?

In addition, you may feel faint when faced with certain triggers such as the sight of blood, the feeling of pain and emotions. This is known as a “vaso-vagal” attack, another type of transient low blood pressure.

For such people, the triggers will lead to an unusual slowing of the heart and dilatation of the blood vessels, and result in a drop in blood pressure; thus making one feels faint (known as “syncopy”).

Postural hypotension vs vaso-vagal attacks

“Postural hypotension and vaso-vagal attacks are very common, and most do not need any treatment as they are usually temporary. If dizziness is felt, sitting or stooping down often helps. Sometimes, such low blood pressure is caused by a sudden loss of blood volume, such as dehydration from severe diarrhoea, or any high blood pressure medication, especially if one has just started on the medication. Older people are more prone to this,” says Dr Ian Phoon, Consultant from SingHealth Polyclinics (SHP) – Pasir Ris, a member of the SingHealth group.

“However, if you are not taking any high blood pressure medication and yet experience persistent dizzy or fainting spells, there may be other underlying medical problems which require further investigations,” he adds.

Low blood pressure (hypotension): How does it occur?

Low blood pressure (hypotension) is a state where not enough blood (carrying oxygen) flows to vital organs such as the brain. It is mainly for this reason that one may experience dizziness.

It is known as “shock” when the drop in blood pressure is severe and persistent. If it is not treated immediately, shock can cause permanent damage to the vital organs, and may result in death.

Normal blood pressure is below 130/80 mmHg. The first reading measures systolic pressure or the amount of blood pressure when the heart is beating (squeezing the blood). The second reading measures diastolic pressure or the amount of blood pressure when the heart is at rest.

Some doctors consider blood pressure to be low when it is below 90/60 mmHg. However, there is no specific number at which day-to-day blood pressure is considered too low as long as it does not cause noticeable signs and symptoms.

People who are physically fit sometimes have lower blood pressure. And some people have naturally low blood pressure, with no ill effects.

Ref: T12