51�Թ�

It's thought pain receptors in the blood vessels and nerve tissue around the brain misfire - sending incorrect signals that something is wrong.

Both techniques use injections to make blood vessels more visible – tumours in the breast have a lot of blood vessels.

Some devices also include photoplethysmography sensors which use light to measure how the volume of blood vessels changes.

The active ingredient in Rush and other poppers is alkyl nitrite, a chemical that instantly dilates blood vessels when inhaled, producing a brief but intense feeling of euphoria.

The heart and your blood vessels also have an easier time as they no longer have to pump blood against gravity - and they start to weaken.