Blood pressure is controlled by various factors, including your arteries’ diameter, heart rate and your body’s total fluid volume. These factors are managed by the part of the nervous system responsible for controlling unconscious bodily functions.
This nervous system compresses the blood vessels in the lower part of the body when we are standing, so that the blood does not end up entirely in the feet and legs. This system regulates the pressure in the body, no matter your position.
Just like the black substance that controls movement, this part of the nervous system is also damaged in people living with Parkinson’s disease.
As a result, the blood pressure maintenance reflex system no longer works properly. The change from sitting or lying down to standing therefore sends blood to the feet and legs, depriving the brain of oxygen. This causes dizziness or fainting.