The researchers looked at 14 patients with autonomic failure, and measured their blood pressure while lying and standing, before, and 15 and 35 minutes after drinking 480ml of distilled water. When asked to stand, before drinking water, this caused a fall in blood pressure.

The 14 patients were divided into two groups, seven of whom had multiple system atrophy (MSA), while the other seven had pure autonomic failure (PAF). MSA is a neurodegenerative disease marked by a combination of symptoms affecting movement, blood pressure, and other body functions. PAF is a disorder affecting only the autonomic nervous system. They both often present in middle to late life.

The patients then drank water causing a significant rise in blood pressure. For the patients with PAF it took five minutes for a significant rise in blood pressure to be recorded, and for patients with MSA it took 13 minutes. In both the fall in blood pressure and symptoms of low blood pressure, was reduced while standing.

Professor Mathias adds: "While autonomic failure itself is generally not life threatening, it can have a significant impact on an individual's quality of life. People with low blood pressure caused by autonomic failure are at a greater risk of fainting when standing upright, after food or even after mild exertion. This can affect their life in many ways, stopping them from driving, or in extreme cases, from being able to work. This discovery could be of considerable use in helping these patients to understand why this happens. It may also benefit the many without autonomic failure who faint as a result of low blood pressure."