Testing the sympathetic nervous system

There are several ways of testing the integrity of the sympathetic nervous system:

• postural blood pressure changes: there is normally a slight rise in blood pressure on standing; in patients with sympathetic denervation, there is a marked fall.
• the Valsalva manoeuvre: there is a temporary fall in blood pressure in patients with autonomic failure.
• tests of positive efferent sympathetic function:
  • a rise in blood pressure during times of stress or application of an ice-pack.
  • reflex sweating and flushing of skin are still intact