Autonomic peripheral evoked potential (APEP): a non-invasive procedure to assess sympathetic responses in humans.

The present study describes skin potential responses during a sequence of extero-, intero- and proprioceptive stimuli in 73 normal human subjects. By plotting the first derivative of skin potential vs. skin potential changes for every stimulus (phase plane) a generally opposite behavior of positive and negative deflections (indicating sympathetic inhibition and activation, respectively) was found. By area subtraction in phase plane analysis, only olfactory stimulation or nasal hyperventilation exhibited a significantly negative (sympathetic activating) skin potential response. Frequency of positive (sympathetic inhibitory) fluctuations of first derivative of skin potential was significantly lower than basal after explosive sound, tactile discrimination, photomotor reflex, and nasal and oral hyperventilation. Frequency of negative (sympathetic activating) fluctuations augmented significantly (as compared to basal) after explosive sound, tactile discrimination, nasal or oral hyperventilation, upright position or trot. These results suggest that activation of the sympathetic nervous system involves a coordinated motor program comprising activation of certain areas, and inhibition (or lack of changes) in others, with different patterns of interrelated activation and inhibition depending upon stimulus.