in 1925, bradbury and eggleston first characterized three patients seemingly with a common syndrome, with what they described as "the occurrence of syncopal attacks after or during exertion or even after standing erect for some minutes. other features in the three patients are a slow, unchanging pulse rate, incapacity to perspire, a lowered basal metabolism and signs of slight and indefinite changes in the nervous system. each of these patients felt much worse during the heat of summer." further research identified multiple causes for these syndromic findings, now grouped as primary autonomic disorders (also called primary dysautonomia), including pure autonomic failure, multiple system atrophy, and parkinson's. the primary differentiating characteristic of pure autonomic failure is decreased circulation and synthesis of norepinephrine, and dysfunction localized peripherally. it is relevant to note that progression to central nervous system neurodegeneration can also occur.