Objective: The sympathetic skin response (SSR) is used as an index of sudomotor sympathetic function. The aim of this
study was to investigate whether there were differences in amplitude, latency and habituation among the different
waveform patterns of SSR in normal subjects.
Material and Methods: Fourteen SSRs were recorded from the palm skins of 47 normal subjects by electrical
stimulations. Waveforms were classified as one of two types, namely, the P type, in which the positive component was
larger than the negative, and the N type, in which the negative component was larger than the positive. The M pattern
had both P and N type waveforms during consecutive recordings.
Results: During successive stimulations, 11 of the 47 subjects had only P type waveforms (P pattern), 10 others only the
N type (N pattern), and the remaining 26 (55.3%) both the P and N types (M pattern). The P pattern had a larger
amplitude and shorter latency than the N pattern. The P type constituted 49.1% of all the SSRs. The P type made up
81% of the first evoked responses but only 13.5% of the last ones in the M pattern. SSR amplitudes gradually decreased
but irregularly during the repeated stimulations, reflecting habituation.
Conclusions: These results suggest that waveform patterns should also be considered when defining the normal ranges of
SSR latency and amplitude. Futhermore, it might be advised to confirm the balanced distribution of the SSR waveform
patterns in patient and control groups before comparing the values of amplitude and latency between the two groups.
Key Words: Waveform; Sympathetic skin response; Habituation
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