Impaired sympathetic skin response in chronic obstructive pulmonary disease

The sympathetic skin response (SSR) is considered as one of the indexes of autonomic nervous system functions, especially related with the sudomotor function of unmyelinated sympathetic fibers. SSRs are recorded as the potentials with biphasic or multiphasic waveforms by conventional electromyography. SSRs are evaluated by measuring latency (time from the stimulus to the onset), amplitude, and area (the space under the curve of the waveform). Although dysautonomia is a feature of chronic obstructive pulmonary disease (COPD), as demonstrated by acetylcholine sweat-spot test, there are no data concerning SSR in COPD patients. In this study, we electrophysiologically investigated the sudomotor function of the sympathetic nervous system in patients with COPD. SSRs were recorded in 30 patients with COPD and 21 healthy volunteers. Normal responses were obtained from all subjects in the control group. No response was observed in three patients with COPD. The mean latency, amplitude and area values of the potentials recorded of the remaining 27 patients were compared to the control. The mean latency was longer (p<0.01) and the mean amplitude and area values were lower (p=0.012, p=0.021, respectively) in the patients compared to the control. We also demonstrated significant correlations between the latency, amplitude, or area values of the SSR and two parameters of pulmonary function tests forced expiratory volume one second/forced vital capacity (FEV1/FVC) and FEV1/FVC %. In conclusion, SSR is impaired in patients with COPD, which indicates the dysfunction of the sympathetic nervous system. Furthermore, the degree of impairment in SSR may reflect the severity of airway obstruction in patients with COPD.