Abstract
To study the effects of respiration on intraepidermal electrical stimulus-evoked potentials (IESEPs), sympathetic activities and pain sensations, we recorded electroencephalogram (EEG), sympathetic skin response (SSR), digital plethysmogram, subjective pain rating scale and exhaled CO2 in 8 healthy volunteers. The electrical stimulation to the epidermis of the dorsum of the left hand or foot was applied once or twice a minute when an exhaled CO2 level abruptly exceeded 20 mmHg (early expiratory phase, EP) or when it fell bellow 20 mmHg (early inspiratory phase, IP). The stimulus intensity was set at the threshold or 4 times the threshold, and unchanged during the experiment. Subjective pain rating scales fluctuated between “No hurt” and “Hurts a little bit” with an intensity of the threshold or between “Hurts a little bit” and “Hurts a little more” with an intensity of 4 times the threshold; but the former was more frequent for EP stimulation in both stimulus sites. The mean amplitudes of P400 in IESEPs and SSR were smaller for EP stimulation than IP stimulation in both stimulus sites. Our findings suggest that pain information processing fluctuates during respiration, and that pain may be partially gated in the expiratory phase in either stimulus site.
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