Intraepidermal electrical stimulation applied during expiration produced weaker subjective pain and smaller amplitudes of evoked potentials and sympathetic skin responses compared to inspiration.
Does expiration compared to inspiration reduce pain processing and subjective pain sensation in healthy volunteers?
Pain processing fluctuates during normal breathing, with pain being gated within the central nervous system during expiration.
To test the hypothesis that a respiratory cycle influences pain processing, we conducted an experimental pain study in 10 healthy volunteers. Intraepidermal electrical stimulation (IES) with a concentric bipolar needle electrode was applied to the hand dorsum at pain perceptual threshold or four times the perceptual threshold to produce first pain during expiration or inspiration either of which was determined by the abrupt change in an exhaled CO2 level. IES-evoked potentials (IESEPs), sympathetic skin response (SSR), digital plethysmogram (DPG), and subjective pain intensity rating scale were simultaneously recorded. With either stimulus intensity, IES during expiration produced weaker pain feeling compared to IES during inspiration. The mean amplitude of N200/P400 in IESEPs and that of SSR were smaller when IES was applied during expiration. The magnitude of DPG wave gradually decreased after IES, but a decrease in the magnitude of DPG wave was less evident when IES was delivered during expiration. Regardless of stimulus timing or stimulus intensity, pain perception was always concomitant with appearance of IESEPs and SSR, and changes in DPG. Our findings suggest that pain processing fluctuates during normal breathing and that pain is gated within the central nervous system during expiration.
Iwabe et al. (Sun,) conducted a other in Healthy volunteers (n=10). Intraepidermal electrical stimulation during expiration vs. Intraepidermal electrical stimulation during inspiration was evaluated on Subjective pain intensity, IES-evoked potentials, sympathetic skin response, and digital plethysmogram. Intraepidermal electrical stimulation applied during expiration produced weaker subjective pain and smaller amplitudes of evoked potentials and sympathetic skin responses compared to inspiration.