Modulation by cold pressor test of single pulse and pulse train electrocutaneous stimulation

Purpose At present our knowledge of various processes involved in chronification of pain is limited. Novel observation techniques can increase our understanding of neurophysiological mechanisms in pain processing. Earlier, a comparison between single pulse (SP) and pulse train (PT) electrocutaneous stimulation was performed. We showed that both SP and PT influence subjective ratings and evoked potentials (EP) components differently. Using an additional modulating pain stimulus might give further insight in these differences. A commonly used modulating stimulus is the cold pressor test (CPT). CPT evokes a diffuse noxious inhibitory control (DNIC) effect. Pain patients show impairment of DNIC and abnormal endogenous modulation. In this study, we analysed the effect of the CPT on the processing of SP and PT stimuli in subjects using subjective pain ratings and EPs. Method Healthy subjects (10m/12f) were electrically stimulated at the left middle fingertip during two protocols. In a protocol the right hand was immersed in water of 0-1°C (CPT) or 32°C (control). Subjects had to withdraw and re-immerse their hand after subsequently 3 and 1 minute until the end of the protocol. Grand average EPs and numeric rating scale (NRS) scores were averaged from 105 stimuli of 5 stimulus amplitudes or number of pulses (NoP). Results The results showed a decrease of amplitude of EP components and decrease of subjective ratings by CPT, for both SP and PT. The relationship between NRS and stimulus amplitude or NoP was unchanged by CPT. For both SP and PT both N150 and P300 EP amplitudes decreased by CPT. Conclusion NRS scores and EP component amplitudes decreased by CPT. The different effects for SP and PT were not changed by CPT. Inhibition by CPT might be ascribed to activation of endogenous pain modulation by DNIC. These results are promising to further our knowledge of the nociceptive system.