Early sympathetic neural responses during a cold pressor test linked to pain perception.

Abstract

There is considerable interindividual variability in the perception of pain. Given that pain management is a major public health problem, gaining insight into the underlying physiology of these perceptual differences is important. We tested the hypothesis that when interindividual variability in initial muscle sympathetic nerve activity (MSNA) responses to a cold pressor test (CPT) is identified, the divergent responses will be linked to differences in pain perception in healthy young men and women. In the supine position, blood pressure (BP) and MSNA were measured at baseline and during a 2-min CPT. Immediately following the CPT, pain was rated (range 0-10). Two groups were established: positive responders (Pos, n = 12) and negative responders (Neg, n = 12) based on the initial (first 30s) MSNA response profiles (Pos: 12 ± 9, Neg: -3 ± 3 bursts/min, P < 0.0001). MSNA response profiles throughout the CPT were different between groups (P < 0.0001). Peak MSNA increases were different (Pos: 27 ± 11, Neg: 9 ± 5 bursts/min, P < 0.0001) and corresponded with initial MSNA responses (R2 = 0.6881, P < 0.0001). Blood pressure responses were also different throughout the CPT (P < 0.0001). Most importantly, the perception of pain induced by the CPT was different between the two groups (Pos: 8 ± 1, Neg: 4 ± 1, P < 0.0001). The results indicate that in healthy young men and women, there are divergent initial sympathetic neural responses to a given painful stimulus that are linked to the magnitude of pain perception. These findings highlight the distinctive sympathetic patterns that may contribute to the considerable interindividual variability in the perception of pain.