Distraction by a cognitive task has a higher impact on electrophysiological measures compared with conditioned pain modulation.

BACKGROUND: Conditioned pain modulation (CPM) evaluates the effect of a painful conditioning stimulus (CS) on a painful test stimulus (TS). Using painful cutaneous electrical stimulation (PCES) as TS and painful cold water as CS, the pain relief was paralleled by a decrease in evoked potentials (PCES-EPs). We now aimed to compare the effect of CPM with cognitive distraction on PCES-induced pain and PCES-EP amplitudes. METHODS: PCES was performed using surface electrodes inducing a painful sensation of 60 (NRS 0-100) on one hand. In a crossover design healthy subjects (included: n = 38, analyzed: n = 23) immersed the contralateral hand into 10 °C cold water (CS) for CPM evaluation and performed the 1-back task for cognitive distraction. Before and during the CS and 1-back task, respectively, subjects rated the pain intensity of PCES and simultaneously cortical evoked potentials were recorded. RESULTS: Both CPM and cognitive distraction significantly reduced PCES-EP amplitudes (CPM: 27.6 ± 12.0 µV to 20.2 ± 9.5 µV, cognitive distraction: 30.3 ± 14.2 µV to 13.6 ± 5.2 µV, p < 0.001) and PCES-induced pain (on a 0-100 numerical rating scale: CPM: 58 ± 4 to 41.1 ± 12.3, cognitive distraction: 58.3 ± 4.4 to 38.0 ± 13.0, p < 0.001), though the changes in pain intensity and PCES-amplitude did not correlate. The changes of the PCES-EP amplitudes during cognitive distraction were more pronounced than during CPM (p = 0.001). CONCLUSIONS: CPM and cognitive distraction reduced the PCES-induced pain to a similar extent. The more pronounced decrease of PCES-EP amplitudes after distraction by a cognitive task implies that both conditions might not represent the general pain modulatory capacity of individuals, but may underlie different neuronal mechanisms with the final common pathway of perceived pain reduction.

Conditioned pain modulation using painful cutaneous electrical stimulation or simply habituation?

BACKGROUND AND AIMS: Cold pressor test was recently reported to significantly reduce painful cutaneous electrical stimulation (PCES)-induced pain and corresponding evoked potentials (PCES-EPs), but whether this reduction is an effect of conditioned pain modulation (CPM) remains unknown. To what extent these findings are confounded by habituation is also unknown. We thus compared the effect of CPM and habituation on PCES-induced pain and PCES-EPs and analysed whether increased attention by a random change of electric stimulation would intensify this possible habituation effect. METHODS: Three custom-built concentric surface electrodes were used to induce a pain intensity of 60 on a 0-100 numerical rating scale (NRS) among 29 healthy subjects (age 20-35y, 16 females). PCES-EPs (including P0N1 and N1P1 amplitudes, N1 latencies) were assessed over Cz. Group A received 14 min of electrical stimulation with constant intensity followed by 14 min of electrical stimulation with variable intensities, group B vice versa. Afterwards, subjects perceived cold-water pain (10 °C) contralaterally as conditioning stimulus to assess CPM. Statistical analysis was conducted with ANOVA and t-test. RESULTS: In both groups, N1 latencies remain unchanged, but the intensity of PCES-induced pain (12 ± 17%; p < 0.01) and N1P1 amplitudes of PCES-EPs (10 ± 16%; p < 0.05) decreased significantly during the 14-min PCES with constant current intensity. CPM also significantly reduced pain ratings (36 ± 19%; p < 0.001) and amplitudes (37.2 ± 15.8%), p < 0.001). A significant decline of P0N1 amplitudes occurred only during CPM (18 ± 61%; p < 0.001). CONCLUSION: We found a significant effect of habituation on PCES-induced pain and PCES-EPs, although the effect of CPM was significantly larger and could not be explained by habituation alone. SIGNIFICANCE: Painful cutaneous electrical stimulation leads to moderate habituation of pain and evoked potential amplitudes, but the conditioned pain modulation effect using this method is significantly larger, which might indicate a different mechanism in central processing.

Role of endometrial concentrations of heavy metals (cadmium, lead, mercury and arsenic) in the aetiology of unexplained infertility.

OBJECTIVE: To determine the role of endometrial concentrations of heavy metals (cadmium, lead, mercury and arsenic) in the aetiology of unexplained infertility. STUDY DESIGN: Thirty-three women with unexplained infertility and 32 fertile women were recruited. Endometrial biopsies were collected during the putative window of implantation (cycle days 20-24). The concentrations of cadmium, lead, mercury and arsenic were measured in endometrial biopsy specimens using atomic absorption spectrometry. RESULTS: Cadmium was detected in 91% (30/33) of women with unexplained infertility, compared with 34% (11/32) of fertile women. The median endometrial cadmium concentration was 19.58 (interquartile range 1.46-30.23)µg/l in women with unexplained infertility, compared with 0.00 (interquartile range 0.00-0.40)µg/l in fertile women. Lead was detected in 15% (5/33) of women with unexplained infertility and 3% (1/32) of fertile women. Mercury and arsenic were not detected in any endometrial samples from either group. CONCLUSION: A significant difference in endometrial cadmium concentration was found between women with unexplained infertility and fertile women. This suggests that cadmium may be a contributing factor in the aetiology of unexplained infertility.