Spinal Cord Injury Center, Balgrist University Hospital, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland.
Biomedical Data Science Lab, Institute of Translational Medicine, Swiss Federal Institute of Technology (ETH) Zurich, Zurich, Switzerland.
Sci Rep. 2024 Sep 27;14(1):22070. doi: 10.1038/s41598-024-73158-5.
Although reduced experimental pain habituation is proposed as a proxy of diminished endogenous pain modulatory capacity in chronic pain, prior studies show contradictory findings. Even across healthy participants, pain habituation varies substantially, which may relate to another measure of endogenous pain modulation, i.e., conditioned pain modulation (CPM). Hence, this study investigated the relationship between pain habituation and CPM. Pain habituation was assessed in 45 healthy participants between two blocks of 15-20 contact-heat stimuli applied to the hand. Habituation of subjective pain ratings and objective neurophysiological readouts (contact-heat evoked potential (CHEP) and palmar sympathetic skin response (SSR)) was investigated. CPM was assessed by comparing heat pain thresholds before and after hand immersion in a noxious cold (9 °C) and lukewarm water bath (32 °C, to control for repeated measures effects). Pain habituation showed a large variability, with subjective but not objective pain habituation correlating with cold-induced CPM effects (r = 0.50; p = 0.025). This correlation was not observed for 'true' CPM effects (corrected for repeated measures effects) nor for CPM effects induced by a lukewarm water bath. These findings suggest that the observed variability in subjective pain habituation may be influenced by both descending endogenous pain modulation and peripheral adaptation processes associated with repeated measures. Objective pain habituation readouts, i.e., CHEPs and SSRs, capture different, complementary aspects of endogenous pain modulation.
虽然减少实验性疼痛习惯化被认为是慢性疼痛中内源性疼痛调节能力降低的替代指标，但先前的研究结果却存在矛盾。即使在健康参与者中，疼痛习惯化也存在很大差异，这可能与内源性疼痛调节的另一种测量方法，即条件性疼痛调节（CPM）有关。因此，本研究调查了疼痛习惯化和 CPM 之间的关系。在两个 15-20 次接触热刺激的手部块之间，对 45 名健康参与者进行了疼痛习惯化评估。研究了主观疼痛评分和客观神经生理读数（接触热诱发电位（CHEP）和手掌交感皮肤反应（SSR））的习惯化。通过比较手部浸入有害冷（9°C）和温水浴（32°C）前后的热痛阈值来评估 CPM，以控制重复测量效应。疼痛习惯化表现出很大的可变性，主观疼痛习惯化而不是客观疼痛习惯化与冷诱导的 CPM 效应相关（r=0.50；p=0.025）。这种相关性在“真正”的 CPM 效应（校正重复测量效应）或温水浴诱导的 CPM 效应中均未观察到。这些发现表明，观察到的主观疼痛习惯化的可变性可能受到与重复测量相关的下行内源性疼痛调节和外周适应过程的影响。客观的疼痛习惯化读数，即 CHEPs 和 SSRs，捕捉到内源性疼痛调节的不同、互补方面。
