Kunz Miriam, Bunk Stefanie F, Karmann Anna J, Bär Karl-Jürgen, Lautenbacher Stefan
Department of Medical Psychology and Sociology, University of Augsburg, Augsburg, Germany.
Department of General Practice and Elderly Care Medicine, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
J Pain Res. 2021 Mar 23;14:793-803. doi: 10.2147/JPR.S300313. eCollection 2021.
Conditioned pain modulation (CPM) is most often assessed using self-report of pain. However, self-report of pain is not always available (eg in individuals with cognitive impairment) and is susceptible to report bias. In comparison, the facial expression of pain is more reflex-like and represents one of the most sensitive and specific non-verbal signals of pain. The aim of the present study was to investigate whether the facial expression of pain is sensitive enough to capture endogenous pain inhibition as elicited during CPM paradigms.
In total, 26 female participants took part in this study. Facial and verbal responses to phasic heat pain were assessed once while participants immersed their hand in a hot water bath and once without additional stimulation. Facial responses were analyzed using the Facial Action Coding System (FACS). Verbal responses were assessed using a Numerical Rating Scale (NRS).
Pain-relevant facial responses as well as pain ratings to phasic heat pain were significantly reduced when participants simultaneously immersed their hand in a hot water bath compared to baseline. Thus, CPM effects could be demonstrated both on subjective as well as on facial responses. Moreover, CPM-induced changes in pain-relevant facial responses and in NRS ratings were significantly correlated.
The present study shows that facial expressions of pain are sensitive enough to capture CPM effects. Given the proven clinical usefulness of assessing CPM, the parallel assessment of verbal and facial CPM effects might be a promising approach with wider scope of applications. Further research in other demographic healthy participant and clinical cohorts is warranted.
条件性疼痛调制（CPM）通常使用疼痛的自我报告来评估。然而，疼痛的自我报告并非总是可行（例如在认知障碍患者中），并且容易受到报告偏差的影响。相比之下，疼痛的面部表情更具反射性，是疼痛最敏感和特异的非语言信号之一。本研究的目的是调查疼痛的面部表情是否足够敏感，以捕捉CPM范式中引发的内源性疼痛抑制。
共有26名女性参与者参加了本研究。在参与者将手浸入热水浴时和无额外刺激时，分别评估一次对阶段性热痛的面部和言语反应。使用面部动作编码系统（FACS）分析面部反应。使用数字评分量表（NRS）评估言语反应。
与基线相比，当参与者同时将手浸入热水浴时，与疼痛相关的面部反应以及对阶段性热痛的疼痛评分显著降低。因此，CPM效应在主观反应和面部反应上均得到证实。此外，CPM引起的与疼痛相关的面部反应变化和NRS评分变化显著相关。
本研究表明，疼痛的面部表情足够敏感，能够捕捉CPM效应。鉴于评估CPM已被证实的临床实用性，同时评估言语和面部CPM效应可能是一种有前景的方法，具有更广泛的应用范围。有必要在其他人口统计学的健康参与者和临床队列中进行进一步研究。
