Foss Jennifer M, Apkarian A Vania, Chialvo Dante R
Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.
J Neurophysiol. 2006 Feb;95(2):730-6. doi: 10.1152/jn.00768.2005. Epub 2005 Nov 9.
Spontaneous pain is a common complaint in chronic pain conditions. However, its properties have not been explored. Here we study temporal properties of spontaneous pain. We examine time variability of fluctuations of spontaneous pain in patients suffering from chronic back pain and chronic postherpetic neuropathy and contrast properties of these ratings to normal subjects' ratings of either acute thermal painful stimuli or of imagined back pain. Subjects are instructed to continuously rate their subjective assessment of the intensity of pain over a 6- to 12-min period. We observe that the fluctuations of spontaneous pain do not possess stable mean or variance, implying that these time series can be better characterized by fractal analysis. To this end, we apply time and frequency domain techniques to characterize variability of pain ratings with a single parameter: fractal dimension, D. We demonstrate that the majority of ratings of spontaneous pain by the patients have fractal properties, namely they show a power law relationship between variability and time-scale length; D is distinct between types of chronic pain, and from ratings of thermal stimulation or of imagined pain; and there is a correspondence between D for pain ratings and D for brain activity, in chronic back pain patients using fMRI. These results show that measures of variability of spontaneous pain differentiate between chronic pain conditions, and thus may have mechanistic and clinical utility.
自发性疼痛是慢性疼痛病症中的常见主诉。然而，其特性尚未得到探究。在此，我们研究自发性疼痛的时间特性。我们考察了慢性背痛和慢性带状疱疹后神经病变患者自发性疼痛波动的时间变异性，并将这些评分的特性与正常受试者对急性热痛刺激或想象性背痛的评分进行对比。受试者被要求在6至12分钟的时间段内持续对疼痛强度的主观评估进行评分。我们观察到，自发性疼痛的波动不存在稳定的均值或方差，这意味着这些时间序列可以通过分形分析得到更好的表征。为此，我们应用时域和频域技术，用一个参数——分形维数D来表征疼痛评分的变异性。我们证明，患者对自发性疼痛的大多数评分具有分形特性，即它们在变异性和时间尺度长度之间呈现幂律关系；分形维数D在慢性疼痛类型之间以及与热刺激评分或想象性疼痛评分之间存在差异；在使用功能磁共振成像的慢性背痛患者中，疼痛评分的分形维数D与大脑活动的分形维数D之间存在对应关系。这些结果表明，自发性疼痛变异性的测量方法能够区分慢性疼痛病症，因此可能具有机制和临床应用价值。
