Effects of stress and relaxation on capsaicin-induced pain

A sizable body of research has been devoted to understanding the relationsh ip between pain sensitivity and the psychological state of the individual. Considerable disagreement as to the direction of the association still exis ts. This study examines the effects of 2 experimental manipulations, cognit ive/emotional stress and relaxation, on capsaicin-induced pain. Subjects we re pretrained in relaxation and then randomized to experimental stress prod uced by a 20-minute Stroop test, relaxation (tape). or a control condition (neutral video), followed by a capsaicin injection in the forearm. Cardiova scular measures were taken at regular intervals, and cortisol, norepinephri ne (NE), and self-reports of arousal (relaxation index) were taken immediat ely before and after the experimental task. The manipulation significantly interacted with sex to predict capsaicin-induced maximum pain. Women in the stress condition reported greater pain than both men in the stress conditi on and women in the relaxation condition. Pain was correlated negatively wi th task-induced changes in NE and cortisol and positively with self-reporte d arousal (decreased relaxation). However, separate analyses showed that so me physiologic indexes of heightened arousal (increased blood pressure and NE) predicted lower pain only in men, whereas subjective increases in arous al predicted higher pain only in women. Multiple hierarchical regression an alyses confirmed that physiologic and self-reported arousal predicted pain independently and in opposite directions, and a model including both accoun ted for 56% of the overall variance. These findings suggest that a unidimen sional model of arousal may be insufficient to explain the effects of stres s on pain and that these effects operate differently in men and women. (C) 2001 by the American Pain Society.