Pain Related Fear And Confrontational Thoughts As Influences On Laboratory Pain And Clinical Pain Responses

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage,or described in terms of such damage.Based on its duration,pain can be classified as acute pain which lasts less than one month,or chronic pain which lasts more than 3 months.The mechanism underlying acute pain and chronic pain are somehow different.The activations of peripheral nociceptors send signals to the spinal cord,finally to the brain,where the acute pain perception forms.However,sometimes chronic pain continues even when the peripheral nociceptors stop sending noxious signal to the central nervous system(e.g.,the condition that an injury has been cured),suggesting that other factors may contribute to the chronicity of pain besides physiological factors.According to recent studies,psychological factors may have comparative,even greater influences than physiological factors upon the development and maintenance of chronic pain.Fear of pain is a fearful or anxious emotional arousal when anticipating or experiencing pain.It generates from interpreting or appraising pain stimuli as high threatening or harmful.Fear of pain has been considered as one of the important factors that influence the development and maintenance of chronic pain.As Fear-Avoidance(FA)model has posited,high level of fear of pain may increase pain experience through avoidance behavior and exacerbating interference as well as emotional distress.Conversely,low fear and confrontational thoughts may facilitate pain adjustment through approach behavior.Thus fear of pain and confrontational thoughts have been treated as two important factors that contribute to chronicity of pain.To date,evidence in applying FA model in the development and maintenance of chronic pain has been far from conclusive.Although cross-sectional and perspective studies have identified high fear of pain as a predictor for both acute and chronic pain outcomes,limited studies focus on the role of low fear and confrontational thoughts play in clinical pain adjustments.In addition,every chronic pain has once been acute.Whether fear of pain has an impact on the process during which acute pain transited to chronic pain is not clear.Furthermore,FA model considers avoidance from pain cues in the environment as an important predictor for future pain impairment.Unfortunately,the reaction time based research fail to reach a consistent result regarding the influences of fear of pain on attention biases to pain cues.The directions of the attention biases to pain information and its association to future pain adjustment is also not clear.To address the above issue,the present thesis designed 6 studies to evaluate the impact of fear of pain in development and maintenance of chronic pain.Study 1 sought to investigate the causal effects of fear of pain and confrontational thoughts on experimental induced pain responses.FA model posited that fear of pain generated from interpreting pain as high threat,while low fear was associated confrontational thoughts with which individual might focus other goals in the daily life over pain.Based on the description,161 undergraduate students were randomly assigned to 3 group,in which they were instructed to read 1)pain is a signal of potential tissue damage,orienting them to appraise pain as threat and generate fear of pain;2)pain is a test of one's ability,orienting them to appraise pain as challenge and generate confrontational thoughts;and 3)experimental procedure was safe,serving as control group.Then all participants completed a cold pressor test.Consistent with the theory,higher threat group had lower pain tolerance and catastrophized more during the cold pressor task than lower threat(control)and challenge appraisal groups.Challenge appraisal group reported using more cognitive strategies(ignoring,diverting attention,coping self-statements)in managing cold pressor task and also reported longer tolerance time in comparison with higher threat appraisal group.These results suggested that fear of pain and confrontational thoughts had an impact on pain coping and pain response within healthy population.In study 2 to study 3,the application of fear of pain and confrontational thoughts of pain from FA model in post-surgery pain was examined.Surgery itself could be viewed as a special injury,except that it is 1)relatively predictable;and 2)facilitating individual's recovery from disease.Viewing surgery as source of pain,we assessed fear of pain in surgery or after surgery and beliefs that other life goals instead of controlling pain as priority as influences in acute and chronic postsurgical pain.In study 2 and 3,we assessed surgery patients' self-reported demographic,clinical and psychological factors(i.e.,pain catastrophizing,depression,surgical fears and pain self-efficacy(measurement of confrontational thoughts)24 hours before surgery(T1);reassessed their pain intensity 2-3days after surgery(T2)as well as 4 months after surgery(T3).Study 2 was to examine the pre-surgery predictors of T2 pain intensity.Logistic regression revealed that higher pre-surgery pain self-efficacy was the only significant predictor for higher acute post-surgery pain.Subsequently,a classification tree analysis(CTA)indicated lower versus higher acute postoperative pain intensity levels were predicted not only by pain self-efficacy but also its interaction with disease onset,pain catastrophizing,and body mass index.Study 3 employed latent growth curve analysis to assess the changes of pain intensity from 24 hours before surgery to 4 months after surgery.In this way,we were to assess which pre-surgery psychological factors influence the transition of post-surgery pain from acute to chronic phase.Our result indicated that pain intensity increased sharply during the interval between T1(24 hours before surgery)and T2(48 to 72 hours after surgery)and decreased during the interval between T2 and T3(4 months after surgery).Higher level of pre-surgery pain self-efficacy predicted both lower T1 and lower T2 pain intensity.Furthermore,higher level of pre-surgery pain self-efficacy predicted smaller increase of pain intensity from T1 to T2 phase and smaller decrease of pain intensity from T2 to T3 phase.These results indicated that confrontational thoughts such as pain self-efficacy might reduce acute post-surgery pain,but was associated with the maintenance of pain intensity from 2-3 days after surgery to 4 month after surgery.One possible explanation could be that individual with higher pain self-efficacy reported a lower T2 pain intensity,thus the changes between T2 and T3 was comparatively small.Study 4-6 examined the role of fear of pain in the maintenance of chronic pain.Based on the description of FA model,hypervigilance to pain information may facilitate pain chronicity through activity avoidance.In addition,fear of pain played important role in influencing attention hypervigilance to pain information.Study 4 used a dot-probe task to evaluate the attention biases to pain information within higher vs.lower fear of pain chronic pain patients.Unlike most previous studies which reaction time index,we employed event-related potential(ERP)response N2 pc and LPP as indices of early attention allocation and sustained attention,respectively.38 high fear of pain chronic pain patients and 39 low fear of pain chronic pain patients were recruited based on Fear of Pain Questionnaire(FPQ-C).Two fear of pain groups completed the dot-probe task featuring painneutral,pain-pain and neutral-neutral image pairs as well as related self-reported clinical variables.6 months later,pain intensity and pain impairment were re-assessed via phone call.Although there were no fear of pain group differences in reaction time to probes that followed image pair offsets or LPP amplitudes,higher fear of pain(Hi-FOP)group members displayed comparatively larger N2 pc amplitudes contralateral to pain images in pain-neutral image pair presentations,reflecting a stronger initial attention allocation to pain information.Critically,within this group,larger N2 pc amplitudes displayed during the dot-probe task predicted higher levels of pain-related impairment at six month follow-up,independent of baseline impairment levels.Together,study 4 provided clinical evidence for the fear-attention hypervigilance-avoidance activity hypothesis in FA model.Study 5 also used a dot-probe task to evaluate the attention biases to pain information within 37 high pain fearful and 38 low pain fearful chronic pain patients.The process was identical to that in study 4 except that pain-neutral,and pain-pain image pairs were followed by a possible painful somatosensory stimuli(10%).This manipulation increased the threat value and ecological validity XI of the task,because chronic pain patients were viewing pain related cues which may cause actual painful sensation in their daily life(e.g.,climbing stairs,bending down or lifting).The results indicated that both high fearful and low fearful chronic pain patients displayed an inverse N2 pc amplitude to pain images in P-N pairs,reflecting an initial attention avoidance from pain information.When the threat value of the pain cues increased,both higher fearful and lower fearful chronic pain patients demonstrated an avoidance from pain related information at early stage of attention.Study 5 revealed that under higher state fear condition,both high and low trait fear CP patients displayed avoidance to pain information.This attention avoidance also influence their subsequent pain adjustment.Study 6 examined whether the attention biases within chronic pain were specific to pain information.Dot-probe task featuring pain-neutral facial expression and happy-neutral facial expression image pairs was used.N2 pc component was used as attention allocation index.71 chronic pain patients completed the dot-probe task and were re-assessed 6 months after the experiment.The results indicated that chronic pain patient would shift their initial attention to emotional salient stimulus including both negative and positive information.However,only the attentional bias to pain information predicted future pain intensity.The attention allocation to positive information(i.e.,happy faces)was not associated with future pain adjustment.In supporting FA model,the present thesis found that both confrontational thoughts(challenge appraisal)and fear of pain(threatening appraisal)have an impact on laboratory induced pain responses.Applying FA model in the development of post-operative pain,self-report confrontational thoughts(pain self-efficacy)before surgery,as well as its interactions with disease duration,pain catastrophizing and BMI value were found to predict acute post-operative pain.Regarding the role of confrontational thoughts and fear of pain in the transition of acute pain to chronic pain,results from growth-curve analysis revealed higher pre-surgery pain self-efficacy was associated smaller decreases of pain intensity from 2-3 days to 4 months after surgery.Applying FA model in the maintenance of chronic pain,ERP study demonstrated attention toward pain information was associated with higher future pain impairment level only within higher fearful chronic pain adults.Nevertheless,when the threat value of the pain information increased,chronic pain patients shifted their initial attention away from pain information signaling possible pain sensation.Finally,we found that chronic pain patients may not exclusively attend to pain information,rather to emotional salient stimulus.However,only attention bias to pain information was associated with future pain intensity.In conclusion,the present thesis partially support the application of FA model in explaining the development and maintenance of pain chronicity.