Anxiety and pain: attentional and endorphinergic influences

The effectiveness of extended reality on relieving pain after total knee arthroplasty: a systematic review and meta-analysis of randomized controlled trials

PURPOSE

Patients with total knee arthroplasty (TKA) often suffer from severe postoperative pain, which seriously hinders postoperative rehabilitation. Extended reality (XR), including virtual reality, augmented reality, and mixed reality, has been increasingly used to relieve pain after TKA. The purpose of this study was to evaluate the effectiveness of XR on relieving pain after TKA.

METHODS

The electronic databases including PubMed, Embase, Web of Science, Cochrane Central Register of Controlled Trials (CENTRAL), and clinicaltrials.gov were searched for studies from inception to July 20, 2023. The outcomes were pain score, anxiety score, and physiological parameters related to pain. Meta-analysis was performed using the Review Manager 5.4 software.

RESULTS

Overall, 11 randomized control trials (RCTs) with 887 patients were included. The pooled results showed XR had lower pain scores (SMD = - 0.31, 95% CI [- 0.46 to - 0.16], P < 0.0001) and anxiety scores (MD = - 3.95, 95% CI [- 7.76 to - 0.13], P = 0.04) than conventional methods. The subgroup analysis revealed XR had lower pain scores within 2 weeks postoperatively (SMD = - 0.49, 95% CI [- 0.76 to - 0.22], P = 0.0004) and XR had lower pain scores when applying XR combined with conventional methods (SMD = - 0.43, 95% CI [- 0.65 to - 0.20], P = 0.0002).

CONCLUSION

This systematic review and meta-analysis found applying XR could significantly reduce postoperative pain and anxiety after TKA. When XR was combined with conventional methods, postoperative pain can be effectively relieved, especially within 2 weeks after the operation. XR is an effective non-pharmacological analgesia scheme.

Virtual Reality Therapy for the Management of Chronic Spinal Pain: Systematic Review and Meta-Analysis

BACKGROUND

The effectiveness of virtual reality (VR) therapy in adults with chronic spinal pain (CSP) is unclear.

OBJECTIVE

This study was conducted to compare the effectiveness of VR therapy and other therapies in adults with CSP, especially patients with inflammation-related pain.

METHODS

PubMed, Web of Science, Cochrane Library, Embase, and CINAHL databases were searched up to November 11, 2023. Randomized controlled trials (RCTs) comparing adults with CSP receiving VR therapy with those receiving other therapies were included. The trial registration platform as well as the reference lists of included studies and previous systematic reviews and meta-analyses were manually searched. Two independent reviewers performed study selection, data extraction, risk-of-bias assessment, and evaluation of the quality of the evidence. The weighted mean difference (WMD) was used as the effect size used to synthesize the outcome measure.

RESULTS

In total, 16 RCTs involving 800 participants were included in this meta-analysis. The pooled data from 15 (94%) RCTs including 776 (97%) participants showed that VR therapy was superior in improving pain intensity (WMD=-1.63, 95% CI -2.11 to -1.16, P<.001, I2=90%) and reducing inflammatory markers, including C-reactive protein (WMD=-0.89, 95% CI -1.07 to -0.70, P<.001, I2=0%), tumor necrosis factor-alpha (WMD=-6.60, 95% CI -8.56 to -4.64, P<.001, I2=98%), and interleukin-6 (WMD=-2.76, 95% CI -2.98 to -2.53, P<.001, I2=0%). However, no significant differences were found in terms of the spinal range of motion (ROM), disability level, or fear of movement. In addition, 10 (63%) of the included RCTs had a high risk of bias.

CONCLUSIONS

VR therapy may be an effective and safe intervention for reducing symptoms in patients with CSP, as it is shown to exert significant analgesic effects and beneficial improvements in inflammatory factor levels. However, this approach may not have significant effects on the spinal ROM, disability level, or fear of movement. Notably, the quality of the evidence from the RCTs included in this study ranged from moderate to low. Therefore, we recommend that readers interpret the results of this study with caution.

TRIAL REGISTRATION

PROSPERO CRD42022382331; https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=382331.

Pain, Fear, Anxiety, and Stress: Relations to the Endogenous Opioid System

Pain, fear, stress, and anxiety are separate yet interrelated phenomena. Each of these concepts has an extensive individual body of research, with some more recent work focusing on points of conceptual overlap. The role of the endogenous opioid system in each of these phenomena is only beginning to be examined and understood. Research examining the ways in which endogenous opioids (e.g., beta-endorphin; βE) may mediate the relations among pain, fear, stress, and anxiety is even more nascent. This chapter explores the extant evidence for endogenous opioid activity as an underpinning mechanism of these related constructs, with an emphasis on research examining βE.

Evidence for Integration of Cognitive, Affective, and Autonomic Influences During the Experience of Acute Pain in Healthy Human Volunteers

Our psychological state greatly influences our perception of sensations and pain, both external and visceral, and is expected to contribute to individual pain sensitivity as well as chronic pain conditions. This investigation sought to examine the integration of cognitive and emotional communication across brainstem regions involved in pain modulation by comparing data from previous functional MRI studies of affective modulation of pain. Data were included from previous studies of music analgesia (Music), mood modulation of pain (Mood), and individual differences in pain (ID), totaling 43 healthy women and 8 healthy men. The Music and Mood studies were combined into an affective modulation group consisting of runs with music and positive-valenced emotional images plus concurrent presentation of pain, and a control group of runs with no-music, and neutral-valenced images with concurrent presentation of pain. The ID group was used as an independent control. Ratings of pain intensity were collected for each run and were analyzed in relation to the functional data. Differences in functional connectivity were identified across conditions in relation to emotional, autonomic, and pain processing in periods before, during and after periods of noxious stimulation. These differences may help to explain healthy pain processes and the cognitive and emotional appraisal of predictable noxious stimuli, in support of the Fields’ Decision Hypothesis. This study provides a baseline for current and future investigation of expanded neural networks, particularly within higher limbic and cortical structures. The results obtained by combining data across studies with different methods of pain modulation provide further evidence of the neural signaling underlying the complex nature of pain.

Using Virtual Reality Exposure Therapy in Pain Management: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

OBJECTIVES

This study aimed to assess the effectiveness of virtual reality (VR) in managing different types of pain in different age groups and to provide evidence for the clinical application of new alternative strategy for pain management.

METHODS

Electronic databases, including the Cochrane Library, PubMed, EMBASE, and the Web of Science, were searched for studies published up to October 2020. Randomized controlled trials that reported on VR for pain management were included.

RESULTS

A total of 31 randomized controlled trials were included. As for the pain intensity, the increase of visual analog scale score in the VR group was 1.62 scores less than that in the control group. In juvenile patients, the VR group had 1.79 scores lower than that in control group. For adult patients, the VR group had 1.34 scores lower than that in control group. As for other pain-related indicators, the VR group had lower levels of anxiety, lower pain unpleasantness, lower pulse rate, and shorter duration of dressing change and spent less time thinking about pain. Nevertheless, there was no statistical difference in pain tolerance. VR can effectively alleviate acute pain. In terms of chronic low back pain and cancer-related pain, there was no statistical difference between VR therapy and standard therapy.

CONCLUSIONS

VR is a feasible alternative therapy for both juveniles and adults in pain management, and it has a greater potential for juveniles. VR can effectively alleviate acute pain. Nevertheless, VR showed little effectiveness in increasing pain tolerance, which may explain in part the ineffectiveness of VR therapy in pain management for chronic pain.

Vulvar Pain-Associations Between First-Time Vaginal Intercourse, Tampon Insertion, and Later Experiences of Pain

This study examines associations between the first experience of vaginal intercourse/tampon insertion and later experiences of vulvar pain. The study is based on questionnaire data from 1,259 Swedish female senior high-school students, aged 18 to 22 years old. Of these, 592 women reported present vulvar pain. Present vulvar pain was associated with first-time experiences of vaginal intercourse (pain, negative experience, against will) and with pain at tampon insertion. First-time experiences were also related to temporal aspects of present vulvar pain during vaginal intercourse (at the beginning, after a while during, and after). Implications of first-time experiences of vaginal intercourse for future symptoms of vulvar pain are discussed.

Neural responses to a modified Stroop paradigm in patients with complex chronic musculoskeletal pain compared to matched controls: an experimental functional magnetic resonance imaging study

Background

Chronic musculoskeletal pain (CMSKP) is attentionally demanding, complex and multi-factorial; neuroimaging research in the population seen in pain clinics is sparse. A better understanding of the neural activity underlying attentional processes to pain related information compared to healthy controls may help inform diagnosis and management in the future.

Methods

Blood oxygenation level dependent functional magnetic resonance imaging (BOLD fMRI) compared brain responses in patients with CMSKP (n = 15) and healthy controls (n = 14) while completing a modified Stroop task using pain-related, positive-emotional, and neutral control words.

Results

Response times in the Stroop task were no different for CMSKP patients compared with controls, but patients were less accurate in their responses to all word types. BOLD fMRI responses during presentation of pain-related words suggested increases in neural activation in patients compared to controls in regions previously reported as being involved in pain perception and emotion: the anterior cingulate cortex, insula and primary and secondary somatosensory cortex. No fMRI differences were seen between groups in response to positive or control words.

Conclusions

Using this modified Stroop tasks, specific differences were identified in brain activity between CMSKP patients and controls in response to pain-related information using fMRI. This provided evidence of differences in the way that pain-related information is processed in those with chronic complex musculoskeletal pain that were not detectable using the behavioural measures of speed and accuracy. The study may be helpful in gaining new insights into the impact of attention in those living with chronic pain.

Neurobiology of stress-induced hyperalgesia

The intensity and severity of perceived pain does not correlate consistently with the degree of peripheral or central nervous system tissue damage or with the intensity of primary afferent or spinal nociceptive neurone activity. In this respect, the modulation of pain by emotion and context is now widely recognized. In particular, stress, fear and anxiety exert potent, but complex, modulatory influences on pain. Stress can either suppress pain (stress-induced analgesia) or exacerbate it (stress-induced hyperalgesia; SIH) depending on the nature, duration and intensity of the stressor. Herein, we review the methods and models used to study the phenomenon of SIH in rodents and humans and then present a detailed discussion of our current understanding of neural substrates and neurobiological mechanisms. The review provides perspectives and challenges for the current and future treatment of pain and the co-morbidity of pain with stress-related psychiatric disorders including anxiety and depression.

Frequency and intensity of pain related to thyroid nodule fine-needle aspiration cytology

BACKGROUND

Quality of life is an important issue in endocrine tumors because of the high prevalence of benign tumors and the indolent course of most malignant tumors.

OBJECTIVE

To evaluate the frequency and the intensity of pain and anxiety in patients undergoing thyroid nodule fine-needle aspiration cytology (FNAC) and to identify factors associated with pain.

METHODS

Single center prospective study in the setting of a one-stop outpatient diagnostic clinic for thyroid nodules. Pain was evaluated using a 100-mm visual analogue scale (VAS) immediately following (VAS1) and 30 minutes after (VAS2) FNAC and was considered significant if ≥ 30. Anxiety symptoms were assessed prior to FNAC using a self-report measure questionnaire: the state form of Spielberger State-Trait Anxiety Inventory (STAI, form Y-A). FNAC was performed with a 25-gauge needle and a moderate aspiration and two passes for each nodule.

RESULTS

Two hundred eighteen consecutive patients (163 females, 55 males; mean age 53 years, range 12-84 years) undergoing FNAC of one to three nodules were included. VAS1 was ≥ 30 in 24% of the patients and VAS(2) was ≥ 30 in 13% of the patients. Independent significant factors correlated to a VAS1 of ≥ 30 were age under 25 years and the number of nodules being biopsied. Independent significant factors correlated to a VAS2 of ≥ 30 were VAS1 ≥ 30 and female sex. No correlation was found between pain and nodule size or nodule depth, nor the duration of application of the eutectic mixture of local anesthetics (EMLA) patch prior to FNAC. The mean STAI score for anxiety was 37 ± 12. The average STAI score was significantly higher in women (39) than in men (33; p = 0.01). There was no significant correlation between STAI score and age under 25 years, previous FNAC, number of nodules biopsied, or acetaminophen administration, but the STAI score was significantly correlated to VAS1 and VAS2.

CONCLUSIONS

FNAC-related pain is frequent and correlates with the number of nodules biopsied, age under 25 years, female sex, and anxiety.

Emotional conflict in a model modulates nociceptive processing in an onlooker: a laser-evoked potentials study

Observing models displaying facial expressions of pain elicits neural activity in onlookers' neural structures involved in first-hand experience of pain and in monitoring conflicting information. We investigated whether the purported conflict between the pain and its emotional expression in a model modulates cortical responses elicited by nociceptive laser stimuli in an onlooker. Seeing happy facial expressions, incongruent with the perceptual status attributed to the model, determined a significant reduction in the laser-evoked N2 potential. One of the main sources of this response is the anterior cingulate cortex, an area involved in pain perception, empathy for pain and conflict detection. A pre-activation of the anterior cingulate cortex due to the detection of the emotional conflict may, therefore, be responsible for the reduction of nociceptive-related response in the same brain area. Thus, top-down variables, like the appraisal of the others' emotional status, modulate onlookers' nociceptive-related neural activity.

Empirical evidence of the validity of the Spanish version of the pain vigilance awareness questionnaire

BACKGROUND

The Spanish version of the Pain Vigilance and Awareness Questionnaire has not been validated.

PURPOSE

The aims of this study were to examine the factor structure of the Spanish version of the Pain Vigilance and Awareness Questionnaire and present empirical evidence regarding its validity.

METHOD

A sample of 468 chronic back pain patients completed a battery of instruments to assess fear-avoidance beliefs, pain anxiety, pain catastrophizing, pain vigilance and awareness, pain acceptance, depression, anxiety, disability, and pain intensity.

RESULTS

Confirmatory factor analysis supported the validity of a nine-item version with two subscales: Active Vigilance and Passive Awareness. Both subscales and the total score were positively and significantly correlated with other fear-related constructs: fear-avoidance beliefs, pain anxiety, and pain catastrophizing. Regression analyses showed that Active Vigilance and the two subscales of the Fear-Avoidance Beliefs Questionnaire were significantly associated with higher anxiety and that the Acceptance Activity Engagement subscale was significantly associated with lower anxiety. The Fear-Avoidance Beliefs Questionnaire-Physical subscale was associated with higher disability and the Acceptance Pain Willingness subscale was associated with lower disability. The Fear-Avoidance Beliefs Questionnaire-Work subscale was significantly associated with higher pain intensity and depression; the Acceptance Activity Engagement and Pain Willingness subscales were significantly associated with lower pain intensity and depression.

CONCLUSION

The Spanish version of the Pain Vigilance and Awareness Questionnaire is a reliable and valid instrument. Pain Acceptance and Fear Avoidance beliefs are better predictors of adjustment to pain than pain hypervigilance.

Individual differences in the effects of music engagement on responses to painful stimulation

Engaged attention, including music listening, has shown mixed results when used as a method for reducing pain. Applying the framework of constructivism, we extend the concept of engagement beyond attention/distraction to include all cognitive and emotional/motivational processes that may be recruited in order to construct an alternative experience to pain and thus reduce pain. Using a music-listening task varying in task demand, we collected stimulus-evoked potentials, pupil dilation, and skin conductance responses to noxious electrocutaneous stimulations as indicators of central and peripheral arousal, respectively. Trait anxiety (Spielberger State-Trait Anxiety Inventory) and absorption (Tellegen Absorption Scale) provided indicators of individual differences. One hundred and fifty-three healthy, normal volunteers participated in a test session in which they received 3 stimulus intensity levels while listening to background tones (No Task) or performing a music-listening task. Linear slopes indicating net engagement (change in stimulus arousal relative to task performance) decreased with increasing task demand and stimulus level for stimulus-evoked potentials. Slopes for pupil dilation response and skin conductance response varied with task demand, anxiety, and absorption, with the largest engagement effect occurring for high anxiety/high absorption participants. Music engagement reduces pain responses, but personality factors like anxiety and absorption modulate the magnitude of effect.

PERSPECTIVE

Engaging in music listening can reduce responses to pain, depending on the person: people who are anxious and can become absorbed in activities easily may find music listening especially effective for relieving pain. Clinicians should consider patients' personality characteristics when recommending behavioral interventions like music listening for pain relief.

Asians differ from non-Hispanic Whites in experimental pain sensitivity

This study examined differences between Asians and non-Hispanic Whites (Whites) in pain sensitivity, and its relationship to mean arterial pressure (MAP) and heart rate (HR). In 30 Whites (50% female) and 30 Asians (50% female), experimental pain sensitivity was assessed with a hand cold pressor task, yielding measures of pain threshold, tolerance, intensity, and unpleasantness. Mean arterial pressure and HR measurements taken at rest and in response to speech stress were assessed. Perceived stress, anxiety, perfectionism, parental criticism, parental expectations and depressive symptoms were also measured. The results indicated that for the cold pain test, Asians demonstrated significantly lower pain threshold and tolerance levels than Whites. Although no ethnic differences were seen for MAP or HR responses to stress, for Whites higher stress MAP levels were correlated with reduced pain sensitivity, while for Asians higher baseline and stress HR levels were correlated with reduced pain sensitivity. Asians reported higher parental expectations and greater parental criticism than Whites. For Asians only, higher levels of perfectionism were related to more depressive symptoms, anxiety and perceived stress. These results indicate that Asian Americans are more sensitive to experimental pain than Whites and suggest ethnic differences in endogenous pain regulatory mechanisms (e.g. MAP and HR). The results may also have implications for understanding ethnic differences in clinical pain.

Stress and tension-type headache mechanisms

Stress is widely demonstrated as a contributing factor in tension-type headache (TTH). The mechanisms underlying this remain unclear at present. Recent research indicates the importance of central pain processes in tension-type headache (TTH) pathophysiology. Concurrently, research with animals and healthy humans has begun to elucidate the relationship between stress and pain processing in the central nervous system, including central pain processes putatively dysfunctional in TTH. Combined, these two fields of research present new insights and hypotheses into possible mechanisms by which stress may contribute to TTH. To date, however, there has been no comprehensive review of this literature. The present paper provides such a review, which may be valuable in facilitating a broader understanding of the central mechanisms by which stress may contribute to TTH.

The modulation of pain by attention and emotion: a dissociation of perceptual and spinal nociceptive processes

Emotions and attention have been shown to influence the perception of pain and several psychophysiological studies have suggested an implication of descending modulatory mechanisms to explain these effects. However, the specificity of the neurophysiological mechanisms underlying the emotional and attentional modulation of pain still remains unclear. In order to differentiate the supra-spinal and spinal mechanisms involved in emotional and attentional modulation of pain, we measured pain perception (self-ratings) and the RIII reflex in healthy volunteers during the presentation of pleasant, unpleasant and neutral pictures, as well as during a baseline condition with no visual distractor (Experiment 1). In a second experiment, we manipulated the emotional arousal induced by pleasant and unpleasant pictures in order to compare more directly the effects of distraction and arousal. Whereas emotional valence influenced pain and the amplitude of the RIII reflex in the same direction (negative > positive), distraction by neutral pictures reduced pain but increased the RIII reflex relative to baseline. Increased arousal further potentiated the effects of negative valence on both pain and the RIII reflex and the effects of positive emotions on pain, as previously reported. However, arousal did not potentiate the inhibitory effect of positive pictures on the RIII and seems insufficient to account for the effect of distraction on the RIII. Overall, these data provide further evidence that attention and emotion modulate pain through partially dissociable neurophysiological mechanisms.

Cold pressor pain reduces phobic fear but fear does not reduce pain

Negative emotion has a variable effect on pain perception. This variability has been explained by the motivational priming hypothesis (MPH) which predicts that emotional stimuli generating low levels of arousal will facilitate pain, while stimuli generating high levels of arousal will inhibit pain. However, a study by Sneddon et al with rainbow trout discovers a relationship not found in the human literature, that fear-related behavior decreased in the presence of a nociceptive stimulus. The current experiment examined this possibility in humans. In Experiment 1, 30 healthy, female subjects with "at least a mild aversion to spiders" participated in 3 trials: 1 in which a Brazilian salmon pink tarantula was present; a second with the right hand immersed in a cold pressor; and a third with both the tarantula and the cold pressor present. Experiment 2 added distance as an extra variable to this methodology. In both experiments it was found that spider presence had no impact upon pain perception but spider fear was reduced by the cold pressor. There was no interaction between trial and either time or distance. These findings are novel in human subjects and not well accounted for by the MPH. We suggest that an explicitly evolutionary framework should be adopted, and that spider fear was reduced to facilitate escape from the more threatening cold-pressor experience.

PERSPECTIVE

This study examined the relationship between pain and fear. Subjects with an aversion to spiders sat next to a tarantula with their right hand in iced water. Subjects reported reduced fear but no change in pain. Consequently, the authors reevaluate the Motivational Priming Hypothesis and emphasize evolutionarily determined threat values.

Stress-induced analgesia

For over 30 years, scientists have been investigating the phenomenon of pain suppression upon exposure to unconditioned or conditioned stressful stimuli, commonly known as stress-induced analgesia. These studies have revealed that individual sensitivity to stress-induced analgesia can vary greatly and that this sensitivity is coupled to many different phenotypes including the degree of opioid sensitivity and startle response. Furthermore, stress-induced analgesia is influenced by age, gender, and prior experience to stressful, painful, or other environmental stimuli. Stress-induced analgesia is mediated by activation of the descending inhibitory pain pathway. Pharmacological and neurochemical studies have demonstrated involvement of a large number of neurotransmitters and neuropeptides. In particular, there are key roles for the endogenous opioid, monoamine, cannabinoid, gamma-aminobutyric acid and glutamate systems. The study of stress-induced analgesia has enhanced our understanding of the fundamental physiology of pain and stress and can be a useful approach for uncovering new therapeutic targets for the treatment of pain and stress-related disorders.

Highly anxious dental patients report more pain during dental injections

OBJECTIVES

In the present study, the relationship between anxiety and pain was investigated using a clinically relevant sample and stimulus.

METHODS

A sample of highly anxious dental patients (n = 23) and a sample of 'normal' subjects (n = 57) were compared with respect to the duration and intensity of pain while receiving a dental anaesthetic injection.

RESULTS

As expected, highly anxious dental patients indicate more pain, which is of longer duration, than normal patients. Most predictive for the amount of pain felt was the pain felt during a previous injection.

CONCLUSION

Dentists should be aware that anxious dental patients with a negative experience regarding dental injections may feel elevated levels of pain which most likely leads to negative expectations for the future.

The effects of anxiety and depression on weekly pain in women with arthritis

This study examined the effects of anxiety and depression on pain in women with rheumatoid arthritis (RA; n=82) or osteoarthritis (OA; n=88). Anxiety and depression symptoms were assessed at the beginning of the study. Arthritis pain, interpersonal stress, negative affect, and positive affect were assessed weekly for 11 consecutive weeks. Multilevel analyses were conducted to investigate direct, indirect, and interactive effects of anxiety and depression on weekly changes in pain. When entered separately into the prediction equations, anxiety and depression were both related to elevations in current and next week pain, although the effects were nearly twice as large for anxiety. In addition, both anxiety and depression were indirectly related to current pain through negative and positive affect and depression interacted with stress to predict current pain in the RA group. When entered together into the prediction equations, anxiety alone was still related to elevations in current and next week pain. In addition, anxiety alone was indirectly related to current pain through negative affect and depression alone was indirectly related to current pain through positive affect. These results highlight the need for careful study of the differential effects of anxiety and depression and treatments that target their unique mechanisms.

Changes in self-perceived role identity modulate pain perception

Pain is an experience including physiological and psychological factors. We assume that emotions may be elicited and increased through self-perceived role identity and that change of role identity alters quality and intensity of pain perception. We used role-play strategies to assess whether pain can be better tolerated whenever, in an unavoidable and unpleasant context, role identity confers pain a meaningful and thus suitable character. We induced antithetic roles in 21 actors who received heat stimuli on their arms before and after role-play conditions. Pain tolerance, skin conductance and voice signals were measured. Pain tolerance increased for heroes/heroines and decreased for faint-hearts. Men showed higher pain tolerance. Heroes/heroines evaluated heat stimuli as more intense. Faint-hearts found pain stimuli more affectively loaded at lower temperatures. Women showed higher pain ratings. Hence, self-perception influences pain perception. Role-play strategies may be of value for new pain management strategies.

Appraisals of pain from controlled stimuli: relevance to quantitative sensory testing

OBJECTIVE

Sensory testing has been advocated for the diagnosis, prognosis, and outcome evaluation of pain patients, but responses to controlled stimuli have not been well correlated to clinical pain. As an initial step for improving the clinical relevance of sensory testing, this investigation compared appraisals of and responses to controlled pain stimuli.

DESIGN

A prospective within subjects design was used.

METHODS

Heat, ischaemic, and delayed-onset muscle pain were induced in the upper extremity of 44 participants (47.7% women) during four experimental sessions.

RESULTS

The threat of heat and ischaemic pain was higher than delayed-onset muscle pain (F(2,86) = 5.30, p<.01, eta(2) = .11). Threat, challenge, predictability, and controllability were related to heat pain most consistently. The affective-sensory ratios of ischaemic and delayed-onset muscle pain resembled those of clinical pain and were higher than heat pain (F(2,84) = 11.64, p<.01, eta(2) = .22). Delayed-onset muscle pain meaningfully affected daily activities, which correlated to delayed-onset muscle pain ratings (rs = .60-.68, ps <.001).

CONCLUSIONS

Heat stimuli may be well suited for instructional manipulations of appraisals to improve the clinical relevance of quantitative sensory testing and delayed-onset muscle pain's effects on daily activities are clinically relevant.

Emotional modulation of pain: is it the sensation or what we recall?

Emotions modulate pain perception, although the mechanisms underlying this phenomenon remain unclear. In this study, we show that intensity reports significantly increased when painful stimuli were concomitant to images showing human pain, whereas pictures with identical emotional values but without somatic content failed to modulate pain. Early somatosensory responses (<200 ms) remained unmodified by emotions. Conversely, late responses showed a significant enhancement associated with increased pain ratings, localized to the right prefrontal, right temporo-occipital junction, and right temporal pole. In contrast to selective attention, which enhances pain ratings by increasing sensory gain, emotions triggered by seeing other people's pain did not alter processing in SI-SII (primary and second somatosensory areas), but may have biased the transfer to, and the representation of pain in short-term memory buffers (prefrontal), as well as the affective assignment to this representation (temporal pole). Memory encoding and recall, rather than sensory processing, appear to be modulated by empathy with others' physical suffering.

Anticipatory brainstem activity predicts neural processing of pain in humans

Previous neuroimaging studies have shown brain activity during not only the application of noxious stimuli, but also prior to stimulation. The functional significance of the anticipatory response, however, has yet to be explored. Two theoretical responses involve either a decrease or an increase in sensitivity of the nociceptive system. In a functional magnetic resonance imaging (fMRI) study, brainstem responses during anticipation and processing of thermal noxious stimuli were investigated. Twelve healthy subjects were warned prior to and then received noxious stimulation to their left hand. Behavioral data showed a positive correlation between the intensity of anticipation and pain. FMRI data revealed brainstem activation in the PAG during the anticipation period. When correlated with individual anticipation ratings, activation during anticipation included significant clusters within the entorhinal cortex and ventral tegmental area (VTA). During receipt, activation within the brainstem included the PAG, VTA, rostral ventromedial medulla (RVM), and the parabrachial nucleus (PB), all elements of descending pain pathways. Using a backward model approach, we explored the functional significance of the anticipatory neural response for subsequent pain processing. Results of this regression analysis revealed that insula activity during receipt was predicted by activity in both the entorhinal cortex and VTA during anticipation. We suggest that activation in both regions before and during pain may underlie anticipation and subsequent pain modulatory responses, possibly involving the appraisal and control of attention necessary for pain modulation. Together, the results suggest a possible role of brainstem areas in anticipatory mechanisms involved in the maintenance of chronic pain.

Vasovagal symptoms mediate the relationship between predonation anxiety and subsequent blood donation in female volunteers

BACKGROUND

Although not universal, a certain amount of predonation anxiety is common and not surprising among inexperienced blood donors. Variations in predonation anxiety, however, may influence the donor's experience in several respects and might be related to the likelihood of subsequent donation even among those who do not report particularly high levels of anxiety.

STUDY DESIGN AND METHODS

A total of 671 inexperienced blood donors (zero or one prior donation) enrolled in a treatment study and completed questionnaires assessing anxiety before and after giving blood. Ratings of pain and blood donation-related symptoms were obtained after giving blood, as well as information from the nurses about the blood donation procedure. Follow-up information on number of additional visits to a blood collection clinic during the subsequent year was also obtained for most participants.

RESULTS

Predonation anxiety was positively related to ratings of blood donation-related symptoms and chair reclining by the nurses and negatively related to the donor's rating, obtained at the end of the procedure, of the likelihood that he or she would give blood again. Women, but not men, with higher predonation anxiety were significantly less likely to return to a blood clinic in the following year. The results of mediation analyses suggest that this was due to the association between anxiety and donation-related symptoms.

CONCLUSION

The results do not indicate whether or not it is feasible or useful to modify predonation anxiety, but highlight the relationships between the emotional state of inexperienced donors and several aspects of the donation experience, including subsequent donor return. Further study of the psychosocial aspects of blood donation and examination of related research (e.g., treatment of dental anxieties) may be worthwhile.

Dissociation between pain and the nociceptive blink reflex during psychological arousal

OBJECTIVE

To investigate the effect of psychological arousal on pain ratings and the R2 component of the electrically evoked blink reflex to a 'pure' noiciceptive stimulus.

METHODS

Pain ratings and R2 to a noiciceptive stimulus (pulse width 0.3ms, 2mA, delivered from a concentric electrode attached to the supraorbital region of the forehead) were investigated in 16 healthy participants before and during a serial subtraction task, and in 16 control participants who sat quietly during nociceptive stimulation.

RESULTS

Pain ratings decreased whereas R2 amplitude increased during the serial subtraction task.

CONCLUSIONS

Supra-spinal rather than spinal mechanisms inhibited pain perception during psychological arousal. Moreover, psychological arousal facilitated the R2 component of the blink reflex to a nociception-specific stimulus.

SIGNIFICANCE

Supra-spinal influences need to be considered during clinical evaluation of the trigeminal nociceptive blink reflex.

Ethnic differences in thermal pain responses: a comparison of South Asian and White British healthy males

The expression and report of pain is influenced by social environment and culture. Previous studies have suggested ethnically determined differences in report of pain threshold, intensity and affect. The influence of ethnic differences between White British and South Asians has remained unexplored. Twenty age-matched, male volunteers in each group underwent evaluation. Cold and warm perception and cold and heat threshold were assessed using an ascending method of limits. Magnitude estimation of pain unpleasantness and pain intensity were investigated with thermal stimuli of 46, 47, 48 and 49 degrees C. Subjects also completed a pain anxiety questionnaire. Data was analysed using t-test, Mann-Whitney and repeated measures analysis of variance as appropriate. There were no differences in cold and warm perception between the two groups. There was a statistically significant difference between the two groups for heat pain threshold (P=0.006) and heat pain intensity demonstrated a significant effect for ethnicity (F=13.84, P=0.001). Although no group differences emerged for cold pain threshold and heat unpleasantness, South Asians demonstrated lower cold pain threshold and reported more unpleasantness at all temperatures but this was not statistically significant. Our study shows that ethnicity plays an important role in heat pain threshold and pain report, South Asian males demonstrated lower pain thresholds and higher pain report when compared with matched White British males. There were no differences in pain anxiety between the two groups and no correlations were identified between pain and pain anxiety Haemodynamic measures and anthropometry did not explain group differences.

Tolerability, gut effects, and pharmacokinetics of methylnaltrexone following repeated intravenous administration in humans

Previous studies have shown that a single dose of methylnaltrexone, a unique peripheral opioid antagonist, reverses opioid-induced gut hypomotility in humans. Because repeated drug doses are likely to be needed to treat patients with opioid-induced or postsurgical bowel dysfunction, the authors have now examined the safety, pharmacological activity, and pharmacokinetics of a multiple-dose regimen of methylnaltrexone, administered as 12 consecutive intravenous doses (0.3 mg/kg every 6 hours) in 12 healthy subjects. Steady state was achieved rapidly, and after repeated dosing for 3 days, methylnaltrexone decreased oral-cecal transit time from a pretreatment baseline value of 101.3 +/- 29.4 min (mean +/- SD) to 82.5 +/- 20.7 min. Maximum observed plasma concentrations, measured 5 minutes postdose, were 538 +/- 237 and 675 +/- 180 ng/mL after doses 1 and 2, respectively. Based on 6-hour sampling periods, the plasma half-life, 2.5 +/- 0.5 and 2.9 +/- 0.9 hours following the 1st and 12th doses, respectively, was unchanged at steady state. There was essentially no accumulation of methylnaltrexone, based on the ratio of AUC values after doses 12 and 1. This study showed that repeated administration of intravenous methylnaltrexone is well tolerated in humans, with no significant adverse events or changes in opioid subjective ratings and no clinically noteworthy alterations in pharmacokinetics. The observation of a significant reduction in the gut transit time after repeated administration of methylnaltrexone to these opioid-naive volunteers suggests that endogenous opioids modulate human gut motility.

Electronic diary assessment of pain-related fear, attention to pain, and pain intensity in chronic low back pain patients

The present study investigated the relationships between pain-related fear, attention to pain, and pain intensity in daily life in patients with chronic low back pain. An experience sampling methodology was used in which electronic diary data were collected by means of palmtop computers from 40 chronic low back pain patients who were followed for one week. Attention to pain was hypothesized to mediate the relation between pain-related fear and pain intensity. Further, pain-related fear as a trait characteristic was expected to moderate the relation between attention to pain and pain intensity. Multi-level analysis was used for all analyses. Although the tested mediation models yielded statistically significant mediation effects, the sizes of these effects were relatively small and clinically irrelevant. Instead, results suggested that pain-related fear and attention to pain independently predicted pain intensity. No evidence for moderation of the relation between attention to pain and pain intensity by pain-related fear as a trait characteristic was found. Implications of the results from this study are discussed and suggestions for future research are provided.

Preoperative ketorolac has a preemptive effect for postoperative third molar surgical pain

There is uncertainty regarding the role of preemptive analgesia in preventing postoperative pain. Most previous studies were of parallel design completed under general anesthesia with many confounding inter-patient's variables. The present study evaluated the efficacy of preemptive ketorolac in a crossover design in patients undergoing bilateral mandibular third molar surgery. This was a double blind, randomized, placebo-controlled study where 34 patients had each of their identical impacted mandibular third molars removed under local anesthesia on two occasions. Each patients acted as their own control; one side was pretreated with intravenous ketorolac 30 mg before surgery followed by placebo injection after surgery, and for the other side, the patient was given placebo injection before surgery and post-treated with intravenous ketorolac 30 mg after surgery. The difference in postoperative pain between pretreated and post-treated side in each patient was assessed by four primary end-points: pain intensity as measured by a 100-mm visual analogue scale hourly for 12 h, time to rescue analgesic, postoperative analgesic consumption, and patient's global assessment. Throughout the 12-h investigation period, patients reported significantly lower pain intensity scores in the ketorolac pretreated sides when compared with the post-treated sides (P = 0.003). Patients also reported a significantly longer time to rescue analgesic (8.9 h versus 6.9 h, P = 0.005), lesser postoperative analgesic consumption (P = 0.007) and better global assessment for the ketorolac pretreated sides (P = 0.01). Pretreatment with intravenous ketorolac has a preemptive effect for postoperative third molar surgery and extended the analgesia by approximately 2 h.

Fear-induced hypoalgesia in humans: Effects on low intensity thermal stimulation and finger temperature

Prior research indicates that exposure to fear-inducing stimuli inhibits finger withdrawal to sudden onset and high intensity radiant heat in humans. Although withdrawal latencies to intense heat are thought to reflect changes in spinal nociceptive processing, supraspinal measures are needed to determine whether pain perception is altered. The present study used gradual onset and low intensity radiant heat to induce a finger withdrawal response that depends on supraspinal processes. After baseline pain threshold tests, 57 healthy human participants were randomly assigned to 1 of 2 groups. In the fear group, participants received 3 brief shocks. In the neutral group, participants did not receive shock. Results suggest that finger withdrawal latencies to low intensity heat were increased after shock presentation, providing additional evidence that fear reduces pain on a measure that is influenced by supraspinal processes. Both self-report and physiological (skin conductance level, heart rate, and blood pressure) measures of emotion confirmed that the intended affective states were induced. Finger temperature was unaffected by emotion manipulations; thus, skin cooling does not appear to mediate increased withdrawal latencies. These findings provide additional evidence that fear not only inhibits spinal nociceptive reflexes, it also inhibits supraspinal measures of pain.

PERSPECTIVE

From a clinical perspective, these data suggest that patients who experience intense fear in response to unpredictable threatening events will show a reduction in pain perception.

The meaning of pain influences its experienced intensity

This experiment tested whether meaning influences the experience of pain. Thirty-one healthy students participated in a study on evaluations of various stimuli placed against the neck. By suggesting that a very cold metal bar was either hot or cold, the potentially tissue-damaging property of the stimulus was experimentally manipulated. A manipulation check revealed that participants believed the experimenter's information, as they rated the bar as more hot in the corresponding condition than in the other condition. Confirming the hypothesis that tissue-damaging meaning influences the experience of pain, participants who were told that the bar was hot rated it as more painful than participants who were told that it was cold. Damage interpretations mediated the effect of information on pain intensity scores, which supported the theory that tissue-damage is a crucial aspect of meaning to influence the subjective intensity of pain.

Sex differences in pain and hypothalamic-pituitary-adrenocortical responses to opioid blockade

OBJECTIVE

Sex differences in pain sensitivity and stress reactivity have been well documented. Little is known about the role of the endogenous opioid system in these differences. This study was conducted to compare adrenocortical, pain sensitivity, and blood pressure responses to opioid blockade using naltrexone in men and women.

METHODS

Twenty-six participants completed 2 sessions during which placebo or 50 mg of naltrexone was administered, using a double-blind, counterbalanced design. Thermal pain threshold and heat tolerance were assessed. Participants also rated pain during a 90-second cold pressor test (CPT) and completed the McGill Pain Questionnaire (MPQ) after each pain challenge. Blood and saliva samples and cardiovascular and mood measures were obtained throughout the sessions.

RESULTS

Plasma cortisol, adrenocorticotropin, beta endorphin, prolactin, and salivary cortisol levels increased similarly in men and women after naltrexone administration compared with placebo. Women reported more pain during both pain procedures and had lower thermal pain tolerance. In response to naltrexone, women exhibited reduced blood pressure responses and reduced MPQ pain ratings after CPT. No effects of naltrexone on these measures were found in men.

CONCLUSIONS

Although men and women exhibited similar hormonal responses to opioid receptor blockade, women reported less pain and showed smaller blood pressure responses during CPT. Results suggest differential effects of the endogenous opioid system on pain perception and blood pressure in men and women.

The effects of failing to control pain: an experimental investigation

Chronic pain patients are often confronted with repeated failure to achieve pain relief. The aim of this study was to experimentally investigate the effects of repeated failing attempts to control pain on pain impact (pain intensity, emotional and physiological responses). Perceived control over an electrocutaneous pain stimulus was manipulated between subjects by success or failure feedback on a task by which control over pain could be acquired. In addition, success or failure at the task was manipulated without suggesting a possibility to control pain. It was hypothesized that successful control would lead to lowest pain impact, whereas failure to control pain would lead to even higher pain impact than absent control. Furthermore, it was hypothesized that failure feedback would increase pain impact when compared to success feedback. Results indicated that repeated failure to control pain increased anger and heart rate responses compared to the other conditions, but not pain intensity. It is concluded that persistent efforts to control pain in the face of failure may lead to the maintenance or exacerbation of physiological and emotional responses.

Noise stress and human pain thresholds: divergent effects in men and women

Considerable animal research suggests that exposure to noxious and nonnoxious fear-inducing stimuli can produce hypoalgesia. Although this effect is thought to generalize across species, only a few studies have examined the pain modulatory effects of nonnoxious fear-eliciting stimuli in humans. The present study examined whether exposure to a series of loud noise bursts would produce a fear-related hypoalgesia in male and female human subjects. Both subjective and physiologic measures (skin conductance level, heart rate) indicated that noise exposure resulted in fear, sympathetic arousal, and decreased pain reactivity in women (n = 20). In contrast, men (n = 20) did not experience fear or physiologic arousal, but reacted with surprise and increased pain reactivity. These findings provide additional evidence that hypoalgesia is mediated by fear and physiologic arousal. Although future studies should directly manipulate surprise, it appears that surprise without fear and physiologic arousal might enhance pain processing.

Individual differences in the emotional reaction to shock determine whether hypoalgesia is observed

OBJECTIVES

Our laboratory has shown that electrical shocks induce fear in human participants and subsequently inhibit pain on the hand receiving shocks. The present study examined whether pain modulation is bilateral, by testing pain on the hand contralateral to the one receiving shocks. We also evaluated whether individual differences in emotional response to the shocks influenced pain modulation.

DESIGN

Following baseline tests, 61 participants were randomly assigned to one of two groups. In the shock group, participants received three surprising electrical shocks. In the control group, stimulating electrodes were removed from participants' fingers, and no shocks were presented. Both groups received two more pain threshold tests 2 and 8 minutes later.

OUTCOME MEASURES

Similarly to the tail-flick test used in rodents, pain threshold was tested by measuring the latency of finger withdrawal to radiant heat. The following manipulation checks assessed the emotional state induced by shocks and the control procedure: Self-reported affect, skin conductance level (SCL), heart rate (HR), and blood pressure (BP).

RESULTS

Surprisingly, self-reported affect data indicate that some participants reacted to the shocks with humor and fear, while others reacted primarily with fear. Therefore, these groups were analyzed separately. Participants reacting with fear only exhibited hypoalgesia; however, participants reacting with mixed fear and humor showed no change in pain. This divergent effect was not mediated by arousal, because SCL, HR, and BP were similar in both shocked groups (fear only, fear + humor).

CONCLUSIONS

These data suggest that fear-induced hypoalgesia occurs bilaterally. However, humor experienced concurrent with fear appears to inhibit hypoalgesia. These findings may help explain individual differences in pain following traumatic events.

Cancer pain and anxiety

Anxiety and pain can be understood with a multidimensional framework that accounts for somatic, emotional, cognitive, and behavioral aspects of these conditions. Patients who have cancer or treatment-related pain are more likely to be anxious than cancer patients without pain. Patients with cancer pain and anxiety cause difficult diagnostic dilemmas because some degree of anxiety is a normal response to having a severe medical illness. Furthermore, the somatic symptoms of anxiety often overlap with symptoms related to underlying disease processes or treatment effects. The degree of disruption in a patient's life often is the critical factor in distinguishing normal from maladaptive anxiety. Making an accurate diagnosis will help guide anxiety treatment and screening instruments can facilitate the recognition of those patients in need of further assessment. The relationship between pain and anxiety is complex and bidirectional, with interactions occurring on physiologic and psychologic levels. There are a variety of psychopharmacologic, psychotherapeutic, and complementary/alternative treatments available. A comprehensive approach to care includes these approaches in an individualized way. Terminal sedation is examined as a compassionate option for relieving intractable distress at the end of life.

Negative affect: effects on an evaluative measure of human pain

Prior work indicates that exposure to fear-inducing shock inhibits finger-withdrawal to radiant heat in humans (hypoalgesia), whereas anxiety induced by threat of shock enhances reactivity (hyperalgesia; Pain 84 (2000) 65-75). Although finger-withdrawal latencies are thought to reflect changes in pain sensitivity, additional measures of pain are needed to determine whether pain perception is altered. The present study examined the impact of negative affect on visual analog scale (VAS) ratings of fixed duration thermal stimuli. One hundred twenty-seven male and female human subjects were randomly assigned to one of three emotion-induction conditions: (1) negative affect induced by exposure to three brief shocks; (2) negative affect elicited by the threat of shock without presentation; and (3) neutral affect, with no intervention. VAS ratings were tested before and after emotion-induction. Results suggest that both negative affect manipulations reduced pain. Manipulation checks indicated that the emotion-induction treatments induced similar levels of fear but with different arousal levels. Potential mechanisms for affect induced changes in pain are discussed.