Biomedical subjects

Michael E Robinson

Publications and source records attributed to Michael E Robinson.

At least 19 recordsLinked to original sources

PubMed2007

Sex and pain-related psychological variables are associated with thermal pain sensitivity for patients with chronic low back pain.

UNLABELLED: Biologic and psychological associations with evoked pain sensitivity have been extensively studied in healthy subjects but not among subjects with clinical pain syndromes. This study involved patients with chronic low back pain and investigated whether: 1) sex differences existed for thermal pain sensitivity; and 2) sex, fear-avoidance beliefs, and/or pain catastrophizing influenced thermal pain sensitivity. Thirty-three consecutive patients enrolled in a pain rehabilitation program completed self-report questionnaires and underwent quantitative sensory testing with an established protocol for thermal stimuli. Women had elevated pain sensitivity for measures of tolerance and temporal summation but not for first pulse response. In the multivariate models predicting thermal pain sensitivity, sex was associated with tolerance, and fear-avoidance beliefs were associated with first pulse response. Sex and pain catastrophizing were associated with temporal summation of thermal pain. Future studies involving clinical samples are necessary to replicate these findings and to explore the involvement of cortical structures. PERSPECTIVE: This study suggests that sex, fear-avoidance beliefs, and pain catastrophizing were associated with thermal pain sensitivity for patients with chronic low back pain. These results corroborated sex differences in tolerance and temporal summation observed in the experimental pain literature for healthy subjects. These results also suggest the potential for these specific pain-related beliefs to be associated with a sensitized state because previous studies have demonstrated their association to clinical pain reports, and this study demonstrated associations with thermal pain sensitivity.

Adolescent↗

PubMed2006

Brain activity related to temporal summation of C-fiber evoked pain.

Temporal summation of "second pain" (TSSP) is considered to be the result of C-fiber-evoked responses of dorsal horn neurons, termed 'windup'. This phenomenon is dependent on stimulus frequency (0.33 Hz) and relevant for central sensitization and chronic pain. Previous brain imaging studies have only been used to characterize neural correlates of second pain but not its temporal summation. We utilized functional magnetic resonance imaging (fMRI) in healthy volunteers to measure brain responses associated with TSSP. Region of interest analysis was used to assess TSSP related brain activation. Eleven pain-free normal subjects underwent fMRI scanning during repetitive heat pulses to the right foot at 0.33 and 0.17 Hz. Stimulus intensities were adjusted to each individual's heat sensitivity to achieve comparable TSSP ratings of moderate pain in all subjects. As predicted, experimental pain ratings showed robust TSSP during 0.33 Hz but not 0.17 Hz stimuli. fMRI statistical maps identified several brain regions with stimulus and frequency dependent activation consistent with TSSP, including contralateral thalamus (THAL), S1, bilateral S2, anterior and posterior insula (INS), mid-anterior cingulate cortex (ACC), and supplemental motor areas (SMA). TSSP ratings were significantly correlated with brain activation in somatosensory areas (THAL, S1, left S2), anterior INS, and ACC. These results show that neural responses related to TSSP are evoked in somatosensory processing areas (THAL, S2), as well as in multiple areas that serve other functions related to pain, such as cognition (ACC, PFC), affect (INS, ACC, PAG), pre-motor activity (SMA, cerebellum), and pain modulation (rostral ACC).

Anxiety↗

PubMed2006

Placebo analgesia is accompanied by large reductions in pain-related brain activity in irritable bowel syndrome patients.

Previous experiments found that placebos produced small decreases in neural activity of pain-related areas of the brain, yet decreases were only statistically significant after termination of stimuli and in proximity to when subjects rated them. These changes could reflect report bias rather than analgesia. This functional magnetic resonance imaging (fMRI) study examined whether placebo analgesia is accompanied by reductions in neural activity in pain-related areas of the brain during the time of stimulation. Brain activity of irritable bowel syndrome patients was measured in response to rectal distension by a balloon barostat. Large reductions in pain and in brain activation within pain-related regions (thalamus, somatosensory cortices, insula, and anterior cingulate cortex) occurred during the placebo condition. Results indicate that decreases in activity were related to placebo suggestion and a second factor (habituation/attention/conditioning). Although many factors influence placebo analgesia, it is accompanied by reduction in pain processing within the brain in clinically relevant conditions.

Adult↗

PubMed2006

Immediate effects of spinal manipulation on thermal pain sensitivity: an experimental study.

BACKGROUND: The underlying causes of spinal manipulation hypoalgesia are largely unknown. The beneficial clinical effects were originally theorized to be due to biomechanical changes, but recent research has suggested spinal manipulation may have a direct neurophysiological effect on pain perception through dorsal horn inhibition. This study added to this literature by investigating whether spinal manipulation hypoalgesia was: a) local to anatomical areas innervated by the lumbar spine; b) correlated with psychological variables; c) greater than hypoalgesia from physical activity; and d) different for A-delta and C-fiber mediated pain perception. METHODS: Asymptomatic subjects (n = 60) completed baseline psychological questionnaires and underwent thermal quantitative sensory testing for A-delta and C-fiber mediated pain perception. Subjects were then randomized to ride a stationary bicycle, perform lumbar extension exercise, or receive spinal manipulation. Quantitative sensory testing was repeated 5 minutes after the intervention period. Data were analyzed with repeated measures ANOVA and post-hoc testing was performed with Bonferroni correction, as appropriate. RESULTS: Subjects in the three intervention groups did not differ on baseline characteristics. Hypoalgesia from spinal manipulation was observed in lumbar innervated areas, but not control (cervical innervated) areas. Hypoalgesic response was not strongly correlated with psychological variables. Spinal manipulation hypoalgesia for A-delta fiber mediated pain perception did not differ from stationary bicycle and lumbar extension (p > 0.05). Spinal manipulation hypoalgesia for C-fiber mediated pain perception was greater than stationary bicycle riding (p = 0.040), but not for lumbar extension (p = 0.105). CONCLUSION: Local dorsal horn mediated inhibition of C-fiber input is a potential hypoalgesic mechanism of spinal manipulation for asymptomatic subjects, but further study is required to replicate this finding in subjects with low back pain.

Adult↗

PubMed2006

An evaluation of the measurement of pain catastrophizing by the coping strategies questionnaire.

Measurement and conceptual issues of pain catastrophizing have been raised in the literature. The issues of construct redundancy and measurement overlap have received particular attention, with suggestions that measures of pain catastrophizing are confounded with measures of negative mood, namely depression. The current study sought to investigate these issues in the coping strategies questionnaire-catastrophizing subscale (CSQ-CAT), a widely used measure of pain catastrophizing. Chronic pain patients (n=152) were recruited from the University of Florida pain clinics and completed a battery of psychological measures. Regression analyses indicated that measures of depression, anxiety, and anger accounted for 69% and 19% of the variance in measures of pain catastrophizing and pain, respectively. Trait anger and the cognitive and fearful dimensions of depression and anxiety were uniquely associated with pain catastrophizing. After controlling for measures of negative mood, pain catastrophizing contributed minimally to the prediction of pain. This study suggests that the CSQ-CAT is highly related to measures of negative mood and raises doubts about its measurement of the construct of pain catastrophizing. Results also provide support for theoretical accounts of the relationships between pain catastrophizing, negative mood, and pain. Clinical implications, future research directions, and alternative measures of pain catastrophizing are discussed.

Adaptation, Psychological↗

PubMed2006

Fear-avoidance beliefs and temporal summation of evoked thermal pain influence self-report of disability in patients with chronic low back pain.

INTRODUCTION: Quantitative sensory testing has demonstrated a promising link between experimentally determined pain sensitivity and clinical pain. However, previous studies of quantitative sensory testing have not routinely considered the important influence of psychological factors on clinical pain. This study investigated whether measures of thermal pain sensitivity (temporal summation, first pulse response, and tolerance) contributed to clinical pain reports for patients with chronic low back pain, after controlling for depression or fear-avoidance beliefs about work. METHOD: Consecutive patients (n=27) with chronic low back pain were recruited from an interdisciplinary pain rehabilitation program in Jacksonville, FL. Patients completed validated self-report questionnaires for depression, fear-avoidance beliefs, clinical pain intensity, and clinical pain related disability. Patients also underwent quantitative sensory testing from previously described protocols to determine thermal pain sensitivity (temporal summation, first pulse response, and tolerance). Hierarchical regression models investigated the contribution of depression and thermal pain sensitivity to clinical pain intensity, and fear-avoidance beliefs and thermal pain sensitivity to clinical pain related disability. RESULTS: None of the measures of thermal pain sensitivity contributed to clinical pain intensity after controlling for depression. Temporal summation of evoked thermal pain significantly contributed to clinical pain disability after controlling for fear-avoidance beliefs about work. CONCLUSION: Measures of thermal pain sensitivity did not contribute to pain intensity, after controlling for depression. Fear-avoidance beliefs about work and temporal summation of evoked thermal pain significantly influenced pain related disability. These factors should be considered as potential outcome predictors for patients with work-related low back pain. SIGNIFICANCE: This study supported the neuromatrix theory of pain for patients with CLBP, as cognitive-evaluative factor contributed to pain perception, and cognitive-evaluative and sensory-discriminative factors uniquely contributed to an action program in response to chronic pain. Future research will determine if a predictive model consisting of fear-avoidance beliefs and temporal summation of evoked thermal pain has predictive validity for determining clinical outcome in rehabilitation or vocational settings.

Avoidance Learning↗

PubMed2006

Placebo analgesia: friend or foe?

The magnitude of placebo analgesia is influenced by environmental and perceptual factors. Environmental factors include past exposure to effective analgesic agents and verbal suggestions and cues that foster a perception of being given an effective treatment. Environmental factors, in turn, influence the proximate psychologic mediators of placebo analgesia, which include decreased desire for and increased expectations of pain relief. Strategies to maximize placebo analgesic effects in clinical practice could focus on using verbal suggestions and external cues to increase expectations of pain relief and/or decrease the perceived need for pain reduction. Placebo analgesic effects could be minimized in clinical trials by avoiding these same suggestions and cues.

Analgesia↗

PubMed2006

Peripheral and central contributions to hyperalgesia in irritable bowel syndrome.

UNLABELLED: Irritable bowel syndrome (IBS) is a common gastrointestinal disorder seen by gastroenterologists. We discuss some recent evidence for potential neural mechanisms that could contribute to somatic and visceral hyperalgesia in IBS patients. The combination of research studies of human IBS patients and studies of rats with delayed rectal hypersensitivity after recovery from experimentally induced neonatal colitis strongly suggests a mechanism wherein both primary visceral hyperalgesia and secondary widespread cutaneous hyperalgesia are dynamically maintained by tonic impulse input from the noninflamed colon and/or rectum. The secondary hyperalgesia is likely to be at least partly related to sensitization of spinal cord dorsal horn neurons and in this respect might be similar to other persistent pain conditions such as fibromyalgia and complex regional pain syndrome. PERSPECTIVE: Pain in irritable bowel syndrome is likely to be at least partly maintained by peripheral impulse input from the colon/rectum and central sensitization, yet it is also highly modifiable by psychological factors such as nocebo and placebo effects. A synergistic interaction might occur between psychological factors and abnormal afferent processing.

Animals↗

PubMed2006

Evidence for sex differences in the relationships of pain, mood, and disability.

UNLABELLED: Disability demonstrates strong univariate associations with pain and negative mood. These relationships are more complex at the multivariate level and might be further complicated by sex differences. We investigated sex differences in the relationships of pain and negative mood to overall disability and to disability in specific functional domains. One hundred ninety-seven consecutive patients with low back, myofascial, neck, arthritis, and fibromyalgia pain were recruited from university pain clinics and completed measures of disability and negative mood. Overall disability and disability in voluntary activities were significantly associated with pain and negative mood (factor score) for both sexes. Significant sex differences emerged in the strength of the disability-mood relationship, with women evincing a stronger relationship. Disability in obligatory activities was also significantly related to pain and negative mood for both sexes; however, there were no sex differences in the strength of these relationships. Mediation analyses indicated that, in men, negative mood partially mediated the relationship between pain and both overall disability and disability in voluntary activities; mediation was not supported for disability in obligatory activities. In women, negative mood fully mediated the relationship between pain and all 3 types of disability. These data suggest that disability is more directly related to pain in men. In women, the effect of pain on disability appears to operate through negative mood. PERSPECTIVE: Results of this study demonstrate that sex differences exist in the relationships of pain, mood, and disability. Men and women might thus benefit from treatment interventions that differentially target these variables.

Adult↗

PubMed2006

Back pain in direct patient care providers: early intervention with cognitive behavioral therapy.

Back pain and injury are a widespread problem for direct care providers and can lead to disability and job loss. Although most intervention studies focus on the number of reported injuries as the outcome variable, pain is a leading indicator of impending injury. More secondary prevention interventions focusing on early detection and treatment of pain are needed to reduce injuries. The primary aim of this study was to assess the feasibility and effect size of a cognitive behavioral therapy (CBT) intervention to reduce the measures of back pain, stress, and disability in direct care providers working with back pain. The secondary aim was to assess the association between affect and outcome variables, particularly unscheduled work absence, which is a component of disability. This randomized clinical trial recruited 32 registered nurses and nursing assistants with a history of back pain in the past year and assigned them to either an intervention or a control group. The CBT intervention was a weekly stress and pain management session over 6 weeks led by a clinical psychologist. Data for both groups were collected at baseline and at 6 weeks, with work absence data caused by back pain self-reported for 12 weeks. Pain intensity scores declined in the intervention group, indicating a large effect. However, stress scores increased. Depression scores accounted for one-third of the variance in hours absent because of back pain. Although there was a high dropout rate in the intervention group, a cognitive-behavioral intervention shows promise as a secondary prevention intervention.

Absenteeism↗

PubMed2006

The use of the coefficient of variation in detecting sincerity of effort: a meta-analysis.

The coefficient of variation (CV) is used to determine sincerity of effort of strength measurements. However, there is a controversy in the literature concerning its validity and effectiveness. We used a meta-analytic approach and calculated the effect size between maximal and submaximal efforts for the CV of grip, elbow flexion and knee extension. We summarized findings concerning stability, sensitivity and specificity of the CV. We found large effect sizes (d > or = 0.8) for all comparisons indicating that submaximal efforts were more variable than maximal efforts. We also found large error rates and low stability of the CV. The error rates and stability values of the CV are unacceptable from both a clinical and a medico-legal standpoint. Therefore, the use of the CV for assessing sincerity of effort needs to be questioned.

Compressive Strength↗

PubMed2005

Isometric exercise has opposite effects on central pain mechanisms in fibromyalgia patients compared to normal controls.

Aerobic exercise has been shown to activate endogenous opioid and adrenergic systems and attenuate experimental pain in normal control subjects (NC). In contrast, fibromyalgia (FM) subjects' experimental pain ratings increase after aerobic exercise, suggestive of abnormal pain modulation. In order to determine whether central or peripheral mechanisms are predominantly involved in the abnormal pain modulation of FM patients, the effects of handgrip exercise on thermal (cutaneous) and mechanical (somatic) experimental pain was tested in local as well as remote body areas of FM and NC subjects. Supra-threshold thermal pain ratings and pressure pain thresholds over both forearms were obtained before and during 90 s of sustained 30% maximal voluntary contraction (MVC). This isometric exercise resulted in substantially decreased thermal pain ratings and increased mechanical thresholds in local as well as remote body areas in NC. Opposite effects were detected in FM patients. Thus, sustained local muscular contraction induced widespread pain inhibitory effects in NC. In contrast, the widespread hyperalgesic effects of exercise on FM patients clearly indicate altered central pain mechanisms. However, whether these exercise effects of FM patients result from abnormal descending inhibition or excessive activation of muscle nociceptive afferents needs to be addressed in future studies.

Exercise↗

PubMed2005

Fear of pain, not pain catastrophizing, predicts acute pain intensity, but neither factor predicts tolerance or blood pressure reactivity: an experimental investigation in pain-free individuals.

Previous studies of the Fear-Avoidance Model of Exaggerated Pain Perception have commonly included patients with chronic low back pain, making it difficult to determine which psychological factors led to the development of an "exaggerated pain perception". This study investigated the validity of the Fear-Avoidance Model of Exaggerated Pain Perception by considering the influence of fear of pain and pain catastrophizing on acute pain perception, after considering sex and anxiety. Thirty-two males and 34 females completed the State-Trait Anxiety Inventory, the Fear of Pain Questionnaire, and the Coping Strategies Questionnaire. Subjects underwent a cold pressor procedure and tolerance, pain intensity, and blood pressure reactivity were measured. Sex, anxiety, fear of pain, and pain catastrophizing were simultaneously entered into separate multiple regression models to predict different components of pain perception. Tolerance was not predicted by fear of pain, pain catastrophizing, or anxiety. Pain intensity at threshold and tolerance were significantly predicted by fear of pain, only. Blood pressure reactivity to pain was significantly predicted by anxiety, only. These results suggest that fear of pain may have a stronger influence on acute pain intensity when compared to pain catastrophizing, while neither of the factors predicted tolerance or blood pressure reactivity.

Acute Disease↗

PubMed2005

Effects of the N-methyl-D-aspartate receptor antagonist dextromethorphan on temporal summation of pain are similar in fibromyalgia patients and normal control subjects.

UNLABELLED: Temporal summation of second pain at least partly reflects temporal summation of dorsal horn neuronal responses, and both have been termed windup (WU), a form of nociception-dependent central sensitization. Animal and human experiments have shown that both forms of WU depend on N-methyl-D-aspartate (NMDA) and substance P receptor systems. WU of second pain (WU(SP)) in patients with fibromyalgia (FM) is enhanced compared with normal control (NC) subjects and is followed by exaggerated WU(SP) aftersensations and prolonged WU(SP) maintenance at low stimulus frequencies. Because the enhanced WU(SP) of FM patients could be related to abnormal endogenous modulation of NDMA receptors, we tested the effects of the NMDA receptor antagonist dextromethorphan (DEX) on WU(SP) in FM and NC subjects in a double-blind, placebo-controlled, crossover study. WU(SP) was elicited by trains of 0.7-second duration thermal pulses applied to the glabrous surface of the hands or by 1-second mechanical stimuli to the adductor pollicis muscle of the hands at a frequency of 0.33 Hz. In comparison to baseline and placebo conditions, single oral doses of DEX 60 and 90 mg reduced thermal and mechanical WU(SP) in NC and FM subjects, with DEX 90 mg being most effective. These effects did not differ for male and female NC subjects. FM subjects required less thermal and mechanical stimulus intensity than NC to achieve maximal WU(SP), but the extent of WU(SP) reduction by DEX did not statistically differ between NC and FM subjects for all study conditions. Thus, central pain processing of FM subjects is not different from NC in at least one important aspect, namely their NMDA receptor system responsiveness to pharmacologic inhibition by DEX. PERSPECTIVE: Results of this study demonstrate that FM patients show abnormal WU(SP) during thermal and mechanical stimulation compared with NC. Because oral doses of the NMDA receptor antagonist DEX attenuated thermal and mechanical WU(SP) similarly in FM patients and NC, other mechanisms than WU(SP) need to be considered for the widespread pain of FM patients. These mechanisms might include tonic nociceptive input from peripheral tissues and/or enhanced descending facilitation.

Adult↗

PubMed2005

Sex differences in the associations among psychological factors and pain report: a novel psychophysical study of patients with chronic low back pain.

UNLABELLED: Previous studies have consistently suggested that there are sex differences in pain report, but there is no consensus regarding sex differences in the associations among psychological factors and pain report. This cross-sectional study used a novel, clinically relevant, psychophysical pain-induction technique to examine sex differences between sensory and affective pain report and sex differences in the association of depression, pain related anxiety, and catastrophizing with pain report. Patients with chronic low back pain (N = 53) were recruited from an outpatient spine clinic, and those consenting completed self-report measures of pain-related anxiety, depression, pain catastrophizing, and pain. A measure of induced low back pain was obtained by having study participants perform a protocol on the MedXtrade mark Low-Back Exercise Apparatus. Our results indicated that no sex differences were detected in psychological factors and self-reported or induced low back pain. However, the relationships between pain related anxiety and self-report of low back pain (z = 2.51, P < .05) and between pain-related anxiety and induced low back pain (z = 3.00, P < .05) were significantly stronger in men than women. These findings suggest that anxiety was linked to self-reported and induced low back pain for men, but not for women. PERSPECTIVE: Results of this study suggest that pain-related anxiety has a stronger association with psychophysical and clinical reports of low back pain for men.

Adolescent↗

PubMed2005

Increased placebo analgesia over time in irritable bowel syndrome (IBS) patients is associated with desire and expectation but not endogenous opioid mechanisms.

A study was conducted to determine whether changes in expected pain levels, desire for pain relief, or anxiety contribute to an increase in placebo analgesia over time as well as to determine whether placebo analgesic effects of IBS patients are related to endogenous opioid mechanisms. Twenty-six women with IBS were exposed to rectal stimulation (35 or 55 mmHg for 30 s) and tested under natural history (NH), rectal placebo (RP) and rectal lidocaine (RL) conditions. During all conditions, 16 patients were given saline intravenously (to test for a placebo effect) and 10 patients were given naloxone intravenously (to test naloxone antagonism of the placebo effect) on a double blind basis. Patients rated expected pain level, desire for pain relief and anxiety at 2 and 22 min after the onset of NH, RP, and RL conditions and they rated actual pain intensity at 5-min intervals for 40 min. There was a large and significant placebo effect (P<0.001) that increased over time. Ratings of expected pain levels, desire for pain relief and anxiety decreased over time and contributed to more variance in placebo and lidocaine responses during the last half of the session. These changes suggest that a reduction in negative emotions may be central to placebo effects. There was no significant difference between psychological mediators (desire, expectation, anxiety) or the placebo effect in the saline and naloxone groups, indicating that neither the psychological mediators nor the placebo analgesic effect were associated with endogenous opioids in this clinically related paradigm.

Adult↗

PubMed2005

Cluster analysis of multiple experimental pain modalities.

Identifying individual differences in pain is an important topic; however, little is known regarding patterns of responses across various experimental pain modalities. This study evaluated subgroups emerging from multiple experimental pain measures. One hundred and eighty-eight individuals (59.0% female) completed several psychological instruments and underwent ischemic, pressure, and thermal pain assessments. Thirteen separate pain measures were obtained by using three experimental pain modalities with several parameters tested within each modality. The pain ratings and scores were submitted to factor analysis that identified four pain factors from which Pain Sensitivity Index (PSI) scores were computed: heat pain (HP), pressure pain (PP), ischemic pain (IP), and temporal summation of heat pain (TS). Cluster analyses of PSI scores revealed four distinct clusters. The first cluster demonstrated high overall pain sensitivity, the second cluster revealed high TS, the third cluster showed particular insensitivity to IP and low sensitivity across pain modalities except PP, and the fourth cluster demonstrated low sensitivity to PP. Significant correlations were found between psychological measures and Index scores and those differed by sex. Cluster membership was associated with demographic variables of ethnicity and sex as well as specific psychosocial variables, although cluster differences were only partially explained by such factors. These analyses revealed that groups respond differently across varied pain stimuli, and this was not related solely to demographic or psychosocial factors. These findings highlight the need for future investigation to identify patterns of responses across different pain modalities in order to more accurately characterize individual differences in responses to experimental pain.

Adolescent↗

PubMed2005

The effect of propofol on thermal pain perception.

We studied the effect of propofol, a widely used sedative-hypnotic drug, on pain perception. Eighteen subjects received propofol in two sedative concentrations that were balanced and randomized in order. Painful (45 degrees C, 47 degrees C, and 49 degrees C) stimulation temperatures were presented in random order, and nonpainful 31 degrees C stimuli were presented on alternate trials. We used a target-controlled infusion and chose effect site concentrations of 0.5 mug/mL for mild sedation and 1.0 mug/mL for moderate sedation. Using a visual analog scale, subjects rated both pain intensity and unpleasantness higher when sedated with propofol. The average pain intensity was 28/100 for placebo, 35/100 for mild, and 40/100 for moderate sedation. Pain unpleasantness was 23/100 for placebo, 29/100 for mild, and 33/100 for moderate sedation. This effect was unexpected and may be explained by a difference of subjective pain experience by a patient and the perceived level of analgesia by a health care provider in sedated patients. This finding calls further attention to the need for adequate analgesia in patients sedated with propofol.

Adult↗