Pain In Healthy Subjects Research Articles

Glutamate-evoked jaw muscle pain as a model of persistent myofascial TMD pain?

Objective Compare pain-related measures and psychosocial variables between glutamate-evoked jaw muscle pain in healthy subjects (HS) and patients with persistent myofascial temporomandibular disorder (TMD) pain. Design Forty-seven female HS and 10 female patients with persistent myofascial TMD pain participated. The HS received an injection of glutamate into the masseter muscle to model persistent myofascial TMD pain. Participants filled out a coping strategies questionnaire (CSQ), the symptom checklist 90 (SCL-90) and McGill pain questionnaire (MPQ). Pain intensity was assessed on an electronic visual analogue scale (VAS). Pain-drawing areas, numerical rating scale (NRS) scores of unpleasantness, pressure pain thresholds (PPTs) and pressure pain tolerance (PPTOL) were measured. Unpaired t-tests and correlation tests were used for analyses. Results The groups were significantly different when comparing the CSQ scores of control, decrease, diverting attention, increase of behavioural activities and somatization. The peak VAS pain, NRS of unpleasantness and MPQ scores were not significantly different between groups, but PPT and PPTOL were significantly lower in the TMD patients. Significant positive correlations were found in the TMD patients between peak VAS pain and CSQ catastrophizing score and SCL-90 somatization. The scores of PPTs and PPTOLs, in patients showed positive correlations with CSQ reinterpreting pain sensations scores and PPTs correlated with CSQ praying/hoping scores. Conclusions Glutamate-evoked pain responses in HS and persistent myofascial TMD pain have similar sensory-discriminative and affective-unpleasantness components but differ in psychosocial features. This study suggests that experimental designs based on glutamate injection into muscle can provide an appropriate model for elucidating persistent myofascial pain conditions.

Establishing a Link Between Heart Rate and Pain in Healthy Subjects: A Gender Effect

Heart rate (HR) is currently used by rehabilitation clinicians as a complementary objective measure of pain. The premise is that, as pain increases, HR should also increase. However, this relationship is not clearly established. The goal of this study was to verify the relationship between HR and pain perception. Thirty-nine healthy volunteers participated in this experimental study. Painful stimuli were induced by a 2-minute immersion of the hand in hot water (47°C). HR was recorded before and during the stimulation and was matched to a pain rating. We observed a rise of 11% in HR after 2 minutes of immersion. There was a significant intrasubject correlation between HR and pain intensity ( r = 0.50, P < .001) and pain unpleasantness ( r = 0.55, P < .001). Furthermore, there was a strong gender effect in the intersubject correlations. Men presented a strong correlation between mean HR and mean pain perception (intensity: r = 0.77, unpleasantness: r = 0.86), whereas this relationship was absent in women (intensity: r = −0.2, unpleasantness: r = 0.001). In conclusion, results show that, for healthy volunteers, experimental pain can elicit a rise in HR up to 11%. Moreover, the relationship between HR response and pain is gender related. Considering that a positive relationship between HR and pain perception was only found in men, these results do not support a clinical significance of the use of HR for pain evaluation in women. Clinical implications need to be further evaluated with patients before clinicians can use HR as a complementary tool in pain assessment. Perspective A positive correlation between HR and pain was observed for men but not for women. These differences underline the importance of taking into account gender differences in the development of complementary pain assessment. Further research should be conducted to verify the role of sex hormones on heart rate and pain.

Neuronal sensitization for itch in patients with chronic pruritus

Itch is one of the major symptoms of various skin diseases. Although specific neuronal pathways for itch were identified both peripherally and centrally, they still fail to explain itchy skin observed in patients with chronic pruritus. In this study, sensitivity to itchy and painful stimuli in patients with atopic dermatitis was investigated. Histamine‐prick evoked enormous itch in their lesional skin, while less itch in their non‐lesional skin than healthy subjects. Flare reaction was not significantly different between their non‐lesional and lesional skin, rather smaller than healthy subjects. Mechanical (pin‐pricks), electrical, heat and chemical (injection of pH3 solution) stimuli evoked intense itch in their lesional skin and partly also in their non‐lesional skin, while only pain in healthy subjects. Itch was also, but not intensely, evoked in healthy subjects by injection of pH3 solution after sufficient histamine stimuli. These results confirm the presence of itchy skin with hyperkinesis (excessive itch by itchy stimuli) and allokinesis (itch by non‐itchy stimuli) in patients with atopic dermatitis, which is so intense that painful stimuli cannot suppress but evoke itch, and suggest that neuronal sensitization is involved in their itch not only peripherally but also centrally.

Perceptual Matching for Assessment of Itch; Reliability and Responsiveness Analyzed by a Rank-Invariant Statistical Method

The aim of this study was to evaluate the reliability and responsiveness of a new device-perceptual matching by Matcher (Cefar Medical AB, Lund, Sweden)-in the assessment of the progress of experimentally induced itch as well as determine the reliability of the method in patients with skin disease and itch. The perceptual matching unit electrically stimulates the skin of the fingers in the left hand. When the amplitude of the sensation corresponded to that of the experienced itch, the subject was instructed to halt the stimulation and a value was automatically saved in the electronic device. A total of 36 healthy subjects and nine patients participated in the study. The healthy subjects were asked to rate the level of itch every 30 s during the first 5 min and thereafter every minute. The reliability was determined in a test-retest procedure of the time points 5, 10, and 15 min after induction of itching. To test the stability of the method, the first sensation of pain in healthy subjects without itch was determined every 10th minute during 60 min. In patients, the test-retest procedure was repeated within 5 min. Perceptual matching was found to be a reliable method of itch assessment, with no evidence for random individual disagreement between the assessments. The augmented rank order coefficient ra was excellent: 1.00 at 5 min; 0.99 at 10 min; and 1.00 at 15 min. There was a clear indication of responsiveness for detecting changes in itch over time, p<or=0.05. The perceptual matcher device can detect immediate changes in perceived itch and is also sensitive to gradual decreases after the induction of itch. The first sensation of pain in healthy subjects without itch was unaffected when assessed every 10th minute during 60 min. In patients, no evidence for random disagreement or systematic disagreement by group between repeated assessments was detected. The augmented rank order coefficient was high (0.98). In conclusion, Matcher measures itch intensity via perceptual matching with a high reliability and excellent responsiveness. The method is stable and can be recommended as an assessment tool for itch intensity both in experimental conditions as well as in patients with skin disease and itch.

An investigation into the analgesic effects of different frequencies of the amplitude-modulated wave of interferential current therapy on cold-induced pain in normal subjects

Johnson MI, Tabasam G. An investigation into the analgesic effects of different frequencies of the amplitude-modulated wave of interferential current therapy on cold-induced pain in normal subjects. Arch Phys Med Rehabil 2003;84:1387–94. Objective: To investigate the analgesic effects of different amplitude-modulated frequencies of interferential current therapy (IFT) on cold-induced pain in healthy subjects. Design: Single-blind parallel group methodology was used. Subjects completed 6 cycles of the cold-induced pain test (2 pretreatment, 2 during treatment, 2 posttreatment). During each cycle, subjects plunged their hand into iced water and the time taken to reach pain threshold was recorded. The hand remained immersed in the iced water for a further 30 seconds, after which the self-reports of pain intensity and pain unpleasantness were recorded. Setting: Laboratory in the United Kingdom. Participants: Sixty unpaid, pain-free volunteers without a known pathology that could cause pain. Interventions: IFT delivered on the nondominant arm at a “strong but comfortable” intensity without visible muscle twitches, using a quadripolar application technique at 1 of 6 possible amplitude modulated “beat” frequencies (20, 60, 100, 140, 180, 220Hz). Main Outcome Measures: The percentage change in pain threshold, pain intensity, and pain unpleasantness from the pretreatment baseline. Results: Two-way repeated-measures analyses of variance found no effects for groups for pain threshold ( P=.11) or pain ratings ( P>.05). There were no effects for cycle for any of the outcome measures. Effects for group by cycle interaction were noted for pain intensity and unpleasantness ratings ( P<.05), although post hoc analysis failed to determine the nature of this interaction. Conclusions: Experimentally induced cold pain was not influenced by IFT frequencies.

The analgesic effects of interferential (IF) current on cold-pressor pain in healthy subjects: a single blind trial of three IF currents against sham IF and control

Interferential (IF) therapy is well documented as a therapeutic medium for pain relief. Despite widespread use by physiotherapists, there remains very limited laboratory or clinical evidence for the analgesic effect of IF.Fifty volunteers were randomly allocated to one of five groups ( n =10): control group (no treatment throughout); IF 100 Hz applied to the ipsilateral limb; IF 100 Hz applied to the contralateral limb; IF 30 Hz applied to the ipsilateral limb; Sham IF applied to the ipsilateral limb. Subjects were given repeated (six) cycles of cold-pressor pain and pain threshold scores were recorded for each cycle and compared using repeated measure ANOVA. Mean pain threshold values for all groups increased with the exception of the control group: where pain threshold values decreased across the cycles. Pain thresholds within IF treatment groups repeatedly increased, but no more than sham IF. IF at 30 Hz and 100 Hz applied to the contralateral limb offered more consistency in the rise in mean values, with the sham group demonstrating more variation in performance. However, statistical analysis failed to show any significant differences for the treatment effects either within groups across repeated cycles (P=0.123) or between the groups across cycles (P=0.552). IF does not significantly alter pain threshold.

Analgesic Effects of Interferential Therapy Current on Cold-Pressor Pain in Healthy Subjects: Single blind trial of three interferential currents against sham interferential currents and control

Analgesic Effects of Interferential Therapy Current on Cold-Pressor Pain in Healthy Subjects: Single blind trial of three interferential currents against sham interferential currents and control

Psychological and functional profiles in select subjects with low back pain

Background context: Some researchers have found a correlation of poor treatment outcomes in patients with low back pain and abnormal psychological profiles, whereas others have failed to confirm this correlation. A critical feature of this debate has been whether abnormal psychological profiles seen in patients with back pain are the result of the ongoing back pain or whether pre-existing psychological features predispose to a poor clinical outcome. Purpose: To determine the relationship of psychometric testing scores to the presence and duration of back pain of differing causes. Study design/setting: This was a prospective observational study of the psychological profiles of groups of patients with low back pain and controls. Patient sample: Subjects having a variety of painful back conditions (n=310) were compared with a control group of subjects without low back complaints who had undergone cervical spine surgery (n=73). Outcomes measures: Psychometric testing (Modified Zung and Modified Somatic Pain Questionnaire) was performed along with pain scores (visual analog scale [VAS]), a standardized Low Back Pain Questionnaire, and the Oswestry Low Back Pain Disability Questionnaire in the evaluation of back pain and control subjects. Methods: The subjects with painful back conditions included patients with presumed discogenic pain undergoing discography (n=95); patients with symptomatic isthmic spondylolisthesis coming to fusion (n=61); patients with chronic vertebral osteomyelitis before diagnosis and treatment (n=39). There was also a nonpatient group of soldiers with chronic low back pain not seeking medical care (n=115). The control subjects without low back pain consisted of a group who had undergone cervical spine surgery (n=73). Psychometric testing was performed and compared in the evaluation of subjects having these different painful back conditions. Analysis was done comparing pain scores, function scores, and psychological testing scores between the symptomatic and asymptomatic groups. Results: The VAS maximum in last week score for the entire group was 7.1, and scores were not significantly different in all low back pain groups. The Oswestry scores were poorest in the discography group compared to spondylolisthesis and osteomyelitis. Functional scores were similar in the soldiers with low back pain and controls without low back pain. Both Depression and Somatic Pain scores were most abnormal in the discogenic low back pain group. Only 21% of this group had normal scores, compared with 71% of the spondylolisthesis group, 79% of osteomyelitis group, and 88% of the group with chronic low back pain not seeking treatment ( p<.001 in all groups). The asymptomatic control group had 85% normal scores. Conclusions: Despite similar pain levels and pain duration, patients with the discographic diagnosis of discogenic back pain have poorer functional scores and very abnormal psychological scores compared with other subjects with chronic low back pain resulting from spondylolisthesis requiring surgery or chronic pyogenic osteomyelitis. Chronic moderately severe mechanical low back pain in healthy subjects was not associated with abnormal psychological scores or functional disability.

The Effects of Controlled Delta Sleep Deprivation on Experimental Pain in Healthy Subjects

Objectives: The interaction between sleep and pain is important in patients suffering from rheumatic illness. Not only can pain disturb sleep, but alterations in the deeper sleep stages induced by the disease process may have the potential to decrease the pain threshold. Previous studies however, have shown diverging results. In the current experiment we studied the effects of deep sleep deprivation using a standardized, computer-assisted system on subjective symptoms and pain elicited by different experimental modalities.Methods: Ten healthy males, mean age 22.7 years, were subjected to deprivation of the deeper sleep stages for three nights. Following a baseline recording, sleep was analyzed in 2 s segments with on-line frequency analysis. If any 30 s epoch contained more than seven 2 s segments dominated by low frequency content corresponding to deep sleep, the sleep was disturbed by an acoustic stimulus. The amount of delta power was computed in sleep stages non-rapid-eye-movement [NREM] 2–4. Subjects...

A double blind placebo controlled investigation into the analgesic effects of inferential currents (IFC) and transcutaneous electrical nerve stimulation (TENS) on cold-induced pain in healthy subjects

Transcutaneous electrical nerve stimulation (TENS) and interferential currents (IFC) are used by physiotherapists for the management of painful conditions. It is claimed that the analgesic profiles of TENS and IFC differ although no studies have directly compared the analgesic effects of the two modalities. The aim of this double blind placebo controlled study was to compare the analgesic effects of TENS and IFC on cold-induced pain in healthy volunteers. Twenty one subjects completed six cycles of the cold-induced pain test (two pre-treatment, two during treatment, and two post-treatment). During each cycle pain threshold was recorded as the time from immersion of the subject's hand in cold water to the first sensation of pain and pain intensity and unpleasantness ratings were recorded using visual analogue scales. Subjects received one of the following treatments during the two treatment cycles: IFC, TENS, or sham electrotherapy. IFC and TENS were delivered at a ''strong but comfortable'' intensity via two electrodes applied over the anterior aspect of the forearm. Sham electrotherapy was administered by a ''dummy'' stimulator with no current output. All stimulators were visually identical. Analysis of the results found that IFC and TENS significantly elevated pain threshold when compared to sham electrotherapy (P <. 05). There were no significant differences in the magnitude of the increase in pain threshold between IFC and TENS. No significant changes in pain intensity or unpleasantness ratings were found between the three treatment groups. We conclude that there were no differences in the analgesic effects of IFC and TENS under the present experimental conditions.

Frequency, intensity, development and repercussions of postoperative pain as a function of the type of surgery

Type of surgery is the most important factor conditioning intensity and duration of postoperative pain. Thoracic and spinal surgery are the most painful procedures. Abdominal, urologic and orthopedic surgery lead to severe postoperative pain. Duration of severe pain rarely exceeds 72 hours. Mobilization increases pain intensity after abdominal, thoracic and orthopaedic surgery. Pain could occur after daycase minor surgical procedures and is often underestimated. Postoperative complications related to pain are difficult to disclose because of the interposition of the direct effects of analgesic treatments. Respiratory and cardiovascular postoperative complications are unrelated to postoperative pain in healthy subjects. This could be different in high risk patients. The surgical procedure is the major determinant of metabolic and psychologic postoperative deterioration. Adequate pain relief allows postoperative rehabilitation and physiotherapy programmes after abdominal and orthopaedic surgery. This could be expected to reduce hospital stay and improve convalescence.

The Analgesic Effects of Different Swing Patterns of Interferential Currents on Cold-induced Pain

Despite the widespread use of interferential currents (IFC) by physiotherapists to manage painful conditions, evidence for analgesic effects is sparse, and information on the optimal stimulating parameters is lacking. The aim of this single-blind placebo controlled preliminary study was to examine the analgesic effects of 6∧6 and 11 swing patterns of IFC on cold-induced pain in healthy subjects. Fifteen healthy university student volunteers were randomly allocated to receive either active IFC 6∧6, active IFC 11 or sham IFC. During the experiment, which lasted a total of 60 minutes, each subject completed six identical ten-minute experimental cycles of the cold-induced pain test. During each cycle the time to pain threshold and pain intensity rating measurements were recorded as outcome measures. Experimental cycles 1 and 2 were pre-treatment, cycles 3 and 4 during treatment (active IFC or sham IFC) and cycles 5 and 6 were post-treatment. The main finding of this study was that there was a larger rise in pain threshold for subjects receiving the 6∧6 swing pattern when compared to 11 IFC or sham IFC. The rise in pain threshold was rapid in onset for the 6∧6 IFC group, occurring within ten minutes of IFC switch on and having returned to baseline within 20 minutes of IFC switch-off. No effects were found for pain intensity ratings during treatment. In conclusion, the differential analgesic effects between 6∧6 and 11 swing patterns of IFC found in the present study may have implications for IFC settings used in the clinic. However, one should be cautious in extrapolating the results of this preliminary study on healthy subjects to patients suffering pain from injury and disease. It is imperative to confirm these findings in patient populations. Despite the widespread use of interferential currents (IFC) by physiotherapists to manage painful conditions, evidence for analgesic effects is sparse, and information on the optimal stimulating parameters is lacking. The aim of this single-blind placebo controlled preliminary study was to examine the analgesic effects of 6∧6 and 11 swing patterns of IFC on cold-induced pain in healthy subjects. Fifteen healthy university student volunteers were randomly allocated to receive either active IFC 6∧6, active IFC 11 or sham IFC. During the experiment, which lasted a total of 60 minutes, each subject completed six identical ten-minute experimental cycles of the cold-induced pain test. During each cycle the time to pain threshold and pain intensity rating measurements were recorded as outcome measures. Experimental cycles 1 and 2 were pre-treatment, cycles 3 and 4 during treatment (active IFC or sham IFC) and cycles 5 and 6 were post-treatment. The main finding of this study was that there was a larger rise in pain threshold for subjects receiving the 6∧6 swing pattern when compared to 11 IFC or sham IFC. The rise in pain threshold was rapid in onset for the 6∧6 IFC group, occurring within ten minutes of IFC switch on and having returned to baseline within 20 minutes of IFC switch-off. No effects were found for pain intensity ratings during treatment. In conclusion, the differential analgesic effects between 6∧6 and 11 swing patterns of IFC found in the present study may have implications for IFC settings used in the clinic. However, one should be cautious in extrapolating the results of this preliminary study on healthy subjects to patients suffering pain from injury and disease. It is imperative to confirm these findings in patient populations.

Ethnocultural differences in the analgesic effects of placebo transcutaneous electrical nerve stimulation on cold-induced pain in healthy subjects: A preliminary study

With the emphasis placed on placebo-controlled methodology in the testing of novel therapies, it is important that placebo effects are studied in their own right. Placebo effects, which may occur whenever a patient and a physician perceive a treatment as effective, may be susceptible to ethnocultural influences. However, experiments utilizing human subjects rarely take ethnocultural effects into account. This preliminary single-blind study examined the analgesic effects of placebo transcutaneous electrical nerve stimulation (TENS) on cold-induced pain in 24 healthy first-generation UK-born Asian and White Anglo-Saxon subjects. Pain threshold and pain intensity rating measurements were taken during six 10-min experimental cycles (two pre-, two during and two post-treatment) of the cold-induced pain test. A portable TENS unit with no current output was used to administer placebo TENS during the two treatment cycles. Two-way RM ANOVA performed on log transformed pain threshold and pain intensity data found significant effects for cycle ( P ≤0.01) and cycle x group interaction ( P ≤0.01). Further analysis found that Asian subjects produced a significantly greater increase in pain threshold and a significantly greater decrease in pain intensity rating during placebo TENS than White subjects. These findings suggest that ethnocultural background is an important determinant in placebo-induced analgesia in the laboratory setting. It is hoped that this preliminary study will serve to emphasize that ethnocultural factors should be considered during experiments utilizing human subjects.

Effects of diclofenac and dextropropoxyphene on experimental thermal pain in healthy subjects

Rundgren M, Kankaanranta H, Nurmikko T, Moilanen E. Effects of diclofenac and dextropropoxyphene on experimental thermal pain in healthy subjects. Inflammophannacology. 1997;5:l-7. In the present double-blind placebo-controlled study the effects of a single oral dose of 50 mg diclofenac or 65 mg dextropropoxyphene were determined on thermal thresholds in 84 healthy subjects. Perception thresholds for warm, cold, heat pain and cold pain as well as heat-pain tolerance were determined by the Marstock method before and 90 min after administration of the drug. No alterations in thermal thresholds were observed except a slight unexpected decrease in heat-pain perception threshold in the dextropropoxyphene group. The data confirms the reproducibility of the Marstock method and the lack of interference with some analgesics in the common use. The apparent lack of analgesic effect of two clinically effective analgesics, diclofenac and dextropropoxyphene, supports the assumption that these compounds have a poor analgesic action in physiological and neural pain. The data suggest that determination of drug effects on heat-pain thresholds in uninjured skin may underestimate clinical action of analgesic drugs and is therefore not sufficient for testing or demonstrating clinical efficacy of analgesic compounds.

An examination of the analgesic effects of microcurrent electrical stimulation (MES) on cold-induced pain in healthy subjects

Microcurrent electrical stimulation (MES) is an electrotherapeutic approach proposed by manufacturers for the management of acute and chronic pain. Evidence for analgesic efficacy is anecdotal and few controlled studies have been performed to date. This single-blind, placebo-controlled study examined the analgesic effects of MES on experimentally induced pain threshold and pain intensity rating in 36 healthy non-paid university student volunteers. Pain threshold and pain intensity recordings to cold-induced pain were made before, during and after a 20 min treatment session. Subjects received either active MES (DC biphasic pulses, 600 μA, 103 pulses per second) or placebo MES (no current output). The results showed no significant differences between active MES and placebo MES for the change in ice pain threshold or pain intensity rating during treatment. However, a significant increase in pain threshold was found in both active MES and placebo MES during the treatment cycles when compared to pre-treatment baseline. This change in pain threshold during active and placebo MES was similar in magnitude to placebo transcutaneous electrical nerve stimulation (TENS) and lower than active TENS as previously reported by ourselves. We conclude that the analgesic effects of active MES on cold-induced pain in healthy subjects were no greater than placebo. It is important to extend these laboratory findings by investigating the clinical efficacy of MES in patients with pain.

The analgesic effects of interferential therapy on cold-induced pain in healthy subjects: a preliminary report

Interferential (IF) therapy is an electrotherapeutic modality used by physiotherapists for the management of a variety of painful conditions. However, the analgesic efficacy of IF remains in doubt and its mechanism of analgesic action is far from understood. This preliminary study examined the effect of IF on cold-induced pain threshold and tolerance in healthy student volunteers. Interferential therapy, when applied to the anterior aspect of the forearm of healthy subjects, significantly elevated ice pain threshold when compared with a control (no treatment) group. These preliminary findings provide objective evidence for the analgesic effects of IF currents.

Suprasensitivity to calcitonin gene-related peptide but not vasoactive intestinal peptide in women with chronic pelvic pain.

Chronic pelvic pain in women is associated with radiological evidence of pelvic venous dilatation and reduced flow, termed 'pelvic congestion'. The aim of this study was to elucidate a possible role in this condition for vasoactive intestinal peptide and calcitonin gene-related peptide, both localized in perivascular nerves in the ovaries and uterus. Healthy volunteers and women with chronic pelvic pain and venous congestion received intravenous infusions of vasoactive intestinal peptide (n = 15), calcitonin gene-related peptide (n = 15) or a bland infusate (n = 7). Changes in the uterovaginal and skin blood flow were assessed by continuous measurement of vaginal, axillary, cheek and hand temperature. During calcitonin gene-related peptide infusion median hand temperature changes were +0.97 degrees C in women with pelvic pain and -0.03 degrees C in healthy volunteers (p < 0.05). There were no differences between groups in hand and cheek temperature responses to vasoactive intestinal peptide infusion. Vasoactive intestinal peptide and calcitonin gene-related peptide appeared to dilate the uterovaginal vasculature in healthy subjects but not in those with pelvic pain. Vasoactive intestinal peptide and calcitonin gene-related peptide did not provoke pain in healthy subjects but in those with pelvic pain, symptoms were significantly exacerbated during calcitonin gene-related peptide infusion but not by vasoactive intestinal peptide. Changes in plasma follicle stimulating hormone, luteinizing hormone and oestradiol during either infusion were not significant. These findings indicate greater sensitivity to calcitonin gene-related peptide in women with pelvic pain and suggest a possible underlying neurovascular disorder.

L-Tryptophan supplementation does not affect postoperative pain intensity or consumption of analgesics

Aiming at optimizing serotonin levels in endogenous pain-modulating systems, l-tryptophan supplementation pre- and postoperatively (2 g/day for 7 days) did not affect pain development or analgesic consumption after third molar surgery. Biological effects related to an increase in mood were observed, however, indicating transport of l-tryptophan to the central nervous system. The findings are discussed in relation to earlier reports on favorable effects of l-tryptophan on experimental pain in healthy subjects and in chronic pain patients.

Adaptive psychophysical methodology applied to sensory-discriminative tests of pain perception

Compare pain-related measures and psychosocial variables between glutamate-evoked jaw muscle pain in healthy subjects (HS) and patients with persistent myofascial temporomandibular disorder (TMD) pain.Forty-seven female HS and 10 female patients with persistent myofascial TMD pain participated. The HS received an injection of glutamate into the masseter muscle to model persistent myofascial TMD pain. Participants filled out a coping strategies questionnaire (CSQ), the symptom checklist 90 (SCL-90) and McGill pain questionnaire (MPQ). Pain intensity was assessed on an electronic visual analogue scale (VAS). Pain-drawing areas, numerical rating scale (NRS) scores of unpleasantness, pressure pain thresholds (PPTs) and pressure pain tolerance (PPTOL) were measured. Unpaired t-tests and correlation tests were used for analyses.The groups were significantly different when comparing the CSQ scores of control, decrease, diverting attention, increase of behavioural activities and somatization. The peak VAS pain, NRS of unpleasantness and MPQ scores were not significantly different between groups, but PPT and PPTOL were significantly lower in the TMD patients. Significant positive correlations were found in the TMD patients between peak VAS pain and CSQ catastrophizing score and SCL-90 somatization. The scores of PPTs and PPTOLs, in patients showed positive correlations with CSQ reinterpreting pain sensations scores and PPTs correlated with CSQ praying/hoping scores.Glutamate-evoked pain responses in HS and persistent myofascial TMD pain have similar sensory-discriminative and affective-unpleasantness components but differ in psychosocial features. This study suggests that experimental designs based on glutamate injection into muscle can provide an appropriate model for elucidating persistent myofascial pain conditions.

Study of expepjivo tal pain measures and nociceptive reflex in chronic pain patients

Compare pain-related measures and psychosocial variables between glutamate-evoked jaw muscle pain in healthy subjects (HS) and patients with persistent myofascial temporomandibular disorder (TMD) pain.Forty-seven female HS and 10 female patients with persistent myofascial TMD pain participated. The HS received an injection of glutamate into the masseter muscle to model persistent myofascial TMD pain. Participants filled out a coping strategies questionnaire (CSQ), the symptom checklist 90 (SCL-90) and McGill pain questionnaire (MPQ). Pain intensity was assessed on an electronic visual analogue scale (VAS). Pain-drawing areas, numerical rating scale (NRS) scores of unpleasantness, pressure pain thresholds (PPTs) and pressure pain tolerance (PPTOL) were measured. Unpaired t-tests and correlation tests were used for analyses.The groups were significantly different when comparing the CSQ scores of control, decrease, diverting attention, increase of behavioural activities and somatization. The peak VAS pain, NRS of unpleasantness and MPQ scores were not significantly different between groups, but PPT and PPTOL were significantly lower in the TMD patients. Significant positive correlations were found in the TMD patients between peak VAS pain and CSQ catastrophizing score and SCL-90 somatization. The scores of PPTs and PPTOLs, in patients showed positive correlations with CSQ reinterpreting pain sensations scores and PPTs correlated with CSQ praying/hoping scores.Glutamate-evoked pain responses in HS and persistent myofascial TMD pain have similar sensory-discriminative and affective-unpleasantness components but differ in psychosocial features. This study suggests that experimental designs based on glutamate injection into muscle can provide an appropriate model for elucidating persistent myofascial pain conditions.