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Influence of skin temperature on heat pain threshold in humans.

We compared the effect of skin temperature on the critical threshold temperature eliciting heat pain with the effect of skin temperature on the response latency to the first heat pain sensation in healthy human subjects. Also, we determined the effect of the duration of a heat stimulus ramp on pain threshold. Furthermore, we determined the effect of skin temperature on mechanically induced pain. We found that the latency to the first pain sensation induced by a radiant heat stimulus was significantly decreased with an increase in the skin temperature (25-35 degrees C). However, independent of the rate of the stimulus rise (3-10 degrees C/s) and independent of the stimulus location (hairy vs glabrous skin), the threshold temperature for eliciting the heat pain sensation, determined with a contact thermostimulator, was not changed by a change in the skin temperature in the same subjects. With a fast rate of stimulus rise, a higher pain threshold was obtained than with a slow rise of stimulus temperature. However, this difference was found only with subject-controlled ascending stimuli (method of limits) but not with experimenter-controlled, predetermined stimulus ramps (method of levels). The heat pain threshold was higher in the glabrous skin of the hand than in the hairy skin of the forearm. With increasing stimulus duration (2.5-10 s), the threshold temperature eliciting the heat pain sensation was significantly decreased. The mechanically induced pain threshold was not influenced by the skin temperature. The results indicate that the critical temperature for eliciting heat pain is independent of the skin temperature in humans. However, a change in skin temperature is an important source of an artefactual change in heat pain sensitivity when the radiant heat method (latency or energy) is used as an index of pain sensitivity. With a method dependent on reaction time (the method of limits), the heat pain threshold was artefactually increased, with fast rates of stimulus rise due to the long delay of slowly conducting heat pain signals in reaching the brain. With an increase in the duration of the heat stimulus, the critical temperature for eliciting pain sensation was significantly decreased, which may be explained by central neuronal mechanisms (temporal summation).

Adult↗

Increased pain threshold following electroacupuncture: analgesia is induced mainly in meridian acupuncture points.

UNLABELLED: Pain thresholds were determined before and after electroacupuncture of the dorsal aspect acupuncture points (AP) of the hand and non acupuncture points (NAP) located 15 mm from the traditional acupuncture points to assess changes in pain threshold thus provoked. METHODS: In eight volunteers the pain threshold of specific points was determined before and after acupuncture in the Hegu point (L.I. 4), at the back of the hand. A pressure dolorimeter was used to evaluate pain threshold at the Yangxi (L.I. 5) and Quchi (L.I. 11) points and at sites 15 mm from them. The effects on pain threshold were also measured at Yingxiang (L.I. 20) on both sides. RESULTS: Before electrostimulation there were no significant differences among the pain thresholds in both AP and NAP. After electrostimulation of the Yangxi point, pain threshold raised from 5.20 kg/sq.cm to 9.20 kg/sq.cm (p < 0.01); acupuncture at Quchi caused the threshold to increase from 5.36 kg/sq.cm to 9.20 kg/sq.cm (p < 0.01) and Yingxiang stimulation changed threshold from 2.63 kg/sq.cm to 3.83 kg/sq.cm (p < 0.051) at the point on the same side and from 2.26 kg/sq.cm to 3.90 kg/sq.cm (p < 0.05) in the opposite side. Before electroacupuncture the pain thresholds at all the tested sites were not statistically different (p > 0.1). After electrostimulation the pain threshold increased 77% at L.I. 5 but went up just 9% and 6% 15 mm from L.I. 5 (p < 0.01); threshold increased by 70% at L.I. 11 but only by 6% and 7% (p < 0.01) 15 mm from L.I. 11. CONCLUSIONS: The pain threshold increased significantly in all tested sites after electroacupuncture but the analgesic effect was predominant in those points lying along the acupuncture meridians.

Acupuncture Analgesia↗

Pressure pain threshold evaluation of the effect of spinal manipulation in the treatment of chronic neck pain: a pilot study.

Nine subjects with chronic mechanical neck pain syndromes were evaluated for pressure pain threshold (PPT) over standardized tender points in the paraspinal area surrounding a manipulable spinal lesion. The subjects were then allocated randomly to an intervention consisting of either an oscillatory mobilization of the cervical spine (n = 4), which was designated as the control procedure, or a rotational manipulation of the cervical spine (n = 5). An assessor-blinded re-evaluation of the pressure pain threshold levels was conducted after 5 min. In the group receiving a manipulation the mean increases in pressure pain threshold ranged from 40-56% with an average of 45%. In the control group no change in any of the pressure pain thresholds was found. These results were analyzed using ANOVA and were found to be statistically significant (p less than 0.0001). This study confirms that manipulation can increase local paraspinal pain threshold levels. The use of the pressure pain threshold meter allows for the determination of such a beneficial effect in the deeper tissues.

Adult↗

Sensory detection and pain thresholds in spinal cord injury patients with and without dysesthetic pain, and in chronic low back pain patients.

In an effort to understand the mechanisms involved in dysesthetic pain syndrome (DPS) in spinal cord injury (SCI) patients, four groups of 13 subjects each--SCI subjects with DPS, SCI subjects without pain, chronic low back pain subjects, and control subjects--were examined for sensory detection and pain thresholds at forearm, neck, and rostral trunk areas. Results indicated that the SCI pain group had significantly lower pain thresholds at all skin sites, compared to the SCI no-pain and chronic low back pain groups, and at the rostral trunk skin site, compared to the control group. The SCI pain group also showed a lower sensory detection threshold at the rostral trunk skin site than did the SCI no-pain group. Equally important, the SCI no-pain group had detection and pain thresholds significantly higher than those of the control group. The results suggest fundamental differences in somatosensory processing when DPS is or is not a consequence of SCI.

Adult↗

Evaluation of pain threshold using a simple pressure algometer.

Pain threshold was measured using a simple pressure algometer in 190 subjects. The measurement had a highly acceptable intra-observer error. Significantly lower pain thresholds were observed in all of the five areas of the body studied in females. The most sensitive area was the forehead. There was a higher pain threshold in the dominant hand. Anxiety and fear of pain significantly reduced the threshold.

Adolescent↗

The effects of non-painful transcutaneous electrical nerve stimulation on cutaneous pain threshold and muscular reflexes in normal men and in subjects with chronic pain.

In healthy subjects and in subjects with chronic myofascial pain of one lower limb, the following was measured in both lower limbs: (i) sequential Hoffman (H) reflex, (ii) sequential Achilles tendon (T) reflex, (iii) cutaneous pain threshold determined with electrical stimuli, before, during and after transcutaneous electrical nerve stimulation (TENS). In healthy subjects no significant differences were observed between the pain thresholds of the two limbs. During and after TENS, changes of the reflexes were related to the pain thresholds. In the pathological subjects a significant difference of pain threshold was present between the affected limb and the contralateral one. An important difference between healthy and pathological subjects is not the quality but the quantity of the changes induced by TENS, in the sense that the levels of inhibition and facilitation of the reflexes are more evident in patients with pain. Indeed, TENS induces a reset of sensory and of motor system and a parallel long lasting effect both on sensory and on muscular function, with concomitant pain relief in the pathological subjects.

Adult↗

[Effect of estrous cycle phase on pain threshold in female white rats].

Pain thresholds and body resistance in female Wistar rats were determined during estrous cycle stages. The flinch and shuffle thresholds were increased on the 3rd day of measurement in diestrus and estrus but not in proestrus and metestrus as compared with the thresholds during the 1st day of recording. The thresholds decreased as of the 7th day to the 14th day. Daily threshold measurements raised the body resistance on the 7th day of recording. In contrast to the pain thresholds, the body resistance change had not a stage-dependent character.

Animals↗

Does acute hyperglycaemia influence heat pain thresholds?

The influence of acute hyperglycaemia on pain sensation was assessed in eight young adult non-diabetic subjects. Acute hyperglycaemia was induced with IV glucose in a double blind fashion, with IV saline as a control. Pain thresholds were assessed by a painful heat stimulus delivered by a Marstock thermode on the thenar eminence. Heat pain thresholds did not significantly alter during either acute hyperglycaemia or the control saline infusion. Previous work demonstrating a lowering of electrical pain thresholds by hyperglycaemia has therefore not been confirmed using a natural painful stimulus.

Adolescent↗

[Auditory training with wide-band white noise: effects on the pain threshold and pure tone thresholds].

The auditory training with wide-band white noise is a methodology for the qualitative recovery of the hearing loss in people suffering from sensorineural hearing loss. It is based on the application of a wide-band white modified noise. In a prospective study, we have assessed the modifications of the total auditory threshold (UAt), the conversational auditory threshold (UAc), and the pain threshold (Ud) in a sample of 48 patients, who have followed a program of 15 auditory training with wide-band white noise sessions. The average improvements of the variables expressed in percentage are 0.78% for the UAt, 0.64% for the UAc, and 5.31% for the Ud. From our results, it can be deduced that the auditory training with wide-band white noise does not modify the pure tone thresholds, but it moves the pain threshold towards higher intensities, enlarging the dynamic auditory field.

Acoustic Stimulation↗

Experimental pain thresholds and plasma beta-endorphin levels during exercise.

Experimental pain thresholds (electrical intracutaneous finger and dental pulp stimulation) and plasma hormone levels (beta-endorphin, cortisol, and catecholamines) were measured in ten healthy sportive men before, during, and after progressively more strenuous physical exercise. In a double-blind study conducted on two different days, 20 mg of the opioid-antagonist naloxone or placebo was administered prior to exercise. A significant pain threshold elevation was found during exercise for finger (ANOVA, P less than 0.004) and dental pulp stimulation (P less than 0.01). Pain threshold elevation was most pronounced during maximal exertion, at which time the subjects reported the greatest subjective fatigue. Thresholds remained elevated 10-15 min after the end of exercise, and, 60 min after exercise, thresholds returned to baseline values. The subjective magnitude estimation of suprathreshold stimuli was significantly reduced (P less than 0.0001) 5-10 min after exercise. Plasma beta-endorphin, cortisol, and catecholamines increased significantly (P less than 0.0005, all values) during exercise. Plasma beta-endorphin levels did not correlate significantly with pain thresholds (r = -0.37, NS). Naloxone failed to affect pain thresholds, although beta-endorphin and cortisol increased significantly more (P less than 0.02) during exercise after naloxone. It is concluded that short-term, exhaustive physical exercise can evoke a transient elevation in pain thresholds. This exercise-induced elevation in pain threshold does not, however, appear to be directly related to plasma endorphin levels.

Adult↗

[Reversal by the calcium ion of the pain threshold elevated by calcium channel blockers].

We investigated calcium ion effects on pain thresholds by iontophoresis in healthy adult volunteers. The pain thresholds were measured by the pain thermometer to evaluate the effect of iontophoresis. At first, one of calcium channel blockers (nicardipine, verapamil or diltiazem) was administered by iontophoresis with 1.0 mA for 10 minutes. Then, next to calcium channel blockers, calcium chloride or saline was locally administered after the elevation of pain threshold had been recognized and the pain threshold had been measured again. Calcium ion decreased the elevation of pain threshold significantly, but saline had no effect. These results suggest that not only sodium channel but also calcium channel influences pain mechanism during iontophoresis.

Adult↗

Aspects of fibromyalgia in the general population: sex, pain threshold, and fibromyalgia symptoms.

OBJECTIVE: To investigate relationships between sex, pain threshold and fibromyalgia (FM) symptoms in the general population. METHODS: Data were obtained from a randomized populations survey of 3,006 persons in Wichita, KS and a subsample of 391 who completed a detailed interview and had an examination. Tender point counts, dolorimetry scores, clinical and psychological variables were measured. RESULTS: Dolorimetry scores were 2.04 kg/cm (1.42-2.66) lower in women than men, and women were almost 10 times more likely to have 11 tender points [OR 9.6 (2.00-46.3)] than men. Women are also more likely to have FM symptoms than men: "Pain all over," [OR 3.94 (1.34-11.38)], sleep disturbance [OR 3.06 (1.45-6.46)], fatigue [OR 4.52 (2.03-10.09)], and irritable bowel syndrome [OR 5.23 (1.83-14.96)]. Tender point counts are more correlated with FM symptoms than dolorimetry scores. CONCLUSION: Symptoms of FM are correlated with pain threshold in the general population, but tender point counts correlate better than dolorimetry. These 2 measures of pain threshold assay different but overlapping factors. Pain threshold is lower in women; and women have more FM symptoms. Decreased pain threshold correlates with all of the symptoms of FM, even in those who do not meet criteria for the syndrome. This suggests that decreased pain threshold, as measured by the tender point counts, is an intrinsically important aspect of patient distress, regardless of the extent and kind of concomitant disease; and that much can be learned about patients by employing this examination.

Disability Evaluation↗

Pain threshold in relation to sex hormones.

Pain threshold to mechanical stimulus was determined in 140 subjects comprising of healthy volunteers of both sexes and of different ages, females taking oral contraceptives and bilaterally oopherectomised females. Pain threshold was observed to be low in oopherectomised females, boys and girls and intermediate in healthy males. It was high in menstruating females aged 18-21 years. There was a marked fluctuation in pain threshold in menstruating females. It was low at menstrual phase. In females taking oral contraceptives it was high at pre and midmenstrual phases. In females not taking oral contraceptives it was low at pre-menstrual and high as midmenstrual phases.

Adolescent↗

Cephalic muscle tenderness and pressure pain threshold in a general population.

Tenderness and pain thresholds in pericranial muscles were studied in a general population. A random sample of 1000 adults aged 25-64 years was drawn as part of the Glostrup Population Studies, and 740 adults were examined. This study was part of a multifacetted, epidemiological study of different headache disorders according to the new headache classification. Manual palpation and pressure pain threshold with an electronic pressure algometer were performed by observers blinded to other information such as the person's history of headache, previous illness and mental state. The muscles most commonly tender to manual palpation were the lateral pterygoid (55%), the trapezius (52%), and the sternocleido-mastoid muscles (51%). Females were more tender than men in all the muscles examined by manual palpation. In total, the young age group was more tender than the old age group (P = 0.03). Pressure pain thresholds on temporal muscles showed lower thresholds in women than in men (P less than 10(-3)), and in the total population thresholds increased with age (P less than 0.05). No side-to-side difference in tenderness by manual palpation was found, while the right side showed increased pain thresholds in right-handed individuals (P less than 10(-4)). No side-to-side difference was found in left-handed persons. This study provides data about the normal population and forms the necessary basis for evaluating the importance of muscle tenderness in headache subjects and other selected groups.

Adult↗

Pressure pain threshold in the detection of masticatory myofascial pain: an algometer-based study.

AIMS: To compare pressure pain threshold (PPT) values for masticatory muscles in patients with signs and symptoms of myofascial pain and in asymptomatic individuals. METHODS: Fifty women with masticatory myofascial pain comprised the symptomatic group (group 1), while 49 TMD symptom-free women were selected as controls (group 2). The PPT was obtained with the aid of an algometer by applying pressure to the masseter and to the anterior, middle, and posterior temporalis. A 90.8% specificity value was used to determine the appropriate PPT cutoff values for all 4 muscles studied. Receiver operator characteristic (ROC) curve areas and the likelihood ratio (LR) were also evaluated. RESULTS: The 3-way ANCOVA test (group, muscle, and side) revealed a significantly lower PPT for all muscles in the symptomatic group (P < .001). The lowest overall PPT was found for the masseter muscle, followed by the anterior, middle, and posterior temporalis (P < .001). The 90.8% specificity was obtained with PPT values of 1.5 kgf/cm2 for the masseter, 2.47 kgf/cm2 for the anterior temporalis, 2.75 kgf/cm2 for the middle temporalis, and 2.77 kgf/cm2 for the posterior temporalis. The anterior temporalis had the highest LR. ROC curve areas of 0.84, 0.92, 0.90, and 0.90 were obtained for the masseter, anterior, middle, and posterior temporalis, respectively. CONCLUSION: The masseter and temporalis muscles require different pressures for distinguishing masticatory myofascial pain patients from asymptomatic individuals. Because the highest sensitivity (77%) and LR were found for the anterior temporalis, this muscle was considered to have the most suitable discriminative capacity.

Adolescent↗

Pain threshold and tolerance in Alzheimer's disease.

We tested both pain thresholds and pain tolerance in patients with Alzheimer's disease (AD) by means of phasic and tonic noxious stimuli. In the first case, electrical stimulation was used, whereas in the second case arm ischemia was studied. By comparing AD patients with normal subjects of the same age, we found no differences in stimulus detection and pain thresholds, whereas a clearcut increase in pain tolerance was present in AD patients. The severity of AD was assessed by means of the Mini Mental State Examination test (MMSE) and the spectral analysis of the electroencephalogram (EEG). There was a straightforward correlation between MMSE scores and pain tolerance such that the more severe the cognitive impairment the higher the tolerance to pain. In addition, analysis of the EEG power spectra indicated that patients with low alpha and high delta peaks showed an increase in pain tolerance to both electrical stimulation and ischemia. These findings show that, whereas the sensory-discriminative component of pain is maintained in AD patients, pain tolerance is altered and depends on cognitive and affective factors. Thus, pain tolerance is tightly related to the severity of the disease according to the rule, 'the more severe the MMSE and EEG changes, the higher the tolerance to pain'.

Aged↗

Extremely low frequency magnetic field exposure modulates the diurnal rhythm of the pain threshold in mice.

The aim of this study was to determine whether exposure to extremely low frequency magnetic field (ELF-MF) affects the normal diurnal rhythm of the pain threshold in mice. Pain thresholds were evaluated in mice using the hot plate test. A significant increase of pain threshold during night was observed compared to that during day. This rhythm was attenuated by both constant exposure to light (LL) and constant exposure to darkness (DD) for 5 days. Under DD exposure, the diurnal rhythm in pain threshold was restored when mice were exposed to ELF-MF (60 Hz, 1.5 mT for 12 h daily, from 08:00 to 20:00 h) for 5 days. The diurnal rhythm was not reversed under dark with reversed ELF-MF cycle (exposure to 1.5 mT from 20:00 to 08:00 h, next day) for 5 days, although pain threshold in the ELF-MF exposed period of night was slightly decreased. The diurnal rhythm of melatonin analgesic effect related to pain threshold was also observed under DD by the exposure of ELF-MF for 5 days, but not for 5 nights. The present results suggest that ELF-MF may participate in the diurnal rhythm of pain threshold by acting on the system that is associated with environmental light-dark cycle.

Animals↗

The effect of an electronic analgesia device on dental pain thresholds.

The effect of UltraCalm, an electronic dental analgesia (EDA) device, on dental pain thresholds was studied in 32 volunteers. For each subject, two initial baseline measurements of dental pain thresholds were made using an electric pulp tester. Pain thresholds were then measured during EDA with either UltraCalm or an inactive (placebo) device. No significant differences were found between the first and second baseline threshold measurements nor between the pain thresholds measured during the application of the UltraCalm and placebo devices. The mean baseline pain threshold was significantly lower than the threshold measured during application of the placebo device, but was not significantly different from the threshold during application of UltraCalm. it is concluded that UltraCalm has no consistent effect in altering dental pain thresholds.

Anesthesia, Dental↗