Fall of skin impedance and bone and joint pain

Utilising electrodermal activity sensor signals to quantify nociceptive response during movement activities

OBJECTIVE

With an increasingly ageing population and osteoarthritis prevalence, the quantification of nociceptive signals responsible for painful movements and individual responses could lead to better treatment and monitoring solutions. Changes in electrodermal activity (EDA) can be detected via changes in skin conductance (SC) and measured using finger electrodes on a wearable sensor, providing objective information for increased physiological stress response.

RESULTS

To provide EDA response preliminary data, this was recorded with healthy volunteers on an array of activities while receiving a noxious stimulus. This provides a defined scenario that can be utilised as protocol feasibility testing. Raw signal extraction, processing and statistical analysis was performed using mean SC values on all participant data. The application of the stimuli resulted in a significant average increase (p < 0.05) in mean SC in four out of five activities with significant gender differences (p < 0.05) in SC and self-reported pain scores and large effect sizes. Though EDA parameters are a promising tool for nociceptive response indicators, limitations including motion artifact sensitivities and lack of previous movement-based EDA published data result in restricted analysis understanding. Refined processing pipelines with signal decomposition tools could be utilised in a protocol that quantifies nociceptive response clinically meaningfully.

Assessment of Low Back Pain in Helicopter Pilots Using Electrical Bio-Impedance Technique: A Feasibility Study

Low back pain (LBP) is known to pose a serious threat to helicopter pilots. This study aimed to explore the potential of electrical bio-impedance (EBI) technique with the advantages of no radiation, non-invasiveness and low cost, which is intended to be used as a daily detection tool to assess LBP in primary aviation medical units. The LBP scales (severity) in 72 helicopter pilots were assessed using a pain questionnaire, while the bilateral impedance measurements of the lumbar muscle were carried out with a high precision EBI measurement system. Results showed that the modulus of lumbar muscle impedance increased with LBP scale whereas the phase angle decreased. For different LBP scales, significant differences were found in the modulus of lumbar muscle impedance sum on both sides (Z_sum), as well as in the modulus and phase angle of lumbar muscle impedance difference between both sides (Z_diff and ϕ_diff), respectively (P < 0.05). Moreover, Spearman’s correlation analysis manifested a strong correlation between Z_sum and LBP scale (R = 0.692, P < 0.01), an excellent correlation between Z_diff and LBP scale (R = 0.86, P < 0.01), and a desirable correlation between ϕ_diff and LBP scale (R = −0.858, P < 0.01). In addition, receiver operator characteristic analysis showed that for LBP prediction, the area under receiver operator characteristic curve of Z_sum, Z_diff, and ϕ_diff were 0.931, 0.992, and 0.965, respectively. These findings demonstrated that EBI could sensitively and accurately detect the state of lumbar muscle associated with LBP, which might be the potential tool for daily detection of LBP in primary aviation medical units.

Virtual reality: physiological and behavioral mechanisms to increase individual pain tolerance limits

ABSTRACT

Immersive virtual reality (VR) consists of immersion in artificial environments through the use of real-time render technologies and the latest generation devices. The users feel just as immersed as they would feel in an everyday life situation, and this sense of presence seems to have therapeutic potentials. However, the VR mechanisms remain only partially known. This study is novel in that, for the first time in VR research, appropriate controls for VR contexts, immersive characteristics (ie, control VR), and multifaceted objective and subjective outcomes were included in a within-subject study design conducted on healthy participants. Participants received heat thermal stimulations to determine how VR can increase individual heat-pain tolerance limits (primary outcome) measured in degrees Celsius and seconds while recording concurrent autonomic responses. We also assessed changes in pain unpleasantness, mood, situational anxiety, and level of enjoyment (secondary outcomes). The VR induced a net gain in heat-pain tolerance limits that was paralleled by an increase of the parasympathetic responses. VR improved mood, situational anxiety, and pain unpleasantness when participants perceived the context as enjoyable, but these changes did not influence the increases in pain tolerance limits. Distraction increased pain tolerance limits but did not induce such mood and physiological changes. Immersive VR has been anecdotally applied to improve acute symptoms in contexts such as battlefield, emergency, and operating rooms. This study provides a mechanistic framework for VR as a low-risk, nonpharmacological intervention, which regulates autonomic, affective (mood and situational anxiety), and evaluative (subjective pain and enjoyment ratings) responses associated with acute pain.

EEG and autonomic responses to nociceptive stimulation in disorders of consciousness

Since behavioral responses to external stimuli of patients presenting disorders of consciousness (DoC) are often difficult to qualify, covert physiological correlates of responsivity are deemed as potentially valuable tools to help assessment procedures. While noxious stimuli seem good candidates to explore DoC patients' responsivity, autonomic and electrophysiological correlates of pain detection in DoC patients are still debated. This research aims at investigating autonomic and cortical activation as covert measure of residual somatosensory and nociceptive processes in patients in vegetative state. Twenty-one patients received touch- and pain-related stimulations while autonomic and cortical measures were recorded, with minimal stress for them. Results showed an increased frontal and parietal activation in response to both touch and pain stimuli. Pain-related stimulation was however associated with greater delta parietal response, lower left frontal activation, and increased electrodermal and heart rate measures. Present findings suggest that both somatic stimulations could induce measurable central responses, which might mirror basic attention orientation and perceptual processes. Nonetheless, the nociceptive stimulation in particular seemed to induce a more consistent and informative pattern of covert response even if we used a mild pain-induction procedure.

Electrical impedance of the torso is associated with the pressure pain threshold on myofascial trigger points in patients with chronic neck pain: A cross-sectional study

BACKGROUND

Myofascial trigger points are dysfunctional structures present in skeletal muscles and are related to sensory, motor, and autonomic changes. Despite scientific advances in recent decades in the measurement of musculoskeletal pain, evaluation of this clinical phenomenon is supported with instruments that, although valid and reliable, have a considerable degree of subjectivity.

OBJECTIVE

To correlate electrical impedance of the upper limbs and torso with pain intensity, functional capacity, catastrophizing, pressure pain threshold, and skin temperature on myofascial trigger points in the upper trapezius muscle of patients with neck pain.

METHODS

A single-blind cross-sectional study. Twenty-eight volunteers of both genders were included in the study, were aged 18-45 years, and had chronic neck pain and myofascial trigger points in the upper trapezius. The volunteers were assessed using the Numeric Rating Scale, the Neck Disability Index, the Pain-Related Self-Statement Scale, algometry, infrared thermography, and electrical bioimpedance.

RESULTS

The following significant results were observed: a negative association between the pressure pain threshold on myofascial trigger point in the right upper trapezius and electrical impedance of the torso at 5 kHz (rs=-0.392, p= 0.032), 50 kHz (rs=-0.406, p= 0.026), 250 kHz (rs=-0.388, p= 0.034), and to the frequency 500 kHz (rs=-0.444, p= 0.014).

CONCLUSION

Electrical impedance of the torso is associated with the pressure pain threshold of myofascial trigger points on the upper trapezius of individuals with neck pain. Thus, individuals with a lower pressure pain threshold have higher electrical impedance values of the torso and vice versa.

Reliability of skin impedance in subjects with chronic neck pain

BACKGROUND

Skin impedance is a biological signal that has been employed in the measurement of pain. However, there are few scientific data on skin impedance, with a great variety of assessment methods and controversial results.

OBJECTIVE

To examine the intra- and inter-rater reliability of skin impedance measurement in individuals with chronic neck pain.

METHODS

This is a blind cross-sectional study. Thirty individuals of both genders, aged between 18 and 45 years and with chronic neck pain were included in the study. Two examiners assessed skin impedance of the upper and lower limbs and torso at two intervals separated by one week. For statistical analysis, we used the intraclass correlation coefficient (ICC2,3) to determine the intra- and inter-rater reliability of skin impedance, with its respective confidence interval of 95%, standard error of measurement (SEM) and minimum detectable change (MDC).

RESULTS

The intra-rater reliability was considered substantial to excellent, with ICC values ranging between 0.843 and 0.978, SEM between 0.58 and 15.26 Ω, and MDC between 1.61 and 42.31 Ω. The inter-rater reliability was moderate to excellent, with ICC values ranging between 0.761 and 0.997, SEM ranging between 0.22 and 16.72 Ω, and MDC ranging between 0.63 and 46.35 Ω.

CONCLUSION

The measurement of skin impedance of the upper and lower limbs and torso in individuals with chronic neck pain has acceptable reliability values when considered at different times and by different examiners.

Comparison of the effects of elcatonin and risedronate on back and knee pain by electroalgometry using fall of skin impedance and quality of life assessment using SF-36

Back and knee pain is a widespread health problem and a serious threat to the quality of life (QOL) in middle-aged and older adults, as it frequently accompanies osteoporosis and osteoarthritis. In order to compare the effects of elcatonin and risedronate on such pain, 20 units of elcatonin was intramuscularly injected to 18 patients, and 5 mg of risedronate was orally administered daily to 20 others with similar backgrounds. Exercise-induced pain was analyzed by measuring the fall of skin impedance by electroalgometry (EAM), and subjective pain was recorded by a visual rating system (VRS) on a scale of 0 (no pain) to 100 (unbearable pain). In patients treated with elcatonin, the mean EAM-estimated pain was significantly reduced after 4, 5 and 6 months of treatment, and the VRS score after 3, 5 and 6 months, indicating a significant analgesic effect. In the risedronate group, however, improvement was less remarkable. Two-way analysis of variance using pain as a dependent variable and treatment group and time as independent variables revealed a significantly greater effect of elcatonin over risedronate on both the EAM and VRS scores, and the influence of treatment time on pain was indistinguishable between the two treatment groups. Effect of exercise load on pain was less on knee load than knee and spine load and spine load, but indistinguishable between the two groups. Changes in QOL were evaluated by the SF-36 system. Norm-based scoring showed significant improvements in 3 of 4 categories for elcatonin and in 2 of 4 for risedronate, suggesting comparable effects on the physical aspects of QOL, whereas responses to emotionally and socially directed questions indicated significant improvements in all 4 categories for risedronate, but none for elcatonin, suggesting a more physical than emotional component in elcatonin effects compared to risedronate.

Effect of different enhancers on the transdermal permeation of insulin analog

Using chemical penetration enhancers (CPEs), transdermal drug delivery (TDD) offers an alternative route for insulin administration, wherein the CPEs reversibly reduce the barrier resistance of the skin. However, there is a lack of sufficient information concerning the effect of CPE chemical structure on insulin permeation. To address this limitation, we examined the effect of CPE functional groups on the permeation of insulin. A virtual design algorithm that incorporates quantitative structure-property relationship (QSPR) models for predicting the CPE properties was used to identify 43 potential CPEs. This set of CPEs was pre-screened using a resistance technique, and the 22 best CPEs were selected. Next, standard permeation experiments in Franz cells were performed to quantify insulin permeation. Our results indicate that specific functional groups are not directly responsible for enhanced insulin permeation. Rather, permeation enhancement is produced by molecules that exhibit positive logK(ow) values and possess at least one hydrogen donor or acceptor. Toluene was the only exception among the 22 potential CPEs considered. In addition, toxicity analyses of the 22 CPEs were performed. A total of eight CPEs were both highly enhancing (permeability coefficient at least four times the control value) and non-toxic, five of which are new discoveries.

Analgesic effect of raloxifene on back and knee pain in postmenopausal women with osteoporosis and/or osteoarthritis

To assess the effect of raloxifene on bone and joint pain, 24 postmenopausal women with back or knee pain or both were randomly divided into two groups, based on the chronological sequence of consultation, to be treated with 60 mg raloxifene and 1 microg alfacalcidol (RA)/day (group RA) or 1 microg alfacalcidol alone (A)/day (group A), respectively, for 6 months. Pain following knee loading (KL) by standing up from a chair and bending the knee by squatting, knee and spine loading (KSL) by walking horizontally and ascending and descending stairs, and spine loading (SL) by lying down supine on a bed and leaving the bed to stand was evaluated by electroalgometry (EAM), based on measurement of the fall of skin impedance, and a visual rating scale (VRS), recording subjective pain on a scale of 0-100 between no pain and unbearable pain. The two groups showed no significant difference as to age, indices of mineral metabolism, back and knee pain, and bone status. RA gave a significantly greater analgesic effect than A by both EAM (P = 0.0158) and VRS (P = 0.0268) on overall comparison of the mean response to all modalities of exercise loading. Paired comparison between pretreatment and posttreatment indicated a significant effect of RA by both EAM (P = 0.0045) and VRS (P = 0.0017), but not that of A. The analgesic effect was more clearly noted on combined knee-spine loading (KSL) and spine loading (SL) than simple knee loading (KL). Monthly comparison of the analgesic effect indicated a significantly better analgesic effect in the fifth month by VRS. RA effect greater than A was more evident by EAM than VRS and during months 3-6 than during 1-2 months, suggesting a slowly progressive effect of RA. Pain evaluation by EAM and VRS mostly gave parallel results, except for a few occasions such as knee loading and spine loading by sitting up and leaving a bed, when EAM detected a positive effect but VRS failed to do so. RA appeared to be more effective on bone and joint pain than A in postmenopausal women according to both EAM and VRS measurements.

Ageing and surface EMG activity patterns of masticatory muscles

The purpose of this study was to evaluate the influence of age on the electromyographic activity of masticatory muscles. All volunteers were Brazilian, fully dentate (except for Group I - mixed dentition), Caucasian, aged 7-80, and divided into five groups: I (7-12 years), II (13-20 years), III (21-40 years), IV (41-60 years) and V (61-80 years). Except for Group V, which comprised nine women and eight men, all groups were equally divided with respect to gender (20 M/20 F). Surface electromyographic records of masticatory muscles were obtained at rest and during maximal voluntary contraction, right and left laterality, maximal jaw protrusion and maximal clenching in the intercuspal position. Statistically significant differences (P < 0.05) were found in all clinical conditions among the different age groups. Considerably different patterns of muscle activation were found across ages, with greater electromyographic activity in children and youth, and decreasing from adults to aged people.

Comparison of the analgesic effects of bisphosphonates: etidronate, alendronate and risedronate by electroalgometry utilizing the fall of skin impedance

Analgesic effects of etidronate, alendronate and risedronate were compared in patients with osteoporosis and/or osteoarthritis by measuring the fall of skin impedance along with conventional subjective pain-estimation by visual rating scale (VRS). One hundred ninety-nine postmenopausal women consulting the Osteoporosis and Osteoarthritis Clinic of Katsuragi Hospital complaining of back and/or knee pain were randomly divided into four groups; Group A (49 subjects) given 5 mg/day alendronate, Group E (50 subjects) 200 mg/day etidronate, Group R (50 subjects) 2.5 mg/day risedronate and Group P no bisphosphonate. None of the four groups showed significant deviation from others as to age and parameters of bone metabolism. Proportions of subjects with osteoporosis was 18-40%. Those with osteoarthritis of the spine and knee, higher than Grade II according to the Nathan and Lawrence-Kellgren scale, respectively, was 45 and 61%, respectively, without a significant difference among the four groups. Significant positive correlation was found between the fall of skin impedance and pain expressed in VRS. Attenuation of exercise-induced fall of skin impedance and also subjective pain expressed in VRS was greatest in Group E with a highly significant difference from Groups A (P = 0.0002 and P < 0.0001), R (P < 0.0001 and P = 0.0014) and P (P < 0.0001 and P < 0.0001). Neither A nor R showed significant difference from P as to the fall of skin impedance. Among the three bisphosphonates tested, etidronate appeared to be outstanding in analgesic effects.

Analgesic and Chondroprotective Effects of Risedronate in Osteoarthritis Assessed by Electroalgometry and Measurement of Collagen Type II Fragments in Urine

We evaluated the effect of the bisphosphonate, risedronate, on pain and cartilage metabolism in 33 patients with osteoarthritis of the knee, randomized into two groups. Group RC was treated with risedronate (2.5 mg/day) and calcium (900 mg/day); group C received calcium (900 mg/day) alone. Pain on exercise was estimated using a subjective visual rating scale (VRS) and an electroalgometric method of measuring decrease in skin impedance, previously shown to be indicative of pain. We measured urinary excretion of cartilage-specific collagen type II fragments as a marker of cartilage degradation. Multiple regression analysis revealed that pain alleviation as measured by skin impedance, but not VRS, was associated with a decrease in collagen fragment excretion. This suggests that, for pain evaluation, reduction in skin impedance may have a greater physiological basis compared with VRS-based evaluation. We consider that the chondroprotective and analgesic effects of risedronate may be related.

Activity of masticatory muscles in subjects with different orofacial pain conditions

The existence of a pathophysiological link between tonic muscle activity and chronic muscle pain is still being debated. The purpose of this retrospective, controlled study was to evaluate the electromyographic (EMG) activity of masticatory muscles in subjects with different orofacial pain conditions. The temporal and masseter EMG activity at rest and the masseteric reflex were recorded in two groups of patients with either myofascial pain (n=33) or neuropathic pain (n=20), one group of non-pain patients with disc derangement disorders (n=27) and one control group of healthy, asymptomatic subjects (n=32). The EMG activities of both muscles at rest were significantly higher in the pain patient groups compared to the asymptomatic control group. There was no significant difference between the disc derangement disorder group and the control group. The masseteric reflex amplitude was reduced in all patient groups when compared with the control group. In pain patient groups, the increased EMG activity at rest and the reduction of the masseteric reflex amplitude were equally distributed in the pain and non-pain sides. In addition, subjects presenting with bilateral pain showed higher EMG activity at rest than those with unilateral pain. These results suggested that the modulation of muscle activity was not the direct consequence of a peripheral nociceptive mechanism and seemed to indicate that a central mechanism was at work. The contrast between the increased EMG activity at rest and the reduction of the masseteric reflex amplitude may reflect modulations of motoneurones that differed in tonic versus phasic conditions in chronic pain patients.

Influence of age on adaptability of human mastication

The objective of this work was to study the influence of age on the ability of subjects to adapt mastication to changes in the hardness of foods. The study was carried out on 67 volunteers aged from 25 to 75 yr (29 males, 38 females) who had complete healthy dentitions. Surface electromyograms of the left and right masseter and temporalis muscles were recorded simultaneously with jaw movements using an electromagnetic transducer. Each volunteer was asked to chew and swallow four visco-elastic model foods of different hardness, each presented three times in random order. The number of masticatory cycles, their frequency, and the sum of all electromyographic (EMG) activity in all four muscles were calculated for each masticatory sequence. Multiple linear regression analyses were used to assess the effects of hardness, age, and gender. Hardness was associated to an increase in the mean number of cycles and mean summed EMG activity per sequence. It also increased mean vertical amplitude. Mean vertical amplitude and mean summed EMG activity per sequence were higher in males. These adaptations were present at all ages. Age was associated with an increase of 0.3 cycles per sequence per year of life and with a progressive increase in mean summed EMG activity per sequence. Cycle and opening duration early in the sequence also fell with age. We concluded that although the number of cycles needed to chew a standard piece of food increases progressively with age, the capacity to adapt to changes in the hardness of food is maintained.