Body mass index and distribution of body fat can influence sensory detection and pain sensitivity

Reliability of nociceptive monitors vs. standard practice during general anesthesia: a prospective observational study

BACKGROUND

Inadequate or excessive nociceptive control during general anesthesia can result in significant adverse outcomes. Using traditional clinical variables, such as heart rate, systolic blood pressure, and respiratory rate, to assess and manage nociceptive responses is often insufficient and could lead to overtreatment with both anesthetics and opioids. This study evaluated the feasibility and effectiveness of three nociception monitoring techniques Nociception Level Index (NOL), Skin Conductance Algesimeter (SCA) and heart rate monitoring in patients undergoing image-guided, minimally invasive abdominal interventions under general anesthesia.

METHOD

This prospective observational study collected data from 2022 to 2024. All patients were anesthetized according to the department's routine, and predetermined events were recorded. Two commercially available nociception monitors, the PMD-200 from Medasense (NOL) and PainSensor from MedStorm (SCA), were used, and their data were collected along with various hemodynamic parameters. The three nociception monitoring techniques were compared during predetermined events.

RESULT

A total of 49 patients were included in this study. NOL and SCA demonstrated higher responsiveness than HR for all events except for skin incision. The comparison of the values above and below the threshold for each nociceptive stimulus showed significance for all measurements using the SCA and NOL. However, using HR as a surrogate for nociception with a threshold of a 10% increase from baseline, the difference was significant only at skin incision. There was no variation in the peak values attributable to differences in patients' age. Weight was a significant predictor of the peak NOL values.

CONCLUSION

NOL and SCA demonstrated superior sensitivity and responsiveness to nociceptive stimuli compared to HR, effectively detecting significant changes in nociceptive thresholds across various stimuli, although responses during skin incision showed no such advantage.

TRIAL REGISTRATION

Clinical trial - NCT05218551.

Methodological Variation Among Studies Evaluating Pain Processing in Tendinopathy: A Scoping Review

Background/Objectives: Tendinopathy is a condition associated with pain and limited function. While upper and lower extremity tendinopathies may have different functional implications, there have been a number of reports supporting different patterns of dysfunction in pain processing and inhibition. The purpose of this scoping review was to examine the methods across studies examining pain processing in patients with upper and lower extremity tendinopathy. Methods: Five electronic databases (PubMed, Scopus, CINAHL, the Cochrane Library, and SPORTDiscus) and gray literature sources were searched from inception through 15 April 2024, using appropriate keywords and relevant synonyms. Results: In total, 3219 titles were retrieved from the searches, with 43 studies retained for final inclusion. Of the 43 studies, 22 were specific to upper extremity tendinopathies, 19 were specific to lower extremity tendinopathies, and 2 studies included mixed samples. Physical testing to detect nervous system sensitization was most commonly performed using pressure pain thresholds. Although infrequent, questionnaire instruments were used mostly to include the central sensitization inventory. Substantial variation was noted across studies in mode of testing and instruments used, while patient demographics and inclusion criteria were not clearly reported in many instances. Thirty-one studies (72%) reported nervous system sensitization or dysfunction in tendinopathy, while 13 (28%) did not. Conclusions: While the difference between pain processing in tendinopathy is likely multifactorial, the results of this review identified substantial variability in methodology used and reporting in tendon pain research. As inconsistency in evidence can limit clinical guidance, efforts to standardize tendinopathy pain research appear warranted.

High Body Mass Index Disrupts the Homeostatic Effects of Pain Inhibitory Control in the Symptomatology of Patients With Fibromyalgia

This study examines the influence of body mass index (BMI) on the relationship between quantitative sensory testing measures and clinical characteristics in fibromyalgia syndrome (FMS). Utilizing BMI as a categorical covariate (≥25 or ≥30 kg/m²) in associations between quantitative sensory testing metrics (pain-60, conditioned pain modulation, and temporal summation of pain [TSP]) and FMS clinical features, we explored BMI's role as both a confounder (change-in-estimate criterion-change equal or higher than 10%) and effect modifier (interaction term). Significant interactions revealed overweight/obese BMI as a modifier in the relationship between conditioned pain modification and both depression and symptom impact, with a homeostatic relationship between better clinical profile and pain inhibitory response observed solely in the normal-weight group. Similar results were found for pain-60 and depression. Additionally, BMI ≥30 kg/m² modified TSP's effect on pain, demonstrating lower pain with increased TSP, exclusively in the nonobese group. This study highlights the significant role of BMI in moderating the relationships of important pain inhibitory control processes and pain intensity, depression, and the overall impact of FMS symptoms. Our results suggest that high BMI states disrupt the homeostatic effects of pain inhibition, reducing its salutogenic response in FMS participants. We discuss the mechanistic and therapeutic implications of targeting BMI in FMS clinical trials and the potential impact of this important relationship. PERSPECTIVE: This investigation highlights the disruptive influence of high BMI on pain inhibitory control in fibromyalgia, unbalancing clinical symptoms such as pain and depression. It underscores the necessity of integrating BMI considerations into therapeutic approaches to enhance pain management and patient outcomes.

Activation of α7 nicotinic receptors attenuated hyperalgesia and anxiety induced by palatable obesogenic diet withdrawal

Consumption of palatable food (PF) can alleviate anxiety, and pain in humans. Contrary, spontaneous withdrawal of long-term PF intake produces anxiogenic-like behavior and abnormal pain sensation, causing challenges to weight-loss diet and anti-obesity agents. Thus, we examined α7-nicotinic acetylcholine receptors (α7nAChR) involvement since it plays essential role in nociception and psychological behaviors.

METHODS

Adult male C57BL/6 mice were placed on a Standard Chow (SC) alone or with PF on intermittent or continuous regimen for 6 weeks. Then, mice were replaced with normal SC (spontaneous withdrawal). Body weight, food intake, and calories intake with and without the obesogenic diet were measured throughout the study. During PF withdrawal, anxiety-like behaviors and pain sensitivity were measured with PNU-282987 (α7nAChR agonist) administration.

RESULTS

Six weeks of SC + PF-intermittent and continuous paradigms produced a significant weight gain. PF withdrawal displayed hyperalgesia and anxiety-like behaviors. During withdrawal, PNU-282987 significantly attenuated hyperalgesia and anxiety-like behaviors.

CONCLUSION

The present study shows that a PF can increase food intake and body weight. Also, enhanced pain sensitivity and anxiety-like behavior were observed during PF withdrawal. α7nAChR activation attenuated anxiolytic-like behavior and hyperalgesia in PF abstinent mice. These data suggest potential therapeutic effects of targeting α7 nAChRs for obesity-withdrawal symptoms in obese subjects.

Single-Level Unilateral Biportal Endoscopic versus Tubular Microdiscectomy: Comparing Surgical Outcomes and Opioid Consumption

BACKGROUND

Unilateral biportal endoscopic (UBE) microdiscectomy is an emerging minimally invasive surgery technique for treating symptomatic lumbar disc herniation. There is limited literature regarding outcomes. Here, we assess surgical outcomes and pain medication consumption for UBE vs. tubular lumbar microdiscectomy.

METHODS

This was a retrospective cohort study of adult patients undergoing primary, single-level UBE or tubular lumbar microdiscectomy surgery at a high-volume institution between 2018 and 2023. Variables of interest included operative time, complications and reoperations, as well as postoperative opioid and nonopioid pain medication consumption from discharge to 6 months. Opioid consumption was converted to morphine milligram equivalents. Standard statistical analyses were performed for comparative analyses.

RESULTS

One hundred two patients-48 UBE and 54 tubular-were included. Average operative time (minutes) was higher for UBE patients (133.1 UBE vs. 86.6 tubular, P < 0.001), which trended downward over time but did not reach statistical significance (P = 0.07). There were no differences in complication or reoperation rates. Average daily MME was lower from discharge to 2-week follow-up in the UBE group (11.1 v. 14.1, P = 0.02), but were comparative thereafter. Nonopioid medication prescription was lower in the UBE cohort from discharge to 2 weeks (70.8% vs. 92.6%, P = 0.01) and 2 to 6 weeks (52.1% vs. 85.2%, P < 0.001), with no significant differences thereafter.

CONCLUSIONS

UBE microdiscectomy is associated with longer operating times. Both opioid and nonopioid pain medication consumption were lower for UBE patients during the initial postoperative period, perhaps owing to the less-invasive nature of the surgery.

Associations Among Changes in Body Composition, Activity, Muscle Recovery, and Obesity Following Total Knee Arthroplasty: A Retrospective Study

PURPOSE

Total knee arthroplasty (TKA) is expected to improve knee pain and enable patients to regain the ability to walk, but the associations between preoperative and postoperative changes in body composition, muscle strength, and activity remain unclear. In this study, we investigated the association between changes in body composition before and after TKA surgery, the recovery process of muscle strength, and changes in activity, as well as the effects of obesity on TKA.

METHODS

A total of 124 patients with unilateral knee osteoarthritis (OA) who underwent TKA were retrospectively evaluated. Body weight (BW) and body composition (body fat percentage (BFP) and diseased limb muscle mass (DLMM)), measured by bioelectrical impedance analysis, quadriceps muscle strength (QMS), measured using the isometric muscle strength meter, number of steps (NOS), and Japanese Orthopaedic Association (JOA) OA knee diseases treatment outcome criteria (JOA score) before the operation, at postoperative six months (PO6M), and at postoperative one year (PO1Y) after the operation were investigated and compared between the non-obese (BMI < 25 kg/m2) group, including underweight (<18.5 kg/m2) and normal weight patients (18.5 to 24.9 kg/m2), and obese (BMI ≥ 25 kg/m2) group, including overweight (25.0 to 29.9 kg/m2) or obese patients (≥30.0 kg/m2).

RESULTS

In all patients, JOA scores significantly improved from 59.7 preoperatively to 81.2 at PO6M, and 82.7 at PO1Y (both p < 0.01). QMS significantly increased from 112.4 N preoperatively to 144.0 N at PO6M, and 151.0 N at PO1Y (both p < 0.01). On the other hand, there was no significant change in BW, BFP, NOS, and DLMM. A comparison between the obese (n = 76) and non-obese (n = 48) groups demonstrated that there was no significant difference in JOA scores preoperatively, but scores at PO1Y were significantly higher in the non-obese group (p < 0.01), and QMS increased significantly postoperatively in both groups, but the enlargement rate at PO1Y was 1.4% in the obese group versus 10.4% in the non-obese group (p = 0.04).

CONCLUSION

In the body composition of TKA patients, BW, BFP, and DLMM/BW did not change significantly from preoperatively to PO1Y, but QMS and JOA scores showed significant improvement at PO6M and PO1Y compared to preoperatively. The obese patients showed less improvement in JOA scores than non-obese patients, and the rate of increase in QMS at PO1Y was smaller, suggesting that rehabilitation focusing on muscle-strengthening training is necessary even at PO6M, especially in obese patients.

The role of obesity and adipose tissue dysfunction in osteoarthritis pain

Obesity has a pivotal and multifaceted role in pain associated with osteoarthritis (OA), extending beyond the mechanistic influence of BMI. It exerts its effects both directly and indirectly through various modifiable risk factors associated with OA-related pain. Adipose tissue dysfunction is highly involved in OA-related pain through local and systemic inflammation, immune dysfunction, and the production of pro-inflammatory cytokines and adipokines. Adipose tissue dysfunction is intricately connected with metabolic syndrome, which independently exerts specific effects on OA-related pain, distinct from its association with BMI. The interplay among obesity, adipose tissue dysfunction and metabolic syndrome influences OA-related pain through diverse pain mechanisms, including nociceptive pain, peripheral sensitization and central sensitization. These complex interactions contribute to the heightened pain experience observed in individuals with OA and obesity. In addition, pain management strategies are less efficient in individuals with obesity. Importantly, therapeutic interventions targeting obesity and metabolic syndrome hold promise in managing OA-related pain. A deeper understanding of the intricate relationship between obesity, metabolic syndrome and OA-related pain is crucial and could have important implications for improving pain management and developing innovative therapeutic options in OA.

Thoracic spinal postures and mobility in patients with cervicogenic headache versus asymptomatic healthy controls: A longitudinal study

INTRODUCTION

Studies analyzing postures and mobility of the thoracic spine in the context of cervicogenic headache are missing. Insight in these parameters is needed since the cervical and thoracic spine are biomechanically related.

OBJECTIVE

To compare self-perceived optimal and habitual postures, active-assisted maximal range of motion, and repositioning error of the upper-thoracic and lower-thoracic spine between a cervicogenic headache-group and matched healthy control-group before and after a 30 min-laptop-task.

METHODS

A non-randomized longitudinal design was used to compare thoracic postures and mobility between 18 participants with cervicogenic headache (29-51 years) and 18 matched healthy controls (26-52 years). Outcomes were: self-perceived optimal and habitual postures, active-assisted maximal range of motion, and repositioning error of the upper-thoracic and lower-thoracic spine evaluated in sitting with a 3D-Vicon motion analysis system.

RESULTS

Habitual upper-thoracic postures in the cervicogenic headache-group were significantly (p = .04) less located toward the maximal range of motion for flexion compared to the control-group, self-perceived optimal upper-thoracic posture was significantly (p = .004) more extended in the cervicogenic headache-group compared to the control-group, and self-perceived optimal lower-thoracic posture could not be reestablished in the cervicogenic headache-group after the laptop-task (p = .009).

CONCLUSION

Thoracic postures differ between a cervicogenic headache-group and control-group. These differences were detected by expressing the habitual thoracic posture relative to its maximal range of motion, and by analyzing the possibility of repositioning the thoracic spine after a headache provoking activity. Longitudinal studies are needed to determine the contribution of these musculoskeletal dysfunctions to the pathophysiology of cervicogenic headache.

Time to sense biofield (Prana) experiences between hands: A preliminary single blinded randomized placebo controlled trial

Aims

There is minimal research on the duration of biofield experiences. This preliminary study used the experiential learning practice of Master Choa Kok Sui's hands sensitisation to determine the duration to experience biofield sensations in between hands and to find the relationship between learning style preferences and biofield sensations.

Methods

This randomized placebo controlled, single blinded trial included 88 male and female pre-service teachers, aged 22.8±1.2 years. Participants completed a ruler drop test for reaction time, and Six Letter Cancellation test for measuring attention, learning style questionnaire for preferred method of learning, before randomization. The experimental (hands facing each other as introduced by Master Choa Kok Sui) and sham (hands facing opposite) groups practiced hands sensitisation. A semi-structured questionnaire was provided to gather information about biofield sensations and the time it took to experience these sensations between the hands.

Results

All (N=44) the participants in the experimental group and 13 participants in the sham group reported experiencing biofield sensations. A significant difference was noticed in experiencing magnetic (X 2 = 38.247, p ≤ .001), physical sensations of energy (X 2 = 12.02, p ≤ .001) and pain (X 2 = 62.259, p ≤ .001) among the experimental and sham group . In the experimental group, the average time taken to first experience magnetic sensation, other biofield sensations and temperature variation was 34.84±12.97seconds, 40.28±20.96 seconds and 42.50±19.79 seconds, respectively. Minimum time taken to first experience biofield sensation was 5 seconds and lasted up to study duration of 120 seconds. There was no correlation found between reaction time, sustained attention, and the time needed to experience biofield sensations.

Conclusions

This study highlights importance of Master Choa Kok Sui hand sensitization in controlled setting revealing differences in experiences of various biofield sensations, showing valuable time-related insights and variability of sensation based on preferred learning.

Tactile acuity and active joint repositioning sense in individuals with and without chronic low back pain: a cross-sectional study

BACKGROUND

Sensorimotor dysfunction, as measured by tactile acuity and active joint repositioning, has been identified as a contributing factor of chronic low back pain (CLBP). Existing research suggests that further research is necessary to improve the characterization of sensorimotor perception in patients with CLBP.

OBJECTIVES

The main aim is to investigate whether tactile acuity and repositioning errors differ between individuals with CLBP and controls without CLBP. A secondary aim was to investigate the association between age, body mass index (BMI) and physical activity, and tactile acuity and repositioning sense.

METHODS

Cross-sectional study. Sixty-eight participants (36 with, 32 without CLBP) were examined. Two-Point Discrimination (TPD) test (four measures: horizontal and vertical run, left and right side) and Active Joint Reposition Sense (AJRS) test (2 directions: to flexion and to extension) were used.

RESULTS

No differences were found for TPD (right horizontal run: p = .069; left horizontal run: p = .066; right vertical run: p = .933; left vertical run: p = .285) or AJRS (flexion: p = .792; extension: p = .956) between participants with and without CLBP. Older subjects had significantly worse tactile acuity (3 sites, p = .018, p = .004, p = .041) and worse repositioning sense (2 directions, p = .026, p = .040,) than younger subjects. Individuals with BMI ≥ 25 had significantly worse TPD compared to individuals with normal weight (2 sites, p = .028, p = .020).

CONCLUSIONS

Individuals with CLBP did not have impaired tactile and repositioning accuracy when compared to controls without CLBP. Future studies comparing sensorimotor performance should consider age and BMI as potential confounding factors.

Pressure Pain Sensitivity and Chronotype: A Population-based Study of Middle-aged Finns

Evening chronotype individuals experience pain more often than morning chronotypes, but relationships with pain sensitivity have rarely been studied. We examined whether chronotype is associated with pressure pain sensitivity, with special reference to mental health disorders, insomnia, and chronic musculoskeletal (MSK) pain as potential moderating factors. The study sample consisted of members of the Northern Finland Birth Cohort 1966 aged 46. Pressure pain threshold and tolerance were measured via the standardized protocol, categorized as lowest quartile versus others. Chronotype (morning [M; the reference], intermediate [I], and evening [E]) was defined using the Short Morningness-Eveningness questionnaire. Sex-stratified binary logistic regression models were separately adjusted for education, body mass index, long-term diseases (fully adjusted model), and for mental health disorders, insomnia, and chronic MSK pain (a residual confounding analysis). Interaction terms (Chronotype × Mental health/insomnia/chronic MSK pain) were tested. The study had 2,132 males and 2,830 females. The E-type males had 1.5-fold odds of having a low pain threshold (fully adjusted odds ratio [OR] 1.45, 95% confidence interval 1.05-2.00) and pressure pain tolerance (fully adjusted OR 1.47, 1.07-2.02), in comparison to M-types. Having a mental health disorder intensified the association with low pain threshold fourfold (4.06, 1.56-10.6). Being an E-type female was also associated with a low pain threshold, but the association was statistically nonsignificant (fully adjusted OR 1.18, .90-1.53). No statistically significant interactions were found among females. These results emphasize the role of chronotype in pain sensitivity and add an understanding of pain experience in light of innate circadian types. PERSPECTIVE: Male evening chronotypes are more sensitive to pain than morning chronotypes. Diagnosed mental health disorders in particular indicate a low pain threshold for evening chronotype males.

Impact of obesity on outcomes of rotator cuff repair: A systematic review and meta-analysis

BACKGROUND

To synthesize the existing evidence on the association between obesity and rotator cuff repair outcomes such as pain, shoulder function, range of motion, and complications.

METHODS

We searched PubMed, EMBASE, and Scopus databases for relevant observational studies (cohort and case-control) and randomized controlled trials (RCTs). The target population in the included studies comprised adults who had undergone rotator cuff repair procedures. The outcomes of interest were functional outcomes (such as range of motion), pain scores, patient-reported outcome measures, and complication rates (such as re-repair and readmission rates). We applied random-effects models and calculated pooled effect sizes reported as standardized mean differences (SMDs) or relative risks (RRs) with 95% confidence intervals.

RESULTS

We analysed data from 11 studies. In most, the follow-up periods ranged from 12 to 60 months. Obese individuals experienced greater pain (SMD 0.30; 95% CI, 0.10, 0.50) and lower shoulder function (SMD -0.33; 95% CI, -0.54, -0.12) than other individuals in the long-term post-operative follow-up. Obese individuals also had higher risks of complications (RR 1.48; 95% CI, 1.11, 1.98) and readmission (RR 1.35; 95% CI, 1.27, 1.43), but a similar likelihood of re-repair (RR, 1.27; 95% CI, 0.82, 1.95) than non-obese/normal BMI individuals. While the forward flexion and external rotation functions were comparable, obese individuals displayed less internal rotation function than other individuals (SMD -0.59; 95% CI, -0.87, -0.30).

CONCLUSION

Obesity was associated with unfavourable outcomes after rotator cuff surgery, including increased pain, reduced shoulder function, high risks of complications, and readmission. These findings emphasize the importance of addressing obesity-related factors to improve post-operative outcomes.

Adults with excess weight or obesity, but not with overweight, report greater pain intensities than individuals with normal weight: a systematic review and meta-analysis

Context

Over 1.9 billion adult people have overweight or obesity. Considered as a chronic disease itself, obesity is associated with several comorbidities. Chronic pain affects approximately 60 million people and its connection with obesity has been displayed in several studies. However, controversial results showing both lower and higher pain thresholds in subjects with obesity compared to individuals with normal weight and the different parameters used to define such association (e.g., pain severity, frequency or duration) make it hard to draw straight forward conclusions in the matter. The objective of this article is to examine the relationship between overweight and obesity (classified with BMI as recommended by WHO) and self-perceived pain intensity in adults.

Methods

A literature search was conducted following PRISMA guidelines using the databases CINAHL, Cochrane Library, EMBASE, PEDro, PubMed, Scopus and Web of Science to identify original studies that provide BMI values and their associated pain intensity assessed by self-report scales. Self-report pain scores were normalized and pooled within meta-analyses. The Cochrane's Q test and I2 index were used to clarify the amount of heterogeneity; meta-regression was performed to explore the relationship between each outcome and the risk of bias.

Results

Of 2194 studies, 31 eligible studies were identified and appraised, 22 of which provided data for a quantitative analysis. The results herein suggested that adults with excess weight (BMI ≥ 25.0) or obesity (BMI ≥ 30.0) but not with overweight (pre-obesity) alone (BMI 25.0-29.9), are more likely to report greater intensities of pain than individuals of normal weight (BMI 18.5-24.9). Subgroup analyses regarding the pathology of the patients showed no statistically significant differences between groups. Also, influence of age in the effect size, evaluated by meta-regression, was only observed in one of the four analyses. Furthermore, the robustness of the findings was supported by two different sensitivity analyses.

Conclusion

Subjects with obesity and excess weight, but not overweight, reported greater pain intensities than individuals with normal weight. This finding encourages treatment of obesity as a component of pain management. More research is required to better understand the mechanisms of these differences and the clinical utility of the findings.

Systematic Review Registration

https://doi.org/10.17605/OSF.IO/RF2G3, identifier OSF.IO/RF2G3.

Obesity Is Associated with Altered Rectal Sensitivity in Chronic Constipation

BACKGROUND

Defecation dysfunction may contribute to chronic constipation (CC), but the impact of obesity on anorectal physiology in CC remains unclear. We aimed to evaluate the relationship between obesity and anorectal function on physiologic testing in patients presenting with CC.

METHODS

This was a retrospective cohort study of consecutive adults who underwent high resolution anorectal manometry (HRAM) at a tertiary center for CC. Patient demographics, clinical history, surgical/obstetric history, medications, and HRAM results were reviewed. Patients were classified into obese (BMI > 30 kg/m2) vs non-obese (BMI < 30 kg/m2) groups at the time of HRAM. Fisher-exact/student t-test for univariate analyses and general linear regression for multivariable analysis were performed.

RESULTS

383 adults (mean 50.3 years; 85.8% female) with CC were included. On HRAM, patients with obesity had lower anal sphincter resting tone (37.3 vs 48.5 mmHg, p = 0.005) and maximum squeeze pressure (104.8 mmHg vs 120.0 mmHg, p = 0.043). No significant differences in dyssynergia (61% vs 53%, p = 0.294) and failed balloon expulsion (18% vs 25%, p = 0.381) were found between obese and non-obese groups. On balloon distention testing, the maximum tolerated (163.5 vs 147.6 mL, p = 0.042) and urge sensation (113.9 vs 103.7 mL, p = 0.048) volumes were significantly increased among patients with obesity. After adjusting for potential confounders, obesity remained independently associated with increased maximum tolerated volume (β-coefficient 13.7, p = 0.049).

CONCLUSION

Obesity was independently associated with altered rectal sensitivity among patients with CC. Altered rectal sensation may play an important role in CC among patients with obesity. Anorectal physiology testing should be considered to understand the pathophysiology and guide management.

Cervical sensitivity, range of motion and strength in individuals with shoulder pain: A cross-sectional case control study

OBJECTIVES

To assess whether cervical sensitivity, range of motion (ROM) and strength are impaired in individuals with shoulder pain and how they interact with sociodemographic and clinical data.

METHODS

Forty-eight individuals with shoulder pain and 48 asymptomatic matched ones were included. Pressure pain thresholds (PPTs) in cervical region and tibialis anterior muscles, ROM of cervical flexion, extension, lateral flexions and rotations and cervical muscle strength of flexion, extension and lateral flexions were assessed. Between-groups comparisons and a logistic multiple regression model were performed.

RESULTS

The symptomatic group showed lower and not meaningful PPTs in trapezius of the unaffected/unmatched side, both sternocleidomastoid muscles, and tibialis anterior and reduced ROM in cervical extension (MD = -9.00°) when compared to the asymptomatic group. No differences were identified in muscle strength. Reduced PPT of the trapezius and reduced cervical extension ROM together accounted for 40.2% of the variance of the chance of presenting shoulder pain.

CONCLUSION

Individuals with shoulder pain have more, but not clinically relevant, cervical sensitivity and lower cervical extension than asymptomatic individuals. The lower the PPT of the upper trapezius and the cervical extension ROM, the higher was the chance to present shoulder pain. Regional interdependence between cervical spine and shoulder may explain cervical physical function alterations in shoulder pain.

Individual endogenous pain modulation profiles within a multidimensional context of people with cervicogenic headache - A retrospective exploratory study

BACKGROUND

One in four individuals with cervicogenic headache (CeH) are unresponsive to therapy. Such therapy involves predominantly biomedical interventions targeting the upper-cervical spine. A recurring theme within musculoskeletal practice is the multidimensional nature and substantial heterogeneity of the condition. Such heterogeneity might be a reason for failure of a biomedical approach. Therefore, future studies investigating efficacy of managing CeH should ideally be based on identification, and better understanding of the heterogeneity of this population based on a comprehensive evaluation of clinically relevant contributing factors.

OBJECTIVES

The objective was to map profiles of individuals with CeH based on pain modulation within a multidimensional context.

DESIGN

Pain Modulation Profiles (PMPs) of 18 adults (29-51 years) with CeH were mapped retrospectively.

METHOD

The PMPs consisted of a Pain-Profile (bilateral suboccipital, erector spinae, anterior tibialis pressure pain thresholds), a Psycho-Social-Lifestyle-Profile (Depression, Anxiety, Stress Scale, Headache Impact test, Pittsburgh Sleep Quality Index), or a combination of both. Individual results were compared to normative data. Two Pain-Profiles were defined: normal or altered. Psycho-Social-Lifestyle-Profiles were categorized based on the number of altered psycho-social-lifestyle factors (range 0-5).

RESULTS

Mapping PMPs in individuals with CeH resulted in 50% presenting with a dominant altered Pain-Profile, 16.7% with a dominant altered Psycho-Social-Lifestyle-Profile, and 5.6% with dominant alterations in both Pain-Profile and Psycho-Social-Lifestyle-Profile.

CONCLUSION

Our results indicate heterogeneity of PMPs within the CeH population. Replication of these results is needed through dynamic assessment of the Pain-Profile before evaluating if these profiles can help patient-stratification.

Reference intervals and sources of variation of pressure pain threshold for quantitative sensory testing in a Japanese population

Quantitative sensory testing (QST) is useful when analysing musculoskeletal pain disorders. A handheld algometer is most commonly used for pressure pain threshold (PPT) tests. However, reference intervals for PPTs are not elucidated. We assessed reference intervals of PPTs for QST in 158 healthy adult Japanese with no history of musculoskeletal or neurological problems. A handheld algometer was used to record PPT at five different assessment sites on the body: lumbar paravertebral muscle, musculus gluteus maximus, quadriceps, tibialis anterior muscle, and anterior talofibular ligament. Multiple regression analysis was performed to explore sources of variation of PPT according to sex, age, body mass index, UCLA Activity Level Rating, and Tegner Activity Score. Reference intervals were determined parametrically by Gaussian transformation of PPT values using the two-parameter Box-Cox formula. Results of multiple regression analysis revealed that age was significantly associated with PPT of lumbar paravertebral muscle and musculus gluteus maximus. In females, body mass index showed significant positive correlation with PPT of anterior talofibular ligament, and UCLA Activity Level Rating also showed significant positive association with tibialis anterior muscle and anterior talofibular ligament. Site-specific reference intervals of PPTs for Japanese are of practical relevance in fields of pain research using a handheld algometer.

Spatial summation of thermal sensitivity is limited to small areas: Comparisons of the forehead, forearm, abdomen, and foot

The purpose of the present study was to examine if spatial summation in thermal sensitivity exists when stimulating areas larger than about 1% of body surface area (BSA) (approximately 200 cm2). We hypothesized that spatial summation would exist within a limited area and the effect would be insignificant for over the 1%BSA. Fifteen young males participated in this study and we measured their warmth and hot sensation thresholds on the four body regions (the forehead, forearm, abdomen, and instep) using the three sizes of radiant film heaters (10 × 10, 15 × 15, and 20 × 20 cm2 heating film area). The heating panel was kept at a distance of 10 cm from the skin and the surface temperature of the heating panel increased by 1 °C·s-1. The results showed that warmth and hot sensation thresholds were higher for the 100 cm2 condition than the 225 or 400 cm2 conditions (P < 0.05), but no differences were found between the 225 and 400 cm2 conditions. Secondly, the instep was most insensitive to the gradual increase of radiant heat among the four body regions for all three stimulating film sizes, even though the hot threshold was lowest for the instep because the initial foot temperature was lower than other skin temperatures. In summary, spatial summation in thermal sensitivity was found for the 100 and 225 cm 2 conditions, but not for the 225 and 400 cm2 conditions. These results suggest that spatial summation exists but limited to small stimulating areas, smaller than approximately 1% BSA.

Enhanced pain sensitivity in obese patients with obstructive sleep apnoea syndrome is partially reverted by treatment: An exploratory study

BACKGROUND

Obesity is frequently associated with obstructive sleep apnoea syndrome (OSA) and chronic pain. OSA as well as continuous positive airway pressure (CPAP) treatment may modulate the pain perception threshold (PT) in patients with obesity.

METHODS

In this prospective, longitudinal study, all patients admitted for obesity assessment were screened for OSA by nocturnal polygraphy (SOMNOcheck^® , IAH ≥10) and performed mechanical (Von Frey electronic device) and electrical (PainMatcher^® ) pain tests. Those with severe OSA were retested for PT 1 month after initiation of CPAP therapy. Newly diagnosed patients with severe OSA (hypopnea apnoea index >30) have been offered to start CPAP treatment.

RESULTS

Among 85 patients, there were 27 OSA patients, aged between 40 ± 13.2 years with a BMI of 42 ± 7.2 kg/m² . Severe OSA patients (N = 11) showed a lower PT than non-OSA patients (N = 58) during mechanical (177 ± 120 vs. 328 ± 136 g, p < 0.01) and electrical methods (7.4 ± 6.4 vs. 12.9 ± 6.7 stimulation duration steps; p = 0.03). In the severe OSA group (N = 7), an increased PT was observed 1 month after CPAP treatment during mechanical pain testing (298 ± 69 vs. 259 ± 68 g, p < 0.05), but not during electrical pain testing (11.5 ± 3.0 vs. 12.4 ± 3.8 stimulation duration steps, p = 0.50).

CONCLUSION

In patients with obesity, this exploratory study showed that the presence of an OSA is associated with a decreased PT, whereas implantation of a CPAP device tends to normalize pain perception.

The association between forward head posture and masticatory muscle pressure pain thresholds in patients with temporomandibular joint dissorders: a cross-sectional observational study

OBJECTIVES

Forward head posture (FHP) is common in patients with temporomandibular joint disorders (TMDs); however, whether it contributes to TMD symptoms remains unclear. The aim of this study was to investigate the association between (1) FHP and masticatory muscle pressure pain thresholds (PPTs) and (2) neck muscle and masticatory muscle PPTs.

MATERIALS AND METHODS

A total of 145 patients diagnosed with TMD were recruited between December 2020 and April 2021. Data regarding FHP and neck and masticatory muscle PPTs were collected. FHP was characterized by the craniocervical angle (CVA) measured between the horizontal line through C7 and the line between the tragus of the ear and C7. Patients were divided into either the FHP group (CVA ≤ 51°) or the non-FHP group. Differences in the masseter and temporalis muscle PPTs between the two groups were analyzed using the Mann-Whitney U test. The correlation between the CVA, neck, and masticatory muscle PPTs in all patients was determined by Spearman's correlation analysis.

RESULTS

There were 70 patients in the FHP group and 75 patients in the non-FHP group. No significant difference in masseter and temporalis muscle PPTs was found between the two groups (p > 0.05). No correlation was found between FHP and masticatory muscle PPTs (p > 0.05). A significant association was found between the neck muscle and masticatory muscle PPTs (p < 0.05). The C5-C6 pillar and masticatory PPTs were either moderately (r = 0.435, masseter muscle) or strongly (r = 0.608, temporalis muscle) correlated, while the correlation between the trapezius and masticatory muscles was moderate (r = 0.378, masseter muscle and r = 0.461, temporalis muscle).

CONCLUSION

FHP was not directly associated with masticatory muscle PPTs. Masticatory muscle PPTs were strongly or moderately associated with neck muscle PPTs. Therefore, the presence of neck pain, not the degree of FHP, in patients with TMD is of significance.

CLINICAL RELEVANCE

In TMD treatment, we should pay attention to and actively relieve neck pain.

Perceived Pain in Athletes: A Comparison between Endurance Runners and Powerlifters through a Cold Experimental Stimulation and Two Sessions of Various Physical Activation

Few studies in the literature have illustrated cold hypoalgesia induced by strength training. Objectives of this contribution were to compare the ratings of perceived pain in endurance running (n = 22) and powerlifting (n = 22) male athletes and controls (n = 22) at baseline and after two bouts of 40 min aerobic/strength training respectively, using the Cold Pressor Test (CPT) and simultaneously monitoring changes in blood pressure (BP), heart rate (HR), and body temperature. A two-way repeated measures ANOVA was conducted to examine the effects of training sessions in endurance runners vs. powerlifting athletes vs. controls on the intensity of perceived pain at CPT. A statistically significant two-way interaction between the group and training resulted in p < 0.001, ηp2 = 0.513. A simple main effects analysis showed that as the participants went through the strength training session, pain perception at CPT was significantly lower in powerlifters compared to runners and controls. Considering the physiological parameters, powerlifters reported significantly higher values of BP and HR. This difference was present at baseline but after training as well, and before and after CPT, despite a slight hypotensive effect. The differences reported after CPT at baseline, but very significantly after the strength activation session in the powerlifters, provide interesting insights into the hypoalgesic effect of high-intensity strength training.

Lean Mass is Associated with, but Does Not Mediate Sex Differences in Pressure Pain Sensitivity in Healthy Adults

Background

Sex differences exist in pain sensitivity, however, the underlying mechanism(s) that explain these differences are not fully understood. Pain sensitivity has been shown to be influenced by body mass index, but limited data exist on the role of body composition on pain sensitivity. The purpose was to examine the influence of body composition on pain sensitivity in males and females.

Methods

This cross-sectional study design used pressure pain thresholds (PPT) of 87 participants (45 female) who were assessed in the vastus lateralis (leg PPT) and brachioradialis (arm PPT) using a pressure algometer. Fat and lean tissue were assessed via dual-energy X-ray absorptiometry (DXA). A two group by two limb, repeated measured ANOVA was used to assess differences between limbs and sex. Spearman correlations and hierarchical regression analyses were employed to determine the association between body composition and PPT.

Results

Males had higher PPTs then females (P<0.05) and had higher DXA assessed lean and lower levels fat mass (P<0.05). Total body and limb specific lean mass was associated with PPTs (r≥0.34; P<0.05). Hierarchical regression analysis revealed lean mass was a significant predictor of 8% of the variance in arm PPT (P<0.006) and 18% of the variance in leg PPT (P<0.001). However, lean mass was not found to statistically mediate the observed sex differences in PPT.

Conclusion

This finding suggests lean mass may play a previously unknown role in sex differences in pressure pain sensitivity. Future studies are needed to confirm this finding and a larger sample size is likely required to have sufficient power to perform the mediation analysis.

Inter-individual variability in mechanical pain sensation in patients with cervicogenic headache: an explorative study

Currently, evidence for effective physiotherapy interventions in patients with cervicogenic headache (CeH) is inconsistent. Although inter-individual variability in pain response is predictive for successful physiotherapy interventions, it was never explored in patients with CeH. Therefore the objective of the current study was to explore inter-individual variability in mechanical pain sensation, and its association with biopsychosocial-lifestyle (BPSL) characteristics in patients with CeH. A cross-sectional explorative analysis of inter-individual variability in mechanical pain sensation in 18 participants with CeH (29-51 years) was conducted. Inter-individual variability in mechanical pain sensation (standard deviations (SDs), F-statistics, Measurement System Analysis) was deducted from bilateral pressure pain thresholds of the suboccipitals, erector spine, tibialis anterior. BPSL-characteristics depression, anxiety, stress (Depression Anxiety Stress Scale-21), quality of life (Headache Impact Test-6), sleep-quality (Pittsburgh Sleep Quality Index), and sedentary time (hours/week) were questioned. Inter-individual variability in mechanical pain sensation explained 69.2% (suboccipital left), 86.8% (suboccipital right), 94.6% (erector spine left), 93.2% (erector spine right), 91.7% (tibialis anterior left), and 82% (tibialis anterior right) of the total variability in patients with CeH. The significant p-values and large F-statistic values indicate inter-individual differences in SDs. Significant associations between (1) lower quality of life and lower SDs of the suboccipital left PPT (p .005), and (2) longer sedentary time and higher SDs of the suboccipital left PPT (p .001) were observed. Results from our explorative study could suggest inter-individual variability in mechanical pain sensation at the left suboccipitals which associates with quality of life and sedentary time. These novel findings should be considered when phenotyping patients and 'individually' match interventions.

Body fat and skeletal muscle mass, but not body mass index, are associated with pressure hyperalgesia in young adults with patellofemoral pain

BACKGROUND

Young adults with patellofemoral pain (PFP) have a high prevalence of being overweight or obese, which is associated with impaired lower limb function and muscle weakness. However, the impact of being overweight or obese on pain sensitivity has not been explored.

OBJECTIVES

We investigated the association between body fat, skeletal muscle mass, and body mass index (BMI) with pressure hyperalgesia and self-reported pain in young adults with PFP.

METHODS

114 adults with PFP (24 ± 5 years old, 62% women) were recruited. Demographics and self-reported pain (current and worst knee pain intensity in the previous month - 0-100 mm visual analog scale) were recorded. Body fat and skeletal muscle mass were measured using bioelectrical impedance. Pressure hyperalgesia was measured using a handheld algometer (pressure pain threshold) at three sites: center of patella of the painful knee, ipsilateral tibialis anterior, and contralateral upper limb. The association between body fat, skeletal muscle mass, and BMI with pressure hyperalgesia and self-reported pain were investigated using partial correlations and hierarchical regression models (adjusted for sex, bilateral pain, and symptoms duration).

RESULTS

Higher body fat and lower skeletal muscle mass were associated with local, spread, and widespread pressure hyperalgesia (ΔR²=0.09 to 0.17, p ≤ 0.001; ΔR²=0.14 to 0.26, p<0.001, respectively), and higher current self-reported pain (ΔR²=0.10, p<0.001; ΔR²=0.06, p = 0.007, respectively). Higher BMI was associated with higher current self-reported pain (ΔR²=0.10, p = 0.001), but not with any measures of pressure hyperalgesia (p>0.05).

CONCLUSION

Higher body fat and lower skeletal muscle mass help to explain local, spread, and widespread pressure hyperalgesia, and self-reported pain in people with PFP. BMI only helps to explain self-reported pain. These factors should be considered when assessing people with PFP and developing their management plan, but caution should be taken as the strength of association was generally low.

Validity of the Central Sensitization Inventory (CSI) through Rasch analysis in patients with knee osteoarthritis

INTRODUCTION/OBJECTIVE

Central sensitization (CS) is a known contributor to chronic pain in people with knee osteoarthritis (KOA) and is commonly measured by psychophysical testing or patient-reported methods such as the Central Sensitization Inventory (CSI). However, previous studies have shown a weak association between the two. We therefore sought to evaluate the validity of the CSI through Rasch analysis in patients with KOA.

METHOD

We performed a secondary analysis of a multicenter cohort study with patients with KOA consulting orthopedic surgeons. Rasch analysis was conducted considering person factors of age, sex, BMI, pain intensity, pain catastrophizing, and quantitative sensory test findings using pressure pain thresholds and temporal summation to assess how the CSI fits to the Rasch model (supporting validity). We used RUMM2030 software to model fit estimates, making adjustments as required to achieve model fit (P > 0.05).

RESULTS

Data from 293 patients were included (58.7% female, mean age 63.6 years, 49.1% obese) Initial evaluation with Rasch modelling indicated misfit. Eleven of 25 items on the CSI displayed disordered thresholds which were rescored by collapsing response categories until the thresholds demonstrated sequential progression. Reanalysis demonstrated persistent model misfit so a subtest was developed to address local dependency of 6 items. Thereafter, model fit was achieved (P = 0.071, indicating not differing from Rasch model) and acceptable unidimensionality (P = 0.068 with 95% CI 0.043-0.093).

CONCLUSIONS

The CSI was able to be fit to the Rasch model after rescoring while retaining all 25 items. The unidimensionality validates CS as measured by the CSI as a singular construct. Key Points • The Central Sensitization Inventory (CSI) was able to be fit to the Rasch model after rescoring while retaining all 25 items. • The unidimensionality of the CSI validates CS as a singular construct. • Our results suggest rescoring of the CSI for people with KOA, but it should be confirmed and replicated in larger samples prior to clinical use.

Vapocoolant Spray for Pain Control in Intramuscular Injection Applications: A Prospective, Randomized Controlled Trial

Background Many pharmacological and nonpharmacological methods have been investigated along with advances in pain treatment. One of these nonpharmacological methods is the use of vapocoolant spray.

Objective This study aimedto demonstrate the effectiveness of vapocoolant spray to reduce pain during intramuscular (IM) injection.

Patients and Methods The study included ≥18 years old patients admitted to the emergency department who were asked to undergo IM injection. Patients were randomly divided into two groups as vapocoolant spray and control group. Demographic data, injection side, and visual analog scale (VAS) of the patients were recorded.

Results Mean VAS values during IM injection were significantly lower in patients treated with vapocoolant spray compared with the control group. The severity of pain during IM injection was lower in the vapocoolant spray group as both moderate pain (VAS > 3 cm) and severe pain (VAS > 5.4 cm) compared with the control group.

Conclusion Vapocoolant spray to be applied before IM injection is effective in reducing pain caused by the injection.

The effect of gestational diabetes mellitus on occurrence of the pelvic girdle pain and symptom severity in pregnant women

The primary objective of this study was to examine the effect of gestational diabetes mellitus (GDM) on pelvic girdle pain (PGP) occurrence and symptom severity. Pregnant women who were with/without GDM, 20-40 years of age, and also in the second and third trimesters of pregnancy were included in the study. PGP provocation tests were administered to 187 pregnant women to determine the presence and severity of PGP. Based on the test results, the study subjects were divided into two groups; Group 1 (GDM+, PGP+; n:32) and Group 2 (GDM-, PGP+; n:35). Both groups were asked to fill in the Pelvic Girdle Questionnaire (PGQ). The relationship between the presence of GDM and the presence of PGP was found to be significant (p = .043). It was found the groups were similar in view of pain, and also in PGQ total/subscale scores (p > .05). Although GDM has no effect on symptom severity, it has been determined that it may relate to the development of PGP. Therefore, early interventions (nutrition, exercise, belt using, etc.) are recommended to prevent the development of PGP in pregnant women with a family history of diabetes, with a previous diagnosis of diabetes and/or with GDM detected in their previous pregnancies. Clinical Trial Number: 04769375Impact of StatementWhat is already known on this subject? Gestational diabetes mellitus and pelvic girdle pain are pathologies that develops secondary to pregnancy-related systemic and biomechanical changes.What do results on this study add? GDM may related the development of PGP.What are the implications of these findings for clinical practice and/or further research? Early interventions (nutrition, exercise, belt using, etc.) and strict control of pregnant women in view of PGP is recommended to prevent the development of PGP in pregnant women with a family history of diabetes, with previous diagnosis of diabetes and/or with GDM detected in their previous pregnancies. The evaluation of pregnant women for PGP before administering interventions, such as exercise and diet (both decrease the pro-inflammatory markers), following the diagnosis of GDM and the measurement of plasma anti- and pro-inflammatory marker values in the same time period will further reveal the relationship between GDM and PGP.

Personal influencing factors for pressure pain threshold in healthy people: A systematic review and meta-analysis

All studies that investigated personal factors influencing pressure pain threshold (PPT) in healthy people were synthesized. Data was summarized, and risk of bias (RoB) and level of evidence were determined. Results were pooled per influencing factor, grouped by body region and included in meta-analyses. Fifty-four studies were eligible. Five had low, nine moderate, and 40 high RoB. Following meta-analyses, a strong conclusion was found for the influence of scapular position, a moderate for the influence of gender, and a weak for the influence of age (shoulder/arm region) and blood pressure on PPT. In addition, body mass index, gender (leg region), alcohol consumption and pain vigilance may not influence PPT. Based on qualitative summary, depression and menopause may not influence PPT. For other variables there was only preliminary or conflicting evidence. However, caution is advised, since the majority of included studies showed a high RoB and several were not eligible to include in meta-analyses. Heterogeneity was high in the performed meta-analyses, and most conclusions were weak. More standardized research is necessary.

Maternal High-Energy Diet during Pregnancy and Lactation Impairs Neurogenesis and Alters the Behavior of Adult Offspring in a Phenotype-Dependent Manner

Obesity is one of the biggest and most costly health challenges the modern world encounters. Substantial evidence suggests that the risk of metabolic syndrome or obesity formation may be affected at a very early stage of development, in particular through fetal and/or neonatal overfeeding. Outcomes from epidemiological studies indicate that maternal nutrition during pregnancy and lactation has a profound impact on adult neurogenesis in the offspring. In the present study, an intergenerational dietary model employing overfeeding of experimental mice during prenatal and early postnatal development was applied to acquire mice with various body conditions. We investigated the impact of the maternal high-energy diet during pregnancy and lactation on adult neurogenesis in the olfactory neurogenic region involving the subventricular zone (SVZ) and the rostral migratory stream (RMS) and some behavioral tasks including memory, anxiety and nociception. Our findings show that a maternal high-energy diet administered during pregnancy and lactation modifies proliferation and differentiation, and induced degeneration of cells in the SVZ/RMS of offspring, but only in mice where extreme phenotype, such as significant overweight/adiposity or obesity is manifested. Thereafter, a maternal high-energy diet enhances anxiety-related behavior in offspring regardless of its body condition and impairs learning and memory in offspring with an extreme phenotype.

Associations of Body Mass Index With Pain and the Mediating Role of Inflammatory Biomarkers in People With Hand Osteoarthritis

OBJECTIVE

To examine the association of body mass index (BMI) with pain in people with hand osteoarthritis (OA), and explore whether this association, if causal, is mediated by systemic inflammatory biomarkers.

METHODS

In 281 Nor-Hand study participants, we estimated associations between BMI and hand pain, as measured by the Australian/Canadian Osteoarthritis Hand Index (AUSCAN; range 0-20) and Numerical Rating Scale (NRS; range 0-10); foot pain, as measured by NRS (range 0-10); knee/hip pain, as measured by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC; range 0-20); painful total body joint count; and pain sensitization. We fit natural-effects models to estimate natural direct and natural indirect effects of BMI on pain through inflammatory biomarkers.

RESULTS

Each 5-unit increase in BMI was associated with more severe hand pain (on average increased AUSCAN by 0.64 [95% confidence interval (95% CI) 0.23, 1.08]), foot pain (on average increased NRS by 0.65 [95% CI 0.36, 0.92]), knee/hip pain (on average increased WOMAC by 1.31 [95% CI 0.87, 1.73]), generalized pain, and pain sensitization. Mediation analyses suggested that the effects of BMI on hand pain and painful total body joint count were partially mediated by leptin and high-sensitivity C-reactive protein (hsCRP), respectively. Effect sizes for mediation by leptin were larger for the hands than for the lower extremities, and were statistically significant for the hands only.

CONCLUSION

In people with hand OA, higher BMI is associated with greater pain severity in the hands, feet, and knees/hips. Systemic effects of obesity, measured by leptin, may play a larger mediating role for pain in the hands than in the lower extremities. Low-grade inflammation, measured by hsCRP, may contribute to generalized pain in overweight/obese individuals.

Simple Quantitative Sensory Testing Reveals Paradoxical Co-existence of Hypoesthesia and Hyperalgesia in Diabetes

Background: Diabetic neuropathy is characterized by the paradoxical co-existence of hypo- and hyperalgesia to sensory stimuli. The literature shows consistently sensory differences between healthy and participants with diabetes. We hypothesized that due to differences in pathophysiology, advanced quantitative sensory testing (QST) might reveal sensory discrepancies between type 1 (T1D) and type 2 diabetes (T2D). Furthermore, we investigated whether vibration detection thresholds (VDT) were associated with sensory response.

Method: Fifty-six adults with T1D [43 years (28–58)], 99 adults with T2D [65 years (57–71)], and 122 healthy individuals [51 years (34–64)] were included. VDT, pressure pain detection thresholds (pPDT) and tolerance (pPTT), tonic cold pain (hand-immersion in iced water), and central pain mechanisms (temporal summation and conditioned pain modulation) were tested and compared between T1D and T2D. VDT was categorized into normal (< 18 V), intermediary (18–25 V), or high (> 25 V).

Results: In comparison to healthy, analysis adjusted for age, BMI, and gender revealed hypoalgesia to tibial (pPDT): p = 0.01, hyperalgesia to tonic cold pain: p < 0.01, and diminished temporal summation (arm: p < 0.01; abdomen: p < 0.01). In comparison to participants with T2D, participants with T1D were hypoalgesic to tibial pPDT: p < 0.01 and pPTT: p < 0.01, and lower VDT: p = 0.02. VDT was not associated with QST responses.

Conclusion: Participants with T1D were more hypoalgesic to bone pPDT and pPTT independent of lower VDT, indicating neuronal health toward normalization. Improved understanding of differentiated sensory profiles in T1D and T2D may identify improved clinical endpoints in future trials.

Taking the strain: An examination of upper back musculoskeletal tissue sensitivity in relation to upper back pain and breast size. A cross-sectional study

BACKGROUND

The physiological basis for upper back pain experienced by women with large breasts is unclear but could relate to sensitivity of musculoskeletal tissues strained from the postural adaptations to large breasts. The aim of this cross-sectional study was to examine if upper back pain and breast size were associated with greater localised sensitivity of upper back musculoskeletal tissues.

METHODS

119 healthy postmenopausal women (mean age 61 years) had their upper back pain (numerical rating scale), breast size (breast size score), and upper back tissue sensitivity (pressure pain thresholds (digital algometry, kPa)) assessed. The pressure pain thresholds of six skeletal sites (T2, T4, T6, T8, T10 and T12) and six muscular sites (pectoralis major, levator scapulae, sternocleidomastoid, and upper, middle, and lower trapezius muscles) were examined. Linear mixed models with random subject effects were used to evaluate differences in sensitivity at each anatomical site between participants grouped by upper back pain (nil-mild, moderate-severe) and breast size (small, large).

FINDINGS

For most sites, the differences in sensitivity between upper back pain groups were highly significant (P < 0.002) with significantly lower pressure pain thresholds (Mean difference (MD): 74.6 to 151.1 kPa) recorded for participants with moderate-severe upper back pain. There were no differences in sensitivity between breast size groups.

INTERPRETATION

Increased upper back musculoskeletal sensitivity is related to perceived upper back pain but not to breast size. It remains unclear if and how structural or mechanical factors related to breast size contribute to upper back pain in women with large breasts.

The Effect of Body Composition on Gait Variability Varies with Age: Interaction by Hierarchical Moderated Regression Analysis

Although body composition has been found to affect various motor functions (e.g., locomotion and balance), there is limited information on the effect of the interaction between body composition and age on gait variability. The purpose of this study was to determine the effect of body composition on gait according to age. A total of 80 men (40 young and 40 older males) participated in the experiment. Body composition was measured using bioelectrical impedance analysis (BIA), and gait parameters were measured with seven-dimensional inertial measurement unit (IMU) sensors as each participant walked for 6 min at their preferred pace. Hierarchical moderated regression analysis, including height as a control variable and age as a moderator variable, was performed to determine whether body composition could predict gait parameters. In young males, stride length decreased as body fat percentage (BFP) increased (R² = 13.4%), and in older males, stride length decreased more markedly as BFP increased (R² = 26.3%). However, the stride length coefficient of variation (CV) of the older males increased significantly as BFP increased (R² = 16.2%), but the stride length CV of young males did not change even when BFP increased. The increase in BFP was a factor that simultaneously caused a decrease in gait performance and an increase in gait instability in older males. Therefore, BFP is more important for a stable gait in older males.

Worst Pain Severity Profiles of Oncology Patients Are Associated With Significant Stress and Multiple Co-Occurring Symptoms

Little is known about the associations between pain, stress, and co-occurring symptoms in oncology patients. Purpose was to identify subgroups of patients with distinct worst pain profiles and evaluate for differences among the subgroups in demographic and clinical characteristics, as well as stress and symptom scores. Oncology outpatients (n = 1305) completed questionnaires prior to their second or third chemotherapy cycle. Worst pain intensity was assessed 6 times over 2 chemotherapy cycles using a 0 to 10 numeric rating scale. The 371 patients (28.4%) who had ≤1 occurrence of pain over the 6 assessments were classified as the None class. For the remaining 934 patients whose data were entered into the latent profile analysis, 3 distinct worst pain profiles were identified (ie Mild [12.5%], Moderate [28.6%], Severe [30.5%]). Compared to None class, Severe class had fewer years of education and a lower annual income; were less likely to be employed and married; less likely to exercise on a regular basis, had a higher comorbidity burden, and a worse functional status. Compared to None class, Severe class reported higher levels of general, disease-specific, and cumulative life stress and lower levels of resilience, as well as higher levels of depressive symptoms, anxiety, fatigue, sleep disturbance, and cognitive dysfunction. This study is the first to identify distinct worst pain profiles in a large sample of oncology patients receiving chemotherapy and associated risk factors. PERSPECTIVE: Unrelieved pain remains a significant problem for oncology patients receiving chemotherapy. High levels of stress and co-occurring symptoms contribute to a more severe pain profile in these patients.

The role of negative emotions in sex differences in pain sensitivity

Pain perception varies widely among individuals due to the varying degrees of biological, psychological, and social factors. Notably, sex differences in pain sensitivity have been consistently observed in various experimental and clinical investigations. However, the neuropsychological mechanism underlying sex differences in pain sensitivity remains unclear. To address this issue, we quantified pain sensitivity (i.e., pain threshold and tolerance) using the cold pressure test and negative emotions (i.e., pain-related fear, pain-related anxiety, trait anxiety, and depression) using well-established questionnaires and collected magnetic resonance imaging (MRI) data (i.e., high-resolution T1 structural images and resting-state functional images) from 450 healthy subjects. We observed that, as compared to males, females exhibited lower pain threshold and tolerance. Notably, sex differences in pain sensitivity were mediated by pain-related fear and anxiety. Specifically, pain-related fear and anxiety were the complementary mediators of the relationship between sex and pain threshold, and they were the indirect-only mediators of the relationship between sex and pain tolerance. Besides, structural MRI data revealed that the amygdala subnuclei (i.e., the lateral and basal nuclei in the left hemisphere) volumes were the complementary mediators of the relationship between sex and pain-related fear, which further influenced pain sensitivity. Altogether, our results provided a comprehensive picture of how negative emotions (especially pain-related negative emotions) and related brain structures (especially the amygdala) contribute to sex differences in pain sensitivity. These results deepen our understanding of the neuropsychological underpinnings of sex differences in pain sensitivity, which is important to tailor a personalized method for treating pain according to sex and the level of pain-related negative emotions for patients with painful conditions.

Exploring multidimensional characteristics in cervicogenic headache: Relations between pain processing, lifestyle, and psychosocial factors

OBJECTIVE

Although multidimensional interventions including physiotherapy, psychology, and education are generally recommended in managing headache, and to prevent chronification, such approach is lacking in cervicogenic headache (CeH). Therefore, exploring CeH within a biopsychosocial framework is deemed an essential first step.

METHODS

Non-randomized cross-sectional design to compare pain processing, lifestyle, and psychosocial characteristics between 18 participants with CeH (CeH group) (40.2 ± 10.9 years) and 18 matched controls (control group) (39.2 ± 13.1 years). Pain processing characteristics included degree of central sensitization (Central Sensitization Inventory), and (extra)-cephalic pressure pain thresholds (kPa/cm²/s). Lifestyle characteristics included sleep quality (Pittsburgh Sleep Quality Index), physical activity, screen time, and sedentary time (hours a week). Psychosocial characteristics included degree of depression, anxiety and stress (Depression Anxiety Stress Scale-21), and quality of life (Headache Impact Test-6).

RESULTS

Pain processing characteristics: More (p = .04) participants in the CeH group showed higher degrees of central sensitization compared to the control group. Lower (p < .05) (extra)-cephalic pressure pain thresholds were revealed in the CeH group compared to the control group for each muscle. Lifestyle and psychosocial characteristics: Compared to the control group, sleep quality and headache-related quality of life were worse (p < .0001) in the CeH group. Severe to extreme stress was experienced by more participants in the CeH group (p = .02). Further, significant relations between pain processing and (1) lifestyle characteristics and (2) psychosocial characteristics were seen in the CeH group.

CONCLUSION

Exploring multidimensional characteristics in CeH exposed relations between pain processing, lifestyle, and psychosocial characteristics. These novel findings fill a gap in the current scientific literature, and highlight the need for outcome research targeting lifestyle and psychosocial factors.

Pain sensitivity does not differ between obese and healthy weight individuals

Introduction

There is emerging evidence suggesting a relationship between obesity and chronic pain.

Objectives

The aim of this study was to determine whether pain-free obese individuals display altered pain responses to acute noxious stimuli, thus raising the possibility of greater pain sensitivity and potential susceptibility for chronic pain development.

Methods

Psychophysical and anthropometric data were collected from 38 individuals with an obese body mass index (BMI) classification (BMI ≥ 30) and 41 age/sex-matched individuals of a healthy BMI (BMI < 24.9). Because BMI may be an inaccurate index of obesity, additional anthropometric parameters of central adiposity and percent body fat were examined. Pain responses to suprathreshold noxious heat and cold stimuli were examined. Subjects provided pain intensity and unpleasantness ratings to noxious heat (49°C) applied at varying durations and locations (ventral forearm/lower leg). Cold pain ratings, thresholds, and tolerances were obtained after immersion of the hand in a cold-water bath (0-2°C). Between-group differences in pain responses, as well as relationships between pain responses and obesity parameters, were examined. Importantly, confounds that may influence pain such as anxiety, depression, impulsivity, sleepiness, and quality of life were assessed.

Results

No between-group differences in pain sensitivity to noxious heat and cold stimuli were found. No relationships were found between central adiposity or body fat (percentage or distribution) and pain responses to noxious heat or cold stimuli.

Conclusions

Obesity has minimal influence on pain sensitivity. Accordingly, it is unlikely that obesity alone increases susceptibility for chronic pain development through amplification of nociceptive processes.

When one suffers less, all suffer less: Individual pain ratings are more effective than group ratings in producing placebo hypoalgesia

Background

Placebo hypoalgesia can be induced by observing a person (model) whose pain relief is the result of the use of an inert substance or procedure. This study examined whether verbal modelling, that is, showing pain ratings provided by other people, is sufficient to induce placebo hypoalgesia.

Methods

Participants from the experimental groups were acquainted with pain ratings (presented on VASs) derived from a single person (groups 1 and 3) or a group of people (groups 2 and 4) that were allegedly subjected to the same painful procedure. The ratings of pain stimuli that were allegedly applied with placebo were lower than the ratings of stimuli applied without placebo. In two of the experimental groups (group 3 and 4), participants also watched a video recording showing individuals who allegedly provided pain ratings; however, they did not observe them undergoing pain stimulation. The control group did not undergo any manipulation. Then, the participants received a series of the same thermal pain stimuli that were applied either with or without placebo and rated their intensity.

Results

Placebo hypoalgesia was induced only in participants presented with pain ratings provided by a single person, regardless of whether this person was previously seen. However, the pain ratings presented to the participants generally decreased individual pain sensations, regardless of whether they came from a group of people or a single person.

Conclusions

Verbal modelling can produce placebo hypoalgesia and reduce pain sensations. It may be effectively used in clinical practice to modify patients' responses to pain treatment.

Significance

This study shows that knowledge about pain ratings provided by another person is sufficient to induce placebo hypoalgesia; thus, neither direct nor indirect observation of a person experiencing pain is necessary to induce this effect. Pain ratings derived from a group of people can decrease pain sensations but they do not produce placebo hypoalgesia.

Incidence of injury and pain in referees in German national handball leagues: a cohort study

Background

Handball referees play an important role during a handball match. Surprisingly, not much is known about their sports-related injuries and resulting pain, therefore the purpose of our study was to focus on injuries and sports-related pain in referees in German handball leagues.

Methods

During the 2018/19 national German handball season, referees of the German Federation of Handball (DHB) were contacted and asked to complete an injury and pain questionnaire on the penultimate matchday of the first and the second round of the season.

Results

Seventy referees participated in the study. One in three referees reported an injury during the last year and perceived some form of pain. Of those suffering from pain, 16.7% referees reported chronic pain disorders. During the season, 31.4% of referees incurred an injury and the majority of the 70 referees officiated despite pain (n = 43). Prospectively-enrolled data suggested an incidence of 11.6 (95% CI: 10.3 to 13.0) injuries per 1000 match hours, and 19.0 (95% CI: 16.8 to 21.3) sports-related pain events per 1000 match hours. The most common injuries were foot and knee injuries and a substantial number of the referees (n = 25) reported taking analgesics for the pain.

Conclusion

German handball referees are at risk of sports-related injuries with subsequent pain. Considering the injury profile, the incidence of sports-related pain events, and the high physiological demands of refereeing, it appears that prevention programs should be developed and integrated into the routine of the referee.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13102-021-00320-1.

Sources of Individual Differences in Pain

Pain is an immense clinical and societal challenge, and the key to understanding and treating it is variability. Robust interindividual differences are consistently observed in pain sensitivity, susceptibility to developing painful disorders, and response to analgesic manipulations. This review examines the causes of this variability, including both organismic and environmental sources. Chronic pain development is a textbook example of a gene-environment interaction, requiring both chance initiating events (e.g., trauma, infection) and more immutable risk factors. The focus is on genetic factors, since twin studies have determined that a plurality of the variance likely derives from inherited genetic variants, but sex, age, ethnicity, personality variables, and environmental factors are also considered.

Modulatory Effect of Probiotic Lactobacillus rhamnosus PB01 on Mechanical Sensitivity in a Female Diet-Induced Obesity Model

Obese animals and humans demonstrate higher sensitivity to pain stimuli. Among the endogenous factors prompting obesity, the intestinal microbiota has been proposed to influence responsiveness to pain. The beneficial effects of probiotics on obesity are well documented, whereas data on their analgesic efficacy is minimal. The protective effect of probiotics on nociception in diet-induced obese male mice has been previously demonstrated, but the sex differences in pain sensitivity and analgesic response do not allow for the generalization of these findings to the female gender. Hence, this study aimed at investigating the potential effects of oral probiotic supplementation on mechanical pain thresholds in female diet-induced obese mice compared with controls. Thirty-two adult female mice (N=32) were randomly divided into two groups receiving standard (normal-weight group; NW) or high-fat diet (diet-induced obesity; DIO). All rats received a single daily dose (1 × 109 CFU) of probiotics (Lactobacillus rhamnosus PB01, DSM14870) for four weeks by gavage. Mechanical pain thresholds were recorded by an electronic von Frey device at baseline, at the end of weeks 2, 4, 6, and 8 in both DIO and NW groups with and without consumption of probiotics. Blood samples were obtained for the measurement of lipid profile and reproductive hormone levels. Bodyweight was considerably lower (P < 0.001) in groups supplied with probiotics than groups without probiotics. Pressure pain threshold values showed a significant (P < 0.001) increase (reduced pain sensitivity) following probiotic supplementation, proposing a modulatory effect of probiotics on mechanical sensory circuits and mechanical sensitivity, which might be a direct consequence of weight loss or an indirect result of the probiotics' anti-inflammatory properties. Understanding the precise underlying mechanism for the effect of probiotics on weight loss and mechanical pain sensitivity seen in this study warrants further investigation.

Efficacy of dexmedetomidine on peritoneal dialysis catheter insertion

PURPOSE

Dexmedetomidine (DEX) is a sedative agent with minimal respiratory and hemodynamic effects. The present study aimed to evaluate its effectiveness in peritoneal dialysis (PD) catheter insertion.

METHODS

This single-center retrospective study included patients who underwent PD catheter insertion under spinal anesthesia in our hospital between January 2016 and December 2020. Patients were divided into the DEX and non-DEX groups according the use of DEX. After 1:1 propensity score matching to adjust for age, sex, body mass index, mean blood pressure (BP), and Charlson comorbidity index, we compared operation-related outcomes, including peak numerical rating scale (NRS), occurrence of nausea, vital signs, or operative time between the two groups.

RESULTS

Of a total of 44 patients, 9 patients received DEX, and 35 did not. After propensity score matching, each group consisted of 8 patients. Peak NRS was significantly lower (P = 0.003) in the DEX group compared with the non-DEX group. Maximum mean BP during the operation was also significantly lower in the DEX group compared with the non-DEX group (P = 0.020), with no significant differences in minimum mean BP between the two groups (P = 0.831). The DEX group showed a trend of shortened operative time (P = 0.068). There were no significant differences in the occurrence of nausea (P = 1.000). Moreover, there was no clinically important adverse event associated with use of DEX.

CONCLUSION

The use of DEX in PD catheter insertion under spinal anesthesia could safely improve operative analgesia.

Alterations in pronociceptive and antinociceptive mechanisms in patients with low back pain: a systematic review with meta-analysis

Altered pronociceptive and antinociceptive mechanisms are often implicated in painful conditions and have been increasingly studied over the past decade. For some painful conditions, alterations are well-established, but in populations with low back pain (LBP), there remains considerable debate whether these mechanisms are altered. The present systematic review aimed to address this issue by identifying studies assessing conditioned pain modulation (CPM) and/or temporal summation of pain (TSP) in patients with LBP, comparing with either a healthy control group or using a method with reference data available. Qualitative synthesis and quantitative meta-analysis of group differences were performed. For CPM and TSP, 20 and 29 original articles were eligible, with data for meta-analysis obtainable from 18 (1500 patients and 505 controls) and 27 (1507 patients and 1127 controls) studies, respectively. Most studies were of poor-to-fair quality with significant heterogeneity in study size, population, assessment methodology, and outcome. Nonetheless, CPM was impaired in patients with LBP compared with controls (standardized mean difference = -0.44 [-0.64 to -0.23], P < 0.001), and the magnitude of this impairment was related to pain chronicity (acute/recurrent vs chronic, P = 0.003), duration (RS = -0.62, P = 0.006), and severity (RS = -0.54, P = 0.02). Temporal summation of pain was facilitated in patients with LBP compared with controls (standardized mean difference = 0.50 [0.29-0.72], P < 0.001), and the magnitude of this facilitation was weakly related to pain severity (RS= 0.41, P = 0.04) and appeared to be influenced by test modality (P < 0.001). Impaired CPM and facilitated TSP were present in patients with LBP compared with controls, although the magnitude of differences was small which may direct future research on the clinical utility.

Safety and tolerability of repeated sessions of deep transcranial magnetic stimulation in obesity

PURPOSE

Repetitive Transcranial Magnetic Stimulation (rTMS) has been demonstrated to be effective in body weight control in individuals with obesity. Most clinical trials on rTMS provided a reassuring safety profile. In the present work, we present an extensive analysis on both severe and mild Adverse Events (AEs) in obese individuals treated with rTMS.

METHODS

We examined the intensity, duration, correlation with the treatment, up to 1 year after the end of rTMS treatment.

RESULTS

Descriptive analysis included a total of 63 subjects undergoing a 5-week deep rTMS experimental treatment for obesity (age 48.3 ± 10.4 years; BMI 36.3 ± 4.4 kg/m²): 31 patients were treated with high-frequency rTMS (HF), 13 with low-frequency rTMS (LF), and 19 were sham treated (Sham). Thirty-two subjects (50.8%) reported a total of 52 AEs, including mainly moderate (51.9%) events. The most frequently reported side effects were headaches of moderate intensity (40.4%) and local pain/discomfort (19.2%) and resulted significantly more frequent in HF group compared to other groups (p < 0.05). No significant differences among groups were found for the other reported AEs: drowsiness, insomnia, paresthesia, vasovagal reactions, hypertensive crisis. No AEs potentially related to the rTMS arised up to 1 year from the end of the treatment.

CONCLUSIONS

This is the first comprehensive safety analysis in obese patients treated with rTMS. The analysis did not reveal any unexpected safety concerns. Only headaches and local pain/discomfort have been significantly more frequent in the HF group, confirming the good tolerability of rTMS even in the obese population potentially more susceptible to side effects of brain stimulation.

Sonographic measures and sensory threshold of the normal sciatic nerve and hamstring muscles

PURPOSE

The sciatic nerve innervates the hamstring muscles. Occasionally, the sciatic nerve is injured along with a hamstring muscle. Detailed biomechanical and sensory thresholds of these structures are not well-characterized. Therefore, we designed a prospective study that explored high-resolution ultrasound (US) at multiple sites to evaluate properties of the sciatic nerve, including cross-sectional area (CSA) and shear-wave elastography (SWE). We also assessed SWE of each hamstring muscle at multiple sites. Mechanical algometry was obtained from the sciatic nerve and hamstring muscles to assess multi-site pressure pain threshold (PPT).

METHODS

Seventy-nine asymptomatic sciatic nerves and 147 hamstring muscles (25 males, 24 females) aged 18-50 years were evaluated. One chiropractic radiologist with 4.5 years of US experience performed the evaluations. Sciatic nerves were sampled along the posterior thigh at four sites obtaining CSA, SWE, and algometry. All three hamstring muscles were sampled at two sites utilizing SWE and algometry. Descriptive statistics, two-way ANOVA, and rater reliability were assessed for data analysis with p ≤ 0.05.

RESULTS

A significant decrease in sciatic CSA from proximal to distal was correlated with increasing BMI (p < 0.001). Intra-rater and inter-rater reliability for CSA was moderate and poor, respectively. Elastographic values significantly increased from proximal to distal with significant differences in gender and BMI (p = 0.002). Sciatic PPT significantly decreased between sites 1 and 2, 1 and 3, and 1 and 4. Significant correlation between gender and PPT was noted as well as BMI (p < 0.001). Hamstring muscle elastographic values significantly differed between biceps femoris and semitendinosus (p < 0.001) and biceps femoris and semimembranosus (p < 0.001). All three hamstring muscles demonstrated increased PPT in males compared to females (p < 0.001). In addition, PPT of the biceps femoris correlated with BMI (p = 0.02).

CONCLUSION

High-resolution US provided useful metrics of sciatic nerve size and biomechanical properties. PPT for the normal sciatic nerve and hamstring muscles was obtained for future clinical application.

Laparoscopic Sleeve Gastrectomy under Awake Paravertebral Blockade Versus General Anesthesia: Comparison of Short-Term Outcomes

AIMS

This study aimed at comparing the pre-, intra-, and early postoperative outcomes, between patients who underwent PVB vs general anesthesia (GA) during LSG. Follow-up of weight loss at least 1 year postoperatively was also evaluated.

METHODS

A cohort study was conducted by selecting all patients who underwent LSG under PVB and GA at Makassed General Hospital between 2010 and 2016. Demographic, social, pre-op health status, body mass index (BMI), operative time, postoperative pain and pain medication consumption, postoperative complications and length of hospital stay, all were studied. Follow-up weight loss was collected up to 5 years postoperatively. Data entry, management, and descriptive and inferential statistics were performed using SPSS.

RESULTS

A total of 210 participants were included in this study of which 48 constituted the PVB group and 162 patients composed the GA group. Both groups were similar in baseline demographic factors, with patients in PVB suffering from higher number and advanced stage of comorbidities than the GA group. Mean operative time was similar in between the two groups with 80 ± 20 min for PVB and 82 ± 18 min for GA group. Intraoperative complications were scarce among both study groups. GA group requested a second dose of analgesia earlier than PVB group. After at least 1 year postoperatively, the mean percentage of excess weight loss was 81.35 ± 15.5% and 77.89 ± 14.3% for the PVB and GA groups, respectively, P value 0.45.

CONCLUSION

Outcomes of LSG under both types of anesthesia (PVB alone and GA alone) were found to be comparable. However, the need for analgesia was significantly less in the PVB group compared to GA group.

Using Portable Ultrasound to Monitor the Neuromuscular Reactivity to Low-Frequency Electrical Stimulation

Neuromuscular electrical stimulation (NMES) is useful for muscle strengthening and for motor restoration of stroke patients. Using a portable ultrasound instrument, we developed an M-mode imaging protocol to visualize contractions elicited by NMES in the quadriceps muscle group. To quantify muscle activation, we performed digital image processing based on the Teager–Kaiser energy operator. The proposed method was applied for 35 voluntary patients (18 women and 17 men), of 63.8 ± 14.1 years and body mass index (BMI) 30.2 ± 6.70 kg/m² (mean ± standard deviation). Biphasic, rectangular electric pulses of 350 µs duration were applied at two frequencies (60 Hz and 120 Hz), and ultrasound was used to assess the sensory threshold (ST) and motor threshold (MT) amplitude of the NMES signal. The MT was 23.4 ± 4.94 mA, whereas the MT to ST ratio was 2.69 ± 0.57. Linear regression analysis revealed that MT correlates poorly with body mass index (R² = 0.004) or with the thickness of the subcutaneous adipose tissue layer that covers the treated muscle (R² = 0.013). Our work suggests that ultrasound is suitable to visualize neuromuscular reactivity during electrotherapy. The proposed method can be used in the clinic, enabling the physiotherapist to establish personalized treatment parameters.

Experimental sleep disruption attenuates morphine analgesia: findings from a randomized trial and implications for the opioid abuse epidemic

Preclinical studies demonstrate that sleep disruption diminishes morphine analgesia and modulates reward processing. We sought to translate these preclinical findings to humans by examining whether sleep disruption alters morphine's analgesic and hedonic properties. We randomized 100 healthy adults to receive morphine versus placebo after two nights of undisturbed sleep (US) and two nights of forced awakening (FA) sleep disruption. Sleep conditions were counterbalanced, separated by a two-week washout. The morning after both sleep conditions, we tested cold pressor pain tolerance before and 40-min after double-blind injection of .08 mg/kg morphine or placebo. The primary outcome was the analgesia index, calculated as the change in cold pressor hand withdrawal latency (HWL) before and after drug injection. Secondary outcomes were ratings of feeling "high," drug "liking," and negative drug effects. We found a significant sleep condition by drug interaction on the analgesia index (95% CI - 0.57, - 0.001). After US, subjects receiving morphine demonstrated significantly longer HWL compared to placebo (95% CI 0.23, 0.65), but not after FA (95% CI - 0.05, 0.38). Morphine analgesia was diminished threefold under FA, relative to US. After FA, females (95% CI - 0.88, - 0.05), but not males (95% CI - 0.23, 0.72), reported decreased subjective "high" effects compared to US. After FA, females (95% CI 0.05, 0.27), but not males (95% CI - 0.10, 0.11), administered morphine reported increased negative drug effects compared to US. These data demonstrate that sleep disruption attenuates morphine analgesia in humans and suggest that sleep disturbed males may be at greatest risk for problematic opioid use.