80 results found
Strutton P, Wong F, Reddy A, et al., 2023, Responders and non-responders to topical capsaicin display distinct temporal summation of pain profiles, PAIN Reports, Vol: 8, Pages: 1-8, ISSN: 2471-2531
Introduction: Topical application of capsaicin can produce an ongoing pain state in healthy participants. However, approximately one-third report no pain response (ie, nonresponders), and the reasons for this are poorly understood.Objectives: In this study, we investigated temporal summation of pain (TSP) profiles, pain ratings and secondary hyperalgesia responses in responders and nonresponders to 1% topical capsaicin cream.Methods: Assessments were made at baseline and then during an early (ie, 15 minutes) and late (ie, 45 minutes) time points post-capsaicin in 37 healthy participants.Results: Participants reporting a visual analogue scale (VAS) rating of >50 were defined as responders (n = 24) and those with <50 VAS rating were defined as nonresponders (n = 13). There was a facilitation of TSP during the transition from an early to the late time point post-capsaicin (P<0.001) and the development of secondary hyperalgesia (P<0.05) in the responder group. Nonresponders showed no changes in TSP or secondary hyperalgesia during the early and late time points. There was an association between baseline TSP scores and the later development of a responder or nonresponder phenotype (r = 0.36; P = 0.03). Receiver operating characteristic analysis revealed that baseline TSP works as a good response predictor at an individual level (area under the curve = 0.75).Conclusion: These data suggest that responders and nonresponders have different facilitatory pain mechanisms. The assessment of TSP may help to identify participants with stronger endogenous pain facilitation who may be more likely to respond to topical capsaicin.
van Helden JFL, Martinez-Valdes E, Strutton PH, et al., 2022, Reliability of high-density surface electromyography for assessing characteristics of the thoracic erector spinae during static and dynamic tasks, Journal of Electromyography and Kinesiology, Vol: 67, ISSN: 1050-6411
PURPOSE: To establish intra- and inter-session reliability of high-density surface electromyography (HDEMG)-derived parameters from the thoracic erector spinae (ES) during static and dynamic goal-directed voluntary movements of the trunk, and during functional reaching tasks. METHODS: Twenty participants performed: 1) static trunk extension, 2) dynamic trunk forward and lateral flexion, and 3) multidirectional functional reaching tasks on two occasions separated by 7.5 ± 1.2 days. Muscle activity was recorded bilaterally from the thoracic ES. Root mean square (RMS), coordinates of the barycentre, mean frequency (MNF), and entropy were derived from the HDEMG signals. Reliability was determined with intraclass correlation coefficient (ICC), coefficient of variation, and standard error of measurement. RESULTS: Good-to-excellent intra-session reliability was found for all parameters and tasks (ICC: 0.79-0.99), whereas inter-session reliability varied across tasks. Static tasks demonstrated higher reliability in most parameters compared to functional and dynamic tasks. Absolute RMS and MNF showed the highest overall reliability across tasks (ICC: 0.66-0.98), while reliability of the barycentre was influenced by the direction of the movements. CONCLUSION: RMS and MNF derived from HDEMG show consistent inter-session reliability in goal-directed voluntary movements of the trunk and reaching tasks, whereas the measures of the barycentre and entropy demonstrate task-dependent reliability.
Chaudhari N, Strutton PH, Wickham AJ, et al., 2022, Heat stress associated with aerosol PPE and its impact, OCCUPATIONAL MEDICINE-OXFORD, ISSN: 0962-7480
van der Kruk E, Strutton P, Koizia LJ, et al., 2022, Why do older adults stand-up differently to young adults?: investigation of compensatory movement strategies in sit-to-walk, npj Aging, Vol: 8, ISSN: 2731-6068
Functional motor redundancy enables humans to move with distinct muscle activation patterns while achieving a similar outcome. Since humans select similar strategies, there seems to be an optimal control. However, older adults move differently to young adults. The question is whether this is this due to an altered reinforcement scheme, altered sensory inputs, or due to alterations in the neuromusculoskeletal systems, so that it is no longer optimal or possible to execute the same movement strategies. The aim of this study was to analyse natural compensation strategies in the vital daily-life-task, sit-to-walk, in relation to neuromuscular capacity and movement objectives in younger (27.2 ± 4.6 years, N = 27, 14♀) and elderly (75.9 ± 6.3 years, N = 23, 12♀) adults. Aspects of the neuromuscular system that are prone to age-related decline and feasible to quantify were assessed (i.e. strength, nerve conductivity, fear of falling). Kinematics and muscle activity were recorded and joint kinetics were estimated using biomechanical models. Elderly men consistently used their arms when standing up. This strategy was not associated with a lack of or a reduction in strength, but with a reduction, but no lack of, ankle joint range of motion, and with increased fear of falling. The results show that humans preferentially maintain a minimum threshold of neuromuscular reserve to cope with uncertainties which results in compensation prior to coming up against physical limitations. Smaller base of support while standing up, a compensatory strategy with possibly greater risk of falls, was associated with muscular weakness, and longer nerve conduction latencies.
Alexander C, Strutton P, Kassam J, et al., 2022, An investigation of the control of quadriceps in people who are hypermobile; a case control design. Do the results impact our choice of exercise for people with symptomatic hypermobility?, BMC Musculoskeletal Disorders, Vol: 23, ISSN: 1471-2474
Background: People with symptomatic hypermobility have altered proprioception however, the origin of this is unclear and needs further investigation to target rehabilitation appropriately. The objective of this investigation was to explore the corticospinal and reflex control of quadriceps and see if it differed between three groups of people: those who have symptomatic hypermobility, asymptomatic hypermobility and normal flexibility. Methods: Using Transcranial Magnetic Stimulation (TMS) and electrical stimulation of peripheral nerves, motor evoked potentials (MEPs) and Hoffman (H) reflexes of quadriceps were evoked in the three groups of people. The threshold and latency of MEPs and the slope of the input-output curves and the amplitude of MEPs and H reflexes were compared across the groups.Results: The slope of the input-output curve created from MEPs as a result of TMS was steeper in people with symptomatic hypermobility when compared to asymptomatic and normally flexible people (p = 0.04). There were no other differences between the groups.Conclusion: Corticospinal excitability and the excitability at the motoneurone pool are not likely candidates for the origin of proprioceptive loss in people with symptomatic hypermobility. This is discussed in the light of other work to suggest the receptor sitting in hypermobile connective tissue is a likely candidate. This suggests that treatment aimed at improving receptor responsiveness through increasing muscle tone, may be an effective rehabilitation strategy.
Gimzewska M, Berthelot M, Sarai P, et al., 2022, Evaluation of a novel wireless near-infrared spectroscopy (NIRS) device in the detection of tourniquet induced ischaemia, BMJ Innovations, ISSN: 2055-8074
Tu W, Cacho-Soblechero M, Terracina D, et al., 2021, A 4-channel SEMG ASIC with real-time muscle fatigue feature extraction, International Symposium on Circuits and Systems, Publisher: IEEE, Pages: 1-5, ISSN: 0271-4310
This paper presents a 4 channel ASIC for sEMG sensing with in-built muscle fatigue and activity feature extraction. Each channel filters and conditions the electrode signal in parallel, while extracting key features for Low Back Pain (LBP) fatigue monitoring and forecasting - Zero Crossing rate and Root Mean Square through sEMG Envelope. The channels are integrated with a Transimpedance Amplifier, an 10-Bit ADC and a Digital Control Unit to digitise and enable transmission of extracted features. Fabricated in TSMC 180nm, these channels present a compact form factor (90µm× 630µm) and a low power consumption (42.61 µW), ideal characteristic for wearable devices utilised for long-term monitoring of activities.
Mehesz E, Karoui H, Strutton PH, et al., 2021, Exposure to an immersive virtual reality environment can modulate perceptual correlates of endogenous analgesia and central sensitization in healthy volunteers, Journal of Pain, Vol: 22, Pages: 707-714, ISSN: 1526-5900
Virtual reality (VR) has been shown to produce analgesic effects during different experimental and clinical pain states. Despite this, the top-down mechanisms are still poorly understood. In this study, we examined the influence of both a real and sham (ie, the same images in 2D) immersive arctic VR environment on conditioned pain modulation (CPM) and in a human surrogate model of central sensitization in 38 healthy volunteers. CPM and acute heat pain thresholds were assessed before and during VR/sham exposure in the absence of any sensitization. In a follow-on study, we used the cutaneous high frequency stimulation model of central sensitization and measured changes in mechanical pain sensitivity in an area of heterotopic sensitization before and during VR/sham exposure. There was an increase in CPM efficiency during the VR condition compared to baseline (P < .01). In the sham condition, there was a decrease in CPM efficiency compared to baseline (P < .01) and the real VR condition (P < .001). Neither real nor sham VR had any effect on pain ratings reported during the conditioning period or on heat pain threshold. There was also an attenuation of mechanical pain sensitivity during the VR condition indicating a lower sensitivity compared to sham (P < .05). We conclude that exposure to an immersive VR environment has no effect over acute pain thresholds but can modulate dynamic CPM responses and mechanical hypersensitivity in healthy volunteers.
Bonsu AN, Nousi S, Lobo R, et al., 2021, Vestibulo-perceptual influences upon the vestibulo-spinal reflex, Experimental Brain Research, Vol: 239, Pages: 2141-2149, ISSN: 0014-4819
The vestibular system facilitates gaze and postural stability via the vestibulo-ocular (VOR) and vestibulo-spinal reflexes, respectively. Cortical and perceptual mechanisms can modulate long-duration VOR responses, but little is known about whether high-order neural phenomena can modulate short-latency vestibulo-spinal responses. Here, we investigate this by assessing click-evoked cervical vestibular myogenic-evoked potentials (VEMPS) during visual roll motion that elicited an illusionary sensation of self-motion (i.e. vection). We observed that during vection, the amplitude of the VEMPs was enhanced when compared to baseline measures. This modulation in VEMP amplitude was positively correlated with the subjective reports of vection strength. That is, those subjects reporting greater subjective vection scores exhibited a greater increase in VEMP amplitude. Control experiments showed that simple arousal (cold-induced discomfort) also increased VEMP amplitude but that, unlike vection, it did not modulate VEMP amplitude linearly. In agreement, small-field visual roll motion that did not induce vection failed to increase VEMP amplitude. Taken together, our results demonstrate that vection can modify the response of vestibulo-collic reflexes. Even short-latency brainstem vestibulo-spinal reflexes are influenced by high-order mechanisms, illustrating the functional importance of perceptual mechanisms in human postural control. As VEMPs are inhibitory responses, we argue that the findings may represent a mechanism whereby high-order CNS mechanisms reduce activity levels in vestibulo-collic reflexes, necessary for instance when voluntary head movements need to be performed.
Deane JA, Lim AKP, McGregor AH, et al., 2021, Understanding the impact of lumbar disc degeneration and chronic low back pain: a cross-sectional electromyographic analysis of postural strategy during predicted and unpredicted postural perturbations, PLoS One, Vol: 16, ISSN: 1932-6203
People with chronic low back pain (LBP) exhibit changes in postural control. Stereotypical muscle activations resulting from external perturbations include anticipatory (APAs) and compensatory (CPAs) postural adjustments. The aim and objective of this study was to determine differences in postural control strategies (peak amplitude, APAs and CPAs) between symptomatic and asymptomatic adults with and without Lumbar Disc Degeneration (LDD) using surface electromyography during forward postural perturbation. Ninety-seven subjects participated in the study (mean age 50 years (SD 12)). 3T MRI was used to acquire T2 weighted images (L1-S1). LDD was determined using Pfirrmann grading. A bespoke translational platform was designed to deliver horizontal perturbations in sagittal and frontal planes. Electromyographic activity was analysed bilaterally from 8 trunk and lower limb muscles during four established APA and CPA epochs. A Kruskal-Wallis H test with Bonferroni correction for multiple comparisons was conducted. Four groups were identified: no LDD no pain (n = 19), LDD no pain (n = 38), LDD pain (n = 35) and no LDD pain (n = 5). There were no significant differences in age or gender between groups. The most significant difference between groups was observed during forward perturbation. In the APA and CPA phases of predictable forward perturbation there were significant differences ankle strategy between groups (p = 0.007–0.008); lateral gastrocnemius and tibialis anterior activity was higher in the LDD pain than the LDD no pain group. There were no significant differences in the unpredictable condition (p>0.05). These findings were different from the remaining groups, where significant differences in hip strategy were observed during both perturbation conditions (p = 0.004–0.006). Symptomatic LDD patients exhibit different electromyographic strategies to asymptomatic LDD controls. Future LBP electromyographic research should benefit from considering asses
Bogomolova K, Sam AH, Misky AT, et al., 2021, Development of a virtual three-dimensional assessment scenario for anatomical education, Anatomical Sciences Education, Vol: 14, Pages: 385-393, ISSN: 1935-9772
In anatomical education three-dimensional (3D) visualization technology allows for active and stereoscopic exploration of anatomy and can easily be adopted into medical curricula along with traditional 3D teaching methods. However, most often knowledge is still assessed with two-dimensional (2D) paper-and-pencil tests. To address the growing misalignment between learning and assessment, this viewpoint commentary highlights the development of a virtual 3D assessment scenario and perspectives from students and teachers on the use of this assessment tool: a 10-minute session of anatomical knowledge assessment with real-time interaction between assessor and examinee, both wearing a HoloLens and sharing the same stereoscopic 3D augmented reality model. Additionally, recommendations for future directions, including implementation, validation, logistic challenges, and cost-effectiveness, are provided. Continued collaboration between developers, researchers, teachers, and students is critical to advancing these processes.
Hughes SW, Basra M, Chan C, et al., 2021, Corrigendum to: Capsaicin-induced changes in electrical pain perception threshold can be used to assess the magnitude of secondary hyperalgesia in humans, Pain Medicine, Vol: 22, Pages: 237-237, ISSN: 1526-2375
Hughes SW, Basra M, Chan C, et al., 2020, Capsaicin-induced changes in electrical pain perception threshold can be used to assess the magnitude of secondary hyperalgesia in humans., Pain Medicine, Vol: 21, Pages: 2830-2838, ISSN: 1526-2375
OBJECTIVES: Areas of secondary hyperalgesia can be assessed using quantitative sensory testing (QST). Delivering noxious electrocutaneous stimulation could provide added benefit by allowing multiple measurements of the magnitude of hyperalgesia. We aimed to characterize the use of electrical pain perception (EPP) thresholds alongside QST as a means by which to measure changes in pain thresholds within an area of secondary mechanical hyperalgesia. METHODS: EPP and heat pain thresholds (HPTs) were measured at five distinct points at baseline and following 1% capsaicin cream application, one within a central zone and four within a secondary zone. Areas of secondary mechanical hyperalgesia were mapped using QST. In a further 14 participants, capsaicin-induced reduction in EPP thresholds was mapped using a radial lines approach across 24 points. RESULTS: There was a reduction in EPP threshold measured at the four points within the secondary zone, which was within the mapped area of mechanical secondary hyperalgesia. The magnitude of secondary hyperalgesia could be split into a mild (∼4% reduction) and severe (∼21% reduction) area within an individual subject. There was no reduction in HPT within the secondary zone, but there was a reduction in both HPT and EPP threshold within the primary zone. EPP mapping revealed differences in the magnitude and spread of hyperalgesia across all subjects. CONCLUSIONS: Measuring capsaicin-induced reduction in EPP thresholds can be used to map hyperalgesic areas in humans. This semi-automated approach allows rapid assessment of the magnitude of hyperalgesia, both within an individual subject and across a study population.
Chiou S-Y, Strutton PH, 2020, Crossed corticospinal facilitation between arm and trunk muscles correlates with trunk control after spinal cord injury, Frontiers in Human Neuroscience, Vol: 14, Pages: 1-11, ISSN: 1662-5161
Objective: To investigate whether crossed corticospinal facilitation between arm and trunk muscles is preserved following spinal cord injury (SCI) and to elucidate these neural interactions for postural control during functional arm movements.Methods: Using transcranial magnetic stimulation (TMS) in 22 subjects with incomplete SCI motor evoked potentials (MEPs) in the erector spinae (ES) muscle were examined when the contralateral arm was at rest or performed 20% of maximal voluntary contraction (MVC) of biceps brachii (BB) or triceps brachii (TB). Trunk function was assessed with rapid shoulder flexion and forward-reaching tasks.Results: MEP amplitudes in ES were increased during elbow flexion in some subjects and this facilitatory effect was more prominent in subjects with thoracic SCI than in the subjects with cervical SCI. Those who showed the increased MEPs during elbow flexion had faster reaction times and quicker anticipatory postural adjustments of the trunk in the rapid shoulder flexion task. The onset of EMG activity in ES during the rapid shoulder flexion task correlated with the trunk excursion in forward-reaching.Conclusions: Our findings demonstrate that crossed corticospinal facilitation in the trunk muscles can be preserved after SCI and is reflected in trunk control during functional arm movements.
Mullington CJ, Low DA, Strutton PH, et al., 2020, A mechanistic study of the tremor associated with epidural anaesthesia for intrapartum caesarean delivery, International Journal of Obstetric Anesthesia, Vol: 43, Pages: 56-64, ISSN: 0959-289X
BackgroundIt is not known if the tremor associated with an epidural top-up dose for intrapartum caesarean delivery is thermoregulatory shivering. A tremor is only shivering if it has the same frequency profile as cold stress-induced shivering. Thermoregulatory shivering is a response to a reduction in actual body temperature, whereas non-thermoregulatory shivering may be triggered by a reduction in sensed body temperature. This mechanistic study aimed to compare: 1. the frequency profiles of epidural top-up tremor and cold stress-induced shivering; and 2. body temperature (actual and sensed) before epidural top-up and at the onset of tremor.MethodsTwenty obstetric patients received an epidural top-up for intrapartum caesarean delivery and 20 non-pregnant female volunteers underwent a cold stress. Tremor, surface electromyography, core temperature, skin temperature (seven sites) and temperature sensation votes (a bipolar visual analog score ranging from −50 to +50 mm) were recorded.ResultsThe mean (SD) primary oscillation (9.9 (1.9) Hz) frequency of epidural top-up tremor did not differ from that of cold stress-induced shivering (9.0 (1.6) Hz; P=0.194), but the mean (SD) burst frequency was slower (6.1 (1.2) × 10−2 Hz vs 6.9 (0.7) × 10−2 Hz, respectively; P=0.046). Before the epidural top-up dose, the mean (SD) core temperature was 37.6 (0.6) °C. Between the epidural top-up dose and the onset of tremor the mean (SD) core temperature did not change (–0.1 (0.1) °C; P=0.126), the mean (SD) skin temperature increased (+0.4 (0.4) °C; P=0.002) and the mean (SD) temperature sensation votes decreased (−12 (16) mm; P=0.012).ConclusionThese results suggest that epidural top-up tremor is a form of non-thermoregulatory shivering triggered by a reduction in sensed body temperature.
Moniri A, Terracina D, Rodriguez-Manzano J, et al., 2020, Real-time forecasting of sEMG features for trunk muscle fatigue using machine learning, IEEE Transactions on Biomedical Engineering, Vol: 68, Pages: 718-727, ISSN: 0018-9294
Objective: Several features of the surface electromyography (sEMG) signal are related to muscle activity and fatigue. However, the time-evolution of these features are non-stationary and vary between subjects. The aim of this study is to investigate the use of adaptive algorithms to forecast sMEG feature of the trunk muscles. Methods: Shallow models and a deep convolutional neural network (CNN) were used to simultaneously learn and forecast 5 common sEMG features in real-time to provide tailored predictions. This was investigated for: up to a 25 second horizon; for 14 different muscles in the trunk; across 13 healthy subjects; while they were performing various exercises. Results: The CNN was able to forecast 25 seconds ahead of time, with 6.88% mean absolute percentage error and 3.72% standard deviation of absolute percentage error, across all the features. Moreover, the CNN outperforms the best shallow model in terms of a figure of merit combining accuracy and precision by at least 30% for all the 5 features. Conclusion: Even though the sEMG features are non-stationary and vary between subjects, adaptive learning and forecasting, especially using CNNs, can provide accurate and precise forecasts across a range of physical activities. Significance: The proposed models provide the groundwork for a wearable device which can forecast muscle fatigue in the trunk, so as to potentially prevent low back pain. Additionally, the explicit realtime forecasting of sEMG features provides a general model which can be applied to many applications of muscle activity monitoring, which helps practitioners and physiotherapists improve therapy.
Hughes SW, Hellyer PJ, Sharp DJ, et al., 2020, Diffusion tensor imaging of lumbar spinal nerves reveals changes in microstructural integrity following decompression surgery associated with improvements in clinical symptoms: A case report, Magnetic Resonance Imaging, Vol: 69, Pages: 65-70, ISSN: 0730-725X
The outcomes from spinal nerve decompression surgery are highly variable with a sizable proportion of elderly foraminal stenosis patients not regaining good pain relief. A better understanding of nerve root compression before and following decompression surgery and whether these changes are mirrored by improvements in symptoms may help to improve clinical decision-making processes. This case study used a combination of diffusion tensor imaging (DTI), clinical questionnaires and motor neurophysiology assessments before and up to 3 months following spinal decompression surgery. In this case report, a 70-year-old women with compression of the left L5 spinal nerve root in the L5-S1 exit foramina was recruited to the study. At 3 months following surgery, DTI revealed marked improvements in left L5 microstructural integrity to a similar level to that seen in the intact right L5 nerve root. This was accompanied by a gradual improvement in pain-related symptoms, mood and disability score by 3 months. Using this novel multimodal approach, it may be possible to track concurrent improvements in pain-related symptoms, function and microstructural integrity of compressed nerves in elderly foraminal stenosis patients undergoing decompression surgery.
Hughes SW, Ward G, Strutton PH, 2020, Anodal transcranial direct current stimulation over the primary motor cortex attenuates capsaicin-induced dynamic mechanical allodynia and mechanical pain sensitivity in humans., European Journal of Pain, Vol: 24, Pages: 1130-1137, ISSN: 1090-3801
BACKGROUND: Anodal transcranial direct current stimulation over the primary cortex has been shown to activate regions of the brain involved in the descending modulation of pain sensitivity. However, more research is required in order to dissect the spinal cord analgesic mechanisms associated with the development of central sensitisation. METHODS: In this randomised, double blind, cross over study 12 healthy participants had baseline mechanical stimulus response (S/R) functions measured before and after the development of capsaicin-induced ongoing pain sensitivity. The effects of 20 min of either real or sham transcranial direct current stimulation (tDCS, 2 mA) over the primary motor cortex on dynamic mechanical allodynia (DMA) and mechanical pain sensitivity (MPS) was then investigated. RESULTS: Topical application of capsaicin resulted in an increase in area under the pain ratings curve for both DMA (p < .01) and MPS (p < .01). The effects of tDCS on the area under the curve ratio (i.e. post/pre-treatment) revealed significant analgesic effects over DMA (p < .05) and MPS (p < .05) when compared to sham. CONCLUSIONS: This study demonstrates that anodal tDCS over the primary motor cortex can reduce both dynamic and static forms of mechanical pain sensitivity associated with the development of DMA and MPS, respectively. The use of tDCS may provide a novel mechanism-driven therapy in chronic pain patients with altered mechanical S/R functions.
Terracina D, Moniri A, Rodriguez-Manzano J, et al., 2019, Real-time forecasting and classification of trunk muscle fatigue using surface electromyography, IEEE Biomedical Circuits and Systems Conference (BioCAS), Publisher: IEEE, Pages: 1-4, ISSN: 2163-4025
Low Back Pain (LBP) affects the vast majority of the population at some point in their lives. People with LBP show altered trunk muscle activity and enhanced fatigability of trunk muscles is associated with the development and future risk of LBP. Therefore, a system that can forecast trunk muscle activity and detect fatigue can help subjects, practitioners and physiotherapists in the diagnosis, monitoring and recovery of LBP. In this paper, we present a novel approach in order to determine whether subjects are fatigued, or transitioning to fatigue, 25 seconds ahead of time using surface Electromyography (sEMG) from 14 trunk muscles. This is achieved using a three-step approach: A) extracting features related to fatigue from sEMG, B) forecasting the features using a real-time adaptive filter and C) performing dimensionality reduction (from 70 to 2 features) and then classifying subjects using a supervised machine learning algorithm. The forecasting classification accuracy across 13 patients is 99.1% ± 0.004 and the area under the micro and macro ROC curve is 0.935 ± 0.036 and 0.940 ±0.034 as determined by 10-fold cross validation. The proposed approach enables a computationally efficient solution which could be implemented in a wearable device for preventing muscle injury.
Hughes S, Zhao H, Auvinet E, et al., 2019, Attenuation of capsaicin-induced ongoing pain and secondary hyperalgesia during exposure to an immersive virtual reality environment, PAIN Reports, Vol: 4, Pages: e790-e790, ISSN: 2471-2531
Introduction: There is growing evidence that virtual reality (VR) can be used in the treatment of chronic pain conditions. However, further research is required in order to better understand the analgesic mechanisms during sensitised pain states. Objectives: We examined the effects of an immersive polar VR environment on capsaicin-induced ongoing pain and secondary hyperalgesia. We also investigated whether the degree of analgesia was related to baseline conditioned pain modulation (CPM) responses. Methods: Nineteen subjects had baseline CPM and electrical pain perception (EPP) thresholds measured prior to the topical application of capsaicin cream. Visual analogue scale (VAS) ratings were measured to track the development of an ongoing pain state and EPP thresholds were used to measure secondary hyperalgesia. The effects of a passive polar VR environment on ongoing pain and secondary hyperalgesia were compared to sham VR (i.e. 2D monitor screen) in responders to capsaicin (n=15). Results: VR was associated with a transient reduction in ongoing pain and an increase in EPP thresholds in an area of secondary hyperalgesia. Baseline CPM measurements showed a significant correlation with VR-induced changes in secondary hyperalgesia, but not with VR-induced changes in ongoing pain perception. There was no correlation between VR-induced changes in pain perception and VR-induced changes in secondary hyperalgesia. Conclusions: Virtual reality can reduce the perception of capsaicin-induced ongoing pain perception and secondary hyperalgesia. We also show that CPM may provide a means by which to identify individuals likely to respond to VR therapy.
To M, Strutton P, Alexander C, 2019, Central fatigue is greater than peripheral fatigue in people with Joint Hypermobility Syndrome, Journal of Electromyography and Kinesiology, Vol: 48, Pages: 197-204, ISSN: 1050-6411
Purpose: People with Joint Hypermobility Syndrome (JHS) suffer with fatigue. The purpose of this project was to investigate the contribution of central and peripheral fatigue.Methods: Electrical stimulation of the musculocutaneous nerve to biceps brachii, and transcranial magnetic stimulation over the motor cortex supplying biceps brachii were used. Peripheral and central fatigue were assessed during a control, fatiguing and recovery phase protocol. Results: JHS participants perceived greater fatigue during the protocol compared to a control group and did not recover. Central and peripheral fatigue did not occur in the control group. However, the JHS group showed central fatigue. MEP amplitude increased in the JHS group during the fatiguing protocol (p<0.01) before recovering. Superimposed twitch amplitude increased in the JHS group during the fatiguing protocol and stayed elevated during the recovery phase (p<0.04). Time to peak (TTP) amplitude of the torque generated by the TMS was longer in the JHS group (p<0.05). RMS during MVCs decreased during the fatiguing protocol reaching significance during the recovery phase (p<0.01).Conclusion: JHS participants suffered central but not peripheral fatigue. A modified strength programme to target this is discussed.
Hughes S, Grimsey S, Strutton PH, 2019, Primary motor cortex transcranial direct current stimulation modulates temporal summation of the nociceptive withdrawal reflex in healthy subjects, Pain Medicine, Vol: 20, Pages: 1156-1165, ISSN: 1526-2375
Objective: Transcranial direct current stimulation (tDCS) over the primary motor cortex (M1) has shown efficacy in a number of chronic pain conditions. Despite attempts to dissect the analgesic mechanisms, it is unknown whether M1 tDCS modulates the central integration of spinal nociception. To test this, we investigated the top-down modulation of spinal excitability using temporal summation (TS) of the nociceptive withdrawal reflex (NWR). Methods: In this randomized, blinded, cross-over study, eight healthy subjects received electrically evoked TS of the NWR, which was delivered at 5 Hz at a threshold and a suprathreshold (1.1× threshold) to elicit TS resulting in different levels of pain. Subjects were asked to rate their pain after each stimulation. Changes in the TS of the NWR and pain ratings were investigated following 20 minutes of 2-mA anodal tDCS or sham stimulation applied over M1. Results: Baseline recordings showed that TS of the NWR was induced with both threshold and suprathreshold stimulation. Suprathreshold stimulation was also associated with a higher pain intensity rating. After brain stimulation, there was no effect over the lower-intensity TS of the NWR or pain ratings in both the tDCS and sham conditions. However, tDCS reduced TS of the NWR and associated pain ratings following higher-intensity suprathreshold stimulation. Conclusions: These results indicate that M1 tDCS can indirectly modulate the central integration of suprathreshold nociceptive processing in the spinal cord. It is possible that the analgesic efficacy of tDCS is dependent on plasticity induced within pain pathways following repeated, high-intensity stimulation, which may explain the beneficial effects seen in chronic pain patients.
Hughes SW, Hellyer PJ, Sharp DJ, et al., 2019, Diffusion tensor imaging reveals changes in microstructural integrity along compressed nerve roots that correlate with chronic pain symptoms and motor deficiencies in elderly stenosis patients, NeuroImage: Clinical, Vol: 23, ISSN: 2213-1582
Age-related degenerative changes in the lumbar spine frequently result in nerve root compression causing severe pain and disability. Given the increasing incidence of lumbar spinal disorders in the aging population and the discrepancies between the use of current diagnostic imaging tools and clinical symptoms, novel methods of nerve root assessment are needed. We investigated elderly patients with stenosis at L4-L5 or L5-S1 levels. Diffusion tensor imaging (DTI) was used to quantify microstructure in compressed L5 nerve roots and investigate relationships to clinical symptoms and motor neurophysiology. DTI metrics (i.e. FA, MD, AD and RD) were measured at proximal, mid and distal segments along compressed (i.e. L5) and intact (i.e. L4 or S1) nerve roots. FA was significantly reduced in compressed nerve roots and MD, AD and RD were significantly elevated in the most proximal segment of the nerve root studied. FA was significantly correlated with electrophysiological measures of root function: minimum F-wave latency and peripheral motor conduction time (PMCT). In addition, FA along the compressed root also correlated with leg pain and depression score. There was also a relationship between RD and anxiety, leg pain and disability score and AD correlated with depression score. Taken together, these data show that DTI metrics are sensitive to nerve root compression in patients with stenosis as a result of age-related lumbar degeneration. Critically, they show that the changes in microstructural integrity along compressed L5 nerve roots are closely related to a number of clinical symptoms associated with the development of chronic pain as well as neurophysiological assessments of motor function. These inherent relationships between nerve root damage and phenotype suggest that the use DTI is a promising method as a way to stratify treatment selection and predict outcomes.
Mullington CJ, Low DA, Strutton PH, et al., 2018, Body temperature, cutaneous heat loss and skin blood flow during epidural anaesthesia for emergency caesarean section, Anaesthesia, Vol: 73, Pages: 1500-1506, ISSN: 0003-2409
It is not clear how converting epidural analgesia for labour to epidural anaesthesia for emergency caesarean section affects either cutaneous vasomotor tone or mean body temperature. We hypothesised that topping up a labour epidural blocks active cutaneous vasodilation (cutaneous heat loss and skin blood flow decrease), and that as a result mean body temperature increases. Twenty women in established labour had body temperature, cutaneous heat loss and skin blood flow recorded before and after epidural top‐up for emergency caesarean section. Changes over time were analysed with repeated measures ANOVA. Mean (SD) mean body temperature was 36.8 (0.5)°C at epidural top‐up and 36.9 (0.6)°C at delivery. Between epidural top‐up and delivery, the mean (SD) rate of increase in mean body temperature was 0.5 (0.5) °C.h−1. Following epidural top‐up, chest (p < 0.001) and forearm (p = 0.004) heat loss decreased, but head (p = 0.05), thigh (p = 0.79) and calf (p = 1.00) heat loss did not change. The mean (SD) decrease in heat loss was 15 (19) % (p < 0.001). Neither arm (p = 0.06) nor thigh (p = 0.10) skin blood flow changed following epidural top‐up. Despite the lack of change in skin blood flow, the most plausible explanation for the reduction in heat loss and the increase in mean body temperature is blockade of active cutaneous vasodilation. It is possible that a similar mechanism is responsible for the hyperthermia associated with labour epidural analgesia.
Chiou S-Y, Strutton PH, Perez MA, 2018, Crossed corticospinal facilitation between arm and trunk muscles in humans, Journal of Neurophysiology, Vol: 120, Pages: 2595-2602, ISSN: 0022-3077
A voluntary contraction of muscles with one arm increases corticospinal excitability of projections to the contralateral resting arm, a phenomenon known as crossed facilitation. Although many motor tasks engage simultaneous activation of the arm and trunk, interactions between corticospinal projections targeting these segments remain largely unknown. Using transcranial magnetic stimulation over the trunk representation of the primary motor cortex we examined motor evoked potentials (MEPs) in the resting erector spinae (ES) muscle when the contralateral arm remained at rest or performed 20% of isometric maximal voluntary contraction (MVC) into index finger abduction, thumb abduction, elbow flexion and elbow extension. We found that MEP size in the ES increased during all voluntary contractions, with greater facilitation occurring during elbow flexion and index finger abduction. To further examine the origin of changes in MEP size we measured short-interval intracortical inhibition (SICI) and cervicomedullary MEPs (CMEPs) in the ES muscle during elbow flexion and index finger abduction and when the arm remained at rest. Notably, SICI decreased and CMEPs remained unchanged in the ES during both voluntary contractions compared with rest, suggesting a cortical origin for the effects. Our findings reveal crossed facilitatory interactions between trunk extensor and proximal and distal arm muscles, particularly for elbow flexor and index finger muscles, likely involving cortical mechanisms. These interactions might reflect the different role of these muscles during functionally relevant arm and trunk movements.
Hughes SW, Ali M, Sharma P, et al., 2018, Frequency-dependent top-down modulation of temporal summation by anodal transcranial direct-current stimulation of the primary motor cortex in healthy adults, European Journal of Pain, Vol: 22, Pages: 1494-1501, ISSN: 1090-3801
BackgroundTranscranial direct‐current stimulation (tDCS) applied over the primary motor cortex has been shown to be effective in the treatment of a number of chronic pain conditions. However, there is a lack of understanding of the top‐down analgesic mechanisms involved.MethodIn this study, we investigated the effects of tDCS on the facilitation of subjective sensory and pain scores using a transcutaneous electrically evoked measure of temporal summation. In this randomized, blinded, cross‐over study healthy subjects received a single stimulus given at 0.9× pain threshold (pTh) over the L5 dermatome on the lateral aspect of the right leg, followed by a train of 5 stimuli given at 0.5, 1, 5 and 20 Hz before and after 20 min of sham or anodal tDCS (2 mA) applied over the primary motor cortex. Ratings of sensation and pain intensity were scored on a visual analogue scale (VAS).ResultsTemporal summation leading to pain only occurred at higher frequencies (5 and 20 Hz). Sham or real tDCS had no effect over temporal summation evoked at 5 Hz; however, there was a significant analgesic effect at 20 Hz. Sham or real tDCS had no effect over acute, single stimuli‐evoked responses.ConclusionThese results indicate that anodal tDCS applied to the primary motor cortex preferentially modulates temporal summation induced by high‐frequency electrical stimulation‐induced pain. The inhibitory effects of tDCS appear to be dynamic and dependent on the degree of spinal cord excitability and may explain the higher analgesic efficacy in patients with moderate to severe chronic pain symptoms.SignificanceThe analgesic effects of tDCS are dependent on spinal cord excitability. This work provides insight into top‐down modulation during acute pain and temporal summation. This knowledge may explain why tDCS has a higher analgesic efficacy in chronic pain patients.
Chiou S-Y, Hurry M, Reed T, et al., 2018, Cortical contributions to anticipatory postural adjustments in the trunk, JOURNAL OF PHYSIOLOGY-LONDON, Vol: 596, Pages: 1295-1306, ISSN: 0022-3751
Voluntary limb movements are associated with increases in trunk muscle activity, some of which occur within a time window considered too fast to be induced by sensory feedback; these increases are termed anticipatory postural adjustments (APAs). Although it is known that the function of APAs is to maintain postural stability in response to perturbations, excitability of the corticospinal projections to the trunk muscles during the APAs remains unclear. Thirty‐four healthy subjects performed rapid shoulder flexion in response to a visual cue in standing and lying positions. Transcranial magnetic stimulation (TMS) was delivered over the trunk motor cortex to examine motor evoked potentials (MEPs) in erector spinae (ES) and in rectus abdominis (RA) muscles at several time points prior to the rise in electromyographic activity (EMG) of anterior deltoid (AD) muscle. TMS was also used to assess short‐interval intracortical inhibition (SICI) and cervicomedullary MEPs (CMEPs) in ES in the standing position. MEPs in ES were larger at time points closer to the rise in AD EMG in both standing and lying positions, whereas MEPs in RA did not differ over the time course examined. Notably, SICI was reduced at time points closer to the rise in AD EMG, with no change in CMEPs. Our results demonstrate that increasing excitability of corticospinal projections to the trunk muscles prior to a voluntary limb movement is likely to be cortical in origin and is muscle specific.
Chiou S, Koutsos E, Georgiou P, et al., 2018, Association between spectral characteristics of paraspinal muscles and functional disability in low back pain patients: a cohort study, BMJ Open, Vol: 8, ISSN: 2044-6055
Objectives. Characteristics of muscle activity, represented by surface electromyography (EMG), have revealed differences between patients with low back pain and healthy adults; how they relate to functional and clinical parameters remains unclear. The purpose of the current study was to examine the correlation between frequency characteristics of EMG (analysed using continuous wavelet transform (CWT) analysis) and patients’ self-rated score of disability. Design and setting. This is a case control study with fifteen patients with mechanical low back pain (LBP) without radicular symptoms. Patients were recruited from the orthopaedic clinic at Charing Cross Hospital. Ten healthy adults were recruited from the staff working in the hospital and associated university. Patients completed the Roland-Morris Disability Questionnaire (RMDQ) and bilateral EMG activity was obtained from erector spinae at vertebral levels L4 and T12. Subjects performed 3 brief maximal isometric voluntary contractions (MVCs) of the back extensors and the torque was measured using a dynamometer. CWT was applied to the EMG signals of each muscle in a 200ms window centred around the peak torque obtained during the MVCs. The ratio (low/high frequencies) of the energy, the peak power, and the frequency of the peak power were calculated for each recording site, averaged and correlated with the individual’s RMDQ score. Results. Patients had lower peak power (T12 and L4) and lower frequency of the peak power (at T12) than the healthy adults. Additionally, RMDQ positively correlated to the average ratio of energy at T12 (rho=0.63; p=0.012), i.e. greater self-rated disability corresponded to a dominant distribution of energy in the lower frequencies. Conclusion. The current findings reveal alterations in EMG profile and its association with self-related back pain disability, suggesting that spectral characteristics of EMG reflect muscle function.
Chiou SY, Hellyer PJ, Sharp DJ, et al., 2017, Relationships between the integrity and function of lumbar nerve roots as assessed by diffusion tensor imaging and neurophysiology, NEURORADIOLOGY, Vol: 59, Pages: 893-903, ISSN: 0028-3940
PurposeDiffusion tensor imaging (DTI) has shown promise in the measurement of peripheral nerve integrity, although the optimal way to apply the technique for the study of lumbar spinal nerves is unclear. The aims of this study are to use an improved DTI acquisition to investigate lumbar nerve root integrity and correlate this with functional measures using neurophysiology.MethodsTwenty healthy volunteers underwent 3 T DTI of the L5/S1 area. Regions of interest were applied to L5 and S1 nerve roots, and DTI metrics (fractional anisotropy, mean, axial and radial diffusivity) were derived. Neurophysiological measures were obtained from muscles innervated by L5/S1 nerves; these included the slope of motor-evoked potential input-output curves, F-wave latency, maximal motor response, and central and peripheral motor conduction times.ResultsDTI metrics were similar between the left and right sides and between vertebral levels. Conversely, significant differences in DTI measures were seen along the course of the nerves. Regression analyses revealed that DTI metrics of the L5 nerve correlated with neurophysiological measures from the muscle innervated by it.ConclusionThe current findings suggest that DTI has the potential to be used for assessing lumbar spinal nerve integrity and that parameters derived from DTI provide quantitative information which reflects their function.
Chiou S-Y, Gottardi SE, Hodges PW, et al., 2016, Corticospinal Excitability of Trunk Muscles during Different Postural Tasks, PLoS One, Vol: 11, ISSN: 1932-6203
Evidence suggests that the primary motor cortex (M1) is involved in both voluntary, goal-directed movements and in postural control. Trunk muscles are involved in both tasks, however, the extent to which M1 controls these muscles in trunk flexion/extension (voluntary movement) and in rapid shoulder flexion (postural control) remains unclear. The purpose of this study was to investigate this question by examining excitability of corticospinal inputs totrunk muscles during voluntary and postural tasks. Twenty healthy adults participated. Transcranial magnetic stimulation was delivered to the M1 to examine motor evoked potentials (MEPs) in the trunk muscles (erector spinae (ES) and rectus abdominis (RA)) during dynamic shoulder flexion (DSF), static shoulder flexion (SSF), and static trunk extension (STE). The level of background muscle activity in the ES muscles was matched across tasks. MEP amplitudes in ES were significantly larger in DSF than in SSF or in STE; however, this was not observed for RA. Further, there were no differences in levels of muscleactivity in RA between tasks. Our findings reveal that corticospinal excitability of the ES muscles appears greater during dynamic anticipatory posture-related adjustments than during static tasks requiring postural (SSF) and goal-directed voluntary (STE) activity. These results suggest that task-oriented rehabilitation of trunk muscles should be considered for optimal transfer of therapeutic effect to function.
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