Establishing a link between heart rate and pain in healthy subjects: a gender effect

Pet dogs succeed where human companions fail: The presence of pet dogs reduces pain

Social support from family and friends, albeit associated with beneficial health effects, does not always help to cope with pain. This may be because humans elicit mixed expectations of social support and evaluative judgment. The present studies aimed to test whether pet dogs are a more beneficial source of support in a painful situation than human companions because they are not evaluative. For this, 74 (Study 1) and 50 (Study 2) women completed a cold-pressor task in the presence of either their own (S1) or an unfamiliar (S2) dog, a friend (S1), or an unknown human companion (S2), or alone. In both studies, participants reported less pain and exhibited less pain behavior in the presence of dogs compared to human companions. Reactions to pain were moderated by attitudes towards dogs in S2. This suggests that pet dogs may help individuals to cope with painful situations, especially if the individual in pain generally feels affectionate towards dogs.

A proposed test to determine physical working capacity at pain intensity threshold (PWCPIT)

PURPOSE

This study aimed to establish a new threshold parameter called the physical working capacity at pain intensity threshold (PWCPIT) using a pain intensity scale and mathematical methods similar to those used to develop the physical working capacity at oxygen consumption threshold (PWCVO2) and physical working capacity at heart rate threshold (PWCHRT). The study had two objectives: (i) to examine the relationship between PWCPIT and traditional PWC measures and (ii) to explore the physiological mechanisms underlying the relationship between pain perception and capacity thresholds.

METHODS

Fourteen male volunteers (age 21 ± 2 years, height 176 ± 6 cm, weight 76 ± 9 kg, VO2peak 37.8 ± 7.8 ml/kg/min-1) underwent an incremental exhaustion test and four 8-min randomly ordered work bouts on different days at 70-100% peak power output (119-320 W) to establish their PWCPIT, PWCHRT and PWCVO2. One-way repeated-measures ANOVA with Bonferroni post hoc tests and a zero-order correlation matrix were used to analyze these thresholds.

RESULTS

PWCPIT significantly correlated with PWCHRT (r = 0.88, P < 0.001), PWCVO2 (r = 0.84, P < 0.001), and gas exchange threshold (GET) (r = 0.7, P = 0.006).

CONCLUSION

The model for estimating PWCHRT and PWCVO2 can be applied to determine the PWCPIT. By examining how PWCPIT aligns with, differs from, or complements existing PWC threshold measures, researchers may provide a more comprehensive understanding of the factors that govern endurance performance.

Pain-induced effects on the pupillary light response under high and low illumination conditions

Objective

The present study investigated the impact of two different light intensities on the pain-modulated pupillary light response (PLR). Additionally, it aimed to demonstrate parasympathetic and sympathetic influences on PLR parameters in response to pain, as predicted by functional models.

Method

A total of 24 participants were included in a randomized, repeated-measures design. The PLR was measured in response to both dark and bright light stimuli within two test cycles. Pain was induced using the cold pressor test (CPT), which involved immersing participants' feet in ice water. PLR measurements were taken during baseline and ice-water immersion within each test cycle. The assessed PLR parameters included initial diameter (INIT), latency (LAT), amplitude (AMP), and re-dilation time (ReDIL25). Along with these parameters, heart rate (HR) and pain ratings were also computed and analyzed.

Main results

The CPT caused moderate pain in participants, and the resulting PLR parameters were found to be congruent with the expected parasympathetic and sympathetic nervous system activities. Although the luminance of the stimulus did influence PLR parameters, no interaction with pain exposure was found.

Significance

The results showed that different aspects of pain experienced by an individual, as modulated through the sympathetic and parasympathetic nervous systems, are visible in their pupillary reactions to light. Notably, within the range used in the current study, light intensity did not significantly affect the pain-related PLR effects.

Predicting Postoperative Pain and Opioid Use with Machine Learning Applied to Longitudinal Electronic Health Record and Wearable Data

BACKGROUND

 Managing acute postoperative pain and minimizing chronic opioid use are crucial for patient recovery and long-term well-being.

OBJECTIVES

 This study explored using preoperative electronic health record (EHR) and wearable device data for machine-learning models that predict postoperative acute pain and chronic opioid use.

METHODS

 The study cohort consisted of approximately 347 All of Us Research Program participants who underwent one of eight surgical procedures and shared EHR and wearable device data. We developed four machine learning models and used the Shapley additive explanations (SHAP) technique to identify the most relevant predictors of acute pain and chronic opioid use.

RESULTS

 The stacking ensemble model achieved the highest accuracy in predicting acute pain (0.68) and chronic opioid use (0.89). The area under the curve score for severe pain versus other pain was highest (0.88) when predicting acute postoperative pain. Values of logistic regression, random forest, extreme gradient boosting, and stacking ensemble ranged from 0.74 to 0.90 when predicting postoperative chronic opioid use. Variables from wearable devices played a prominent role in predicting both outcomes.

CONCLUSION

 SHAP detection of individual risk factors for severe pain can help health care providers tailor pain management plans. Accurate prediction of postoperative chronic opioid use before surgery can help mitigate the risk for the outcomes we studied. Prediction can also reduce the chances of opioid overuse and dependence. Such mitigation can promote safer and more effective pain control for patients during their recovery.

Interactive effects of pain and arousal state on heart rate and cortical activity in the mouse anterior cingulate and somatosensory cortices

Sensory disconnection is a hallmark of sleep, yet the cortex retains some ability to process sensory information. Acute noxious stimulation during sleep increases the heart rate and the likelihood of awakening, indicating that certain mechanisms for pain sensing and processing remain active. However, processing of somatosensory information, including pain, during sleep remains underexplored. To assess somatosensation in natural sleep, we simultaneously recorded heart rate and local field potentials in the anterior cingulate (ACC) and somatosensory (S1) cortices of naïve, adult male mice, while applying noxious and non-noxious stimuli to their hind paws throughout their sleep-wake cycle. Noxious stimuli evoked stronger heart rate increases in both wake and non-rapid eye movement sleep (NREMS), and resulted in larger awakening probability in NREMS, as compared to non-noxious stimulation, suggesting differential processing of noxious and non-noxious information during sleep. Somatosensory information differentially reached S1 and ACC in sleep, eliciting complex transient and sustained responses in the delta, alpha, and gamma frequency bands as well as somatosensory evoked potentials. These dynamics depended on sleep state, the behavioral response to the stimulation and stimulation intensity (non-noxious vs. noxious). Furthermore, we found a correlation of the heart rate with the gamma band in S1 in the absence of a reaction in wake and sleep for noxious stimulation. These findings confirm that somatosensory information, including nociception, is sensed and processed during sleep even in the absence of a behavioral response.

Autonomic responses to pressure sensitivity of head, face and neck: Heart rate and skin conductance

Subjective scales are frequently used in the design process of head-related products to assess pressure discomfort. Nevertheless, some users lack fundamental cognitive and motor abilities (e.g., paralyzed patients). Therefore, it is vital to find non-verbal measurements of pressure discomfort and pressure pain. This study gathered the autonomic response data (heart rate and skin conductance) of 30 landmarks in head, neck and face from 31 participants experiencing pressure discomfort and pressure pain. The results indicate that pressure stimulation can change heart rate (HR) and skin conductance (SC). SC can be more useful in assessing pressure discomfort than HR for specific landmarks, and SC also possesses a faster arousal rate than HR. Moreover, HR decreased in response to pressure stimulation, while SC decreased followed by an increase. In comparisons between genders, the subjective pressure discomfort threshold (PDT) and pressure pain threshold (PPT) of women were lower than those of men, but men's autonomic responses (HR and SC) were more intense. Furthermore, there was no linear correlation between subjective pressure thresholds (PDT and PPT) and autonomic response intensity. This study has significant implications for resolving ergonomic issues (pressure discomfort and pain) associated with head-related products.

Denoising task-related fMRI: Balancing noise reduction against signal loss

Preprocessing fMRI data requires striking a fine balance between conserving signals of interest and removing noise. Typical steps of preprocessing include motion correction, slice timing correction, spatial smoothing, and high-pass filtering. However, these standard steps do not remove many sources of noise. Thus, noise-reduction techniques, for example, CompCor, FIX, and ICA-AROMA have been developed to further improve the ability to draw meaningful conclusions from the data. The ability of these techniques to minimize noise while conserving signals of interest has been tested almost exclusively in resting-state fMRI and, only rarely, in task-related fMRI. Application of noise-reduction techniques to task-related fMRI is particularly important given that such procedures have been shown to reduce false positive rates. Little remains known about the impact of these techniques on the retention of signal in tasks that may be associated with systemic physiological changes. In this paper, we compared two ICA-based, that is FIX and ICA-AROMA, two CompCor-based noise-reduction techniques, that is aCompCor, and tCompCor, and standard preprocessing using a large (n = 101) fMRI dataset including noxious heat and non-noxious auditory stimulation. Results show that preprocessing using FIX performs optimally for data obtained using noxious heat, conserving more signals than CompCor-based techniques and ICA-AROMA, while removing only slightly less noise. Similarly, for data obtained during non-noxious auditory stimulation, FIX noise-reduction technique before analysis with a covariate of interest outperforms the other techniques. These results indicate that FIX might be the most appropriate technique to achieve the balance between conserving signals of interest and removing noise during task-related fMRI.

Hierarchical Classification Strategy for Mitigating the Impact of The Presence of Pain in fNIRS-based BCIs

Brain computer interfaces (BCIs) can find applications in assistive systems for patients who experience conditions that impede their motor abilities. A BCI uses signals acquired from the brain to control external devices. As physical pain influences cortical signals, the presence of pain can negatively impact the performance of the BCI. In this work, we propose a strategy to mitigate this negative impact. Cortical signals are acquired from test subjects while they performed two mental arithmetic tasks, in the presence and the absence of painful stimuli. The task of the BCI is to reliably classify the two mental arithmetic tasks from the cortical recordings, irrespective of the presence or the absence of pain. We propose to do this classification, hierarchically, in two levels. In the first level, the data is classified into those captured in the presence and the absence of pain. Depending on the results of the classification from the first level, in the second level, the BCI performs the classification of tasks using a classifier trained either in the presence or the absence of pain. A 1-dimensional convolutional neural network (1D-CNN) is used for classification at both levels. It is observed that using this hierarchical strategy, the BCI is able to classify the tasks with an accuracy greater than 90%, irrespective of the presence or the absence of pain. Given that the presence of physical pain has shown previously to reduce the classification accuracy of a BCI to almost chance levels, this mitigation strategy will be a significant step towards enhancing the performance of BCIs when they are used in assistive systems for patients.

Functional magnetic resonance imaging of headache: Issues, best-practices, and new directions, a narrative review

OBJECTIVE

To ensure readers are informed consumers of functional magnetic resonance imaging (fMRI) research in headache, to outline ongoing challenges in this area of research, and to describe potential considerations when asked to collaborate on fMRI research in headache, as well as to suggest future directions for improvement in the field.

BACKGROUND

Functional MRI has played a key role in understanding headache pathophysiology, and mapping networks involved with headache-related brain activity have the potential to identify intervention targets. Some investigators have also begun to explore its use for diagnosis.

METHODS/RESULTS

The manuscript is a narrative review of the current best practices in fMRI in headache research, including guidelines on transparency and reproducibility. It also contains an outline of the fundamentals of MRI theory, task-related study design, resting-state functional connectivity, relevant statistics and power analysis, image preprocessing, and other considerations essential to the field.

CONCLUSION

Best practices to increase reproducibility include methods transparency, eliminating error, using a priori hypotheses and power calculations, using standardized instruments and diagnostic criteria, and developing large-scale, publicly available datasets.

Development and validation of a mathematical model to simulate human cardiovascular and respiratory responses to battlefield trauma

Mathematical models of human cardiovascular and respiratory systems provide a viable alternative to generate synthetic data to train artificial intelligence (AI) clinical decision-support systems and assess closed-loop control technologies, for military medical applications. However, existing models are either complex, standalone systems that lack the interface to other applications or fail to capture the essential features of the physiological responses to the major causes of battlefield trauma (i.e., hemorrhage and airway compromise). To address these limitations, we developed the cardio-respiratory (CR) model by expanding and integrating two previously published models of the cardiovascular and respiratory systems. We compared the vital signs predicted by the CR model with those from three models, using experimental data from 27 subjects in five studies, involving hemorrhage, fluid resuscitation, and respiratory perturbations. Overall, the CR model yielded relatively small root mean square errors (RMSEs) for mean arterial pressure (MAP; 20.88 mm Hg), end-tidal CO₂ (ETCO₂ ; 3.50 mm Hg), O₂ saturation (SpO₂ ; 3.40%), and arterial O₂ pressure (PaO₂ ; 10.06 mm Hg), but a relatively large RMSE for heart rate (HR; 70.23 beats/min). In addition, the RMSEs for the CR model were 3% to 10% smaller than the three other models for HR, 11% to 15% for ETCO₂ , 0% to 33% for SpO₂ , and 10% to 64% for PaO₂ , while they were similar for MAP. In conclusion, the CR model balances simplicity and accuracy, while qualitatively and quantitatively capturing human physiological responses to battlefield trauma, supporting its use to train and assess emerging AI and control systems.

Pain-autonomic measures reveal nociceptive sensitization in complex regional pain syndrome

BACKGROUND

Allodynia and hyperalgesia are common signs in individuals with complex regional pain syndrome (CRPS), mainly attributed to sensitization of the nociceptive system. Appropriate diagnostic tools for the objective assessment of such hypersensitivities are still lacking, which are essential for the development of mechanism-based treatment strategies.

OBJECTIVES

This study investigated the use of pain-autonomic readouts to objectively detect sensitization processes in CRPS.

METHODS

Twenty individuals with chronic CRPS were recruited for the study alongside 16 age- and sex-matched healthy controls (HC). All individuals underwent quantitative sensory testing and neurophysiological assessments. Sympathetic skin responses (SSRs) were recorded in response to 15 pinprick and 15 noxious heat stimuli of the affected (CRPS hand/foot) and a control area (contralateral shoulder/hand).

RESULTS

Individuals with CRPS showed increased mechanical pain sensitivity and increased SSR amplitudes compared with HC in response to pinprick and heat stimulation of the affected (p < 0.001), but not in the control area (p > 0.05). Habituation of pinprick-induced SSRs was reduced in CRPS compared to HC in both the affected (p = 0.018) and slightly in the control area (p = 0.048). Habituation of heat-induced SSR was reduced in CRPS in the affected (p = 0.008), but not the control area (p = 0.053).

CONCLUSIONS

This is the first study demonstrating clinical evidence that pain-related autonomic responses may represent objective tools to quantify sensitization processes along the nociceptive neuraxis in CRPS (e.g. widespread hyperexcitability). Pain-autonomic readouts could help scrutinize mechanisms underlying the development and maintenance of chronic pain in CRPS and provide valuable metrics to detect mechanism-based treatment responses in clinical trials.

SIGNIFICANCE

This study provides clinical evidence that autonomic measures to noxious stimuli can objectively detect sensitization processes along the nociceptive neuraxis in complex regional pain syndrome (CRPS) (e.g. widespread hyperexcitability). Pain-autonomic readouts may represent valuable tools to explore pathophysiological mechanisms in a variety of pain patients and offer novel avenues to help guide mechanism-based therapeutic strategies.

Analysis of Physiological Responses during Pain Induction

Pain is a complex phenomenon that arises from the interaction of multiple neuroanatomic and neurochemical systems with several cognitive and affective processes. Nowadays, the assessment of pain intensity still relies on the use of self-reports. However, recent research has shown a connection between the perception of pain and exacerbated stress response in the Autonomic Nervous System. As a result, there has been an increasing analysis of the use of autonomic reactivity with the objective to assess pain. In the present study, the methods include pre-processing, feature extraction, and feature analysis. For the purpose of understanding and characterizing physiological responses of pain, different physiological signals were, simultaneously, recorded while a pain-inducing protocol was performed. The obtained results, for the electrocardiogram (ECG), showed a statistically significant increase in the heart rate, during the painful period compared to non-painful periods. Additionally, heart rate variability features demonstrated a decrease in the Parasympathetic Nervous System influence. The features from the electromyogram (EMG) showed an increase in power and contraction force of the muscle during the pain induction task. Lastly, the electrodermal activity (EDA) showed an adjustment of the sudomotor activity, implying an increase in the Sympathetic Nervous System activity during the experience of pain.

Assessing the specificity of the relationship between brain alpha oscillations and tonic pain

Recent research proposed that the slowing of individual alpha frequency (IAF) could be an objective marker of pain. However, it is unclear whether this research can fully address the requirements of specificity and sensitivity of IAF to the pain experience. Here, we sought to develop a robust methodology for assessing the specificity of the relationship between alpha oscillations and acute tonic pain in healthy individuals. We recorded electroencephalography (EEG) of 36 volunteers during consecutive 5-minute sessions of painful hot water immersion, innocuous warm water immersion and aversive, non-painful auditory stimulus, matched by unpleasantness to the painful condition. Participants rated stimulus unpleasantness throughout each condition. We isolated two regions of the scalp displaying peak alpha activity across participants: centro-parietal (CP) and parieto-occipital (PO) ROI. In line with previous research our findings revealed decreased IAF during hot compared with warm stimulation, however the effect was not specific for pain as we found no difference between hot and sound in the CP ROI (compared to baseline). In contrast, the PO ROI reported the same pattern of differences, but their direction was opposite to the CP in that this ROI revealed faster frequency during hot condition than controls. Finally, we show that IAF in both ROIs did not mediate the relationship between the experimental manipulation and the affective experience. Altogether, these findings emphasize the importance of a robust methodological and analytical design to disclose the functional role of alpha oscillations during affective processing. Likewise, they suggest the absence of a causal role of IAF in the generation of acute pain experience in healthy individuals.

Kynurenic Acid and Its Analogue SZR-72 Ameliorate the Severity of Experimental Acute Necrotizing Pancreatitis

The pathophysiology of acute pancreatitis (AP) is not well understood, and the disease does not have specific therapy. Tryptophan metabolite L-kynurenic acid (KYNA) and its synthetic analogue SZR-72 are antagonists of the N-methyl-D-aspartate receptor (NMDAR) and have immune modulatory roles in several inflammatory diseases. Our aims were to investigate the effects of KYNA and SZR-72 on experimental AP and to reveal their possible mode of action. AP was induced by intraperitoneal (i.p.) injection of L-ornithine-HCl (LO) in SPRD rats. Animals were pretreated with 75-300 mg/kg KYNA or SZR-72. Control animals were injected with physiological saline instead of LO, KYNA and/or SZR-72. Laboratory and histological parameters, as well as pancreatic and systemic circulation were measured to evaluate AP severity. Pancreatic heat shock protein-72 and IL-1β were measured by western blot and ELISA, respectively. Pancreatic expression of NMDAR1 was investigated by RT-PCR and immunohistochemistry. Viability of isolated pancreatic acinar cells in response to LO, KYNA, SZR-72 and/or NMDA administration was assessed by propidium-iodide assay. The effects of LO and/or SZR-72 on neutrophil granulocyte function was also studied. Almost all investigated laboratory and histological parameters of AP were significantly reduced by administration of 300 mg/kg KYNA or SZR-72, whereas the 150 mg/kg or 75 mg/kg doses were less or not effective, respectively. The decreased pancreatic microcirculation was also improved in the AP groups treated with 300 mg/kg KYNA or SZR-72. Interestingly, pancreatic heat shock protein-72 expression was significantly increased by administration of SZR-72, KYNA and/or LO. mRNA and protein expression of NMDAR1 was detected in pancreatic tissue. LO treatment caused acinar cell toxicity which was reversed by 250 µM KYNA or SZR-72. Treatment of acini with NMDA (25, 250, 2000 µM) did not influence the effects of KYNA or SZR-72. Moreover, SZR-72 reduced LO-induced H₂O₂ production of neutrophil granulocytes. KYNA and SZR-72 have dose-dependent protective effects on LO-induced AP or acinar toxicity which seem to be independent of pancreatic NMDA receptors. Furthermore, SZR-72 treatment suppressed AP-induced activation of neutrophil granulocytes. This study suggests that administration of KYNA and its derivative could be beneficial in AP.

Elevated Heart Rate and Pain During a Cold Pressor Test Correlates to Pain Catastrophizing

To understand the variable response to pain, researchers have examined the change in cardiovascular measures to a uniform painful stimulation. Pain catastrophizing is the tendency to magnify or exaggerate pain sensations, and it affects the outcome of rehabilitation in a clinical setting. Its effect on cardiovascular changes during a painful stimulus is unclear. Twenty-four healthy human participants completed the study. All participants completed a cold pressor test while subjective pain intensity was measured with a numeric pain scale from 0-10. Continuous cardiac output measurements were obtained with finger-pulse plethysmograph waveform analysis. The measurements included systolic and diastolic blood pressure, heart rate averaged over 30 s intervals. Pain catastrophizing and anxiety were assessed using the pain catastrophizing scale (PCS), and Spielberger's State-Trait Anxiety Inventories, respectively. Peak pain was correlated to pain catastrophizing (r = 0.628, p < 0.01). There was a strong correlation between change in heart rate (HR) and subjective peak pain (r = 0.805, p < 0.01), total PCS (r = 0.474, p < 0.05), and the helplessness subscale of the PCS (r = 0.457, p < 0.05). Peak pain and catastrophizing explained a significant amount of the variance for the change in HR during the cold pressor test (R² of 0.649 and 0.224 respectively, p = 0.019). These novel findings demonstrate a psycho-physiological relationship between cardiovascular changes and pain catastrophizing. Further research should include participants with subacute or persistent pain.

Upper Extremity Superficial Vein Thromboses Presenting as Acute Neck Pain in a Young and Healthy Male: A Case Report

BACKGROUND AND PURPOSE

Neck pain in the United States is pervasive and contributes to disability. While the majority of neck pain in young and healthy individuals is neuromusculoskeletal in nature, screening for red flags is necessary for ruling-out serious medical pathologies. The purpose of this case report is to describe a young and healthy male subject with a primary complaint of acute neck pain with multiple underlying upper extremity superficial vein thromboses (UESVTs).

CASE DESCRIPTION

The subject was a 27-year-old male active-duty Soldier referred to physical therapy by his primary care provider (PCP) for acute left-sided neck pain. Prior to physical therapy, the subject had been treated with cyclobenzaprine, oxycodone-acetaminophen, trigger point injection and had undergone a D-dimer to rule out a potential thrombus due to air travel and lower extremity immobilization.

OUTCOMES

The subject underwent a D-dimer, Doppler ultrasound, pharmacological treatment of Rivaroxaban, and was referred to hematology/oncology to rule out systemic causes of SVTs. Evidence of subtle increases in blood pressure over the course of three months, a positive D-dimer, and symptoms incongruent with clinical presentation contributed to referral to a hematology/oncology specialist and a diagnosis of multiple UESVTs. The subject was able to return to his previous level of activity by six months and remained free of SVTs at two-year follow-up.

DISCUSSION

UESVT events are rare and can be challenging to identify. This case report describes a unique presentation of acute neck pain caused by underlying UESVTs in an otherwise healthy and active young male.

LEVEL OF EVIDENCE

Level 4.

Wearable Devices: Current Status and Opportunities in Pain Assessment and Management

INTRODUCTION

We investigated the possibilities and opportunities for using wearable devices that measure physical activity and physiometric signals in conjunction with ecological momentary assessment (EMA) data to improve the assessment and treatment of pain.

METHODS

We considered studies with cross-sectional and longitudinal designs as well as interventional or observational studies correlating pain scores with measures derived from wearable devices. A search was also performed on studies that investigated physical activity and physiometric signals among patients with pain.

RESULTS

Few studies have assessed the possibility of incorporating wearable devices as objective tools for contextualizing pain and physical function in free-living environments. Of the studies that have been conducted, most focus solely on physical activity and functional outcomes as measured by a wearable accelerometer. Several studies report promising correlations between pain scores and signals derived from wearable devices, objectively measured physical activity, and physical function. In addition, there is a known association between physiologic signals that can be measured by wearable devices and pain, though studies using wearable devices to measure these signals and associate them with pain in free-living environments are limited.

CONCLUSION

There exists a great opportunity to study the complex interplay between physiometric signals, physical function, and pain in a real-time fashion in free-living environments. The literature supports the hypothesis that wearable devices can be used to develop reproducible biosignals that correlate with pain. The combination of wearable devices and EMA will likely lead to the development of clinically meaningful endpoints that will transform how we understand and treat pain patients.

Sex differences in fatigability after ischemic preconditioning of non-exercising limbs

Background

Ischemic preconditioning (IPC) is suggested to decrease fatigability in some individuals but not others. Sex differences in response to IPC may account for this variability and few studies systematically investigated the effects of IPC in men and women. The goal of this study was to determine if time to task failure, perception of pain, and neuromuscular mechanisms of fatigability were altered by IPC in men and women.

Methods

Ten women (29 ± 5 years old) and 10 men (28 ± 6 years old) performed isometric contractions with the plantar flexor muscles of the dominant leg at 20% of maximal voluntary contraction until task failure. We used a repeated measures design where each individual performed 3 randomized and counterbalanced test sessions: (A) IPC session, cuff inflation and deflation (5 min each repeated 3 times) performed before the exercise by inflating cuffs to the non-dominant leg and arm; (B) sham session, cuffs were inflated for a short period (1 min); and (C) control session, no cuffs were involved.

Results

Compared with control, IPC increased time to task failure in men (mean difference, 5 min; confidence interval (CI) of mean difference, 2.2; 7.8 min; P = 0.01) but not women (mean difference, − 0.6 min; CI of mean difference, − 3.5; 2.4 min; P = 0.51). In men, but not women, the IPC-induced increase in time to task failure was associated with lower response to pressure pain (r = − 0.79). IPC further exposed sex differences in arterial pressure during fatiguing contractions (session × sex: P < 0.05). Voluntary activation, estimated with the twitch interpolation technique, and presynaptic inhibition of leg Ia afferents were not altered after IPC for men and women. The tested variables were not altered with sham.

Conclusions

The ergogenic effect of IPC on time to task failure was observed only in men and it was associated with reductions in the perception of pain. This pilot data suggest the previously reported inter-individual variability in exercise-induced fatigability after IPC could be a consequence of the sex and individual response to pain.

The effectiveness of electronic pulsed soft tissue vibration compared with topical anaesthesia in reducing the pain of injection of local anaesthetics in adults: a randomized controlled split-mouth clinical trial

The purpose of this study was to evaluate the effectiveness of an electronic hand-held pulsed vibration device on the pain of local analgesia (LA) injection and physiologic changes. A prospective randomized controlled clinical trial using split-mouth (crossover) design was implemented. The control-side injection was performed after using topical anaesthesia. The experimental side injection was carried out without topical anaesthesia, but with the aid of a switched-on vibration device. Overall, 332 dental LA injections were given to 166 patients for routine exodontia. The pain at penetration and pain during injection were significantly lower in the experimental sides (vibrations sides) compared with those of the controls (P<0.001). Similarly, the heart rate changes at penetration and during injections were significantly lower in the experimental sides (P<0.001). The vibration device was clinically and statistically more effective than topical anaesthesia in the reduction of dental injection pain in adults, measured subjectively and objectively, regardless of the gender, injection technique (infiltration or block) or anxiety level.

Technologies for Opioid Use Disorder Management: Mobile App Search and Scoping Review

Background

Advances in technology engender the investigation of technological solutions to opioid use disorder (OUD). However, in comparison to chronic disease management, the application of mobile health (mHealth) to OUD has been limited.

Objective

The overarching aim of our research was to design OUD management technologies that utilize wearable sensors to provide continuous monitoring capabilities. The objectives of this study were to (1) document the currently available opioid-related mHealth apps, (2) review past and existing technology solutions that address OUD, and (3) discuss opportunities for technological withdrawal management solutions.

Methods

We used a two-phase parallel search approach: (1) an app search to determine the availability of opioid-related mHealth apps and (2) a scoping review of relevant literature to identify relevant technologies and mHealth apps used to address OUD.

Results

The app search revealed a steady rise in app development, with most apps being clinician-facing. Most of the apps were designed to aid in opioid dose conversion. Despite the availability of these apps, the scoping review found no study that investigated the efficacy of mHealth apps to address OUD.

Conclusions

Our findings highlight a general gap in technological solutions of OUD management and the potential for mHealth apps and wearable sensors to address OUD.

A comparison of pain responses, hemodynamic reactivity and fibre type composition between Bergström and microbiopsy skeletal muscle biopsies

This study tested the hypotheses that 1) skeletal muscle biopsies performed with the Bergström needle evoke larger perceptions of pain and greater hemodynamic reactivity compared to biopsies performed with the microbiopsy needle, and 2) both needles yield samples with similar fibre type compositions when samples are collected at similar skeletal muscle depths. Fourteen healthy (age: 21.6 ± 3.2 years; VO₂peak: 41.5 ± 5.8 mL/kg/min) males (n = 7) and females (n = 7) provided two resting skeletal muscle biopsies, one with each needle type, following a randomized crossover design. Participants completed the short-form McGill Pain Questionnaire and the Brief Pain Inventory before, during, and after the skeletal muscle biopsies. Hemodynamic reactivity was assessed by measuring heart rate (HR) and mean arterial pressure (MAP) at rest and during the biopsy procedures. Immunofluorescence analysis was used to assess fibre type composition in vastus lateralis samples. Compared to the microbiopsy needle, the Bergström needle elicited a larger perception of pain but similar hemodynamic reactivity during the biopsy. Both needles yielded skeletal muscle samples with similar fibre type composition and resulted in similar perceptions of pain and pain-related interference during the post-biopsy recovery period. Collectively, these findings suggest that studies should consider using the microbiopsy needle rather than the Bergström needle unless large amounts of muscle tissue or certain muscle fibre lengths are required. However, future work should determine whether our findings are generalizable to biopsies performed with different procedures and/or types of Bergström/microbiopsy needles.

•

The first characterization of responses to two muscle biopsy techniques.

•

Compared to the Bergström, the microbiopsy needle evokes smaller pain responses.

•

Both needles resulted in similar hemodynamic reactivity and fibre type composition.

•

If analysis permits, future work should consider using the microbiopsy needle.

Increased morphine requirements are predictive of acute compartment syndrome in adults with tibia fractures

PURPOSE

The purpose of this study was to determine if increased milligram morphine equivalent (MME) requirements are a predictor of adult compartment syndrome in patients with tibia fractures.

METHODS

A retrospective case-control study at a level-1 trauma center was performed over a five year period. Patients with tibia fractures who had acute compartment syndrome (ACS) requiring fasciotomy (n = 26) were matched with controls (n = 25). MME and pain scores were assessed within the 24 hour period preceding fasciotomy (cases) or fixation (controls). The presence or absence of the "6 Ps" and other clinical signs (diastolic blood pressure [DBP]) were also analyzed.

RESULTS

Mean MMEs two hours before surgery was 25.5 ± 39.2 for ACS patients versus 8.6 ± 11.1 in controls (P = 0.043), while the mean pain scores were 8.8 ± 1.8 and 7.0 ± 2.5 (P = 0.049), respectively. Multivariable regression showed patients with ACS consumed 16.9 MME more than controls within two hours of surgery (P = 0.043) and scored 1.8 points higher on the numeric pain rating scale (P = 0.049). The mean number of clinical signs of compartment syndrome in the ACS patients was 3.4 ± 1.3 compared to 0.84 ± 0.85 in controls (P < 0.001). DBP was significantly higher in ACS patients within two to four hours of surgery (P = 0.005).

CONCLUSION

Increased MME requirements and pain scores within two hours of surgery were significant predictors of ACS following tibia fracture. Increased narcotic requirements, pain scores, and DBP may be useful objective indicators of evolving ACS, in addition to the traditional signs, and should be closely monitored in the at-risk patient.

Use of Mobile Health Apps and Wearable Technology to Assess Changes and Predict Pain During Treatment of Acute Pain in Sickle Cell Disease: Feasibility Study

BACKGROUND

Sickle cell disease (SCD) is an inherited red blood cell disorder affecting millions worldwide, and it results in many potential medical complications throughout the life course. The hallmark of SCD is pain. Many patients experience daily chronic pain as well as intermittent, unpredictable acute vaso-occlusive painful episodes called pain crises. These pain crises often require acute medical care through the day hospital or emergency department. Following presentation, a number of these patients are subsequently admitted with continued efforts of treatment focused on palliative pain control and hydration for management. Mitigating pain crises is challenging for both the patients and their providers, given the perceived unpredictability and subjective nature of pain.

OBJECTIVE

The objective of this study was to show the feasibility of using objective, physiologic measurements obtained from a wearable device during an acute pain crisis to predict patient-reported pain scores (in an app and to nursing staff) using machine learning techniques.

METHODS

For this feasibility study, we enrolled 27 adult patients presenting to the day hospital with acute pain. At the beginning of pain treatment, each participant was given a wearable device (Microsoft Band 2) that collected physiologic measurements. Pain scores from our mobile app, Technology Resources to Understand Pain Assessment in Patients with Pain, and those obtained by nursing staff were both used with wearable signals to complete time stamp matching and feature extraction and selection. Following this, we constructed regression and classification machine learning algorithms to build between-subject pain prediction models.

RESULTS

Patients were monitored for an average of 3.79 (SD 2.23) hours, with an average of 5826 (SD 2667) objective data values per patient. As expected, we found that pain scores and heart rate decreased for most patients during the course of their stay. Using the wearable sensor data and pain scores, we were able to create a regression model to predict subjective pain scores with a root mean square error of 1.430 and correlation between observations and predictions of 0.706. Furthermore, we verified the hypothesis that the regression model outperformed the classification model by comparing the performances of the support vector machines (SVM) and the SVM for regression.

CONCLUSIONS

The Microsoft Band 2 allowed easy collection of objective, physiologic markers during an acute pain crisis in adults with SCD. Features can be extracted from these data signals and matched with pain scores. Machine learning models can then use these features to feasibly predict patient pain scores.

Essential oil inhaler (AromaStick®) improves heat tolerance in the Hot Immersion Test (HIT). Results from two randomized, controlled experiments

BACKGROUND

A recent review article on an aromatherapeutic inhaler demonstrated clinical effects on a number of bodily systems, like the cardiovascular system, the respiratory system, the nervous system and the endocrine system.

OBJECTIVE

This paper extends these findings and investigates whether specially designed essential oils inhalers are capable to counter experimentally induced stressful heat sensations.

METHOD

Two prospective, randomized, controlled experiments using the Hot Immersion Test Paradigm (HIT) were conducted to investigate whether deep odor inhalations increase heat tolerance.

RESULTS

In both experiments, the inhaler strongly prolonged pain tolerance and increased blood oxygenation (1 < d < 1.3). In the second experiment, the inhaler also increased heart rate variability (d = 1.3) as a mechanism to cope with heat stress.

CONCLUSION

The ability to resist a stressful thermal stimulus can be exogenously improved by short and deep inhalations of essential scents directly delivered to the olfactory system.

Continuous Pain Assessment Using Ensemble Feature Selection from Wearable Sensor Data

Sickle cell disease (SCD) is a red blood cell disorder complicated by lifelong issues with pain. Management of SCD related pain is particularly challenging due to its subjective nature. Hence, the development of an objective automatic pain assessment method is critical to pain management in SCD. In this work, we developed a continuous pain assessment model using physiological and body movement sensor signals collected from a wearable wrist-worn device. Specifically, we implemented ensemble feature selection methods to select robust and stable features extracted from wearable data for better understanding of pain. Our experiments showed that the stability of feature selection methods could be substantially increased by using the ensemble approach. Since different ensemble feature selection methods prefer varying feature subsets for pain estimation, we further utilized stacked generalization to maximize the information usage contained in the selected features from different methods. Using this approach, our best performing model obtained the root-mean-square error of 1.526 and the Pearson correlation of 0.618 for continuous pain assessment. This indicates that subjective pain scores can be estimated using objective wearable sensor data with high precision.

Low intensity blood flow restriction exercise: Rationale for a hypoalgesia effect

Exercise-induced hypoalgesia is characterised by a reduction in pain sensitivity following exercise. Recently, low intensity exercise performed with blood flow restriction has been shown to induce hypoalgesia. The purpose of this manuscript is to discuss the mechanisms of exercise-induced hypoalgesia and provide rationale as to why low intensity exercise performed with blood flow restriction may induce hypoalgesia. Research into exercise-induced hypoalgesia has identified several potential mechanisms, including opioid and endocannabinoid-mediated pain inhibition, conditioned pain modulation, recruitment of high threshold motor units, exercise-induced metabolite production and an interaction between cardiovascular and pain regulatory systems. We hypothesise that several mechanisms consistent with prolonged high intensity exercise may drive the hypoalgesia effect observed with blood flow restriction exercise. These are likely triggered by the high level of intramuscular stress in the exercising muscle generated by blood flow restriction including hypoxia, accumulation of metabolites, accelerated fatigue onset and ischemic pain. Therefore, blood flow restriction exercise may induce hypoalgesia through similar mechanisms to prolonged higher intensity exercise, but at lower intensities, by changing local tissue physiology, highlighting the importance of the blood flow restriction stimulus. The potential to use blood flow restriction exercise as a pain modulation tool has important implications following acute injury and surgery, and for several load compromised populations with chronic pain.

The Female Heart: Sex Differences in the Dynamics of ECG in Response to Stress

Sex differences in the study of the human physiological response to mental stress are often erroneously ignored. To this end, we set out to show that our understanding of the stress response is fundamentally altered once sex differences are taken into account. This is achieved by comparing the heart rate variability (HRV) signals acquired during mental maths tests from ten females and ten males of similar maths ability; all females were in the follicular phase of their menstrual cycle. For rigor, the HRV signals from this pilot study were analyzed using temporal, spectral and nonlinear signal processing techniques, which all revealed significant statistical differences between the sexes, with the stress-induced increases in the heart rates from the males being significantly larger than those from the females (p-value = 4.4 × 10⁻⁴). In addition, mental stress produced an overall increase in the power of the low frequency component of HRV in the males, but caused an overall decrease in the females. The stress-induced changes in the power of the high frequency component were even more profound; it greatly decreased in the males, but increased in the females. We also show that mental stress was followed by the expected decrease in sample entropy, a nonlinear measure of signal regularity, computed from the males' HRV signals, while overall, stress manifested in an increase in the sample entropy computed from the females' HRV signals. This finding is significant, since mental stress is commonly understood to be manifested in the decreased entropy of HRV signals. The significant difference (p-value = 2.1 × 10⁻⁹) between the changes in the entropies from the males and females highlights the pitfalls in ignoring sex in the formation of a physiological hypothesis. Furthermore, it has been argued that estrogen attenuates the effect of catecholamine stress hormones; the findings from this investigation suggest for the first time that the conventionally cited cardiac changes, attributed to the fight-or-flight stress response, are not universally applicable to females. Instead, this pilot study provides an alternative interpretation of cardiac responses to stress in females, which indicates a closer alignment to the evolutionary tend-and-befriend response.

The influence of reward sensitivity, heart rate dynamics and EEG-delta activity on placebo analgesia

Personality traits have been shown to interact with environmental cues to modulate biological responses including treatment responses, and potentially having a role in the formation of placebo effects. Here we used the Reinforcement Sensitivity Theory Personality Questionnaire (RST-PQ) to identify personality traits that predict placebo analgesic responding. Cardiac inter-beat (RR) time series and electroencephalographic (EEG) band oscillations were recorded from healthy women in a cold-pain (Pain) and placebo analgesia (PA) condition. The measures of Hypnotizability, and self-reported ratings of Hypnotic Depth, Motivation, Pain Expectation, Involuntariness in PA responding, Pain and Distress intensity were obtained. Separate principal components factor analyses with varimax rotation were performed on summarized heart rate variability (HRV) measures of time, frequency, nonlinear Complexity, and EEG-band activity. Both analyses yielded a similar three-factor solution including Frequency HRV (factor-1), Complexity HRV dynamics (factor-2), and time HRV & EEG-delta activity (factor-3). Reward Interest sub-trait of the Behavioral Approach System (BAS-RI), Pain Expectation, Involuntariness in PA responding, and Hypnotic Depth were positively associated, whereas negative changes in time-HRV & EEG-delta scores were associated with Pain Reduction. Multiple mediation analyses disclosed that BAS-RI, potentially served by the dopaminergic system, through Involuntariness in PA responding can alter placebo responding to laboratory pain. Our results also show that a linear compound of HR slowing and higher EEG delta activity during PA explains a substantial proportion of the variance in placebo analgesic responses. Future studies should examine the potential role that these individual difference measures may play in patient responsiveness to treatments for clinical pain.

Touch-induced pupil size reflects stimulus intensity, not subjective pleasantness

Interpersonal touch is known to influence human communication and emotion. An important system for interpersonal touch is the C-tactile (CT) system, which is activated by a soft stroke on hairy skin with a velocity of 1–10 cms⁻¹. This system been proposed to play a unique role in hedonic valence and emotion of touch. For other sensory modalities, hedonic processing has been associated with pupil dilation. However, it is unclear whether pupil dilation can be modulated by hedonic touch. The current study investigated in two experiments how pupil size reacts to both affective and non-affective stroking. Pupil-size data were obtained to investigate differences between stroking conditions. In addition, an adjusted version of the Touch Perception Task (TPT) was used to assess subjective touch pleasantness ratings. In Experiment 1, affective (3 cms⁻¹) and non-affective (0.3 and 30 cms⁻¹) stroking was applied to the dorsal side of the right hand. Results revealed that stroking velocity had a significant effect on TPT-item scores, showing higher that affective touch was rated as more pleasant compared to non-affective touch, thereby replicating the previous studies. Results, however, revealed no specific pupil dilation for the 3 cms⁻¹ condition; instead, a logarithmic relation was found between pupil-size dilation and stroking velocity. This relation was confirmed in a second experiment. Furthermore, the palm of the hand was used as a control site for tactile stimulation, for which similar findings were obtained as for the dorsal side of the hand. In addition, skin conductance recordings showed a pattern of response to different stroking velocities similar to pupil dilation. These results suggest that pupil-size dilation does respond to tactile input, but that this response is related to arousal caused by changes in stimulus intensity (e.g., stroking velocity) rather than specific C-tactile stimulation.

Can Perfusion Index be used as an Objective Tool for Pain Assessment in Labor Analgesia?

Objective:

To establish a relationship between the Visual Analog Scale for pain (VAS) in the recovery time of epidural analgesia and the Perfusion Index (PI) values at that time and to test the possibility of using PI as an objective tool for pain assessment.

Methods:

Thirty women were included in the study. After inserting epidural catheter, the initial applicationtime of epidural analgesia was taken as 0^th minute. Hemodinamics, VAS, and PIvalues were recorded at 5^th, 10^th, 30^th, 60^th minutes and every two hours until the birth and the 30^th minute after the birth.

Results:

HR, SAP, DAP, PI, VAS values before the procedure were different than all follow-ups (p<0.001). A negative and significant correlation was found at 10^th, 30^th, 60^th minutes and 2^nd hour after drug administration from epidural catheter(rho:0.38; p:0.03, rho:0.47; p:0.009, rho:0.75; p<0.001, rho:0.46; p:0.009, respectively). As the pain decreased, the perfusion index increased. In 17 patients requiring additional doses, PI increased after the all medications, but a decrease was observed in the VAS values(p<0.05).

Conclusions:

In this study, it was determined that the pain decreased with epidural analgesia, perfusion index increased and the pain level increased significantly when the perfusion index started to decrease.

Contextual modulation of autonomic pain reactivity

Although modulation of cardiac activity may be influenced by several factors, interaction between autonomic nociceptive responses and the high-level of cortical processes is not clearly understood. Here, we studied in 26 subjects whether empathetic or unempathetic contexts could interact with autonomic pain responses. RR intervals variability was used to approach parasympathetic and sympathetic responses to painful thermal stimulations, according to contexts evoked by experimenters' comments. We observed that unempathetic context increased sympathetic reactivity to comments and to painful stimulations without any parasympathetic change. These results show an interaction between context and nociceptive processes in cardiovascular control.

Improving Pain Management in Patients with Sickle Cell Disease from Physiological Measures Using Machine Learning Techniques

Pain management is a crucial part in Sickle Cell Disease treatment. Accurate pain assessment is the first stage in pain management. However, pain is a subjective response and hard to assess via objective approaches. In this paper, we proposed a system to map objective physiological measures to subjective self-reported pain scores using machine learning techniques. Using Multinomial Logistic Regression and data from 40 patients, we were able to predict patients' pain scores on an 11-point rating scale with an average accuracy of 0.578 at the intra-individual level, and an accuracy of 0.429 at the inter-individual level. With a condensed 4-point rating scale, the accuracy at the inter-individual level was further improved to 0.681. Overall, we presented a preliminary machine learning model that can predict pain scores in SCD patients with promising results. To our knowledge, such a system has not been proposed earlier within the SCD or pain domains by exploiting machine learning concepts within the clinical framework.

Unique Autonomic Responses to Pain in Yoga Practitioners

OBJECTIVE

Autonomic nervous system activity is associated with neurobehavioral aspects of pain. Yogis use breathing, relaxation, and mindfulness to tolerate pain, which could influence autonomic responses. To evaluate how the link between autonomic responses and pain is altered by other factors, we compared perceptual and autonomic responses to pain between yogis and controls.

METHODS

Nineteen yogis and 15 controls rated warm and painfully hot stimuli (1-cm thermode on calf), with visual anticipatory cues indicating certainly painful, certainly nonpainful, or uncertainly either painful or nonpainful. Heart rate, skin conductance, respiration, and blood pressure were measured.

RESULTS

At baseline, yogis breathed slower and deeper than did controls, with no differences in other autonomic measures. During the task, perceptual ratings did not differ between groups in either the certain or uncertain conditions. Nevertheless, yogis had higher phasic skin conductance responses in anticipation of and response to all stimuli, but particularly during painful heat in uncertain contexts (uncertain: 0.46 [0.34] μS; certain: 0.37 [0.28] μS; t(18) = 3.962, p = .001). Furthermore, controls showed a decrease in heart rate to warm (-2.51 [2.17] beats/min) versus painful stimuli (0.83 [1.63] beats/min; t(13) = 5.212, p < .001) and lower respiratory sinus arrhythmia during pain compared with warm trials, whereas yogis had similar reactions to painful and nonpainful stimuli.

CONCLUSIONS

Autonomic responses to pain differed in yogis and healthy volunteers, despite similar pain ratings. Thus, autonomic reactivity to pain may be altered by environmental and psychological factors throughout an individual's life.

Effect of spinal manipulative treatment on cardiovascular autonomic control in patients with acute low back pain

Background

This study aimed to quantify the effect of spinal manipulative treatment (SMT) from an analysis of baroreflex, systolic blood pressure and heart rate variability (HRV) on patients with acute back pain. It was hypothesized that SMT would increase the parasympathetic cardiovascular autonomic control.

Methods

Twenty-two patients with acute back pain were randomly divided into two groups: one receiving sham treatment (Sham) and the other receiving SMT. Recordings were completed during the first day and the seventh day, immediately before and after treatment on both days. ECG and systolic blood pressure were continuously recorded to compute cardiovascular variability and baroreflex sensitivity components. The perceived level of pain was measured with the numeric pain scale (NPS) 48 h before, just before and just after each treatment. The NPS ranged from 0 to 100% (peak of pain before treatment). ECG and systolic blood pressure recordings were analyzed in time frequency domain using the Smoothed pseudo Wigner-Ville distribution.

Results

Root mean square of the successive differences, high frequency power of the heart rate variability, and high frequency baroreflex sensitivity differences between post and pre tests were higher in the SMT group than in the Sham group (p < 0.01), whereas no differences were observed with the other heart rate variability components. Also, no differences were observed with the systolic blood pressure components. Although the estimated pain scale values decreased over time, no difference was observed between the SMT and Sham groups.

Conclusions

This seems to be the first study to assess the effect of SMT on both heart rate variability and baroreflex sensitivity in patients with acute back pain. SMT can be seen to provoke an increase in parasympathetic control known to relate to a person's healthy state. Thus, cardiovascular variability analysis may be a useful tool for clinicians to quantify and objectify the beneficial effects of spinal manipulation treatment.

Pain Prediction From ECG in Vascular Surgery

Varicose vein surgeries are routine outpatient procedures, which are often performed under local anaesthesia. The use of local anaesthesia both minimises the risk to patients and is cost effective, however, a number of patients still experience pain during surgery. Surgical teams must therefore decide to administer either a general or local anaesthetic based on their subjective qualitative assessment of patient anxiety and sensitivity to pain, without any means to objectively validate their decision. To this end, we develop a 3-D polynomial surface fit, of physiological metrics and numerical pain ratings from patients, in order to model the link between the modulation of cardiovascular responses and pain in varicose vein surgeries. Spectral and structural complexity features found in heart rate variability signals, recorded immediately prior to 17 varicose vein surgeries, are used as pain metrics. The so obtained pain prediction model is validated through a leave-one-out validation, and achieved a Kappa coefficient of 0.72 (substantial agreement) and an area below a receiver operating characteristic curve of 0.97 (almost perfect accuracy). This proof-of-concept study conclusively demonstrates the feasibility of the accurate classification of pain sensitivity, and introduces a mathematical model to aid clinicians in the objective administration of the safest and most cost-effective anaesthetic to individual patients.

Effects of explicit cueing and ambiguity on the anticipation and experience of a painful thermal stimulus

Many factors can influence the way in which we perceive painful events and noxious stimuli, but less is known about how pain perception is altered by explicit knowledge about the impending sensation. This study aimed to investigate the impact of explicit cueing on anxiety, arousal, and pain experience during the anticipation and delivery of noxious thermal heat stimulations. Fifty-two healthy volunteers were randomised to receive explicit instructions about visual cue-stimulus temperature pairings, or no explicit instructions about the cue-stimulus pairs. A pain anxiety task was used to investigate the effects of explicit cueing on anticipatory anxiety, pain experience and electrophysiological responses. Participants who received explicit instructions about the cue-stimulus pairs (i.e., the relationship between the colour of the cue and the temperature of the associated stimuli) reported significantly higher subjective anxiety prior to the delivery of the thermal heat stimuli (p = .025, partial eta squared = .10). There were no effects of explicit cueing on subsequent pain intensity, unpleasantness, or the electrophysiological response to stimulus delivery. The perceived intensity and unpleasantness of the stimuli decreased across the blocks of the paradigm. In both groups anticipating the ambiguous cue elicited the largest change in electrophysiological arousal, indicating that not knowing the impending stimulus temperature led to increased arousal, compared to being certain of receiving a high temperature thermal stimulus (both p < .001). Perceived stimulus intensity varied between ambiguous and non-ambiguous cues, depending on the temperature of the stimulus. Together these findings highlight the impact and importance of explicit cueing and uncertainty in experimental pain studies, and how these factors influence the way healthy individuals perceive and react to noxious and innocuous thermal stimuli.

Observing continuous change in heart rate variability and photoplethysmography-derived parameters during the process of pain production/relief with thermal stimuli

Continuously monitoring and efficiently managing pain has become an important issue. However, no study has investigated a change in physiological parameters during the process of pain production/relief. This study modeled the process of pain production/relief using ramped thermal stimulation (no pain: 37°C water, process of pain production: a heating rate of 1°C/min, and subject feels pain: water kept at the painful temperature for each subject, with each segment lasting 10 min). In this duration, the variation of the heat rate variability and photoplethysmography-derived parameters was observed. A total of 40 healthy individuals participated: 30 in the trial group (14 males and 16 females with a mean age of 22.5±1.9 years) and 10 in the control group (7 males and 3 females with a mean age of 22.5±1.3 years). The results showed that the numeric rating scale value was 5.03±1.99 when the subjects felt pain, with a temperature of 43.54±1.70°C. Heart rate, R-R interval, low frequency, high frequency, photoplethysmography amplitude, baseline, and autonomic nervous system state showed significant changes during the pain production process, but these changes differed during the period Segment D (painful temperature 10: min). In summary, the study observed that physiological parameters changed qualitatively during the process of pain production and relief and found that the high frequency, low frequency, and photoplethysmography parameters seemed to have different responses in four situations (no pain, pain production, pain experienced, and pain relief). The trends of these variations may be used as references in the clinical setting for continuously observing pain intensity.

Pain Catastrophizing, rather than Vital Signs, Associated with Pain Intensity in Patients Presenting to the Emergency Department for Pain

This study examined the relationships of self-reported pain intensity with vital signs, pain catastrophizing, and state anxiety in patients presenting to the emergency department (ED) for acute pain, exacerbations of chronic pain, or acute pain with concurrent chronic (combined) pain, comparing the pattern of relationships among these three pain groups. One hundred fifty-eight patients presenting to the ED for pain were recruited. Vital signs and self-reported pain intensity were obtained at triage, then participants completed self-report measures of pain catastrophizing, state anxiety, and demographic information. No significant associations were found between vital signs and pain intensity at triage in any of the pain groups. Pain catastrophizing was significantly associated with self-reported pain intensity in the acute pain group (r = .34, p < .05) and combined pain group (r = .30, p < .05), and state anxiety was significantly associated with self-reported pain intensity in with the acute pain group (r = .27, p < .05). When pain catastrophizing and state anxiety were used in a stepwise multiple regression analysis to predict self-reported pain intensity in the acute pain group, only pain catastrophizing emerged as a unique predictor (β = .405, p < .01). Consistent with previous research, vital signs were not associated with self-reported pain intensity in patients presenting to the ED for pain, including those with chronic pain. Given the significant association of pain catastrophizing and pain intensity among patients presenting to the ED for acute pain, brief measurement of pain catastrophizing may inform pain treatment in the ED.

Effectiveness of Two Topical Anaesthetic Agents used along with Audio Visual Aids in Paediatric Dental Patients

INTRODUCTION

Topical anaesthetic agents enable pain free intraoral procedures, symptomatic pain relief for toothache, superficial mucosal lesions and pain related to post extraction time. Most common anxiety provoking and fearful experience for children in dental operatory is administration of local anaesthesia because on seeing the needle, children usually become uncooperative. One of recent trend of behaviour management technique is using non-aversive techniques out of which audiovisual distraction has emerged as a very successful technique for managing children in dental settings. Audio visual distraction could decrease the procedure related anxiety of patients undergoing dental treatment and can be very relaxing for highly anxious patients.

AIM

The aim of the present study was to compare the efficacy of topical anaesthetics EMLA (Eutectic Mixture of Local Anaesthetics) cream and benzocaine (20%) gel in reducing the pain during the needle insertion with and without the use of Audio Visual (AV) aids.

MATERIALS AND METHODS

The study was conducted on 120 children, the age range of 3-14 years attending the outpatient department for their treatment. EMLA and benzocaine gel (20%) were assessed for their effectiveness in reducing the pain on needle insertion during local anaesthesia administration. Based on the inclusion and the exclusion criteria, children requiring local anaesthesia for the dental treatment were randomly divided into four equal groups of 30 children based upon whether AV aids were used or not. AV aids were given using Sony Vaio laptop with earphones with nursery rhymes and cartoon movies DVD. The pain assessment was done by using the Visual Analogue Scale (VAS) scale and measurement of the physiological responses of pulse rate and oxygen saturation were done by pulse oximeter.

RESULTS

There was a statistically significant difference in the mean pain score, pulse rate and mean oxygen saturation rate when it was compared between the four groups. EMLA with AV aids was found to be a better topical anaesthestic agent as compared to other three groups.

CONCLUSION

EMLA with AV aids was better when compared with EMLA without AV aids followed by benzocaine with AV aids. Benzocaine topical anaesthetic agent without AV aids was least effective in reducing the pain scores and improving the oxygen saturation rate.

Maternal microcirculation and sidestream dark field imaging: a prospective assessment of the association between labour pain and analgesia on the microcirculation of pregnant women

BACKGROUND

Pregnancy places significant demands on the cardiovascular system leading to measurable changes in the macrocirculation and potentially the microcirculation. During labour, both uterine contractions and labour pain can further impact cardiovascular status. The objective of this observational study was to compare sublingual microcirculation in labouring parturients before and after epidural analgesia.

METHODS

Healthy pregnant, labouring women requesting epidural analgesia were approached to participate. Participants with cardiovascular disease, diabetes, obesity, smoking or caffeine intake were excluded. The sidestream dark field device was applied to the sublingual mucosa obtaining images of at least 20 seconds in 5 visual fields before and after epidural analgesia. Video clips were analyzed randomly and blindly. The primary outcome was mean microvascular flow index (MFI).

RESULTS

Twelve participants completed this study. The results demonstrate no statistically significant difference in the MFI during labour pain (2.9±0.1) compared to after epidural analgesia (3.0±0.04, p = 0.31). Furthermore, there were no statistically significant differences in any secondary outcomes.

CONCLUSION

Our findings indicate that epidural analgesia may not impact sublingual microcirculation in labouring women. This agrees with literature supporting epidural analgesia as a safe, appropriate method of pain relief during labour with limited impact on peripheral macro or microcirculation.

Exercise-induced hypoalgesia: Pain tolerance, preference and tolerance for exercise intensity, and physiological correlates following dynamic circuit resistance exercise

Previous research has demonstrated significant decreases in pain perception in healthy individuals following both aerobic and upper body resistance exercise, but research on circuit training has been limited. The purpose of the study was to determine the effects of a strenuous bout of dynamic circuit resistance exercise on pain threshold and pain tolerance in conjunction with changes in blood lactate levels, heart rate (HR), and perceived exertion. A sample of 24 college-age students participated in 2 sessions: (1) a maximal strength testing session and (2) a circuit training bout of exercise that consisted of 3 sets of 12 repetitions with a 1:1 work to rest ratio at 60% one-repetition maximum (1-RM) predicted from a three-repetition maximum (3-RM) for 9 exercises. Participants exhibited increases in pain tolerance, blood lactate levels, HR and perceived exertion following resistance exercise. Preference for exercise intensity was positively correlated with lactate post exercise and tolerance for exercise intensity was positively correlated with pain tolerance and lactate post exercise. In conclusion, this is the first study to demonstrate increases in pain tolerance following a dynamic circuit resistance exercise protocol and disposition for exercise intensity may influence lactate and pain responses to circuit resistance exercise.

PATTERN: Pain Assessment for paTients who can't TEll using Restricted Boltzmann machiNe

Background

Accurately assessing pain for those who cannot make self-report of pain, such as minimally responsive or severely brain-injured patients, is challenging. In this paper, we attempted to address this challenge by answering the following questions: (1) if the pain has dependency structures in electronic signals and if so, (2) how to apply this pattern in predicting the state of pain. To this end, we have been investigating and comparing the performance of several machine learning techniques.

Methods

We first adopted different strategies, in which the collected original n-dimensional numerical data were converted into binary data. Pain states are represented in binary format and bound with above binary features to construct (n + 1) -dimensional data. We then modeled the joint distribution over all variables in this data using the Restricted Boltzmann Machine (RBM).

Results

Seventy-eight pain data items were collected. Four individuals with the number of recorded labels larger than 1000 were used in the experiment. Number of avaliable data items for the four patients varied from 22 to 28. Discriminant RBM achieved better accuracy in all four experiments.

Conclusion

The experimental results show that RBM models the distribution of our binary pain data well. We showed that discriminant RBM can be used in a classification task, and the initial result is advantageous over other classifiers such as support vector machine (SVM) using PCA representation and the LDA discriminant method.

Total Sleep Deprivation and Pain Perception during Cold Noxious Stimuli in Humans

BACKGROUND AND AIMS

A substantial portion of the population suffers from chronic pain leading to significant health care costs and lost productivity. Loss of sleep duration and quality are widely reported in patients suffering from a variety of acute or chronic pain conditions. Conversely, sleep loss has been known to elevate pain perception; thus a potential bi-directional relationship exists between sleep deprivation and pain. To date, the majority of studies examining the relationship between experimentally induced pain and sleep loss have focused on the measurement of pain threshold. Additionally, despite evidence of sex differences in ratings of perceived pain, previous studies examining pain following sleep loss have not probed for sex differences. We examined the effects of 24-hour total sleep deprivation (TSD) on perceived pain during a 2-minute cold pressor test (CPT). We hypothesized that TSD would augment perceived pain and that women would demonstrate an elevated pain response compared to men.

METHODS

Testing was carried out in 14 men and 13 women. All subjects reported to be nonsmokers with no history of cardiovascular disease, autonomic dysfunction, asthma, or diabetes. All female subjects were free of oral contraceptive use, and were tested during the early follicular phase of the menstrual cycle. Trial order was randomized and testing sessions (Normal sleep (NS) and TSD) were separated by approximately one month. Subjects immersed their left hand, up to the wrist, in an ice water bath (~1°C), and perceived pain was recorded every 15 seconds from a modified Borg scale (6-20 arbitrary units a.u.).

RESULTS

Perceived pain responses during CPT were augmented following TSD (Δ1.2 a.u.; time × condition, p<0.05). The augmented pain response following TSD was noted when perceived pain was expressed as mean (NS Δ7.0±0.5 vs. TSD Δ8.2±0.5 a.u.; p<0.05) or peak (NS Δ8.9±0.6 vs. TSD Δ10.2±0.5 a.u.; p<0.05) perceived pain. The effects of TSD on perceived pain were similar in both men and women (condition × time × sex, p>0.05).

CONCLUSIONS AND IMPLICATIONS

We conclude that TSD significantly augments perceived pain during CPT, but this response was not sex dependent. These findings support emerging evidence that adequate sleep represents a relevant, and cost effective, preventative/therapeutic strategy to reduce self-perceived pain in both men and women.

Neuroimaging brainstem circuitry supporting cardiovagal response to pain: a combined heart rate variability/ultrahigh-field (7 T) functional magnetic resonance imaging study

Central autonomic control nuclei in the brainstem have been difficult to evaluate non-invasively in humans. We applied ultrahigh-field (7 T) functional magnetic resonance imaging (fMRI), and the improved spatial resolution it affords (1.2 mm isotropic), to evaluate putative brainstem nuclei that control and/or sense pain-evoked cardiovagal modulation (high-frequency heart rate variability (HF-HRV) instantaneously estimated through a point-process approach). The time-variant HF-HRV signal was used to guide the general linear model analysis of neuroimaging data. Sustained (6 min) pain stimulation reduced cardiovagal modulation, with the most prominent reduction evident in the first 2 min. Brainstem nuclei associated with pain-evoked HF-HRV reduction were previously implicated in both autonomic regulation and pain processing. Specifically, clusters consistent with the rostral ventromedial medulla, ventral nucleus reticularis (Rt)/nucleus ambiguus (NAmb) and pontine nuclei (Pn) were found when contrasting sustained pain versus rest. Analysis of the initial 2-min period identified Rt/NAmb and Pn, in addition to clusters consistent with the dorsal motor nucleus of the vagus/nucleus of the solitary tract and locus coeruleus. Combining high spatial resolution fMRI and high temporal resolution HF-HRV allowed for a non-invasive characterization of brainstem nuclei, suggesting that nociceptive afference induces pain-processing brainstem nuclei to function in concert with known premotor autonomic nuclei in order to affect the cardiovagal response to pain.