Sleep onset insomnia symptoms during hospitalization for major burn injury predict chronic pain

Heat of the night: sleep disturbance activates inflammatory mechanisms and induces pain in rheumatoid arthritis

Sleep has a homeostatic role in the regulation of the immune system and serves to constrain activation of inflammatory signalling and expression of cellular inflammation. In patients with rheumatoid arthritis (RA), a misaligned inflammatory profile induces a dysregulation of sleep-wake activity, which leads to excessive inflammation and the induction of increased sensitivity to pain. Given that multiple biological mechanisms contribute to sleep disturbances (such as insomnia), and that the central nervous system communicates with the innate immune system via neuroendocrine and neural effector pathways, potential exists to develop prevention opportunities to mitigate the risk of insomnia in RA. Furthermore, understanding these risk mechanisms might inform additional insomnia treatment strategies directed towards steering and reducing the magnitude of the inflammatory response, which together could influence outcomes of pain and disease activity in RA.

Sleep deprivation increases pain sensitivity following acute muscle soreness

OBJECTIVE

The aim of this cross-sectional group comparison study was to investigate whether sleep disturbance facilitates pain sensitivity caused by an acute muscle injury.

METHODS

Thirty-six healthy individuals were included and randomly assigned to one of three groups in a non-balanced manner: a control group (n = 11) and two groups who performed eccentric exercise for quadriceps to cause delayed onset of muscle soreness (DOMS). The difference between the DOMS groups was that one followed their habitual sleep pattern (Sleep group, n = 12) and the other had their sleep withdrawn for one night (No-Sleep group, n = 13). The level of DOMS was indicated using a 6-point Likert Scale and pain sensitivity was assessed using Pressure Pain Thresholds (PPT) at the lower legs and shoulder at baseline (Day-1) and after 48 h (Day-3). Additionally, pain distribution following suprathreshold pressure stimulation (STPS) on the quadriceps muscle was assessed on the same days.

RESULTS

PPTs were significantly reduced at Day-3 compared with Day-1 in both DOMS groups. The relative change between days was larger in the No-Sleep group compared with controls (P<0.05) whilst no significant change was seen in the Sleep group compared with controls. Furthermore, no significant differences were found between groups nor days for the subjective perception of DOMS (Likert Scale) and the size of the area of STPS.

CONCLUSIONS

The loss of sleep further increases pain sensitivity following an acute soft tissue injury, demonstrating a potential causative role of the lack of sleep on complex pain states following musculoskeletal injuries.

Sleep quality as a mediator of the relation between depression and chronic pain: a systematic review and meta-analysis

BACKGROUND

Chronic pain and depression represent two global health problems with considerable economic consequences. Although existing literature reports on the relation between depression and pain conditions, meta-analytic evidence backing the mediating role of sleep disturbance as one of the main symptoms of depression is scarce. To examine the extent to which sleep disturbance mediates the depression-chronic pain association, we conducted a systematic review and meta-analysis of the associations of chronic pain, depression, and sleep quality.

METHODS

We systematically searched for literature in MEDLINE and other relevant databases and identified cohort and case-control studies on depression, sleep disturbance, and chronic pain. Forty-nine studies were eligible, with a total population of 120 489 individuals. We obtained direct and indirect path coefficients via two-stage meta-analytic structural equation modelling, examined heterogeneity via subgroup analyses, and evaluated primary studies quality.

RESULTS

We found a significant, partial mediation effect of sleep disturbance on the relation between depression and chronic pain. The pooled path coefficient (coef.) of the indirect effect was 0.03 (95% confidence interval [CI]: 0.01-0.05) and accounted for 12.5% of the total effect of depression on chronic pain. This indirect effect also existed for cohort studies (coef. 0.02; 95% CI: 0.002-0.04), European studies (coef. 0.03; 95% CI: 0.004-0.05), and studies that adjusted for confounders (coef. 0.04; 95% CI: 0.01-0.09).

CONCLUSIONS

Sleep disturbance partially mediates the association between depression and pain. Although plausible mechanisms could explain this mediation effect, other explanations, including reverse causation, must be further explored.

SYSTEMATIC REVIEW PROTOCOL

PROSPERO CRD42022338201.

Sleep Quantity and Quality During Inpatient Rehabilitation After Stroke

OBJECTIVE

To identify sleep patterns and their association with recovery after stroke during inpatient rehabilitation, and to determine if clinical outcomes are different between participants demonstrating abnormal sleep patterns as compared to those with normal sleep patterns.

METHODS

Cohort study in which participants were undergoing inpatient rehabilitation after a stroke. Sleep quantity and quality was measured using an actigraph that participants wore for up to 7 nights during the first week of inpatient rehabilitation. Medicare Quality Indicators (GG code), Barthel Index, gait speed, and Berg balance scale were collected at admission and discharge. Participants were categorized into groups based on meeting or not meeting recommended sleep quantity and quality guidelines. Association between sleep patterns and outcomes were assessed using Pearson correlation and differences in outcomes and length of stay between participants who met or did not meet sleep quantity and quality guidelines were determined using independent sample t-test.

RESULTS

69 participants were in the study. Sleep quantity and quality was poor for all the participants. None of the participants met all the sleep quantity and quality guidelines. There were moderate to small associations (-0.42 to 0.22) between some sleep quantity and quality parameters and clinical outcomes. Participants who's sleep efficiency (SE) was <85% had a significantly longer length of stay compared to those who's SE was >=85% (17.4 vs. 21.5 days, p<0.05).

CONCLUSIONS

People with stroke undergoing inpatient rehabilitation have poor sleep quantity and quality. There is a small to moderate association between sleep patterns and clinical outcomes and participants with poor sleep quality had longer length of stay compared to those with good sleep quality. Further research is necessary to better understand the complex relationship between sleep and recovery after stroke.

IMPACT

Sleep is associated with functional recovery during inpatient rehabilitation after stroke.

Sleep in hospitalized pediatric and adult patients – A systematic review and meta-analysis

Background

Sleep is essential for recovery from illness. As a result, researchers have shown a growing interest in the sleep of hospitalized patients. Although many studies have been conducted over the past years, an up to date systematic review of the results is missing.

Objective

The objective of this systematic review was to assess sleep quality and quantity of hospitalized patients and sleep disturbing factors.

Methods

A systematic literature search was conducted within four scientific databases. The search focused on synonyms of 'sleep’ and 'hospitalization’. Papers written in English or Dutch from inception to April 25th,2022 were included for hospitalized patients >1 year of age. Papers exclusively reporting about patients receiving palliative, obstetric or psychiatric care were excluded, as well as patients in rehabilitation and intensive care settings, and long-term hospitalized geriatric patients. This review was performed in accordance with the PRISMA guidelines.

Results

Out of 542 full text studies assessed for eligibility, 203 were included, describing sleep quality and/or quantity of 17,964 patients. The median sample size of the studies was 51 patients (IQR 67, range 6–1472). An exploratory meta-analysis of the Total Sleep Time showed an average of 7.2 h (95%-CI 4.3, 10.2) in hospitalized children, 5.7 h (95%-CI 4.8, 6.7) in adults and 5.8 h (95%-CI 5.3, 6.4) in older patients (>60y). In addition, a meta-analysis of the Wake After Sleep Onset (WASO) showed a combined high average of 1.8 h (95%-CI 0.7, 2.9). Overall sleep quality was poor, also due to nocturnal awakenings. The most frequently cited external factors for poor sleep were noise and number of patients in the room. Among the variety of internal/disease-related factors, pain and anxiety were most frequently mentioned to be associated with poor sleep.

Conclusion

Of all studies, 76% reported poor sleep quality and insufficient sleep duration in hospitalized patients. Children sleep on average 0.7–3.8 h less in the hospital than recommended. Hospitalized adults sleep 1.3–3.2 h less than recommended for healthy people. This underscores the need for interventions to improve sleep during hospitalization to support recovery.

•

An overview of the magnitude of sleep deprivation in hospitalized patients.

•

A meta-analysis of studies reporting on some of the main sleep outcomes.

•

An overview of internal and external factors affecting sleep in hospitalized patients.

•

Guidance for potential interventions to improve sleep during clinical admission.

•

Uncovers a knowledge gap regarding the sleep quality of hospitalized children and daytime sleep of hospitalized adults.

Acute sleep interventions as an avenue for treatment of trauma-associated disorders

Scientific evidence that acute, posttrauma sleep disturbances (eg, nightmares and insomnia) can contribute significantly to the pathogenesis of trauma-induced disorders is compelling. Sleep disturbances precipitating from trauma are uniquely predictive of daytime posttrauma symptom occurrence and severity, as well as subsequent onset of mental health disorders, including post-traumatic stress disorder. Conversely, adequate sleep during the acute posttrauma period is associated with reduced likelihood of adverse mental health outcomes. These findings, which are broadly consistent with what is known about the role of sleep in the regulation of emotion, suggest that the acute posttrauma period constitutes a "window of opportunity" during which treatment of sleep disturbances may be especially effective for preventing or mitigating progression of aberrant psychophysiological processes. At this point, the weight of the scientific evidence supporting this possibility warrants initiation of clinical trials to confirm the benefits of targeted prophylactic sleep enhancement, and to establish treatment guidelines as appropriate.

CITATION

Swift KM, Thomas CL, Balkin TJ, Lowery-Gionta EG, Matson LM. Acute sleep interventions as an avenue for treatment of trauma-associated disorders. J Clin Sleep Med. 2022;18(9):2291-2312.

Association between sleep duration and chest pain in US adults: A cross-sectional study

Objective

Herein, we purposed to explore the association of sleep duration with chest pain among adults in US.

Methods

This research work enrolled 13,274 subjects in the National Health and Nutrition Examination Survey (NHANES) from 2011 to 2018. The association of sleep duration with chest pain among adults in US was evaluated by Multivariable logistic regression.

Results

To elucidate the association, we made adjustments for gender, BMI, diabetes, smoking status, drinking status, race, marital status, annual family income, hyperlipoidemia, Hypertension. Chest pain incidence decreased by 5% [OR = 0.95 (0.93, 0.98), p = 0.0004] for an increase in sleep duration by 1 h. A generalized additive model (GAM) was used to reseal a U-shaped relationship of sleep duration with incident chest pain. When duration of sleep was <6.5 h, chest pain incidence negatively correlated to sleep duration [OR = 0.77 (0.72, 0.82) P < 0.0001]. However, when sleep duration was ≥6.5 h, chest pain incidence rose with escalating sleep duration [OR = 1.07 (1.03, 1.11) p = 0.0014].

Conclusions

Duration of sleep was established to be independently linked with an increase in the occurrence of chest pain. Excessive sleep, as much as insufficient sleep, increases the risk of chest pain. Both excessive sleep and insufficient sleep are associated with an increased risk of chest pain.

Sleep Quality Among Burn Survivors And The Importance Of Intervention: A Systematic Review And Meta-Analysis

Burn survivors undergo a plethora of physiologic disturbances which can greatly affect quality of life (QOL) and healing processes. This review aimed to systematically examine sleep quality among individuals with burns and to explore the effectiveness of interventions using a meta-analytic approach. A systematic review of the literature was conducted by searching for articles using various databases. Titles and abstracts were screened and full texts of retained articles were assessed based on eligibility criteria. Methodological quality was ascertained in all articles using various scales. Overall, 5,323 articles were screened according to titles and abstracts and 25 articles were retained following full-text screening. Of the twenty-five articles, 17 were assessed qualitatively while 8 were included in the meta-analysis. Based on the qualitative analysis, sleep was found to be negatively affected in burn patients. The subsample of 8 articles included in the meta-analysis showed an overall weighted mean effect size (Hedges's g) of 1.04 (SE = 0.4, 95% CI, z = 3.0; p < 0.01), indicating a large, positive effect of intervention on sleep quality for burn patients. This review was able to demonstrate the detrimental effects of burn injury on sleep quality. Several interventions have been examined throughout the literature and have shown to be beneficial for sleep quality. However, there is great heterogeneity between existing interventions. The results from this review suggest that further research is needed before recommendations can be made as to which intervention is most effective at improving sleep in patients suffering from burn injuries.

Nonpharmacologic Management of Procedural Pain in Pediatric Burn Patients: A Systematic Review of Randomized Controlled Trials

Pain following burn injury is associated with long-term health consequences in the pediatric population. Literature suggests nonpharmacologic treatment may provide improved pain control as an effective adjunct for these patients. This study aims to summarize randomized controlled trials on nonpharmacologic procedural pain management in pediatric burn patients. A systematic review was conducted on nonpharmacologic procedural pain management techniques used in the pediatric burn population. Fifteen studies were included and involved virtual reality, distraction devices, child life therapy, directed play, digital tablet games, cartoons, hypnosis, and music therapy. Treatment was effective in 8 out of 15 studies. Compared to controls, nonpharmacologic treatments reduced mid procedure pain by 19.7% and post procedure pain by 20.1%. This study demonstrates nonpharmacologic therapy can be an effective adjunct in pediatric procedural burn pain management, however further studies are needed to develop standardized algorithms to integrate nonpharmacologic treatments with pharmacologic therapies.

Insomnia Symptoms and Chronic Pain among Patients Participating in a Pain Rehabilitation Program-A Registry Study

Insomnia and chronic pain are prevalent health complaints. Previous research has shown that they are closely associated, but their interaction and causality are not completely understood. Further research is needed to uncover the extent to which a treatment strategy focusing on one of the conditions affects the other. This study aimed to map the prevalence of insomnia symptoms among patients in interdisciplinary pain rehabilitation program (IPRP) and investigate associations between the degree of insomnia at baseline and the treatment outcome regarding pain intensity, physical function, social function, mental well-being, anxiety, and depression. Of the 8515 patients with chronic pain, aged 15–81 who were registered in the Swedish Quality Registry for Pain Rehabilitation during 2016–2019 and participated in IPRP, 7261 had follow-up data after treatment. Logistic regression analysis was used to investigate associations. The prevalence of clinical insomnia, according to Insomnia Severity Index (ISI), among chronic pain patients in IPRP was 66%, and insomnia symptoms were associated with both country of birth and educational level. After IPRP, the prevalence of clinical insomnia decreased to 47%. There were statistically significant associations between the degree of insomnia symptoms before IPRP and physical function (p < 0.001), social function (p = 0.004) and mental well-being (p < 0.001). A higher degree of insomnia symptoms at baseline was associated with improvement after IPRP. In conclusion, IPRP seem to have beneficial effects on insomnia symptoms in chronic pain patients. Nevertheless, almost half of the patients still suffer from clinical insomnia after IPRP. The possible effect of systematic screening and treatment of insomnia for improving the effect of IPRP on pain is an important area for future research.

Incidence of and Factors Associated with New-Onset Insomnia Among Lebanese Hospitalised Patients: A single-centre study

Objectives

This study aimed to determine the incidence and post-discharge resolution of new-onset insomnia in hospitalised patients with no previous history of insomnia, as well as to define major correlates of in-hospital insomnia.

Methods

This prospective observational study was conducted between November 2019 and January 2020 at a tertiary care centre in Lebanon. All hospitalised patients >18 years of age with no history of insomnia were screened for new-onset insomnia using the Insomnia Severity Index (ISI) scale. Subsequently, patients were re-assessed two weeks after discharge to determine insomnia resolution.

Results

A total of 75 patients were included in the study. Of these, nine (12%) had no insomnia, 34 (45.3%) had subthreshold insomnia, 22 (29.3%) had moderate insomnia and 10 (13.3%) had severe insomnia. The mean ISI score was 14.95 ± 6.05, with 88% of patients having ISI scores of >7 (95% confidence interval: 0.822–0.965). The frequency of new-onset insomnia was significantly higher among patients who shared a room compared to those in single-bed rooms (95.7% versus 75%; P = 0.011). Other factors were not found to be associated with new-onset insomnia, including the administration of medications known to cause insomnia, in-hospital sedative use, overnight oxygen, cardiac monitoring and self-reported nocturnal toilet use. Overall, insomnia resolution occurred in 78.7% of patients two weeks after discharge.

Conclusion

There was a high incidence of acute new-onset insomnia among hospitalised patients at a tertiary centre in Lebanon. Additional research is recommended to further examine inhospital sleep disturbance factors and to seek convenient solutions to limit insomnia.

Risk factors of persistent insomnia among survivors of traumatic injury: a retrospective cohort study

STUDY OBJECTIVES

Insomnia is a diagnosis with broad health and economic implications that has been increasingly recognized in military service members. This trend was concurrent with an increase in traumatic wartime injuries. Accordingly, we sought to determine longitudinal predictors of persistent insomnia in combat veterans who sustained traumatic injuries.

METHODS

Retrospective cohort study of service members deployed to conflict zones from 2002-2016, with longitudinal follow-up in the Veterans Affairs and Military Health Systems. Two cohorts were derived: 1) service members who sustained traumatic injuries and 2) an age, sex, and service component matched cohort of uninjured service members who deployed to a combat zone. Insomnia was defined using International Classification of Diseases Ninth Revision or International Classification of Diseases Tenth Revision Clinical Modification codes.

RESULTS

The final population of 17,374 service members was followed from date of injury (or date of matched participant's injury) for a median of 8.4 (IQR 5.3-10.7) years. Service members with traumatic injury were at significantly greater risk of developing insomnia than uninjured service members (HR=1.43, 95% CI 1.30-1.58) after adjustment. Traumatic brain injury (TBI) was associated with insomnia when compared to patients without TBI in the multivariable model: mild/unclassified TBI (HR=2.07, 95% CI 1.82-2.35), moderate/severe/penetrating TBI (HR=2.43, 95% CI 2.06-2.86). Additionally, burn injury (HR=1.95, 95% CI 1.47-2.59) and amputation (HR=1.61, 95% CI 1.26-2.06) significantly increased the risk of a diagnosis.

CONCLUSIONS

Traumatic injuries significantly predicted a diagnosis of insomnia after controlling for mental health disorders. Our findings strongly suggest the need for long-term surveillance of sleep disorders in trauma survivors.

Suicidality After Burn Injuries: A Systematic Review

Burn survivors may be at increased risk for suicide due to the nature of their injury and psychiatric comorbidities. The purpose of this review is to assess the evidence as to the prevalence of suicidal ideations and behaviors (attempts and completed suicides) in burn survivors as well as evaluate risk and protective factors. PubMed, EMBASE, CINAHL, Cochrane, PsycINFO, and Web Science databases were searched using search terms regarding suicide, suicidality, and burn. Fourteen full-text manuscripts and two published abstracts were included in the review. Overall, burn survivors demonstrate elevated suicidal ideations and a higher lifetime prevalence of suicide attempts compared to the general population. There is mixed evidence as to rates of completed suicide postburn injury, though rates appear to be relatively low. Risk factors include pain at discharge, perceived level of disfigurement, premorbid psychiatric comorbidities, and past suicide attempts. Results of this systematic review shed light on the scarcity of data on rates of suicidality among burn survivors, which is surprising given the multiple risk factors burn survivors possess including chronic pain, sleep disturbances, history of substance abuse, posttraumatic stress disorder, social isolation, and depression which are linked to suicidality in the general population. Suicide risk screening should be included as an integral part of burn survivors' care, and more research is needed to better understand the magnitude of this phenomenon and offer targeted interventions to vulnerable individuals.

MicroRNA-19b predicts widespread pain and posttraumatic stress symptom risk in a sex-dependent manner following trauma exposure

Posttraumatic widespread pain (PTWP) and posttraumatic stress symptoms (PTSS) are frequent comorbid sequelae of trauma that occur at different rates in women and men. We sought to identify microRNA (miRNA) that may contribute to sex-dependent differences in vulnerability to these outcomes. Monte Carlo simulations (x10,000) identified miRNA in which predicted targeting of PTWP or PTSS genes was most enriched. Expression of the leading candidate miRNA to target PTWP/PTSS-related genes, miR-19b, has been shown to be influenced by estrogen and stress exposure. We evaluated whether peritraumatic miR-19b blood expression levels predicted PTWP and PTSS development in women and men experiencing trauma of motor vehicle collision (n = 179) and in women experiencing sexual assault trauma (n = 74). A sex-dependent relationship was observed between miR-19b expression levels and both PTWP (β = -2.41, P = 0.034) and PTSS (β = -3.01, P = 0.008) development 6 months after motor vehicle collision. The relationship between miR-19b and PTSS (but not PTWP) was validated in sexual assault survivors (β = -0.91, P = 0.013). Sex-dependent expression of miR-19b was also observed in blood and nervous tissue from 2 relevant animal models. Furthermore, in support of increasing evidence indicating a role for the circadian rhythm (CR) in PTWP and PTSS pathogenesis, miR-19b targets were enriched in CR gene transcripts. Human cohort and in vitro analyses assessing miR-19b regulation of key CR transcripts, CLOCK and RORA, supported the potential importance of miR-19b to regulating the CR pathway. Together, these results highlight the potential role that sex-dependent expression of miR-19b might play in PTWP and PTSS development after trauma/stress exposure.

Positive Encounters as a Buffer: Pain and Sleep Disturbances in Older Adults' Everyday Lives

Objectives: To test whether older adults' pain was bidirectionally associated with nighttime sleep disturbances and whether daily positive encounters attenuated these associations. Methods: Participants (N = 292, mean = 73.71 years old) from the Daily Experiences and Well-being Study indicated pain and positive encounters with close partners (e.g., family and friends) and nonclose partners (e.g., acquaintances and service providers) every 3 hours throughout each day across 4-6 days. They also reported nighttime sleep disturbances the following morning. Results: Multilevel models revealed that participants with more prior nighttime sleep disturbances reported more severe pain the next day. This link was attenuated on days when participants had a greater proportion of positive encounters or viewed encounters as more pleasant, especially when these encounters occurred with close partners. Discussion: This study identifies benefits of positive encounters to older adults and sheds light on ways that may alleviate their pain from a social perspective.

Increased risk for sleep disorders in burn patients: A 14-year nationwide, population-based cohort study

BACKGROUND

Burn is a major trauma that causes physical and psychosocial impairments, leading to sleep disorders. However, the data about risks for sleep disorders in patients over 3 years following burn injury are limited.

AIM

To investigate the long-term risks for sleep disorders in patients after burn injury and identify the high-risk population.

METHODS

A 14-year population-based cohort study was performed using data from the 2000-2013 Taiwan National Health Insurance Research Database (NHIRD) which was a valid representative sample of the total population. All diagnoses of medical records in NHIRD were made by physicians and coded according to the ICD-9-CM. Cases diagnosed with burns (ICD-9 CM: N-code 940-949 and E-code 890-899) were included. The control group (non-burn injury group) was comprised quadruple the number of cases matched by index date, sex and age.

RESULTS

In 2000-2013, among the 10,289 burn patients included and followed-up after the index year, burn injury significantly increased the risks for sleep disorders (Hazard Ratio; HR = 1.36, p = 0.044), including insomnia (HR = 1.41, p = 0.036), sleep disturbance (HR = 2.39, p = 0.005) and sleep apnoea (HR = 1.38, p = 0.029). Compared with the control group, those who were women (HR = 1.73, p = 0.021), adolescents (HR = 5.45, p < 0.001), aged 19-24 years (HR = 1.36, p = 0.034), aged 25-44 years (HR = 1.67, p = 0.007), had low income (HR = 2.14, p = 0.001), and without a history of mental disorders (HR = 1.41, p = 0.024) had significantly higher risks for developing sleep disorders when suffered burn injury.

CONCLUSION

Burn had long-term negative effects on sleep during both the first year of burn injury and the subsequent follow-up 14 years. It is important for physicians to long-term assess the sleep quality of burn patients regardless of the number of years after burn injury.

Sex differences in measures of central sensitization and pain sensitivity to experimental sleep disruption: implications for sex differences in chronic pain

Study Objectives

Females demonstrate heightened central sensitization (CS), a risk factor for chronic pain characterized by enhanced responsivity of central nervous system nociceptors to normal or subthreshold input. Sleep disruption increases pain sensitivity, but sex has rarely been evaluated as a moderator and few experiments have measured CS. We evaluated whether two nights of sleep disruption alter CS measures of secondary hyperalgesia and mechanical temporal summation in a sex-dependent manner. We also evaluated differences in measures of pain sensitivity.

Methods

Seventy-nine healthy adults (female n = 46) participated in a randomized crossover experiment comparing two consecutive nights of eight pseudorandomly distributed forced awakenings (FA [-200 min sleep time]) against two nights of undisturbed sleep (US). We conducted sensory testing the mornings following Night 2; the heat-capsaicin pain model was used to induce secondary hyperalgesia.

Results

FA reduced total sleep time (REM and NREM Stage 3) more profoundly in males. We observed divergent, sex-dependent effects of FA on secondary hyperalgesia and temporal summation. FA significantly increased secondary hyperalgesia in males and significantly increased temporal summation in females. Sex differences were not attributable to differential sleep loss in males. FA also significantly reduced heat-pain threshold and cold pressor pain tolerance, independently of sex.

Conclusions

Sleep disruption enhances different pain facilitatory measures of CS in males and females suggesting that sleep disturbance may increase risk for chronic pain in males and females via distinct pathways. Findings have implications for understanding sex differences in chronic pain and investigating sleep in chronic pain prevention efforts.

Cross-lagged longitudinal analysis of pain intensity and sleep disturbance

BACKGROUND

There is substantial evidence that pain intensity and sleep are related, with findings generally suggesting more support for the influence of sleep on pain intensity than vice versa. However, the strength and direction of the relationship has been found to vary among different populations, with few studies in individuals with chronic physical disabilities.

OBJECTIVE

Examine the directionality of the sleep and pain relationship in individuals with chronic physical disabilities.

METHODS

Cross-lagged effects models were generated using data from a longitudinal observational survey study of individuals (N = 1660) with multiple sclerosis (MS), muscular dystrophy (MD), post-polio syndrome (PPS), and spinal cord injury (SCI). Models evaluated the correlational effects of sleep disturbance and pain intensity, as well as the cross-lagged effects of sleep disturbance to pain intensity and vice versa.

RESULTS

The effects of pain on sleep were stronger than sleep on pain, although the magnitude of the effects were both relatively weak. Analyses within individual samples were consistent with the overall sample results for MS, MD, and PPS. In the SCI sample the magnitude and direction of the cross-lagged model paths were more variable than in the other samples.

CONCLUSIONS

The relationship between pain intensity and sleep disturbance appears bi-directional, but the effects are small in a sample of individuals with long-term disabilities. The temporal effects of pain on sleep disturbance appear stronger than the effects of sleep disturbance on pain intensity. Future research is needed to better understand this relationship in the context of pain and/or sleep disturbance treatments.

Chronic Pain and Sleep Disturbances: A Pragmatic Review of Their Relationships, Comorbidities, and Treatments

Objective

The objective of this review is to answer three questions: 1) How are chronic pain severity and pain duration affected in patients with chronic pain and sleep disturbances that occur simultaneously? 2) What are common comorbidities and pain-related symptoms seen in patients with chronic pain and sleep disturbances? and 3) What are potentially effective pharmacological and nonpharmacological treatment options for both conditions?

Methods

Ovid Medline and PubMed were searched. Search terms included sleep wake disorder, chronic pain, fibromyalgia, treatment outcome, psychotherapy, complementary therapies, and therapeutics. Studies that assessed outcomes between individuals with chronic pain and those with concurrent chronic pain and sleep disturbances were included. Randomized controlled clinical trials of treatments for both conditions were included.

Results

Sixteen studies indicated that patients with both chronic pain and sleep disturbances have greater pain severity, longer duration of pain, greater disability, and are less physically active than those without sleep disturbances. Patients with both conditions are more likely to have concurrent depression, catastrophizing, anxiety, and suicidal ideation. Thirty-three randomized controlled trials assessed treatment for both chronic pain and sleep disturbances. Pregabalin was the most frequently studied medication, showing improvement in pain and sleep symptoms. Cognitive behavioral therapy for insomnia showed long-term improvement in sleep for patients with chronic pain.

Conclusions

Individuals with chronic pain and sleep disturbances have greater symptom severity, longer duration of symptoms, more disability, and additional comorbidities. Pharmacological and nonpharmacological treatments may be useful in the treatment of concurrent chronic pain and sleep disturbances, but further study is needed.

The relationship between obstructive sleep apnoea and postoperative delirium and pain: an observational study of a surgical cohort

Patients with obstructive sleep apnoea are at increased risk of adverse postoperative outcomes, such as cardiac and respiratory complications. It has been hypothesised that obstructive sleep apnoea also increases the risk for postoperative delirium and acute postoperative pain. We conducted a retrospective, observational study investigating the relationship of obstructive sleep apnoea with postoperative delirium and acute postoperative pain severity. Patients were classified as being at high risk for obstructive sleep apnoea if they had been diagnosed with this condition, or if they were positive for more than four factors using the 'STOP-BANG' screening tool. Adjusted logistic regression was used to investigate the association between obstructive sleep apnoea and postoperative delirium, and multivariable linear regression to study the relationship between obstructive sleep apnoea and postoperative pain severity. The incidence of postoperative delirium was 307 in 1441 patients (21.3%; 95%CI 19.2-23.5%). In unadjusted analysis, high risk for obstructive sleep apnoea was associated with delirium, with an odds ratio (95%CI) of 1.77 (1.22-2.57; p = 0.003). After adjustment for pre-specified variables, the association was not statistically significant with odds ratio 1.34 (0.80-2.23; p = 0.27). The mean (SD) maximum pain (resting or provoked) reported for the entire cohort was 63.8 (27.9) mm on a 0-100 mm visual analogue scale. High risk for obstructive sleep apnoea was not associated with postoperative pain severity (β-coefficient 2.82; 95%CI, -2.34-7.97; p = 0.28). These findings suggest that obstructive sleep apnoea is unlikely to be a strong risk factor for postoperative delirium or acute postoperative pain severity.

An Open Trial of Morning Bright Light Treatment Among US Military Veterans with Chronic Low Back Pain: A Pilot Study

OBJECTIVE

To examine the feasibility, acceptability, and effects of a home-based morning bright light treatment on pain, mood, sleep, and circadian timing in US veterans with chronic low back pain.

DESIGN

An open treatment trial with a seven-day baseline, followed by 13 days of a one-hour morning bright light treatment self-administered at home. Pain, pain sensitivity, mood, sleep, and circadian timing were assessed before, during, and after treatment.

SETTING

Participants slept at home, with weekly study visits and home saliva collections.

PARTICIPANTS

Thirty-seven US veterans with medically verified chronic low back pain.

METHODS

Pain, mood, and sleep quality were assessed with questionnaires. Pain sensitivity was assessed using two laboratory tasks: a heat stimulus and an ischemia stimulus that gave measures of threshold and tolerance. Sleep was objectively assessed with wrist actigraphy. Circadian timing was assessed with the dim light melatonin onset.

RESULTS

Morning bright light treatment led to reduced pain intensity, pain behavior, thermal pain threshold sensitivity, post-traumatic stress disorder symptoms, and improved sleep quality (P < 0.05). Phase advances in circadian timing were associated with reductions in pain interference (r = 0.55, P < 0.05).

CONCLUSIONS

Morning bright light treatment is a feasible and acceptable treatment for US veterans with chronic low back pain. Those who undergo morning bright light treatment may show improvements in pain, pain sensitivity, and sleep. Advances in circadian timing may be one mechanism by which morning bright light reduces pain. Morning bright light treatment should be further explored as an innovative treatment for chronic pain conditions.

Temporal Analysis of Chronic Musculoskeletal Pain and Sleep in Postmenopausal Women

STUDY OBJECTIVES

To investigate the temporal association between chronic musculoskeletal pain (CMP) and sleep in women who are postmenopausal in a 10-day actigraphic study. This is a microlongitudinal study in which 52 participants were allocated to 4 groups women who are postmenopausal: control (CTRL, n = 10), chronic musculoskeletal pain (CMP, n = 12), insomnia (INS, n = 15) and chronic musculoskeletal pain+insomnia (CMP+INS, n = 15).

METHODS

All volunteers underwent a clinical interview and completed questionnaires, used an actigraph, and kept sleep diaries for 10 consecutive days.

RESULTS

Women in the CMP+INS group presented more sleep episodes (mean of 1.02 episodes) and longer sleep latency (8.97 minutes), as well as higher pain intensity during the day compared to the other groups. Sleep duration recorded by actigraphy directly predicted pain intensity the following morning on waking, with a 1-unit increase in pain intensity, for every 6.9 minutes more of sleep. Higher pain intensity at bedtime was a significant predictor of both increased time in bed and sleep duration, meaning that for each 1-unit increase in pain intensity at bedtime, sleep duration increased by an average of 6.7 minutes.

CONCLUSIONS

Data showed that the coexistence of insomnia and CMP results in greater pain intensity and alterations in sleep homeostasis. Collectively, the data indicate that there is a bidirectional and directly proportional relationship between sleep duration and pain intensity in women who are postmenopausal with insomnia. This result strongly suggests that both sleep and pain conditions should be targeted in the treatment of women who are postmenopausal.

Effect of sleep restriction on somatosensory sensitivity including occlusal sensation in the orofacial area

PURPOSE

To investigate the effect of sleep restriction on somatosensory sensitivity related to occlusion.

METHODS

Twelve healthy participants participated in an experimental voluntary total sleep restriction (SR) study. In a study design, they were invited to sleep as usual, normal sleep (NS) or to restrict their sleep for four nights. Following the SR night, participants were followed for 3 consecutive days including the 2 sleep nights. In NS experiment, all participants were instructed to maintain NS both nights. During all nights, actigraphy data were collected and total sleep time was estimated. On days before and after sleep conditions, all participants underwent measurements of tactile detection threshold (TDT), interocclusal detection threshold (IDT), perception of unpleasantness (POU), and the Epworth sleepiness scale (ESS).

RESULTS

As expected, total sleep time on the first night in SR experiment was significantly shorter than on the second night in SR experiment and on the first night in NS experiment (P<0.05). ESS values on Day-2 following SR experiment were significantly higher than on Day-1 and Day-3 in SR experiment and Day-2 in NS experiment (P<0.05). There were no significant differences in TDT and IDT between each day at each measurement point in both experiments. POU was significantly lower on Day-2 in SR experiment than on Day-1 and Day-3 in SR experiment and on Day-2 in NS experiment (P<0.05).

CONCLUSIONS

The present results suggest that SR affects to occlusal sensation related to POU.

The Nature of Trauma Pain and Its Association with Catastrophizing and Sleep

BACKGROUND

Nearly 2.8 million people are hospitalized in the USA annually for traumatic injuries, which include orthopedic and internal organ injuries. Early post-injury pain is predictive of poor outcomes, including inability to eventually return to work, and long-term psychological distress. The goal of the present study was to improve our scientific understanding of trauma-related pain by examining (1) the nature and frequency of inpatient trauma pain and (2) the associations between inpatient trauma pain, education, opioid analgesic equivalent use, pain catastrophizing, and sleep quality.

METHOD

The study included 120 patients hospitalized at a major level I regional trauma center for the care of (1) closed long bone or calcaneus fractures and/or (2) an intraabdominal injury caused by blunt force trauma and requiring surgical repair (i.e., laparotomy). Medical records were reviewed to obtain demographic information and information about opioid use during hospitalization. In addition, participants were administered measures of average pain intensity, pain catastrophizing, and sleep quality.

RESULTS

Education, opioid analgesic equivalents, catastrophizing, and poor sleep quality together accounted for 28% of the variance of average pain intensity over a 24-h period (p < .001), with each variable making a significant independent association.

CONCLUSION

Two of the factors associated with pain intensity in the study sample-catastrophizing and sleep quality-are modifiable. It is therefore possible that interventions that target these variables in patients who are hospitalized for trauma could potentially result in better long-term outcomes, including a reduced risk for developing chronic pain. Research to evaluate this possibility is warranted.

Sleep, Sleep Disorders, and Circadian Health following Mild Traumatic Brain Injury in Adults: Review and Research Agenda

A rapidly expanding scientific literature supports the frequent co-occurrence of sleep and circadian disturbances following mild traumatic brain injury (mTBI). Although many questions remain unanswered, the preponderance of evidence suggests that sleep and circadian disorders can result from mTBI. Among those with mTBI, sleep disturbances and clinical sleep and circadian disorders contribute to the morbidity and long-term sequelae across domains of functional outcomes and quality of life. Specifically, along with deterioration of neurocognitive performance, insufficient and disturbed sleep can precede, exacerbate, or perpetuate many of the other common sequelae of mTBI, including depression, post-traumatic stress disorder, and chronic pain. Further, sleep and mTBI share neurophysiologic and neuroanatomic mechanisms that likely bear directly on success of rehabilitation following mTBI. For these reasons, focus on disturbed sleep as a modifiable treatment target has high likelihood of improving outcomes in mTBI. Here, we review relevant literature and present a research agenda to 1) advance understanding of the reciprocal relationships between sleep and circadian factors and mTBI sequelae and 2) advance rapidly the development of sleep-related treatments in this population.

Preemptive Caffeine Administration Blocks the Increase in Postoperative Pain Caused by Previous Sleep Loss in the Rat: A Potential Role for Preoptic Adenosine A2A Receptors in Sleep-Pain Interactions

Sleep and pain are reciprocally related, but the precise mechanisms underlying this relationship are poorly understood. This study used a rat model of surgical pain to examine the effect of previous sleep loss on postoperative pain and tested the hypothesis that preoptic adenosinergic mechanisms regulate sleep-pain interactions. Relative to ad libitum sleep, 6 hours of total sleep deprivation prior to a surgical incision significantly enhanced postoperative mechanical hypersensitivity in the affected paw and prolonged the time to recovery from surgery. There were no sex-specific differences in these measures. There were also no changes in adrenocorticotropic hormone and corticosterone levels after sleep deprivation, suggesting that this effect was not mediated by the stress associated with the sleep perturbation. Systemic administration of the nonselective adenosine receptor antagonist caffeine at the onset of sleep deprivation prevented the sleep deprivation-induced increase in postoperative hypersensitivity. Microinjection of the adenosine A2A receptor antagonist ZM 241385 into the median preoptic nucleus (MnPO) blocked the increase in surgical pain levels and duration caused by prior sleep deprivation and eliminated the thermal hyperalgesia induced by sleep deprivation in a group of nonoperated (i.e., without surgical incision) rats. These data show that even a brief sleep disturbance prior to surgery worsens postoperative pain and are consistent with our hypothesis that adenosine A2A receptors in the MnPO contribute to regulate these sleep-pain interactions.

Obstructive sleep apnea as an independent predictor of postoperative delirium and pain: protocol for an observational study of a surgical cohort

Introduction: Postoperative delirium and pain are common complications in adults, and are difficult both to prevent and treat. Obstructive sleep apnea (OSA) is prevalent in surgical patients, and has been suggested to be a risk factor for postoperative delirium and pain. OSA also might impact pain perception, and alter pain medication requirements. This protocol describes an observational study, with the primary aim of testing whether OSA is an independent predictor of postoperative complications, focusing on (i) postoperative incident delirium and (ii) acute postoperative pain severity. We secondarily hypothesize that compliance with prescribed treatment for OSA (typically continuous positive airway pressure or CPAP) might decrease the risk of delirium and the severity of pain. Methods and analysis: We will include data from patients who have been enrolled into three prospective studies: ENGAGES, PODCAST, and SATISFY-SOS. All participants underwent general anesthesia for a non-neurosurgical inpatient operation, and had a postoperative hospital stay of at least one day at Barnes Jewish Hospital in St. Louis, Missouri, from February 2013 to May 2018.  Patients included in this study have been assessed for postoperative delirium and pain severity as part of the parent studies. In the current study, determination of delirium diagnosis will be based on the Confusion Assessment Method, and the Visual Analogue Pain Scale will be used for pain severity. Data on OSA diagnosis, OSA risk and compliance with treatment will be obtained from the preoperative assessment record. Other variables that are candidate risk factors for delirium and pain will also be extracted from this record. We will use logistic regression to test whether OSA independently predicts postoperative delirium and linear regression to assess OSAs relationship to acute pain severity. We will conduct secondary analyses with subgroups to explore whether these relationships are modified by compliance with OSA treatment.

The National Institute on Disability, Independent Living, and Rehabilitation Research Burn Model System: Twenty Years of Contributions to Clinical Service and Research

The National Institute on Disability, Independent Living, and Rehabilitation Research (NIDILRR) established the Burn Model System (BMS) in 1993 to improve the lives of burn survivors. The BMS program includes 1) a multicenter longitudinal database describing the functional and psychosocial recovery of burn survivors; 2) site-specific burn-related research; and 3) a knowledge dissemination component directed toward patients and providers. Output from each BMS component was analyzed. Database structure, content, and access procedures are described. Publications using the database were identified and categorized to illustrate the content area of the work. Unused areas of the database were identified for future study. Publications related to site-specific projects were cataloged. The most frequently cited articles are summarized to illustrate the scope of these projects. The effectiveness of dissemination activities was measured by quantifying website hits and information downloads. There were 25 NIDILRR-supported publications that utilized the database. These articles covered topics related to psychological outcomes, functional outcomes, community reintegration, and burn demographics. There were 172 site-specific publications; highly cited articles demonstrate a wide scope of study. For information dissemination, visits to the BMS website quadrupled between 2013 and 2014, with 124,063 downloads of educational material in 2014. The NIDILRR BMS program has played a major role in defining the course of burn recovery, and making that information accessible to the general public. The accumulating information in the database serves as a rich resource to the burn community for future study. The BMS is a model for collaborative research that is multidisciplinary and outcome focused.

National Institute on Disability, Independent Living, and Rehabilitation Research Burn Model System: Review of Program and Database

The Burn Model System (BMS) centers program was created in 1994 to evaluate the long-term outcomes of burn injuries. As part of this multicenter program, a comprehensive longitudinal database was developed to facilitate the study of a number of functional and psychosocial outcomes after burn injury. In this article, we provide an overview of the data collection procedures, measures selection process, and an overview of the participant data collected between 1994 and 2016. Surveys were administered during hospitalization and at 6, 12, and 24 months after discharge, and in the most recent funding cycle, data collection at every 5 years postinjury was added. More than 7200 people with burn injury were eligible to participate in the BMS National Longitudinal Database. Of these, >5900 (82%) were alive at discharge and consented to follow-up data collection. The BMS National Longitudinal Database represents a large sample of people with burn injury, including information on demographic characteristics, injury characteristics, and health outcomes. The database is publicly available and can be used to examine the effect of burn injury on long-term outcomes.

Decreased alertness due to sleep loss increases pain sensitivity in mice

Extended daytime and nighttime activities are major contributors to the growing sleep deficiency epidemic, as is the high prevalence of sleep disorders like insomnia. The consequences of chronic insufficient sleep for health remain uncertain. Sleep quality and duration predict presence of pain the next day in healthy subjects, suggesting that sleep disturbances alone may worsen pain, and experimental sleep deprivation in humans supports this claim. We demonstrate that sleep loss, but not sleep fragmentation, in healthy mice increases sensitivity to noxious stimuli (referred to as 'pain') without general sensory hyper-responsiveness. Moderate daily repeated sleep loss leads to a progressive accumulation of sleep debt and also to exaggerated pain responses, both of which are rescued after restoration of normal sleep. Caffeine and modafinil, two wake-promoting agents that have no analgesic activity in rested mice, immediately normalize pain sensitivity in sleep-deprived animals, without affecting sleep debt. The reversibility of mild sleep-loss-induced pain by wake-promoting agents reveals an unsuspected role for alertness in setting pain sensitivity. Clinically, insufficient or poor-quality sleep may worsen pain and this enhanced pain may be reduced not by analgesics, whose effectiveness is reduced, but by increasing alertness or providing better sleep.

Sleep Fragmentation Hypersensitizes Healthy Young Women to Deep and Superficial Experimental Pain

The effect of sleep deprivation on pain sensitivity has typically been studied using total and partial sleep deprivation protocols. These protocols do not mimic the fragmented pattern of sleep disruption usually observed in individuals with clinical pain conditions. Therefore, we conducted a controlled experiment to investigate the effect of sleep fragmentation on pain perception (deep pain: forearm muscle ischemia, and superficial pain: graded pin pricks applied to the skin) in 11 healthy young women after 2 consecutive nights of sleep fragmentation, compared with a normal night of sleep. Compared with normal sleep, sleep fragmentation resulted in significantly poorer sleep quality, morning vigilance, and global mood. Pin prick threshold decreased significantly (increased sensitivity), as did habituation to ischemic muscle pain (increased sensitivity), over the course of the 2 nights of sleep fragmentation compared with the night of normal sleep. Sleep fragmentation did not increase the maximum pain intensity reported during muscle ischemia (no increase in gain), and nor did it increase the number of spontaneous pains reported by participants. Our data show that sleep fragmentation in healthy, young, pain-free women increases pain sensitivity in superficial and deep tissues, indicating a role for sleep disruption, through sleep fragmentation, in modulating pain perception.

PERSPECTIVE

Our findings that pain-free, young women develop hyperalgesia to superficial and deep muscle pain after short-term sleep disruption highlight the need for effective sleep management strategies in patients with pain. Findings also suggest the possibility that short-term sleep disruption associated with recurrent acute pain could contribute to increased risk for future chronic pain conditions.

Pain Severity in Relation to the Final Menstrual Period in a Prospective Multiethnic Observational Cohort: Results From the Study of Women's Health Across the Nation

The development of pain is common in midlife, resulting in increased health care utilization and costs. The aim of this study was to determine the longitudinal trajectory of overall bodily pain among women during the transition between the reproductive years and menopause. We conducted analyses on a community-based, longitudinal cohort of women enrolled in the Study of Women's Health Across the Nation. One thousand four hundred ninety-five women met inclusion criteria, including: 1) defined date of the final menstrual period (FMP), and 2) complete data on Short Form-36 bodily pain. The primary exposure was time to/from the FMP. The primary outcome was the rate of change in Short Form-36 bodily pain, measured on a scale of 0 to 100 with 100 being the most severe pain. We performed within-person trajectory analyses using piecewise regression following nonparametric modeling of functional forms. Mean bodily pain score at the time of the FMP was 29. Mean bodily pain increased at a rate of .26 per year during the transmenopause (the interval spanning 4.5 years before the FMP through .5 years after the FMP), and decreased at a rate of .23 per year after that. Depression and sleep problems were associated with greater increases in pain during the late reproductive years, whereas abdominal cramps at baseline predicted greater decreases in pain during the late reproductive years.

PERSPECTIVE

This article shows that bodily pain increases during the transmenopause and then diminishes during postmenopause. These differences may reflect differences in underlying mechanisms of pain in the 2 periods. Although mean changes were small and unlikely to be clinically meaningful, the magnitude of change varied across subgroups of women.

Opioid Analgesics and Depressive Symptoms in Burn Patients: What Is the Real Relationship?

Objective

Major burn injuries are strongly associated with both psychological trauma and severe pain, and opioids are the mainstay analgesics for the treatment of severe burn pain. The objectives of this study are to find the complex relationship between opioid dose, depression, and post-traumatic stress disorder (PTSD) symptoms during the acute management of pain in burn patients.

Methods

The symptoms of depression and PTSD were assessed in 43 burn patients immediately following wound stabilization and 2 weeks after the initial evaluation.

Results

Total opioid doses and Hamilton Depression Scale (HAMD) scores obtained during the second evaluation were positively but weakly correlated after controlling for age and total burn surface area (R=0.33, p=0.03). Moreover, pain management with opioids was significantly more common in burn patients with low Clinician Administered PTSD Scale scores (evaluation 1) and high HAMD scores (evaluation 2) (F=6.66, p=0.001).

Conclusion

High opioid dose following acute burn trauma might have correlation with depressive symptoms. Monitoring of depressive symptoms may be important following acute burn trauma and consequent opioids pain management, particularly when PTSD symptoms appear minimal during the early stabilization of patients.

Health-related quality of life (EQ-5D) early after injury predicts long-term pain after burn

BACKGROUND

Chronic pain after burn can have severe physical and psychological effects on former patients years after the initial injury. Although the issue of pain after burn has gained increased attention over the past years, prospective, longitudinal studies are scarce. Our aim was to prospectively investigate consecutive burn patients for pain severity over time and to evaluate the prevalence and characteristics of post-burn pain to 2-7 years after the burn. As an additional aim, the effects of burn and individual-related factors, especially health-related Quality of Life (HRQoL), were investigated.

METHOD

Sixty-seven consecutive burn patients were assessed during acute care at 3, 6, 12 and 24 months, as well as at 2-7 years post-burn. HRQoL, symptoms of post-traumatic stress disorder (PTSD) and other psychiatric disorders were investigated. During the interviews that took place 2-7 years after the injury (mean 4.6±1.9 years), current chronic post-burn pain was assessed using the Brief Pain Inventory-Short Form (BPI-SF).

RESULTS

One-third of the patients still reported pain 2-7 years after the injury. Pain severity and interference with daily life were mainly mild to moderate though they were found to be associated with significantly lower HRQoL. Chronic pain after burn was associated with both burn- and individual-related factors. In logistic regression analysis HRQoL at 3 and 12 months and symptoms of PTSD at 12 months were independent factors in predicting chronic pain after burn.

CONCLUSION

Pain after burn becomes a chronic burden for many former burn patients and decreases HRQoL. A novel finding in this study was that HRQoL assessed early after burn was a predictor for the development of chronic pain. This finding may help to predict future pain problems and serve as an indicator for pain preventive measures.

Progress of clinical practice on the management of burn-associated pain: Lessons from animal models

Opioid-based analgesics provide the mainstay for attenuating burn pain, but they have a myriad of side effects including respiratory depression, nausea, impaired gastrointestinal motility, sedation, dependence, physiologic tolerance, and opioid-induced hyperalgesia. To test and develop novel analgesics, validated burn-relevant animal models of pain are indispensable. Herein we review such animal models, which are mostly limited to rodent models of burn-induced, inflammatory, and neuropathic pain. The latter two are pain syndromes that provide insight into the pain caused by systemic pro-inflammatory cytokines and direct injury to nerves (e.g., after severe burn), respectively. To date, no single animal model optimally mimics the complex pathophysiology and pain that a human burn patient experiences. No currently available burn-pain model examines effects of pharmacological intervention on wound healing. As cornerstones of pain and wound healing, pro-inflammatory mediators may be utilized for insight into both processes. Moreover, common clinical concerns such as systemic inflammatory response syndrome and multiple organ dysfunction remain unaddressed. For development of analgesics, these aberrations can significantly alter the potential efficacy and/or adverse effects of a prescribed analgesic following burn trauma. We therefore suggest that a multi-model strategy would be the most clinically relevant when evaluating novel analgesics for use in burn patients.

Obstructive sleep apnea, pain, and opioids: is the riddle solved?

PURPOSE OF REVIEW

Perioperative opioid-based pain management of patients suffering from obstructive sleep apnea (OSA) may present challenges because of concerns over severe ventilatory compromise. The interaction between intermittent hypoxia, sleep fragmentation, pain, and opioid responses in OSA, is complex and warrants a special focus of perioperative outcomes research.

RECENT FINDINGS

Life-threatening opioid-related respiratory events are rare. Epidemiologic evidence suggests that OSA together with other serious renal and heart disease, is among those conditions predisposing patients for opioid-induced ventilatory impairment (OIVI) in the postoperative period. Both intermittent hypoxia and sleep fragmentation, two distinct components of OSA, enhance pain. Intermittent hypoxia may also potentiate opioid analgesic effects. Activation of major inflammatory pathways may be responsible for the effects of sleep disruption and intermittent hypoxia on pain and opioid analgesia. Recent experimental evidence supports that these, seemingly contrasting, phenotypes of pain-increasing and opioid-enhancing effects of intermittent hypoxia, are not mutually exclusive. Although the effect of intermittent hypoxia on OIVI has not been elucidated, opioids worsen postoperative sleep-disordered breathing in OSA patients. A subset of these patients, characterized by decreased chemoreflex responsiveness and high arousal thresholds, might be at higher risk for OIVI.

SUMMARY

OSA may complicate opioid-based perioperative management of pain by altering both pain processing and sensitivity to opioid effect.

Sleep Deprivation and Recovery Sleep Prior to a Noxious Inflammatory Insult Influence Characteristics and Duration of Pain

STUDY OBJECTIVES

Insufficient sleep and chronic pain are public health epidemics. Sleep loss worsens pain and predicts the development of chronic pain. Whether previous, acute sleep loss and recovery sleep determine pain levels and duration remains poorly understood. This study tested whether acute sleep deprivation and recovery sleep prior to formalin injection alter post-injection pain levels and duration.

METHODS

Male Sprague-Dawley rats (n = 48) underwent sleep deprivation or ad libitum sleep for 9 hours. Thereafter, rats received a subcutaneous injection of formalin or saline into a hind paw. In the recovery sleep group, rats were allowed 24 h between sleep deprivation and the injection of formalin. Mechanical and thermal nociception were assessed using the von Frey test and Hargreaves' method. Nociceptive measures were performed at 1, 3, 7, 10, 14, 17 and 21 days post-injection.

RESULTS

Formalin caused bilateral mechanical hypersensitivity (allodynia) that persisted for up to 21 days post-injection. Sleep deprivation significantly enhanced bilateral allodynia. There was a synergistic interaction when sleep deprivation preceded a formalin injection. Rats allowed a recovery sleep period prior to formalin injection developed allodynia only in the injected limb, with higher mechanical thresholds (less allodynia) and a shorter recovery period. There were no persistent changes in thermal nociception.

CONCLUSION

The data suggest that acute sleep loss preceding an inflammatory insult enhances pain and can contribute to chronic pain. The results encourage studies in a model of surgical pain to test whether enhancing sleep reduces pain levels and duration.

Sleep, Pain Catastrophizing, and Central Sensitization in Knee Osteoarthritis Patients With and Without Insomnia

OBJECTIVE

Osteoarthritis (OA), a chronic degenerative joint disorder, is characterized by joint pain. Emerging research demonstrates that a significant number of patients evidence central sensitization (CS), a hyperexcitability in nociceptive pathways, which is known to amplify and maintain clinical pain. The clinical correlates of CS in OA, however, are poorly understood. Insomnia is prevalent in older adults with OA, and recent experiments suggest associations between poor sleep and measures of CS. Catastrophizing, a potent predictor of pain outcomes, has also been associated with CS, but few studies have investigated possible interactions between catastrophizing, sleep, and CS.

METHODS

We conducted a case-control study of 4 well-characterized groups of adults with insomnia and/or knee OA. A total of 208 participants completed multimodal sleep assessments (questionnaire, diary, actigraphy, and polysomnography) and extensive evaluation of pain using clinical measures and quantitative sensory testing to evaluate associations between CS, catastrophizing, and insomnia. Descriptive characterization of each measure is presented, with specific focus on sleep efficiency and CS.

RESULTS

The knee OA-insomnia group demonstrated the greatest degree of CS compared to controls. In the overall sample, we found that catastrophizing moderated the relationship between sleep efficiency and CS. Specifically those with low sleep efficiency and high catastrophizing scores reported increased levels of CS. In addition, CS was significantly associated with increased clinical pain.

CONCLUSION

These findings highlight the importance of assessing sleep efficiency, CS, and catastrophizing in chronic pain patients and have important clinical implications for treatment planning.

Exploring the associations between sleep problems and chronic musculoskeletal pain in adolescents: a prospective cohort study

Sleep problems and chronic pain are intimately connected, with pain causing poor sleep, which, in turn, leads to increased pain intensity. This may be particularly relevant among adolescents, in whom sleep patterns are more likely to be disrupted. In this study, the relationship between sleep problems at 15 years of age, and chronic regional pain as well as chronic widespread pain at 17 years of age was explored.

BACKGROUND:

The prevalence of musculoskeletal chronic pain in adolescents is estimated to be approximately 4% to 40%. The development of musculoskeletal pain during teenage years could have a marked impact on physical, psychological and social well-being.

OBJECTIVE:

To examine whether sleep problems during adolescence are associated with musculoskeletal pain, particularly chronic regional pain and chronic widespread pain.

METHODS:

Using data from the Avon Longitudinal Study of Children, the relationship between sleep problems at 15 years of age and the presence of chronic regional and widespread pain at 17 years of age was explored. Pain data were not available at 15 years of age. A total of 2493 participants with complete data were identified. Relationships among sleep problems and musculoskeletal pain were examined using logistic regression. ORs were calculated after adjusting for sex, ethnicity, socioeconomic position and depression (15 years of age).

RESULTS:

Sleep disturbance (usually wakes up more than two or three times), difficulties with hypersomnolence and poor subjective sleep perception were associated with the presence of both musculoskeletal regional and widespread pain. Finally, using ordered logistic regression, poor subjective sleep perception was also found to be associated with greater pain severity in participants with chronic musculoskeletal regional and widespread pain.

DISCUSSION:

The results of the present study suggest an association between sleep problems during adolescence and the presence of musculoskeletal pain at a later stage. These findings are consistent with adult literature suggesting a link between sleep problems and musculoskeletal pain. Given these associations, sleep problems in adolescence may be an important risk factor for musculoskeletal pain.