Influence of Morphine and Naloxone on Pain Modulation in Rheumatoid Arthritis, Chronic Fatigue Syndrome/Fibromyalgia, and Controls: A Double-Blind, Randomized, Placebo-Controlled, Cross-Over Study.

BACKGROUND: Impaired pain inhibitory and enhanced pain facilitatory mechanisms are repeatedly reported in patients with central sensitization pain. However, the exact effects of frequently prescribed opioids on central pain modulation are still unknown. METHODS: A randomized, double-blind, placebo-controlled cross-over trial was carried out. Ten chronic fatigue syndrome (CFS)/fibromyalgia (FM) patients, 11 rheumatoid arthritis (RA) patients and 20 controls were randomly allocated to the experimental (10 mg morphine or 0.2 mg/mL Naloxone) and placebo (2 mL Aqua) group. Pressure pain thresholds (PPTs) and temporal summation at the Trapezius and Quadriceps were assessed by algometry. Conditioned pain modulation (CPM) efficacy and deep tissue pain pressure were assessed by adding ischemic occlusion at the opposite upper arm. RESULTS: Deep tissue pain pressure was lower and temporal summation higher in CFS/FM (P = 0.002 respectively P = 0.010) and RA patients (P = 0.011 respectively P = 0.047) compared to controls at baseline. Morphine had only a positive effect on PPTs in both patient groups (P time = 0.034). Accordingly, PPTs increased after placebo (P time = 0.015), and no effects on the other pain parameters were objectified. There were no significant effects of naloxone nor nocebo on PPT, deep tissue pain, temporal summation or CPM in the control group. CONCLUSIONS: This study revealed anti-hyperalgesia effects of morphine in CFS/FM and RA patients. Nevertheless, these effects were comparable to placebo. Besides, neither morphine nor naloxone influenced deep tissue pain, temporal summation or CPM. Therefore, these results suggest that the opioid system is not dominant in (enhanced) bottom-up sensitization (temporal summation) or (impaired) endogenous pain inhibition (CPM) in patients with CFS/FM or RA.

Differential effects of childhood trauma subtypes on fatigue and physical functioning in chronic fatigue syndrome.

OBJECTIVE: There is wide consensus that childhood trauma plays an important role in the aetiology of chronic fatigue syndrome (CFS). The current study examines the differential effects of childhood trauma subtypes on fatigue and physical functioning in individuals suffering from CFS. METHODS: Participants were 155 well-documented adult, predominantly female CFS patients receiving treatment at the outpatient treatment centre for CFS of the Antwerp University Hospital in Belgium. Stepwise regression analyses were conducted with outcomes of the total score of the Checklist Individual Strength (CIS) measuring fatigue and the scores on the physical functioning subscale of the Medical Outcomes Short Form 36 Health Status Survey (SF-36) as the dependent variables, and the scores on the five subscales of the Traumatic Experiences Checklist (TEC) as the independent variables. RESULTS: The patients' fatigue (ß=1.38; p=0.025) and physical functioning scores (ß=-1.79; p=0.034) were significantly predicted by childhood sexual harassment. There were no significant effects of emotional neglect, emotional abuse, bodily threat, or sexual abuse during childhood. CONCLUSION: Of the childhood trauma subtypes investigated, sexual harassment emerged as the most important predictor of fatigue and poor physical functioning in the CFS patients assessed. These findings have to be taken into account in further clinical research and in the assessment and treatment of individuals coping with chronic fatigue syndrome.

Chronic Fatigue Syndrome and DNA Hypomethylation of the Glucocorticoid Receptor Gene Promoter 1F Region: Associations With HPA Axis Hypofunction and Childhood Trauma.

OBJECTIVES: Chronic fatigue syndrome (CFS) has been associated with hypothalamic-pituitary-adrenal axis hypofunction and enhanced glucocorticoid receptor (GR) sensitivity. In addition, childhood trauma is considered a major risk factor for the syndrome. This study examines DNA methylation of the GR gene (NR3C1) in CFS and associations with childhood sexual and physical trauma. METHODS: Quantification of DNA methylation within the 1F promoter region of NR3C1 was performed in 76 female patients (46 with no/mild and 30 with moderate/severe childhood trauma) and 19 healthy controls by using Sequenom EpiTYPER. Further, we examined the association of NR3C1-1F promoter methylation with the outcomes of the low-dose (0.5 mg) dexamethasone/corticotropin-releasing factor test in a subset of the study population. Mann-Whitney U tests and Spearman correlations were used for statistical analyses. RESULTS: Overall NR3C1-1F DNA methylation was lower in patients with CFS than in controls. After cytosine guanine dinucleotide (CpG)-specific analysis, CpG_1.5 remained significant after Bonferroni correction (adjusted p = .0014). Within the CFS group, overall methylation (ρ = 0.477, p = .016) and selective CpG units (CpG_1.5: ρ = 0.538, p = .007; CpG_12.13: ρ = 0.448, p = .025) were positively correlated with salivary cortisol after dexamethasone administration. There was no significant difference in NR3C1-1F methylation between traumatized and nontraumatized patients. CONCLUSIONS: We found evidence of NR3C1 promoter hypomethylation in female patients with CFS and the functional relevance of these differences was consistent with the hypothalamic-pituitary-adrenalaxis hypofunction hypothesis (GR hypersuppression). However, we found no evidence of an additional effect of childhood trauma on CFS via alterations in NR3C1 methylation.

Antidepressants and the risk of hyponatremia: a class-by-class review of literature.

BACKGROUND: Antidepressant-induced hyponatremia can cause significant morbidity and mortality. It is mostly associated with the use of selective serotonin reuptake inhibitors (SSRIs), but its frequency and class specificity are uncertain. OBJECTIVES: To determine the relationship between hyponatremia and antidepressants and to define the incidence and odds ratios for antidepressant classes. METHODS: A review of the literature prior to March 2013 was performed using Web of Science and PubMed by employing combinations of search strings "antidepressants" and antidepressant class and generic drug names with "hyponatr(a)emia," "SIADH," or "inappropriate ADH." RESULTS: Overall, 21 effect studies and more than 100 case reports were considered, most concerning SSRIs. Because of variations in study designs, populations, and cutoff values, incidence rates diverged between 0.06% and 40% for SSRIs and 0.08% and 70% for venlafaxine. Although based on less solid evidence, incidence figures for mirtazapine and tricyclic antidepressants were lower. Regarding classes, odds ratios for SSRIs (1.5-21.6) were consistently higher than for tricyclic antidepressants (TCAs) (1.1-4.9). The risks associated with monoamine oxidase inhibitors, reboxetine, and bupropion could not be established owing to insufficient information. Patient risk factors included older age (odds ratios = 6.3) and concomitant use of (thiazide) diuretics (odds ratios = 11.2-13.5). CONCLUSION: Hyponatremia is a potentially dangerous side effect of antidepressants and is not exclusive to SSRIs. Current evidence suggests a relatively higher risk of hyponatremia with SSRIs and venlafaxine, especially when combined with patient risk factors, warranting clinicians to be aware of this complication. The risks associated with mirtazapine are moderate, supporting this antidepressant as an alternative treatment for patients with (an increased risk of) hyponatremia.

Combined ultrasound of m. quadriceps and diaphragm to determine the occurrence of sarcopenia and prolonged ventilation in a COVID-19 ICU cohort: The COVID-SARCUS trial.

OBJECTIVE: The aim of this study was to determine the development of sarcopenia in a COVID-19 intensive care unit population by sequential quadriceps and diaphragm ultrasound and its relationship with hospital outcomes. METHODS: We assessed muscle thickness, cross-sectional area, fascicle length, pennation angle, and echo intensity within 48 h after intubation, at days 5 and 10 and at discharge from the intensive care unit in 30 critically ill patients with confirmed COVID-19. RESULTS: A different evolution of muscle thickness of the diaphragm and m. rectus femoris was observed; the changes between the two muscles were not correlated (Pearson's χ2 3.91, P = 0.419). The difference in muscle thickness was linked to the outcome for both m. rectus femoris and diaphragm, with the best survival seen in the group with stable muscle thickness. The greatest loss of muscle thickness occurred between days 5 and 10. The echo intensity was higher in the patients with increased muscle thickness, who also had a worse prognosis. There was a correlation between cross-sectional area on day 5 and handgrip strength (r = 0.290, P = 0.010). Only 31% of patients were able to return to their preadmission residence without any additional rehabilitation. CONCLUSIONS: Muscle atrophy and decline in muscle strength appear in the earliest stages after admission to the intensive care unit and are related to functional outcome.

Comprehensive geriatric assessment as an essential tool to register or update DNR codes in a tertiary care hospital.

PURPOSE: To investigate the prevalence of Do not Resuscitate (DNR) code registration in patients with a geriatric profile admitted to Antwerp University Hospital, a tertiary care hospital in Flanders, Belgium, and the impact of comprehensive geriatric assessment (CGA) on DNR code registration. PATIENTS AND METHODS: Retrospective analysis of a population of 543 geriatric patients (mean age 82.4 ± 5.19 years, 46.4% males) admitted to Antwerp University Hospital from 2018 to 2020 who underwent a CGA during admission. An association between DNR code registration status before and at hospital admission and age, gender, ethnicity, type of residence, clinical frailty score (CFS), cognitive and oncological status, hospital ward and stay on intensive care was studied. Admissions before and during the first wave of the pandemic were compared. RESULTS: At the time of hospital admission, a DNR code had been registered for 66.3% (360/543) of patients. Patients with a DNR code at hospital admission were older (82.7 ± 5.5 vs. 81.7 ± 4.6 years, p = 0.031), more frail (CFS 5.11 ± 1.63 vs. 4.70 ± 1.61, p = 0.006) and less likely to be admitted to intensive care. During the hospital stay, the proportion of patients with a DNR code increased to 77% before and to 85.3% after CGA (p < 0.0001). Patients were consulted about and agreed with the registered DNR code in 55.8% and 52.1% of cases, respectively. The proportion of patients with DNR codes at the time of admission or registered after CGA did not differ significantly before and after the start of the COVID-19 pandemic. CONCLUSION: After CGA, a significant increase in DNR registration was observed in hospitalized patients with a geriatric profile.

Influence of symptom expectancies on stair-climbing performance in chronic fatigue syndrome: effect of study context.

BACKGROUND: In patients with chronic fatigue syndrome (CFS), performance of physical activities may be affected by an anticipated increase in symptoms after these activities. Nijs et al. previously studied the influence of symptom expectancies and related psychological processes on the performance of an isolated physical activity [Nijs J, Meeus M, Heins M, Knoop H, Moorkens G, Bleijenberg G. Kinesiophobia, catastrophizing and anticipated symptoms before stair climbing in chronic fatigue syndrome: an experimental study. Disabil Rehabil 2012. doi: 10.3109/09638288.2011.641661 .]. PURPOSE: We aimed to validate the previous findings in a larger group of patients in a different setting. We also extended the possible underlying psychological processes studied. METHOD: In 49 CFS patients, we measured performance (duration and increase in heart rate) during self-paced climbing and descending of two floors of stairs. Before this task, patients rated experienced fatigue and anticipated fatigue after stair climbing. In addition, kinesiophobia, catastrophising and focusing on bodily symptoms were measured. Using correlational and regression analyses, we tested whether performance during stair climbing could be explained by experienced and anticipated fatigue and psychological factors. RESULTS: Longer duration of stair climbing correlated with higher anticipated fatigue, independently of sex, age, body mass index and fatigue before stair climbing. Focusing on bodily symptoms and fatigue-related catastrophising were related to anticipated fatigue. CONCLUSION: Symptom expectations affect the performance of physical activity in CFS patients, possibly through focusing on bodily symptoms and catastrophising. These findings partially contradict the findings of the previous study, which stresses the importance of study context in conducting this type of experiments (i.e., patient characteristics, instructions).

In the mind or in the brain? Scientific evidence for central sensitisation in chronic fatigue syndrome.

BACKGROUND: Central sensitisation entails several top-down and bottom-up mechanisms, all contributing to the hyperresponsiveness of the central nervous system to a variety of inputs. In the late nineties, it was first hypothesised that chronic fatigue syndrome (CFS) is characterised by hypersensitivity of the central nervous system (i.e. central sensitisation). Since then, several studies have examined central sensitisation in patients with CFS. This study provides an overview of such studies. MATERIALS AND METHODS: Narrative review. RESULTS: Various studies showed generalised hyperalgesia in CFS for a variety of sensory stimuli, including electrical stimulation, mechanical pressure, heat and histamine. Various tissues are affected by generalised hyperalgesia: the skin, muscle tissue and the lungs. Generalised hyperalgesia in CFS is augmented, rather than decreased, following various types of stressors like exercise and noxious heat pain. Endogenous inhibition is not activated in response to exercise and activation of diffuse noxious inhibitory controls following noxious heat application to the skin is delayed. CONCLUSIONS: The observation of central sensitisation in CFS is in line with our current understanding of CFS. The presence of central sensitisation in CFS corroborates with the presence of several psychological influences on the illness, the presence of infectious agents and immune dysfunctions and the dysfunctional hypothalamus-pituitary-adrenal axis as seen in these severely debilitated patients.

Bedside medication review with cognitive and depression screening by a clinical pharmacist as part of a comprehensive geriatric assessment in hospitalized older patients with polypharmacy: A pilot study.

BACKGROUND: Polypharmacy is highly prevalent in older patients with multimorbidity and is associated with increased risk of adverse drug events. This pilot study investigated the added value of a bedside medication review with cognitive and depression screening by a clinical pharmacist to identify potentially inappropriate medications (PIMs) and medication use issues in older patients with polypharmacy. METHODS AND RESULTS: In the period from September 2018 to March 2019, a clinical pharmacist took part in the comprehensive geriatric assessment of 37 older patients hospitalized at Antwerp University Hospital and conducted a medication review consisting of a record review, a bedside interview questionnaire covering medication use, evaluation of cognitive function (abbreviated MMSE), depression (GDS-4), and systematic check for possible PIMs (STOPP/START criteria). Patients were 83±4 years old and on a median of 12 home medications (range 5-20). The clinical pharmacist formulated an average of 7.7 recommendations to optimize medication use per patient, of which 89.9% were considered clinically relevant by the geriatrician. Only 2 out of 286 PIMs were discovered during routine electronic validation of medication prescriptions. Supervision of medication intake was absent in 75% of cognitively impaired patients, but advice to do so was implemented in 86.4% of cases. The multidisciplinary geriatric advice was communicated to the treating physician, who fully implemented 33.8% of the recommendations. CONCLUSIONS: Bedside medication review with cognitive and depression screening by a clinical pharmacist is useful to discover polypharmacy related problems and medication intake issues in a population of geriatric patients. Systematic screening for cognitive impairment and depression are needed to detect patients in need of support for correct medication use and therapy compliance.

Psychomotor function and response inhibition in chronic fatigue syndrome.

Most research points to cognitive slowing in chronic fatigue syndrome (CFS), although there have been negative reports. The present study is one of few that examines fine motor processing and the inhibition of automatic responses in a well-characterised CFS population. A total of 35 female CFS patients without current major depression and 25 female controls performed two computerised figure-copying tasks. The cognitive and fine motor processing of visual-spatial information was measured by recording reaction time (RT) and movement time (MT), respectively. The inhibition of automatic responses was assessed by introducing 'conflicting patterns' (i.e., patterns that were difficult to draw from the preferred left to right). A multivariate general linear model was adopted for the statistical analysis of the movement recordings. As a result, CFS was significantly associated with longer RT and MT in the pooled and in the task-specific analyses. However, there was no interaction between disease status and conflicting character of the patterns. In conclusion, these performance data on the figure-copying tasks provide confirmatory evidence for psychomotor slowing in CFS, but not for a disturbed inhibition of automatic responses. Computerised figure-copying tasks may be promising tools for use in neurobiological research and clinical trials in CFS.

Reduced Parasympathetic Reactivation during Recovery from Exercise in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome.

Although autonomic nervous system (ANS) dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) has been proposed, conflicting evidence makes it difficult to draw firm conclusions regarding ANS activity at rest in ME/CFS patients. Although severe exercise intolerance is one of the core features of ME/CFS, little attempts have been made to study ANS responses to physical exercise. Therefore, impairments in ANS activation at rest and following exercise were examined using a case-control study in 20 ME/CFS patients and 20 healthy people. Different autonomous variables, including cardiac, respiratory, and electrodermal responses were assessed at rest and following an acute exercise bout. At rest, parameters in the time-domain represented normal autonomic function in ME/CFS, while frequency-domain parameters indicated the possible presence of diminished (para)sympathetic activation. Reduced parasympathetic reactivation during recovery from exercise was observed in ME/CFS. This is the first study showing reduced parasympathetic reactivation during recovery from physical exercise in ME/CFS. Delayed HR recovery and/or a reduced HRV as seen in ME/CFS have been associated with poor disease prognosis, high risk for adverse cardiac events, and morbidity in other pathologies, implying that future studies should examine whether this is also the case in ME/CFS and how to safely improve HR recovery in this population.

The Relationship Between Childhood Trauma and the Response to Group Cognitive-Behavioural Therapy for Chronic Fatigue Syndrome.

OBJECTIVE: To examine the relationship between childhood trauma and the response to group cognitive-behavioural therapy (GCBT) for chronic fatigue syndrome (CFS). METHODS: A single cohort study conducted in an outpatient university referral center for CFS including a well-documented sample of adult patients meeting the CDC criteria for CFS and having received 9 to 12 months of GCBT. A mixed effect model was adopted to examine the impact of childhood trauma on the treatment response in general and over time. The main outcome measures were changes in fatigue, as assessed with the Checklist Individual Strength (total score), and physical functioning, as gauged with the Short Form 36 Health Survey subscale, with the scales being completed at baseline, immediately after treatment completion and after 1 year. RESULTS: We included 105 patients with CFS. Childhood trauma was not significantly associated with the response to GCBT over time on level of fatigue or physical functioning. CONCLUSION: Childhood trauma does not seem to have an effect on the treatment response to dedicated GCBT for CFS sufferers over time. Therefore, in the allocation of patients to this kind of treatment, a history of childhood trauma should not be seen as prohibitive.

Use of the Temperament and Character Inventory (TCI) for assessment of personality in chronic fatigue syndrome.

BACKGROUND: Chronic fatigue syndrome (CFS) is characterized by severe and prolonged fatigue, along with a set of nonspecific symptoms and signs, such as sore throat, muscle pain, headaches, and difficulties with concentration or memory. OBJECTIVE: The study examined whether CFS is associated with specific dimensions of Cloninger's psychobiological model of personality. METHOD: Personality profiles were compared between 38 CFS patients and 42 control subjects by means of the Temperament and Character Inventory (TCI). RESULTS: The CFS group showed significantly higher scores on Harm-Avoidance and Persistence. CONCLUSION: The current study shows a significant association between specific personality characteristics and CFS. These personality traits may be implicated in the onset and/or perpetuation of CFS and may be a productive focus for psychotherapy.

Chronic fatigue syndrome and DSM-IV personality disorders.

OBJECTIVE: Personality is an important factor in the research of the chronic fatigue syndrome (CFS). Although some studies report a high rate of personality disorders--around the 40% level--in samples of patients with CFS, the generalizability of these findings can be questioned. The present study evaluates the prevalence of Diagnostic and Statistical Manual for Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) personality disorders in a sample of female CFS patients and in two control groups. METHOD: The ADP-IV questionnaire (Assessment of DSM Personality Disorders IV) was used to assess the DSM-IV-TR personality disorders at a dimensional and categorical level in a sample of 50 female CFS patients and in two matched control samples of Flemish civilians (n=50) and psychiatric patients (n=50). RESULTS: The results indicate a striking lack of statistical significant differences between the CFS sample and the Flemish control group at the level of dimensional Trait scores, number of criteria, and prevalence rates of personality disorder diagnoses. Unsurprisingly, higher scores at these levels were obtained within the psychiatric sample. The prevalence of an Axis II disorder was 12% in the Flemish and CFS samples, whereas the psychiatric sample obtained a prevalence of 54%. CONCLUSION: The prominent absence of any significant difference in personality disorder characteristics between the female Flemish general population and the CFS samples seems to suggest only a minor etiological role for personality pathology, as defined by the DSM-IV Axis II, within CFS.

Scoring of Hypersomnolence and Fatigue in Patients With Obstructive Sleep Apnea Treated With a Titratable Custom-Made Mandibular Advancement Device.

STUDY OBJECTIVES: The objective of this study was to measure fatigue and hypersomnolence in patients with obstructive sleep apnea (OSA) treated with a mandibular advancement device (MAD), using Epworth Sleepiness Scale (ESS) for hypersomnolence and Checklist Individual Strength questionnaire (CIS20R) for fatigue. METHODS: This was a single-center, prospective cohort study. A total of 58 patients with OSA filled out ESS and CIS20R questionnaires at baseline and after 3 months of MAD treatment. A total of 39 full datasets were collected. Statistical analysis for reliability of the questionnaires, comparison between baseline and 3-month follow-up, correlation between the changes in the values of the two questionnaires, and changes in apnea-hypopnea index (AHI) were performed. RESULTS: CIS20R showed excellent reliability in this patient group at baseline and 3-month follow-up (Cronbach α = .97), ESS showed a marginally good reliability (Cronbach α = .82). The CIS20R (82/140) expressed high levels of fatigue at baseline, and ESS showed a normal level of daytime sleepiness. AHI, ESS, and CIS20R were significantly reduced under MAD treatment. A significant correlation between ESS and CIS20R was observed. No significant correlation between any of the questionnaires and the change in AHI was found. CONCLUSIONS: The CIS20R questionnaire results showed a high level of fatigue in the patients with OSA, and the questionnaire can be used to evaluate changes in fatigue due to MAD treatment after 3 months. The ESS failed to show similar characteristics. Therefore, a combination of ESS for hypersomnolence with CIS20R for fatigue is proposed for the follow-up of patients with OSA treated with MAD.

Assessing chronic fatigue syndrome: Self-reported physical functioning and correlations with physical testing.

The pathophysiology of chronic fatigue syndrome (CFS) remains unclear; no biomarkers have thus far been identified or physical tests designed to underpin its diagnosis. Assessment mainly uses Fukuda's criteria and is based on the exclusion of symptoms related to other diseases/syndromes, subjective self-reporting, and outcomes of self-report questionnaires. In order to improve the baseline assessment and progress evaluation of individuals suspected of CFS and using an association-oriented research strategy and a cross-correlational design, this study investigates possible associations between the performance on two physical tests, i.e. 'Timed Loaded Standing' (TLS), assessing trunk-arm endurance, and the 'Stops Walking with Eyes Closed while performing a secondary Cognitive Task' (SWECCT), measuring impaired automaticity of gait, and the results of two self-report questionnaires, the Checklist Individual Strength (CIS, total score and fatigue subscale score) and the physical functioning and vitality subscales of the Short Form Health Survey (SF-36) to gauge the participants' subjective feelings of fatigue and beliefs regarding their abilities to perform daily-life activities. Comparisons of the outcomes obtained in 27 female patients with a confirmed diagnosis of CFS revealed that trunk-arm endurance as measured with the TLS correlated with the SF-36 physical functioning subscale only (raw p value: 0.004). None of the other correlations were statistically significant. It is concluded that the TLS may have potential as an objective assessment tool to support the diagnosis and monitoring of treatment effects in CFS.

Relationship Between Exercise-induced Oxidative Stress Changes and Parasympathetic Activity in Chronic Fatigue Syndrome: An Observational Study in Patients and Healthy Subjects.

PURPOSE: Oxidative stress has been proposed as a contributor to pain in patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). During incremental exercise in patients with ME/CFS, oxidative stress enhances sooner and antioxidant response is delayed. We explored whether oxidative stress is associated with pain symptoms or pain changes following exercise, and the possible relationships between oxidative stress and parasympathetic vagal nerve activity in patients with ME/CFS versus healthy, inactive controls. METHODS: The present study reports secondary outcomes from a previous work. Data from 36 participants were studied (women with ME/CFS and healthy controls). Subjects performed a submaximal exercise test with continuous cardiorespiratory monitoring. Levels of thiobarbituric acid-reactive substances (TBARSs) were used as a measure of oxidative stress, and heart rate variability was used to assess vagal activity. Before and after the exercise, subjects were asked to rate their pain using a visual analogic scale. FINDINGS: Significant between-group differences in pain at both baseline and following exercise were found (both, P < 0.007). In healthy controls, pain was significantly improved following exercise (P = 0.002). No change in oxidative stress level after exercise was found. Significant correlation between TBARS levels and pain was found at baseline (r = 0.540; P = 0.021) and after exercise (r = 0.524; P = 0.024) in patients only. No significant correlation between TBARS and heart rate variability at baseline or following exercise was found in either group. However, a significant correlation was found between exercise-induced changes in HRV and TBARS in healthy controls (r = -0.720; P = 0.001). IMPLICATIONS: Oxidative stress showed an association with pain symptoms in people with ME/CFS, but no exercise-induced changes in oxidative stress were found. In addition, the change in parasympathetic activity following exercise partially accounted for the change in oxidative stress in healthy controls. More research is required to further explore this link.