Self-reported post-exertional fatigue in Gulf War veterans: roles of autonomic testing

Autonomic dysfunction and gastroparesis in Gulf War veterans

Over 25% of veterans with Gulf War illness developed chronic gastrointestinal (GI) symptoms of unknown etiology after they returned from deployment to the Persian Gulf. To determine the prevalence of delayed gastric emptying and its association with autonomic dysfunction in returning Gulf War (GW) veterans with chronic GI symptoms, we prospectively studied 35 veterans who were deployed to the Persian Gulf and developed chronic nausea, vomiting, postprandial abdominal pain, and bloating during their tour of duty and 15 asymptomatic controls. All veterans underwent 5 standardized cardiovascular tests to assess autonomic function. Each test was scored from 0 (normal) to 5 (severe disease) and the mean was calculated. A composite score >1.5 was considered abnormal, with 5 representing severe autonomic dysfunction. A standardized gastric emptying test with a solid phase was performed in each veteran. A gastric retention of >50% at 100 minutes was considered abnormal. The composite autonomic score was 3.7 in veterans with GI symptoms (vs 1.3 in controls) (p<0.01). The mean solid phase retention at 100 minutes was 72.6% in the symptomatic veterans versus 24.6% in controls (p<0.001). Our results suggest that autonomic dysfunction and delayed gastric emptying are common in returning GW veterans with GI symptoms. Autonomic dysfunction was positively correlated with the severity of delayed gastric emptying and may account for the GI symptoms of nausea, vomiting, postprandial abdominal pain, and bloating. These new findings are important for an increasing number of veterans who are serving in the Persian Gulf and are at a high risk of developing GI disorders while deployed.

Self-Reported Autonomic Dysregulation in Gulf War Illness

INTRODUCTION

Autonomic nervous system dysregulation is commonly observed in Gulf War illness (GWI). Using a new sample, we sought to replicate and extend findings from a previous study that found autonomic symptoms predicted physical functioning in Veterans with GWI.

MATERIALS AND METHODS

A linear regression model was used to predict physical functioning (36-item Short Form Health Survey (SF-36); n = 73, 75% male). First, we examined the predictive value of independent variables individually in the model including: the 31-item Composite Autonomic Symptom Score (COMPASS-31) total score, body mass index (BMI), mental health burden (i.e., post-traumatic stress disorder [PTSD] and/or depression), and COMPASS-31 subscales: orthostatic intolerance, vasomotor, secretomotor, gastrointestinal, bladder, and pupillomotor. Next, we estimated linear regression models containing the three variables (autonomic symptoms, BMI, and mental health burden) identified as predictors of physical functioning from the prior study.

RESULTS

These linear regression models significantly predicted physical functioning and accounted for 15% of the variance with COMPASS-31, 36.6% of variance with COMPASS-31 and BMI, and 38.2% of variance with COMPASS-31, BMI, and mental health burden. Then, forward step-wise linear regressions were applied to explore new models including COMPASS-31 subscales. Two new models accounted for more of the variance in physical functioning: 39.3% with added gastrointestinal symptoms (β = -2.206, P = .001) and 43.4% of variance with both gastrointestinal (β = -1.592, P = .008) and secretomotor subscales (β = -1.533, P = .049). Unlike the previous study we intended to replicate, mental health burden was not a significant predictor in any of our models.

CONCLUSIONS

Treatments that address autonomic dysregulation should be prioritized for research and clinical recommendations for Veterans with GWI who experience chronic pain.

The relationship between Gulf War Illness symptom severity and heart rate variability: A pilot study

INTRODUCTION

Gulf War Illness (GWI) is a chronic multisymptom illness affecting 250,000+ veterans of the '90-'91 Gulf War which remains under-explored in terms of its physiological characteristics. We investigated whether subjective GWI symptom severity scores were related to objective measures of autonomic nervous system activity.

METHODS

We estimated activity in the two major branches of the autonomic nervous system (the parasympathetic nervous system [PNS] and the sympathetic nervous system [SNS]) via metrics of heart rate variability in a sample of Veterans who met established criteria for GWI with varying degrees of self-reported symptom severity. We hypothesized that subjective symptom severity scores would be inversely related to PNS activity and positively related to SNS activity.

RESULTS

Significant negative relationships were observed between the root mean square of successive differences of beat-to-beat intervals (a measure of PNS activity) and symptom severity, both overall and across specific GWI symptom categories (sp. fatigue [r = -0.574], gastrointestinal [r = -0.544]). Furthermore, significant positive relationships were observed between the cardiac sympathetic index and symptom severity, both overall and across specific symptom categories (sp. cognitive [r = 0.721], fatigue [r = 0.560], gastrointestinal [r = 0.694], skin [r = 0.686]).

CONCLUSIONS

Metrics of PNS activation revealed a negative relationship with self-reported symptom severity, while metrics of SNS activation revealed a positive relationship. The present results improve our understanding of the physiology of GWI and provide a new window from which to consider this medically unexplained illness.

Biological measures and diagnostic tools for Gulf War Illness - A systematic review

AIMS

Gulf War Illness (GWI) is a chronic multisymptom illness with debated etiology and pathophysiology. This systematic review catalogues studies of validated biological tests for diagnosing GWI and of associations between biological measures and GWI for their promise as biomarkers.

MAIN METHODS

We searched multiple sources through February 2020 for studies of diagnostic tests of GWI and of associations between biological measures and GWI. We abstracted data on study design, demographics, and outcomes. We assessed the risk of bias of included studies.

KEY FINDINGS

We did not identify any studies validating tests of biomarkers that distinguish cases of GWI from non-cases. We included the best-fitting studies, 32 completed and 24 ongoing or unpublished studies, of associations between GWI and biological measures. The less well-fitting studies (n = 77) were included in a Supplementary Table. Most studies were of the central nervous and immune systems and indicated a significant association of the biological measure with GWI case status. Biological measures were heterogeneous across studies.

SIGNIFICANCE

Our review indicates that there are no existing validated biological tests to determine GWI case status. Many studies have assessed the potential association between a variety of biological measures and GWI, the majority of which pertain to the immune and central nervous systems. More importantly, while most studies indicated a significant association between biological measures and GWI case status, the biological measures across studies were extremely heterogeneous. Due to the heterogeneity, the focus of the review is to map out what has been examined, rather than synthesize information.

Post-exertional malaise in veterans with gulf war illness

Post-exertional malaise (PEM) is a potentially debilitating aspect of Gulf War Illness (GWI) that has received limited research attention. The purpose of the present investigation was to determine symptom severity changes following exercise in Veterans with GWI compared to control Veterans without GWI (CO). Sixty-seven Veterans (n = 39 GWI; n = 28 CO) underwent a 30-minute submaximal exercise challenge at 70% of heart rate reserve. Symptom measurements (e.g. fatigue, pain) occurred pre-, immediately post-, and 24-hour post-exercise. Self-reported physical and mental health, and physiological and perceptual responses to exercise were compared between groups using descriptive statistics, independent samples t-tests and repeated measures Analysis of Variance (RM-ANOVA). Post-exertional malaise was modeled using Group by Time (2 × 3) doubly-multivariate, RM-MANOVAs for (1) mood, (2) pain and (3) GWI-related symptoms, respectively (α = 0.05). Data were analyzed for the full sample of Veterans with GWI (n = 39) compared to CO (n = 28) and a subsample of Veterans (n = 18) who endorsed "feeling unwell after physical exercise or exertion" ("PEM endorsers") during screening. Veterans with GWI reported significantly lower physical and mental health. Groups exercised at similar relative exercise intensities, but GWI perceived exercise as more painful and fatiguing. Group-by-Time interactions were not significant for the entire sample for the three PEM models, however limiting the GWI sample to "PEM endorsers" resulted in significant interactions for Pain- and GWI-related PEM models. These results indicate that not all GVs with GWI experience PEM 24 h after exercise, and that more research is needed to determine the extent that exercise worsens symptoms in GWI.

Motor Unit Number Estimate and Isometric Hand Grip Strength in Military Veterans with or Without Muscular Complaints: Reference Values for Longitudinal Follow-up

INTRODUCTION

It remains unclear if Gulf War (GW) veterans have a higher risk of developing motor neuron disorder. We intended to establish baseline neurophysiological values, including thenar motor unit number estimate (MUNE) and isometric hand grip (IHG) strength, to compare future follow-ups of deployed GW veterans with or without muscular complaints.

MATERIALS AND METHODS

We evaluated 19 GW veterans with self-reported weakness, cramps, or excessive muscle fatigue (Ill-19) and compared them with 18 controls without such muscular complaints (C-18). We performed MUNE on hand thenar muscles using adapted multipoint stimulation method for Ill-19 and 15 controls (C-15). We measured IHG strength (maximum force, endurance, and fatigue level) on Ill-19 and C-18 with a hand dynamometer. We performed nerve conduction studies on all study participants to determine which subjects had mild carpal tunnel syndrome (CTS). We compared the MUNE and IHG strength measures between Ill group and controls and between those with CTS and those without CTS.

RESULTS

We obtained thenar MUNE of Ill-19 (95% CI of mean: 143-215; mean age: 46 yr) and compared it with that of C-15 (95% CI of mean: 161-230; mean age: 45 yr), and 95% of CI of mean among IHG strength variables (maximum force: 324-381 Newton; endurance: 32-42 s; fatigue level: 24%-33%) compared with C-18 (maximum force: 349-408 Newton; endurance: 35-46 s; fatigue level: 21%-27%). There was no significant difference in either MUNE or IHG strength between Ill-19 group and controls. The MUNE and IHG maximum forces were significantly lower in those with CTS compared with those without CTS. As a surrogate of mild CTS, the median versus ulnar distal sensory latency on nerve conduction study was only weakly associated with MUNE, maximum force, and fatigue level, respectively.

CONCLUSION

To our knowledge, no published study on MUNE reference values of military veteran population has been available. The quantifiable values of both thenar MUNE and IHG strength of military veterans serve as baselines for our longitudinal follow-up of motor neuron function of deployed troops. These reference values are also useful for other laboratories to study veterans' motor system with or without mild CTS.

[Role of the sympathetic nervous system in vasovagal syncope and rationale for beta-blockers and norepinephrine transporter inhibitors]

Vasovagal or neurocardiogenic syncope is a common clinical situation and, as with other entities associated with orthostatic intolerance, the underlying condition is a dysfunction of the autonomic nervous system. This article reviews various aspects of vasovagal syncope, including its relationship with orthostatic intolerance and the role of the autonomic nervous system in it. A brief history of the problem is given, as well as a description of how the names and associated concepts have evolved. The response of the sympathetic system to orthostatic stress, the physiology of the baroreflex system and the neurohumoral changes that occur with standing are analyzed. Evidence is presented of the involvement of the autonomic nervous system, including studies of heart rate variability, microneurography, cardiac innervation, and molecular genetic studies. Finally, we describe different studies on the use of beta-blockers and norepinephrine transporter inhibitors (sibutramine, reboxetine) and the rationality of their use to prevent this type of syncope.