Heat Tolerance Testing and the Return to Duty Decision: A Two-Year Case Cohort Analysis.

BACKGROUND: Among individuals with prior exertional heat illness (EHI), heat tolerance testing (HTT) may inform risk and return to duty/activity. However, little is known about HTT's predictive validity, particularly for EHI recurrence. Our project sought to demonstrate the predictive validity of HTT in EHI recurrence and HTT's utility as a diagnostic tool in exertional heat stroke (EHS). METHODS: Participants with prior EHS were recruited for the study by a physician's referral and were classified as heat tolerant or intolerant after completing demographics and an HTT. Participants were further categorized as single/simple (SS) EHI or recurrent/complex (RC) EHI by conducting a retrospective record review of the following two years. We calculated the positive (PPV) and negative predictive values (NPV) of HTT. RESULTS: The retrospective review of HTT records was used to categorize 44% of Servicemembers as RC, with 77% classified as heat tolerant, 14% as heat intolerant, and 9% as borderline. When borderline cases were classified as heat intolerant, HTT had a high NPV, indicating a high probability that heat-tolerant individuals did not have recurrent EHI. When borderline cases were classified as heat tolerant, NPV and sensitivity decreased while specificity increased. CONCLUSION: We demonstrated that the HTT had a 100% NPV for future EHI over two years of follow-up for Servicemembers with a history of recurrent heat injury and negative HTT results. An HTT can provide critical data points to inform return to duty decisions and timelines by predicting the risk of EHI recurrence.

Effects of training service dogs on service members with PTSD: A pilot-feasibility randomized study with mixed methods.

This pilot-feasibility randomized control trial examined effects of an adjunctive short-term service dog training program (SDTP) for service members in out-patient treatment for PTSD. Twenty-nine volunteer participants were randomly assigned to either the SDTP (n = 12) or waitlist (n = 17); 20 participants were available for post-treatment evaluation. SDTP protocol consisted of six structured one-hour sessions with a dog-trainer conducted over two weeks, intended to train a service dog to help a fellow Veteran. SMs completed symptom questionnaires (PTSD, insomnia, stress, depression, anxiety), and the SDTP group completed a post-intervention quantitative interview. Most effect sizes demonstrated moderate symptom reductions, both between-groups and within the SDTP group. Between-group effects were strongest for intrusive thoughts (Hedge's g = -0.66; 95%CI: -1.72, 0.23) and overall PTSD symptoms (g = -0.45; 95%CI: -1.47, 0.45); within-SDTP group effects were strongest for stress (d = -1.31, 95%CI: -2.17, -0.42), intrusive thoughts (d = -0.78, 95%CI: -1.55, 0.01) and hypervigilance (d = -0.77, 95%CI: -1.48, -0.04). Qualitative analyses indicated participants found SDTP in some ways challenging yet beneficial in multiple aspects of personal and social lives. Future work should examine optimal treatment parameters (e.g., duration, "dosing") when training dogs as an adjunct to other PTSD treatment.

Perceptual strain in a compensable hot environment: Accuracy and clinical correlates.

Heat strain monitoring indexes are important to prevent exertional heat illness (EHI) and uncover risk factors. Two indexes are the Physiological Strain Index (PSI) and a subjective PSI analogue, the Perceptual Strain Index (PeSI). The PeSI is a feasible alternative to PSI in field conditions, although the validity has been variable in previous research. However, the PeSI has been rarely examined at a low heat strain with compensable heat stress, such as during a heat tolerance test (HTT). This study evaluated the discrepancy between the maximal PeSI and maximal PSI achieved during a HTT and determined their association with EHI risk factors, including history of EHI, percent body fat (%BF), relative VO2max, fatigue and sleep status (n = 121; 47 without prior EHI, 74 with prior EHI). The PSI was calculated using the change in rectal temperature (Tre) and heart rate (HR) and PeSI was calculated based on the formula containing thermal sensation (TS), a Tre analogue, and rate of perceived exertion (RPE), a HR analogue. Significant associations were identified between PSI and PeSI and between PSIHR and PeSIHR in the total sample and between PSI and PeSI in the EHI group. Bland-Altman analyses indicated PeSI underestimated PSI in the total sample, PSIHR was greater than PeSIHR, and that PSIcore and PeSIcore were not significantly different, but values varied widely at different heat strains. This indicates the use of RPE underestimates HR and that the accuracy of TS to predict Tre may be subpar. This study also demonstrated that participants with higher %BF have a decreased perception of heat strain and that post-fatigue, sleep status and a prior EHI may increase the perception of heat strain. Overall, these results suggest that PeSI is a poor surrogate for PSI in a compensable heat stress environment at low heat strain.

A nature-based health intervention at a military healthcare center: a randomized, controlled, cross-over study.

We describe a mixed qualitative and quantitative research study in a military facility regarding the role of nature in well-being. Study intervention included two 20-minute walks. One walk was in an intentionally designed woodland environment (Green Road) and the other was on a busy campus road in a medical treatment facility (Urban Road). Twelve volunteers from a military facility participated in both walks in a cross-over experimental design. The two walking sessions were randomly ordered and preceded by pre-walk instructions appropriate to each road's characteristics and incorporated focused attention and present moment orientation. A semi-structured post-walk interview, the primary outcome, was conducted after the conclusion of each walk. Qualitative data analyses consisted of sentiments and themes by using NVivo 12 software. The Green Road was unanimously rated as positive (100%). Responses to Urban Road were evenly distributed among positive (33.3%), negative (33.3%), and neutral/mixed (33.3%) sentiments. The Green Road yielded predominantly positive themes such as enjoyment of nature, relaxation, and feelings of privacy and safety. Urban Road produced significantly more negative themes such as concerns for safety, dislike of noise and other noxious experiences. Quantitative assessment of distress and mindfulness with Distress Thermometer (DT) and Mindful Attention Awareness Scale-state version (MAAS) demonstrated that a walk on the Green Road significantly decreased distress and increased mindfulness compared to a walk on the Urban Road. We also observed that pre-walk instructions could direct attention to both obvious and subtle elements of experience and enhance awareness. Results support the notion that an intentional nature-based environment may produce significantly more positive experiences and result in health-promoting benefits in a military health-care setting compared to an urban environment. Future studies with clinical populations could advance our understanding of the healing value of nature-based interventions. The impact of intentional green environments may be enhanced by well-designed instructions for both recreational and therapeutic use.

Gene expression profiling of humans under exertional heat stress: Comparisons between persons with and without exertional heat stroke.

Exertional heat stroke (EHS) is a leading cause of preventable morbidity and mortality among both athletes and warfighters. Therefore, it is important to find blood biomarkers to predict susceptibility to EHS. We compared gene expression profiling from blood cells between two groups of participants - those with and those without a history EHS - by using genome-wide microarray analysis. Subjects with a history of EHS (n = 6) and non-EHS controls without a history of EHS (n = 18) underwent a heat tolerance test and a thermoneutral exercise challenge on separate days. The heat tolerance test comprised of 2-h of walking, at 5 km/h and 2% incline, with ambient conditions set at 40 °C, 40% relative humidity; the thermoneutral test was similar, but had ambient conditions set at 22 °C. Next, we examined gene expression profiles, quantified based on arithmetic differences (post minus pre) during the heat test minus changes during the thermoneutral test. Genes related to interleukins and cellular stress were significantly down-regulated in participants with a history of EHS compared to their non-EHS counterparts. Suppression of these genes may be associated with susceptibility to exertional heat injury. Prospective research is required to determine whether similar gene expression profiling can be potentially used as blood biomarkers to predict susceptibility to EHS.

Army Combat Medic Resilience: The Process of Forging Loyalty.

This study presents a grounded theory analysis of in-depth interviews of United States Army Combat Medics (CMs) who had served in Iraq and/or Afghanistan. The study explores how 17 CMs nominated by their peers as resilient cope with military stressors in order to identify the factors that enable them to thrive amidst harsh conditions. Four distinct categories of characteristics unique to this group emerged: (1) social bonding, (2) readiness, (3) dual loyalty as performance, and (4) leader by example. Forging loyalty underpins these characteristics and represents the main process used by resilient CMs and comprised three behavior patterns: (1) commitment to the family, (2) commitment to the military mission, and (3) commitment to their guiding religious and spiritual beliefs. Prominent behavioral tendencies of forging loyalty likely developed during childhood and re-enforced by families, friends, and other role models. Based on the findings, new training and education efforts should focus on developing positive emotional, environmental, and social resources to enhance the health and well-being of service members and their families.