Age- and Sex-Based Differences in Exertional Heat Stroke Incidence in a 7-Mile Road Race

Exertional Heat Stroke Survival at the Falmouth Road Race: 180 New Cases With Expanded Analysis

CONTEXT

A high number of exertional heat stroke (EHS) cases occur during the Falmouth Road Race.

OBJECTIVES

To extend previous analyses of EHS cases during the Falmouth Road Race by assessing or describing (1) EHS and heat exhaustion (HE) incidence rates, (2) EHS outcomes as they relate to survival, (3) the effect of the environment on these outcomes, and (4) how this influences medical provider planning and preparedness.

DESIGN

Descriptive epidemiologic study.

SETTING

Falmouth Road Race.

PATIENTS OR OTHER PARTICIPANTS

Patients with EHS or HE admitted to the medical tent.

MAIN OUTCOME MEASURE(S)

We obtained 8 years (2012 to 2019) of Falmouth Road Race anonymous EHS and HE medical records. Meteorologic data were collected and analyzed to evaluate the effect of environmental conditions on the heat illness incidence (exertional heat illness [EHI] = EHS + HE). The EHS treatment and outcomes (ie, cooling time, survival, and discharge outcome), number of HE patients, and wet bulb globe temperature (WBGT) for each race were analyzed.

RESULTS

A total of 180 EHS and 239 HE cases were identified. Overall incidence rates per 1000 participants were 2.07 for EHS and 2.76 for HE. The EHI incidence rate was 4.83 per 1000 participants. Of the 180 EHS cases, 100% survived, and 20% were transported to the emergency department. The WBGT was strongly correlated with the incidence of both EHS (r2 = 0.904, P = .026) and EHI (r2 = 0.912, P = .023).

CONCLUSIONS

This is the second-largest civilian database of EHS cases reported. When combined with the previous dataset of EHS survivors from this race, it amounts to 454 EHS cases resulting in 100% survival. The WBGT remained a strong predictor of EHS and EHI cases. These findings support 100% survival from EHS when patients over a wide range of ages and sexes are treated with cold-water immersion.

Are young military personnel at a disproportional risk of heat illness?

Heat illnesses (HI) define a continuum of conditions where patients become incapacitated due to uncompensable heat stress. In the military, HI has a significant health, financial and operational burden that requires vigilant management. Military training and operations regularly expose personnel to known HI risk factors, meaning that prevalence remains high despite stringent attempts to reduce risk to as low as reasonably practicable. While prepubertal children and elderly adults are widely demonstrated to be at greater risk of classic HI than young adults due to impaired physiological and/or behavioural thermoregulation, in military personnel, it is young recruit-age individuals (16-19 years) who consistently experience the highest prevalence of exertional HI. Mechanistically, controlled laboratory studies have never directly compared thermoregulation between young recruit-age individuals and other groups of adults, though research highlighting impaired thermoregulation in prepubertal children potentially has some relevance to late-developing young recruit-age personnel. Aside from potential age-related differences in thermoregulation, a major consideration must also be given to the increased prevalence of organisational risk factors for HI in younger military personnel (eg, education, physical load, rank, job roles), which is likely to be the primary explanation behind age-related trends in HI prevalence, at least in the military. The aims of this article are to review: (i) the epidemiology of HI between young recruit-age individuals and older military personnel; (ii) the theoretical basis for age-associated differences in thermoregulatory function and (iii) pertinent areas for future research.

Exertional Heat Stroke and Rhabdomyolysis: A Medical Record Review and Patient Perspective on Management and Long-Term Symptoms

INTRODUCTION

Exertional heat stroke (EHS) is a medical emergency, occurring when the body generates more heat than it can dissipate, and frequently associated with exertional rhabdomyolysis (ERM). In the present study we aimed to (I) identify clinical features and risk factors, (II) describe current prehospital management, (III) investigate long-term outcomes including the impact on mental health, and review the guidance received during restarting activities. We hope that our approach will improve individual and organizational heat illness preparedness, and improve follow-up care.

METHODS

We performed a prospective online survey and retrospective medical record review among athletes and military personnel with an episode of EHS/ERM in the Netherlands between 2010 and 2020. We evaluated prehospital management, risk factors, clinical features and long-term outcomes at 6 and 12 months after the event, including mental health symptoms. Furthermore, we investigated what guidance participants received during follow-up, and assessed the patients' perspective on these outcomes.

RESULTS

Sixty participants were included, 42 male (70%) and 18 female (30%), of which 47 presented with EHS (78%) and 13 with ERM (22%). Prehospital management was inconsistent and in the majority of participants not conducted according to available guidelines. Self-reported risk factors included not feeling well-acclimatized to environmental heat (55%) and peer pressure (28%). Self-reported long-term symptoms included muscle symptoms at rest (26%) or during exercise (28%), and neurological sequelae (11%). Validated questionnaires (CIS, HADS and SF-36) were indicative of severe fatigue (30%) or mood/anxiety disorders (11%). Moreover, 90% expressed a lack of follow-up care and that a more frequent and intensive follow-up would have been beneficial for their recovery process.

CONCLUSION

Our findings indicate major inconsistencies in the management of patients with EHS/ERM, emphasizing the compelling need for implementing standardized protocols. Based on the results of long-term outcome measures, we recommend to counsel and evaluate every patient not only immediately after the event, but also in the long-term.

Comparison of Slate Safety Wearable Device to Ingestible Pill and Wearable Heart Rate Monitor

BACKGROUND

With the increase in concern for deaths and illness related to the increase in temperature globally, there is a growing need for real-time monitoring of workers for heat stress indicators. The purpose of this study was to determine the usability of the Slate Safety (SS) wearable physiological monitoring system.

METHODS

Twenty nurses performed a common task in a moderate or hot environment while wearing the SS device, the Polar 10 monitor, and having taken the e-Celsius ingestible pill. Data from each device was compared for correlation and accuracy.

RESULTS

High correlation was determined between the SS wearable device and the Polar 10 system (0.926) and the ingestible pill (0.595). The SS was comfortable to wear and easily monitored multiple participants from a distance.

CONCLUSIONS

The Slate Safety wearable device demonstrated accuracy in measuring core temperature and heart rate while not restricting the motion of the worker, and provided a remote monitoring platform for physiological parameters.

Body mass index, but not sex, influences exertional heat stroke risk in young healthy men and women

Exertional heat stroke (EHS) remains a persistent threat for individuals working or playing in the heat, including athletes and military and emergency service personnel. However, influence of biological sex and/or body mass index (BMI) on the risk of EHS remain poorly understood. The purpose of this study was to retrospectively assess the influence of sex and BMI on risk of EHS in the active-duty US Army. We analyzed data from 2016 to 2021, using a matched case-control approach, where each individual with a diagnosis of EHS was matched to five controls based on calendar time, unit ID, and job category, to capture control individuals who were matched to EHS events by location, time, and activity. We used a multivariate logistic regression model mutually adjusted for sex, BMI, and age to compare 745 (n = 61 F) individuals (26 ± 7 yr) with a diagnosed EHS to 4,290 (n = 384 F) case controls (25 ± 5 yr). Group average BMI were similar: 26.6 ± 3.1 (EHS) and 26.5 ± 3.6 kg/m² (CON). BMI was significantly (P < 0.0001) associated with higher risk of EHS with a 3% increase in risk of EHS for every unit increase in BMI. Notably, sex was not associated with any difference in risk for EHS (P = 0.54). These data suggest that young healthy people with higher BMI have significantly higher risk of EHS, but, contrary to what some have proposed, this risk was not higher in young women.

The impact of castration on physiological responses to exertional heat stroke in mice

INTRODUCTION

The capability of male mice to exercise in hot environments without succumbing to exertional heat stroke (EHS) is markedly blunted compared to females. Epidemiological evidence in humans and other mammals also suggests some degree of greater vulnerability to heat stroke in males compared to females. The origins of these differences are unknown, but testosterone has previously been shown to induce faster elevations in core temperature during acute, passive heat exposure. In this study, we tested the hypothesis that loss of testosterone and related sex hormones through castration would improve the performance and heat tolerance of male mice during EHS exposure.

METHODS

Twenty-four male mice were randomly divided into 3 groups, untreated EHS mice (SHAM-EHS), castrated EHS mice (CAS+EHS) and naïve exercise controls (NAIVE). Exercise performance and physiological responses in the heat were monitored during EHS and early recovery. Two weeks later, blood and tissues were collected and analyzed for biomarkers of cardiac damage and testosterone.

RESULTS

Core temperature in CAS+EHS rose faster to 39.5°C in the early stages of the EHS trial (P<0.0001). However, both EHS groups ran similar distances, exhibited similar peak core temperatures and achieved similar exercise times in the heat, prior to symptom limitation (unconsciousness). CAS+EHS mice had ~10.5% lower body mass at the time of EHS, but this provided no apparent advantage in performance. There was no evidence of myocardial damage in any group, and testosterone levels were undetectable in CAS+EHS after gonadectomy.

CONCLUSIONS

The results of these experiments exclude the hypothesis that reduced performance of male mice during EHS trials is due to the effects of male sex hormones or intact gonads. However, the results are consistent with a role of male sex hormones or intact gonads in suppressing the early and rapid rise in core temperature during the early stages of exercise in the heat.

The influence of sex and biological maturation on the sudomotor response to exercise-heat stress: Are girls disadvantaged?

Both adult females and children have been reported to have a lower sweating capacity and thus reduced evaporative heat loss potential which may increase their susceptibility to exertional hyperthermia in the heat. Compared to males, females have a lower maximal sweat rate and thus a theoretically lower maximum skin wettedness, due to a lower sweat output per gland. Similarly, children have been suggested to be disadvantaged in high ambient temperatures due to a lower sweat production and therefore reduced evaporative capacity, despite modifications of heat transfer due to physical attributes and possible evaporative efficiency. The reported reductions in sudomotor activity of females and children suggests a lower sweating capacity in girls. However, due to the complexities of isolating sex and maturation from the confounding effects of morphological differences (e.g., body surface area-to-mass ratio) and metabolic heat production, limited evidence exists supporting whether children and, more specifically, girls are at a thermoregulatory disadvantage. Furthermore, a limited number of child-adult comparison studies involve females and very few studies have directly compared regional and whole-body sudomotor activity between boys and girls. This mini review highlights the exercise-induced sudomotor response of females and children, summarises previous research investigating the sudomotor response to exercise in girls and suggests important areas for further research.

Are there sex differences in risk for exertional heat stroke? A translational approach

NEW FINDINGS

What is the topic of this review? This review discusses the current status of the literature in sex differences in exertional heat stroke. What advances does this review highlight? We utilize a translational model to explore possible physical and physiological differences with respect risk and treatment of exertional heat stroke.

ABSTRACT

Exertional heat stroke (EHS) is a potentially fatal condition brought about by a combination of physical activity and heat stress and resulting in central nervous system dysfunction and organ damage. EHS impacts several hundred individuals each year ranging from military personnel, athletes, to occupational workers. Understanding the pathophysiology and risk factors can aid in reducing EHS across the globe. While we know there are differences between sexes in mechanisms of thermoregulation, there is currently not a clear understanding if/how those differences impact EHS risk. The purpose of this review is to assess the current status of the literature surrounding EHS from risk factors to treatment using both animal and human models. We use a translational approach, considering both animal and human research to elucidate the possible influence of female sex hormones on temperature regulation and performance in the heat and highlight the specific areas with limited research. While more work is necessary to comprehensively understand these differences, the current research presented provides a good framework for future investigations. This article is protected by copyright. All rights reserved.