Use of the heat tolerance test to assess recovery from exertional heat stroke

Abstract

Exercise or work in hot environments increases susceptibility to exertional heat illnesses such as exertional heat stroke (EHS). EHS occurs when body heat gain exceeds body heat dissipation, resulting in rapid body heat storage and potentially life-threatening consequences. EHS poses a dangerous threat for athletes, agriculture workers, and military personnel, as they are often exposed to hot environmental conditions that restrict body heat loss or contribute to body heat gain. Currently, there is limited guidance on return to activity (RTA) after an episode of EHS. While examining biomarkers in the blood is thought to be beneficial for determining RTA, they are not sensitive or specific enough to be a final determining factor as organ damage may persist despite blood biomarkers returning to baseline levels. As such, additional assessment tests to more accurately determine RTA are desired. One method used for determining RTA is the heat tolerance test (HTT, 120 minutes treadmill walking; 40°C, 40% relative humidity). Unfortunately, the HTT provides even less information about EHS recovery since it offers no test sensitivity or specificity even after years of implementation. We provide an overview of the HTT and the controversy of this test with respect to assessment criteria, applicability to tasks involving high metabolic workloads, and the lack of follow-up analyses to determine its accuracy for determining recovery in order to diminish the likelihood of a second EHS occurrence.

Epidemiology of Exertional Heat Illness in the Military: A Systematic Review of Observational Studies

“…However, in this review, only one study identified haematological biomarkers (leucocytosis, and anaemia). While the evidence in this review may be limited given the few number of articles investigating and reporting haematological biomarkers, evidence from the literature suggests that EHS results in SIRS which causes coagulopathies and DIC [ 4 ]. These biomarkers are useful in determining the severity of EHS.…”

“…The underpinning physiological mechanism of EHS is currently unknown, but evidence suggests that vascular endothelial damage occurs in response to hyperthermia [ 4 ]. Direct thermal injury to tissues facilitates endotoxin leakage from the intestinal mucosa and the release of cytokines into systemic circulation, thus inducing a systemic inflammatory response syndrome (SIRS) [ 5 ].…”

“…Direct thermal injury to tissues facilitates endotoxin leakage from the intestinal mucosa and the release of cytokines into systemic circulation, thus inducing a systemic inflammatory response syndrome (SIRS) [ 5 ]. SIRS amplifies coagulation cascade, causing coagulopathies that progressively lead to disseminated intravascular coagulation (DIC), resulting in tissue damage and subsequent multiorgan dysfunction [ 4 , 5 ]. Multiorgan damage, renal failure, metabolic acidosis, electrolyte imbalance, acute hepatic dysfunction and death are resultant complications of EHS [ 6 ].…”

The Gastrointestinal Exertional Heat Stroke Paradigm: Pathophysiology, Assessment, Severity, Aetiology and Nutritional Countermeasures

“…These health-complications include: heat intolerance [22], neurological impairment [23], chronic kidney disease [24] and cardiovascular disease [25]. The burden of EHS not only relates to the health of the patient, but can also result in reduced occupational effectiveness [26,27], significant medical/legal expenses [28,29], and in some instances high-profile media criticism [30,31] of concerned governance bodies (e.g. employer).…”

Association between occupational heat stress and DNA damage in lymphocytes of workers exposed to hot working environments in a steel industry in Southern India

“…Excess heat exposures is not only an environmental threat but also an occupational hazard for a large worker population engaged in hard manual labor in tropical settings [3] exposed to heat stress and strain [4]. Workers in high-heat industries such as iron and steel, foundries, smelters, brick-firing and ceramic, glass and rubber, bakeries, commercial kitchens, and mining are already subjected to high heat exposures on a day-to-day basis and have high potential for heat-related illnesses like heat exhaustion, heat stroke, and death [5][6][7][8][9] which is likely to increase in the future climate change scenario [10,11].…”