Decision support tools for hot and cold environments: state-of-the-art and future opportunities for predictive and diagnostic biomarkers

Introduction: Strenuous physical activities under extreme environmental conditions might expose a soldier to exercise related injuries; among them exertional heat injuries (EHI). Such injuries might compromise the soldier's health but also his/her combat effectiveness. In order to understand the level of tolerance to heat and better understand the extent of EHI pathology, a reliable scale of correlative biomarkers is indispensable. Such biomarkers, beyond the traditional systemic physiological responses known to date, should be integrated for explaining the hazards of impaired systemic homeostasis. In this presentation an implementation of this concept will be addressed, emphasizing the dynamics of biomarkers in assessing the soldier’s tolerance to heat and the extent of EHI. Endotoxemia and systemic inflammatory responses: Endotoxin leakage from the gastro-intestinal (GI) tract to the bloodstream, for example, has long been considered as a contributing factor in the pathophysiology of heat stroke. This is supported by direct experimental evidence on the impairment of intestinal tight junction integrity under heat stress and by clinical observations. Subsequently, in recent years, the intestinal microbial flora has also drawn attention concerning the individual's inherent tolerance to heat stress. It follows that a complex array of molecular changes mediates the magnitude of the heat strain response to heat stress. Hence, to differentiate between heat tolerant or intolerant individuals, the observation of dynamic changes in peripheral biomarkers in blood and/or GI/saliva microbiota can potentially be used. Not less important is the protracted systemic inflammatory response syndrome (SIRS), including a progressive cytokine storm, which is associated with the severity of EHI. Additional processes, such as induction of the heat shock response correlate with EHI severity. In this regard, heat shock proteins (HSPs) are of interest in depicting heat vulnerability and injury. Conclusion and future perspectives: An integration of the traditionally used systemic parameters together with accepted molecular markers may serve in helping to identify heat intolerant individuals. These markers may also serve to monitor the progression of heat adaptation and the extent and severity of injury upon heat stress exposure, thereby assisting the clinician in assessing the patient's condition and in determining the prognosis and proper choice of treatment. In military scenarios this will help in enhancing the soldier's survivability and effectiveness.