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South-Eastern Australia experiences the most frequent and severe bushfires in the world. In 2009, bushfires in Victoria claimed 173 lives and cost more than $4 billion in structural damage. As a consequence, the establishment of building standards that might govern the construction of bushfire shelters was recommended. Since no relevant standards existed, it was suggested that if these shelters could keep the internal conditions to a maximal mean Modified Discomfort Index (MDI) of 39o for 60 min, then they could restrain the rise in core temperature to no more than 2oC. The current investigators were invited to test this hypothesis and, in this communication, provide a physiological evaluation of this recommendation across two experiments. In the first experiment, the aim was to evaluate the physiological impact of a 10oC variation in air temperature that could be encountered at a constant Modified Discomfort Index of 39o. The objective of the second experiment was to explore changes within the internal environment of an air-tight shelter containing pre-heated and sweating occupants.

Many groups have investigated cognitive performance during hyperthermia and dehydration, with few demonstrating convincing and unequivocal influences. Some reports show neither thermalnor hydration-induced influences, others have found improved, whilst some report reduced cognitive performance. This confusion has arisen due to methodological limitations that have resulted in many previous experiments not being optimally designed to evaluate these effects. For instance, few studies have appropriately induced hyperthermia and dehydration, and then clamped these states during the cognitive challenge. Many investigators have used physical exercise to induce these states, yet exercise may independently affect cognitive performance. Furthermore, task difficulty has rarely been controlled across cognitive functions, with the difficulty level for many tasks being too low, whilst inter-task comparisons have often been performed across different levels of difficulty. The former introduces bias, such that only performance decrements can be observed, whilst the latter renders it almost impossible to compare either the baseline data or subsequent changes in cognitive performance during altered thermal and hydration states. As a consequence of these limitations, our understanding of the affects of these stresses upon cognitive performance is less than optimal, and this study was designed to address these design limitations.

Measuring cutaneous blood flow is an essential building block for understanding thermoeffector responses to changes in central and peripheral tissue temperatures. Under thermoneutral conditions, skin blood flow modifications are the primary pathway for heat exchange. Outside this zone, flow changes provide information pertaining to the thermoregulatory control mechanisms that modulate vasomotor tone. Whilst there are numerous methods available for measuring regional blood flow in humans, the most common method for evaluating the cutaneous flow is via venous-occlusion plethysmography, which has been used for over a century (an older tool), with strain-gauge plethysmographs being most commonly used today.