Anecdotal evidence from operational and training units of fighter platforms include observations such as 1) the cockpit is hot, particularly early in flight, 2) the flight equipment is thermally burdensome, and 3) pilots intentionally dehydrate before flying to avoid urinating in the aircraft. No concrete evidence exists investigating the potential detrimental impact of thermal stress and/or dehydration on task performance in mild hypobaria (e.g. ~8,000 ft pressure equivalent).

The combined impact of cockpit thermal stress (temperature and humidity) and pilot flight equipment was explored in the 1970s during the development of the Fighter Index of Thermal Stress (Nunneley and Stribley, 1979a). The FITS was an attempt to estimate cockpit conditions and develop rational guidelines, specifically for the protection of aircrews operating in hot climates. Unfortunately, newer pilot flight equipment is more burdensome than the 1970s (e.g. ATAGS, full coverage anti-g suit, flight jacket) and potentially limits the applicability of the FITS tool.

Dehydration is a well-established detriment to physical performance (Maughan and Shirreffs, 2010), including acceleration tolerance (Nunneley and Stribley, 1979b). Dehydration may also cause decrements in cognitive function (Lindseth, et al., 2013). Further, dehydration may worsen symptoms of hypoxia and acute mountain sickness at 3,048 m (~10,000 ft) (Castellani et al., 2010). To the best of our knowledge, the impact of dehydration on cognitive task performance in a flight-relevant environment (e.g. hypobaria) has not been studied.

The purpose of this study is to determine the individual and combined effects of thermal stress and dehydration on cardiopulmonary strain and cognitive task performance in mild hypobaria.