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Comparison of Rectal and Gastrointestinal Core Temperatures During Heat Tolerance Testing
Melissa J Crowe1, Michael T Meehan1, Rhondda E Jones2
1College of Medicine and Dentistry, James Cook University, Townsville, QLD 4811, Australia.
Gastrointestinal core temperature is not a reliable substitute for rectal core temperature during heat tolerance testing for military personnel. Relying on it may lead to premature return to duty before full recovery from heat illness.
Area of Science:
- Environmental Physiology
- Military Medicine
- Thermoregulation
Background:
- Exertional heat stroke (EHS) can impair military capability in hot environments.
- Heat tolerance testing (HTT) assesses fitness for duty after EHS.
- Traditional HTT uses rectal core temperature (Tre), but gastrointestinal core temperature (Tgi) is explored as an alternative.
Purpose of the Study:
- To evaluate Tgi as a substitute for Tre in HTT.
- To compare physiological factors between heat-tolerant and heat-intolerant individuals.
Main Methods:
- Compared Tgi and Tre measurements during HTT in Australian Defence Force personnel and controls.
- Used confusion matrices to assess agreement on heat tolerance outcomes.
- Analyzed correlations, bias, and non-parametric tests for physiological comparisons.
Main Results:
- Tgi correlated well with Tre (ρ = 0.893, bias 0.2 °C) but showed inconsistent differences.
- Tgi and Tre agreed on heat tolerance in only 80% of trials.
- Tgi failed to identify heat intolerance in 6 of 8 cases identified by Tre.
- Heat-tolerant trials showed lower resting heart rate, lower systolic blood pressure, and higher body surface area to mass ratio.
Conclusions:
- Tgi is not recommended as a replacement for Tre in HTT due to potential misdiagnosis of heat intolerance.
- Findings suggest aerobic fitness and body composition influence heat tolerance.
- Accurate temperature monitoring is crucial for safe return to duty after heat illness.
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