Residual analysis in the determination of factors affecting the estimates of body heat storage in clothed subjects |
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Authors: | Yukitoshi Aoyagi Tom M McLellan Roy J Shephard |
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Institution: | (1) Graduate Department of Community Health, University of Toronto, M5S 1A8 Toronto, Ontario, Canada;(2) Environmental Physiology Section, Defence and Civil Institute of Environmental Medicine, M3M 3139 North York, Ontario, Canada;(3) School of Physical and Health Education, University of Toronto, 320 Huron Street, M5S 1A1 Toronto, Ontario, Canada;(4) Health Studies Program, Brock University, L2S 3A1 St. Catharines, Ontario, Canada;(5) Defence and Civil Institute of Environmental Medicine, Canada |
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Abstract: | Body heat storage can be estimated by calorimetry (from heat gains and losses) or by thermometry from changes (Δ) in mean
body temperature (T
b) calculated as a weighted combination of rectal (T
re) and mean skin temperatures (T
sk)]. If an invariant weighting factor ofT
re andT
sk were to be used (for instance, ΔT
b = 0.8 · ΔT
re + 0.2 · ΔT
sk under hot conditions), body heat storage could be over- or underestimated substantially relative to calorimetry, depending
on whether the subject was wearing light or protective clothing. This study investigated whether discrepancies between calorimetry
and thermometry arise from methodological errors in the calorimetric estimate of heat storage, from inappropriate weightings
in the thermometric estimate, or from both. Residuals of calorimetry versus thermometric estimates were plotted against individual
variables in the standard heat balance equation, applying various weighting factors toT
re andT
sk. Whether light or protective clothing was worn, the calorimetric approach generally gave appropriate estimates of heat exchange
components and thus heat storage. One exception was in estimating latent heat loss from sweat evaporation. If sweat evaporation
exceeded 650 g·h−1 when wearing normal clothing, evaporative heat loss was overestimated and thus body heat storage was underestimated. Nevertheless,
if data beyond this ceiling were excluded from the analyses, the standard 4:1 weighting matched calorimetric heat storage
estimates quite well. When wearing protective clothing, the same 4:1 weighting approximated calorimetric heat storage with
errors of less than approximately 10%, but only if environmental conditions allowed a subject to exercise for more than 90
min. The best thermometric estimates of heat storage were provided by using two sets of relative weightings, based upon the
individual's metabolic heat production (
in kilojoules per metre squared per hour): {4 − (
)·
] 2}:1 for an initial, thermoneutral environment and {4 + (
) ·
] · 5}: 1 for a final, hot environment; the optimal value of
lay between 450 and 500 kJ m−2 · h−1. We concluded that the accuracy of thermometric estimates of heat storage can be improved by modifying weighting factors
ofT
re andT
sk according to the environment, type of clothing, and metabolic rate. |
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Keywords: | Rectal temperature Mean skin temperature Mean body temperature Heat exchange Heat balance |
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