Physiological index of strain and body heat storage in hyperthermia

¹ Biomedical Laboratory, Wright Air Development Division, Wright-Patterson Air Force Base, Ohio

Individual variability of a modified Craig index of physiological strain and body heat storage was determined, and the relationship between these parameters defined for five healthy, nonacclimatized male subjects exposed five times to each of three heat stress levels: 38°C, 54°C and 71°C at a vapor pressure of 10 mm Hg. This index contains the variables of heart rate, sweat rate and rate of rectal temperature change, measured by EKG, nude pre- and post-experimental weighings, and a rectal thermistor, respectively. Body heat storage was calculated from initial and terminal weighted mean skin and rectal temperatures. Subjects were sitting and wore 1 clo of body insulation. Individual and group variation for strain index and body heat storage was determined. The data show a linear relationship between these expressions over the thermal stress range investigated although individual variability was considerable at the higher stress levels. A statistically significant correlation between strain index and body heat storage is shown.

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