Effect of change in ambient temperature on core temperature of female subjects during the daytime and its sex differences

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Abstract
Tympanic temperature (Tty), skin temperature, and regional dry heat loss were measured continuously in eight female subjects under three conditions: (1) stepwise increases in ambient temperature (Ta) from 26 °C at 09:00 to 30 °C at 18:00, (2) steady Ta at 28 °C from 09:00 to 18:00, and (3) stepwise decreases in Ta from 30 °C at 09:00 to 26 °C at 18:00. Oxygen consumption, body weight loss, thermal sensation, and comfort levels were periodically recorded. The Tty increased significantly (p < 0.01) from 36.1 ± 0.36 °C to 36.6 ± 0.23 °C at 18:00 under condition 1 but remained virtually unchanged under conditions 2 and 3. Thermal comfort was observed at 15:00 and 17:00 under condition 3, whereas subjects reported that they felt slightly cool at 15:00. The rate of body heat storage (S), changes in Tty, mean skin temperature (\( \overline{T} \)sk), and mean body temperature during each period were calculated, and confirmed that changes in \( \overline{T} \)sk was correlated with S. Diurnal changes in core temperature (Tc) appeared to be more dependent on diurnal rhythm than on changes in Ta, except when Ta increased continuously. Thus, it may be difficult to predict diurnal changes in women’s Tc using a body-heat-balance equation during thermal transient.