Assoc. Prof. Akimasa Hirata, Research Assoc. Prof. Ilkka Laakso, and their colleagues have developed a computational code to track the temperature elevation and thermoregulatory response in the human under heat load (such as ambient heat exposure). In the code, a thermal diffusion equation taking into account the thermoregulatory response in the human is solved computationally in the time domain. Reduced thermal sensitivity of the hypothalamus (body core) in the aged adults is also estimated from literature data and taken into account. Note that the decline of the thermal sensitivity of the skin was confirmed in the group's previous study even for the elderly (over 65 years). For an ambient temperature of 35 °C and a relative humidity of 60%, the computed core temperature elevation in the model corresponding to the thermophysiological response of the aged is 0.92 °C, which is higher than that for the younger adults, 0.25 °C, and for the elderly, 0.45 °C. This difference in the core temperature elevation is mainly attributable to the decline in the thermal sensitivity of the body core.

Figure: Computed temperature elevation distribution on human body surfaces at ambient heat exposure (35 °C and 60%) at 90 min for (a) younger adults, (b) the elderly (-65 years), and (c) the aged (-75 years).