Auditory canal temperature measurement using a wearable device during sleep: Comparisons with rectal temperatures at 6, 10, and 14 cm depths.

Monthly rhythms in the body core temperature of women during sleep can provide significant information concerning hormonal fluctuations. The purpose of the present study was to examine and evaluate auditory canal temperature (Tauditory), measured with a newly-developed wearable and wireless device, as a practical index to estimate body core temperature variations during a 7-h sleep period. Comparisons with rectal temperature (Tre) at different depths were conducted. Nine young females slept in a climate chamber at an air temperature of 27 °C with 50% relative humidity. Rectal temperatures at 6, 10 and 14 cm depths, as well as partially insulated Tauditory were simultaneously measured every 5 s during sleep. The results showed that Tauditory was, on average, 0.32 °C lower than Tre at 14 cm depth (P = 0.010), while significant relationships between Tauditory and Tre at 10 cm (r2 = 0.634, P = 0.010), and at 14 cm depths were also found (r2 = 0.826, P = 0.001). Rectal temperatures at 6 cm and 10 cm depths fell between those of Tauditory and Tre at 14 cm. We concluded that Tauditory, as measured using the newly-developed wearable device, can be a reliable, practical and continuous estimate of body core temperature during sleep.