Comparison of double sensor, skin, and rectal temperature recording for determining circadian rhthm

Background: In chronobiology studies, the circadian rhythm of core body temperature has often been monitored via rectal temperature recordings. Compliance with rectal recordings, however, limits voluntary participation and prevents a broader spectrum of investigations. With the progress of technology, systems have been developed which allow a measurement of the core body temperature from an intact skin surface, such as the Double Sensor [1], a skin surface temperature and heat-flux combining device. Studies regarding how well such systems reflect the circadian rhythm of core body temperature, however, are lacking. Material & Methods: As part of the 2nd Berlin BedRest Study (BBR2-2), subjects underwent micro-g simulated conditions, i.e. 6° head-down tilt bed-rest. On bed-rest day 49, 24 hours temperature profiles were obtained in seven health men by a single skin surface temperature sensor and the Double Sensor, each placed at forehead (Tfhd, DSfhd) and sternum (Tste, DSste), and by a rectal probe (Trec). The degree of parallelism between measured temperature variables was assessed by calculating the Pearson correlation coefficient r. Rhythm characteristics determined by fitting a single cosine curve included MESOR, amplitude, and acrophase, and were statistically tested for significance by Student's paired t- test. Results: Averaged value (± SD) of Pearson’s r was .867 (.059), .797 (.097), .519 (.373), -.021 (.549) for correlation between Trec with DSfhd, Tfhd, DSste, and Tste, respectively. The correlation mean demonstrated a good parallelism between Trec and temperatures obtained from the forehead. Regarding the rhythm parameters MESOR, amplitude, and acrophase, no significant difference was found between Trec and DSfhd, but between Tfhd and DSfhd as well as between Tfhd and Trec. Discussion & Conclusions: Not the skin surface temperature recordings, but the temperatures of the Double Sensor from the forehead seem promising for determining the circadian rhythm of core body temperature in occupational and environmental medicine on earth and space, where the use of rectal probes is not feasible or desired. References: 1. Gunga HC, Sandsund M, Reinertsen RE, Sattler F and Koch J. A non-invasive device to continuously determine heat strain in humans. Journal of Thermal Biology 33: 297-307, 2008.