Purpose: The validity and the reliability of using intestinal temperature (Tint) via ingestible temperature sensors (ITS) to measure core body temperature have been demonstrated. However, the effect of elapsed time between ITS ingestion and Tint measurement has not been thoroughly studied.
Methods: Eight volunteers (six men and two women) swallowed ITS 5 h (ITS-5) and 29 h (ITS-29) before 4 h of varying intensity activity. Tint was measured simultaneously from both ITS, and Tint differences between the ITS-5 and the ITS-29 over the 4 h of activity were plotted and compared relative to a meaningful threshold of acceptance (±0.25°C). The percentage of time in which the differences between paired ITS (ITS-5 vs ITS-29) were greater than or less than the threshold of acceptance was calculated.
Results: Tint values showed no systematic bias, were normally distributed, and ranged from 36.94°C to 39.24°C. The maximum Tint difference between paired ITS was 0.83°C with a minimum difference of 0.00°C. The typical magnitude of the differences (SE of the estimate) was 0.24°C, and these differences were uniform across the entire range of observed temperatures. Paired Tint measures fell outside of the threshold of acceptance 43.8% of the time during the 4 h of activity.
Conclusions: The differences between ITS-5 and ITS-29 were larger than the threshold of acceptance during a substantial portion of the observed 4-h activity period. Ingesting an ITS more than 5 h before activity will not completely eliminate confounding factors but may improve accuracy and consistency of core body temperature.