The Influence of Ingestion Time on the Validity of Gastrointestinal Pill Temperature as an Index of Body Core Temperature During Work in the Heat
Authors: D'Souza Andrew W. , Notley Sean R. , Meade Robert D. , Rutherford Maura M. , Kenny Glen P. 
Published: June 2021

Ingestible, telemetric pills are increasingly used to estimate body core temperature from the gastrointestinal tract when gold‐standard measurements (e.g., rectal temperature) are unfeasible. While gastrointestinal temperature has been shown to provide acceptable validity, it has been suggested that the time between pill ingestion and the measurement period can influence the precision of those estimates, with sensors spending a greater time in the gastrointestinal tract providing better agreement with rectal temperature. However, a within‐subjects comparison of the effects of various sensor ingestion times on the validity of gastrointestinal temperature as an index of body core temperature during steady‐state and variable‐intensity exercise (more reflective of occupational tasks) is currently unavailable. We therefore sought to quantify the agreement between rectal temperature and gastrointestinal temperatures measured from telemetric pill sensors ingested at various periods prior to exercise in the heat. On two separate occasions, six young (mean±SD; 27±4 years) males consumed a telemetric pill sensor (Vital Sense capsule thermometer; Mini Mitter, Bend, OR) 12, 6, 3 and 1 hour(s) prior to arriving at the laboratory. Thereafter, participants performed 15‐min seated rest followed by 90‐min of either constant or variable intensity cycling eliciting an average rate of metabolic heat production of ~200 W/m2 and a 45‐min recovery, in hot, dry conditions (40°C, ~20% relative humidity). Metabolic heat production as well as rectal and gastrointestinal temperatures were measured continuously (1 min intervals). Agreement between pairs of measurements from each pill sensor and the criterion (rectal temperature) were assessed by the residual mean square error and the percentage of data points exceeding a meaningful threshold of acceptance (±0.25°C). Individual rectal temperature ranged between 36.62–38.43°C, while gastrointestinal temperature ranged between 36.51–38.32°C, 36.46–38.46°C, 36.29–38.34°C and 36.19–38.32°C for the sensors ingested 12, 6, 3 and 1 hour(s) prior to work in the heat (respectively) across both trials. During the constant work trial, the residual mean square error for each sensor averaged 0.12±0.10°C (12 hours), 0.14±0.11°C (6 hours), 0.12±0.09°C (3 hours) and 0.13±0.11°C (1 hour), with 13±16 %, 17±21 %, 11±14 % and 8±9 % of measurements exceeding the predefined acceptance threshold (±0.25°C). Residual square errors averaged 0.18±0.12°C (12 hours), 0.14±0.12°C (6 hours), 0.19±0.16°C (3 hours) and 0.14±0.10°C (1 hour) during the variable work trial, while 27±28 %, 14±15 %, 28±24 % and 14±7 % of measurements exceeding the predefined acceptance threshold. These preliminary outcomes indicate that ingestion times ranging between 12‐1 hour(s) prior to use do not demonstrably modify the precision of estimates of body core temperature from the gastrointestinal tract during either constant or variable work of moderate intensity under hot, dry conditions, with 72–92% of measurements falling within an acceptable error range.Support or Funding InformationFunded by the Government of Ontario and Natural Sciences and Engineering Research Council of Canada.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.