Gastrointestinal Telemetric Pills Used as Rectal Probes Provide Inaccurate Measurements of Absolute Rectal Temperatures

Abstract

Continuous measurement of rectal temperature (RT) using a wired rectal probe (WRP) comes with obvious technical difficulties and practical limitations. Measurement of RT using a telemetric pill (TP) inserted as a suppository to act as a rectal probe would circumvent some of those problems. PURPOSE: Validate the use of a commercially available gastrointestinal TP (HQ Inc.) for the continuous measurement of RT during slow and rapid increase and decrease in core temperature induced by periods of passive cooling, passive heating, active heating and active cooling. METHODS: Nine (8 men, 1 woman) physically active participants (30 ± 9 yrs; 175 ± 7 cm; 75 ± 9 kg) underwent a research protocol where they completed, while wearing a WRP (YSI 401) linked to a TP: 1) a 30 min sitting period (23°C) followed by 2) a 45 min sitting period inside a head-out environmental chamber (40-42 °C); 3) a 45 min sitting period (23°C) while ingesting, over the first 30 min, 7.5 g of shaved-ice (-1°C )/kg body weight; 4) a running exercise period (38 °C, 20-30% RH) at 68% VO2max until a WRP temperature of 39.5°C and; 5) a cold-water (10°C) immersion period until a WRP decrease in temperature of 1.5°C. The WRP and each TP were calibrated before experiments. A bias ± random error contained within ± 0.35°C (daily variation in RT of ± 0.25°C + sensors measurement error of ± 0.1°C) around the zero line was deemed acceptable between sensors. RESULTS: The rate of change in WRP and TP temperatures during phases 1, 2, 3, 4 and 5 was respectively of -0.008 ± 0.007°C/min and -0.006 ± 0.004°C/min, 0.003 ± 0.005°C/min and 0.002 ± 0.004°C/min, -0.011 ± 0.004°C/min and -0.011 ± 0.002°C/min, 0.057 ± 0.010°C/min and 0.054 ± 0.008°C/min and -0.141 ± 0.124°C/min and -0.091 ± 0.065°C/min. Mean biases (WRP - TP) and random errors during phases 1, 2, 3, 4 and 5 were of 0.12°C/± 0.30°C, 0.15°C/± 0.22°C, 0.12°C/± 0.26°C, 0.21°C/± 0.34°C and 0.24°C/± 0.66°C, respectively CONCLUSION: The use of TPs (HQ Inc.) as suppositories tracked slow and rapid increases in RT and slow decreases in RT as measured by WRP, but did not detect the rapid decrease in RT. In all instances, however, the absolute difference between WRP and TP exceeded +/- 0.35°C. Therefore, we conclude that a TP inserted as a suppository to act as a rectal probe does not provide acceptable absolute measure of RT.