Abstract
There is increasing interest in the use of pill-sized ingestible capsule telemetric sensors for assessing core body temperature (Tc) as a potential indicator of variability in metabolic efficiency and thrifty metabolic traits. The aim of this study was to investigate the feasibility and accuracy of measuring Tc using the CorTemp® system. Tc was measured over an average of 20 h in 27 human subjects, with measurements of energy expenditure made in the overnight fasted state at rest, during standardized low-intensity physical activity and after a 600 kcal mixed meal. Validation of accuracy of the capsule sensors was made ex vivo against mercury and electronic thermometers across the physiological range (35-40°C) in morning and afternoon of 2 or 3 consecutive days. Comparisons between capsule sensors and thermometers were made using Bland-Altman analysis. Systematic bias, error, and temperature drift over time were assessed. The circadian Tc profile classically reported in free-living humans was confirmed. Significant increases in Tc (+0.2°C) were found in response to low-power cycling at 40-50 W (~3-4 METs), but no changes in Tc were detectable during low-level isometric leg press exercise (<2 METs) or during the peak postprandial thermogenesis induced by the 600 kcal meal. Issues of particular interest include fast "turbo" gut transit with expulsion time of <15 h after capsule ingestion in one out of every five subjects and sudden erratic readings in teletransmission of Tc. Furthermore, ex vivo validation revealed a substantial mean bias (exceeding ±0.5°C) between the Tc capsule readings and mercury or electronic thermometers in half of the capsules. When examined over 2 or 3 days, the initial bias (small or large) drifted in excess of ±0.5°C in one out of every four capsules. Since Tc is regulated within a very narrow range in the healthy homeotherm's body (within 1°C), physiological investigations of Tc require great accuracy and precision (better than 0.1°C). Although ingestible capsule methodology appears of great interest for non-invasively monitoring the transit gut temperature, new technology requires a reduction in the inherent error of measurement and elimination of temperature drift and warrants more interlaboratory investigation on the above factors.
Highlights
During the past decades, there has been considerable debate about the potential role of a low resting energy expenditure (EE) as a “thrifty” metabolic trait in the development of obesity [1, 2] and in the ease with which weight is regained after therapeutic slimming [3]
No significant differences in Tc in response to the light exercise or meal were observed due to differences in body mass index (BMI)
The interest in Tc as a potential thrifty metabolic trait stems from a few studies, which have shown a relationship between Tc and BMI or fat mass [10,11,12,13]
Summary
There has been considerable debate about the potential role of a low resting energy expenditure (EE) as a “thrifty” metabolic trait in the development of obesity [1, 2] and in the ease with which weight is regained after therapeutic slimming [3]. There has been renewed interest in examining a low core (or central) body temperature (Tc) as another potential thrifty metabolic trait [4]. Designed to measure exercise and occupational heat stress, telemetric Tc ingestible capsules have been extended for use in the measurement of intestinal Tc in the research setting. Tc capsules offer significant advantages over the traditional measurements of rectal and esophageal temperature, in free-living research participants, and good agreements between telemetric capsules and esophageal and rectal temperature have previously been reported during exercise heat stress [8, 9]. There is increasing interest in the use of pill-sized ingestible capsule telemetric sensors for assessing core body temperature (Tc) as a potential indicator of variability in metabolic efficiency and thrifty metabolic traits. The aim of this study was to investigate the feasibility and accuracy of measuring Tc using the CorTemp® system
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