The Validity of Temperature-Sensitive Ingestible Capsules for Measuring Core Body Temperature in Laboratory Protocols

Abstract

The human core body temperature (CBT) rhythm is tightly coupled to an endogenous circadian pacemaker located in the suprachiasmatic nucleus of the anterior hypothalamus. The standard method for assessing the status of this pacemaker is by continuous sampling of CBT using rectal thermometry. This research sought to validate the use of ingestible, temperature-sensitive capsules to measure CBT as an alternative to rectal thermometry. Participants were 11 young adult males who had volunteered to complete a laboratory protocol that extended across 12 consecutive days. A total of 87 functional capsules were ingested and eliminated by participants during the laboratory internment. Core body temperature samples were collected in 1-min epochs and compared to paired samples collected concurrently via rectal thermistors. Agreement between samples that were collected using ingestible sensors and rectal thermistors was assessed using the gold-standard limits of agreement method. Across all valid paired samples collected during the study (n = 120,126), the mean difference was 0.06°C, whereas the 95% CI (confidence interval) for differences was less than ±0.35°C. Despite the overall acceptable limits of agreement, systematic measurement bias was noted across the initial 5 h of sensor-transit periods and attributed to temperature gradations across the alimentary canal. (Author correspondence: [email protected])

Keywords:

• Circadian rhythm
• Core body temperature
• Ingestible sensors
• Limits of agreement
• Validation

ACKNOWLEDGMENTS

This study was financially supported by the Australian Research Council under the Discovery Project grant scheme.

Declaration of Interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Notes

¹The range (mean ± 2SD) of normal human body temperature measured via rectal thermistor is reported to be 34.4°C to 37.8°C, based on meta-analytic review of 20 studies that included 347 participants (Sund-Levander et al., 2002).