Validation of a new telemetric core temperature monitor

The purpose of this study was to validate the accuracy and acceptability of the new VitalSense^® telemetric physiological monitoring system (Mini Mitter Co., Inc., Bend, OR). It consists of a receiver/monitor and a thermistor-based ingestible capsule for core body temperature measurement. For comparison, each subject was also monitored with a standard thermistor probe inserted 11 cm beyond the anal sphincter (Mini-Logger^® Series 2000). Both the measurement systems have specified accuracy of ±0.1 °C.

Ten volunteers, four females, six males, mean age 51.1±11.8 years, gave informed consent to wear the two systems for the duration of the passage of the temperature capsule through their digestive tracts. Minute-by-minute comparisons were made between the temperatures recorded by the two systems. Parameters reported include: average transit time of the capsule; temperature at each minute of the experiment; mean difference in temperature at each time point; correlation coefficient for the two temperature measurements; and number of missed data points for each system.

Mean capsule transit time was 48.6±35.5 h with a range of 12.4–136.2 h. The mean temperature for all subjects was 36.93 °C±0.15 °C and 36.96 °C±0.16 °C for the capsule and rectal probe respectively, with no significant difference between the means. The mean difference between readings (capsule–rectal probe) was 0.04 °C±0.03 °C. There was a significant correlation between the capsule and rectal probe temperatures, R²=0.80,p<0.05 and R²=0.90,p<0.05 for all data points and quiescent periods respectively. Of the average 2916±2132 data points per subject, there was a significant (p<0.05) difference in data points lost, 105±120 with VitalSense vs. 449±697 with the rectal probe. The percentage of missing data points was 3.1%±2.5% for the capsule (monitor out of the one-meter range of the capsule) and 11.4%±15.9% for the rectal probe (primarily due to probe slippage, but also due to removal for personal hygiene). The data support the finding that the VitalSense core body temperature monitoring system is at least as accurate as rectal probe monitors and the subjects found it to be much more acceptable.