TELEMETRY PILL MEASUREMENT OF CORE TEMPERATURE IN HUMANS DURING ACTIVE HEATING AND COOLING

Purpose: This study compared the agreement between core temperature me asurements obtained using an ingestible temperature pill telemetry sys tem (T-pill) with those obtained from rectal (T-re) and esophageal (T- es) thermocouples under conditions of increasing and decreasing body t emperature. Methods: Four men and five women (age 25 +/- 2 yr, BSA 1.8 1 +/- 0.05 m(2), (V)over dot O-2 peak 3.1 +/- 0.4 L.min(-1)) participa ted in four 3-h trials: cold (18 degrees C) water rest (CWR), cold wat er exercise (CWE), warm (36 degrees C) water rest (WWR), and warm wate r exercise (WWE). Subjects were immersed to the neck for each trial. D uring resting trials, subjects sat quietly. During exercise trials, su bjects completed three bouts of 15 min of rest, followed by 45 min of exercise on a cycle ergometer at 50% of peak oxygen uptake. The temper ature pill was taken 10-12 h before testing, after which the subjects fasted. Results: The trials created conditions of constantly decreasin g (GWR) or increasing (WWR) core temperature, as well as periods of os cillating core temperature (CWE and WWE). Root mean squared deviation (RMSD) was calculated for each pair of measurements (T-pill vs T-re, T -pill vs T-es, T-re vs T-es) for each trial. An RMSD of ''0'' indicate s perfect agreement; as RMSD increases, agreement worsens. On CWR, the RMSD for T-pill-T-es (0.23 +/- 0.04) was lower (P < 0.05) than for T- pill-T-re (0.43 +/- 0.10) or T-re-T-es (0.46 +/- 0.09). There were no significant differences in RMSD between measurement pairs on any other trial (average RMSD = 0.26 degrees C). Telemetry pill temperature and response time tended to be intermediate between T-re and T-es. Conclu sion: These results suggest the telemetry pill system provides a valid measurement of core temperature during conditions of decreasing as we ll as increasing body temperature and during steady state.