Reexamination of tympanic membrane temperature as a core temperature

Controversies surrounding tympanic temperature (T(ty)) itself and techniques for measuring it have dampened the potential usefulness of T(ty) in determining core temperature (operationally defined here as the body temperature taken at a deep body site). The present study was designed to address the following questions. 1) Can a tympanic membrane probe be made that is safer and more reliable than its predecessors? 2) Why is the effect of facial cooling and heating on T(ty) so inconsistent in reports from different laboratories? 3) Is T(ty) still useful as a measure of core temperature? Data from this study, obtained with a modified thermocouple probe, suggest that the widely reported facial skin cooling effect on T(ty) is most probably due to thermal contamination from the surrounding ear canal wall and/or suboptimal contact of the probe sensor with the tympanic membrane because 1) T(ty) that fell during facial cooling was increased to the precooling level by the repositioning of the probe sensor; 2) T(ty) determined by using a probe with a larger sensor area (the sensor soldered to a steel wire ring) tended to fall in response to facial cooling, whereas T(ty) determined with a thermally insulated probe ring did not; and 3) T(ty) obtained under careful positioning of the insulated probe was relatively insensitive to facial cooling or heating. Because T(ty) was practically identical to esophageal temperature (T(es)) in the steady state, i.e., 36.83 ± 0.20 (SD)°C for T(ty) and 36.87 ± 0.16°C for T(es) at room temperature (n = 11), and because facial cooling had little effect on both T(ty) and T(es) (36.86 ± 0.17°C for T(ty) and 36.86 ± 0.26°C for T(es) during facial or scalp skin cooling), we support the postulate that T(ty) is a good measure of core temperature. The temperature transient in response to foot warming was detected 5 min (n = 2) faster with T(ty) than with T(es). Thus, with further improvements in the design of the probe, T(ty) can become a standard for determination of core body temperature.