Infrared tympanic temperature as a predictor of rectal temperature in warm and hot conditions.

BACKGROUND

Infrared (IR) thermometry has been proposed as a rapid, non-invasive means of monitoring core temperature. However, it has not been validated for use in warm to hot environments.

HYPOTHESIS

IR tympanic temperature (Tty) accurately predicts rectal temperature (Tre) during simulated marching in warm and hot conditions.

METHODS

Tty, and thermistor-derived Tre, aural canal (Tac) and cheek skin (T cheek) temperatures were monitored in seven males during 100 min of treadmill walking, in combat uniforms, at 5 km.h-1, slope 6%, in warm (30 degrees C, 60% RH) and hot (40 degrees C, 30% RH) conditions.

RESULTS

Tty was significantly different to Tre in hot, but not warm, conditions. Final Tty was 0.2 degrees C < Tre in warm, but 0.4 degrees C > Tre in hot, conditions. From 60-100 min of the warm trial, Tty predicted Tre with a standard error of estimate (SEE) of 0.15 degrees C (r = 0.9, p < 0.0001). In a multiple regression model, the combination of Tty, Tac, and Tcheek reduced this SEE to 0.1 degrees C. In the H trial, from 60-100 min Tty predicted Tre with a SEE of 0.21 degrees C (r = 0.7, p < 0.0001). Tty and Tac correlated significantly in both trials.

CONCLUSIONS

(1) the IR method should provide useful estimates of Tre in the field provided the influence of ambient conditions is taken into account; (2) the IR method is not as reliable as rectal monitoring in distinguishing accurately between degrees of heat strain; and (3) Tre prediction with the IR device may be improved in warm conditions if skin temperatures are combined with Tty.