Oral temperature as an index of core temperature during heat transients

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Abstract
Rectal (Tre), oral (Tor) and oesophageal (Tes) temperatures were measured in five exercising subjects exposed for two hours to five conditions (1) a steady condition (WR) involving a constant work load (50 W) at a constant air temperature (Ta=36.5‡ C); (2) air temperature variations (δTa) between 28‡ C and 45‡ C and (3) between 23‡ C and 50‡ C at constant work load (50 W); (4) and (5) to work load variations (δW) between 25 W and 75 W at a constant Ta (=36.5‡ C). Oral temperature recordings were taken sublingually and were either continuous or discontinuous. When discontinuous, the time needed for Tor to stabilize after the mouth opening was taken into account. The respective reliability of Tor and Tre as estimates of Tes were compared in each condition. Results showed that the resting (Tor−Tes) difference (+0.12‡ C) was barely modified after two hours of exposure, whereas Tre overestimated Tes by 0.2‡ C to 0.4‡ C depending on the condition. The Tor variations were highly correlated with Tes variations under steady condition and under air temperature variations. In these conditions, Tor represented the best estimate of Tes. Under work-load variations, Tor was less closely related to Tes than was Tre. It is suggested that the relative inertia of Tor to step changes in exercise intensity could be ascribed to work induced variations in mouth blood flow.