No evidence for brain stem cooling during face fanning in humans.

The interpeak latencies (IPLs) of the acoustically evoked brain stem potentials depend on brain stem temperature. This was used to see whether face fanning during hyperthermia lowers brain stem temperature. In 15 subjects, three thermally stable conditions were maintained by a water bath. In each condition the IPLs were determined in 10 separate trials. In condition A esophageal temperature (Tes) was 36.9 +/- 0.3 degrees C and increased to 38.6 +/- 0.2 degrees C in condition B. In conditions A and B the head was enclosed in a ventilated hood (air temperature 38 degrees C, relative humidity 100%) to suppress any direct heat loss from the head. From conditions A to B the IPL at peaks I-V decreased by 0.146 ms/degrees C change in Tes, reflecting a change in brain stem temperature. In condition C the hood was removed and the face was fanned by a cold air-stream (8-15 degrees C, 4-10 m/s) to maximize direct heat loss from the head. Skin temperature at the sweating forehead decreased from 38 to 23 degrees C, whereas Tes in condition C was maintained at the same level as in condition B (38.5 +/- 0.2 degrees C). The IPL at peaks I-V showed no difference between conditions B and C. It is concluded that face fanning in hyperthermic subjects does not dissociate brain stem temperature from Tes.