COMPARISON OF BRAIN AND TYMPANIC TEMPERATURES DURING PASSIVE HEATING AND EXERCISE IN EWES

Tympanic temperature (Tty) is considered a valid index of brain temperature (1). However, several researchers have questioned its validity as a measure of brain temperature because it may be significantly influenced by ambient temperature (2,3). In spite of this controversy, use of a portable, noninvasive, infrared thermometer to assess tympanic temperature has become wide-spread. Although infrared thermometry has been validated against other indices of core temperature during hypothermic conditions in humans (4), comparison of infrared thermometry to direct assessment of brain temperature has not been made. Furthermore, whether infrared Tty may provide a better index of elevated brain temperature when ambient temperature is held constant is unknown. Therefore, the purpose of the present investigation was to compare Tty using infrared thermometry with brain temperature (fbr) during exercise and passive heating in ewes. METHODS Three adult Dorset ewes were chronically implanted with a multiple guide cannula assembly attached to the skull. Using roentgenograms, we determined the specific guide cannula for placement of a copper-constantan thermocouple into the 3rd ventricle for assessment of Tbr. Using this model we have been able to simultaneously measure brain temperature and neuropeptides during exercise (5). Tty was determined using two brands of infraredthermometers (ftyl =Thermoscan®PRO-l; Tty2 =FirstTemp®Genius™) set to the "core&quot