Nasal mucosal vasodilatation in response to passive hyperthermia in humans

The present study was conducted to measure nasal mucosal blood flow (NMBF) during body warming. Five subjects [mean (SD) 24 (2) years], wearing only shorts and a thick felt hat with ear flaps, were immersed to the neck in a bath at 40 (0.5) degrees C. Tympanic (Tty), esophageal (Tes), mean unweighted skin (Tsk), nose skin and ear pinna skin were recorded at 1-min intervals. NMBF on the lower septal wall was estimated using a laser Doppler flow meter. At rest Tty and Tes were both 36.5 degrees C. Tty dropped significantly below Tes during body warming, despite impeded heat loss from the head due to the felt hat. Tty increased to 37.3 degrees C and Tes increased to 37.5 degrees C during the immersion. During the immersion all skin temperatures were steady or increasing, ruling out the possibility of a contamination of Tty from Tsk. Body warming significantly (P = 0.001) increased NMBF by approximately three times from resting values at the end of immersion. During the period of increasing core temperatures NMBF was significantly correlated to Tty (r = 0.93, P = 0.0001) and Tes (r = 0.97, P = 0.0001), suggesting the blood flow change in this tissue was a thermoregulatory response. The increased NMBF during hyperthermia supports the hypothesis of respiratory cooling involvement in selective brain cooling of humans.