Technique for continuously monitoring core body temperatures to prevent heat stress disorders in workers engaged in physical labor.

OBJECTIVES Measuring core body temperature is crucial for preventing heat stress disorders in workers. We developed a method for measuring auditory canal temperatures based on a thermocouple inserted into a sponge-type earplug. We verified that the tip of this thermocouple is positioned safely, allowing the wearer to engage in normal physical tasks; this position averaged 6.6 mm from the tympanic membrane. METHODS To assess this technique, we had six healthy male students repeat three cycles of exercise and rest (20 min of exercise and 15 min of rest) in a temperature-controlled chamber with temperatures set at 25, 30, or 35 degrees C, while monitoring the auditory canal, esophageal, rectal, and skin temperatures. RESULTS We observed differences of a mere 0.30-0.45 degrees C between rectal temperatures and auditory canal temperatures measured with the thermocouple, the smallest such difference reported to date in studies involving auditory canal temperature measurement. CONCLUSIONS We conclude that monitoring temperatures based on a technique involving an auditory canal plug can be used to estimate rectal temperatures accurately, and thereby to avoid conditions leading to heat stress disorders.