Thermographic study on the preservability of heat effects of footbath with salt.

Infrared thermography provides a non-invasive and dynamic measure of heat. The thermal preservability effects of a salt footbath were evaluated by the infrared thermography technique. The subjects were 23 healthy college students. Feet were soaked for 10 min in a 40-42 degrees C normal footbath. Room temperature was set at 26.5-28 degrees C. At the same time on another day within 3 days of the normal footbath experiment, the same feet were soaked for 10 min in a 40-42 degrees C salt footbath. We measured blood pressure, heart rate and temperatures of the feet, second toes, hands and middle fingers, just before and after immersion and at 10-min intervals thereafter. Mean blood pressure changes showed no difference between the normal and the salt footbath. Mean heart rate changes were higher during the normal footbath than at 0, 15 and 20 min during the salt footbath, respectively (p < 0.05). Mean thermal preservability of the feet tended to be lower after the normal footbath than at 20 and 30 min, respectively, after the salt footbath, but these differences did not reach a statistical significance. Mean thermal preservability of the hands and middle fingers was significantly lower after the normal footbath than at 20 and 30 min, respectively, after the salt footbath (p < 0.05). The results suggest that stimulation by a salt footbath affects surface skin temperature, and that stimulation aimed at increasing skin thermal preservability shows a significant difference between normal and salt footbaths.