title: Optimal siting of heat flux transducers for the assessment of body heat loss when immersed in water.
abstract: Regional heat flux (intensity of heat flow rate, W m-2) was measured using heat flux transducers affixed to the skin surface at 14 sites on the left arm and 15 sites on both the left leg and the trunk (total of 44 locations) of human subjects during head-out immersion in water at temperatures between 11 and 28 degrees C. The heat flux data and skin temperature data were collected continuously over a 30-min period taking approximately 2.5 min to scan through all transducers in sequence before repeating the process. There were 3 immersions per individual, monitoring the arm or the leg or the trunk. The local measurements of heat flux from each of the body segments were summated and meaned to obtain a value of overall flux for each area of the body for each 2- to 3-min interval. This mean value was taken as the optimal value (Hopt) for any particular body segment. Every permutation of the positions of any 1, 2, 3, 4, or 5 heat flux transducers from the possible 14 or 15 sites was used to obtain a mean value which could be compared to the Hopt over the total duration of each immersion. Comparisons could be made between the best individual sites (Iopt) and Hopt as well as between the overall best site for the group of 10 people (Gopt) and Hopt. All possible permutations could be ranked in ascending order of preference based on a decreasing sum of the squares of the differences between Hopt and either Iopt or Gopt. Confirmation of the validity of this simple ranking system was based on an analysis of the percentage differences between Iopt or Gopt and Hopt. Such an analysis indicated that the better choice of discs when using a small number of transducers was between 3 and 5 sites, affording both reasonable accuracy and practicality. It is recommended that between 3 and 5 discs be used per body segment at specific locations and the calculated heat loss from each segment be weighted according to its area of representation to give a value for the mean rate of total body heat loss. A reasonable level of accuracy was demonstrated using Gopt permutations for measuring both the rate of heat flow as well as the integral of the data to obtain a value of the quantity of heat (Joules) lost from the body.
mesh_terms: D000328:Adult; D001833:Body Temperature Regulation; D006801:Humans; D007101:Immersion / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D012881:Skin Temperature; D013821:Thermometers; D014159:Transducers