Errors involved in using thermal flux transducers under various conditions.

Commercially available sensors are being used by several investigators to measure thermal flux through the skin and skin temperature at a given site. Since these transducers place an additional thermal resistance into the system, they perturb the quantities that are being measured. This problem has been analyzed theoretically to obtain the following relatively simple equations: (Q0 - Q)/Q0 = EQ = QRt/(Ta - Te) and (Ts - Ts,0)/(Ta - Te) = [EQ/(1 - EQ)] [1 - EQ2 - (Ts - Te)/(Ta - Te)] in which Q = measured thermal flux; Rt = thermal resistance of the transducer; Ta, Ts, and Te = deep tissue, skin, and environmental temperatures, respectively; and the subscript 0 denotes unperturbed values. These equations can be rearranged easily to obtain improved estimates for the unperturbed values, Q0 and Ts,0, using the measured values, Q and Ts. Use of these relationships to estimate errors for various conditions previously reported in the literature reveals that the EQ can be as large as 10% to 20% for nude subjects in hyperbaric heliox or water, and the error in skin temperature can exceed 1 degree C. When used under a 1-clo garment, the transducer will perturb Q by 4% and Ts by 0.3 degrees C.