Estimating changes in volume-weighted mean body temperature using thermometry with an individualized correction factor
This study investigated whether the estimation error of volume-weighted mean body temperature (ΔT̄b) using changes in core and skin temperature can be accounted for using personal and environmental parameters. Whole body calorimetry was used to directly measure ΔT̄b in an Experimental group (EG) of 36 participants (24 males, 12 females) and a Validation group (VG) of 20 (9 males, 11 females) throughout 90 min of cycle ergometry at 40°C, 30% relative humidity (RH) ( n = 9 EG, 5 VG); 30°C, 30% RH ( n = 9 EG, 5 VG); 30°C, 60% RH ( n = 9 EG, 5 VG); and 24°C, 30% RH ( n = 9 EG, 5 VG). The core of the two-compartment thermometry model was represented by rectal temperature and the shell by a 12-point mean skin temperature (ΔT̄sk). The estimation error (X0) between ΔT̄b from calorimetry and ΔT̄b from thermometry using core/shell weightings of 0.66/0.34, 0.79/0.21, and 0.90/0.10 was calculated after 30, 60, and 90 min of exercise, respectively. The association between X0 and the individual variation in metabolic heat production (M − W), body surface area (BSA), body fat percentage (%fat), and body surface area-to-mass ratio (BSA/BM) as well as differences in environmental conditions (Oxford index) in the EG data were assessed using stepwise linear regression. At all time points and with all core/shell weightings tested, M − W, BSA, and Oxford index independently correlated significantly with the residual variance in X0, but %fat and BSA/BM did not. The subsequent regression models were used to predict the thermometric estimation error (X0_pred) for each individual in the VG. The value estimated for X0_pred was then added to the ΔT̄b estimated using the two-compartment thermometry models yielding an adjusted estimation (ΔT̄b_adj) for the individuals in the VG. When comparing ΔT̄b_adj to the ΔT̄b derived from calorimetry in the VG, the best performing model used a core/shell weighting of 0.66/0.34 describing 74%, 84%, and 82% of the variation observed in ΔT̄b from calorimetry after 30, 60, and 90 min, respectively.