A simplified procedure of direct calorimetry for bedside monitoring of the resting metabolic rate

A simplified procedure of direct calorimetry (SPDC) for determination of resting metabolic rate of respiratory uncompromised subjects in a supine position is presented. This procedure was based on computer-assisted measurements of heat losses due to evaporation, radiation, conduction, and convection. The subject's total loss of mass was recorded hydraulically with a beam scale and afterwards transformed into a digital electric signal. Differences between dry bulb temperature and mean skin temperature were measured by semiconductor thermistors and also transformed into digital signals. With special software an interfaced personal computer assisted in performing SPDC and in calculating heat losses due to evaporation, radiation, and conduction. In a thermoneutral environment,six healthy volunteers were investigated to determine the mean convective heat transfer coefficient (h_c) from the difference in an individual between the metabolic energy transformation (M) measured by indirect calorimetry (IC) and the sum of heat losses by radiation, conduction, and evaporation. The room-specific value of h_c of 2.12 (SD 0.22) W·m^–2·°C^–1 was in good agreement with data in the literature. Compared to the results of M from a second series of IC, the total heat loss (THL) measured by SPDC in a thermoneutral environment was calculated as 100.5 (SD 6.0) %. The THL by SPDC performed three times at 3-h intervals on ten other volunteers revealed a mean difference of 0.22 (SD 1.74) W·m^–2. Thus, SPDC would seem to be a valid and reproducible method under conditions of thermal neutrality.