Partitional calorimetry

Abstract

For thermal physiologists, calorimetry is an important methodological tool to assess human heat balance during heat or cold exposures. A whole body direct calorimeter remains the gold standard instrument for assessing human heat balance; however, this equipment is rarely available to most researchers. A more widely accessible substitute is partitional calorimetry, a method by which all components of the conceptual heat balance equation-metabolic heat production, conduction, radiation, convection, and evaporation-are calculated separately based on fundamental properties of energy exchange. Since partitional calorimetry requires relatively inexpensive equipment (vs. direct calorimetry) and can be used over a wider range of experimental conditions (i.e., different physical activities, laboratory or field settings, clothed or seminude), it allows investigators to address a wide range of problems such as predicting human responses to thermal stress, developing climatic exposure limits and fluid replacement guidelines, estimating clothing properties, evaluating cooling/warming interventions, and identifying potential thermoregulatory dysfunction in unique populations. In this Cores of Reproducibility in Physiology (CORP) review, we summarize the fundamental principles underlying the use of partitional calorimetry, present the various methodological and arithmetic requirements, and provide typical examples of its use. Strategies to minimize estimation error of specific heat balance components, as well as the limitations of the method, are also discussed. The goal of this CORP paper is to present a standardized methodology and thus improve the accuracy and reproducibility of research employing partitional calorimetry.

Keywords: convection; evaporation; heat loss; heat production; heat storage; radiation.

Fig. 1.

Estimated combinations of air temperature, air velocity, relative humidity (RH), and metabolic heat production (H_prod) that elicit a skin wettedness required for heat balance (ω_req) of 0.50, the critical value above which the evaporative efficiency of sweat is reported to decline from 100%. Note that selected conditions should be cooler, drier, windier, and/or with a lower heat production so that the actual ω_req is lower than 0.50. Example given for a 1.8-m² individual cycling [fraction of body surface participating in radiative heat transfer (A_r/A_D) = 0.73] with light clothing [dry heat transfer resistance of clothing (R_cl): 0.045 m²⋅°C⋅W⁻¹ (0.3 clo); evaporative resistance of clothing (R_e,cl): 0.010 m²⋅kPa⋅W⁻¹].

Fig. 2.

Example of total quantities of energy exchanged and stored with the ingestion of cold (1.5°C) or body temperature-controlled (38°C) water during exercise under neutral environmental conditions. ΔH_b, change in body heat storage; H_fluid, energy exchanged between body tissues and ingested water; H_{evap_skin}, evaporative heat loss; H_res, respiratory heat loss; H_dry__skin, dry heat loss; H_prod, metabolic heat produced. Negative values indicate heat loss (i.e., cooling). In this example, net body heat storage is slightly greater with the ingestion of cold fluid because of a corresponding attenuation in whole body evaporative heat loss.