Partitional calorimetry

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.

Relationship between body heat content and finger temperature during cold exposure

The purpose of the present experiment was to examine the relationship between rate of body heat storage (S˙), change in body heat content (ΔHb), extremity temperatures, and finger dexterity. S˙, ΔHb , finger skin temperature (Tfing), toe skin temperature, finger dexterity, and rectal temperature were measured during active torso heating while the subjects sat in a chair and were exposed to −25°C air. S˙ and ΔHb were measured using partitional calorimetry, rather than thermometry, which was used in the majority of previous studies. Eight men were exposed to four conditions in which the clothing covering the body or the level of torso heating was modified. After 3 h, Tfing was 34.9 ± 0.4, 31.2 ± 1.2, 18.3 ± 3.1, and 12.1 ± 0.5°C for the four conditions, whereas finger dexterity decreased by 0, 0, 26, and 39%, respectively. In contrast to some past studies, extremity comfort can be maintained, despite S˙ that is slightly negative. This study also found a direct linear relationship between ΔHb and Tfing and toe skin temperature at a negative ΔHb. In addition, ΔHb was a better indicator of the relative changes in extremity temperatures and finger dexterity over time than S˙.

Determination of heat debt in the cold: partitional calorimetry vs. conventional methods

Measurements of core temperature (Tc) at different sites produce on some occasions different cooling curves in cold-exposed humans, suggesting that the corresponding thermometric heat debts (HD) could be equally different when calculated by conventional methods [via the change in either Tc or mean body temperature (Tb)]. The present study also compared these thermometric HD values with the calorimetric HD obtained by partitional calorimetry (S). Nine subjects who showed similar initial but different final Tc [rectal (Tre) and auditory canal temperatures (Tac)] during nude cold exposure (2 h at 1 degrees C at rest) were used. Tc-derived HD corresponded to a heat gain of 12 +/- 21 kJ and an HD of 78 +/- 20 kJ with use of Tre and Tac, respectively, whereas the Tb-derived HD varied from 266 +/- 35 to less than or equal to 1,479 +/- 71 kJ with the use of various well-known Tb weighing coefficients. In contrast, S corresponded to 504 +/- 79 kJ, a level that could have been obtained only if the thermoneutral/cold Tb weighing coefficients had been 0.818/0.818 for Tre and 0.865/0.865 for Tac. The results demonstrate that calculation by conventional methods can markedly overestimate or underestimate HD. These differences could not be explained by the site chosen to represent Tc, inasmuch as about the same effect was observed with use of either Tre or Tac. It is concluded that the thermometric value of HD in the cold is not, at least under the present conditions, as accurate and reliable as S.

Thermal balance in ketamine-anesthetized rhesus monkey Macaca mulatta

A partitional calorimetry study compared thermoregulatory responses of unanesthetized adult rhesus monkeys (4 female, 1 male) to those anesthetized with ketamine HCl and exposed to ambient temperature (Ta) of 18, 29, 38 degrees C. Steady-state metabolic heat production (M), mean skin temperature (Tsk), rectal temperature (Tre), respiratory evaporative heat loss (Eres), and total evaporative heat loss (Etot) were measured at each Ta. Average Tre of anesthetized animals was reduced by approximately 1 degree C at Ta 18 degrees C, but thermal balance in anesthetized and control animals was maintained by reflexly decreased tissue conductance and shivering. For anesthetized animals, the average M increased 1.8 times over the lowest value of 40.13 W/m2 at Ta 29 degrees C, compared to a 1.5-fold increase for controls. Responses for both groups were not different at Ta 29 degrees C, both groups regulated body temperatures by vasodilation and increased sweating, but with ketamine sweating was reduced (35%). Effective tissue thermal conductance (K) was lowest at Ta 18 (10.8 W/m2 . degrees C) and increased to 39.4 W/m2 . degrees C at Ta 38 degrees C. No significant difference in K was found between ketamine and control groups at other Ta's.

Experimental study of convective heat transfer coefficient for the human body in water

The steady-state convective heat transfer coefficient in water has been determined by partitional calorimetry for 17 nude subjects. Four water velocities were investigated: 0, 0.05, 0.10, and 0.25 m-s-1; and the water temperature ranged from 33.7 to 18 degrees C. In still water, hc varied from 43 W-m-2-degrees C-1 in thermoneutral conditions and a shivering rate less than 90 W-m-2 to 54 W-m-2-degrees C-1 in cold water with a shiver rate greater than 110 W-m-2. The equation, hc=0.09 (Gr-Pr)0.275, give a good approximation of this coefficient. In stirred water and for the same limits of shivering, hc can be expressed as a power function of the velocity: hc = 272.9 v0.5 and hc = 497.1 v0.65, respectively. These equations show that the flow is laminar in thermoneutral conditions and intermediate between laminar and turbulent in cold water. A study of the influence of skinfold on the magnitude of hc shows that higher values of this coefficient were obtained for thin subjects than for fat ones, concomitant with more intense shivering. The utilization of a theoretical physical model for computations of hc gave excessively high values because such methods do not embody the body shape factor and reduction of water flow adjacent to the skin.

Thermoregulation during marathon running in cool, moderate, and hot environments

A well-trained subject, age 38, ran continously for periods ranging from 60 to 165 min on a motor-driven treadmill at 255.7 m/min while confronted with an airflow equivalent to running speed in cool, moderate, and hot environments. After a period of intensive heat acclimatization, treadmill runs were repeated in the moderate and hot conditions. Measurements were also obtained outdoors in a competitive marathon race. Sweat rate (SR) and mean skin temperature (Ts) were linearly related to Tdb. Acclimatization did not alter VO2max or metabolic rate during the treadmill runs, but heart rat (HR),rectal temperature (Tre), and Ts were lower, SR was higher, and maximal run duration longer in the hot environment, postacclimatization. Maximum runs in the hot environment were terminated by a spiralling increase in Tre to hyperthermic levels, due largely to a marked reduction in cutaneous blood flow, probably reflecting cardiovascular overload from the combined muscular and thermoregulatory blood flow demands, coupled with the effects of progressive dehydration. Utilizing partitional calorimetry and the subject's metabolic heat production, two examples of limiting environmental conditions for his marathon running speed were given.