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      Partitional calorimetry

      1 , 2 , 3
      Journal of Applied Physiology
      American Physiological Society

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          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.

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          Most cited references67

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          Heat stroke: role of the systemic inflammatory response.

          Heat stroke is a life-threatening illness that is characterized clinically by central nervous system dysfunction, including delirium, seizures, or coma and severe hyperthermia. Rapid cooling and support of multi-organ function are the most effective clinical treatments, but many patients experience permanent neurological impairments or death despite these efforts. The highest incidence of heat stroke deaths occurs in very young or elderly individuals during summer heat waves, with ∼ 200 deaths per year in the United States. Young, fit individuals may experience exertional heat stroke while performing strenuous physical activity in temperate or hot climates. Factors that predispose to heat stroke collapse include pre-existing illness, cardiovascular disease, drug use, and poor fitness level. For decades the magnitude of the hyperthermic response in heat stroke patients was considered the primary determinant of morbidity and mortality. However, recent clinical and experimental evidence suggests a complex interplay between heat cytotoxicity, coagulation, and the systemic inflammatory response syndrome (SIRS) that ensues following damage to the gut and other organs. Cytokines are immune modulators that have been implicated as adverse mediators of the SIRS, but recent data suggest a protective role for these proteins in the resolution of inflammation. Multi-organ system failure is the ultimate cause of mortality, and recent experimental data indicate that current clinical markers of heat stroke recovery may not adequately reflect heat stroke recovery in all cases. Currently heat stroke is a more preventable than treatable condition, and novel therapeutics are required to improve patient outcome.
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            The evaporative requirement for heat balance determines whole-body sweat rate during exercise under conditions permitting full evaporation.

            Although the requirements for heat dissipation during exercise are determined by the necessity for heat balance, few studies have considered them when examining sweat production and its potential modulators. Rather, the majority of studies have used an experimental protocol based on a fixed percentage of maximum oxygen uptake (% ). Using multiple regression analysis, we examined the independent contribution of the evaporative requirement for heat balance (Ereq) and % to whole-body sweat rate (WBSR) during exercise. We hypothesised that WBSR would be determined by Ereq and not by % . A total of 23 males performed two separate experiments during which they exercised for 90 min at different rates of metabolic heat production (200, 350, 500 W) at a fixed air temperature (30°C, n = 8), or at a fixed rate of metabolic heat production (290 W) at different air temperatures (30, 35, 40°C, n = 15 and 45°C, n = 7). Whole-body evaporative heat loss was measured by direct calorimetry and used to calculate absolute WBSR in grams per minute. The conditions employed resulted in a wide range of Ereq (131-487 W) and % (15-55%). The individual variation in non-steady-state (0-30 min) and steady-state (30-90 min) WBSR correlated significantly with Ereq (P < 0.001). In contrast, % correlated negatively with the residual variation in WBSR not explained by Ereq, and marginally increased (∼2%) the amount of total variability in WBSR described by Ereq alone (non-steady state: R(2) = 0.885; steady state: R(2) = 0.930). These data provide clear evidence that absolute WBSR during exercise is determined by Ereq, not by % . Future studies should therefore use an experimental protocol which ensures a fixed Ereq when examining absolute WBSR between individuals, irrespective of potential differences in relative exercise intensity.
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              Respiratory gas-exchange ratios during graded exercise in fed and fasted trained and untrained men.

              We evaluated the hypotheses that endurance training increases relative lipid oxidation over a wide range of relative exercise intensities in fed and fasted states and that carbohydrate nutrition causes carbohydrate-derived fuels to predominate as energy sources during exercise. Pulmonary respiratory gas-exchange ratios [(RER) = CO2 production/O2 consumption (VO2)] were determined during four relative, graded exercise intensities in both fed and fasted states. Seven untrained (UT) men and seven category 2 and 3 US Cycling Federation cyclists (T) exercised in the morning in random order, with target power outputs of 20 and 40% peak VO2 (VO2 peak) for 2 h, 60% VO2 peak for 1.5 h, and 80% VO2 peak for a minimum of 30 min after either a 12-h overnight fast or 3 h after a standardized breakfast. Actual metabolic responses were 22 +/- 0.33, 40 +/- 0.31, 59 +/- 0.32, and 75 +/- 0.39% VO2 peak. T subjects showed significantly (P 40% maximal VO2, they will not oxidize a greater proportion of lipids compared with untrained subjects, regardless of nutritional state.
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                Author and article information

                Journal
                Journal of Applied Physiology
                Journal of Applied Physiology
                American Physiological Society
                8750-7587
                1522-1601
                February 01 2019
                February 01 2019
                : 126
                : 2
                : 267-277
                Affiliations
                [1 ]Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
                [2 ]Thermal Ergonomics Laboratory, Faculty of Health Sciences, The University of Sydney, Sydney, NSW, Australia
                [3 ]Charles Perkins Centre, The University of Sydney, Sydney, NSW, Australia
                Article
                10.1152/japplphysiol.00191.2018
                6397408
                30496710
                f240e306-65ac-4268-a167-0a0605aefb2d
                © 2019
                History

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