Energy direct calorimetry

Direct calorimetry Energy expenditure can be measured from the heat lost by an individual, which is the same as that produced. All the energy used in the daily activities of the body is released as heat. For example, the mechanical energy expended walking to work, sprinting for the train or running a marathon is converted into heat. The method used for measuring heat production is known as direct calorimetry (Box 2.1). The individual lives in a... 

Heat capacity is best determined with a calorimeter incorporating an electric heater. The net energy input and the resultant temperature rise are both measured. Procedures and precautions for such direct calorimetry are discussed thoroughly by Sturtevant (1959). Differential scanning calorimetry is convenient to use for the determination of heat capacity (Watson et al. 1964). 

Direct calorimetry (heat production) represents a reliable method for the estimation of total benthic community metabolism, because it is a direct measurement of the energy flow through the system. Although the heat release from the activity of extracellular enzymes and from chemical oxidations are also included, the latter two components are thought to be of minor importance for total heat loss from sediments (Pamatmat, 1982). 

Information about this energy has been obtained from isotherm measurements over a temperature range (3, 7, 8, 9), by calorimetry 18, 19), and by differential thermal analysis (JJ). From the isotherms and by direct calorimetry, the isosteric heats, q t, may be found as functions of the amount of water sorbed. However, some disadvantages may be associated with each procedure. Such is the affinity between water and zeolites that to determine q t for small uptakes may require isotherm measurements at temperatures above 200°C. At these temperatures, lattice breakdown can take place by side reactions involving the water. 

Calculating Energy Expenditures Direct Calorimetry Metabolic Rate... 

The methods of indirect and direct calorimetry may not always result in the same values for energy expenditure. Indirect calorimetry is a measure of the heat produced by oxidative processes. Direct calorimetry measures the rate of dissipation of heat from the body. An increase in the rate of heat production, as with exercise, may not always result in an immediate, measurable increase in heat released by the body (from the skin). Instead, the increase in heat production may result in a rise in body temperature. That part of the energy requirement used to raise... 

The use of direct calorimetry is not a convenient technique, since it requires a specially constructed room and the confinement of human subjects for a day or longer in the room. The doubly labeled water technique offers a convenient alternative, providing that one has a machine to perform isotope ratio mass spectrometry. The doubly labeled water technique is used to measure the rate of total CO2 production in the body. This number alone is not sufficient to allow one to calculate the total energy expenditure. But the value for COj production (moles COi/day), along with the RQ, allows one to calculate the oxygen consumption using the following formula ... 

The energy expenditure of an animal or human may also be determined by the method of direct calorimetry. Direct calorimetry requires the use of an insulated room, chamber, or suit for the human or animal. The enclosure contains a water jacket. The water passes from one end of the jacket to the other, maintaining the room, chamber, or suit at a constant temperature. The temperature of the water leaving the jacket is used to calculate the energy expended by the subject. The principles behind the use of the chamber are identical to those behind the use of the bomb calorimeter. The major difference is that in bomb calorimetry combustion is catalyzed by a small spark. In addition, in the bomb calorimeter oxygen is present at a high pressure to facilitate combustion. With direct calorimetry, combustion is catalyzed by enzymes. This combustion proceeds more slowly than that catalyzed by a spark, and the temperature of the subject does not increase much over the normal resting body temperature with the various activities. 

Other measurements that have been used in the study of defects include HaU effect, thermoluminescence (another direct observation), stored energy (by calorimetry), electrical transport, and electron microscopy. The study of dislocations by this last technique has been an outstanding recent development (33). 

Thermogravimetry (TGA), differential thermoanalysis (DTA), and differential scanning calorimetry (DSC) are the main methods which can be used in the analysis of petroleum and its products. DSC is preferred to DTA, because DSC supplies values of energies directly, whereas the DTA supplies only temperature differences. 

The heat production of animals can be measured physically using a procedure known as direct calorimetry. Alternatively, heat production can be estimated from the respiratory exchange of the animal. For this, a respiration chamber is normally used and the approach is one of indirect calorimetry. Respiration chambers can also be used to estimate energy retention rather than heat production, by a procedure known as the carbon and nitrogen balance technique. 

Although indirect calorimetry has considerable advantages over direct calorimetry, it still only permits measurement of energy expenditure over a period of a few hours. A more recent technique permits estimation of total energy expenditure over a period of 1—2 weeks. This method depends on the administration of dual isotopically labelled water, The rate at which the labelled water is lost from the body is determined... 

Measurement of Energy Expenditures Direct Calorimetry Indirect Calorimetry Basal Metabolic Rate (BMR)... 

Direct calorimetry is the most accurate method of measuring the heat production of people, but it is costly and arduous. The machine itself is very expensive to build and maintain and considerable labor is involved in running the machine and analyzing the results. For these reasons, indirect calorimetry is usually the method of choice for the measurement of energy expenditures. 

The two most crucial differences between the two techniques are (a) in DSC, the sample and reference have their own heaters and temperature sensors as compared to DTA where there is one common heater for both (b) DTA measures AT versus temperature, and, therefore, must be calibrated to convert AT into transition energies, while DSC obtains the transition energy directly from the heat measurement. The confusion is also partly due to the fact that there are at least three different types of DSC instruments a DTA calorimeter, a heat-flux type (Fig. 2c), and a power compensation (Fig. Id) one. This, in turn, arises from the fact that some define calorimetry as quantitative-DTA. As opposed to conventional DTA, the thermocouples in a DSC instrument do not come into contact with either the sample or reference. Instead, they either surround the sample (thermopiles) or are simply outside the sample (thermocouples). Furthermore, the sample and reference weights are usually under 10 mg. 

The determination of the related surface enthalpy terms //Jq and H[q from direct calorimetry measurements provides an alternative way to evaluate the hydrophobic-hydrophilic character of a solid surface [38, 42-44], since the following deconvolution procedures may be proposed for the surface enthalpy in analogy with those holding for the Gibbs energy (Eqs. 6.8-6.13a, 6.13b) ... 

The thermodynamic values tabulated are derived from the full arsenal of methods available such as enthalpy or internal energy measurements by direct calorimetry, cryogenic heat capacity measurements from sufficiently low temperature to permit entropy evaluation at room temperature, as well as some... 

It was often stated that energy allocation in ecological systems can be described by dry mass distribution and that it is not necessary to perform calorimetric experiments. Other authors hold that "For the ecologist dealing with specific time and energy budgets or population energetics, direct calorimetry of representative members of the population is a prerequisite for accuracy" [26]. Hickman and Pi-... 

For the ecologist dealing with specific time and energy budgets or population energetics, direct calorimetry of representative members of the population is a prerequisite for accuracy." [26]. 

Since enthalpy change is measurable by direct calorimetry, a balance can be set-up and verified with the experimentally determined reaction rates. At constant pressure (which is the case of bioreactors) and if no work is performed, the energy balance reads ... 

Direct calorimetry gives insight in the thermodynamics of growth. Although Gibbs energy dissipation, which is the fundamental thermodynamic variable to determine, can not be directly measured, the difference with enthalpy production, which is determined by direct calorimetry, is small for aerobic processes, or can be calculated for anaerobic processes. 

Calorimetry is still in use today, but the emphasis in biological and medical research went from direct to indirect calorimetry in the last decades. This was mainly caused by two reasons. The first one is a huge improvement in gas analysis instrumentation compared with that of the instrumentation of direct calorimetry. The second reason is, that indirect calorimetry provides not only with measures of energy expenditure, but the substrate oxidation rates too. This is in biology related fields probably of at least the same significance than energy expenditure alone. 

It is possible, of course, to use direct calorimetry, often in combination with the indirect approach (OUR) to investigate the properties of muscle under different physiological conditions and in the diseased state. Chinet s group [70] found that the slow- and fast-twitch skeletal muscle fibres from the murine model of Duchenne muscular dystrophy had a reduced sarcoplasmic energy metabolism as measured by the combined direct and indirect calorimeter [69]. The possibility that this could be due to diminished glucose availability was then examined [71] but was dismissed in favour of decreased oxidative utilisation of glucose and free fatty acids, conceivably due to defective mitochondria. 

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