Calorimetric chamber

An additional benefit of the TAM system is that it is possible to purchase a range of apparatus that fit within the calorimetric chambers. Examples of such equipment include RH vessels, titration vessels, and a solution calorimeter. It is also not outside the bounds of possibility to construct a piece of apparatus to do a specific job oneself, if no such item is commercially available. 

With fixed-cell instruments, samples must be loaded directly into the calorimetric chamber, and the need for a metal pan or batch cell is eliminated. Such a system... 

Whole room calorimetry is considered the gold standard for measuring energy expenditure in humans. Although the subject is free to move around in the calorimetric chamber, spontaneous physical activity is greatly reduced. Furthermore, the measurement is carried out under strictly controlled, artificial environmental conditions and often is of short duration (<24 hr). However, indirect calorimetry does provide important information about the basal metabolic rate, respiratory quotient, sedentary energy expenditure, and sleeping metabolic rate. 

Amer. Ceram. Soc., 38,27,1955). A stack of ceramic rings, each 2 in. (50 mm) o.d. and 1 in. (25 mm) i.d., and V2 in. (12.5 mm) long, are heated from the inside by a heating element and cooled from the outside by a calorimetric chamber. Both thermal conductivity and thermal-shock resistance can be evaluated (cf. brittle-ring test). 

Fig. 11.17 Scheme of the calorimetric device (1) calorimetric chambers (2) calorimetric cells (reaction and blank) (3-8) needle valves (9) vacuum gauge (10) pressure gauge (11) hydrogen source... 

In order to circumvent the low flexibility of use of the heat conduction calorimeters, a conventionally equipped bioreactor is coupled to a small heal conduction calorimeter [14]. The by-pass enters the calorimeter and heat production is measured by the difference between the voltage signal measured between the reaction chamber and the reference vessel. The advantage of this configuration is the concurrent operation of the bioreactor in a classical fashion and the measurement the heat flow rate with a low detection limit (2-3 mW dm ). However, the by-pass leads to a time delay, heat losses are possible and there is no proof that environment conditions in the calorimetric chamber are those in the bioreactor. In particular, pH and substrate concentrations are certainly different. 

Whole body calorimetry is not necessarily confined to a calorimetric chamber, although this type of equipment is dominant. Direct calorimetry is also possible with a water cooled garment [11]. Indirect calorimetry can perfectly be done in a chamber, but also by using a mask, a canopy or a ventilated hood. A canopy is a hard cover for the head or the upper part of the body, usually applied to patients laying on a bed. Calorimetry on animals is usually done in a calorimetric chamber or cage on farm animals masks have also been used. 

A calorimetric chamber is used for periods of between a day and a week or even longer. So the chamber has to be as similar to a living room as possible, although its volume has to be limited to improve the response time and accuracy of the system. Chambers contain, in addition to the necessary sensors, air locks for the transfer of food, excreta and blood samples, etc. and some utilities for comfortable housing the subjects. This includes a foldable bed, personal hygiene facilities, a desk and chair, some consumer electronics and typically some workout equipment like a bicycle ergometer. An example of a chamber is shown in Figure 1. 

Direct calorimetry is the measurement of the heat loss (HL) of a subject. It is usually be done in specialised calorimetric chambers [12-14], but was done with heat exchanging body suits [II] too. Heat dissipation may occur in different ways. It can be direct heat transfer to the stationary environment (usually the chamber) or heat transfer to the air being pumped through the chamber. Another way is heat used to vaporise body water (and probably other water from inside the chamber like washing water or sweat, previously stored in clothing or chamber interior) ... 

Figure 1, View of the combined direct and indirect calorimetric chamber at USDA Beltsville, MD, USA, The gas in- and outlet is located on the left wall. The door includes a window and two locks for transfer of food and waste. The whole system is controlled by a PC...

The heat content of the chamber depends under well-defined conditions only on chamber temperature. This is, however, not always balanced with the air temperature in the chamber. If the chamber temperature remains constant the heat content can be assumed to be constant, especially if the experimental schedule is comparable for different measurements. This constant heat content is than added to resulting in the nonevaporative heat loss of the subject. Most experimentors did so in the past however, there are some papers dealing with heat storage compensation in the calorimetric chamber [13,15]... 

Normal and comfortable living conditions have to be maintain in the calorimetric chamber, at least under normal conditions and for humans. This requires... 

So the term BM was introduced and called metabolic body mass (MBM), which is, in fact, proportional to HL within a species or related species. Assuming a proportionality of HL and MBM the heat balance of the body requires a proportionality between EE and MBM too. This, however, introduces a differentiation of indirect calorimetric measurements by body mass. On first hand there is calorimetry on humans and large (farm) animals, often done in relatively large (and convenient) calorimetric chambers with volumes (V) of up to 25 m On the other hand there is indirect calorimetry on small (laboratory) animals, even organ tissue or cell clusters. Small animal calorimetry can perfectly be done in relative small cages with volumes of Just a few litres, whereas tissues or cell clusters can be investigated in small ampoules [25]. 

Depending on the objective of a study the time and duration of calorimetric measurements have to be defined typical measurements in calorimetric chambers are about a full day or even several full days. Experimentors often use comparative methods to measure physiological, pharmacological or dietetic values. 

Labelled bicarbonate on its own can be used to assess EE instead of doubly labelled water. This technique is valuable for short intervals of about 1-3 days because of the shorter biological half life of bicarbonate compared with water. It is applicable to humans only, if stable marked bicarbonate (NaH CO,) is used. This substance is less expensive than doubly labelled water, but relies like DLW on the quite expensive technology of IRMS. The bicarbonate is con.stant-ly infused and will reach rapidly an equilibrium with the CO2-P00I of the subject s body. COj-production will dilute this pool. The CO production rate can be calculated from the variations in the dilution of labelled COj and the infusion rate. The method assumes no isotope exchange or fixation and a constant pool of bicarbonate. It is not as accurate as the doubly labelled water method Elia [39] found individual accuracies of up to 6%, validated against whole body calorimetry in a calorimetric chamber. 

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