Perfusion calorimeter

Heat production rate (P) of different muscles from healthy human subjects, obtained with a perfusion calorimeter without stirring. Source reference 75. 

Heat production rate (P) in muscle from healthy subjects treated with 3 different beta - adrenoceptor blockers. Measurements were performed with a perfusion calorimeter. Source reference 77. 

In a group of haemodialysis patients, muscle thermogenesis was evaluated by measurement of heat production in skeletal muscle samples [112]. Biopsies were taken from the vastus lateralis muscle by needle technique, using the same amount of muscle for each patient, about 45 mg. Microcalorimetric measurements were made in a perfusion calorimeter of the thermopile heat conduction type, as previously described. Blood samples for measurement of thyroid hormone concentration were collected the morning before dialysis after the patients had been fasting for 12 h. About 40% of the group of haemodialysis patient were found to have decreased muscle heat production... 

Calorespirometry measurements of animal tissues, cell cultures, and microbial populations have typically been made in perfusion calorimeters or flow calorimeters [23-25]. Flow methods allow continuous monitoring of input and output materials as well as heat and gas fluxes. However, flow systems often do not work well with most plant. samples. Plant cell cultures commonly clump badly, interfering with the mechanics of the perfusion process. Marine plants. 

The aquatic oligochaete Lumbriculus variegatus is known to survive long periods of anoxia so that it represents a suited object for various calorimetric investigations. Groups of 10 individuals of this species with 1 to 2 mg dry weight were placed in a perfusion chamber of a flow calorimeter connected to a twin-flow respirometer (section 3.3.1.) for simultaneous direct and indirect calorimetry [170]. They were exposed to normoxic and anoxic conditions and showed a drastic reduction of heat dissipation under anoxia down to 15 % of the aerobic rates. Switching back to aerobic conditions, heat dissipation increased immediately. 

Hentschel et al. [139] measured heat production and nitrate respiration rates simultaneously in the gill tissue of L aequizonata to answer the above questions. After an aerobic trace had been established, perfusion conditions were switched to anoxia. Upon the addition of nitrate to the anoxic perfusion medium of the open-flow calorimeter, an immediate increase in heat dissipation was seen (Figure 11). A second point to be observed from Figure 11 was that the nitrate-stimulated heat production was proportional to the concentration of nitrate added (30 mol 1 to 1 mmol 1 ). Nitrite appearance in the effluent seawater followed the same pattern as the heat dissipation (data not shown). Half-maximal stimulation of heat production by nitrate was achieved at 0.81 mmol 1 nitrate. The mean experimental ratio of heat produced per mole nitrite was -130+22.6 kJ mol nitrite (N = 13, +SEM). Gill tissue from Mytilus edulis, which does not contain symbionts, was used as a negative control. A change in heat flux was not observed upon exposure to 1 mmol 1 nitrate. Similarly, a calorimetrie run without gill tissue showed that nitrate or nitrite had no effect on the baseline. 

For studies of anchored cells, modifications need to be made in many cases. For instance, cultures on tenterframes [35] have been inserted into the lOO-cm batch vessel of a Calvet calorimeter [3] and glass plates with cell monolayers on them have been stacked in the ampoules of a Thermometric BAM instrument [36]. In one recent case [37], the stirrer blades of a Thermometric perfusion vessel were modified to act as monolayer plates. It would seem preferable these days to attach the cells to beads that are suspended in a stirred ampoule (see for instance Reference [38]). 

Figure 11. Scheme of one of the microcalorimeters used for the simultaneous measurements of O2 consumption and heat production rates in perfused preparations. The thermal gradient layers (1) are made of semiconductor thermocouples mounted in series on each chamber. The preparation (2) is placed near the upstream extremity of one of the 8-cm long tantalum chambers, so that most of the heat it produces is transmitted to the surrounding aluminium block that functions as a heat sink. The four-way distributor, driven from outside the thermostatic jacket by a torsion bar and a pneumatic valve, directs the effluents of the preparation chamber and the control chamber to the drain, alternately via a jet in front of the O2 cathode (3) or directly (4) every 2 to 5 min. Immediately upstream of the calorimeter chambers, the downstream components of the heat exchangers (5) are wound together, in co-current, in close contact with an extension of the aluminium block (not represented on the drawing) (Reproduced from Reference [70] with permission). 

There is an alternative to pumping cell suspensions through a flow calorimeter from a culture and measuring changes in the concentrations of metabolites off-line. At the microanalytical scale, it is to make on-line estimations using probes situated in the calorimetric vessel. The Thermometric TAM has a series of different batch insertion vessels with a small volume (see Reference [3]). One type of vessel is designed for tissue perfusion and has a 4-... 

Duplicate measurements of heat production rate (P) on human obliquus internus muscle using two different calorimeters static and perfusion instrument. Source reference 75. 

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