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PubMed2004

Measuring energy expenditure in cardiac patients using the Body Media Armband versus indirect calorimetry. A validation study.

AIM: The purpose of this study was to compare differences in energy expenditure using the newly developed SenseWear Armband body monitor to indirect calorimetry in cardiac rehabilitation patients. METHODS: Twenty-four (62+/-8.1 years) patients completed steady state exercise for 8 minutes on 4 modes of exercise (arm ergometry, treadmill walking, recumbent stepping and rowing ergometry). Total cumulative kilojoules were recorded simultaneously by indirect calorimetry and the SenseWear Armband. Statistical analyses assessed the degree of agreement between the 2 measurement methods and 3 different versions of the SenseWear software. RESULTS: The correlations between indirect calorimetry and version 2.2 of the SenseWear armband for arm and rowing ergometry, the treadmill and recumbent stepper were r=0.90, r=0.67, r=0 .80 and r=0.74, respectively. There were no between method differences during arm ergometry (p<1.000) and the recumbent stepper (p<0.102). Bland and Altman plots revealed the greatest spread of scores for the rower and the treadmill. Between method differences were minimal when using the preliminary cardiac software. The correlations for arm and rowing ergometry, the treadmill and recumbent stepper were r=0.90, r=0.84, r=0.78 and r=0.82, respectively. CONCLUSIONS: The accuracy of the BodyMedia SenseWear Armband appears to be exercise modality dependent in those with heart disease when using software developed for the general population. Therefore, the information should be interpreted cautiously, particularly during treadmill walking and rowing. Initial experiments with cardiac-focused software are promising, but preliminary.

Calorimetry, Indirect↗
PubMed1984

Thermal denaturation of tryptophan synthase alpha-subunit. Comparison of the values of thermodynamic parameters of unfolding obtained from van't Hoff analysis of CD measurement with those from calorimetry.

Thermal denaturation for the wild-type of tryptophan synthase alpha-subunits from E. coli and one of its mutant proteins was followed by CD measurements at various pHs in the alkaline region and the results from van't Hoff analyses of the thermal denaturation curves were compared with those from calorimetry. Although the far-u.v. CD spectra of the thermally denatured proteins differed from those of the completely denatured states in 3.2 M guanidine hydrochloride, the titration curves by denaturants at higher temperatures were not sigmoidal but straight lines, indicating that the cooperative structure of the proteins has been completely destroyed by heating. The ratio of calorimetric enthalpy change to van't Hoff enthalpy change obtained from calorimetric study was unity, indicating that the thermal denaturation of the proteins was a two-state system. The unfolding heat capacity change (delta Cp) of the wild-type protein from van't Hoff analysis of the thermal denaturation curves by CD measurement was estimated to be 2.45 kcal/mol X deg, which was similar to that from calorimetry. The values of unfolding enthalpy change at denaturation temperatures were lower by about 15 kcal/mol compared to those from calorimetry.

Calorimetry↗
PubMed1978

Prospective applications of calorimetry in the clinical laboratory.

Calorimetric analysis depends on the direct proportionality between the heat changes that occur during chemical reactions and the amount of reacting substances. Potential uses of calorimetry in the clinical laboratory are discussed, with examples. The calorimetric technique does not require optically clear specimens, and if the specificity of the measured reaction is assured, calorimetry can be used for quantitative determinations of components that are present in a complex matrix system such as body fluids. Specific enzymic reactions have been used to measure substrates and enzyme activities in biological specimens calorimetrically, with precision, sensitivity, and accuracy comparable to routine photometric techniques. The application of calorimetry in the clinical laboratory is limited now by its slowness, but development of automated instruments may enable the technique to become competitive with conventional analytical techniques in the clinical laboratory.

Calorimetry↗
PubMed1981

Differential scanning calorimetry of cytoplasmic aspartate transaminase.

Differential scanning calorimetry has been applied to study factors affecting the thermally induced denaturation of cytoplasmic aspartate aminotransferase, a dimeric pyridoxal enzyme. The consequences of binding of coenzyme and substrate derivatives to both the apo and holo forms of the enzyme were investigated and are interpreted in terms of the stabilization of the native form of the enzyme. The binding of pyridoxal phosphate coenzyme increases the thermal stability of the apoenzyme by approximately 27 kcal mol-1 as judged by the change in free energy differences between the native and denatured states of the protein. The stabilization produced by coenzyme binding to the apoprotein appears to be primarily due to the Schiff's base and phosphoryl moieties of the coenzyme; association of the pyridine ring component is without significant structural consequence. Pyridoxal phosphate binding to the subunits of the dimer occurs in a noncooperative fashion as judged by the appearance of transitions unique to the apo, holo, and intermediate enzyme forms in a calorimetric titration. Holoenzyme stability depends on the chemical nature of the catalytically significant group occupying the C-4' position of the bound coenzyme. The stabilization afforded by binding of the aldehyde form (pyridoxal phosphate) which exists as an internal Schiff's base with Lys 258 is diminished when this bond is chemically reduced or when the aldehyde is replaced by an amine (pyridoxamine phosphate). Apoenzyme is also shown to be stabilized by the presence of substrates in the absence of coenzyme. The differential scanning calorimetry results thus confirm previous findings derived from nuclear magnetic resonance studies on the ability of apoenzyme to bind substrates (Martinez-Carrion, M. Cheng, S., and Relimpio, A. (1973) J. Biol. Chem. 248, 2153-2160). Substrates and their analogues perturb the holoenzyme stability and the order of increasing influence on the pyridoxal form of the holoenzyme is aspartate, erythro-hydroxyaspartate, alpha-ketoglutarate, and alpha-methylaspartate. While all these compounds form stable binary enzyme-substrate complexes (Jenkins, W.T., and D'Ari, L. (1966) J. Biol. Chem. 541, 5667-5674), the complex with alpha-methylaspartate produces anomalous changes in the protein structure which are reflected in the calorimetric parameters. This suggests that caution be exercised in the use of analogues as substrate substitutes in crystallographic work. Differential scanning calorimetry also appears as a sensitive method with which to study the stereochemical dependence of ligand binding on enzyme-induced thermal stabilization. This is illustrated by the use of 4-carbon dicarboxylic acids where only those in the conformation favorable for binding are effective in stabilizing the holoenzyme.

Animals↗
PubMed1994

[A stable conformer of IgG, prepared by an acidic influence: study by calorimetry, binding of the C1q complement component, and monospecific anti-IgG].

Thermal stability and functional activity of rabbit IgG in its native conformation and after incubation at pH 2.0 were studied using differential scanning calorimetry and binding of conformational probes, i.e., the C1q component of the complement and two monospecific anti-IgG antibodies. The latter reacted selectively with the "hinge" region joining the Fab and Fc fragments of IgG or with the CH2 domain in the Fc fragment. At pH 2.0 complete unfolding of rabbit IgG did not occur: the protein demonstrated the presence of secondary and compact tertiary structures but differed from the native conformation by decreased overall enthalpy and TM of thermal denaturation as well as by changed secondary structure parameters as could be evidenced from CD spectroscopy and scanning calorimetry data. Incubation at pH 2.0 followed by renaturation at neutral pH led to irreversible conformational changes in IgG. The most significant differences between the two IgG conformers were demonstrated by calorimetry at pH 3.5 which revealed that the acid-treated conformer differs from the native one by enhanced thermal stability of the CH2 domain. Using the combination of thermodynamic and functional studies, it was shown that the origin of stabilization was the increase in the extent of interaction between the CH2 domain in the Fc fragment and the CHI domain in the Fab fragment. This resulted in the increase of the functional link between the antigen-binding domain and the C1q binding site in the CH2 domain of the acid-induced IgG conformer. In parallel with the increase in stability of the CH2 domain, conformational changes in the "hinge" region were found, together with the absence of intrinsic conformational changes in the CH2 domain proper as could be judged from C1q and monospecific anti-IgG binding assays. The results obtained demonstrate one of possible mechanisms whereby functionally significant rearrangements in the IgG molecule can be induced by changes in the interactions between invariably folded domains rather than by intrinsic changes in the domain conformation.

Animals↗
PubMed1996

Effect of prepuberal and postpuberal gonadectomy on heat production measured by indirect calorimetry in male and female domestic cats.

OBJECTIVE: To use indirect calorimetry to compare heat production between gonadectomized and sexually intact male and female cats. DESIGN: Male (n = 6) and female (n = 6) kittens were gonadectomized at 7 weeks or 7 months of age, or left sexually intact. Body heat production was measured by indirect calorimetry in all cats at 12, 18, and 24 months of age. ANIMALS: 18 male and 18 female clinically normal domestic shorthair cats. PROCEDURE: Heat production was measured, using an open-circuit, respiratory, indirect calorimeter. All cats underwent calorimetry at 12, 18, and 24 months of age. The heat coefficient, a measure of resting metabolic rate, was calculated for each cat at each test; heat coefficient is defined as logarithm of heat (kcal/h) divided by logarithm of body weight (kg). RESULTS: Heat production did not vary with age in male or female cats. Heat coefficient was higher in sexually intact male and female cats than in gonadectomized male and female cats at 12, 18, and 24 months of age (12 months, females, P < 0.01, males, P = 0.04; 18 months, females, P < 0.01, males, P = 0.02; and 24 months, females and males, P < 0.01). CONCLUSIONS: These data suggest that resting metabolic rate in cats decreases after gonadectomy. CLINICAL RELEVANCE: A decrease in metabolic rate is synonymous with a decrease in caloric requirements. Gonadectomized animals fed in a manner similar to sexually intact animals may be predisposed to obesity and its sequelae.

Analysis of Variance↗
PubMed1998

[An experimental study on ischemically induced brain damage by whole body calorimetry and pathohistology in the gerbil].

Moderate hypothermia has been reported to mitigate neuronal damage in the gerbil brain following brief periods of forebrain ischemia, but the relationship between brain damage and whole body calorimetry has not been clarified. We report the effect of hypothermia on the brain damage by whole body calorimetry using Bio Dynamic Calorimeter (BDC200, ESCO Ltd JAPAN). Although it is an indirect method, whole body calorimetry may be able to measure the brain damage, thereby enabling investigations on alleviation of brain damage.

Animals↗
PubMed1999

Hydration and Lyotropic Melting of Amphiphilic Molecules: A Thermodynamic Study Using Humidity Titration Calorimetry.

The hydration of the lipid 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) and of the cationic detergent dodecyltrimethylammonium bromide (DTAB) has been studied by means of isothermal titration calorimetry (ITC), gravimetry, and infrared (IR) spectroscopy. During the experiments films of the amphiphiles are perfused by an inert gas of variable relative humidity. The measurement of adsorption heats using ITC represents a new adaptation of adsorption calorimetry which has been called the humidity titration technique. This method yields the partial molar enthalpy of water upon adsorption. It is found to be endothermic with respect to the molar enthalpy of water on condensation for the water molecules which interact directly with the headgroups of POPC and DTAB. Consequently, the spontaneous hydration of the amphiphiles is entropy driven in an aqueous environment. IR spectroscopy shows that hydration is accompanied by the increase in the conformational and/or motional freedom of the amphiphilic molecules upon water binding. In particular, a lyotropic chain melting transition is induced at a certain characteristic relative humidity. This event is paralleled by the adsorption of water. The corresponding exothermic adsorption heat is consumed completely (POPC) or partially (DTAB) by the hydrocarbon chains upon melting. Differential scanning calorimetry was used as an independent method to determine transition enthalpies of the amphiphiles at a definite hydration degree. Water binding onto the headgroups is discussed in terms of hydrogen bonding and polar interactions. The adsorption isotherms yield a number of approximately 2.6 tightly bound water molecules per POPC and DTAB molecule. Copyright 1999 Academic Press.

Journal Article↗
PubMed1996

Anaerobic metabolism in the leech (Hirudo medicinalis L.): direct and indirect calorimetry during severe hypoxia.

Anaerobic metabolism in the limnic annelid Hirudo medicinalis L. was investigated by direct and indirect calorimetry. During long-term severe hypoxia, the rate of heat dissipation was reduced up to 13% of the aerobic rate. At the same time, the rate of ATP turnover was reduced to about 30% of the aerobic rate, indicating that metabolic depression is an important mechanism to ensure survival of the leech during environmental anaerobiosis. Heat dissipation during hypoxia was monitored under two experimental conditions, favouring either concomitant hypocapnia (continuous N2 bubbling) or hypercapnia (self-induced hypoxia). The reduction in heat dissipation during hypocapnic hypoxia was less pronounced than during hypercapnic hypoxia, indicating that the different experimental conditions may influence anaerobic metabolism and the extent of metabolic depression. Biochemical analysis of known anaerobic substrates and endproducts provided the basis for indirect calorimetry during self-induced hypoxia. From changes in metabolites, the expected heat dissipation was calculated for initial (0-8 ,h) and long-term severe hypoxia (8-72 h). During the initial period, the calculated heat dissipation fully accounted for direct calorimetric determination. During long-term hypoxia, only 71% of the measured heat production could be explained from biochemical analysis of metabolites. Therefore, an additional unknown endproduct cannot be excluded, especially when anaerobic ammonia production and analysis of the carbohydrate balance are considered.

Aerobiosis↗
PubMed1989

[Postoperative energy requirements following large abdominal surgery interventions: comparison of measuring by indirect calorimetry with estimated values].

Energy requirement after major abdominal operations, as calculated according to the formula for basic energy expenditure by Harris-Benedict, was increased by 30% in the early and by 50% in the late postoperative period. Correlation of these calculated values to measurements by indirect calorimetry was good. Even more simply a good estimation of caloric requirements can be obtained by multiplication of the body weight with a factor 30. The development of septic complications does not increase considerably postoperative energy expenditure, however, the correlation between measured and estimated values becomes poor. As supposed from isotope studies measuring gas exchange for indirect calorimetry for one hour provides sufficiently stable results.

Aged↗
PubMed1977

Differential scanning calorimetry and enzymic activity of rat liver microsomes in the presence and absence of delta1-tetrahydrocannabinol.

The thermal transitions of rat liver microsomes and isolated lipids were investigated by using differential scanning calorimetry. Endothermic transitions at approximately-5 degrees C and between approximately18 degrees and 40 degrees C were detected in the membranes and at approximately-10 degrees C and between approximately 10 degress and 20 degrees C in the extracted lipids. Interaction with delta1-tetrahydrocannabinol of microsomal membranes and of extracted lipids influences the thermotrophic behaviour as revealed by differential scanning calorimetry and eliminates the break in the Arrhenius plot of the enzymic activity of O-demethylase.

Animals↗
PubMed2006

Fecal energy losses in enterally fed intensive care patients: an explorative study using bomb calorimetry.

BACKGROUND & AIMS: Early enteral nutrition and tailored supply of nutrients have become standard in most of the intensive care units (ICU). So far little attention has been given to losses of energy in the stools. The purpose of this explorative study was to evaluate the energy losses of patients with loose stools, necessitating the use of a feces-collector device in a tertiary academic ICU. METHODS: In a group of 13 fully enterally fed and mechanically ventilated patients with loose stools, the daily energy loss in feces was determined, using bomb calorimetry. Malabsorption was defined as an absorption capacity of 85% or less. Energy expenditure was determined with indirect calorimetry. RESULTS: Six out of 13 (46%) patients fulfilled the criterion of malabsorption. The mean total energetic absorption capacity was 84.6+/-13.3%. The mean capacity of absorption of fat was 89.7+/-16.3%. The caloric value of energy loss had a mean of 301+/-259 kcal/day. Fecal fat loss proved not to be a good indicator of total fecal energy loss. A total of 4/13 patients (31%) had a net negative energy balance of over 500 kcal/day. A daily feces production of 250 g or more was a good predictor of malabsorption. Energy loss could accurately be predicted by using a factor 4.87 for the combined energetic value of protein and carbohydrates, if dry weight and fecal fat content are known. CONCLUSIONS: In this clinical study on ICU patients with loose stools, malabsorption proved to be a frequently occurring and so far unrecognized problem, contributing strongly to negative energy balances in 1/3 of the patients.

Adult↗
PubMed1998

Proton induced vesicle fusion and the isothermal lalpha-->HII phase transition of lipid bilayers: a 31P-NMR and titration calorimetry study.

The proton-induced isothermal fusion of unilamellar lipid vesicles (Duzgunes et al., Biochemistry 24 (1985) 3091-3098) is compared with the lamellar (Lalpha)-->hexagonal (HII) phase transition of multilamellar lipid dispersions. Both lipid systems are composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and oleic acid (OA) at a 7:3 molar ratio. Using solid-state phosphorus-31 nuclear magnetic resonance (31P-NMR) it is demonstrated that the multilamellar lipid dispersions are in the bilayer state at physiological pH and undergo a Lalpha-->HII phase transition between pH 6.3 and 5.7. This phase transition can also be induced at constant pH by increasing the temperature. The midpoint of the temperature-induced Lalpha-->HII transition is Th=56 degrees C (at pH 7.4) and the corresponding transition enthalpy is DeltaH=0. 7+/-0.1 kcal/mol as determined with differential scanning calorimetry. Both the proton-induced and the temperature-induced phase transition can be completely inhibited by addition of 30 mol% of 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine (LPC). In a second set of experiments unilamellar vesicles are prepared either by sonication or by extrusion through polycarbonate filters at pH 7. 4 and are titrated into buffer at pH 5.7. The proton-induced fusion of the lipid vesicles is monitored with isothermal titration calorimetry, light scattering and fluorescence spectroscopy. The fusion reaction is characterized by an endothermic enthalpy of DeltaH=0.5+/-0.2 kcal/mol (at 28 degrees C). The fusion enthalpy is independent of the vesicle diameter and is only slightly reduced by an increase in temperature to 50 degrees C. Vesicle fusion is accompanied by an increase in light scattering, indicating the formation of larger lipid structures. The transition from unilamellar vesicles to fused lipid structures occurs in the same narrow pH range of 6.3-5.7 as observed for the Lalpha-->HII transition of multilamellar dispersions. Vesicle fusion can be inhibited with 30% LPC. The virtually identical set of parameters found for the Lalpha-->HII phase transition and the vesicle fusion reaction suggests that vesicle fusion also entails a Lalpha-->HII phase transition.

Calorimetry↗
PubMed1988

Interaction of diacylglycerols with phosphatidylcholine vesicles as studied by differential scanning calorimetry and fluorescence probe depolarization.

Mixtures of 1,2-dipalmitoylglycerol (1,2-DPG), 1,2-dioleylglycerol (1,2-DOG), 1,2-dicapryloylglycerol (1,2-DCG), 1,3-dioleylglycerol (1,3-DOG), and 1,3-dicapryloylglycerol (1,3-DCG) with dipalmitoylphosphatidylcholine (DPPC) have been studied by means of differential scanning calorimetry (DSC) and fluorescence depolarization of the probe diphenylhexatriene (DPH). DSC measurements showed that the tested diacylglycerols (DG's) modified both the pretransition and the main transition of DPPC, but whereas increasing concentrations of 1,2-DPG tended to produce mixtures with transition temperatures higher than that of pure DPPC, all the other diacylglycerols tested tended to decrease this temperature. This is interpreted as a preferential partitioning of 1,2-DPG into rigid domains whereas all the other DG's preferentially partition into fluid domains. Lateral phase separation was detected in all the mixtures, so that the presence of diacylglycerols produced lipid immiscibilities. The phase diagrams constructed from the calorimetric data showed that 1,2-DPG induced solid-phase immiscibility from 0 to 12.5 mol%, whereas 1,2-DCG produced fluid-phase immiscibility at low concentrations, with an eutectic point at 0.64 mol%. 1,2-DOG also showed fluid-phase immiscibility. 1,3-DCG behaved differently than 1,2-DCG, but 1,3-DOG was rather similar in its effects to 1,2-DOG. Fluorescence depolarization of DPH included in these lipid mixtures was measured at different temperatures, so that phase transitions and the order of the bilayer were monitored. The phase transitions observed by the fluorescence technique were in general in agreement with those monitored by calorimetry.(ABSTRACT TRUNCATED AT 250 WORDS)

Calorimetry↗
PubMed2003

Aggregation of bovine insulin probed by DSC/PPC calorimetry and FTIR spectroscopy.

Pressure perturbation calorimetry (PPC), differential scanning calorimetry (DSC), and time-resolved Fourier transform infrared spectroscopy (FTIR) have been employed to investigate aggregation of bovine insulin at pH 1.9. The aggregation process exhibits two distinguished phases. In the first phase, an intermediate molten globule-like conformational state is transiently formed, reflected by loose tertiary contacts and a robust H/D-exchange. This is followed by unfolding of the native secondary structure. The unfolding of insulin is fast, endothermic, partly reversible, and accompanied by a volume expansion of approximately 0.2%. The second phase consists of actual aggregation: an exothermic irreversible process revealing typical features of nucleation-controlled kinetics. The volumetric changes associated with the second phase are small. The concentration-dependence of DSC scans does not support a monomer intermediate model. While insulin aggregation under ambient pressure is fast and quantitative, pressure as low as 300 bar is sufficient to prevent the aggregation completely, as high-pressure FTIR spectroscopy revealed. This is explained in terms of the high pressure having an adverse effect on the thermal unfolding of insulin, and therefore preventing occurrence of the aggregation-prone intermediate. A comparison of the aggregation in H(2)O and D(2)O shows that the isotopic substitution has diverse effects on both the phases of aggregation. In heavy water, a more pronounced volume expansion accompanies the unfolding stage, while only the second phase shifts to higher temperature.

Amides↗
PubMed2025

A consensus guide to preclinical indirect calorimetry experiments.

Understanding the complex factors influencing mammalian metabolism and body weight homeostasis is a long-standing challenge requiring knowledge of energy intake, absorption and expenditure. Using measurements of respiratory gas exchange, indirect calorimetry can provide non-invasive estimates of whole-body energy expenditure. However, inconsistent measurement units and flawed data normalization methods have slowed progress in this field. This guide aims to establish consensus standards to unify indirect calorimetry experiments and their analysis for more consistent, meaningful and reproducible results. By establishing community-driven standards, we hope to facilitate data comparison across research datasets. This advance will allow the creation of an in-depth, machine-readable data repository built on shared standards. This overdue initiative stands to markedly improve the accuracy and depth of efforts to interrogate mammalian metabolism. Data sharing according to established best practices will also accelerate the translation of basic findings into clinical applications for metabolic diseases afflicting global populations.

Calorimetry, Indirect↗
PubMed1976

Thermic effect of glucose in obese subjects studied by direct and indirect calorimetry.

1. The thermic effect of a glucose load (50 g) was studied in ten control and eleven obese female subjects, using both direct and indirect calorimetry simultaneously. Experiments were done under conditions of thermal equilbrium (28 degrees and 30% relative humidity). 2. Thermal balance (heat production measured by indirect calorimetry minus heat losses measured directly) was negative in the control group during the fasting period (heat deficit -14-2 +/- 5-0 kJ/m2 per h), whereas that of the obese group was in equilibrium (+ 1-4 +/- 4-8 kJ/m2 per h). 3. After the glucose load, metabolic rate increased 13-0 +/- 1-5 and 1-3% in the control and obese groups respectively. 4. In contrast to the metabolic rate, total heat losses were not significantly altered in either group after the glucose load. Total heat losses of the obese group were significantly lower than those of the control group throughout the experimental period. 5. During the experiments the amount of heat stored was increased in both groups. Thermal balance in the control group became positive while that of the obese group remained positive. 6. During the fasting period, the control subjects oxidized more carbohydrates (90-4 mg/min) than lipids (68-8 mg/min), whereas obese subjects oxidized more lipids (103-7 mg/min) than carbohydrates (50.2 mg/min). After the glucose load, the oxidation rate of carbohydrates was increased in both groups to 158-1 mg/min in control subjects and 95-6 mg/min in obese subjects. 7. The mean skin temperature of the control subjects was significantly higher than that of the obese subjects and remained higher throughout the postprandial period. 8. These results indicate that: (a) during the fasting period, the energy sources utilized and the thermal balance of the two groups were different; (b) the thermic effect of glucose was less in the obese subjects and, therefore, might be a factor contributing to their low energy expenditure.

Adult↗
PubMed2005

Direct and indirect calorimetry of lactate oxidation: implications for whole-body energy expenditure.

Whole-body energy expenditure for heavy/severe exercise is currently accounted for by either: (1) anaerobic and oxygen uptake measures during exercise where recovery energy expenditure is omitted; or (2) oxygen uptake during, and an EPOC (excess post-exercise oxygen consumption), measure following exercise where substrate level phosphorylation during exercise is considered part of EPOC. Simultaneous direct/indirect calorimetry enabled us to determine if a thermodynamic reversal (i.e. heat consumption) takes place as the highly exothermic pyruvate to lactate reaction proceeds in the opposite direction. Reversibility implies that oxygen uptake (e.g. EPOC) can indeed account for rapid glycolytic ATP production regardless if lactate is formed or not (e.g. 1.2 g glucose catabolism = 20.9 kJ x l O2(-1)). Cultured hybrid cells and mouse cardiac muscle fibres were utilized in simultaneous calorimetry and respirometry experiments where pyruvate or lactate was predominantly oxidized. The calorimetric to respiratory ratio was determined using heat flux (pW x cell(-1)) and oxygen flux (pmol x s(-1) cell(-1)) measures. Ten cell experiments gave calorimetric to respiratory ratios that showed no statistical difference (P= 0.97) whether cells respired predominantly on lactate (-516+/-53 kJ x mol O2(-1)) or pyruvate (- 517+/-89 kJ x mol O2(-1)). In three cardiac preparations, the calorimetric to respiratory ratio was -502+/-15 kJ x mol O2(-1) for lactate and -506+/-47 kJ x mol O2(-1) for pyruvate, again a non-significant difference (P= 0.91). Heat consumption did not occur during lactate oxidation. These results suggest that rapid glycolytic ATP and lactate production, and lactate oxidation, are both independently associated with heat production and thus represent separate and additive components to the measurement of total energy expenditure for exercise and recovery.

Calorimetry↗