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PubMed1993

[Indirect calorimetry and nitrogen balance in patients with elective craniotomy].

The aim of this study was to assess resting energy expenditure and nitrogen excretion in patients with cranial injury. In 25 patients subjected to elective craniotomy and 23 healthy volunteers, energy expenditure was measured using indirect calorimetry and compared with estimations according to Harris-Benedict equations. During the second postoperative day, measured energy expenditure in patients was 100 +/- 19% (range 66-185) of estimation and 115 +/- 22% (range 76-159%) of measured values in control subjects. In sedated patients with flaccid muscular paralysis, measured energy expenditure was 82 +/- 12% of estimation and 94 +/- 15% of measured values in control subjects. Urinary urea nitrogen excretion in patients was 10.2 +/- 5.4 g/day and catabolic index was 6.8 +/- 5.1. Patients receiving corticoids had increased urinary urea nitrogen excretion and no differences in measured energy expenditure, compared to patients not receiving this medication. It is concluded that the great variability in measured energy expenditure and its lack of correlation with the degree of catabolism, set forth the need to perform an indirect calorimetry in these patients to plan an adequate nutritional support.

Adolescent↗
PubMed1976

[Heat debt and thermal insulation in women exposed to cold : contribution of direct calorimetry to the study of a mathematical model (author's transl)].

1. Measurements of total heat losses by direct calorimetry, metabolic heat production by indirect calorimetry, body temperatures by thermometry, and thickness of subcutaneous fat with skin-fold calipers were made in four groups of subjects (anorexic, controls, trend to obesity, and obesity) at ambient temperatures of 28 degrees C and 20 degrees C. 2. At 28 degrees C, the four groups of subjects reached thermal equilibrium after 30 min. 3. Both metabolic heat production and total heat losses were lower in the anorexic group than in the control group. 4. Body thermal insulation was not simply related to the thickness of subcutaneous fat (passive insulation), but was actively regulated in such a way that thermal balance was attained by all subjects at 28 degrees C. Body tissues underlying the subcutaneous fat contributed to the thermal insulation of the subjects at both 28 degrees C and 20 degrees C. 5. At 28 degrees C, total body thermal insulation was higher in anorexic subjects than in controls. 6. At 20 degrees C, heat debt was similar in three of the four groups : the anorexic subjects showed a higher debt. 7. A highly significant correlation between subcutaneous fat and weight/area ratio, was found. 8. The heat exchange coefficient of radiation and convection was found to be 6,47 Wm-2 degrees C-1. 9. By combining our measured values with those of various tissue physical characteristics, it was possible to produce a mathematical model. With this model one can calculate the penetration of the thermal gradient into the body, and estimate the mean temperature of each tissue participating in the thermal insulation for moderately cold ambient temperatures.

Adolescent↗
PubMed1993

Prolonged oral glucose tolerance test combined with indirect calorimetry and estimation of several substrates and hormones in obese subjects.

OGTT prolonged to 4 hours was performed in untreated 50 obese outpatients (mean age 37.9 years and BMI 37.2). Parallel to glucose, insulin, growth hormone (GH), cortisol, beta-hydroxybutyrate (BOHB), nonesterified fatty acids (NEFA) and indirect calorimetry (RQ) were estimated at hourly intervals. Basal values of thyroxine (T4), triiodothyronine (T3), total cholesterol and triacylglycerols were also obtained. Mean glycemia after overnight fasting as well as after 75 g glucose reached upper limits of the normal range. The subsequent decrease was slower. Insulinemia followed a similar trend. The initial drop of GH after the glucose load reverted to an increase above the basal value. A similar pattern was observed with cortisolemia, but the decrease and increase were less important. The basal value of RQ was rather low and glucose ingestion produced only a small increase, followed by a greater decrease. Serum levels of NEFA and BOHB sharply decreased one hour after glucose intake and afterwards regained the initial values. The mean basal values of T4 and T3 were within the normal range--the low T3 syndrome was not involved in the large majority of cases. Cholesterol and triacylglycerols approached the upper normal limit. The correlations brought additional information. Insulinemia increased parallel with the amount of body fat. The basal level was decisive for most hormones and substrates--the high or low set level could be followed in the course of the whole test. Increased insulinemia and increased glycemia suggested the presence of a mild insulin resistance with the participation of GH and cortisol. Increased levels of fasting insulinemia and glycemia were present also in obese subjects with a normal OGTT. The correlations permitted to disclose insulin-like effects of GH on basal conditions. Increased BOHB was responsible for a high cholesterol. It is suggested that even small fluctuations of glycemia related to food intake may produce a substantial modification of the hormonal status in obese subjects and initiate or support the metabolic disorders in obesity. In this respect a greater role is ascribed to the phase of decreasing glycemia in comparison to the increasing phase. Lipids are the prevailing source of energy in insulin resistant subjects. The rather stable values of indirect calorimetry indicate that energy metabolism of obese subject works on a low, pre-set level-independently on the supply of some relevant hormones and substrates.

3-Hydroxybutyric Acid↗
PubMed1997

Applications of pressure differential scanning calorimetry in the study of pharmaceutical hydrates. I. Carbamazepine dihydrate.

The dehydration of carbamazepine dihydrate (C(15)H(12)N(2)O.2H(2)O) was studied by both conventional differential scanning calorimetry (DSC) and by pressure differential scanning calorimetry. Variable temperature powder X-ray diffractometry (VTXRD) and thermogravimetric analysis were used as complementary techniques. By performing DSC at elevated pressures, the dehydration and vaporization endotherms were separated and it was possible to determine the enthalpy of dehydration. Over the range of 100-600 psi, the enthalpy of dehydration was unaffected by pressure. However, the solid-state of the anhydrous phase formed was influenced by the DSC conditions. At ambient pressure, dehydration resulted in the formation of the gamma-form of anhydrous carbamazepine while at elevated pressures, the anhydrous beta-form appeared which converted to the gamma-form at higher temperatures. At high pressures, the water liberated on dehydration is not immediately removed and its presence appears to be responsible for the formation of beta-carbamazepine. VTXRD permitted in situ study of dehydration and this confirmed the DSC results. A specially fabricated sample holder permitted VTXRD studies at elevated pressures.

Journal Article↗
PubMed1997

Characterization of binding interactions by isothermal titration calorimetry.

Isothermal titration calorimetry is a high-accuracy method for measuring binding affinities. Titration calorimetry is a universal method that has broad impact throughout biotechnology. In recent years, microcalorimeters that are capable of characterizing binding interactions of biological macromolecules have become commercially available. Results from these studies are providing new insight into the molecular nature of macromolecular interactions.

Journal Article↗
PubMed2006

Thermodynamics of activated phase transitions of 8CB: DSC and MC calorimetry.

The present paper reports the heating rate effect on the phase transitions of a pure liquid crystal octylcyanobiphenyl (8CB) with use of Differential Scanning Calorimetry (DSC) and Modulation Calorimetry (MC) techniques. The DSC runs were taken at various temperature ramp rates from 20 to 0.5 K/min for heating and cooling scans. Well-defined endothermic/exothermic peaks were found at the melting/crystallization, smectic-A to nematic (SmA-N), and nematic to isotropic (N-I) transitions on heating/cooling scans, respectively. All transitions shift in temperature significantly with different ramp rates. The temperature shift of C(p) peaks between heating and cooling scans indicates the order of the transitions. In addition, all transitions follow an Arrhenius behavior. The activation energy of a transition increases as the total energy involved in the transition decreases. The respective enthalpy and entropy change of each transition provides information on the Gibbs free energy. The significance of the results is discussed in terms of the order of transitions. A comparative analysis of MC and DSC techniques highlights the significance of the two techniques. MC is a practicable tool for observing the phase dynamics whereas DSC is a good tool for studying the rate kinematics of the transitions.

Journal Article↗
PubMed1986

Use of differential scanning calorimetry for structural analysis of fungally degraded wood.

This paper assesses the potential use of differential scanning calorimetry for analyzing sound and decayed wood. With sound wood, this method permitted the detection of cellulose, hemicellulose, and lignin components as discrete peaks of combustion at defined temperatures. Characteristic changes in the calorimetric thermogram of birchwood (temperature of maxima, peak height, and peak area) were obtained from wood samples degraded by the basidiomycetes Fomes fomentarius and Piptoporus betulinus. Additional peaks in the thermograms of white rotted birchwood were assigned to lignin degradation products and to mycelium. Results obtained by the differential scanning calorimetry method are compared with those of chemical determination, with particular emphasis on Klason lignin.

Journal Article↗
PubMed2004

Monitoring energy metabolism with indirect calorimetry: instruments, interpretation, and clinical application.

Indirect calorimetry is the best measure to guide calorie administration during nutrition support. This article presents an update of the types of currently available indirect calorimeters and reviews the recent advances that guide the clinical application of indirect calorimetry. The emphasis of this report is placed on issues that the practicing clinician can use to evaluate, interpret, and apply measurements of energy expenditure.

Journal Article↗
PubMed1985

Application of differential scanning calorimetry to the study of solid drug dispersions.

The present study describes the application of differential scanning calorimetry (DSC) to ascertain the crystalline state of a drug with a melting point of approximately 53 degrees C after dispersion on hydrophilic carriers by either simple mixing or by fusion. The carriers examined include polyethylene glycol 6000 and colloidal silicon dioxides. The most interesting of the systems investigated, in which the drug is gradually transformed from the crystalline to the amorphous state at room temperature, are physical mixtures of the drug and colloidal silicon dioxides. The crystalline transformation is manifested by the gradual decrease in the endothermic transition energy of the physical mixture with time. The crystalline transformation is characteristically biphasic with initially fast first-order kinetics, followed by a slow conversion process. The rate of transformation is dependent on the drug-silicon dioxide ratio, temperature, and certain physical properties of the silicon dioxides. An inverse relationship exists between transition energy and the in vitro dissolution rate of the drug in the physical mixtures with silicon dioxide. This suggests that DSC may provide a useful method for evaluating the effects of formulation variables upon dissolution rate.

Calorimetry↗
PubMed2001

Phase transitions and hydrogen bonding in a bipolar phosphocholine evidenced by calorimetry and vibrational spectroscopy.

As a model for natural archaebacterial bolalipids, we have synthesized omega-hydroxybehenylphosphocholine (HBPC, HO-(CH(2))(22)-OP(O(-)(2))O-(CH(2))(2)-N+(CH(3))(3)) and investigated it, by Fourier-transform infrared and Raman spectroscopy and differential scanning calorimetry, both as fully hydrated dispersions (varying temperature) and as aligned films (varying hydration) in terms of particular structural features predestining such bipolar lipids for their occurrence in extremophilic organisms. The phase behavior of HBPC in dispersions depends on sample pretreatment as it comprises metastabilities in annealed samples. However, main transition proceeds consistently near 81 degrees C. Some (extra) deal of headgroup (phosphate) hydration accompanying a gel-gel phase transition near 66 degrees C appears to precede chain melting. Studies with HBPC films revealed lamellar interdigitated-like solid phases with an extraordinarily strong omega-OH--OPO(-) omega-OH--OPO(-) omega-OH hydrogen-bond pattern formed along both sides of the resulting monolayers. The "clamping" effect inherent to such structures provides a clue to explain the relatively high main-transition temperature of HBPC assemblies.

Adsorption↗
PubMed1987

Dynamic analysis of differential scanning calorimetry data.

The apparent heat capacity function measured by high-sensitivity differential scanning calorimetry contains dynamic components of two different origins: (1) an intrinsic component arising from the finite instrument time response; and (2) a sample component arising from the kinetics of the thermal transition under study. The intrinsic instrumental component is always present and its effect on the shape of the experimental curve depends on the magnitude of the calorimeter response time. Usually, high-sensitivity instruments exhibit characteristic time constants varying from 10 to 100 s. This slow response introduces distortions in the shape of the heat capacity function especially at fast scanning rates. In addition to this instrumental component, dynamic effects due to sample relaxation processes also contribute to the shape of the experimental heat capacity profile. Since the nature and magnitude of these effects are a function of the kinetic parameters of the transition, they can be used to obtain kinetic information. This communication presents a dynamic deconvolution technique directed to remove artificial distortions in the shape of the heat capacity function measured at any scanning rate, and to obtain a kinetic characterization of a thermally induced transition. The kinetic characterization obtained by this method allows the researcher to obtain transition relaxation times as a continuous function of temperature. This technique has been applied to the thermal unfolding of ribonuclease A and the pretransition of dipalmitoylphosphatidylcholine (DPPC). In both systems the transition relaxation times are temperature dependent. For the protein system the relaxation time is very slow below the transition temperature (approximately 30 s) and very fast above Tm (less than 1 s) in agreement with direct kinetic measurements. For the pretransition of DPPC, the relaxation time is maximal at the transition midpoint and of the order of approx. 40 s.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1995

Calorimetry of proteins and nucleic acids.

The availability of sensitive calorimetric instrumentation has led to a considerable increase in thermodynamic studies of proteins, nucleic acids, and their interactions. This article reviews some of the recent contributions of calorimetry to characterizing the thermodynamic origins of protein and nucleic acid stability and conformational preferences, as well as the interactions of proteins with each other, with small molecules, and with nucleic acids.

Calorimetry↗
PubMed1996

DNA melting investigated by differential scanning calorimetry and Raman spectroscopy.

Thermal denaturation of the B form of double-stranded DNA has been probed by differential scanning calorimetry (DSC) and Raman spectroscopy of 160 base pair (bp) fragments of calf thymus DNA. The DSC results indicate a median melting temperature Tm = 75.5 degrees C with calorimetric enthalpy change delta Hcal = 6.7 kcal/mol (bp), van't Hoff enthalpy change delta HVH = 50.4 kcal/mol (cooperative unit), and calorimetric entropy change delta Scal = 19.3 cal/deg.mol (bp), at the experimental conditions of 55 mg DNA/ml in 5 mM sodium cacodylate at pH 6.4. The average cooperative melting unit (nmelt) comprises 7.5 bp. The Raman signature of 160 bp DNA is highly sensitive to temperature. Analyses of several conformation-sensitive Raman bands indicate the following ranges for thermodynamic parameters of melting: 43 < delta HVH < 61 kcal/mol (cooperative unit), 75 < Tm < 80 degrees C and 6 < (nmelt) < 9 bp, consistent with the DSC results. The changes observed in specific Raman band frequencies and intensities as a function of temperature reveal that thermal denaturation is accompanied by disruption of Watson-Crick base pairs, unstacking of the bases and disordering of the B form backbone. These three types of structural change are highly correlated throughout the investigated temperature range of 20 to 93 degrees C. Raman bands diagnostic of purine and pyrimidine unstacking, conformational rearrangements in the deoxyribose-phosphate moieties, and changes in environment of phosphate groups have been identified. Among these, bands at 834 cm-1 (due to a localized vibration of the phosphodiester group), 1240 cm-1 (thymine ring) and 1668 cm-1 (carbonyl groups of dT, dG and dC), are shown by comparison with DSC results to be the most reliable quantitative indicators of DNA melting. Conversely, the intensities of Raman marker bands at 786 cm-1 (cytosine ring), 1014 cm-1 (deoxyribose ring) and 1092 cm-1 (phosphate group) are largely invariant to melting and are proposed as appropriate standards for intensity normalizations.

Animals↗
PubMed1987

Indirect calorimetry.

Indirect calorimetry is a method which allows the non-invasive measurement of energy expenditure and substrate utilization in humans. The procedure is described and the main equations to calculate energy expenditure and substrate utilization are presented. The limitations of the method include physiological effects, such as hyperventilation, and the influence of metabolic processes such as gluconeogenesis, ketogenesis and lipogenesis. The general principle is that intermediate processes do not influence overall conclusions, provided that the intermediate substrates which are formed do not accumulate within the body or are not excreted. Continuous measurements of metabolic rate and respiratory quotient using the ventilated hood system have been carried out during the last 5 years to study carbohydrate and lipid metabolism in lean subjects, in obese and diabetic patients. By using the euglycaemic insulin clamp technique or by giving oral glucose loads, it has been shown that the main effect of insulin on carbohydrate metabolism is to stimulate glucose storage. By raising plasma free fatty acid levels with a neutral fat infusion in lean subjects, both glucose oxidation and glucose storage were imparied during euglycaemic insulin clamps. Glucose storage was found to be markedly impaired in non-diabetic obese patients, during euglycaemic insulin clamps in the presence of elevated lipid oxidation. In obese diabetic patients, the impairment in glucose storage was more pronounced than in non-diabetic obese; this defect was particularly marked during euglycaemic insulin clamps, but it was also present after an oral glucose load. It is concluded that impairment of glucose storage is a major defect of glucose utilization in type II diabetes.

Blood Glucose↗
PubMed2006

Evidence of a two-stage thermal denaturation process in lysozyme: a Raman scattering and differential scanning calorimetry investigation.

Raman spectroscopy (in the low-frequency range and the amide I band region) and modulated differential scanning calorimetry investigations have been used to analyze temperature-induced structural changes in lysozyme dissolved in 1H2O and 2H2O in the thermal denaturation process. Low-frequency Raman data reveal a change in tertiary structure without concomitant unfolding of the secondary structure. Calorimetric data show that this structural change is responsible for the configurational entropy change associated with the strong-to-fragile liquid transition and correspond to about 1/3 of the native-denaturated transition enthalpy. This is the first stage of the thermal denaturation which is a precursor of the secondary structure change and is determined to be strongly dependent on the stability of the hydrogen-bond network in water. Low-frequency Raman spectroscopy provides information on the flexibility of the tertiary structure (in the native state and the transient folding state) in relation to the fragility of the mixture. The unfolding of the secondary structure appears as a consequence of the change in the tertiary structure and independent of the solvent. Protein conformational stability is directly dependent on the stability of the native tertiary structure. The structural transformation of tertiary structure can be detected through the enhanced 1H/2H exchange inhibited in native proteins. Taking into account similar features reported in the literature observed for different proteins it can be considered that the two-stage transformation observed in lysozyme dissolved in water is a general mechanism for the thermal denaturation of proteins.

Amides↗
PubMed2004

Protein stabilization by osmolytes from hyperthermophiles: effect of mannosylglycerate on the thermal unfolding of recombinant nuclease a from Staphylococcus aureus studied by picosecond time-resolved fluorescence and calorimetry.

2-O-alpha-Mannosylglycerate, a negatively charged osmolyte widely distributed among (hyper)thermophilic microorganisms, is known to provide notable protection to proteins against thermal denaturation. To study the mechanism responsible for protein stabilization, pico-second time-resolved fluorescence spectroscopy was used to characterize the thermal unfolding of a model protein, Staphylococcus aureus recombinant nuclease A (SNase), in the presence or absence of mannosylglycerate. The fluorescence decay times are signatures of the protein state, and the pre-exponential coefficients are used to evaluate the molar fractions of the folded and unfolded states. Hence, direct determination of equilibrium constants of unfolding from molar fractions was carried out. Van't Hoff plots of the equilibrium constants provided reliable thermodynamic data for SNase unfolding. Differential scanning calorimetry was used to validate this thermodynamic analysis. The presence of 0.5 m potassium mannosylglycerate caused an increase of 7 degrees C in the SNase melting temperature and a 2-fold increase in the unfolding heat capacity. Despite the considerable degree of stabilization rendered by this solute, the nature and population of protein states along unfolding were not altered in the presence of mannosylglycerate, denoting that the unfolding pathway of SNase was unaffected. The stabilization of SNase by mannosylglycerate arises from decreased unfolding entropy up to 65 degrees C and from an enthalpy increase above this temperature. In molecular terms, stabilization is interpreted as resulting from destabilization of the denatured state caused by preferential exclusion of the solute from the protein hydration shell upon unfolding, and stabilization of the native state by specific interactions. The physiological significance of charged solutes in hyperthermophiles is discussed.

Calorimetry↗
PubMed1989

A mathematical analysis of indirect calorimetry measurements in acutely ill patients.

Beside indirect calorimetry is generally accepted as reliable for evaluating energy expenditure (EE) and oxidation of carbohydrate (dCH) and fat (dF) in critically ill patients. Daily measurement of nitrogen excretion is usually included in the calculation of EE, dCH, and dF but it is difficult to perform in the clinical setting and is not necessary for accurate determination of EE. In this paper new equations, which are suitable for use with critically ill patients, are given for calculating EE, dCH, and dF without N-excretion measurements. With these equations the maximum errors for EE, dCH, and dF were 56, 179, and 306 kcal/d, respectively. The mean errors in 38 measurements of 26 critically ill patients were 27, 86, and 143 kcal/d, respectively. Measurement of EE by these equations is very accurate and suitable for both research and clinical use. Although the calculation of dCH and dF is much less precise, it can still given an indication of fuel utilization.

Acute Disease↗
PubMed1990

Repeatability of 24-h energy expenditure measurements in humans by indirect calorimetry.

To estimate sources and extent of variation in energy expenditure (EE), as measured by indirect calorimetry in a room-sized human calorimeter, a number of 24-h measurements were compiled. Measured oxygen consumption and carbon dioxide production from alcohol combustion experiments averaged 101.5% of the theoretical value with a coefficient of variation (CV) of 1.4%. Experiment 1 consisted of four men who had the following averages: age, 41 y; height, 179 cm; weight, 84.6 kg; and fat, 23.5%. Five measurements, separated by 1 d, were made on each subject. Daily and basal EE averaged 2852 and 1691 kcal/d, respectively, with a within-subject CV of 2.7% and 2.4%, respectively. Experiment 2 consisted of five men who had the following averages: age, 48 y; height, 181.6 cm; weight, 87 kg; and fat, 23%. Five measurements made on each subject were separated by 1-3 wk. Daily and basal EE averaged 2619 and 1837 kcal/d, respectively, with a within-subject CV of 4.6% and 2.9%, respectively.

Adult↗