Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CALORIMETRY”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14Linked to original sources
PubMed1990

A randomized trial of indirect calorimetry-based feedings in thermal injury.

To assess the superiority of indirect calorimetry (IC)-based enteral nutrition in burned patients, 49 adults with mean burns of 47% TBSA received feedings based either on the Curreri formula (CURR), or on IC, using enteral formulas with nonprotein calorie:nitrogen ratios of either 86:1, or 125:1. Intake in CURR patients was a mean 3,490 kcal/day, which exceeded resting energy expenditure (REE) by 43%, while IC patients received 3,530 kcal/day (1.2 x REE; p less than 0.05). Both groups maintained body weight and lymphocyte counts; survival was equal. Complications (diarrhea, nausea, hyperglycemia) were frequent in both groups, but their incidence did not differ. Patients fed the lower calorie:nitrogen ratio had greater cumulative nitrogen balance, with no increase in nitrogen excretion. It appears advisable to nourish burned patients with the minimal effective intake. While use of IC facilitates this goal, use of the Curreri formula provides acceptable approximation of caloric requirements in the early postburn period.

Adult↗
PubMed1986

Differential scanning calorimetry of bacteria.

Thermograms obtained by differential scanning calorimetry of a range of bacteria of different heat resistances were compared. Equations were derived to calculate the rate at which the numbers of viable organisms in a calorimeter decline as the temperature is raised at a constant rate. Vegetative bacteria scanned at 10 degrees C min-1 showed multi-peaked thermograms with four major peaks (denoted m, n, p and q) occurring in the regions 68-73, 77-84, 89-99 and 105-110 degrees C respectively. Exceptions were that peak m (the largest peak) occurred at 79-82 degrees C in Bacillus stearothermophilus and an additional peak, r, was detected in Escherichia coli at 119 degrees C. At temperatures below the main peak m there were major differences in thermograms between species. There was a direct relationship between the onset of thermal denaturation and the thermoresistance of different organisms. Heat-sensitive organisms displayed thermogram features which were absent in the more heat-resistant types. When samples were cooled to 5 degrees C and re-heated, a small endothermic peak, pr, was observed at the same temperature as p. Peaks p and pr were identified as the melting endotherms of DNA. In all vegetative organisms examined, maximum death rates, computed from published D and z values, occurred at temperatures above the onset of thermal denaturation, i.e. cell death and irreversible denaturation of cell components occurred within the same temperature range.

Bacillus cereus↗
PubMed1997

Synchronous direct gradient layer and indirect room calorimetry.

A dual direct/indirect room-sized calorimeter is used at the Beltsville Human Nutrition Research Center to measure heat emission and energy expenditure in humans. Because the response times of a gradient layer direct calorimeter and an indirect calorimeter are not equivalent, the respective rate of heat emission and energy expenditure cannot be directly compared. A system of equations has been developed and tested that can correct the respective outputs of the direct gradient layer calorimeter and indirect calorimeter for delays due to the response times of the measurement systems. Performance tests using alcohol combustion to simulate a human subject indicate accurate measurements of heat production from indirect (99.9 +/- 0.4%), indirect corrected for response time (99.9 +/- 0.5%), direct (99.9 +/- 0.8%), and direct corrected for response time (99.9 +/- 0.8%) calorimetry systems. Results from 24-h measurements in 10 subjects indicate that corrected heat emission is equivalent to (99.8 +/- 2.0%) corrected energy expenditure. However, heat emission measured during sleep was significantly greater (14%) than energy expenditure, suggesting a change in the energy stored as heat in the body. This difference was reversed during the day. These results illustrate how the simultaneous measurement of heat emission and energy expenditure provides insights into heat regulation.

Basal Metabolism↗
PubMedDate not supplied

Indirect calorimetry: comparison of hood and mask systems for measuring resting energy expenditure in healthy volunteers.

Controversy exists as to the validity and reliability of hood and mask systems in measuring indirect calorimetry. The purpose of this study was to evaluate the accuracy and reproducibility of repeat measurements of resting energy expenditure (REE) in volunteers. Paired REE measurements were performed in 23 subjects after an overnight fast using hood and mask systems. Lean body mass was calculated from four skinfold measurements and body weight determinations. Data were normalized to body weight and lean body mass and were calculated as percent predicted REE in paired tests taken within 5 minutes on the same subject. No significant difference in mean REE was noted between hood and mask systems. Linear regression analysis showed a strong positive correlation (r = 0.91, p less than 0.001) between hood and mask measurements of REE.

Adult↗
PubMedDate not supplied

Indirect calorimetry in malnutrition: nutritional assessment or therapeutic reference?

The measurement of gas exchange for use in indirect calorimetry is a clinical research tool struggling to find its proper place in the care of acutely ill and nutritionally depleted patients. Some investigators have proposed that it should be used as part of the nutritional assessment. Unfortunately, in common with many other measurements for nutritional assessment, the information provided must be integrated with other information. It is recognized that factors other than malnutrition may influence the level of the metabolic rate. Despite the lack of precision and specificity, the measurement of energy expenditure provides an important reference for determining patients' requirements for energy intake. As with many other procedures in clinical medicine, the more severely ill the patient, the less the accuracy of standard formulas for estimating energy expenditure. Thus, actual measurements of energy expenditure assume special value.

Body Constitution↗
PubMed1986

Insulin sensitivity and exogenous insulin clearance in Graves' disease. Measurement by the glucose clamp technique and continuous indirect calorimetry.

Insulin sensitivity was measured in a group of seven thyrotoxic patients and in a group of seven normal subjects by means of the glucose clamp technique. Infusion of insulin at a rate of 0.80 +/- 0.05 mU/kg X min in the hyperthyroid patients and of 0.55 +/- 0.04 mU/kg X min in the control group was performed to obtain a steady-state plasma insulin concentration of approximately 50 microU/ml. Substrate oxidation rates were measured in the postabsorptive state and during the 2 h of the clamp by means of continuous indirect calorimetry. In the postabsorptive state, hyperthyroid patients presented a preferential oxidation of lipids. During the period 60-120 min of the clamp, mean plasma glucose (92 +/- 2 versus 93 +/- 2 mg/dl), insulin (50 +/- 5 versus 58 +/- 3 microU/ml), and total glucose metabolism (5.8 +/- 0.7 versus 6.1 +/- 0.3 mg/kg X min) were similar in the hyperthyroid patients and the control subjects. The rate of glucose oxidation was higher in hyperthyroid patients than in control subjects (4.3 +/- 0.5 versus 2.2 +/- 0.2 mg/kg X min, P less than 0.001), while that of lipid oxidation was similar in both groups (0.6 +/- 0.2 versus control 0.7 +/- 0.1 mg/kg X min). The calculated metabolic clearance rate of insulin was markedly higher in the hyperthyroid patients (1144 +/- 132 ml/min) than in the normal subjects (812 +/- 56 ml/min, P less than 0.025). It is concluded that insulin sensitivity is not altered in the thyrotoxic state. The major route of insulin-stimulated glucose disposal in the hyperthyroid patients appears to be glucose oxidation.

Adult↗
PubMed1979

Differential scanning calorimetry of the thermal denaturation of human serotransferrin.

The thermal denaturation of iron-free and iron human serotransferrin has been studied by differential scanning calorimetry. At pH 7.9 in 0.05M Tris, 0.1M NaHCO3 buffer, two transitions (Td = 60.1 degrees, 70.7 degrees C), at a 5 degrees C/min heating rate, were observed for iron-free serotransferrin. The respective enthalpies of denaturation were found to be 143 and 229 kcal/mol. Iron serotransferrin exhibits a single thermogram peak with Td = 83.4 degrees C and delta H = 616 +/- 15 kcal/mol (linearly extrapolated to 0 degrees C/min heating rate), at pH 7.8. An activation energy of 104 kcal/mol was computed by the procedure of Beech. A value of 112 kcal/mol was calculated from a first-order kinetics Arrhenius plot. Rate constants were determined at several temperatures from the onset temperature to Td. Denaturation temperatures and enthalpies were linearly dependent on heating rates. The thermal denaturations of iron-free and iron serotransferrins are irreversible, under the experimental conditions used. In contrast to conalbumin, thermograms of serotransferrin solutions partially saturated with ferric ions exhibit only the peaks corresponding to those obtained on separate DSC scans of iron-free and iron serotransferrin, respectively.

Apoproteins↗
PubMedDate not supplied

[Use of a differential calorimetry method for studying the energy mechanisms of the protective action of anti-ischemic agents].

Differential calorimetry is suggested for quantitative estimation of antiischemic activity of the drugs by determining total energy losses, the critical level of energy losses and permissible times of ischemia of isolated organs. The method allows the unraveling of the mechanisms by which antiischemic resistance of cells and organs is formed with pharmacological means.

Animals↗
PubMed1996

Water vaporization from heated tissue: an in vitro study by differential scanning calorimetry.

BACKGROUND AND OBJECTIVE: The heat balance equation is central to modeling laser vaporization of tissue. Because about 70% of tissue is water, energy loss due to water vaporization becomes an important consideration in modeling. In this study, the rate and pattern of water vaporization from various animal tissues studied by differential scanning calorimetry (DSC) are reported. STUDY DESIGN/MATERIALS AND METHODS: DSC thermograms of fresh muscle, liver, and kidney tissues were made at heating rates of 2 degrees C/min, 5 degrees C/min, and 10 degrees C/min in the temperature range of 30-150 degrees C. Thermograms of vacuum-dried muscle sample were also made to establish that the endotherms obtained were essentially due to the water in the tissue. RESULTS AND CONCLUSION: Two broad peaks-one below and the other above 100 degrees C-are seen in all the endotherms. The peaks are attributed to the structural and compositional features of tissue and tissue water. The two-stage vaporization pattern has importance in modeling tissue heating by a continuous-wave Nd:YAG laser.

Animals↗
PubMed1999

Effect of thermal denaturation on water-collagen interactions: NMR relaxation and differential scanning calorimetry analysis.

The dependence of the proton spin-lattice relaxation rate, and of the enthalpy and temperature of denaturation on water content, were studied by nmr and differential scanning calorimetry (DSC) in native and denatured collagen. Collagen was first heated at four different temperatures ranging from 40 to 70 degrees C. The percentage of denatured collagen induced by these preheating treatments was determined from DSC measurements. The DSC results are discussed in terms of heat-induced structural changes. A two-exponential behavior for the spin-lattice relaxation was observed with the appearance of denatured collagen. This was attributed to the presence of a noncollagen protein fraction. The variations in the different longitudinal relaxation rates as a function of the moisture content and of the denatured collagen percentage are described within the multiphase water proton exchange model. This study highlights the complementarity of the information obtained from the two analytical tools used.

Animals↗
PubMed1996

A differential scanning calorimetry study of retrieved orthopedic implants made of ultrahigh molecular weight polyethylene.

Differential scanning calorimetry (DSC) was used to examine thermal and thermooxidative properties of ultrahigh molecular weight polyethylene (UHMW-PE) of five acetabular components of failed orthopedic implants retrieved at revision of total hip arthoplasty. The results were compared with controls (unimplanted acetabular cups, a 20-year-old slab of UHMW-PE, and raw material). Profiles of exothermic peaks indicated increased levels of oxidation in all retrieved cups. In three retrieved cups, DSC revealed an additional peak of endotherm that was not seen in control samples. The additional endotherm peaks were not artifacts due to oxidation during scanning, heat buildup during cutting of the samples, or the sterilization method after retrieval. The additional peak was associated with the bulk of the polymer that was extracted with hexane. It varied in relative area, depending on its original location of the sample in a cup, implicating local variability in the extent of changes in material property. The distribution of the changes suggests that, during implantation, tissue exposure and friction affected the level of oxidation and degree of crystallinity in the UHMW-PE to a greater degree than did loading alone. Overall results showed that DSC may be a useful tool in evaluating changes in the properties of UHMW-PE orthopedic components in vivo.

Acetabulum↗
PubMed1998

Identification and quantification of the crystalline structures of poly(vinylidene fluoride) sutures by wide-angle X-ray scattering and differential scanning calorimetry.

The outstanding biocompatibility of the polyvinylidene fluoride (PVDF) monofilament suture together with other desirable characteristics, such as ease of handling and resistance to biodegradation, makes it an attractive alternative monofilament suture material for cardiovascular surgery. However, to achieve a high performance suture, the polymeric raw material must be exposed to different treatments, which lead to different degrees and types of crystallization. Since these crystalline modifications deeply influence the mechanical characteristics and the biostability of the sutures, the authors hereby propose a method of quantifying the different structures of PVDF using wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The commercial devices are achieved by coloring and processing the polymeric raw material. The white and unprocessed 4-0 unswaged suture presents 19% of the alpha phase, 38% of the beta structure, and no gamma form. Coloration increases the amount of the beta phase by 5-9% at the expense of the alpha phase. On the other hand, processing the fibers lead to the conversion of some of the amorphous phase to the gamma structure, the importance of which is 6-7%. Finally, tensile measurements performed on the different PVDF fibers clearly proves that their mechanical characteristics depend on the presence of these crystalline forms in the polymeric structure of PVDF.

Calorimetry, Differential Scanning↗
PubMed2000

Differential scanning calorimetry of albumin solders: interspecies differences and fatty acid binding effects on protein denaturation.

BACKGROUND AND OBJECTIVE: Understanding albumin solder denaturation is important for laser tissue soldering. Human (HSA), bovine (BSA), porcine (PSA), and canine (CSA) albumin both fatty acid containing (FAC) and fatty acid free (FAF) were evaluated by using differential scanning calorimetry (DSC). STUDY DESIGN/MATERIALS AND METHODS: DSC was used to measure difference thermograms to determine the irreversible thermal denaturation profile for 50% albumin solutions. The denaturation transition's onset, end and peak temperatures, and enthalpy were measured. RESULTS: All FAC species, except BSA, exhibited twin peaked endotherms. Single endotherms were observed for all FAF species and BSA-FAC. Onset and end temperatures were significantly [P < 0.001] lower for all FAF species (except BSA's end temperature). There was a 30% decrease in the denaturation enthalpy between FAF and FAC groups. CONCLUSION: FAF albumin solders were found to denature at significantly lower temperatures, while also having a 30% reduction in enthalpy when compared with their FAC counterparts.

Animals↗
PubMed2000

Differential scanning calorimetry, biochemical, and biomechanical analysis of human skin from individuals with diabetes mellitus.

The aim of this work was to compare biochemical, two-dimensional biomechanical and calorimetric parameters of diabetic skin vs. control skin. Skin specimens taken from the palms and backs of the hands of aged persons with non-insulin-dependent diabetes mellitus (NIDDM) and of controls (CO) were compared (age range 68-85 years). Only skin specimens from individuals with diabetes mellitus (DM) showed an increased fluorescence specific for the formation of advanced glycation end-products (AGEs) and the presence of tissue AGEs, such as N(e)-(Carboxymethyl)lysine (CML). Differential scanning calorimetry (DSC) revealed an elevation of the heat flow per unit mass during collagen denaturation in diabetic skin samples. However, the temperatures of the heat flow maximum and the onset of the phase transformation were not uniformly altered. Young's moduli were found to be increased in diabetic skin and correlated with AGE-fluorescence and tissue AGEs. The ratio between the Young's moduli, which defines a measure for the degree of anisotropy, was higher for dorsal skins from hands. In dorsal skin specimens from diabetic subjects the degree of anisotropy was more pronounced than in healthy controls. In general, neither of the measured parameters showed any correlation with age. However, E(1) moduli were clearly associated with the duration of diabetes.

Aged↗
PubMed2000

Differential scanning calorimetry study of the hydrophobic hydration of the elastin-based polypentapeptide, poly(VPGVG), from deficiency to excess of water.

The polypentapeptide of elastin, poly(VPGVG), has become an interesting model polypeptide in understanding the mechanism of protein folding and assembly. Due to its simple amino acid composition and the predominance of apolar side chains, this polymer shows strong hydrophobic-hydration phenomena. This paper explores, by calorimetric methods, the nature and structure of the clathrate-like arrangements that take place, surrounding the apolar side chains of the polymer. The performance of these methods, especially differential scanning calorimetry, has a well-gained reputation. In this work, the development of the clathrate-like structures around this model polymer has been followed from water deficiency to water-excess states. Two main conclusions have been obtained from the data obtained. First, there is an upper limit of about 170 water molecules per pentamer as the number of water molecules required to form all the possible clathrate-like structures. Second, these structures exist as an inhomogeneous population with energies spreading in a significantly broad range, which is likely related to differences in geometrical parameters (bond lengths and angles) of the clathrate structure.

Amino Acid Sequence↗
PubMed2002

The anatomy of the energetics of molecular recognition by calorimetry: chiral discrimination of camphor by alpha-cyclodextrin.

The molecular recognition of both camphor enantiomers 2 with the chiral alpha-cyclodextrin (alpha-CD) 1 in water and D(2)O was examined by calorimetry. On the basis of statistically supported determinations the thermodynamics of 2:1 host-guest binding and chiral discrimination was evaluated. The energetic signature strongly supports hydrophobic interaction as the dominant driving force for camphor encapsulation by alpha-CD in water. The solvent isotope effect on the binding equilibrium served to dissect the experimental enthalpy DeltaH(ass) into direct interaction (DeltaH(intr)) and solvent reorganization (DeltaH(solv)) terms. From this analysis the mutual interaction of two cyclodextrin and one camphor molecules contributes only 25 % to the observed enthalpy of binding DeltaH(ass), all the rest is attributed to solvent restructuring. Furthermore, the dramatic change in the pattern of thermodynamic state functions on solvent transfer from water to D(2)O is taken as compeling evidence for the involvement of water as a structural tectone in the supramolecular architecture of the 2:1 complex. As a corollary, bilateral host-guest interactions as conveyed by the lock-and-key metaphor of molecular recognition provide an inadequate description of this seemingly simple artificial host-guest system.

Calorimetry↗
PubMed1990

The molecular features of membrane perturbation by anaesthetic steroids: a study using differential scanning calorimetry, small angle X-ray diffraction and solid state 2H NMR.

We have studied the interactions of the anaesthetic steroid alphaxalone and its inactive isomer delta 16-alphaxalone with model membrane bilayers using differential scanning calorimetry, small angle X-ray diffraction and solid state NMR. Our data show that the anaesthetic steroid broadens the membrane phase transition and increases the ratio of gauche to trans conformers in the membrane. Delta 16-Alphaxalone has only small effects on membrane and incorporates to a limited degree in the bilayer. The amphipathic anaesthetic steroid alphaxalone is located near the membrane interface (the junction of the polar and hydrophobic regions of the phospholipids forming the bilayer). It orients with its long axis parallel to the chains of the lipid membranes and its 3 alpha-hydroxyl group near the sn-2 carbonyl. Anchoring of the steroid at the membrane interface and imperfect packing with the bilayer chains may be involved in membrane perturbation and eventually lead to anaesthesia.

Anesthetics↗
PubMed1990

Differential scanning calorimetry studies of the inverse temperature transition of the polypentapeptide of elastin and its analogues.

Differential scanning calorimetry studies have been carried out on the sequential polypeptide of elastin, (L-Val1-L-Pro2-Gly3-L-Val4-Gly5)n, abbreviated as PPP, and its more hydrophobic analogues (L-Leu1-L-Pro2-Gly3-L-Val4-Gly5)n, referred to as Leu1-PPP, and (L-Ile1-L-Pro2-Gly3-L-Val4-Gly5)n, referred to as Ile1-PPP Consistent with inverse temperature transitions, the temperatures of the transitions for which maximum heat absorption occurs are inversely proportional to the hydrophobicities of the polypentapeptides (31 degrees C for PPP, 16 degrees C for Leu1-PPP, and 12 degrees C for Ile1-PPP), and the endothermic heats of the transitions are small and increase with increasing hydrophobicity, i.e., 1.2, 2.9, and 3.0 kcal/mol pentamer for PPP, Leu1-PPP, and Ile1-PPP, respectively. Previous physical characterizations of the polypentapeptides have demonstrated the occurrence of an inverse temperature transition since increase in order, as the temperature is raised above that of the transition, has been repeatedly observed using different physical characterizations. Furthermore, the studies demonstrated identical conformations for PPP and Il21-PPP above and below the transition. Both heats and temperatures of the transitions vary with hydrophobicity, but not in simple proportionality.

Amino Acid Sequence↗