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PubMed1996

Water calorimetry for radiation dosimetry.

Calorimetry has a long history as a technique for establishing the absorbed dose, and graphite calorimetry has often been used to establish absorbed dose standards for use in radiation therapy. However, a conversion process is necessary to convert from dose to graphite to dose to water, which is the quantity of clinical interest. In order to more directly measure the dose to water, considerable effort has been devoted in the last fifteen years to the development of water calorimetry. This article reviews these developments and summarizes the present status of water calorimetry. Absorbed dose standards based on water calorimetry and with a relative standard uncertainty of 0.5-1% now seem achievable.

Calorimetry↗

PubMed1990

Nonprotein caloric requirements for patients with pancreatic abscess as measured by indirect calorimetry.

Few data exist regarding nutritional assessment during pancreatic abscess. We compared nonprotein caloric requirements calculated by Harris-Benedict equation and measured by indirect calorimetry in patients with pancreatic abscess. Seven patients with pancreatitis and pancreatic abscess had determinations of resting energy expenditure via Medicor metabolic cart with 20% added for activity. Caloric requirements were also estimated using the Harris-Benedict equation with stress factors. Determinations from indirect calorimetry ranged from 22.4-46.8 (mean 36.1) kcal/kg/d. Harris-Benedict calculations with stress factor 1.7 differed from indirect calorimetry by at least 15% in seven of ten determinations. Stress factor 1.9 results overestimated indirect calorimetry by over 25% in four of ten determinations. Energy requirements via indirect calorimetry of some patients with pancreatic abscess cover a wide range and do not correlate with Harris-Benedict calculations. Harris-Benedict equation with a stress factor of 1.9 may estimate adequate nonprotein calories for hyperalimentation, but there is risk of overfeeding.

Abscess↗

PubMed1990

Indirect calorimetry: methodological and interpretative problems.

The technique of indirect calorimetry is now widely used to examine rates of energy production and substrate oxidation in humans. Although the basic principles of indirect calorimetry are well established, it is important to recognize that there are several potential pitfalls in the methodology and data interpretation that must be appreciated to properly understand and apply the results derived from this technique. In particular, one must recognize that the fundamental measurement provided by indirect calorimetry is the net disappearance rate of a substrate regardless of the metabolic interconversions that the substrate may undergo before its disappearance from its metabolic pool. Under most circumstances, direct oxidation represents the major route by which a substrate disappears from its metabolic pool, and the two terms are often used interchangeably. However, under conditions when rates of gluconeogenesis, ketogenesis, or lipogenesis are elevated, the presumed equivalence between oxidation and disappearance may no longer apply, even though the actual measurements derived from indirect calorimetry remain valid. When indirect calorimetry is combined with other in vivo metabolic techniques (e.g., the insulin clamp or radioisotope turnover methods) it can provide a powerful tool for noninvasively examining complex metabolic processes.

Body Temperature Regulation↗

PubMed2005

[Nutritional assessment in patients with cirrhosis: the use of indirect calorimetry].

BACKGROUND: Malnutrition is frequent in cirrhotic patients, and its assessment is difficult. Functional assessment through a dynamometer is a simple method and could minimize these drawbacks. Harris-Benedict prediction formulae estimates the resting energy expenditure but has not been validated for this population. One alternative is the use of indirect calorimetry. AIM: To assess nutritional status in cirrhotic patients and estimates the resting energy expenditure through indirect calorimetry and compares it to Harris-Benedict. PATIENTS AND METHODS: Thirty four adult hepatitis C cirrhotic outpatients were studied, classified by Child-Pugh and model of end-stage liver disease score. The resting energy expenditure was predicted through Harris-Benedict and measured by indirect calorimetry. Nutritional assessment was done through anthropometry, subjective global assessment, hand-grip strength and a 3-day recall. RESULTS: Fifteen (44.2%) were Child-Pug A, 12 (35.3%) B and 7 (20.6%) C, and 33 (97.1%) had model of end-stage liver disease scores less than 20. The resting energy expenditure predicted was higher than the measured (Harris-Benedict 1404.5 +/- 150.3 kcal; indirect calorimetry 1059.9 +/- 309.6 kcal). The prevalence of malnutrition varied between methods (body mass index, muscle arm circumference, subjective global assessment, triceps skinfold thickness and hand-grip strength: 0; 5.9; 17.6; 35.3 and 79.4%, accordingly). Calories and proteins intake were 80% and 85% of recommended amounts and there was inadequate intake of calcium, magnesium, iron and zinc. CONCLUSION: Malnutrition was frequent and hand-grip strength seemed to be the most sensitive method for its diagnosis. Calories and protein intakes were inadequate. Considering that the predicted resting energy expenditure was higher than the measured one and the need to offer higher caloric intake, the use of the predicting equation may replace indirect calorimetry.

Adult↗

PubMed2005

Application of solution calorimetry in pharmaceutical and biopharmaceutical research.

In solution calorimetry the heat of solution (Delta(sol)H) is recorded as a solute (usually a solid) dissolves in an excess of solvent. Such measurements are valuable during all the phases of pharmaceutical formulation and the number of applications of the technique is growing. For instance, solution calorimetry is extremely useful during preformulation for the detection and quantification of polymorphs, degrees of crystallinity and percent amorphous content; knowledge of all of these parameters is essential in order to exert control over the manufacture and subsequent performance of a solid pharmaceutical. Careful experimental design and data interpretation also allows the measurement of the enthalpy of transfer (Delta(trans)H) of a solute between two phases. Because solution calorimetry does not require optically transparent solutions, and can be used to study cloudy or turbid solutions or suspensions directly, measurement of Delta(trans)H affords the opportunity to study the partitioning of drugs into, and across, biological membranes. It also allows the in-situ study of cellular systems. Furthermore, novel experimental methodologies have led to the increasing use of solution calorimetry to study a wider range of phenomena, such as the precipitation of drugs from supersaturated solutions or the formation of liposomes from phospholipid films. It is the purpose of this review to discuss some of these applications, in the context of pharmaceutical formulation and preformulation, and highlight some of the potential future areas where solution calorimetry might find applications.

Algorithms↗

PubMedDate not supplied

[Energy expenditure at rest: indirect calorimetry vs the Fick principle].

UNLABELLED: The objectives of this study ere to assess the reproducibility of the energy expenditure at rest in patients with mechanical ventilation, using the indirect calorimetry method and the Fick principle, and to verify whether both methods of measuring the energy expenditure, are interchangeable. 15 critically ill patients on mechanical ventilation were studied. Each study consisted of the determination, in duplicate, of the energy expenditure at rest, using indirect calorimetry and the Fick principle. Each patient was studied on two occasions, thus yielding a total of 30 studies. The determination of the energy expenditure at rest using indirect calorimetry was carried out using an apparatus based on the closed circuit method (Calorimet), and the Fick principle was carried out using a thermodilution catheter placed in the pulmonary artery. The reproducibility coefficient of the indirect calorimetry method was 132 kcal/day, which is equivalent to 7% of the average energy expenditure at rest. The reproducibility coefficient of the Fick method was 344 kcal/day, which is equivalent to 18% of the average energy expenditure at rest. The difference between both methods, 6 +/- 50 kcal/day, was not significant. The corresponding limits in both methods were between-306 kcal/day and 294 kcal/day, which is equivalent to 15% of the average energy expenditure at rest. CONCLUSIONS: The determination of the energy expenditure at rest using the Fick method, has a worse reproducibility coefficient that obtained by indirect calorimetry, but from a clinical point of view, both methods are interchangeable.

Calorimetry↗

PubMedDate not supplied

A simple and accurate indirect calorimetry system for assessment of resting energy expenditure.

An indirect calorimetry system was assembled from three readily available major components: a digital pneumotachograph, an oxygen analyzer, and a carbon dioxide analyzer. A one-way valve, face mask, and meteorological balloon completed the system. Accuracy was assessed by comparison to direct calorimetry in hospitalized patients undergoing enteral hyperalimentation. Each subject was on continuous infusion of formula during a 7-day metabolic balance. Direct and indirect calorimetry was performed over the last 4 days of the balance. The overall agreement between the two methods was within 1%. A simple and inexpensive calorimetry system can therefore be assembled to provide an accurate measure of resting energy expenditure.

Adult↗

PubMed2006

Pressure perturbation calorimetry of helical peptides.

Pressure perturbation calorimetry quantifies the temperature dependence of a solute's thermal expansion coefficient, providing information about solute-solvent interactions. We tested the idea that pressure perturbation calorimetry can provide information about solvent-accessible surface area by studying peptides with different secondary structures. The peptides comprised two host-guest series: one predominately an alpha-helix, the other predominately a polyproline II helix. In aqueous buffer, we find a correlation between the amount of secondary structure as assessed by circular dichroism spectropolarimetry and the pressure perturbation calorimetry data. We conclude that pressure perturbation calorimetry can provide information about the exposure of polar and nonpolar surface area. Data acquired in a buffered urea solution, however, are not as easily interpreted.

Calorimetry↗

PubMed2006

Thermodynamic stability and formation of aggregates of human immunoglobulin G characterised by differential scanning calorimetry and dynamic light scattering.

The final process step of polyclonal human immunoglobulin G is formulation with agents such as sugars, polyols, amino acid and salts. Often the most stable formulations were empirically identified. Physicochemical methods, such as differential scanning calorimetry and dynamic light scattering, provide a deeper insight on the biophysical properties of such a protein solution. The combination of these methods proved to be sensitive enough to detect fine differences in the properties relevant for the development of stable protein solutions. The influence of additives, such as maltose and glycine in combination with water or low concentrations of salts, on human immunoglobulin preparations was analysed. Differential scanning calorimetry illustrated that 0.2 M glycine had better stabilising effects compared to 10% maltose. Dynamic light scattering and differential scanning calorimetry revealed that solutions preventing aggregation were not optimal in terms of thermodynamic stability. Aggregation was minimised with increasing ionic strength, shown by dynamic light scattering, whereas thermodynamic stability for heat sensitive parts of human immunoglobulin G, analysed with differential scanning calorimetry, was decreased.

Biophysical Phenomena↗

PubMed1991

The hydration pressure between lipid bilayers. Comparison of measurements using x-ray diffraction and calorimetry.

The hydration pressure between dipalmitoyl phosphatidyl-N,N-dimethylethanolamine (DPPE-Me2) bilayers has been analyzed by both x-ray diffraction measurements of osmotically stressed liposomes and by differential scanning calorimetry. By the x-ray method, we obtain a magnitude (Po) and decay length (lambda) for the hydration pressure which are both quite similar to those found for bilayers of other zwitterionic lipids, such as phosphatidylcholines. That is, x-ray analysis of DPPE-Me2 in the gel phase gives lambda = 1.3 A, the same as that previously measured for the analogous gel phase lipid dipalmitoylphosphatidylcholine (DPPC), and Po = 3.9 x 10(9) dyn/cm2, which is in excellent agreement with the value of 3.6 x 10(9) dyn/cm2 calculated from the measured Volta potential of DPPE-Me2 monolayers in equilibrium with liposomes. These results indicate that the removal of one methyl group to convert DPPC to DPPE-Me2 does not markedly alter the range or magnitude of the hydration pressure. Calorimetry shows that the main gel to liquid-crystalline phase transition temperature of DPPE-Me2 is approximately constant for water contents ranging from 80 to 10 water molecules per lipid molecule, but increases monotonically with decreasing water content below 10 waters per lipid. A theoretical fit to these temperature vs. water content data predicts lambda = 6.7 A. The difference in observed values of lambda for x-ray and calorimetry measurements can be explained by effects on the thermograms of additional intra- and intermolecular interactions which occur at low water contents where apposing bilayers are in contact. We conclude that, although calorimetry provides important data on the energetics of bilayer hydration, it is difficult to obtain quantitative information on the hydration pressure from this technique.

Biophysical Phenomena↗

PubMed1996

Calorimetry of apolipoprotein-A1 binding to phosphatidylcholine-triolein-cholesterol emulsions.

The thermotropic properties of triolein-rich, low-cholesterol dipalmitoyl phosphatidylcholine (DPPC) emulsion particles with well-defined chemical compositions (approximately 88% triolein, 1% cholesterol, 11% diacyl phosphatidylcholine) and particle size distributions (mean diameter, approximately 1000-1100 A) were studied in the absence and presence of apolipoprotein-A1 by a combination of differential scanning and titration calorimetry. The results are compared to egg yolk PC emulsions of similar composition and size. Isothermal titration calorimetry at 30 degrees C was used to saturate the emulsion surface with apo-A1 and rapidly quantitate the binding constants (affinity Ka = 11.1 +/- 3.5 x 10(6) M-1 and capacity N = 1.0 +/- 0.09 apo-A1 per 1000 DPPC) and heats of binding (enthalpy H = -940 +/- 35 kcal mol-1 apo-A1 or -0.92 +/- 0.12 kcal mol-1 DPPC). The entropy of association is -3070 cal deg-1 mol-1 protein or -3 cal deg-1 mol-1 DPPC. Without protein on the surface, the differential scanning calorimetry heating curve of the emulsion showed three endothermic transitions at 24.3 degrees C, 33.0 degrees C, and 40.0 degrees C with a combined enthalpy of 1.53 +/- 0.2 kcal mol-1 DPPC. With apo-A1 on the surface, the heating curve showed the three transitions more clearly, in particular, the second transition became more prominent by significant increases in both the calorimetric and Van't Hoff enthalpies. The combined enthalpy was 2.70 +/- 0.12 kcal mol-1 DPPC and remained constant upon repeated heating and cooling. Indicating that the newly formed DPPC emulsion-Apo-A1 complex is thermally reversible during calorimetry. Thus there is an increase in delta H of 1.17 kcal mol-1 DPPC after apo-A1 is bound, which is roughly balanced by the heat released during binding (-0.92 kcal) of apo-A1. The melting entropy increase, +3.8 cal deg-1 mol-1 DPPC of the three transitions after apo-A1 binds, also roughly balances the entropy (-3 cal deg-1 mol-1 DPPC) of association of apo-A1. These changes indicate that apo-A1 increases the amount of ordered gel-like phase on the surface of DPPC emulsions when added at 30 degrees C. From the stoichiometry of the emulsions we calculate that the mean area of DPPC at the triolein/DPPC interface is 54.5 A2 at 41 degrees C and 54.2 A2 at 30 degrees C. The binding of apo-A1 at 30 degrees C to the emulsion reduces the surface area per DPPC molecule from 54.2 A2 to 50.8 A2. At 30 degrees apo-A1 binds with high affinity and low capacity to the surface of DPPC emulsions and increases the packing density of the lipid domain to which it binds. Apo-A1 was also titrated onto DPPC emulsions at 45 degrees C. This temperature is above the gel liquid crystal transition. No heat was released or adsorbed. Furthermore, egg yolk phosphatidylcholine emulsions of nearly identical composition were also titrated at 30 degrees C with apo-A1 and were euthermic. Association constants were previously measured using a classical centrifugation assay and were used to calculate the entropy of apo-A1 binding (+28 cal deg-1 mol-1 apo-A1). This value indicates that apo-A1 binding to a fluid surface like egg yolk phosphatidylcholine or probably DPPC at 45 degrees C is hydrophobic and is consistent with hydrocarbon lipid or protein moities coming together and excluding water. Thus the binding of apo-A1 to partly crystalline surfaces is entropically negative and increases the order of the already partly ordered phases, whereas binding to liquid surfaces is mainly an entropically driven hydrophobic process.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1998

Photoacoustic calorimetry of proteins.

We have described two examples of time-resolved photoacoustic calorimetry for the study of heme protein transient intermediates. Before photoacoustic calorimetry, determining thermodynamic information on short-lived intermediates was difficult. Along with being sensitive to enthalpic and volume changes, photoacoustic calorimetry can detect conformational changes in a time-resolved manner. In complex protein systems, the interpretation of the structural origins of a conformational change is sometimes difficult. Site-directed mutagenesis has been used successfully to identify the residues that play important roles in the ligand binding to both Mb and cytochrome P450cam. In both systems the hydration state of salt bridges gave rise to volume changes that were identified through mutagenesis of the residues involved. With its increasing popularity and the power of site-directed mutagenesis, time-resolved photoacoustic calorimetry is fast becoming a technique to probe conformational dynamics in proteins.

Acoustics↗

PubMed1997

Indirect calorimetry in critically ill patients: clinical applications and practical advice.

Indirect calorimetry is the method by which metabolic rate and substrate utilization are estimated in human beings starting from respiratory gas exchange measurements and urinary nitrogen excretion. This method is based on some models and assumptions that must be known and taken into consideration to correctly interpret the results obtained. Recent advances in technology and the availability of precise and portable metabolic carts have made this technique practical at the beside even in critically ill patients. It must be considered that, particularly in the ICU, there may be several sources of error and many technical difficulties in applying this methodology. Taking into account the relevant clinical studies related to the outcomes of critically ill patient, this article defines when the assessment of energy expenditure by indirect calorimetry may provide useful and valid information. Review of the literature suggests that the clinical application of indirect calorimetry in critically ill patients, although promising, requires further evaluation. Currently, the potential useful clinical applications of indirect calorimetry in this category of patients can be summarized as follows: (1) assessment of energy expenditure in patients who fail to adequately respond to the estimated nutritional needs; (2) assessment of energy expenditure in patients with single- or multiple-organ dysfunction who need prolonged ICU care and artificial nutritional support; (3) assessment of the effects induced by artificial nutrition on the cardiocirculatory and respiratory systems in mechanically ventilated patients with acute respiratory failure; and (4) monitoring of VO2 during weaning from mechanical ventilation.

Calorimetry, Indirect↗

PubMed1997

Comparison of energy expenditure measurements by diet records, energy intake balance, doubly labeled water and room calorimetry.

OBJECTIVES: The purpose of this study was to compare estimates of daily energy expenditure (EE) using energy intake from self reported diet records, metabolizable energy intake balance, doubly labeled water and room calorimetry methods. DESIGN: Cross sectional design. SETTING: Beltsville Human Nutrition Research Center, Beltsville, MD USA. INTERVENTIONS: Energy intake was measured using seven-day self reported diet records (EI), and metabolizable energy (ME) intake balance. EE was measured using doubly labeled water (TEE) and 24 h indirect room calorimetry (24 EE). Body composition was measured using stable isotope dilution and DEXA. RESULTS: EI measured by self reported diet records was 22% less than ME intake balance, 23% less than TEE by doubly labeled water and 8% less than 24 EE by room calorimetry. 24 EE was 16% less than TEE and 16% less than ME. TEE was not significantly greater than ME (0.3%). While mean ME, TEE and 24 EE measurements were significantly lower in female compared to male subjects, mean EI and the mean percent difference between measurement methods were not. CONCLUSIONS: Direct comparison of these methods indicate self reported diet records and room calorimetry underestimate daily energy expenditure. While EI balance accurately estimates energy expenditure, EE measured by doubly labeled water is a more direct approach.

Absorptiometry, Photon↗

PubMed1997

Indirect calorimetry: variability of consecutive baseline determinations of carbohydrate and fat utilization from gas exchange measurements.

During the past years, substantial methodological and interpretational limitations of indirect calorimetry, particularly concerning fuel utilisation, have been discussed. The aim of the present study was to evaluate short-time intraindividual variability of two consecutive gas exchange measurement series and of calculated data on total energy expenditure/24 h and carbohydrate and fat utilisation. 24 healthy volunteers (16 f, 8 m, 34.7 +/- 13.1 yrs) were admitted to the study. Trials were performed supine after an 12 h overnight fast. After a resting period of 30-45 min and following equilibration of respiratory values for at least 10 min prior to the test, indirect calorimetry measurements were performed using the Sensor-Medics 2.900 device (canopy). Two measurements series lasting up to 30 min each were performed 15-20 min apart. Total energy production/24 h as well as that obtained from carbohydrate and fat utilisation were calculated in both measurement series. Protein utilisation was derived from estimated urinary 24 h nitrogen excretion. O2-consumption, CO2-production, the respiratory quotient and total energy production/24 h show acceptable mean coefficients of variation of 3.7%, 4.6%, 3.5% and 3.6%, respectively. In contrast, carbohydrate and fat utilisation values demonstrate a coefficient of variation of 21.2% and 17.4%, respectively, suggesting considerable impression of estimates of fuel utilisation by indirect calorimetry. We conclude that for research purposes, particularly over short-time periods, indirect calorimetry provides sufficient accuracy only in estimating total resting energy production, while considerable uncertainty exists in using this method to assess carbohydrate and fat utilisation.

Adult↗

PubMed1994

Salt-induced formation of the molten globule state of cytochrome c studied by isothermal titration calorimetry.

Although the molten globule state has been proposed as a major intermediate of protein folding, it has proven difficult to obtain thermodynamic data characterizing this state. To explore another approach for characterizing the molten globule state, salt-induced formation of the molten globule state of horse cytochrome c at pH 1.8 was studied by isothermal titration calorimetry. By titrating the acid-unfolded cytochrome c with sodium perchlorate, an exothermic reaction was observed. The titration curve obtained from the heat was cooperative and agreed well with the conformational transition curve measured by CD at 222 nm. This result indicated that the salt-induced conformation change is well approximated by a two-state transition between the acid-unfolded and molten globule states. The heat for formation of the molten globule state estimated by isothermal titration calorimetry was consistent with the enthalpy change for unfolding of the sodium perchlorate-stabilized molten globule state at pH 1.8, which was measured by differential scanning calorimetry and CD. These results indicate that the heat of titration largely reflects the enthalpy change of the conformational transition. From these results, we consider that isothermal titration calorimetry will become a useful approach for investigating the molten globule state.

Animals↗

PubMed1989

A direct comparison of water calorimetry and Fricke dosimetry.

Considerable effort has been devoted to measuring the absorbed dose to water using water calorimetry. Most of these efforts have been hampered by a lack of adequate knowledge of the heat defect of water. We argue that there is now sufficient information to establish with considerable confidence the heat defect of high-purity water containing various dissolved gases. For the present work we used water saturated with a 50/50 mixture of H2 and O2 gases, for which the heat defect is calculated to be -2.1%. As a test of this assignment, we have compared the absorbed dose to water as measured using water calorimetry with that obtained from Fricke dosimetry. The water calorimeter consisted of a small sealed vessel containing 100 ml of stirred water saturated with a 50/50 mixture of H2 and O2 gases. It was irradiated with 20 MV x-rays at a dose rate of about 0.4 Gy s-1. The same vessel was then filled with Fricke dosemeter solution, and irradiated under identical conditions. Our Fricke dosimetry is based on the Svensson and Brahme value of epsilon G (3.515 x 10(-3) 1 cm-1 J-1) and agrees to within 0.2% with the dose to water for 60Co gamma-rays obtained via graphite calorimetry. We find that for 20 MV x-rays, the dose to water determined by water calorimetry is 1.006 +/- 0.004 times the dose determined by Fricke dosimetry. Within 0.6(+/- 0.4)%, this result supports the calculated heat defect of -2.1% for water saturated with a 50/50 mixture of H2 and O2 gases.

Calorimetry↗

PubMed1991

Comparison of extracellular and net glucose oxidation measured isotopically and by indirect calorimetry during high and low glucose turnover.

To determine the extent to which glucose oxidation measured by indirect calorimetry reflects glucose oxidation measured isotopically, subjects were studied during a 6-h hyperinsulinemic euglycemic clamp (1 mU.kg-1.min-1) and during infusion of saline. [6-14C]glucose was infused on both occasions. Breath was collected for determination of the specific activity of carbon dioxide, oxygen consumption, and carbon dioxide production. Glucose turnover during hyperinsulinemia was approximately eightfold higher than during saline infusion. During the final 1.5 h of the hyperinsulinemic glucose clamp, oxidation measured isotopically remained slightly but consistently lower (P less than 0.05) than that measured by indirect calorimetry (13.8 +/- 1.1 vs 16.5 +/- 1.7 mumol.kg-1.min-1, respectively). In contrast, during the saline infusion, glucose oxidation measured isotopically did not differ from that measured by indirect calorimetry (8.3 +/- 0.6 vs 7.2 +/- 2.8 mumol.kg-1.min-1, respectively). We conclude that although net glucose oxidation measured isotopically was slightly lower than that measured by indirect calorimetry, both techniques provide similar estimates of glucose oxidation over a wide range of glucose disposal.

Adult↗