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PubMedDate not supplied

Isothermal titration calorimetry and differential scanning calorimetry as complementary tools to investigate the energetics of biomolecular recognition.

The principles of isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC) are reviewed together with the basic thermodynamic formalism on which the two techniques are based. Although ITC is particularly suitable to follow the energetics of an association reaction between biomolecules, the combination of ITC and DSC provides a more comprehensive description of the thermodynamics of an associating system. The reason is that the parameters DeltaG, DeltaH, DeltaS, and DeltaCp obtained from ITC are global properties of the system under study. They may be composed to varying degrees of contributions from the binding reaction proper, from conformational changes of the component molecules during association, and from changes in molecule/solvent interactions and in the state of protonation.

Animals↗
PubMed1991

Direct calorimetry using Swan-Ganz catheter for evaluation of general metabolic expenditure in acute cerebrovascular disease--comparison between direct Fick method and indirect calorimetry technique.

Oxygen consumption calculated by the direct Fick method using a Swan-Ganz catheter (D-VO2) and indirect calorimetry using a metabolic computer (ID-VO2), carbon dioxide production calculated by the latter method, and respiratory quotient were determined pre- and postoperatively in 12 patients with acute hypertensive intracerebral hemorrhage and eight patients with acute ruptured intracranial aneurysm. The mean D-VO2 value was slightly lower than the mean ID-VO2 value, but had a significantly positive correlation. The regression curve was very close to the line of identity. The total metabolic expenditure can be calculated from D-VO2 and daily urinary nitrogen excretion. Direct calorimetry using a Swan-Ganz catheter is a simple method to evaluate metabolic expenditure in acute hemorrhagic cardiovascular disease.

Acute Disease↗
PubMed2001

Pathogenesis of obesity and diabetes mellitus: insights provided by indirect calorimetry in humans.

Energy homeostasis is the balance between energy intake and energy expenditure. Assessment of energy intake is unreliable, especially in obese individuals. On the contrary it is possible to assess energy expenditure by means of different techniques. In this review, the contributions of indirect calorimetry to its assessment and to the comprehension of the pathogenic mechanisms of obesity and diabetes mellitus are discussed. Knowledge regarding energy expenditure and its components (basal metabolic rate, food-induced thermogenesis, expenditure related to physical activity), obtained in obese individuals by means of indirect calorimetry, is summarized. The effects of dietetic manipulation of the relative fractions of macronutrients (fat, carbohydrate and protein) and fiber intake on energy expenditure are described with implications regarding the pathogenesis of obesity. Besides environmental factors, energy expenditure is strongly influenced by inherited features. The application of indirect calorimetry to study recently discovered polymorphisms of genes strongly related to energy expenditure in humans is also summarized. The role of indirect calorimetry in the identification of the glucose metabolic pathways (oxidative and non-oxidative) affected in the insulin resistance syndrome is also described. Indirect calorimetry has been useful in realizing that the alterations typical of insulin resistance are reproducible in vivo in healthy humans, increasing the availability of free fatty acids. In fact, indirect calorimetry contributed to understanding the in vivo mechanisms of substrate competition, which was hypothesized more than forty years ago. In this field of application, the identification of simple (non-invasive and inexpensive) markers of insulin resistance is urgent for primary and secondary prevention of these diseases with high morbidity and mortality. The postabsorptive assessment of resting energy expenditure and macronutrient partitioning in fuel metabolism may be helpful and is discussed with advantages and limitations. The treatment of multifactorial diseases will probably require the use of poly-therapeutic interventions. In fact, drugs that act purely on one pathogenic factor of these diseases frequently fail. To better design strategic therapeutic approaches for each patient, to achieve significant long-term efficacy in the treatment of these diseases and to prevent their complications, indirect calorimetry has to be considered a landmark of quality control for nutritional support.

Calorimetry, Indirect↗
PubMed1978

Indirect calorimetry as a guide to caloric replacement during total parenteral nutrition.

Fifty patients were studied by indirect calorimetry to assess caloric needs. Seventeen patients received total parenteral nutrition (TPN) in a fixed dose of 45 +/- 3 kcal/kg. Thirty-three patients were studied after acute injury. Indirect calorimetry and the basal energy expenditure equation (BEEE) were compared. In male patients receiving TPN, indirect calorimetry more closely approximated caloric needs than did the BEEE X 1.75. In female patients, the BEEE X 1.75, indirect calorimetry value, and calories infused were more equivalent, and positive nitrogen balance was consistently achieved. In thirty-three trauma patients, indirect calorimetry and the BEEE were compared. Indirect calorimetry consistently predicted higher caloric expenditure than did the BEEE X 1.75. In assessing caloric requirements in acutely catabolic patients, the BEEE X 1.75 appears to be inadequate. The BEEE does not take into account changes in temperature or degree of illness. Indirect calorimetry is easy to perform and gives more pointed information about the patient's caloric needs.

Adolescent↗
PubMed2001

Indirect calorimetry and nutritional problems in clinical practice.

Indirect calorimetry is a simple and affordable tool for measuring energy expenditure and for quantifying the utilization of macronutrients. Its use is becoming increasingly widespread, but it is necessary to know its methodological features and its theoretical and practical limitations. Indirect calorimetry measures the rate of resting energy expenditure (REE), the major component of the total daily energy expenditure. Thus, indirect calorimetry reliably estimates the individual energy needs. Coupling the measurement of body composition to that of REE expands the diagnostic potential of indirect calorimetry. Once the lean and fat compartments have been measured, it is possible to establish on the basis of REE whether an individual is hyper- or hypometabolic. The evaluation of substrate oxidation by indirect calorimetry is subject to more severe theoretical constraints, because certain metabolic assumptions must be made. The clinical applications are practically unlimited. In the critically ill, a major goal is to maintain energy balance during the hypermetabolic response following trauma. The REE measurement is valuable from the diagnostic standpoint, because it recognizes discrepancies from the expected time-course of hypermetabolism, for example signaling a potentially catastrophic hypometabolic response. REE is also indispensable for providing correct nutritional support because both hyper- and undernutrition lead to increased mortality. In young or elderly patients, in whom energy consumption may be very different from that predicted from equations based on anthropometric measures, indirect calorimetry is particularly useful.

Aging↗
PubMed1999

Comparison of indirect calorimetry, the Fick method, and prediction equations in estimating the energy requirements of critically ill patients.

BACKGROUND: Accurate measurement of resting energy expenditure (REE) is helpful in determining the energy needs of critically ill patients requiring nutritional support. Currently, the most accurate clinical tool used to measure REE is indirect calorimetry, which is expensive, requires trained personnel, and has significant error at higher inspired oxygen concentrations. OBJECTIVE: The purpose of this study was to compare REE measured by indirect calorimetry with REE calculated by using the Fick method and prediction equations by Harris-Benedict, Ireton-Jones, Fusco, and Frankenfield. DESIGN: REEs of 36 patients [12 men and 24 women, mean age 58+/-22 y and mean Acute Physiology and Chronic Health Evaluation II score 22+/-8] in a hospital intensive care unit and receiving mechanical ventilation and total parenteral nutrition (TPN) were measured for > or = 15 min by using indirect calorimetry and compared with REEs calculated from a mean of 2 sets of hemodynamic measurements taken during the metabolic testing period with an oximetric pulmonary artery catheter. RESULTS: Mean REE by indirect calorimetry was 8381+/-1940 kJ/d and correlated poorly with the other methods tested (r = 0.057-0.154). This correlation did not improve after adjusting for changes in respiratory quotient (r2 = 0.28). CONCLUSIONS: These data do not support previous findings showing a strong correlation between REE determined by the Fick method and other prediction equations and indirect calorimetry. In critically ill patients receiving TPN, indirect calorimetry, if available, remains the most appropriate clinical tool for accurate measurement of REE.

APACHE↗
PubMed1992

Energy expenditure and gas exchange measurements in postoperative patients: thermodilution versus indirect calorimetry.

OBJECTIVE: To compare a method of measuring energy expenditure and gas exchange using the Fick principle with the standard indirect calorimetry technique. DESIGN: Prospective study of a consecutive sample of postoperative patients. Oxygen consumption (VO2), CO2 production (VCO2), respiratory quotient, and energy expenditure were derived from measurements of variables, including oxygen content and cardiac output. Energy expenditure and gas exchange were measured simultaneously by continuous indirect calorimetry over a 60-min period. SETTING: Surgical ICU in a university hospital. PATIENTS: Twenty-six consecutive patients (45 to 80 yrs) who underwent sustained surgical trauma. Excluded from the study entry were patients with time-related fluctuations of hemodynamic variables, poor cooperation, patients who required supplemental oxygen, or mechanical ventilation. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: While the measurements of VO2 and VCO2 by calorimetry and thermodilution were significantly correlated with one another (for VO2, r2 = .93, p less than .001; for VCO2, r2 = .26, p less than .01), VO2 and VCO2 values by indirect calorimetry were consistently greater than VO2 and VCO2 values by the Fick method (p less than .01). The respiratory quotient calorimetric measurements ranged between 0.69 and 0.99, whereas the corresponding thermodilution measurements spread to impossible values, from 0.24 to 1.30 (0.821 +/- 0.07 vs. 0.740 +/- 0.24, p less than .05). There was an insignificant relationship (r2 = .06, p = .21) between the values of respiratory quotient by the two methods. A strong, positive correlation between energy expenditure measured by indirect calorimetry and energy expenditure measured by the Fick method was observed (r2 = .92, p less than .001). The limit of agreement between the two methods was -0.24 +/- 73 kcal/day/m2 (-1.00 +/- 305 kJ/day/m2). CONCLUSIONS: In postoperative patients, while VO2 and energy expenditure measurements by thermodilution are easy to perform and accurate for clinical purposes, VCO2, and respiratory quotient measurements are too imprecise and inaccurate to serve any useful function. Therefore, in those clinical situations in which an evaluation of respiratory quotient and substrate utilization may be useful for purposes of metabolic care of the surgical patient, precise measurements of gas exchange with indirect calorimetry are mandatory.

Calorimetry, Indirect↗
PubMed1993

Methodological evaluation of indirect calorimetry data in lean and obese rats.

1. The applicability of current indirect calorimetry formulae to the study of energy and substrate balances on obese rats has been evaluated. The energy consumption of series of 60-day rats of Wistar, lean and obese Zucker stock were studied by means of direct and indirect calorimetry, and by establishing their energy balance through measurement of food intake and retention. Calorimetric studies encompassed a 24 h period, with gas and heat output measurements every 2 or 5 min, respectively, for direct and indirect calorimetry. 2. The analysis of fat composition (diet, whole rat, and synthesized and oxidized fat) showed only small variations that had only a limited effect on the overall energy equation parameters. 3. A gap in the nitrogen balance, which represents a urinary N excretion lower than the actual protein oxidized, resulted in significant deviations in the estimation of carbohydrate and lipid oxidized when using the equations currently available for indirect calorimetry. 4. Analysis of the amino acid composition of diet and rat protein as well as of the portion actually oxidized, and correcting for the nitrogen gap allowed the establishment of a set of equations that gave better coincidence of the calculated data with the measured substrate balance. 5. The measured heat output of all rats was lower than the estimated values calculated by means of either indirect calorimetry of direct energy balance measurement; the difference corresponded to the energy lost in water evaporation, and was in the range of one-fifth of total energy produced in the three rat stocks. 6. Wistar rats showed a biphasic circadian rhythm of substrate utilization, with alternate lipid synthesis/degradation that reversed that of carbohydrate, concordant with nocturnal feeding habits. Zucker rats did not show this rhythm; obese rats synthesized large amounts of fat during most of the light period, consuming fat at the end of the dark period, which suggests more diurnal feeding habits. Lean Zucker rats showed a similar, but less marked pattern. 7. The results obtained indicate that lean and obese rats can be studied using the same indirect calorimetry formulae provided that there is an adequate measure of protein oxidation and the composition of diet does not differ.

Amino Acids↗
PubMed1998

The effect of indirect calorimetry measurement on claudication pain in patients with peripheral arterial occlusive disease.

The effect of indirect calorimetry measurement on the duration to onset and maximal claudication pain and hemodynamic measures was evaluated. Fifteen male patients with peripheral arterial occlusive disease (PAOD) performed two graded exercise tests (GXTs) in random order, one with and the other without the use of indirect calorimetry measurement. During the tests the time to onset and maximal claudication pain was recorded. Before and after the tests, ankle/brachial systolic pressure index (ABI) was determined. The time to onset of claudication pain was shorter for the test with indirect calorimetry (4:49+/-3:50 vs 5:44+/-4:39 min:sec, p < 0.005). Time to maximal claudication pain was not significantly different between the two conditions (8:58+/-3:01 min:sec with indirect calorimetry, 9:39+/-3:36 min:sec, without). There were no significant differences in ABI between the two testing sessions at any time point. Results of this study suggest that indirect calorimetry measurement can be utilized without compromising maximal claudication pain time or hemodynamic measurements but that time to onset of claudication pain is hastened with indirect calorimetry measurement in patients with PAOD.

Aged↗
PubMed2001

Evaluation of accuracy and reliability of indirect calorimetry for the measurement of resting energy expenditure in healthy dogs.

OBJECTIVE: To assess accuracy and reliability of open-flow indirect calorimetry in dogs. ANIMALS: 13 clinically normal dogs. PROCEDURE: In phase 1, oxygen consumption per kilogram of body weight (VO2/kg) was determined in 6 anesthetized dogs by use of open-flow indirect calorimetry before and after determination of VO2/kg by use of closed-circuit spirometry. In phase 2, four serial measurements of VO2 and carbon dioxide production (VCO2) were obtained in 7 awake dogs by use of indirect calorimetry on 2 consecutive days. Resting energy expenditure (REE) was calculated. RESULTS: Level of clinical agreement was acceptable between results of indirect calorimetry and spirometry. Mean VO2/kg determined by use of calorimetry before spirometry was significantly greater than that obtained after spirometry. In phase 2, intraclass correlation coefficients (ICC) for REE and VO2 were 0.779 and 0.786, respectively, when data from all 4 series were combined. When the first series was discounted, ICC increased to 0.904 and 0.894 for REE and VO2, respectively. The most reliable and least variable measures of REE and VO2 were obtained when the first 2 series were discounted. CONCLUSIONS AND CLINICAL RELEVANCE: Open-flow indirect calorimetry may be used clinically to obtain a measure of VO2 and an estimate of REE in dogs. Serial measurements of REE and VO2 in clinically normal dogs are reliable, but a 10-minute adaption period should be allowed, the first series of observations should be discounted, multiple serial measurements should be obtained, and REE.

Animals↗
PubMed1996

Resting energy expenditure in patients with cirrhosis of the liver measured by indirect calorimetry, anthropometry and bioelectrical impedance analysis.

Energy expenditure was investigated in 15 patients with liver cirrhosis and 20 healthy controls by three methods: indirect calorimetry, anthropometry using the Harris-Benedict equation and bioelectrical impedance analysis. The energy expenditure was expressed in kcal/day, kcal/kg BW/day (BW - body weight), kcal/kg LBM/day (LBM - lean body mass, derived by bioelectrical impedance analysis) or in kcal/m2/day. We did not find statistical differences between values of resting energy expenditure obtained in patients with cirrhosis of the liver and healthy controls whichever method we used. We also did not find statistical differences between values obtained by indirect calorimetry, anthropometry and bioelectrical impedance analysis. There was a significant correlation between indirect calorimetry and anthropometry in both groups. We found significant correlations between indirect calorimetry and anthropometry, and between indirect calorimetry and bioelectrical impedance analysis, in the control group only. We can conclude that (1) resting energy expenditure of patients with cirrhosis of the liver is not changed when compared with healthy controls, and (2) bioelectrical impedance is a useful method to calculate body composition from which energy expenditure is derived; however, it gives an appropriate result only in healthy people, and only approximate values in patients with cirrhosis.

Adult↗
PubMed1996

Indirect calorimetry in critically ill patients: role of the clinical dietitian in interpreting results.

Evaluation and interpretation of energy needs of critically ill patients require the expertise of clinical dietitians: Dietitians must be knowledgeable about the methods available to quantify energy needs and able to communicate effectively with physicians and nurses regarding nutritional requirements. Several prediction equations are available for calculating energy needs of critically ill patients. Indirect calorimetry is also used frequently to measure energy requirements in this patient population. This article defines when energy expenditure measured by indirect calorimetry may provide clinically useful information. Data obtained by indirect calorimetry must be interpreted carefully. Indirect calorimetry is based on the equations for oxidation of carbohydrate, protein, and fat. Errors in interpretation can be made when metabolic pathways other than oxidation dominate or when clinical conditions exist that affect carbon dioxide excretion from the lungs. Before incorporating data obtained from indirect calorimetry into a nutrition care plan, the clinical dietitian should carefully evaluate the following factors for a patient: clinical conditions when the measurement was made, desired weight loss or gain, tolerance to food or nutrition support, relationship between protein intake and energy need, and need for anabolism or growth. This article provides clinical examples illustrating how measured values compare with calculated values and recommendations for how to incorporate measured values into nutrition care plans.

Adult↗
PubMed1992

Direct correlation of structure changes and thermal events in hydrated lipid established by simultaneous calorimetry and time-resolved x-ray diffraction.

In many lipid systems, polymorphic and mesomorphic behavior depends on sample thermal history. To establish unequivocally the structural origin of endothermic and exothermic events in such systems, we have performed simultaneous calorimetry and time-resolved x-ray diffraction (SCALTRD). To this end, aluminum calorimetry crucibles were used to contain the hydrated lipid sample, and the calorimeter was mounted with the base of the crucible oriented perpendicular to a synchrotron-derived focused monochromatic x-ray beam for SCALTRD data collection. Measurements were made with hydrated monoelaidin and 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (DEPE) contained in hermetically sealed crucibles. Time-resolved x-ray diffraction (TRXRD) data were collected using an x-ray image intensifier/video system and a streak camera containing an x-ray sensitive image plate and/or film. SCALTRD analysis of the lamellar gel to lamellar liquid crystalline phase transition in hydrated monoelaidin gives identical progress curves by calorimetry and TRXRD at a scan rate of 1 degree C/min. At faster rates, calorimetry shows a broader phase transition that starts at a lower and ends at a higher temperature than is observed by TRXRD. The disparity arises in part because the x-ray beam used in TRXRD interrogates only a small portion of the sample, whereas the calorimeter responds to the entire sample volume. Because data collection times are relatively long, radiation damage is an important potential problem for SCALTRD measurements. Such an effect was observed with DEPE/water in that TRXRD shows the lamellar gel to lamellar liquid crystalline phase transition occurring at a lower temperature than observed by calorimetry. We speculate that the sample accumulates impurities locally as a result of radiation damage that has the effect of lowering the phase transition temperature at the site of interrogation by the x-ray beam. This "methods-in-combination" SCALTRD approach facilitates the direct correlation of structure rearrangements and thermal events in the same sample under identical conditions of thermal history. The information content of the data so derived far surpasses that available from either method used in isolation.

Calorimetry↗
PubMed2002

Resting energy expenditure in children and adolescents: agreement between calorimetry and prediction equations.

BACKGROUND AND AIMS: To assess the degree of agreement between indirect calorimetry and five equations commonly used to predict resting energy expenditure (REE) in obese and non-obese children and adolescents. METHODS: In 116 children and adolescents (57 obese and 59 non-obese) aged between 7.8 and 16.6 years, REE was measured (MREE) by open-circuit indirect calorimetry under standardized conditions. REE was predicted (PREE) in all subjects with equations from the Food and Agriculture/World Health Organization/United Nations University (FAO/WHO/UNU), Maffeis et al., Harris and Benedict, and two from Schofield: one using weight (W) and one using height and weight (H-W). Agreement between indirect calorimetry and equations was assessed following the Bland-Altman method. RESULTS: In the entire cohort group, only data from FAO/WHO/UNU, Schofield-W and Schofield-HW equations showed non-statistic differences against calorimetry results. When agreement between equations and calorimetry was tested, Schofield-HW equation showed the lowest mean MREE-PREE difference: 3.7 kcal/d (limits of agreement -293 and 300 kcal/d; 95% confidence interval for the bias -24.0 to 31.5 kcal/d) and the best agreement. Group by group, equations which obtained the best agreement were: FAO/WHO/UNU in girls, Schofield-HW in boys, Schofield-HW in obese, and Schofield-W in non-obese. CONCLUSIONS: Until more accurate prediction equations are developed, we recommend Schofield-HW equations for REE studies with a mixed population of obese and non-obese children and adolescents; however, FAO/WHO/UNU equation may also be useful in girls and Schofield-W equation in non-obese children.

Adolescent↗
PubMedDate not supplied

[Application of indirect calorimetry in monitoring feeding of low birth-weight preterm infants].

BACKGROUND: We investigated the practical use of indirect calorimetry for the individual nutritional support of preterm infants in order to answer the question whether it is possible to reliably calculate energy expenditure, fat and carbohydrate oxidation in preterm infants individually by using the results of a timed 6-hour-measurement of oxygen consumption and carbon dioxide production. PATIENTS: Measurements were performed in 20 preterm infants (gestational age 30.2 +/- 0.6 weeks, birth weight 1.09 +/- 0.07; mean +/- SEM) at a mean postnatal age of 25 +/- 4 days and with a body weight of 1.35 +/- 0.06 kg. METHODS: Carbon dioxide production (24 h-VCO2), oxygen consumption (24 h-VO2) and respiratory quotient (24 h-RQ) were measured by indirect calorimetry for 24 hours using the Deltatrac II metabolic monitor (Datex, Helsinki, Finland). Additionally, 6 h-VCO2, 6 h-VO2 and 6 h-RQ were determined by measurement over 6 hours. The patients' energy expenditure, fat and carbohydrate oxidation were calculated from VCO2 and VO2 measured over a 24 hour- and 6 hour-period with or without consideration of urinary nitrogen excretion (NU). RESULTS: If NU was not included in the calculation of energy expenditure, the values differed by maximally 1.1% from the calculations including NU. The correlations between the 24 h-RQ and the calculated 24 h-fat or 24 h-carbohydrate oxidation values were statistically significant (r = -0.99; p = 0.0001 and r = 0.773; p = 0.0002 respectively). However, in individual patients, it was not possible to predict 24 h energy expenditure, fat and carbohydrate oxidation of preterm infants using values determined by 6 h indirect calorimetry. CONCLUSION: The determination of the urine-nitrogen excretion is not necessary for calculation of energy expenditure of preterm infants. It is possible to estimate fat and carbohydrate oxidation of preterm infants by the measured 24 h-RQ, but 6 h indirect calorimetry is not accurate enough for calculating the individual nutritional needs of preterm infants in clinical practice. Indirect calorimetry over 24 h may be helpful in the management of selected patients with nutritional problems.

Calorimetry, Indirect↗
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↗