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PubMed1979

Comparison of carbohydrate utilization in man using indirect calorimetry and mass spectrometry after an oral load of 100 g naturally-labelled [13C]glucose.

1. Carbohydrate (CHO) oxidation was measured simultaneously in a group of five normal subjects after an oral load of 100 g naturally-labelled [13C]glucose, using indirect calorimetry and mass spectrometry. 2. CHO utilization, calculated from the results of indirect calorimetry, increased 30 min after the glucose load to reach a peak at 90 min. It then decreased to reach basal values at 380 min. Cumulative total CHO oxidation at 480 min was 83 +/- 8 g, and CHO oxidized above basal levels, 37 +/- 3 g. 3. Enrichment of expired carbon dioxide with 13C began at 60 min and maximum values were observed at 270 min. At 480 min, cumulative CHO oxidation measured by use of [13C]glucose was 29 g. The difference from calorimetric values can be attributed in part to the slow isotopic dilution in the glucose and bicarbonate pools. 4. Thus, approximately 30% of the glucose load was oxidized during the 8 h after its ingestion and this accounts for a significant part of the increased CHO oxidation (37 g), as measured by indirect calorimetry.

Adolescent↗
PubMed1996

Validation of a 5-minute steady state indirect calorimetry protocol for resting energy expenditure in critically ill patients.

OBJECTIVE: Numerous protocols are used for indirect calorimetry in research and clinical settings. The objective of the current study was to validate in critically ill patients an abbreviated protocol that uses five consecutive stable 1-minute readings of oxygen consumption (VO2), carbon dioxide production (VCO2), and minute ventilation (VE) in a range of +/- 5%, versus a more standard protocol that uses 30 consecutive stable one minute readings of VO2, VCO2, and VE in a range of +/- 10%. METHODS: Indirect calorimetry was performed on resting, mechanically ventilated, critically ill patients. The first 5-minute period in which coefficients of variation for VO2, VCO2, and VE were < or = 5% was compared to the first 30-minute period in which coefficients of variation for these variables were < or = 10%. RESULTS: Thirty-four critically ill patients were studied. Twenty four patients (70%) successfully completed both protocols (Success Group). Eighteen percent of subjects completed neither the abbreviated nor the 30 minute protocol, and 12% completed only one protocol (Fail Group). The Success Group was marked by a higher incidence of sedation and/or medical paralysis. There were no significant differences in VE, VO2, VCO2, respiratory quotient, or energy expenditure between the protocols in the Success Group or the Fail Group. Coefficients of determination (R2) for VO2 and VCO2 between the two methods in the Success Group were 0.99. In the Fail Group, R2 values ranged from 0.75 for VCO2 to 0.91 for VO2. CONCLUSION: In sedated, mechanically ventilated patients, an indirect calorimetry test of five consecutive 1-minute periods with coefficient of variation < or = 5% is equivalent to a longer test consisting of 30 consecutive 1-minute periods with coefficient of variation < or = 10%.

Aged↗
PubMed2004

Determination of amorphous content of lactose samples by solution calorimetry.

Earlies studies suggest that solution calorimetry can be used to determine the extent of amorphous content of drug and excipient, when the solubility and dissolution rate of the compound in the chosen solvent are reasonably high. In the present study, the use of solution calorimetry for assessment of amorphous content of a sample that is not completely dissolved in a solvent was evaluated. Physical mixtures of lactose and spray-dried lactose samples were analysed. The amorphous content of the physical mixtures and the spray-dried samples varied from 0% to 100% determined by isothermal microcalorimetry. The enthalpy of solution (delta(sol)H) was determined in water. The lactose samples were dissolved quickly in water. In addition, the enthalpy accompanied with an addition of a lactose sample in an over saturated aqueous solution (delta(sat)H) (prepared from the corresponding lactose sample) was determined. The lactose sample did not completely dissolve in the over saturated aqueous solution. An excellent correlation was observed between delta(sol)H and the amorphous content of the samples. Interestingly, there was a linear correlation also between delta(sat)H and the amorphous content of the samples. Further, a linear relationship was observed between the delta(sat)H and the delta(sol)H of the samples. Therefore, solution calorimetry may represent a rapid and simple method for determining the amorphous content also in samples that are not completely dissolved in the solvent.

Calorimetry↗
PubMed1994

Similar 24-h pattern and rate of carbon dioxide production, by indirect calorimetry vs. stable isotope dilution, in healthy adults under standardized metabolic conditions.

We investigated the applicability of the bicarbonate stable isotope dilution technique for accurate determination of 24-h energy expenditure in humans and in reference to the conduct of short-term (< or = 8 h) metabolic studies. Five healthy adult subjects consumed for 4 d a standard diet providing approximately 188 kJ.kg-1.d-1 and 1.0 g.kg-1.d-1 of egg protein. From d 4 at 1800 h to d 5 at 1800 h, a 24-h metabolic study, combining indirect calorimetry with an intravenous infusion of 13C-labeled sodium bicarbonate, was performed under standardized conditions of 12 h fasting-12 h feeding. "Measured" CO2 production (VCO2) (indirect calorimetry) over 24 h was not significantly different from "predicted" VCO2 (bicarbonate dilution) (218.31 +/- 20.91 vs. 221.51 +/- 19.44 mmol CO2.kg-1.d-1, respectively) (P = 0.34). Further, 24-h VCO2 and energy expenditure were determined by extrapolating from "predicted" VCO2 during the last hour of fasting (15th hour following last meal) and the fifth hour of the small hourly meal-feeding phase. The maximum difference for an individual subject between the above-calculated 24-h energy expenditure and that from 24-h indirect calorimetry measurements was < 4%. These results support use of the present experimental protocol, and the bicarbonate dilution technique, lasting < or = 8 h, to obtain reliable quantitative estimates of 24-h CO2 production and energy expenditure in healthy adult humans.

Adult↗
PubMed1997

Technical and methodologic considerations for performance of indirect calorimetry in ventilated and nonventilated preterm infants.

OBJECTIVE: To evaluate and refine indirect calorimetry measurement techniques so that accurate metabolic measurements can be performed in mechanically ventilated and convalescing preterm infants who require supplemental oxygen. DESIGN: Laboratory validation of an indirect calorimeter; clinical and laboratory assessments of technical problems in performing metabolic measurements; and clinical indirect calorimetry studies in mechanically ventilated and nonventilated preterm infants. SETTING: Neonatal intensive care unit (ICU) in a tertiary care university hospital. PATIENTS: Level II and level III mechanically ventilated (n = 10) and nonventilated (n = 14) neonatal ICU patients who required FIO2 levels ranging from 0.21 to 0.42. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: System calibration was assessed by combustion of 100% ethanol; the mean respiratory quotient was 0.667 +/- 0.001 (SEM). In addition, oxygen consumption (Vo2) and CO2 production (Vco2) were simulated by CO2/nitrogen infusions within the range expected for 0.5- to 7-kg infants. Mean relative errors were 0.6 +/- 0.3% and 1.8 +/- 0.3% for expected Vo2 and Vco2 values, respectively. In 27 mechanically ventilated patients with no audible endotracheal tube leak, measured endotracheal tube leak ranged from 0.0% to 7.5%. Fluctuations in FIO2 during mechanical ventilation were monitored in 30-min studies, using wall-source (n = 27) or tank-source (n = 11) supplemental oxygen. Mean FIO2 variation was 0.00075 +/- 0.00013 vs. 0.00011 +/- 0.00001 using wall-source and tank-source oxygen, respectively. Some of the difficulties of obtaining accurate measurements in supplemental hood oxygen studies were overcome by using tank-source vs. wall-source oxygen and a unique hood design. CONCLUSIONS: Accurate indirect calorimetry studies can be performed in both ventilated and nonventilated infants weighing as little as 500 g, providing that sufficient attention is paid to technical and methodologic measurement details.

Calorimetry, Indirect↗
PubMed1998

A comparison between the Fick method and indirect calorimetry for determining oxygen consumption in patients with fulminant hepatic failure.

OBJECTIVE: To compare the Fick method of determining oxygen consumption (VO2) with a gas exchange method in a group of patients in whom the cardiac output and mixed venous oxygen saturation values were consistently high. DESIGN: A prospective, observational study. SETTING: A ten-bed intensive therapy unit at a university teaching hospital. PATIENTS: Seventeen patients suffering from fulminant hepatic failure who required ventilatory support and invasive hemodynamic monitoring. All patients were sedated and paralyzed throughout the study period. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: VO2 was determined simultaneously by indirect calorimetry and by the Fick method five or six times in each patient over a 5-hr period after resuscitation with fluids and, if clinically indicated, norepinephrine infusion. The agreement between the methods was poor (limits of agreement +19 to -101 mL/min/m2) and the Fick method consistently underestimated gas exchange measurements (mean bias 41 mL/min/m2). The bias varied widely, both between and within individual patients. The reproducibility of the Fick-derived VO2 was worse than the indirect calorimetry measurements, indicating that the dispersion of data attributable to measurement error was greater with the Fick method. CONCLUSIONS: Under clinical conditions, the agreement between Fick calculations and indirect calorimetry measurements of VO2 in hyperdynamic patients with fulminant hepatic failure was extremely poor. The reproducibility of Fick calculations was less than the reproducibility derived by gas exchange measurements because of the large measurement errors that may occur with the Fick method when the cardiac output is large and the arterial-venous oxygen content difference is small. Fick calculations systematically underestimate gas exchange measurements. The Fick method is inaccurate and unreliable when an estimation of VO2 is required in patients with this hemodynamic pattern.

Adult↗
PubMed2000

Use of indirect calorimetry to optimize nutrition support and assess physiologic dead space in the mechanically ventilated ICU patient: a case study approach.

Indirect calorimetry (IC) is an accurate method of estimating a patient's energy expenditure, particularly the complex critically ill patient who benefits most from an individualized regimen of nutritional support. This bedside technique measures variables related to gas exchange and replaces assumptions about physiologic stress. When indirect calorimetry data are augmented by an arterial blood gas analysis of carbon dioxide (PaCO2), the dead space to tidal volume ratio (VD/VT) can be determined for an individual patient. These data can be valuable to the healthcare team when checking reasons for weaning failure. A case study approach to a 69-year-old man with acute respiratory distress syndrome and biliary sepsis will demonstrate the utility of this measurement. Attention to precise nutritional support and optimal gas exchange can influence the outcome of critically ill mechanically ventilated patients. This discussion highlights the potential benefits of indirect calorimetry for critical care nurses.

Aged↗
PubMed2004

Predicted versus measured energy expenditure by continuous, online indirect calorimetry in ventilated, critically ill children during the early postinjury period.

OBJECTIVE: Compare the energy expenditure, predicted by anthropometric equations, with that measured by continuous on-line indirect calorimetry in ventilated, critically ill children during the early postinjury period. DESIGN: Prospective, clinical study. SETTING: Pediatric intensive care unit of a pediatric university hospital. PATIENTS: A total of 43 ventilated, critically ill children during the first 6 hrs after injury. INTERVENTIONS: An indirect calorimeter was used to continuously measure the energy expenditure for 24 hrs. MEASUREMENTS AND MAIN RESULTS: Clinical data collected were age, gender, actual and ideal weight, height, and body surface. Nutritional status was assessed by Waterlow and Shukla Index. Severity of illness was determined by Pediatric Risk of Mortality, Physiologic Stability Index, and Therapeutic Intervention Scoring System. Energy expenditure was measured (MEE) by continuous on-line indirect calorimetry for 24 hrs. Predicted Energy Expenditure (PEE) was calculated using the Harris-Benedict, Caldwell-Kennedy, Schofield, Food and Agriculture/World Health Organization/United Nation Union, Maffeis, Fleisch, Kleiber, Dreyer, and Hunter equations, using the actual and ideal weight. MEE and PEE were compared using paired Student's t-test, linear correlation (r), intraclass correlation coefficient (pI), and the Bland-Altman method. Mean MEE resulted in 674 +/- 384 kcal/day. Most of the predictive equations overestimated MEE in ventilated, critically ill children during the early postinjury period. MEE and PEE differed significantly (p<.05) except when the Caldwell-Kennedy and the Fleisch equations were used. r2 ranged from 0.78 to 0.81 (p<.05), and pI was excellent (>.75) for the Caldwell-Kennedy, Schofield, Food and Agriculture/World Health Organization/United Nation Union, Fleisch, and Kleiber equations. The Bland-Altman method showed poor accuracy; the Caldwell-Kennedy equation was the best predictor of energy expenditure (bias, 38 kcal/day; precision, +/- 179 kcal/day). The accuracy in the medical group was higher (pI range,.71-.94) than in surgical patients (pI range,.18-.75). CONCLUSIONS: Predictive equations do not accurately predict energy expenditure in ventilated, critically ill children during the early postinjury period; if available, indirect calorimetry must be performed.

Algorithms↗
PubMed1996

High energy phosphates and direct calorimetry as predictive parameters for metabolic recovery of the rat liver following ischemia.

BACKGROUND AND METHODS: Alteration of the hepatocellular function following ischemic damage may play a crucial role in the limited recovery after reperfusion. In spite of numerous efforts, finding a simple technique for predicting recovery of the liver after ischemic damage is still an unresolved problem. During ischemic storage of isolated rat livers at 25 degrees C tissue concentrations of high energy phosphates and lactate were determined photometrically and interstitial pH was measured by glass electrodes. In comparison, the metabolic rate was measured continuously by direct calorimetry. In a second series of experiments these results were compared with functional recovery after ischemia and reperfusion. Following ischemic storage at 25 degrees C for 60, 120 or 240 min, the isolated livers were reperfused for 30 min in a non-recirculating system with a constant flow rate. During reperfusion functional recovery, as assessed by oxygen consumption and bile flow, was determined. At the end of reperfusion tissue samples were taken for biochemical analysis of adenine nucleotides. Furthermore, morphologic integrity was determined by electron microscopy. RESULTS: Whereas the ATP concentration drops within 60 min of ischemia to 6.9% of the control value without further significant change, the continuously measured metabolic rate as assessed by direct calorimetry decreases in an exponential manner. Accordingly, a better correlation of hepatocellular secretory function and calorimetrically measured heat output (r2 = 0.85; P < 0.001) was observed than with high energy phosphates (r2 = 0.56; P < 0.001). CONCLUSIONS: These data suggest that if the metabolism of the ischemic rat liver falls below a critical level, recovery is incomplete or impossible. Therefore, assessment of the global metabolic rate by direct calorimetry seems not only to be a very good predictor of recovery after ischemic damage but also a good tool in the laboratory for studies concerning the sequelae of ischemic metabolism and for improvement of tissue protection.

Adenine Nucleotides↗
PubMed1996

Water calorimetry and ionization chamber dosimetry in an 85-MeV clinical proton beam.

In recent years, the increased use of proton beams for clinical purposes has enhanced the demand for accurate absolute dosimetry for protons. As calorimetry is the most direct way to establish the absorbed dose and because water has recently been accepted as standard material for this type of beam, the importance of water calorimetry is obvious. In this work we report water calorimeter operation in an 85-MeV proton beam and a comparison of the absorbed dose to water measured by ionometry with the dose resulting from water calorimetric measurements. To ensure a proper understanding of the heat defect for defined impurities in water for this type of radiation, a relative response study was first done in comparison with theoretical calculations of the heat defect. The results showed that pure hypoxic water and hydrogen-saturated water yielded the same response with practically zero heat defect, in agreement with the model calculations. The absorbed dose inferred from these measurements was then compared with the dose derived from ionometry by applying the European Charged Heavy Particle Dosimetry (ECHED) protocol. Restricting the comparison to chambers recommended in the protocol, the calorimeter dose was found to be 2.6% +/- 0.9% lower than the average ionometry dose. In order to estimate the significance of chamber-dependent effects in this deviation, measurements were performed using a set of ten ionization chambers of five different types. The maximum internal deviation in the ionometry results amounted to 1.1%. We detected no systematic chamber volume dependence, but observed a small but systematic effect of the chamber wall thickness. The observed deviation between calorimetry and ionometry can be attributed to a combination of the value of (Wair/e)p for protons, adopted in the ECHED protocol, the mass stopping power ratios of water to air for protons, and possibly small ionization chamber wall effects.

Calorimetry↗
PubMed2004

Percent relative cumulative frequency analysis in indirect calorimetry: application to studies of transgenic mice.

Indirect calorimetry is commonly used in research and clinical settings to assess characteristics of energy expenditure. Respiration chambers in indirect calorimetry allow measurements over long periods of time (e.g., hours to days) and thus the collection of large sets of data. Current methods of data analysis usually involve the extraction of only a selected small proportion of data, most commonly the data that reflects resting metabolic rate. Here, we describe a simple quantitative approach for the analysis of large data sets that is capable of detecting small differences in energy metabolism. We refer to it as the percent relative cumulative frequency (PRCF) approach and have applied it to the study of uncoupling protein-1 (UCP1) deficient and control mice. The approach involves sorting data in ascending order, calculating their cumulative frequency, and expressing the frequencies in the form of percentile curves. Results demonstrate the sensitivity of the PRCF approach for analyses of oxygen consumption (.VO2) as well as respiratory exchange ratio data. Statistical comparisons of PRCF curves are based on the 50th percentile values and curve slopes (H values). The application of the PRCF approach revealed that energy expenditure in UCP1-deficient mice housed and studied at room temperature (24 degrees C) is on average 10% lower (p < 0.0001) than in littermate controls. The gradual acclimation of mice to 12 degrees C caused a near-doubling of .VO2 in both UCP1-deficient and control mice. At this lower environmental temperature, there were no differences in .VO2 between groups. The latter is likely due to augmented shivering thermogenesis in UCP1-deficient mice compared with controls. With the increased availability of murine models of metabolic disease, indirect calorimetry is increasingly used, and the PRCF approach provides a novel and powerful means for data analysis.

Acclimatization↗
PubMed1992

Comparison of indirect calorimetry and a new breath 13C/12C ratio method during strenuous exercise.

A new stable isotope method for the determination of substrate oxidation rates in vivo is described and compared with indirect calorimetry at rest and during high-intensity exercise (30 min at 80-85% maximal O2 uptake capacity) in six well-trained cyclists. This method uses the absolute ratios of 13C/12C in expired air, endogenous glucose, fat, and protein in addition to O2 consumption and is independent of CO2 production (VCO2). Carbohydrate and fat oxidation rates at rest, calculated by both methods, were not significantly different. During exercise the breath 13C/12C ratio increased and reached a steady state after 15-20 min. Carbohydrate oxidation rates during exercise were 39.4 +/- 5.2 and 41.7 +/- 5.7 mg.kg-1.min-1 [not significant (NS)], and fat oxidation rates were 7.3 +/- 1.3 and 6.9 +/- 1.2 mg.kg-1.min-1 (NS), using indirect calorimetry, and the breath ratio method, respectively. We conclude that the breath 13C/12C ratio method can be used to calculate substrate oxidation under different conditions, such as the basal state and exercise. In addition, the results obtained by this new method support the validity of the underlying assumption that indirect calorimetry regards VCO2 as a reflection of tissue CO2 production, during exercise in trained subjects, even up to 80-85% maximal O2 uptake.

Adult↗
PubMed1993

Glucose metabolism during fasting through human pregnancy: comparison of tracer method with respiratory calorimetry.

Glucose turnover and glucose oxidation were quantified in six normal pregnant women serially throughout pregnancy, using [U-13C]glucose tracer in combination with open-circuit indirect respiratory calorimetry. Five normal nonpregnant women were studied for comparison. With advancing gestation and increase in maternal body weight, there was a proportionate increase in the rate of appearance (Ra) of glucose so that Ra expressed per kilogram body weight did not change from the first to third trimester. The tracer measured rate of glucose oxidation expressed per kilogram body weight also did not change significantly throughout pregnancy. Oxygen consumption (VO2) in pregnant subjects did not differ from that in nonpregnant subjects. However, the respiratory exchange ratio (RER) increased significantly during pregnancy (0.88 +/- 0.53 3rd trimester and 0.76 +/- 0.50 nonpregnant, P < 0.01). The estimated contribution of carbohydrate to VO2 measured by respiratory calorimetry was greater than that measured by the tracer method. This discrepancy became wider as the respiratory quotient increased in late pregnancy. These data suggest that maternal glucose metabolism adjusts throughout pregnancy to meet the increased demands of the conceptus. The discrepancy between tracer method and respiratory calorimetry was probably due to the contribution of (fetal) lipogenesis and (maternal) gluconeogenesis to RER.

Adult↗
PubMed1992

Determining energy expenditure in preterm infants: comparison of 2H(2)18O method and indirect calorimetry.

The doubly labeled water (2H(2)18O) method used to estimate total energy expenditure (EETotal) is particularly sensitive to analytic error in preterm infants, because of their high percentage of body water and the high ratio of water flux to CO2 production. To evaluate further use of this method, the EE of 12 preterm infants was measured by indirect calorimetry and 2H(2)18O simultaneously and continuously for 5 days. Initial infant weight, age, and postconceptional age were (means +/- SD) 1,674 +/- 173 g, 4.4 +/- 2.6 wk, and 34.6 +/- 1.6 wk, respectively. The indirect calorimeter system included an air-temperature-controlled chamber and heart rate monitor. EE was measured by indirect calorimetry for 85.6 +/- 4.7% of study time and estimated from the linear regression of heart rate on EE for 14.4 +/- 4.7% of study time. The 2H(2)18O method entailed an initial dose of 100 mg 2H2O and 250 mg 18O/kg and a final dose of 75 mg 18O/kg; urine was collected twice daily. 2H and 18O enrichments were measured by gas-isotope-ratio mass spectrometry. EE was calculated from measured 2H and 18O dilution spaces (NH, NO), turnover rates (kH, kO), and measured respiratory quotient. The ratio of 2H to 18O dilution spaces was 1.01 +/- 0.01 and the ratio of kO to kH was 1.16 +/- 0.04. Estimation of EE from 2H(2)18O and indirect calorimetry agreed within 1%, although individual variability in methods was large.

Anthropometry↗
PubMedDate not supplied

The thermodilution technique for measuring resting energy expenditure does not agree with indirect calorimetry for the critically ill patient.

BACKGROUND: The complications associated with overfeeding critically ill patients are well documented. Indirect calorimetry is touted as the gold standard for measuring resting energy expenditure (REE). Unfortunately, the device is expensive, and many centers do not have this technology. The thermodilution technique for measuring cardiac output and calculating REE using the Fick equation has been reported to be an acceptable alternative. This study compared these techniques in a critically ill population. METHODS: Forty consecutive patients with indwelling Swan-Ganz catheters in the surgical intensive care unit were prospectively studied while under the consultative care of the nutrition support service. REE was determined in all patients by both techniques within a 2-hour period. An error of 5% (approximately+/-100 kcal/d) between the two methods was deemed acceptable for clinical use. RESULTS: Mean values for REE were 1928+/-558 vs 1898+/-518 kcal/d for the indirect calorimetry and thermodilution methods, respectively, and were not significantly different. However, there was great variation between the two techniques for the majority of patients such that REE determinations did not agree (t = 6.8; p < .0005). In 70% of the patients, REE determinations differed by > or =20% and in 10% of the patients by 50%. Additionally, the greater the difference between the two methods, the more the thermodilution method tended to overestimate REE. CONCLUSIONS: When compared with indirect calorimetry in a critically ill population, the thermodilution method demonstrated an intersubject variability that is unacceptable for clinical use.

Adolescent↗
PubMed2004

Correlation between oxygen consumption calculated using Fick's method and measured with indirect calorimetry in critically ill patients.

OBJECTIVE: To compare the oxygen consumption index measured by using indirect calorimetry (VO2I Delta) with a portable metabolic cart and calculated according to Fick's principle (VO2 I Fick) in critically ill patients. METHODS: Fourteen patients (10 men and 4 women, mean age 39.4 +/- 5.4 years) were analyzed, 5 of them trauma victims and 9 sepsis victims. The following mean scores were obtained for these patients: APACHE II = 21.3+/-1.8, ISS = 24.8+/-6, and sepsis score = 19.6+/-2.3. The mortality risk (odds ratio), calculated from APACHE II, was 41.9+/-7.1%. All patients underwent mechanical ventilation and invasive hemodynamic monitoring with a Swan-Ganz catheter. VO2 was obtained using the 2 methods (VO2I Delta and VO2I Fick) at 4 different times (T1-T4). RESULTS: A good correlation was found between the 2 methods (r=0.77) for the mean of the 4 serial measurements. No statistically significant differences were observed between indirect calorimetry and Fick's equation at T1 (VO2I Delta = 138+/-28 and VO2I Fick = 59+/-38 mL.min-2.m-2, P=0.10) and T3 (VO2I Delta = 144+/-26 and VO2I Fick = 158+/-35 mL.min-2.m-2, P=0.14), but a significant difference was observed at T2 (VO2I Delta = 141+/-27 and VO2I Fick = 155+/-26 mL.min-2.m-2, P=0.03) and T4 (VO2I Delta = 145+/-24 and VO2I Fick = 162+/-26 mL.min-2.m-2, P=0.01). CONCLUSION: We may state that indirect calorimetry can be used for oxygen consumption analysis in critically ill patients and is as efficient as Fick's reverse equation, with the benefit of being a noninvasive and risk-free procedure.

APACHE↗
PubMed2005

Differential scanning calorimetry in life science: thermodynamics, stability, molecular recognition and application in drug design.

All biological phenomena depend on molecular recognition, which is either intermolecular like in ligand binding to a macromolecule or intramolecular like in protein folding. As a result, understanding the relationship between the structure of proteins and the energetics of their stability and binding with others (bio)molecules is a very interesting point in biochemistry and biotechnology. It is essential to the engineering of stable proteins and to the structure-based design of pharmaceutical ligands. The parameter generally used to characterize the stability of a system (the folded and unfolded state of the protein for example) is the equilibrium constant (K) or the free energy (deltaG(o)), which is the sum of enthalpic (deltaH(o)) and entropic (deltaS(o)) terms. These parameters are temperature dependent through the heat capacity change (deltaCp). The thermodynamic parameters deltaH(o) and deltaCp can be derived from spectroscopic experiments, using the van't Hoff method, or measured directly using calorimetry. Along with isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC) is a powerful method, less described than ITC, for measuring directly the thermodynamic parameters which characterize biomolecules. In this article, we summarize the principal thermodynamics parameters, describe the DSC approach and review some systems to which it has been applied. DSC is much used for the study of the stability and the folding of biomolecules, but it can also be applied in order to understand biomolecular interactions and can thus be an interesting technique in the process of drug design.

Calorimetry, Differential Scanning↗
PubMedDate not supplied

[Energy requirements in the ICU. Calorimetry and expert opinion].

GOAL: To compare the method for calculating the energy requirements in critical patients as calculated by our computer software with those measured using calorimetry and using the recommendations of experts in nutritional support. REFERENCE POPULATION: 18 critical patients with mechanical ventilation and admitted to our ICU during 1998. ACTIONS TAKEN: Indirect calorimetry was carried out over a 24 hour period in critical patients with mechanical ventilation and their requirements were calculated using computer software. Ten of the measurements were placed on Internet web pages in order to receive the comments and recommendations of nutritional support experts. Those responses which fell into the range between 80% and 120% of the calorimetric measurement were considered correct. RESULTS: Calorimetric determinations were effected on 31 occasions in 18 patients, with an average APACHE score of 19 +/- 3. The energy requirements measured by calorimetry were 34 +/- 3 kcal/kg/day with 0.34 +/- 16 g/kg/day of nitrogen in urine, whereas the recommendations of the computer programme were 31 +/- 1 kcal/kg/day and 0.28 +/- 0.04 g/kg/day of nitrogen in urine, i.e. 92 +/- 8% of the former values. The responses by the experts to 10 of these measurements came very close to those of the programme, with 33 +/- 6 kcal/kg/day and 0.29 +/- 0.06 gr/kg/day of nitrogen, with a percentage of correct responses of around 68%. CONCLUSIONS: The method for calculating the energy requirements used by our computer software constitutes around 92% of the calorimetric measurements in critical patients with mechanical ventilation and the responses are very similar to the average of the responses given by experts in nutritional support.

APACHE↗