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At least 19 recordsLinked to original sources
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↗
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↗
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↗
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↗
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↗
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↗
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↗
PubMed1992

Continuous breathing circuit flow and tracheal tube cuff leak: sources of error during pediatric indirect calorimetry.

OBJECTIVE: To determine whether continuous gas flow in the breathing circuit or an airleak around the tracheal tube cuff will introduce errors into the measurement of oxygen consumption (VO2) with indirect calorimetry. DESIGN: Nonrandomized, controlled trial. SETTING: Experimental laboratory. SUBJECTS: Ten healthy, anesthetized mongrel dogs, weighing 8 to 12 kg. INTERVENTIONS: Data were recorded at seven levels of flow, from 0 to 12 L/min in excess of minute ventilation, through a continuous breathing circuit. Data were recorded at five levels of tracheal tube cuff leak from 0% to 40% of inspiratory minute volume. MEASUREMENTS AND MAIN RESULTS: VO2 was measured using an indirect calorimeter with constant internal gas flow and calculated from results of blood gas analysis, cooximetry, and thermodilution cardiac output determinations at all levels of continuous breathing circuit flow and cuff leak. BP, heart rate, respiratory rate, arterial and mixed venous blood gases, and body temperature were measured to assess stability of cardiopulmonary function. Continuous breathing circuit flow did not affect the accuracy of indirect calorimetry until the total flow reached a critical value (11.5 L/min) that was slightly below the internal flow constant of the metabolic monitor (12.4 L/min). At higher circuit flows, measured VO2 decreased in a linear fashion, while calculated VO2 remained unchanged. Above the critical flow, the error of indirect calorimetry correlated significantly only with the total circuit flow (r2 = .64), not with the exhaled concentration of CO2 (r2 = .005) or the inspiratory-expiratory oxygen difference (r2 = .004). The continuous flow rate at the critical circuit flow was 66 +/- 15% of the subjects' peak inspiratory flow. Increasing tracheal tube cuff leak produced a progressive decrease in measured VO2 but not in calculated VO2. The difference between measured and calculated VO2 was linearly related to the magnitude of the leak (r2 = .56), and was statistically significantly larger at all levels of cuff leak, when compared with measurements during complete cuff seal. CONCLUSIONS: An indirect calorimeter in which measurement of VO2 is based on internal constant flow rather than spirometry can be used to accurately measure VO2 from a continuous-flow breathing circuit, if the total circuit flow is less than the internal flow. This limitation may restrict the use of continuous flow to a level below the subject's peak inspiratory flow. The accuracy of indirect calorimetry cannot be guaranteed for any amount of tracheal tube cuff leak.

Analysis of Variance↗
PubMed1986

Direct calorimetry and the energetics of exercise and weight loss.

Laboratory studies using direct calorimetry, a technique which is no longer either rare or difficult, have shown no essential differences between men and women who gain weight easily and the always lean. Both groups gained weight similarly when overeating by 1,000 kcal X d-1. Thermogenic responses to eating and the energy losses in food and urine were similar in the overweight and lean. Daily sedentary energy expenditure is a function of fat-free mass, and fat-free mass increases with obesity. During exercise, calorimetry has shown that heat losses are not always exactly matched to heat production as calculated from respiratory gas exchange, but a 24-h exercise period with a cycle ergometer showed reasonable energy balance when subjects ate as much as they spent. During weight loss from restricting food intake by 1,000 kcal X d-1, calorimetry showed a 12% reduction in sedentary energy expenditure. Based on calorimetry studies and other evidence in the literature, exercise increases energy expenditure, it may eliminate the reduced energy expenditure of caloric restriction, and it can increase muscle mass and thus increase both fat-free mass and daily expenditure.

Adult↗
PubMed1989

Evaluation of methods for indirect calorimetry with a ventilated lung model.

A combined lung and ventilator model was built, validated and used to test commercial systems for indirect calorimetry. It simulates O2 uptake and CO2 excretion under ventilator treatment conditions. In the model inspiratory gases are diluted with N2 and CO2 to give the desired expiratory concentrations. Minute volume, FIO2, ventilatory pressure, VO2, VCO2 and consequently RQ can be altered to simulate the adult clinical situation. A selected respiratory pattern is maintained by the lung model. Equipment for indirect calorimetry can then be connected to it and the results compared. Reference values are derived from measurements with a mass spectrometer and a Godart spirometer. Three commercially available instruments (Beckman MMC, Horizon MMC and Engström MC) were evaluated with this system. The limits of agreement with the reference values under different conditions (FIO2 0.4-0.7, ventilatory pressure 0-50 cmH2O) were determined. Differences as high as 15% from the true values of VO2 and V CO2 were observed. The pattern of mechanical ventilation and the intrinsic properties of the analyzers in the equipment used for indirect calorimetry influence measurements to a significant extent.

Calorimetry↗
PubMed1988

The theoretical bases of indirect calorimetry: a review.

Indirect calorimetry is the method by which the type and rate of substrate utilization, and energy metabolism are estimated in vivo starting from gas exchange measurements. This technique provides unique information, is noninvasive, and can be advantageously combined with other experimental methods to investigate numerous aspects of nutrient assimilation, thermogenesis, the energetics of physical exercise, and the pathogenesis of metabolic diseases. Since its use as a research tool in metabolism is growing, the theoretical bases of indirect calorimetry are here reviewed in a detailed and orderly fashion. Special cases, such as the occurrence of net lipid synthesis or gluconeogenesis, are formally considered with derivation of explicit stoichiometric equations. The limitations of indirect calorimetry, both theoretical and technical, are discussed in the context of circumstances of clinical interest in metabolism.

Adenosine Triphosphate↗
PubMed1986

[Study of metabolism in critically ill patients by indirect calorimetry].

Indirect calorimetry was performed in 48 postsurgical critically ill patients including those with multiple organ failure. The patients were divided into two groups, organ failure group (OF group) and postsurgical control group (C group), according to the presence of postsurgical organ failure and severe infection. The following results were obtained. The ratio of energy expenditure to basal energy expenditure, reflecting a degree of hypermetabolism, was 1.44 +/- 0.38 in OF group and 1.26 +/- 0.23 in C group respectively. The change in respiratory quotient by caloric intake was greater in OF group than in C group, indicating that it is more important to maintain an adequate intake for the prevention of increased respiratory work and excess lipogenesis in OF group. When nitrogen intake as amino acids was sufficient (0.1-0.2 g/kg/day), nitrogen balance could be maintained around 0 by a caloric intake being equal to measured energy expenditure. A positive correlation was observed between arterial ketone body ratio reflecting energy charge in hepatocytes and respiratory quotient, indicating that in patients with impaired mitochondrial function in hepatocytes as shown by a decrease in ketone body ratio, glucose cannot be utilized effectively. These results let us conclude that calorimetry is indispensable in the management of critically ill patients and that adequate energy intake should be cautiously determined according to the calorimetry.

Calorimetry↗
PubMed1991

Multifrequency calorimetry of the folding/unfolding transition of cytochrome c.

The folding-unfolding transition of Fe(III) cytochrome c has been studied with the new technique of multifrequency calorimetry. Multifrequency calorimetry is aimed at measuring directly the dynamics of the energetic events that take place during a thermally induced transition by measuring the frequency dispersion of the heat capacity. This is done by modulating the folding/unfolding equilibrium using a variable frequency, small oscillatory temperature perturbation (approximately 0.05-0.1 degrees C) centered at the equilibrium temperature of the system. Fe(III) cytochrome c at pH 4 undergoes a fully reversible folding/unfolding transition centered at 67.7 degrees C and characterized by an enthalpy change of 81 kcal/mol and heat capacity difference between unfolded and folded states of 0.9 kcal/K*mol. By measuring the temperature dependence of the frequency dispersion of the heat capacity in the frequency range of 0.1-1 Hz it has been possible to examine the time regime of the enthalpic events associated with the transition. The multifrequency calorimetry results indicate that approximately 85% of the excess heat capacity associated with the folding/unfolding transition relaxes with a single relaxation time of 326 +/- 68 ms at the midpoint of the transition region. This is the first time that the time regime in which heat is absorbed and released during protein folding/unfolding has been measured.

Animals↗
PubMed1992

Thermodynamics of ion binding to phosphatidic acid bilayers. Titration calorimetry of the heat of dissociation of DMPA.

The heat of dissociation of the second proton of 1,2-dimyristoylphosphatidic acid (DMPA) was studied as a function of temperature using titration calorimetry. The dissociation of the second proton of DMPA was induced by addition of NaOH. From the calorimetric titration experiment, the intrinsic pK0 for the dissociation reaction could be determined by applying the Gouy-Chapman theory. pK0 decreases with temperature from ca. 6.2 at 11 degrees C to 5.4 at 54 degrees C. From the total heat of reaction, the dissociation enthalpy, delta Hdiss, was determined by subtracting the heat of neutralization of water and the heat of dilution of NaOH. In the temperature range between 2 and 23 degrees C, delta Hdiss is endothermic with an average value of ca. 2.5 kcal.mol-1 and shows no clear-cut temperature dependence. In the temperature range between 23 and 52 degrees C, delta Hdiss calculated after subtraction of the heat of neutralization and dilution is not the true dissociation enthalpy but includes contributions from the phase transition enthalpy, delta Htrans, as the pH jump induces a transition from the gel to the liquid-crystalline phase. The delta Cp for the reaction enthalpy observed in this temperature range is positive. Above 53 degrees C, the pH jump induces again only the dissociation of the second proton, and the bilayers stay in the liquid-crystalline phase. In this temperature range, delta Hdiss seems to decrease with temperature. The thermodynamic data from titration calorimetry and differential scanning calorimetry as a function of pH can be combined to construct a complete enthalpy-temperature diagram of DMPA in its two ionization states.

Calorimetry, Differential Scanning↗
PubMed1989

Interaction of the local anesthetics dibucaine and tetracaine with sarcoplasmic reticulum membranes. Differential scanning calorimetry and fluorescence studies.

The local anesthetics dibucaine and tetracaine inhibit the (Ca2+ + Mg2+)-ATPase from skeletal muscle sarcoplasmic reticulum [DeBoland, A. R., Jilka, R. L., & Martonosi, A. N. (1975) J. Biol. Chem. 250, 7501-7510; Suko, J., Winkler, F., Scharinger, B., & Hellmann, G. (1976) Biochim. Biophys. Acta 443, 571-586]. We have carried out differential scanning calorimetry and fluorescence measurements to study the interaction of these drugs with sarcoplasmic reticulum membranes and with purified (Ca2+ + Mg2+)-ATPase. The temperature range of denaturation of the (Ca2+ + Mg2+)-ATPase in the sarcoplasmic reticulum membrane, determined from our scanning calorimetry experiments, is ca. 45-55 degrees C and for the purified enzyme ca. 40-50 degrees C. Millimolar concentrations of dibucaine and tetracaine, and ethanol at concentrations higher than 1% v/v, lower a few degrees (degrees C) the denaturation temperature of the (Ca2+ + Mg2+)-ATPase. Other local anesthetics reported to have no effect on the ATPase activity, such as lidocaine and procaine, did not significantly alter the differential scanning calorimetry pattern of these membranes up to a concentration of 10 mM. The order parameter of the sarcoplasmic reticulum membranes, calculated from measurements of the polarization of the fluorescence of diphenylhexatriene, is not significantly altered at the local anesthetic concentrations that shift the denaturation temperature of the (Ca2+ + Mg2+)-ATPase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
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↗