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PubMed1992

An indirect calorimetry system for ventilator dependent very low birthweight infants.

With neurodevelopmental outcome of very low birthweight (VLBW) infants being adversely affected by inadequate nutrition during the first few weeks of life, there is an urgent need for more specific nutritional data on the sick VLBW ventilator dependent infant. The development of a new mass spectrometry gas analysis indirect calorimetry system which is non-invasive and can operate over several hours or days is described. Technical evaluation of each of the components of the system indicates a total random error of less than 5%. Systematic error was determined using gas infusions which simulated carbon dioxide production and oxygen consumption. The relative error in the measurement of carbon dioxide production was less than or equal to 1.5% (coefficient of variation (CV) 6.0%)) with carbon dioxide infusion rates ranging from 3.86 to 13.98 ml/min. The relative error in oxygen 'consumption' was less than or equal to 4.3% (CV 2.8%) for infusions of oxygen at rates of 7.5 to 14.80 ml/min. With nitrogen infusions simulating oxygen consumptions of 2.0 and 5.5 ml/min the relative error in the calculated nitrogen infusion was 1.5% (CV 4.1%) and 1.4% (CV 5.7%) respectively. Clinical studies on 10 infants demonstrated a mean energy expenditure of 161.7 kJ/kg/day and a respiratory quotient in excess of 1.0. The energy expenditure of ventilated VLBW infants may be less than previously indicated and the energy mix and nitrogen content of parenteral nutrition regimens recommended for these infants may be inappropriate.

Calorimetry↗
PubMed1987

Differential scanning calorimetry studies of rabbit cardiac sarcolemma.

Thermal transitions were measured by differential scanning calorimetry for rabbit cardiac sarcolemma in 3-(N-morpholino)propanesulfonic acid buffer at pH 7.5, in glycerol-buffer and dimethyl sulfoxide - buffer mixtures, after heat denaturation, and after enzymatic degradation of the proteins. Specific solvent effects on the protein transitions were observed. Glycerol stabilized some of the four protein transitions, while dimethyl sulfoxide destabilized all protein transitions. The thermal transitions in the lower temperature range were studied for both the membranes and the lipid extracted from the membranes. A very small endotherm was observed for both the lipid extracted from the sarcolemma and the intact membrane (0.1-0.2 cal/g; 1 cal = 4.1868 J). A larger endotherm was observed in both the glycerol-buffer and dimethyl sulfoxide - buffer mixtures. Major perturbation of the protein by enzymatic degradation (papain or trypsin digestion), by heat denaturation, or by reaction with excess N-ethylmaleimide all produced larger endotherms near 20 degrees C. The very small magnitude of the endotherm near 20 degrees C suggests that it is not a typical gel - liquid crystalline transition of the bilayer. However, the occurrence of an endotherm in the extracted lipid suggests that some reorientation of lipid is involved.

Adenosine Triphosphatases↗
PubMed1990

Differential scanning calorimetry of dispersions of products of oxidation of 1-stearoyl-2-linoleoyl-sn-glycero-3-phosphocholine.

Ultraviolet light was used to promote the autoxidation of 1-stearoyl-2-linoleoyl-sn-glycero-3-phosphocholine (SLPC). The extent of oxidation was monitored by ultraviolet spectroscopy, reaction with thiobarbituric acid, fatty acid analysis, and thin-layer chromatography. Fatty acid analysis and thin-layer chromatography appeared to provide the most consistent estimates of oxidation, especially when extensive oxidation had taken place. The oxidized samples were separated by flash chromatography into fractions enriched in different oxidation products. Differential scanning calorimetry of aqueous dispersions of these fractions indicated that oxidation products had higher transition temperatures than the original SLPC.

Calorimetry, Differential Scanning↗
PubMed1991

Differential scanning calorimetry and X-ray diffraction studies of a series of synthetic beta-D-galactosyl diacylglycerols.

We have investigated the physical properties of a homologous series of synthetic, saturated 1,2-di-O-acyl-3-O-(beta-D-galactopyranosyl)-sn-glycerols using calorimetry and X-ray diffraction. Unannealed aqueous dispersions of these compounds exhibit a lower temperature, moderately energetic, chain-melting (L beta/L alpha) phase transition and a higher temperature, weakly energetic, bilayer/nonbilayer phase transition. On annealing below the L beta/L alpha phase transition, the L beta phase converts to an LC phase, which may undergo a highly energetic LC/L alpha or LC/HII phase transition at very high temperatures on reheating. The temperatures of these phase transitions are higher than those seen in the corresponding alpha- and beta-D-glucosyl diacylglycerols. However, the L beta/L alpha and bilayer/nonbilayer phase transition temperatures of the beta-D-galactosyl diacylglycerols are lower than those of the corresponding diacyl phosphatidylethanolamines. These observations are discussed in terms of the hydration and hydrogen bonding properties of their respective headgroups.

Calorimetry, Differential Scanning↗
PubMed2005

Effects of 2 wk of GH administration on 24-h indirect calorimetry in young, healthy, lean men.

The present study was designed as a randomized, double-blind placebo (Plc)-controlled study to determine the effect of 2 wk of growth hormone administration (GH-adm.) on energy expenditure (EE) and substrate oxidation in healthy humans. Sixteen young healthy men were divided into two groups. The study consisted of two 24-h measurements (indirect calorimetry), separated by 2 wk of either Plc or GH injections (6 IU/day). At baseline, no significant differences were observed between the two groups in any of the measured anthropometric, hormonal, or metabolic parameters, neither did the parameters change over time in the Plc group. GH-adm. resulted in a 4.4% increase in 24-h EE (P < 0.05) and an increase in fat oxidation by 29% (P < 0.05). However, a decrease in the respiratory quotient was only observed in the postabsorptive phase after an overnight fast (0.84 +/- 0.1 to 0.79 +/- 0.1, P < 0.05). Furthermore, lean body mass (LBM) was increased by GH-adm. only [62.8 +/- 2.5 kg (baseline) vs. 64.7 +/- 2.4 kg (after), P < 0.001]. In conclusion, GH-adm. increases 24-h EE, which may be partly explained by increased LBM. Furthermore, GH-adm. stimulates fat combustion, especially in the postabsorptive state.

Adult↗
PubMed1984

Measurement of fetal heat production using differential calorimetry.

These experiments were undertaken to measure heat production of fetal lambs in utero by using differential calorimetry. We used the principle that fetal heat production, H(fetus), can be calculated from measurements of base-line temperature difference between mother and fetus, delta T(fetus), heat introduced from an external source, H(heater), and the increase in body temperature, delta T(heater), that results, i.e., H(fetus) = H(heater) X delta T(fetus)/delta T(heater). We placed microheaters (1.8 mm diam) in the inferior vena cavae of eight near-term lambs and placed thermistors and catheters into maternal and fetal vessels and amniotic fluid. Five days later, fetal arterial temperature averaged 0.54 +/- 0.02 degrees C (SE) higher than maternal arterial temperature. When the heater was turned on to dissipate 29-103 cal/min, fetal temperature increased to approach 0.1-0.5 degrees C higher than control; the final temperature was estimated using the rate of increase during the first 20 min. Fetal heat production averaged 47.1 +/- 4.1 cal X min-1 X kg-1 during the warming phase in these lambs, which weighed 3.26 +/- 0.36 kg. This value would be 3-4% less if corrected for the increase in metabolic rate caused by heating, assuming a Q10 of 2.5. Fetal heating did not alter fetal heart rate, blood pressure, or blood gas values significantly, nor was hemolysis visible in plasma samples. When heat production was calculated from the decrease in fetal temperature after the heater was turned off, an average value of 41.2 +/- 2.5 cal X min-1 X kg-1 was found. Because this value is comparable to the heating phase, fetal metabolic rate and the insulating properties of the fetal shell are not likely to have been changed by the heating.

Animals↗
PubMed1992

Determination of heat debt in the cold: partitional calorimetry vs. conventional methods.

Measurements of core temperature (Tc) at different sites produce on some occasions different cooling curves in cold-exposed humans, suggesting that the corresponding thermometric heat debts (HD) could be equally different when calculated by conventional methods [via the change in either Tc or mean body temperature (Tb)]. The present study also compared these thermometric HD values with the calorimetric HD obtained by partitional calorimetry (S). Nine subjects who showed similar initial but different final Tc [rectal (Tre) and auditory canal temperatures (Tac)] during nude cold exposure (2 h at 1 degrees C at rest) were used. Tc-derived HD corresponded to a heat gain of 12 +/- 21 kJ and an HD of 78 +/- 20 kJ with use of Tre and Tac, respectively, whereas the Tb-derived HD varied from 266 +/- 35 to less than or equal to 1,479 +/- 71 kJ with the use of various well-known Tb weighing coefficients. In contrast, S corresponded to 504 +/- 79 kJ, a level that could have been obtained only if the thermoneutral/cold Tb weighing coefficients had been 0.818/0.818 for Tre and 0.865/0.865 for Tac. The results demonstrate that calculation by conventional methods can markedly overestimate or underestimate HD. These differences could not be explained by the site chosen to represent Tc, inasmuch as about the same effect was observed with use of either Tre or Tac. It is concluded that the thermometric value of HD in the cold is not, at least under the present conditions, as accurate and reliable as S.

Adult↗
PubMed1993

Seven-day validation of doubly labeled water method using indirect room calorimetry.

Carbon dioxide production, water production, and energy expenditure (EE) determined with 2H2(18)O were validated using a room calorimeter. Nine human subjects (5 males, 4 females) resided in the calorimeter for five to seven consecutive 23.5-h days. Daily carbon dioxide and water production and EE were averaged from calorimeter data and compared with 2H2(18)O results for the same period and for the following week. Isotope concentrations were measured by isotope ratio mass spectroscopy (18O) and infrared spectrophotometry (2H). Isotope clearance rates and pool sizes were determined by two multipoint methods and the two-point method. No significant differences were measured between calorimetry and 2H2(18)O results for the period within the chamber [multipoint A.M. urine 1.55% +/- 2.57 (SD) %, multipoint A.M. + P.M. urine 0.98% +/- 8.19%, two-point 1.59% +/- 4.50%]. Free-living EE was 13% +/- 7% greater. The results indicate that the 2H2(18)O method as applied is a valid technique for measuring EE, that multipoint calculation methods can be as precise as the two-point method, and that EE was greater in free-living than in calorimeter-confined conditions.

Adult↗
PubMed1993

Indirect calorimetry with a hood: flow requirements, accuracy, and minute ventilation measurement.

Flow-dilution-based hood systems for indirect calorimetry eliminate the conventional mouthpiece or mask of sealed-circuit systems allow measurements with improved patient comfort. This feature is particularly relevant when measurements are made over long periods of time or are repeated often. The flow of air pulled through the hood into the calorimeter in these systems is necessary to clear CO2 from inside the hood. The errors in these systems are greater than those in the sealed-circuit systems and are proportional to the flow. We show that the CO2 concentration within the hood at steady state does not depend on hood size. We describe the accuracy in determination of O2 consumption (VO2), CO2 production, and respiratory exchange ratio with a hood system as a function of the accuracy of the O2 and CO2 analyzers and the water vapor in collected gas. For example, we show that if there is a 1% error in O2 concentration, the percent error in VO2 changes from 5% in a sealed circuit to 51% when a cleansing flow of 50 l/min is introduced. The error in VO2 caused by a 5% error in CO2 determination is 10.6% at this cleansing flow. Removal of 90% of the water vapor (instead of 100%) before analysis of the expired gas introduces a 15.8% error in VO2. By use of the equations described, the accuracy of any measurement system can be determined. In addition, we demonstrate that the measurement of ventilation, usually lost in a hood system, can be preserved using dual pneumotachographs and a sealed hood.

Air Movements↗
PubMed1998

Comparison of normal and in vitro aging by non-enzymatic glycation as verified by differential scanning calorimetry.

The biomechanical parameters of rat tail tendons (RTTs) from 35-, 64-, 180- and 900-day-old animals, corresponding to the early maturation phase, the mature and the senescent state were determined. The increase of maximum stiffness, ultimate stress and the elastic fraction of stress was most pronounced in the maturation phase. Differential scanning calorimetry (DSC) experiments were performed showing an almost linear increase of the collagen denaturation temperature in the age range 35-139 days. After 14 days incubation in glucose, we observed a marked increase of the biomechanical parameters in the young, an increase of maximum stiffness in mature, and only slight alterations of the biomechanical behavior in senescent RTTs. Both glucose incorporation and formation of advanced glycation end products were most prominent in 35-day-old RTTs. These biochemical findings were in excellent agreement with the enhancement of the collagen denaturation temperature after the incubation phase. Results suggest that the validity of the term 'accelerated aging' depends on the experimental approach, i.e. biomechanical tests, thermal isometric contraction or DSC.

Aging↗
PubMed2004

Assessment of hepatic glucose metabolism by indirect calorimetry in combination with a non-invasive technique using naturally enriched 13C glucose in healthy children and adolescents.

The metabolic fate of hepatic glucose can be best studied using invasive techniques such as tracer infusions and frequent blood sampling which have been revealed to be impractical in the pediatric age group. The aim of this study was to develop a non-invasive method based on indirect calorimetry and expired 13CO2 monitoring in order to gain insight into the mechanisms leading to impaired glucose tolerance in children and teenagers. As a first step, net glucose oxidation (NGO) and energy expenditure (EE) were measured in 47 subjects (range 7.5-17.3 years) of whom 18 were prepubertal (P1), 11 in early puberty (P2-P3) and 18 in late puberty (P4-P5) after 3-hourly loads of 180 mg/kg of oral maize glucose containing naturally enriched 13C. Isotope analysis allowed to calculate exogenous and endogenous glucose oxidation (EXGO, ENGO) and, hence, to derive TGS and NGS, that is glycogen turnover. NGO and EE decreased significantly with pubertal progression, reflecting higher metabolism at younger ages, whereas EXGO remained constant. TGS did not change significantly whereas NGS showed a significant negative correlation with pubertal progression: this can be explained by the fact that glycogenolysis exceeded glycogen synthesis in this experimental setting. This non-invasive method appears to be a promising tool to study the fate of hepatic glucose and therefore glycogen turnover in children at risk of developing glucose intolerance and/or type 2 diabetes.

Adolescent↗
PubMed2006

Thermal behaviour of human stratum corneum. A differential scanning calorimetry study at high scanning rates.

PURPOSE: To use high-speed differential scanning calorimetry (DSC) in the identification of transitions in human stratum corneum (SC). Several scanning rates (100 degrees C/min to 400 degrees C/min) are used. RESULTS: Eight transitions from 0 to 120 degrees C are detected in a significant number of samples. Most of these transitions have already been identified in previous studies, but have been labeled considering essentially that only four are present. Results also indicate some degree of reversibility for transitions occurring at temperatures above 90 degrees C. Dehydrated SC samples displayed slightly more defined transition peaks and a less frequent presence of the transitions below 50 degrees C. In turn, the delipidised SC matrix showed two major endothermic signals, centered around 55 and 100 degrees C, in conjunction with other much less marked features. CONCLUSIONS: The interpretation of DSC traces in terms of four main transition temperatures must be complemented having in mind the occurrence of other transitions, some of them at physiological temperatures. This work further suggests that transitions at temperatures above 90 degrees C may to a large degree be associated to lipids, while transition at approx. 55 degrees C is probably related to lipids covalently linked to proteins, as previously suggested.

Adult↗
PubMed1983

The clinical use of direct calorimetry for measuring energy expenditure.

Energy output measurements are an actual problem since the 18th century. Together with the technical development very good solutions for direct calorimetry are available. Vienna Whole Body Calorimeter is a measuring system in which man can live 24 and more hours under defined activity and well known diet. Utilisation of ingested food energy is discussed and unmeasured energy shown during overfeeding. Beside increasing energy content of body mass gaining weight costs 1969 kcal/kg. Comparison of direct and indirect measurement is necessary to define energy need in different catabolic situations.

Body Temperature Regulation↗
PubMed1991

Comparison of short term indirect calorimetry and doubly labeled water method for the assessment of energy expenditure in preterm infants.

The accuracy of 8-hour indirect calorimetry (IDC) as an estimate of energy expenditure was investigated in 8 healthy preterm infants (birth weight 1,270 +/- 193 g, gestational age 32 +/- 3 weeks, mean +/- SD) in comparison with an analysis over 5 days using the doubly-labeled water (2H2(18)O) method (DLW). The infants that were fed continuously by nasogastric drip with 120 kcal/kg/day of special infant formula were measured twice under thermoneutral conditions in a closed system indirect calorimeter during 8 h with a 4-day interval; simultaneously isotope decay was measured by isotope ratio mass spectrometry in urine samples collected daily during 5 days from 6 h after an oral dose of 2H2(18)O on the first day of IDC, all during the 4th postnatal week. The mean differences between carbon dioxide production rate (rCO2) measured either by single 8-hour IDC or by duplicate 8-hour IDC and the 5-day DLW method, using the two-point analysis or the multipoint analysis were not significantly different from zero. The rCO2 calculated from the DLW method using the two-point analysis differed -1.4 +/- 1.7% from that measured by the multipoint analysis. The mean differences between the metabolic rate estimated from 8 h of IDC and from the 5-day DLW method based on a measured RQ of 0.90 was -6.7 +/- 6.2% and based on the RQ of the feeding -4.5 +/- 6.0%. These differences were not significantly different from zero. We conclude that IDC over 8 h and two-point DLW measurement over 5 days, both methods that can be applied with relative ease in practice, offer an adequate average estimate of energy expenditure in continuously fed preterm infants under thermoneutral conditions.

Calorimetry, Indirect↗
PubMed1986

Determination of the state and content of water in normal avian, fish, porcine, bovine, and human lenses as studied by differential scanning calorimetry.

Differential scanning calorimetry was used to measure the relative amounts of 'bulk' and 'bound' water in normal avian, bovine, fish, human, and porcine lenses. The amounts of bound water (mg bound water/mg lens dry weight) found in avian and porcine lenses were statistically different from each other in addition to being statistically different from fish, human, and bovine lenses. There were no significant differences in the mean values between human, fish, and bovine lenses. Avian lenses had the highest amount of bound water, while fish lenses had the lowest bound water content. Significant differences in total water content (mg total water/mg lens dry weight) were observed between all of the lenses, with the exception of bovine and human lenses which were not statistically different. Fish lenses had the lowest amount of total water, and avian lenses had the highest total water content. There were significant differences in bulk water content (mg bulk water/mg lens dry weight) between all of the lenses. Avian lenses had the highest bulk water content, and fish lenses had the lowest bulk water content.

Adult↗
PubMed1994

Determination of the content of water in bovine corneas by differential scanning calorimetry and thermogravimetric analysis.

The 'bound', 'bulk', and total water contents in bovine corneas were investigated using differential scanning calorimetry and thermogravimetric analysis. The amount of total water (expressed as a function of total wet mass) was observed to be 83.7 +/- 1.1% using lyophilization and 84.1 +/- 0.8% using thermogravimetric analysis. These values are not significantly different from one another, but some discrepancies are observed when these values are compared with the values reported in the literature, thus indicating a need for guidelines concerning sample handling and analysis of these tissues. The 'bound' water was observed to be 62.3 +/- 2.7 (% of total water) and the amount of 'bulk' water was calculated to be 20.8 +/- 2.5 (% of total water).

Animals↗
PubMed1997

In vitro simulation of thermotherapy for benign prostatic hyperplasia by Fourier transform infrared microspectroscopy combined with differential scanning calorimetry.

Thermo-dependent changes in the secondary structure of the epithelium and stroma of benign prostatic hyperplasia (BPH) were investigated by Fourier transform infrared (FT-IR) microspectroscopy combined with differential scanning calorimetry (DSC). This microscopic FT-IR/DSC system was used to simulate transurethral thermotherapy for BPH in vitro. The results indicate that thermal-induced conversion from an alpha helix to a beta structure was found in the epithelium and stroma of BPH. However, this thermal-induced conversion behavior in the stroma was less sensitive than that in the epithelium during thermal treatment. The different thermal response between the epithelium and stroma of BPH might be due to the different constitutions of the epithelium and stroma of BPH.

Amides↗