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At least 937 records · Page 52Linked to original sources
PubMed1985

[Indirect calorimetry in the artificially respirated polytraumatized patient. I. Studies in adults].

Significant changes in oxygen uptake (VO2) and carbon dioxide output (VCO2) as well as resting energy expenditure (RMR) can be observed in critically ill patients. Reliable data, although needed by the clinician especially in long term ventilated patients, have not been obtainable so far. We developed a modular system which provides by means of mass-spectrometry, accurate reproducible results. Furthermore, the design of the gas sampling module minimalizes systemical failures in the expiratory branch. Two groups of polytraumatized patients (n = 10, n = 7 respectively) with different amounts of intravenous amino-acid support and identical energy supply were included in the study. During the first week all patients showed significantly elevated values for VO2 and VCO2 with a tendancy to increase. High amino-acid supply resulted in higher rate of gas exchange and disproportional increase in energy expenditure. Subsequently reduced carbohydrate intake was found to be effective in reduction of gas exchange earliest after 24 h. Oxidation rates for glucose and fat did not correspond to energy supply ratio of substrates. It can be stated that in polytraumatized patients amino-acid supply more than 75 g/24 h/m2 is not economical in terms of energy gains and is therefore not generally recommended. Reduction of carbohydrates in the weaning period of respirator in these patients is likely to be effective only in borderline cases and started early before weaning (greater than 24 h). Energy supply by means of carbohydrates should exceed the energy derived from fat supply in the nutritional regime according to oxidation rates in polytraumatized patients.

Adult↗
PubMed1985

[Indirect calorimetry in artificially respirated children. 2. A measuring procedure and its evaluation in a newly developed metabolism-lung model].

A new device for continuous measuring oxygen uptake (VO2) and carbondioxide elimination (VCO2) in artificially ventilated or CPAP-system breathing children has been developed. A dual-channel analyzer system based on zirconiumoxyd cells measures oxygen fractions. This allows not only single measurements but also continuous determination of fraction differences for oxygen (delta FO2) (accuracy +/- 0.003 Vol%). Carbondioxide is measured by infrared absorption. A mixing device for inspiratory gas was designed to smooth fluctuations of inspired oxygen fractions almost completely. The reliable sampling system for expiratory gases has already been described [19]. The breathing-e.g. ventilating-system was modified in such a way that the total gas flow is independent of mode and breathing volume (equally 15 l/min). For which purpose we use a self aspirating, time-cycled, volume limited respirator or a high-flow-CPAP-system. The prototype described ran test performances on a specially developed pneumatic metabolic-lung-model. This new lung model enables free choice of respiratory quotient (R) by independent setting of O2-uptake and CO2-elimination. Under these controlled laboratory conditions gasvolume-balances correspond to expected values in children really as shown during simulated trials. In the metabolic-lung-model accuracy and reproduction averaged +/- 1% for VCO2. Both were independent of the mode of ventilatory support, FIO2, and R. Determinations of VO2 were more dependent on FIO2 and R. After computing primary data according to a special formula which equalizes differences between VI and VE the maximal error was +/- 7%. Maximum difference between preset and measured R-values ranging from 0.769 to 1.429 was -4.6%, determined at R = 1.429. By means of this independent test series insights into clinically expected measurement errors and dimensions of limits of accuracy could be demonstrated. It seems to be justified that our newly developed device for accurate measuring O2-uptake and CO2-elimination is highly recommendable for use in extremely difficult conditions as in ventilated children.

Calorimetry↗
PubMed1996

Effects of batch to batch variations and test methodology on degree of crystallinity and melting temperature of UHMW-PE as measured by differential scanning calorimetry.

The thermal and structural analysis of a total 22 batches from three medical grade ultrahigh molecular weight polyethylene (UHMW-PE) resins was determined using the DSC method. Batch to batch variations of approximately 5% were obtained for the melting temperature and the degree of crystallinity. The variations correlated both to the changes caused by gamma-irradiation sterilization and subsequent aging, and to the differences in DSC results obtained from various laboratories on materials believed to exhibit essentially similar clinical performances. Varying the sample weight from 4.4 to 27.1 mg resulted in a significant relative increase of 5% in the degree of crystallinity. The study shows that the standard double melting/recrystallisation procedure for DSC evaluation produces variations in the melting behaviors of approximately the same magnitude as those indicated by batch lot or sterilization/aging.

Calorimetry, Differential Scanning↗
PubMed2000

Defining the heating characteristics of ferromagnetic implants using calorimetry.

The induction heating of small, cylindrical ferromagnetic implants for localized tumors is currently under investigation. These thermal rods are implanted within a lesion in 1 cm(2) arrays and subsequently exposed to an externally applied alternating magnetic field. Implants absorb energy from the field and transfer it as heat to the surrounding tissue. To achieve a uniform temperature rise throughout the tissue volume and to account for any field-rod misalignment, 400 mW of power per implant is used as the design specification. The temperature to necrose cells must be greater than 46 degrees C. A calorimeter was constructed to confirm that the rod power output specification is satisfied at temperatures adequate for inducing cell death. The rods were designed to undergo a ferromagnetic to paramagnetic transition at temperatures of 55 degrees C, 60 degrees C, 65 degrees C, and 70 degrees C; this transition produces rods that are temperature self-regulating. Calorimetric results demonstrated that 55 degrees C, 60 degrees C, 65 degrees C, and 70 degrees C rods provided 400 mW at 47-51 degrees C, 51-53.5 degrees C, 57 degrees C, and 62.5-63.5 degrees C, respectively. Thermal rods provide sufficient power output at the temperatures necessary to cause thermal ablation of tumors. The higher-temperature rods give a greater margin to ensure that necrotizing temperatures can be achieved throughout the rod array even with minor misalignment.

Algorithms↗
PubMed2001

Interaction of L-tryptophan with alpha-cyclodextrin: studies with calorimetry and proton nuclear magnetic resonance spectroscopy.

The interaction of L-tryptophan with alpha-cyclodextrin was investigated in a 0.1 M phosphate buffer at pH 7.4 with a LKB 2277 microcalorimeter, using flow mixed mode at 25 degrees C. The thermodynamic parameters for inclusion complex formation obtained are as follows; DeltaG(0) = - 7.03 kJ/mol (K = 17.0), DeltaH(0) = - 9.50 kJ/mol, DeltaS(0) = - 8.3 J/mol K. The driving force for inclusion complex formation was considered to be mainly van der Waals-London dispersion force, and the contribution of hydrogen bonding was secondary in importance. Also, from the measurements of the proton nuclear magnetic resonance spectra and the model building with Corey-Pauling-Koltum atomic models, the probable structures of the complex, together with conformational change of L-tryptophan by complexation, were determined.

Calorimetry↗
PubMed2004

Flow calorimetry and dielectric spectroscopy to control the bacterial conversion of toxic substrates into polyhydroxyalcanoates.

The microbial conversion of toxic substrates into valuable products in continuous culture requires the equivalent of a tight rope walk between formation of the desired product and intoxication of the microbial catalyst. The condition of the latter is reflected immediately by changes in heat flow rate and beta-dispersion in an electrical RF field. Therefore, these were applied to the example of the continuous growth-associated synthesis of polyhydroxyalcanoates (PHA) from phenol by the bacterial strain Variovorax paradoxus DSM 4065. By controlling the supply of phenol to the chemostat, the rates of degradation, biomass formation, and synthesis of target product, respectively, were increasingly elevated until the onset of poisoning the organisms. The boundary between the maximum rates and the initiation of intoxication coincided with a sudden change in the heat flux. Using this occurrence, it was possible to develop a control strategy and test it successfully for a time period of 80 h. After 40 h the process stabilized at mean values, i.e., at rates of 92% phenol degradation, 100% biomass formation, and 70 - 75% of PHA formation compared with the situation shortly before poisoning the organisms. Using a moving-average technique to filter the raw dielectric spectroscope data, changes were followed in biomass concentration of approximately 100 mg/L. However, this technique was not sensitive or rapid enough to control the process.

Alcaligenes↗
PubMed2006

Control of continuous polyhydroxybutyrate synthesis using calorimetry and flow cytometry.

The substrate-carbon flow can be controlled in continuous bioreactor cultures by the medium composition, for example, by the C/N ratio. The carbon distribution is optimal when a maximum fraction flows into the desired product and the residual is just sufficient to compensate for the dilution of the microbial catalyst. Undershooting of the latter condition is reflected immediately by changes in the Gibbs energy dissipation and cellular states. Two calorimetric measurement principles were applied to optimize the continuous synthesis of polyhydroxybutyrate (PHB) by Variovorax paradoxus DSM4065 during growth with constantly increasing supply rates of fructose or toxic phenol. Firstly, the changed slope of the heat production rate in a complete heat balanced bioreactor (CHB) indicated optimum carbon channeling into PHB. The extent of the alteration depended directly on the toxic properties of the substrate. Secondly, a flow through calorimeter was connected with the bioreactor as a "measurement loop." The optimum substrate carbon distribution was indicated by a sudden change in the heat production rate independent of substrate toxicity. The sudden change was explained mathematically and exploited for the long-term control of phenol conversion into PHB. LASER flow cytometry measurements distinguished between subpopulations with completely different PHB-content. Populations grown on fructose preserved a constant ratio of two subpopulations with double and quadruple sets of DNA. Cells grown on phenol comprised a third subpopulation with a single DNA set. Rising phenol concentrations caused this subpopulation to increase. It may thus be considered as an indicator of chemostress.

Bioreactors↗
PubMed1976

Application of dynamic calorimetry for monitoring fermentation processes.

The rate of heat evolution (kcal/liter-hr) in mycelial fermentations for novobiocin and cellulase production with media containing noncellular solids was measured by an in situ dynamic calorimetric procedure. Thermal data so obtained have proved significant both in monitoring cell concentration during the trophophase (growth phase) and in serving as a physiological variable in the fermentation process. The validity of this technique has been demonstrated by closing the overall material and energy balances. The maintenance energy in a batch fermentation can be calculated by integrating heat evolution data. This integration method is applicable to a fermentation lacking a precise cell growth curve. The maintenance coefficient, obtained for the novobiocin fermentation by Streptomyces niveus, is equal to 0.028 g glucose equivalent/g cell-hr. The production of novobiocin in the idiophase (production phase) also correlates well with the amount of energy catabolized for maintenance and this results in an observed conversion yield of glucose to novobiocin of 11.8 mg of novobiocin produced per gram of glucose catabolized. A new physiological variable, kilocalories of heat evolved per millimole of oxygen consumed, has been proposed to monitor the state of cells during the fermentation. This method may provide a simple way to monitor on-line shifts in the efficiency of cell respiration and changes in growth yields during a microbial process.

Calorimetry↗