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Schadewaldt P.,Institute of Clinical Biochemistry and Pathobiochemistry | Schadewaldt P.,Institute For Klinische Biochemie And Pathobiochemie | Nowotny B.,Institute of Clinical Diabetology | Strassburger K.,Institute of Biometry and Epidemiology | And 3 more authors.
American Journal of Clinical Nutrition

Background: Indirect calorimetry (IC) with metabolic monitors is widely used for noninvasive assessment of energy expenditure and macronutrient oxidation in health and disease. Objective: To overcome deficiencies in validity and reliability of metabolic monitors, we established a procedure that allowed correction for monitor-specific deviations. Design: Randomized comparative IC (canopy mode) with the Deltatrac MBM-100 (Datex) and Vmax Encore 29n (SensorMedix) was performed in postabsorptive (overnight fast >8 h) healthy subjects (n = 40). In vitro validation was performed by simulation of oxygen consumption (VO2) and carbon dioxide output (VCO2) rates by using mass-flow regulators and pure gases. A simulation-based postcalorimetric calibration of cart readouts [individual calibration control evaluation (ICcE)] was established in adults (n = 24). Results: The comparison of carefully calibrated monitors showed marked differences in VCO2 and VO2 (P < 0.01) and derived metabolic variables [resting energy expenditure (REE), respiratory quotient (RQ), glucose/carbohydrate oxidation (Gox), and fat oxidation (Fox); P < 0.001]. Correlations appeared to be acceptable for breath gas rates and REE (R2 ~ 0.9) but were unacceptable for RQ (R2 = 0.3), Gox, and Fox (R2 = 0.2). In vitro simulation experiments showed monitor-dependent interferences for VCO2 and VO2 as follows: 1) within series, nonlinear and variable deviations of monitor readouts at different exchange rates; 2) between series, differences and unsteady variability; and 3) differences in individual monitor characteristics (eg, rate dependence, stability, imprecision). The introduction of the postcalorimetric recalibration by ICcE resulted in an adjustment of gas exchange rates and the derived metabolic variables with reasonable correlations (R2 > 0.9). Conclusions: Differential, metabolic, monitor-specific deviations are the primary determinants for lack of accuracy, comparability, and transferability of results. This problem can be overcome by the present postcalorimetric ICcE procedure. Copyright © 2013 American Society for Nutrition. Source

Mindukshev I.,Institute For Klinische Biochemie And Pathobiochemie | Mindukshev I.,RAS Sechenov Institute of Evolutionary Physiology and Biochemistry | Gambaryan S.,Institute For Klinische Biochemie And Pathobiochemie | Gambaryan S.,RAS Sechenov Institute of Evolutionary Physiology and Biochemistry | And 10 more authors.
Clinical Chemistry and Laboratory Medicine

Background: Determinations of platelet receptor functions are indispensable diagnostic indicators of cardiovascular and hemostatic diseases including hereditary and acquired receptor defects and receptor responses to drugs. However, presently available techniques for assessing platelet function have some disadvantages, such as low sensitivity and the requirement of large sample sizes and unphysiologically high agonist concentrations. Our goal was to develop and initially characterize a new technique designed to quantitatively analyze platelet receptor activation and platelet function on the basis of measuring changes in low angle light scattering. Methods: We developed a novel technique based on low angle light scattering registering changes in light scattering at a range of different angles in platelet suspensions during activation. Results: The method proved to be highly sensitive for simultaneous real time detection of changes in size and shape of platelets during activation. Unlike commonly-used methods, the light scattering method could detect platelet shape change and aggregation in response to nanomolar concentrations of extracellular nucleotides. Furthermore, our results demonstrate that the advantages of the light scattering method make it a choice method for platelet receptor monitoring and for investigation of both murine and human platelets in disease models. Conclusions: Our data demonstrate the suitability and superiority of this new low angle light scattering method for comprehensive analyses of platelet receptors and functions. This highly sensitive, quantitative, and online detection of essential physiological, pathophysiological and pharmacological-response properties of human and mouse platelets is a significant improvement over conventional techniques. © 2012 by Walter de Gruyter • Berlin • Boston. Source

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