Biomedical subjects

A Christophersen

Publications and source records attributed to A Christophersen.

4 recordsLinked to original sources

PubMed1996

Laser-based detection of PAHs and BTXE-aromatics in oil polluted soil samples.

Time-resolved laser-induced fluorescence spectroscopy and fiber optics are applied for the detection of aromatic hydrocarbons in oil contaminated water and soil samples. Time-integrated data accumulation of fluorescence intensities in an "early" and in a "late" time window with respect to the exciting laser pulse simplifies the method in such a way that it becomes very attractive for practical applications. For ultraviolet laser excitation at 337 nm and recording fluorescence signals at 400 nm, typical detection limits of the present set-up are 0.5 mg engine oil/L in water and 5 mg engine oil/kg in soil. A discrimination between BTXE-aromatics and PAHs in oil polluted soil or water samples is possible, when more than one laser wavelength in the ultraviolet is used for the excitation. The possibilities for a thermal discrimination between different aromatics are also discussed.

Journal Article↗

PubMed1986

Turbidimetric determination of prothrombin time by clotting in a centrifugal analyzer.

Two thromboplastin reagents ("Thrombotest" and "Normotest Automated") were used in evaluation of an automated method for determination of prothrombin time based on turbidimetric measurement of clot formation in a centrifugal analyzer. We used 60 plasma samples from patients with various diseases or being treated with oral anticoagulant and 16 normal plasma samples. Prothrombin times were calculated by a computer connected to the analyzer, a reading being made at either a certain per cent increase in total absorbance or a fixed absorbance increase. Both correlated well with the manual method (r = 0.98-0.99). The reading points best fitting the manually obtained data were estimated by minimizing the residual sum of squares in regression analyses performed at various absorbance increases. The per cent reading was better in this respect. Normotest Automated could be nearly perfectly related to the manual method, whereas Thrombotest showed a (negligibly) small deviation. Reproducibility was good within run (CV less than or equal to 3.2%) as well as between batch of the reagents, as assessed from variation in INR (CV less than or equal to 4.9%). We conclude that turbidimetry of clot formation may be validly used in automation of the prothrombin-time test. The equipment needed and the total time per analysis are about as for chromogenic substrate methods, but reagent cost is considerably lower.

Anticoagulants↗

PubMed1984

Energy metabolism in rats with ventromedial hypothalamic lesions.

Rats with ventromedial hypothalamic lesions (VMH) have increased ability to accumulate energy. The aim of this investigation was to characterize the main processes responsible for the reduced energy expenditure, using indirect calorimetry, nitrogen, and energy balance techniques. Metabolism was studied during different metabolic conditions created by a strict feeding regimen with concentrated feeding periods. A computerized system for indirect calorimetry enabled continuous study of individual animals for prolonged time periods. We found a mean decrease of 15.5% in total energy expenditure and decreased nitrogen retention in VMH rats. Calculation of respiratory quotient (RQ), energy expenditure, and the metabolic mixture demonstrated fluctuations in metabolism in accordance with the feeding regimen. The same percent reduction in resting postabsorptive energy expenditure was found as in total expenditure. Quantitatively, this main finding means that metabolic processes that occurred both in the resting and postabsorptive state were responsible for two-thirds of the total reduction in energy expenditure, whereas only one-third could be attributed to differences in dietary-induced thermogenesis and/or physical activity. It is concluded that VMH-animals spent as much as 10.3% of their total energy expenditure on liponeogenesis compared with 2.5% in controls.

Animals↗

PubMedDate not supplied

INAKT--an interactive non-linear regression program for enzyme inactivation and affinity labelling studies.

An interactive program for analysing enzyme activity-time data using non-linear regression analysis is described. Protection studies can also be dealt with. The program computes inactivation rates, dissociation constants and promotion or inhibition parameters with their standard errors. It can also be used to distinguish different inactivation models. The program is written in SIMULA and is menu-oriented for refining or correcting data at the different levels of computing.

Affinity Labels↗