Showing papers by "Dietrich W. Lübbers published in 1980"

Continuous measurement of concentrations of alcohol using a fluorescence-photometric enzymatic method

Abstract: Using fluorescence optical techniques instead of electrodes [1] we have developed a method for determining concentrations of ethanol in biological fluids. The determination is based on the measurement of the oxygen consumption caused by oxidation of ethanol. The reaction is catalyzed by alcohol oxidase (AOD) EC 1.1.3.13. The formed aldehyde must be promptly converted to physiologically indifferent products. The enzymes are incorporated in a gel layer. Dependent on its concentration, alcohol diffuses into the layer and reacts with oxygen (1 M alcohol consumes 1 M oxygen). An oxygen pressure difference develops across the gel layer which is proportional to the alcohol concentration provided that 1) oxygen is available in excess; 2) the enzyme concentration is in a range where velocity is proportional to the substrate concentration; 3) the reaction products are in diffusion equilibrium with the medium to be measured. Under these conditions, Po2 decreases across the enzyme layer in a cosh-function. Pyrene butyric acid was used as an oxygen indicator. The oxygen sensitivity of the fluorescence intensity of the indicator is according to Vaughan and Weber [4]: Io = ] + K P o z (1) I

A sensitive dual wavelength microspectrophotometer for the measurement of tissue fluorescence and reflectance

Abstract: The construction of a microscope photometer using prefabricated elements is described. To illuminate the tissue, a Leitz Ultropac is applied. To enlarge the wavelength range, its illuminating glass lens is replaced by an Acryl glass zonal lens. Two separate light channels with separate lamps, monochromators and photomultipliers allow the measurement of fluorescence excitation and emission spectra as well as of reflection spectra. By chopping the light, light pulses and dark currents are measured 8.33 times a second. By an integration circuit the signal-to-noise ratio for small signals is improved. The instrument allows us to detect the increase of 4 ng/ml NADH (solution of pH 7.38) in an area of 0.2 mm2.

Distribution of oxygen partial pressure in the carotid body region and in the carotid body (rabbit).

Abstract: In the specific tissue of the rabbit carotid body as well as in the connective tissue surrounding the organ,pO2 distribution was measured with membranecovered needle electrodes (tip diameter 1–2 μm). The histograms resulting from measurements in the specific tissue were shifted to lowpO2 values as compared to other tissues. The oxygen blowing test, i.e. exposure of the carotid boyd to humidified 100% oxygen was employed to decide upon the site of measurement:pO2 increased when the electrode measured in the surrounding tissue (type 1 response);pO2 remained stable or slightly decreased when the electrode sampled in the specific carotid body tissue (type 2 response). After the experiment, the electrode track was reconstructed from histological serial sections and the type of reaction was related to the type of tissue. LowpO2 values were found to prevail in the specific carotid body tissue, which leads to the conclusion that the amount of lowpO2 values determines the degree of chemoreceptor activity.