Showing papers by "Dietrich W. Lübbers published in 1986"

Optical Fluorescence and Its Application to an Intravascular Blood Gas Monitoring System

Abstract: Optical fluorescence has an extensive history of application in the laboratory to the measurement of ionic concentrations and the partial pressures of oxygen and carbon dioxide. The use of optical fluorescence based sensors to fulfill a recognized need for continuous invasive monitoring of arterial blood gases offers a number of inherent advantages. However, the requirements placed upon a blood gas probe and supporting instrumentation appropriate for use in the clinical environment result in significant design challenges in selection of suitable fluorescent dyes, maintenance of mechanical integrity while obtaining required miniaturization of sensors, and in the transmission, acquisition, and processing of low level light signals. An optical fluorescence based intravascular blood gas monitoring system has been developed which is particularly suited for the critical care and surgical settings and which has a sensor probe that can be introduced into the patient via a radial artery catheter. This system has shown an excellent agreement of measured with true values of pH, pCO2, and P02 in both in vitro and animal studies. Linear regression analysis of typical in vitro data, where true levels were established via tonometry and standardization to a high accuracy laboratory pH measuring instrument, shows slope/intercept values very close to 1.0/0.0 and correlation coefficients of greater than 0.99 for all three parameters.

Investigations of oxygen transfer into Penicillium chrysogenum pellets by microprobe measurements

Abstract: A microcoaxial needle sensor with a tip diameter of ca. 0.7 microm was used as a microprobe to measure profiles of dissolved oxygen tension (DOT) within fixed pellets of Penicillium chrysogenum as a function of the DOT level around the pellet, in the presence and absence of bulk convective flow and turbulence. The investigations indicate that the oxygen transfer mechanism is complex. The results were interpreted by assuming the penetration convective flow into the entire pellet and penetration of turbulence into the outer range. A model was developed which was able to describe the measured DOT profiles very well. The model takes into account molecular and turbulent diffusion as well as convective flow as transfer mechanisms inside of the pellet. Structures of pellets used for microprobe measurements were evaluated by histological investigations. Considerable variations of mycelial density with radius within the pellets were found.

Estimation of concentration ratios and the redox states of the cytochromes from noisy reflection spectra using multicomponent analysis methods.

Abstract: To quantify tissue reflection spectra, multicomponent analysis methods have been successfully used. These methods reconstruct the measured reflection spectra using a set of basic absorption spectra, which describe the single chromophoric substances of the multicomponent system, and applying the Kubelka-Munk algorithm (Kubelka and Munk, 1931; Hoffmann et al., 1984). Since basic absorption spectra differ in distinctness and sharpness of absorption peaks, multicomponent analysis methods give concentration ratios of the components with different uncertainties.

Determination of oxygen transfer from single air bubbles to liquids by oxygen microelectrodes

Abstract: For the investigation of mass transfer from gas bubbles into liquids the concentration gradient of oxygen migrating from air bubbles was measured by means of oxygen microelectrodes. For this purpose a single air bubble was fixed by a platinum wire spiral with the liquid flowing downward. Thus the ascent of the bubble in an aerated liquid was simulated. Liquid-side mass transfer coefficients determined from concentration gradients were higher than values calculated from theory. Sherwood numbers obtained from experimental results for bubbles of larger diameters were distinctly higher than those for smaller bubbles (diameter ≅1 mm); the difference corresponds approximately to that predicted theoretically between bubbles with mobile and those with rigid interfaces.

Improved quantitative analysis of reflection spectra obtained from the surface of the isolated perfused guinea pig heart.

Abstract: The chromophoric substances which cause light absorption of optical spectra of the perfused Langendorff heart in the wavelength range of 500 to 650 nm are myoglobin and the cytochromes of the respiratory chain. We use a modified multicomponent analysis based on the two-flux theory of Kubelka and Munk (1931; Kubelka, 1948; 1954) to quantify the reflection spectra. Since the absorption spectra of the involved substances have overlapping absorption peaks and different forms, their concentration ratios are determined within different accuracy. The experiments show that the accuracy can be improved by the introduction of constraints, e.g. the reduction of the number of the basic absorption spectra. The constraints are worked out for the special measuring conditions.

Oxygen Pressure Measurements on Moving Organ Surfaces by Fluorescence Sensor Membranes Using Contactless Signal Transmission Via Fluorescence Sensor Radiation

Abstract: Polarographic oxygen measurements on moving organ surfaces can disturb free blood circulation due to the weight of the sensor directly coupled to the organ. It has been proposed to compensate the weight of the sensor, e.g. by a balancing mechanism, but such a compensation does not work any more with movements in the range of higher frequency, e.g. on the beating guinea-pig heart with a frequency of 4–5 Hz.