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Biomedical subjects

Orjan G Martinsen

Publications and source records attributed to Orjan G Martinsen.

5 recordsLinked to original sources
PubMed2005

Cole electrical impedance model--a critique and an alternative.

The Cole single-dispersion impedance model is based upon a constant phase element (CPE), a conductance parameter as a dependent parameter and a characteristic time constant as an independent parameter. Usually however, the time constant of tissue or cell suspensions is conductance dependent, and so the Cole model is incompatible with general relaxation theory and not a model of first choice. An alternative model with conductance as a free parameter influencing the characteristic time constant of the biomaterial has been analyzed. With this free-conductance model it is possible to separately follow CPE and conductive processes, and the nominal time constant no longer corresponds to the apex of the circular arc in the complex plane.

Algorithms↗
PubMed2005

Electrode polarization impedance in weak NaCl aqueous solutions.

In this paper, we characterize the polarization impedance behavior of several common metals in diluted NaCl solution operated at low current densities. The objective was to provide a useful reference for those wishing to calculate the electrode polarization impedance in diluted NaCl solutions. Serial equivalent resistance (R) and capacitance (C) for silver, aluminum, gold, platinum, and medical stainless-steel were measured as a function of frequency (10(-2)-10(3) Hz) and NaCl concentration (2.4-77.0 mmol/L). The ratio of electrode polarization impedance with respect to the bulk resistance was calculated and plotted against concentration for each metal. Such a ratio shows the effect of the electrode polarization contribution as a function of electrolyte concentration when the bulk resistance of the solution changes. All metals showed a decrease of serial resistance Rp and capacitance Cp as a function of frequency. The medical stainless-steel electrode showed largest impedance values at lower frequencies compared to the other electrodes, and was concentration independent at all frequencies. Aluminum had smallest polarization impedance at low frequencies. Pure gold and platinum behaved similar with the exception that the serial resistance for gold showed a lower value at higher frequencies.

Electric Impedance↗
PubMed2004

A new biomedical sensor for measuring PCO2.

Measuring PCO2 (partial pressure of carbon dioxide) in an organ can enable early detection of ischemia. However, there are few clinical applicable solutions for measuring PCO2. Based upon the requirement for clinical applications, a conductivity based PCO2 sensor is proposed. A conductivity based PCO2 sensor measures conductance in an aqueous solution separated from the measured object by a gas-permeable membrane. A bridge design with two cavities is favored for such a sensor. A planar and a cylindrical macro prototype based upon the bridge design were studied. The design criteria were based on the contribution from the electrode polarization, stray capacitances, contact area with the sample and design ability to miniaturize the sensor. The cylindrical sensor is favored because of its large contact area and advantages for miniaturization. Further investigation has to be done to confirm the functionality of such a design in a miniaturized form and its clinical performance.

Biomedical Technology↗
PubMed2004

Miniaturization of a biomedical gas sensor.

In a previous study, we concluded that a conductivity based PCO2 sensor is an attractive solution for early detection of ischemia and presented two design geometries. For organ surface measurements, the planar design was suitable but it was difficult to insert the sensor into the tissue. A cylindrical design solution was favored for insertion due to the large membrane contact area and easy placement in a medical catheter. Since the previous cylindrical prototype was large and could damage the tissue, a more miniaturized sensor was needed. In the current paper, we present a miniaturized sensor with an outer diameter of 1 mm. The applied technology for manufacturing the sensor was a combination of mechanical turning, excimer laser drilling and conventional molding technique. The materials applied were PEEK (polyetherether ketone), PI (polyimide) with gold layers and polysiloxane. The membrane had to be gas permeable while acting as a barrier for ion transport, and was made of polysiloxane and had a thickness of 100-150 microm. The miniaturized sensor was tested for calibration, response time, drifting and pressure sensitivity. The results show that the miniaturized PCO2 sensor is capable of rapid and stable measurements both in vitro and ex vivo. The result from this study will be applied for the industrial manufacturing of such a biomedical sensor as a clinical product.

Biosensing Techniques↗