Biomedical subjects
Publications and source records attributed to W Sansen.
An experimental study of the electrical impedance of cortical bone and medullary cavity and on the effect of a D.C. or a periodically interrupted D.C. on the healing of fractures in rabbits, suggests that the bone behaves as a capacitance of about 20 muF in parallel with a high D.C. resistance. Also a 10 muA periodically interrupted D.C. current stimulates osteogenesis.
The first real-time, online measurements obtained using a screen-printed planar sensor to continually monitor urea in the spent dialysate are described. Evaluation of the sensor performance in the real clinical situation involves an extensive comparison of pre and post dialysis characteristics. Steady-state response and calibration curves show excellent reproducibility (typically within 5%; maximum deviation, 15%). The real-time results show that the characteristics predicted from the predialysis characterization are preserved during and after the prolonged period of continuous contact with the dialysate without needing recalibration. An operational stability of more than 10 hours of continuous use has been observed. Stability including intermittent wet-storage was found to be more than 5 days. Zero-baseline stability greater than 0.2 mmol/l (1.2 Og/dl) during the 4 hr treatment period and a resolution of 0.2 mmol/l were achieved, with a full-scale range of 15 mmol/l (90 mg/dl). A response time of less than 3 minutes allows dialysate urea levels to be monitored as a function of dialysis parameters such as varying blood flow. Parallel analysis of dialysate samples taken at 15 min intervals shows good correlation with the recorded data, although correspondence of the absolute values requires that the real-time data be rescaled. Because no degradation of the sensor performance was observed in vitro, this deviation can be explained only in terms of a dialysate based interference, probably caused by changes in pH and buffer.
A proposed general-purpose implantable biomedical system is described. This Internal Human Conditioning System (IHCS) is capable of measuring biomedical data of various kinds on a number of independent input channels. The number and specifications of these channels are software selectable by means of a low-power microprocessor. The system is also equipped with different programmable stimulation devices. These stimulators can deliver a programmable waveform in order to stimulate a specific muscle or to carry out an impedance measurement. The on-board eight bit microprocessor is used for communication with the outside world, by means of a serial link. The processor used is the 68HC11 from Motorola. By extensive use of the processor's 'sleep' mode and by switching off all unnecessary electronics, the amount of power consumed is drastically reduced. At present, a two-channel input chip and a programmable stimulator chip have been developed so that a complete system can be produced. For the sake of illustration, some realized and possible future applications are discussed.
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A new sensor for the on-line measurement of urea in the dialysate output is described. The sensor is based on a differential measurement of conductivity changes induced by the urease-catalyzed hydrolysis of urea. The use of screen printing for the batch-fabrication of the basic transducers results in cheap disposable devices. In addition, the sensor has been designed to fit into a standard male luer-adapter, and can be plugged directly into the dialysate line. The in vitro response is linear to urea concentrations exceeding 6620mM. A resolution of 20020 microM has been achieved with a baseline stability of 50 microM/hr. Interferences caused by fluctuations in the ionic strength and the consequent conductivity changes are effectively suppressed by the differential sensor pair. The efficiency of this suppression is expressed in a common mode rejection ratio of typically 40 to 50. Preliminary ex vivo results show the feasibility of the concept. The sensor principle is not restricted to urea but can be extended to other molecules of interest for hemodialysis monitoring, such as creatinine and L- and D-amino acids.