Capacitive on-line hematocrit sensor design based on impedance spectroscopy for use in hemodialysis machines

• Published in: 2009 Annual International Conference of the IEEE Engineering in Medicine and Biology Society Vol. 2009; pp. 1208 - 1211
• Main Authors: Trebbels, D., Hradetzky, D., Zengerle, R.
• Format: Conference Proceeding Journal Article
• Language: English
• Published: United States IEEE 01-01-2009
• Subjects: Biomedical Engineering; Biomedical equipment; Blood; Capacitive sensors; Dielectric measurements; Electric Impedance; Electrochemical impedance spectroscopy; Electrodes; Equipment Design; Finite Element Analysis; Hematocrit - instrumentation; Humans; In Vitro Techniques; Measurement standards; Plastics; Renal Dialysis - instrumentation; Sensor systems; Spectrum Analysis - instrumentation; Temperature sensors
• ISSN: 1094-687X; 1557-170X; 1558-4615
• DOI: 10.1109/IEMBS.2009.5332420

This paper presents a new design for an on-line and in-line hematocrit (HCT) sensor. Special feature of the sensor is the capability to measure the hematocrit of a blood sample inside standard plastic tubing widely used in medical equipment. No blood sample has to be extracted out of existing extracorporeal blood circulation systems such as hemodialysis machines or heart-lung machines. The sensor principle is based on electrical impedance spectroscopy. Dielectric properties of the blood and the plastic tubing are measured at various frequencies. In order to optimize the sensitivity, a unique electrode configuration is developed and optimized by Finite Element Simulation. The new electrode design optimizes the overall sensitivity of the sensor towards a change in dielectric properties of the blood caused by the HCT value and therefore decreases the sensitivity to side effects caused by temperature drift and component tolerances. As a result of the optimized overall sensor performance the complexity of a sensor readout circuitry can be reduced to a minimum which leads to an unmatched price-performance ratio for a complete measurement system.