Relaxation Time Distribution (RTD) Analysis for Online and Real-time Monitoring of Heparin Volume in Blood Extracorporeal Circulation

Abstract

The relaxation strength Δεm (m: dielectric relaxation number) regarding heparin volume in blood has been extracted by relaxation time distribution (RTD) analysis implementing in electrical impedance spectroscopy (EIS) for the online and non-invasive monitoring of heparin volume in blood extracorporeal circulation. Extracorporeal circulation experiment was performed under conditions where heparin volume in blood varied over time due to metabolism and heparin administration. By applying the RTD analysis with m as an unknown parameter, the Δεm were extracted from dielectric spectra of circulating blood which were measured by an impedance sensor located at a local section in extracorporeal circuit. As a result, four Δεm (m=1, 2, 3 and 4) were extracted by RTD analysis. Among the extracted Δεm, the variation of Δε3 was in good agreement with heparin volume in blood which was indirectly estimated from the activated clotting time (ACT). By comparing the variations of Δε3 and the variation of ACT, the Δε3 reflects the dielectric relaxation due to heparin-induced aggregation of blood cells and heparin complex with other plasma macromolecules. Therefore, the Δε3 has been shown to be one of the most important measurement indexes for the online and non-invasive monitoring of heparin volume in blood extracorporeal circulation.

Keywords

• heparin
• blood extracorporeal circulation
• electrical impedance spectroscopy
• dielectric relaxation
• relaxation time distribution