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Abstract

Impedance plethysmography of extremities typically uses band electrodes around limbs to monitor changes in blood volume. This often causes monitored blood variations to only generate minuscule impedance values relative to the measured baseline, attributed to the tissue surrounding the artery or vein of interest. Smaller, ECG type electrodes can provide a larger signal, however their output is very easily affected by the placement of the electrodes relative to the targeted vasculature. This paper presents a novel method to adjust the active surface of electrodes, introducing Dynamically Re-sizeable Electrodes (DRE), to only target the exact area of interest, forming localised electrodes, without having to manually re-position them. Elongated rectangular electrodes were partitioned into smaller electrode segments, interconnected through custom circuitry. For the development and assessment of the DRE system, work was carried out both experimentally in-vitro on gelatine phantoms using custom switching circuits and through finite element modelling (FEM) simulations in COMSOL. A scanning sequence made use of DRE in single segment variable tetra-pole (SSVT) mode proved capable to identify the transcutaneous location of the blood vessel of interest and the specific electrode segments located in its vicinity. Impedance measurements were then taken using these segments connected to form localised electrodes only placed over the targeted vessel. The resulting localised electrodes exhibited up to 28% increased sensitivity to blood variations relative to larger electrodes.

Publication Type:	Article
Additional Information:	© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
Publisher Keywords:	Impedance plethysmography, segmented electrodes, impedance, localised measurements
Subjects:	T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments:	School of Science & Technology > Engineering
SWORD Depositor:	Symplectic Administrator

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