Abstract

Cardiovascular disease is the leading cause of death in the United States. In-home physiological monitoring systems have a potential to track daily changes in cardiovascular health and to provide health care professionals data about the recovery or deterioration of their patient’s cardiac health. Various in-home monitoring systems have been designed to capture physiological signals from both standard (chest, wrist) and non-standard (palms, buttocks) locations. Unfortunately, most in-home monitoring systems provide poor signal quality due to the use of dry electrodes. Dry electrodes have an unstable electrochemical interface that results in high and variable contact impedance and poor signal quality. The present work focuses on investigating the dependence of the electrode-skin impedance, and resulting signal quality, on the electrode material, electrode area, and skin hydration. This overall goal is accomplished by three separate studies. First, a novel equivalent circuit model for the skin-electrode interface impedance model was developed, which was validated on human skin and with a first of its kind skin phantom. The results of the model suggest the relative permittivity of the native oxide for the electrode material can provide insight into the electrode performance for biopotential measurements. Second, this work demonstrates an application of previous model to evaluate the feasibility of using the dry electrodes to capture clinically relevant Electrocardiogram (ECG) signals by using large dry titanium electrodes integrated into a toilet seat cardiovascular monitoring system. In vivo skin-electrode contact impedance and ECG measurements were conducted across ten healthy human subjects, and quantitative comparisons were performed to compare the ECG signal quality between different electrode configurations. It was found that large titanium electrodes resulted in better signal quality than large stainless steel electrodes. Third, this work demonstrates the use of large dry titanium electrodes to monitor respiration by measuring changes in impedance from the back of the thigh, which may be useful for several conditions including COVID-19 recovery, and progression of edema during heart failure management. The feasibility of the thigh and the sensitivity of impedance to respiration were investigated empirically, by comparing thorax and thigh-thigh bioimpedance measurements to spirometer measurements, and computationally, using finite element modeling (FEM). Empirical thigh-thigh bioimpedance resulted in a high correlation (0.87) to the respiration rate and tidal volume. The FEM model predicts that thigh-thigh bioimpedance measurements might not be sensitive to pulmonary edema detection, however, the ability to effectively measure respiratory rate and tidal volume from the back of the thigh can be used for tracking COVID-19 recovery.

Library of Congress Subject Headings

Ambulatory electrocardiography; Electrodes--Materials; Titanium

Publication Date

7-17-2023

Document Type

Dissertation

Student Type

Graduate

Degree Name

Microsystems Engineering (Ph.D.)

Department, Program, or Center

Microsystems Engineering (KGCOE)

Advisor

Steven W. Day

Advisor/Committee Member

David A. Borkholder

Advisor/Committee Member

Dan Phillips

Campus

RIT – Main Campus

Plan Codes

MCSE-PHD

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