Wireless implantable microdevices: Chronic in-vivo monitoring of physiological signals

Abstract

A better understanding of physiological systems relies on measurement of in-vivo-physiological signals. A valuable tool for obtaining these signals without disturbing the system generating them is the use of wireless implantable microdevices. The purpose of this thesis is to present advancements in the field of chronic monitoring in small rodents. Telemetry technology trades off size,duration of use and signal quality attributes.Oxygen is an essential substance for biochemical reactions, which highlights the importance of the ability for researchers to measure dissolved oxygen concentration. Existing measurement techniques for the chronic monitoring of oxygen has been limited by restrictive tethers, or non-implantable telemetry systems affecting the natural state of the physiological system. The telemetry system developed in this PhD research overcomes the power and miniaturisation barriers to provide the first system which allows the continuous and life time measurement of oxygen concentration in freely moving rats from a fully implanted telemeter. The system was compared against a Clark electrode in kidney tissue and demonstrated the ability to successfully detect a change of7.2 μM from a step change in inspired O2 (room air to 18%). The electrocardiogram is the most sensitive early indicator of cardiac toxicity or malfunction, the measurement of which has found significant use by both clinicians and researchers. While mice are commonly used in research studies, the measurement of electrocardiogram in mice has been limited due to the poor signal fidelity and finite operational life of existing telemetry systems. This thesis describes the first telemetry system which has a telemeter size suitable for implantation in mice whilst enabling the high fidelity (2 kHz) life time measurement of electrocardiogram in a freely moving mouse. QT intervals from mice were obtained with a resolution of <1 ms. An important contribution is the control of a wireless power system to energise the implanted device.The outcomes from this PhD research provide new tools for physiological monitoring from research animals. It is now possible to obtain lifetime monitoring of oxygen in rats, and high fidelity electrocardiograms from mice.