Analog/Mixed-Signal Techniques for Luminescent Lifetime Estimation with Applications in Transcutaneous Oxygen Measurements

Costanzo, Ian

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Analog/Mixed-Signal Techniques for Luminescent Lifetime Estimation with Applications in Transcutaneous Oxygen Measurements

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The importance and challenges of miniaturized, low-power, noninvasive measurement techniques for remote and continuous monitoring are rapidly growing in the “smart and connected health” era. For example, in the United States, 300,000 neonates are admitted to the neonatal intensive care unit (NICU) every year, primarily due to respiratory distress. After a successful medical treatment in the NICU, earlier discharge to a more stable home life could improve their chance of survival. However, the lack of continuous monitoring at home precludes the outpatient management of infants with fragile respiratory status. Accurate remote vitals monitoring would help caregivers improve care quality and give patients greater freedom outside the hospital environment. This dissertation aims to develop a noninvasive, luminescence-based oxygen sensing device to provide a foundation for future wireless, wearable respiratory monitoring systems. We have investigated the need for miniaturized sensors to monitor respiration effectiveness and the available state-of-the-art devices. Transcutaneous oxygen monitoring is a noninvasive method to continuously measure the partial pressure of oxygen that diffuses through the skin and correlates closely with changes in arterial blood gases. However, the contemporary commercially available electrochemical-based technology is bulky, corded, and expensive sensing units. Optical oxygen sensors, leveraging luminescent materials whose emission intensity and lifetime change with the partial pressure of oxygen, provide a practical path toward miniaturization. This work demonstrates several noninvasive, miniaturized prototypes that use luminescence-based technology to measure the partial pressure of transcutaneous oxygen. The first is a discrete transimpedance amplifier, used to assess the behavior of the film and compare the performance of intensity and lifetime-based measurements. The second prototype is a traditional differential signal chain and is our first attempt at an integrated system. Finally, the third prototype demonstrates a nonuniform sampling technique for measuring the lifetime of luminescent materials for oxygen sensing. The system features an integrated switched-capacitor circuit to implement fixed-voltage steps for quantization. The offset immune algorithm calculates the lifetime of the sensor emission using the time differences between the voltage steps. These prototypes demonstrate the feasibility of miniaturized blood gas monitors and provide the groundwork for future wearable, wireless medical devices.

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