Title:  Cuffless Blood Pressure Monitoring Technologies Based on Pulse Transit Time

Committee:

Dr. Omer Inan, ECE, Chair , Advisor

Dr. Hua Wang, ECE

Dr. Robert Butera, ECE

Dr. Farrokh Ayazi, ECE

Dr. Mozziyar Etemadi, Northwestern

Abstract:

The objective of this thesis is to develop cuffless sensing techniques for monitoring pulse transit time (PTT) to estimate blood pressure. Developing such techniques is imperative to providing an at-home solution that is more convenient than current monitoring systems, such as an oscillometry cuff. PTT, or the time interval for an arterial pulse wave to travel along the arterial wall from a proximal to a distal site, relative to the heart, has been shown in previous works to have an inverse relationship with blood pressure. However, limited techniques exist to conveniently measure PTT in daily life. This work focuses on developing two techniques for convenient PTT measurements using a scale-based and wearable approach. First, a scale-based approach utilizes full-body vibrations, called the ballistocardiogram, to provide a measurement of the pulse at a proximal location to the heart. By attaching a custom-made optical sensor on the foot and thus measuring a distal pulse timing, the scale-based approach captures true aortic pulse transit time and provides a superior estimation compared to conventional timing based methods. We further refined the measurement of the distal pulse by developing an array-based optical sensor and signal selection techniques to capture a pulse wave while a subject simply stands quietly to obtain a measurement. Second, a watch-based sensor, SeismoWatch, allows the user to sense pulse timings at the chest and the wrist. To acquire two timing references for PTT, an inertial sensor detects the vibrations of the chest associated with opening of the aorta, based on seismocardiography, and an optical sensor at the wrist measures the distal pulse wave. SeismoWatch is non-invasive and compact, allowing for convenient and portable blood pressure tracking.