05/2018 – 10/2018
In order to discover irregularities in blood pressure (BP) or disorders in the autonomic BP regulation under real live conditions outside of the doctor’s laboratory the BP has to be monitored continuously. One prominent example for such a disorder is Parkinson’s Disease (PD) that does not only affect the motor system, but also causes autonomic failures in blood pressure and heart rate regulation, leading to orthostatic dysregulation . To receive valuable information, it is of particular importance to combine continuous blood pressure and heart rate measurement with contextual information on posture changes, e.g. changes from lying to sitting or standing. Under these situations, the autonomic nervous system regulates the cardiovascular system mostly to prevent dizziness and impairment of consciousness . Additionally, unobtrusive monitoring in a home environment is beneficial in order to reduce influences of the environment on the patients’ physiology (also commonly referred to as white-coat syndrome ) and therefore increase the quality of results . Unobtrusive BP monitoring is frequently implemented using methods based on the measurement of pulse transit time (PTT) through the cardiovascular system . Leveraging this, it allows a cuffless and continuous blood pressure measurement and therefore increases the user’s daily-life usability . However, a problem of PTT-based methods is that the correlation between PTT and BP is highly influenced by changes in hydrostatic pressure that changes with the user’s arm position. For that reason, accurate calibration would be needed to be done for different arm positions .
The goal of this bachelor’s thesis is therefore to create a system for continuous BP measurement during daily-life activities using PTT. In this work, PTT will be calculated using information from an ECG sensor, worn as a chest strap and from a wrist-worn PPG sensor. Therefore, PTT is defined as the time delay between the R-wave of the ECG and the arrival of the pulse wave at the wrist. The main focus however lies on the development of an unobtrusive measurement technology for home-monitoring applications by automatically detecting the user’s arm position and using this information to achieve better blood pressure measurement, complementing a heart rate analysis during orthostatic maneuvers (e.g. transition from lying to sitting or sitting to standing). For that reason, a calibration procedure will be developed where blood pressure data obtained by a reference system from various arm positions is correlated to the acquired pulse transit time data via linear regression .
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