Cuffless Blood Pressure Monitor

Abstract

Many countries around the world are currently concerned about the control and early detection of hypertension. Regular blood pressure monitoring is a way to monitor health and detect potential diseases with a high risk of death, such as heart disease or stroke. A variety of blood pressure measurement devices and methods either invasively or non-invasively have been introduced and developed in recent years. The non-invasive method is mainly based on the Korotkoff-sound and consists of compressing the arm’s artery using a cuff which is inflated then deflated which yields systolic and diastolic pressures and possible heartrate. Although, this method is better and commonly used, it is still uncomfortable for the patients especially for those whose blood pressures need to be monitored continuously. This thesis aims to investigate and develop a compact blood pressure measuring device without using a cuff. Its principle is based on the fact that the Pulse transit time (PTT) which is the pulse that the heart transmits between two arterial sites determined from the peak of Photoplethysmographic PPG signal has an inverse relationship with blood pressure. The difficulty is estimating the PTT from the two peaks of the PPG signal requires going through signal processing steps that include smoothing the signal, determining the measurement location, and determining the sensor's sampling frequency. In this thesis, blood pressures were calculated based on a linear regression model built on PTT values obtains from 10 people. The results of the linear regression model showed that the fit of the model to the data was at an acceptable level with a rather low R-squared values (0.6176 was the highest and 0.5066 was the lowest). The experiments showed that PTT had a high correlation for systolic blood pressure with a correlation coefficient of -0.76 and low for diastolic blood pressure with -0.71. The device showed high error performance when tested on 5 different people with the highest error of +13 mmHg for diastolic blood pressure and +9 mmHg for systolic blood pressure.