Impedance Measurement System for Blood Pressure Registration
Dimitra Markou
Abstract
Cardiovascular disease threatens the lives of millions of people and it's the leading cause of death worldwide according to the World Health Organization (WHO) on all continents, except Africa. The term cardiovascular disease represents a wide range of disorders related to the heart and the blood vessels. The diagnosis of these diseases depends on some hemodynamic parameters. It is estimated that up to 90% of cardiovascular diseases can be prevented. A preventative factor is the regular monitoring of hemodynamic parameters which may differ signiffcantly during the day. The commercially available devices for measuring these parameters do not allow a 24-hour continuous measurement. This fact limits the accuracy of diagnosis. Wearable devices with sensors on them allow the continuous monitoring and the recording of the hemodynamic parameters and improves the quality of diagnosis as well as the accuracy of measurements. The aim of this thesis is to develop a portable system for measuring the blood pressure which is based on measuring the impedance of the human body. The measurement is noninvasive, by placing electrodes in the area of the radial artery in the left hand of the human subject. With the help of a pair of electrodes, a current is injected in the area of interest and with the use of another pair the induced voltage is measured. The impedance is calculated according to Ohm's law. With this system, it is possible to continuously record and monitor the systolic and the diastolic blood pressure by detecting the changes in impedance and by matching those changes with the changes of the blood volume. Within the portable system's construction with the purpose of effective modelling, the relationship between the parameters of the body and the parameters of the impedance became the subject of our study. The effect of electrodes on the quality of the measurement, the required structure of the system as well as various parameters for maximizing the effciency and the accuracy of the measurements were also investigated.