• Phonocardiogram
• sensor
• sensor for phonocardiography
• wearable

The present study aims at developing a wearable sensor able to analyse the heart sounds for integration in a remote monitoring device.
A graphical representation of the waveform of heart sounds is called phonocardiogram (PCG).
To obtain the PCG, a microphone is placed on the patient chest and the digitally-recorded signal is plotted on a chart.
With the development of PCG, the timing of heart sounds has been used in cooperation with other sensors to obtain and monitor important cardiovascular parameters, such as blood pressure (BP) or cardiac output (CO), that provide crucial information about cardiovascular diseases, nowadays cause of death worldwide.
The need for a continuous remote monitoring of people health is fostered by several factors.
First, current cardiovascular disease measurement methods are usually invasive, require specific skills and hospitalisation. Second healthcare costs are increasing and finally the world population is ageing.
Therefore, there is the need to monitor a patient’s health status also outside the hospital.
For these reasons, non-invasive, low-cost and wearable devices have been produced with the aim of providing real-time feedback information about people health condition.
The present study was performed in the Advanced System Technology (AST) Remote Monitoring Team of STMicroelectronics.
The team is in charge of research and development about wearable devices for remote and continuous monitoring of physiological parameters.
This group developed a monitoring device called Bodygateway, worn as a patch on the thorax.
The Bodygateway (BGW) is a biomedical device, which is able to detect physiological parameters because it is equipped with four electrodes in the patch, to record electrocardiogram (ECG) and thoracic bioimpedance, and an accelerometer. In this way, it is able to compute, in a non-invasive
manner, the heart rate and cardiac beats from the ECG signal, estimate the physical body activity thanks to the accelerometer signals and the breathing rate and amplitude from the bioimpedance signal. The BGW includes a low-power microcontroller, for digital signal processing and elaboration in real time, and a Bluetooth module, for data transmission to external devices, such as a smartphone, a tablet or a personal computer (PC).
For the evolution of the device, one of the most important challenges remains the integration of other sensors to increase the number of the detectable physiological parameters.
In this context, this thesis focuses on the study, analysis and development of a wearable PCG sensor, using a wireless electronic board developed in a previous work and based on a STMicroelectronics MEMS microphone.
The main goals of this thesis are:
- the design of a wearable package for the sensor;
- the development of the setup for data collection;
- the validation of the device through the comparison with a reference instrument;
- the analysis of performances in different subjects.
The organisation of the thesis is as follows.
The first chapter provides a general introduction about the origin and features of the heart sounds and about the non-invasive diagnostic techniques for the heart sounds measurements, paying particular attention to the role of phonocardiography to clinical applications and to the opportunities and limits of wearable devices for remote monitoring.
The second chapter proposes a detailed description of the PCG board developed in a previous thesis work and used in this research study.
The third chapter describes the system integration. First of all, the development of the acquisition setup is presented. In particular, it is explained how a firmware previously implemented by AST team for a multi-integrated system is modified in order to adapt it to the PCG sensor for the data
transmission through Bluetooth Low Energy (BTLE) to the PC.
After that, the chapter describes the design of an effective case for the PCG acquisition module thought to to achieve the best coupling between PCG sensor and the insulation of the cardiac sound from any source of noise.
Finally, the integration of the case with a chest band and a patch, to obtain a wearable device, is presented.
The fourth chapter presents the method used to validate the PCG device. For the validation, the detected PCG signal is compared with a signal coming from a commercial electronic stethoscope.
The chapter begins with a brief description of the electronic stethoscope (Littman) through the evaluation of the signal to noise ratio (SNR) of the two.
At the end of the chapter, the validation results are shown, including the identification of the best auscultation area and the issues related to the pressure applied to the sensor.
The fifth chapter provides the description of the experimental protocol for the tests conducted on ten volunteers in order to evaluate the stability and performance of the package developed in this thesis.
Thereafter, this chapter discloses the results of the experimental trials and the related comments on the most meaningful and encouraging results.