Abstract
In recent years, a number of proposals for electrocardiogram (ECG) monitoring based on mobile systems have been delivered. We propose here an STM32F-microcontroller-based ECG mobile system providing both long-term (several weeks) Holter monitoring and 12-lead ECG recording, according to the clinical standard requirements for these kinds of recordings, which in addition can yield further digital compression at stages close to the acquisition. The system can be especially useful in rural areas of developing countries, where the lack of specialized medical personnel justifies the introduction of telecardiology services, and the limitations of coverage and bandwidth of cellular networks require the use of efficient signal compression systems. The prototype was implemented using a small architecture, with a 16-bits-per-sample resolution. We also used a low-noise instrumentation amplifier TI ADS1198, which has a multiplexer and an analog-to-digital converter (16 bits and 8 channels) connected to the STM32F processor, the architecture of which incorporates a digital signal processing unit and a floating-point unit. On the one hand, the system portability allows the user to take the prototype in her/his pocket and to perform an ECG examination, either in 12-lead controlled conditions or in Holter monitoring, according to the required clinical scenario. An app in the smartphone is responsible for giving the users a friendly interface to set up the system. On the other hand, electronic health recording of the patients are registered in a web application, which in turn allows them to connect to the Internet from their cellphones, and the ECG signals are then sent though a web server for subsequent and ubiquitous analysis by doctors at any convenient terminal device. In order to determine the quality of the received signals, system testing was performed in the three following scenarios: (1) The prototype was connected to the patient and the signals were subsequently stored; (2) the prototype was connected to the patient and the data were subsequently transferred to the cellphone; (3) the prototype was connected to the patient, and the data were transferred to the cellphone and to the web via the Internet. An additional benchmarking test with expert clinicians showed the clinical quality provided by the system. The proposed ECG system is the first step and paves the way toward mobile cardiac monitors in terms of compatibility with the electrocardiographic practice, including the long-term monitoring, the usability with 12 leads, and the possibility of incorporating signal compression at the early stages of the ECG acquisition.
Highlights
A number of physiological systems in the human body generate a wide variety of signals with different natures, the monitoring of which can provide us with highly useful information about their usual functioning and changes in health state
The prototype has the ability to function in a flexible form as a Holter and as an electrocardiograph thanks to the designed hardware architecture, and providing the prototype with the ability to deliver ECG signals with high clinical quality
Our system is flexible enough to combine the processing power of the prototype, with that of the cellphone and that of the remote server in order to properly perform compression processes such as adaptive-band filtering, baseline wander and artefact cancellation, multichannel decomposition with principal component analysis or independent component analysis, feature extraction, delineation analysis, and arrhythmic event detection
Summary
A number of physiological systems in the human body generate a wide variety of signals with different natures, the monitoring of which can provide us with highly useful information about their usual functioning and changes in health state. According to the previous considerations, we propose here a prototype of an ECG mobile system, based on the STM32F microcontroller, which provides us with long-term Holter monitoring and high-resolution 12-lead ECG recording, and this same architecture enables us to make efficient compression processing close to the acquisition stages. The system allows the real-time execution of compression algorithms using filter banks as an implementation example, and it allows the system to send the ECG information through narrow communication channels The use of this lossy compression algorithm has shown the ability to considerably reduce the required bandwidth (especially useful in rural areas of developing countries), and the quality of the ECG signals subject to compression has been checked in the present work to be clinically valid.
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