Monitoring Platform for Biomedical Sensors [302724]

[anonimizat]. The collection of locally waveforms is resulting in real time parameters inside a database; this is performed by the patient at home and can be used to verify the status of the illness via specific algorithms ([anonimizat], and diagnosis). [anonimizat], pulse and temperature algorithms. [anonimizat] a [anonimizat]. The advantage of such a [anonimizat] a [anonimizat].

Additionally, the created prototype will occupy a small space that can be loaded quickly into a specific box and the webpages and databases can be uploaded online. Designing of the software is done using the Java and C [anonimizat]. [anonimizat], [anonimizat]. It is possible to discuss of the emergence of the medical and engineering field by using an application as a communication channel. [anonimizat], [anonimizat].

[anonimizat]. [anonimizat], such as: EKG, pulse, temperature and so on. [anonimizat]. Thus, a [anonimizat].

This is the main reason why there is an importance of understanding the signal and illness before building an application useful to medical personnel. Last but not least, a [anonimizat]. Thus, it is possible to choose a medical database close to the application model that is to be implemented.

[anonimizat]. [anonimizat] or Raspberry Pi. As a framework for the electronical part, databases contributions play an important role in encapsulating the information and providing quality access to the medical data.

Telemedicine increasing services in modern society lead to an explosion in the application field, especially as a result of aging population over 60 years old in the European continent. Additionally, a constant monitoring is made on people between 80 and 90 years old, as a key element of the home care. As an example, PANCEA platform is used to facilitate the monitoring of cardiac functions inside home, with usage of different sensors located inside the rooms. [1]

Another approach is using Raspberry Pi to hold the sensor nodes and send biomedical data such as heart rate collected via ZigBee or Bluetooth to the user email accounts and support health monitoring. Project can be organized such that cardiovascular diseases are monitored for applications including anxiety or diabetes. Temperature sensors can also be used. Proposal methods can additionally include respiration information such as: respiration rate or body movement, the result being the same approach of using a server and sending data with normal/abnormal notification to the doctor/patient email. [2]

Bio-monitoring solutions also approaches the rise of wireless sensor networks (WSN), expanding the quality of clinical monitoring. The cheap and easily implemented solutions help at the construction of smart environment for the chronic illnesses monitoring or other long term monitoring cases such as daily activity recognition (ADL). Special standards have to be used in order to send the data. Normally, the IEEE 802.15.4 standard is used in hospital applications, at approximately 250 Kb/s. [3]

Furthermore, advances in micro-electro-mechanical systems (MEMS) allow the construction of low cost solution networks. Security and optimization are key terms in the challenges of WSN and wireless body area networks (WBAN). Also the biocompatibility is important to be considered, especially if device attached to the body or sensors implanted to a specific target organ. The functionality of such devices works using similar principles: user is automatically sent to a screen device, whereas the receiver unit can be connected to the user. Data is being further pushed using ZigBee as one possible approach. [4],[5]

In conclusion, physiological parameters can be easily monitored and easily sent via a receiving unit or server to be displayed. Other alternative options might be to alert the doctor via email. One important aspect is the sensor signals might be susceptible to noise and this has to be considered especially in high risk illness or elderly monitoring.

1.1.1. Types of sensors and biomedical uses

Another important aspect is understanding of the types of bio signals and therefore the means of data collecting. The electrical effects on living organisms results from the fundamental cellular properties, meaning the transmembrane potential and potential action. The mentioned properties appear because of the cellular excitation from the exterior and interior electrical charge. [6] The potential is given by the non-uniform ionic distribution in the intra and extra cellular space, as a consequence of active transportation. The cellular excitability lead to a manifestation in less than a fraction of millisecond, followed by a potential increase and a stabilization at the normal value with the enclosing and opening of the ionic channels, as seen in figure 1.1. [7]

Figure 1.1 – Ionic channel: General View

For the informational exchange in the medical world and the unification of medical and functional devices, methods were accepted as gathering techniques, as well as methods of interpreting the bioelectrical signals given by the human body. Therefore, the electrical activity generated by the functioning heart, detectable in the most parts of the body, is called electrocardiogram (EKG). This recording is made on different axes, conventionally chosen. It is discussed about frontal, transverse and sagittal plane. These anatomical planes are hypothetically used for the characterization of the human body, such that the sagittal plane divides the body into right and left, coronal into anterior and posterior, and transversal into superior and inferior respectively. [8]

The knowledge given by the positioning is important for the gathering of the data. Practically, the signal is gathered in the form of a vector given by the electrode positioning. The wrong positioning might lead to an error in diagnosis of the patient. The Einthoven triangle includes the positioning of the sensors in an equilateral triangle. Therefore, the points are right and left hand, plus the left foot. The reference in this case is the right foot. [9]

The signal appreciates the pump function determined by the moving muscular muscle of the heart (myocardium). The regular, rhythmic contraction of it determines a cardiac cycle and is correlated with the depolarization of its cells, cells of the type pacemaker. This auto depolarization takes place automatically and therefore, can be considered that the cardiac muscle has the property of inherent rhythmicity. The cells have a rate of 60-100 depolarizations per minute and are located in the sinoatrial node. The structure of the heart is presented in figure 1.2. [10]

Figure 1.2 – Heart structure

This parameter of depolarization indicates also if there is a good functioning of the heart. In the moment at which the parameter reaches 40-50 depolarizations per minute, the source can be further taken by the atrioventricular node and further, at 20-40 depolarizations per minute, by the ventricular muscle. The problems can be therefore detected at the level of EKG, a normal functioning being presented in the figure 1.3.

Figure 1.3 – Electrical activity of heart

Other parameters are given by the registered QRS complex, such that every segment presents itself at a specific duration and amplitude. The most important information can be taken from the P wave (atrial depolarization), QRS complex (ventricular depolarization) and T wave (ventricular repolarization). [4], [12]

Figure 1.4 – EKG: QRS complex

All the data presented above are only the base of what the EKG represents and the type of information taken from it. This proves the importance of knowing this particular data in order to realize an interface that would properly display and store the signal. The most frequent utilized processing method is using the frontal plane. Still, other variation can be given by the vector cardiogram, an analysis of the cardiac vector and distribution at the separation level between polarized and non-polarized field. One example for this system is the Frank system. Another important knowledge is given by the type of EKG signal also. A usual EKG signal gathered by 3 electrodes is different than an abdominal fetal EKG, for example. In the case of extracting the fetal EKG (f-EKG), different processing algorithms are used. [13]

As a complementary technique to EEG, a discussion can be made on medical imaging, as well as EMG signals. Of course, a variety of parameters can be discussed, but the most important in case of monitoring is the cardiac function. It is therefore demonstrated that the multiple information achieved by each of the signal is important, although different fields are accessed by it. From this the importance of the bioengineer to find the best interface that can integrate the information, depending on the analysis. It is necessary the type of data, the informational content, connection to the biological world and possibilities given to display the data to an unauthorized medical staff.

1.1.2. Commercial solutions

For the purpose of analysis of commercial solutions, different monitoring solutions are presented in respect to sensing and market availability. If referring to simple EKG monitoring solutions, the price of a medical device ranges from $73 to $158. Nevertheless, as the solution gets more personalized and includes more signals, the price can rise up over $1000.

Modern solutions try to integrate them on single chips such that the price might decay in large productions. Samsung is therefore one example for bio-monitoring solutions, integrated on a single chip. The bio-processor is dedicated to smart accessories such as mobile devices. In principle, the technology can be integrated to fitness applications, but not only. Besides the pulse, the system integrates also bioelectrical impedance, PPG and EKG, as well as GSR. [18] It can operate as co-processor or just stand-alone system. The configurations available are presented in figure 1.5.

Figure 1.5 – Samsung Monitoring Solution: Hardware View

Another solution implemented in Japan is the bio-signal telemetry application, gathering bio-medical data and transmitting it via wireless connection to the phone or PC. The solution called HRS-I is collecting data through sensors attached to the chest, leading to information such as body temperature, EKG or stress levels from the fluctuation of the heart beating.

The majority of technologies used are integrating Bluetooth for data transmission to medical or other personnel, such that personal activity can be tracked. A solution for long term monitoring is given by 9Solutions, implementing also some alarm functions in case of caregivers requirement. [19]

The directions of the applications do not stop here. Smart textile implementation lead to existing of biomonitoring t-shirts for EKG, EEG or EMG signals. Cameras can be also integrated for monitoring, although the discussion about ethical aspects holds here. Solutions examples include AiQ Smart Clothing, presented in figure 1.6 a).

Figure . – Commercial Monitoring Devices: a) – Sirpa and BioMac monitoring health solutions

Of course, solutions can also be implemented by just directly adding them to the body. This can be done by using bio compatible adhesives, such that data is being collected and send to a mobile phone. Such a system is implemented by Metria Wearable Sensor, presented in figure 1.6 b).

Figure 1.6 – Commercial Monitoring Devices: b) – Metria and Imec’s biomonitoring solutions

Depending on the signal needed, devices can be focused on a signal solely. For example, the Imec’s EEG headsets develop a monitoring signal that gives a better EEG quality and sends the data in real time. [20]

What can be summed up after the commercial medical solutions description is that the advances are made regarding both efficiency and price balance, such that the research and development currently done in the field might lead to worldly used integrated devices. This is the main reason why the current device performed in this thesis is meant to be a both feasible and cheap solution, according to current market solutions.

1.2. Rheumatic heart disease

Rheumatic heart disease (RHD) is the most common acquired heart disease in children in many countries of the world, caused by one of the top 10 deathly infections, bacteria A Streptococcus (GAS). Still, RHD is a condition that can be prevented and controlled with strep throat antibiotics, such as penicillin. Furthermore, normal strep injection might bring benefits for avoiding the catching of other infections. [21], [22]

One common result is the fever that primarily has effect on the heart, nervous system, skin and joints, leading to fibrosis or heart failure if not treated. Moreover, the damage might lead to a valve disorder (mitral valve particularly) that remains even after treatment and modification of the pericardium and endocardium. [23], [24]

RHD became into medical attention after reaching the number of 325.000 children each year and about 18 million people having the illness.

In India, the first clinical evidence of RF came in 1935, being a relatively new disease. The figure 1.7 presents the admissions in hospitals under RHD diagnosis for India, as a special case example. [25, p. 50]

Figure 1.7 – Case Study: Percentage of RHD patients in India

Globally, the estimation of the children reaches the number of 2.4 million, as seen in figure 1.8. In Asia, the number raised from 1.9 to 2.21 million, reaching a mortality of 1.5 % per year and estimated global deaths up to 290.000 per year.

About 282.000 cases of RF are added each year, whereas the remaining hospitalizing cases have potentially RHD.

Figure 1.8 – Case Study: Global and Asian cases of RF and RHD

Studies were also made in Australia, from which 1.479 cases were reported in 2010. Out of them, 969 were reported in females and 510 in males, data being grouped into age intervals in figure 1.9.

Figure 1.9 – Case Study: RHD in Australia, Northern Territory

1.2.1. Description of biological changes

In this subchapter, a short overview of the biological changes is presented, in order to better link the diagnosis methods. As an inflammatory illness, the debut comes at approximately 3 weeks after a streptococcus respiratory infection. Usually is a pharyngeal infection and is caused by beta-hemolytic streptococcus that causes the hemolysis of red blood cells. Nevertheless, not all patients with streptococcus infection can inquire rheumatic fever symptoms.

A streptococcal infection is mostly located in the upper respiratory tract: rhino pharyngitis. The most common form of manifestation is that of an erythematous angina, accompanied by fever and dysphagia, the intensity of which is particularly variable. It should be kept in mind that this precursor angiogram, which prepares the disease-causing pathogenic reactions, has no characteristic of differentiation in favor of streptococcal etiology, other than positive pharyngeal cultures, which cannot be available within a few days. Local phenomena yield promptly to antibiotics administered at the dose and for the appropriate period, when the pharyngeal cultures usually fail. [26] The mechanism of RHD is shortly described by figure 1.10.

Figure 1.10 – Mechanism of RHD

Since there is no criterion identifying the rheumatic future at this stage, any erythematous angina should be suspected as streptococcal etiology, especially in children and adolescents, even before bacteriological confirmation.

The following latency period is a period of definitive development of the multiple manifestations of the disease, which is presented first in the analytical aspect, then in their sequence and grouping. In the status period, general manifestations, arthritis, cerebral, cutaneous and other manifestations are included. General manifestations refer to fever, tachycardia, sweating, pallor, and asthenia with weight loss. Fever is the most common sign, which has been present since its inception and has been relatively loyal to the morbid process.

The duration of the fever usually does not exceed three weeks, but spontaneous developments in which the fever persisted for over a month have also been described. Still, it can be deduced that the absence of fever does not definitely signify the extinction of the active rheumatic process. Weight loss is more characteristic of children and is, as it seems, one of the clinical arguments for affirming the evolution of rheumatic disease. [23],[27]

Symptoms of the disease are therefore extremely variable. Children that suffer from cardiac damage have frequent skin manifestations and joint manifestations are more likely to be articular pains than arthritis. Instead, adults experience a more nocturnal arthralgia and rarely cause neurological and cutaneous damage.

Out of all, cardiac damage is the most severe manifestation of the disease. Symptoms are the result of affecting all cardiac structures: endocardium, myocardium, pericardium, and are chest pain, palpitations, fatigue, choking. Most of the time, however, cardiac damage is completely asymptomatic, being discovered late in adulthood. [24]

In conclusion, a constant monitoring is needed to prevent this possible complication, especially when referring to children.

1.2.2. Diagnosis of rheumatic heart disease

One of the major problems of RHD is that there is not a simple test in order to diagnose it, meaning that it might look at first as an inflammation in the body, arthritis seen with redness and pain in joints (knee, ankles) or fatigue. Therefore, the test combined with discussions with the patient might lead to a final diagnosis [28]

Rheumatic heart disease is most accurately diagnosed using ultrasound, referred to as echocardiography. For this specific analysis type, standard guidelines have been developed, the importance being put on heart valves and the severity of damage to each of them. The doctor may order a throat culture or a blood test to check for strep throat or signs of a recent strep infection, as well as performing other blood tests. Analysis involves EKG, MRI or chest X-ray to check size of heart/excess fluid in lungs. The doctor might also look for skin nodules or listen to hear possible heart abnormalities, especially at children in first phase of examination. [29], [30]

Additionally, it might me that some valves are affected and symptoms are not noticed for a period of years, regardless of developing small ones such as murmur or chest pain, weakness and breathlessness. The risk factors might also have a strong influence on patients, such as family history or environmental factors (sanitation condition, working in overcrowded places, etc.). [31], [32]

Figure 1.11 – a) Hematoxylin and eosin stain of RHD b) Culture of streptococcal in 16 years old12

A number of different blood tests may also be used to look for indications of rheumatic fever. These include:

C reactive protein (CRP) – produced by the liver and shows inflammation in the body if seen in a larger amount;

Antistreptolysin O titre (ASOT) – antibodies produced in response to streptococcal infection;

Erythrocyte sedimentation rate (ESR) – changes due to various substances produced during the immune response. [33]

Furthermore, CD4 and CD8 T-cell subsets are present within acute rheumatic fever valves, immunochemistry test being able to confirm the diagnosis. [34]

The Jones criteria, introduced in 1944, are as a set of clinical guidelines, based on the prevalence and specificity of manifestations of rheumatic fever summarized from major and minor considerations, as referred in figure 1.12.

Figure 1.12 – Case Study: Changes following reviews from AHA and WHO

1.3. Online medical platforms

Biomedical databases represent a modern field of study, especially if referring to the medical image storage and to intelligent systems for detection of specific illnesses. The growth of medical databases revolutionized telemedicine as adjacent field, bringing essential advantages to the survival rate through distance treatment or under specific unexpected situations.

The main goal is the possibility of offering a variety of parameters and data that might lead to high benefits in the medical community through the organization of databases as qualitative as possible, under main categories of illnesses and medical changes. A better understanding of physiological and pathological changes in humans can be reflected in a growth in the living quality, as well as in medical applications for diagnosis and treatment. [35], [36], [37] The necessity of understanding the human physiology lead to the construction of a database such as PhysioNet, database held by NIH National Center for Research Resources. This became in short time a main location of interest for over 50 types of physiological signals, as well as the adjacent hardware. There exist over 650 published documents, all of which contributed to the growth of the academic and research medium. Having the main motivation the display of the data, in the last 16 years researchers had a wish to reduce hard configuration for accessing the database.

If we extend this software idea to open source, massive resources organized in databases could represent the foundation for new projects, bringing benefits to not only the data, but also to the research itself. The studies and results in computational field lead to a future growth of the algorithms that support the instrumentation. Even if the progress might be visible, the interest in extraction of the right amount of data comes with some problems to overcome. [38], [39]

Different applications in beta or commercial versions offer the interaction with databases, difficulties coming into account when there is a matter of interface standardization. In other words, they are destined to a specific signal and permit one predefined function. It exists nowadays solution to gather EKG, EMG and EEG signals, as well as genetic information, each coming with a series of parameters. Moreover, the actual interfaces permit full access to the code. This is an advantage for the engineers that might want to create open source programs, but not in case of an unauthorized medical staff.

Furthermore, since the doctor meetings on long distance are becoming a routine, it is important that data is shown for discussions, whereas not compressed with errors that can disturb the information presented to the patient/nurse. The images presenting skin rupture for example, or ultrasound images or X-ray images, should preserve the colors and image quality without adding additional noise. The key of success in telemedicine therefore includes the accepting of a specific format accessible to physicians, medical staff, bio-engineers, etc. [40]

1.3.1. Importance of online platforms and current research facilities

Essentially, medical databases follow the access facilitation and information display for the authorized medical staff. On the other hand, the integrated systems have a different behavior, but in the end the tendency and desire of engineers towards standardization of the data gathering is applicable. [41]

The studies involve the medical, as well as the engineering-related fields, massively depending on the quantity of the medical data. Therefore, it can be estimated, for example, that 82% of the medical files in Taiwan already adopted a digital model. As a result, over 200 articles from scientific domain mentioned techniques for design and integration of the medical data. The National Health Institute from Taiwan supports scientific research, emphasizing the importance of the clinical data management in different countries. [42] The National Health Insurance System in France organized as well a database through the National Informing System for Illnesses that covers the whole country population (over 65 million inhabitants). For study facilitation, the medical data were made available for using in applications. [43]

Furthermore, once with the appearance of such medical databases, an increased interest also arose from the medical error costs perspective in healthcare institution. The perspectives from 2010 were to prevent such errors, leading to large amount of money invested in projects. Of course, additional to the repercussions on patients, such errors reduce the hospital profit. [44] Methods for management of the databases can depend also of the information type, acquisition location or sampling method. The methods that are content-based became an efficient instrument for interrogation. The features and right representation is therefore an important aspect of the topic. [47], [48]

Besides these methods, it is necessary to have a support system that can take the decision, having the capacity to sustain the clinical process through continuous learning, from diagnosis to investigations or long term treatment. Nowadays, informational system for web management can be found, being used in processes of neuroscience and clinical data processing. [49], [50] The growth in computer science also lead to an informational explosion, subject to security and recovery of the data. This can lead to pattern based organization of the data, where the term machine learning refers to the learning process and adaptation through genetic algorithms most frequently. [51] Principally, the algorithms used are named data mining (DM) algorithms, the success depending on the minimizing and decision making processes, without information loss. [52],[53] Of great interest is the category making and processing, storage and also reconstruction, realizable more or less stable by using fuzzy algorithms. [54]

In the presented context, it can be concluded that, together with the management of the data, there is a general concert regarding protection. In the present there is a discussion of integrating large amount of biomedical information, therefore smart integration is required.

1.3.2. Examples, interface use cases and issues

Databases are one key element for storage and gathering all together biomedical information. Databases as NCBI offer informational support and data acquisition through different technologies, such that the signal data can be stored and analyzed. Once with the understanding of this necessity, the management of such information comes into account. With this purpose, different databases available online can be accessed and compared.

ECG Web Database is an online database, created especially for the academic field, in association with Northwestern Medical University and Technological Academy from the same institution. It presents a collection of ECG signals and their interpretation, for a didactical purpose. The interface is presented in figure 1.13.

Figure 1.13 – Search into the ECG Web Database

Nevertheless, the database presents the data in an image format, being just physical scans of the acquired biomedical data. Therefore, they cannot be used for the purpose of automatic data gathering and processing. One data sample is listed in figure 1.14.

Figure 1.14 – EKG Analysis from ECG Web Database14

One online available database, held by Dean Jenkins, was set up from early 1995 under the name ECG Library. The data is presented in form of scans, with different affections presented. A shortcoming of these types of databases is the format in which the data is presented, leading to problems for the following processing steps.

As a conclusion to the analysis given in this sub chapter, a table containing some databases is presented. In it, advantages and disadvantages are presented, supporting the reference n close link with the EKG signal, as a priority data in this master thesis.

Table 1.1 – Database review for EKG

1.3.3. Current solutions and security issues

As presented in previous chapters, there are special principles for guidance in designing such databases. For example, finding and organizing the necessary data from the current management system. Such an application becomes a complex program to provide user interface for the medical staff and patients. Therefore, security is the first issue that comes into account, completed by the personalized version made for different users.

Another aspect is existence of special categories such as: age, sex, id or other necessary additional information needed to compare or parse for the biomedical data. This comes with disadvantages mostly for the table based databases. Still, some solutions already exist in the hospitals, not available online and not outside internal network.

Such an application is given by NORAV ECG Management System, being used for the management of patients. Is an easily implemented interface designed for hospitals and allows data availability by an SQL interrogation application. The interface is presented in the figure 1.15 below.

Figure 1.15 – NORAV ECG Management System Interface

All such applications come also with the possibility of data transmission, in and outside the medical unit. For example, systems such as AcqKnowledge come as support of the acquisition system Biopac, representing a simple and interactive program that can be used for different monitor types, as well as for just data storage. The system permits processing of the data, but in an engineering approach. Functions such as display of the EKG signal or calculating the heart rate are included.

Other applications can be related to genetic engineering study or bioinformatics related fields. Experimental databases for genetic expression have to, in this case, deal with subsets of relevant bio-information. [57] Institutions as Illumina offer programs of detection for sequences of mRNA type, genetic information search from RNA, as well as methods for segmentation of the data. Computational analysis over genes is also provided by ZENONBio, where marker identification is introduced to help potential therapies. [58], [59]

Because of legislation and ethical issues, there exists standards specially integrated to protect and add non visible watermarks without modification of the data. Initially created to offer multimedia rights, watermarks were successfully integrated into the healthcare field. [60] Furthermore, the personal data should not be shared by any means outside the medical network. Although security platforms already exist for data administration (BlackBerry Secure), the problem of medical data extends also the ethical aspect of data scarring.

The policy of data security inside health institutions always requires special terms and conditions for usage. Besides personal/general information such as phone, address, sex or family data, the biomedical and physical data is being included. A concrete security definition of the system is therefore needed.

Inside EU, directives and norms are already implemented regarding electronical health data. In the official monitor of each country, the health ministry is required to add specific information regarding the medical historical data, medical data as well as personal data. All of the data given by medical service provides has to present an electronical signature and fulfill the requirements.

To conclude with, the development of the platforms includes not only the solution itself, but also the security requirements presented in the respective country. Without it, the solution cannot be valid or taken to commercial stage. Furthermore, the ethical aspect is always taken into account, irrespective of the laws and rules available.

Methods

Biomonitoring device

This section presents the implementation of the data collecting and monitoring device, as well as additional web and storage related topics. The sensor selection, algorithm and solution description for the web platform is further described in detail. Additionally, a full description of the processing of the data, transmission protocol and data flow and management is presented. Figure 2.1 illustrates a hardware model of the used sensors used in the implementation stage of the prototype for data monitoring and data collecting device as complete medical equipment.

Figure 2.1 – Architecture of the biomonitoring device

For the implementation, a Raspberry Pi 3 and an Arduino Feather M0 are used in order to present the biomonitoring and storage solution. The signal acquired by the selected sensors is being encapsulated inside the Arduino microcontroller, together with additional code for extraction of: temperature, pulse, and EKG, as well as for the final data transmission. The main steps in the data collecting part are the following:

Figure . – Arduino implementation as data collecting device

Furthermore, the Raspberry Pi holds the other part of the communication algorithm. The remaining elements from figure 2.3 will be incorporated in the data storage and management subchapter, including the realization of the additional web platforms: locally, for the user and outside the internal network, to any user that hold login rights (normally, the medical staff but also technicians).

Figure 2.3 – Raspberry Pi implementation as data monitoring device

Description of sensors used

For the acquisition of the EKG signal, sensors provided from OLIMEX together with the Arduino shield were used. The passive electrodes allow biofeedback capture and therefore, biomonitoring. The hardware elements are presented in figure 2.4.

Figure 2.4 a) EKG/EMG sensors b) EKG/EMG Olimex shield

The shield provided by OLIMEX allows the Arduino to easily connect to the sensors and record the cardiac information. The data comes in 6 channels as analog input signals (A0-A6), generation of calibration signals being seen on digital outputs D4-D9. The product is working connected to Arduino boards at 3.3 and 5 V (default is 3.3V).

The OLIMEX solution converts the analog differential signal attached to its inputs into a single stream of analog data, discretized for processing. The total gain is made out of the instrumental amplifiers and 3rd order Bessel filter, with a cutoff frequency set to 40Hz. [61]

Figure 2.5 – Connections available on OLIMEX EKG/EMG shield

Nevertheless, the shield brings some problems in regard to usage of the 3V connection for the other 5 sensors, making the Adafruit’s Arduino product Feather M0 more approachable because of the size and the 4 extra pin extensions available, compared with Arduino Uno. This implies reducing the number of cables and solves the problem of the voltage quality.

Figure 2.6 – Arduino Feather M0

For the new EKG testing, the AD8232 Heart Rate Monitor Sensor has been used. The block-integrated solution is designed to amplify bio-potential signals in noisy condition, with an operating voltage of 3.3 V. The sensor gives an analog output and has a 3.5mm Jack for the pad connections. The pins SDN, LO+, LO-, OUTPUT, 3.3V and GND are connected together with RA, RL and LA in order to remove wire connections. The sensors include a gain of 100 and a low-pass filter with adjustable gain, being presented in figure below.

Figure 2.7 – AD8232 Heart Monitor solution

For the connection, five pins needed for the board are: GND, 3.3V, OUTPUT, LO- and LO+, all of which are initially attached to male-male header strips on the Feather. The pads are already attached, therefore the RA, LA and RL are considered predefined in the hardware solution. The table 2.1 presents the reference connections on the Arduino side, in our case Feather M0 device.

Table 2.1 – Pin connections between Arduino and AD8232 Heart Monitoring

The sensor has pins for the input signals (IN+ and IN- of the instrumentation amplifier) connected to the left and right arm, as well as for the right leg feedback. It contains elements as reference buffers, operational amplifiers and comparators that detects a possible disconnection of the electrodes. Shutdown control inputs, as well as power supplies ground and terminals are also available in the pin configuration. The complete table for the schematic at figure 2.8 is presented below.

Table 2.2 – Pin function description for AD8232 Heart Monitoring Sensor

Figure 2.8 – Functional block diagram for AD8232 EKG sensor24

For the electrodes marked with L, R and DRL for left, right and right leg respectively, some possibilities of positioning are presented in figure 2.9.

Figure 2.9 – EKG: different sensor connections23

In the testing procedure, the Lionheart 1 ECG/Arrhythmia Simulator was used to verify the accuracy of the chosen AD 8232 solution. The resulting EKG waveform was compared to the original one displayed using Biopac systems solution.

The specification of the chosen simulator includes using different EKG waveforms as well as amplitudes and different configurations. In this particular case, only the RL, RA and LA were used. Best pads were also chosen during this testing: SKINTACT EKG sensors. The configuration for the testing phase is presented in the next figure.

Figure 2.10 – Lionheart 1 ECG/Arrhythmia Simulator and connections to AD8232 and Arduino Feather M0

SKINTACT Monitoring ECG Electrodes chosen for the monitoring device are of 50 mm diameter and used for single data gathering. This implies a hygienically usage for the patient and easy application method due to the solid adhesive hydrogel. The patient can attach the electrode for long, as well as short term, with minimal skin reaction even in not prepared skin (no medical preparation needed). The electrodes have an Ag/AgCl layer and the AgCl solution is only positioned at the interface to the gel to prevent possible corrosive effects.

Figure 2.11 – SKINTACT Monitoring EKG Electrodes

The next sensor used is a pulse sensor that connects to the Arduino device in order to refer to the oxygen load in the blood. The model used is the one represented in figure 2.12.

Figure 2.12 – Pulse Sensor

Pulse oximetry refers to O2 concentration in blood (hemoglobin bounded or dissolved in plasma). The principle of the sensor is referring spectrophotometry, as well as Bees’ law that determines absorbance based on detected light intensity. The modification comes in two types of hemoglobin (Hb), which is: reduced and oxygenated.

The light can be of visible source in infrared (IR) and in visible spectrum (red light). Furthermore, the source and light sensors are coupled mounted. As the consistency of the tissue remains the same, the only variation is in Hg concentration. The differences of absorption are calculated for both sources, as they have significantly different optical spectra in the wavelength range from 500nm to 1000nm. [62], [63] Then, in the direction in which the proteins are aligned orthogonal to the flow direction, a high flows appear (systolic phase). The reflective area of the blood cells is decreasing during the systolic and increasing and diastolic phase. [64]

Figure 2.13 – a) Absorption spectra of Hb and HbO2 b) the systolic and diastolic phase

Figure 2.14 – Sensor parts and connections of the Pulse Sensor

Conventionally, the time at which pulse waveform reaches 50% of its maximum value is used to indicate the beginning of a pulse, therefore the N-N interval is the time between pulses or between the R’s wave of the EKG, as illustrated in figure 2.15. [65]

Figure 2.15 – R-R and N-N interval for the pulse sensor signal registration

For the connections, the ground and supply are firstly considered for connection. The signal is connected to the microcontroller’s analog pin.

For the BPM extraction needed, the signal is registered every 2 ms such that interval between beats (IBI) is being tracked as a sample difference between two consecutive peaks. In this case, the track is made according to the steepest slope point, when signal is reaching 50% of its maximum value. An additional testing is done for the presence of the pulse.

Another important bio-parameter to be recorded is the body temperature, of which presence can indicate a malfunction in the immune system or better said a first stage body reaction to illness. For this, DS18B20 temperature sensor is being used with the 1-wire protocol. For the connections, 3 main wires are available to be set as GND, voltage (between 3 and 5.5V maximum) and the digital pin connection on the Arduino side. [66] The connections, as well as the temperature sensor are presented in figure 2.16.

Figure 2.16 – DS18B20 Digital temperature sensor

The chosen sensor has a good range up to 125°C, temperature that can never be overpassed. Furthermore, the precision of the sensor is of 12 bits and a 4.7k resistor was added as pullup when using the sensor. [67] The temperature data acquisition was further added to both database and online local web page, as well as in all rheumatic heart disease algorithms.

2.1.2. Wireless communication

Figure 2.17 – The CC1101 Wireless module (RF1100SE) with pins available

For the wireless connections, the CC1101 modules were chosen. The sensor can operate on a range of frequencies from 433 to 915 MHz, being of ideal use for the Arduino microcontroller range, as well as Raspberry Pi. The minimum operating speed is 1.2kbps, whereas the highest is 500kbps.

Figure 2.18 – Arduino Connections Example to CC1101

The other connections for Raspberry Pi are presented in table 2.3. When communicating using the SPI bus, GDO0/GDO2 header is not needed.

Table 2.3 – Pin Connections for Arduino Uno and Raspberry Pi 3 with the CC1101 module

The first part of the communication protocol was the set-up of the registers such that on both Arduino and Raspberry Pi side, the data would match. This registers used in the transmission code also implies the chosen parameters for frequency, channel, address or modulation. In this particular case, the 868 MHZ. 115 kBaud for data rate and a 2-FSK modulation format with the 199 kHz channel spacing was chosen. Furthermore, a carrier-sense above threshold solution was chosen for the sync word, as well as a fixed length (PKTLEN). The data was first tested with the software provided by Texas Instruments, SmartRF Studio, as shown in figure 2.19.

Figure 2.19 – Register settings for CC1101 module inside SmartRF Studio