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Embedded Sensors System for Real Time Biomedical Data Acquisition and Analysis
Embedded Sensors System for Real Time Biomedical Data Acquisition and Analysis Tereza Otahalova*, Zdenek Slanina*, David Vala*
Department of cybernetics and biomedical engineering, Technical University of Ostrava, 17. Listopadu 15, 70833 Czech Republic (e-mail: [email protected], [email protected], [email protected]).
Abstract: Design of the prototype embedded sensors system for biomedical data acquisition and analysis. It introduces to issues of measuring vital functions and processing data in real-time and suggestion of mobile embedded system for measuring biometric data. The main aim of the research work is the implementation of a prototype sensor system. Data captured from the body of a person are measured and transmitted to the superior system in real time, where they are processed, evaluated and archived. To transfer data to the nearest superior system is used Bluetooth interface. Keywords: biosensor, sensor system, biotelemetry, electrocardiography.
1. INTRODUCTION Medical devices for monitoring and diagnostics become more portable through miniaturization of electronic circuits, progress in the development of batteries (size and endurance), extending the possibility of wireless technology and reducing the price of all the necessary technologies. Biotelemetry engages in wireless transmission of biometric data. Nowadays biotelemetry becomes an integral part of everyday life. It develops the idea of wireless systems with embedded biosensors, when the device is able to scan more vital functions. Evaluating the monitored variables of the sensing person can follow physical and psychological stress and evaluate load and stress factors. It also allows observing reaction of the sensing person to changes in the environment. Using distant monitoring enable team reaction to unexpected changes. These changes can be physiological nature, such as behaviour modification, stress, or it can be a reaction to changes in the environment. The immediate reaction to any change or impairment of vital functions may often avoid lifethreatening or any adverse change in the health. Embedded sensor system worked is intended for use in prototype vehicles Kaipan or Hydrogenix. Described sensor system is meant for capturing vital functions and for evaluating actual physical condition of the pilot vehicle. 2. ELECTROCARDIOGRAPHY Electrocardiography (ECG) is a simple, inexpensive and noninvasive diagnostic method for sensing and recording the electrical activity of the heart. Record of the time changes of electric potential caused by cardiac activity is called an electrocardiogram. ECG is the basic function test of the electrical activity of heart muscle. An electrical signal
generated by cardiac muscle fibres is spread in all directions, because the body tissues are good electrical leaders. The signal penetrates into the surrounding organs, and reaches the skin with little attenuation. Therefore, ECG capture virtually anywhere on the surface of the human body. The electric array of the heart begins by transmission of the action potential through cardiac conduction system and surrounding muscles. Record of the heart electrical array is obtained by measuring the potential of this array.
Fig. 1. Measured ECG curve with modulation of respiratory rate. The electrical activity of heart, see Fig. 1, is recorded by electrocardiograph. Electric field is established during each cycle of the electrical activation. The device records electric field by system of the electrocardiographic leads from the body surface and displays electrocardiogram depending on time. Unipolar leads according to Einthoven, bipolar leads according to Goldberger and thoracic leads according to Wilson scan electrocardiogram. Electrocardiogram will be measured according to Einthoven convention in this system. Einthoven’s limb leads record electrical potential difference between two electrodes on the limbs, see Fig. 2. The right hand is marked with the letter RA (right arm, red) and the left hand with the letter LA (left arm, yellow), the RA-LA signal
is marked as Lead I. The third electrode is fixed near the left ankle and is marked with the letter LL (left leg, green). Potential difference LL-RA is marked as Lead II and potential difference LL-LA as Lead III. Electrode N (neutral, black) is connected to the right leg and is not included into the sensing, serves as grounding.
other on the same level on the left rib. Electrodes placed this way directly create a vector through the heart. Methods of obtaining respiratory rate from the ECG: - Method of envelopes - envelopes acquisition of selected characteristics of the ECG recording. RR is the envelope curve connecting all the R oscillations. This curve is calculated by cubic interpolation of R oscillations. - Mean ECG - derived from an average amplitude of the ECG recording. The method captures the mean oscillation of the baseline ECG. The advantage of this method is resistant to interference. The method involves finding the mean valueduring one heart beat (starting just before the P wave and P wave ends before the next contraction the heart). Weak increasing and decreasing the mean value of the selected segment represents breathing.
Fig. 2. Unipolar limb leads according to Einthoven. Lead I (electrodes RA and LA) is used for the measurement. In this lead is the course of electrocardiogram most visible. But the electrodes are not placed on the limbs, but are shifted closer to the heart. They are located under the right and left clavicle about its centre. 3. HEART RATE Heartbeat is a pressure wave that is caused by expulsion of blood from the left ventricle into the aorta (the aorta), from where it is spread to other arteries throughout the body. In medicine a series of these waves corresponds to the heart rhythm and rate. Heart rate is the number of beats (contractions) of the heart in one minute. As the only measured variable accurately reflects the body load.
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The average heart rate has a value of about 75 beats per minute for men and women around 82, but may be lower and may not be a sign of disease. The lower value of the pulse usually occurs in athletes who have a strong heart pump capable of a large amount of blood. The value can then be around 40 beats per minute. When heart rate is below 60 beats per minute, we are talking about the bradycardia. In contrast, when the acceleration of heart rate is above 100 beats per minute, we are talking about the tachycardia. With increased heart rate is impaired oxygen supply to the heart, there is insufficient oxygenation and insufficient heart function, resulting in a higher risk of heart attack. The increase in heart rate occurs in stressful situations, for example, can also be caused by pharmacologically 4. BREATH RATE Respiratory rate is obtained from the ECG, because breathing is closely related to the ECG and affects the ECG recording, e.g. is showed as a change in the amplitude of the ECG recording. ECG recording is sourced using surface electrodes. One electrode is placed on the sternum (breastbone) and the
- Interval method - obtained from the time interval selected characters ECG signal. RR interval is defined by the time period between two consecutive cycles. Changes in RR interval are affected by breathing 5. TEMPERATURE For temperature measurement are used thermistors. There are two types of thermistors - NTC (Negative Temperature Coefficient) and PTC (Positive Temperature Coefficient). NTC whose resistance decreases with increasing temperature is suitable. PTC are used as sensors indicate overtemperature. Linear temperature dependence of the resistance temperature coefficient can be expressed as:
αT R0 1 α Δ β ΔT 2 γ ΔT 3 T 100
where T [K] is the thermodynamic temperature, R0 [Ω] is the resistance at the reference temperature T0, α [K-1] is the temperature coefficient of resistance at temperature T0. The average human body temperature ranges from 35.8 ° C to 37.3 ° C. This temperature ensures the correct functioning of all organs and responses that run through them. From the medical point of view for hypothermia in humans the temperature has to decrease below 35° C. If the temperature exceeds human 37 ° C, these may be overheating, or the defensive reaction of the immune system to infection. 6. ACCELEROMETRY Accelerometry allows the measurement of acceleration using accelerometers. They operate on the determination of a variation of the motion of a body (located in accelerometer) in the acceleration segment. These changes are transferred and measured (e.g. piezoelectric) with an electric output signal. Depending on the number of accelerometers can measure acceleration in one axis in the plane or in space. Three-dimensional acceleration can be determined using three accelerometers placed so that their axes are perpendicular to each other. The actual sensor is integrated micromechanical polysilicon surface structure "floating" on the surface of silicon single crystals. Silicon springs allow movement of the whole
mechanical structure of the single crystal surface, while providing mechanical resistance force caused by acceleration. Bending and deformation of such a structure is converted to a differential change of capacity capacitor, see Fig. 3. It is composed of two fixed plates and plates firmly attached to the deforming beam.
includes all the features that are commonly required in applications for ECG measuring. It can measure up to 12-lead ECG.
Fig. 5. Block diagram. Figure. 3 The principle of the accelerometer sensor. Effects of acceleration changes distance (increases or decreases) by moving capacitor electrodes, which changes the capacity of the sensor depending on the intensity of acceleration. 7. EMBEDDED SENSOR SUBSYSTEM Embedded sensor system collects physiological and mechanical data with built-in sensors. The device includes a sensor system, signal processing and system for display data. Data captured from the body of a measured person are collected in sensor network. The acquired data are transmitted to the vehicle via Bluetooth communication interface; it is used to transmit data over short distances. Data are passed from the vehicle to a web site using databases.
For temperature sensing is chosen sensor Pt 100. The signal from the sensor is then processed using the ADS1247. For the device is selected miniature 3 axis accelerometer LIS331DLH, that has a 16 bit digital output, high resolution and sensitivity. It can be used for low values of gravity acceleration in the LGA16 (Land Grid Array Package). The complete device includes a sensing component and interface IC, which is able to receive information from sensor and provide signal through I2C or serial interface SPI. Therefore it is possible to directly connect the device to any CPU or MCU and information of the accelerations in all directions X, Y and Z are transmitted together via one serial bus.
Fig. 4. Measuring chain. Embedded system consists of the ECG module, from which are indicated heart rate and respiratory rate, temperature sensor and system for determining speed and position of measured person. The block diagram of a measuring chain is on Figure 4. Two electrodes for ECG measurements are placed on the pilot; they are marked with red dots. Sensor for measuring temperature and sensor for measuring acceleration and position is marked with a yellow dot. The device consists of the connection of particular integrated circuits for measuring ECG, temperature, position and acceleration and microprocessor, see block diagram in Fig. 5. The microprocessor communicates with integrated circuits by peripheral interface SPI. The data are then sent via Bluetooth. Terminal equipment ADS1298 is selected for the ECG recording. It is a multi-channel, 24-bit analog to digital deltasigma converter with built-in programmable amplification. It
Fig. 6. Demonstration application on PDA. 4. VISUALIZATION Mobile version of visualization is designed for testing embedded system. This application allows connecting to the sensor system via Bluetooth. One of the implemented versions is an application for PDAs running on Windows Mobile. This application is usable both for displaying sensor data in real time and also can be used to record measured data to internal memory of PDA or to other data medium. Archived data can be also displayed on the PDA device.
Fig. 7. ECG graph in LabView software. Application for processing and visualization of measured data is established in the graphical programming software LabView. It allows viewing incoming data in real time, performing their analysis, such as breathing and heart rate, analysis of power effects on the pilot of vehicle and analysis of the temperature of sensing person. The application can also display historical trends and archived data. Archived data can be processed using other software and tools (e.g. Matlab) too. 8. CONCLUSION The realized prototype of the sensor subsystem is designed especially for use in prototype vehicles Kaipan Voltage. In its current form it is a technological means of demonstrating the possibilities in measuring biotelemetry in vehicles, especially as a tool designed for suggestion for vehicle ergonomics, which leads to optimization of mental and physical load of crew. In the case that the communication interface of the vehicle will be used, the data are matched with the telemetry and transmitted to the storage of the database system based on Oracle tools via GPRS modem. The device is designed to implement itself to the standard gear of the prototype vehicle. It can be modified for use in other areas of human activity, especially where exact information of the physiological condition sensed persons could improve physical performance and avert potential health risks. ACKNOWLEDGEMENTS This research was supported by the project "Comprehensive solutions to electric propulsion units," supported by public funds from MIT in the TIP FR-TI1/223 and by the project SP2012/182, “Control of technological systems with OAZE providing an independent sustainable development of complex systems.” of Student Grant System, VSB-TU Ostrava. REFERENCES Joshi, A., Ravindran, S., Miller, A. (2011). EKG-Based Heart-Rate Monitor Implementation on the LaunchPad Value Line Development Kit Using the MSP430G2452 MCU. Texas Intruments Application Report. Labza, Z., Korpas, D., Penhaker, M. (2008). The measurement and evaluation of the electric parameters of a dual-chamber pacemaker. Lékař a technika, 38, 2, 61-63.
Department of cybernetics and biomedical engineering, Technical University of Ostrava, 17. Listopadu 15, 70833 Czech Republic (e-mail: [email protected], [email protected], [email protected]).
Abstract: Design of the prototype embedded sensors system for biomedical data acquisition and analysis. It introduces to issues of measuring vital functions and processing data in real-time and suggestion of mobile embedded system for measuring biometric data. The main aim of the research work is the implementation of a prototype sensor system. Data captured from the body of a person are measured and transmitted to the superior system in real time, where they are processed, evaluated and archived. To transfer data to the nearest superior system is used Bluetooth interface. Keywords: biosensor, sensor system, biotelemetry, electrocardiography.
1. INTRODUCTION Medical devices for monitoring and diagnostics become more portable through miniaturization of electronic circuits, progress in the development of batteries (size and endurance), extending the possibility of wireless technology and reducing the price of all the necessary technologies. Biotelemetry engages in wireless transmission of biometric data. Nowadays biotelemetry becomes an integral part of everyday life. It develops the idea of wireless systems with embedded biosensors, when the device is able to scan more vital functions. Evaluating the monitored variables of the sensing person can follow physical and psychological stress and evaluate load and stress factors. It also allows observing reaction of the sensing person to changes in the environment. Using distant monitoring enable team reaction to unexpected changes. These changes can be physiological nature, such as behaviour modification, stress, or it can be a reaction to changes in the environment. The immediate reaction to any change or impairment of vital functions may often avoid lifethreatening or any adverse change in the health. Embedded sensor system worked is intended for use in prototype vehicles Kaipan or Hydrogenix. Described sensor system is meant for capturing vital functions and for evaluating actual physical condition of the pilot vehicle. 2. ELECTROCARDIOGRAPHY Electrocardiography (ECG) is a simple, inexpensive and noninvasive diagnostic method for sensing and recording the electrical activity of the heart. Record of the time changes of electric potential caused by cardiac activity is called an electrocardiogram. ECG is the basic function test of the electrical activity of heart muscle. An electrical signal
generated by cardiac muscle fibres is spread in all directions, because the body tissues are good electrical leaders. The signal penetrates into the surrounding organs, and reaches the skin with little attenuation. Therefore, ECG capture virtually anywhere on the surface of the human body. The electric array of the heart begins by transmission of the action potential through cardiac conduction system and surrounding muscles. Record of the heart electrical array is obtained by measuring the potential of this array.
Fig. 1. Measured ECG curve with modulation of respiratory rate. The electrical activity of heart, see Fig. 1, is recorded by electrocardiograph. Electric field is established during each cycle of the electrical activation. The device records electric field by system of the electrocardiographic leads from the body surface and displays electrocardiogram depending on time. Unipolar leads according to Einthoven, bipolar leads according to Goldberger and thoracic leads according to Wilson scan electrocardiogram. Electrocardiogram will be measured according to Einthoven convention in this system. Einthoven’s limb leads record electrical potential difference between two electrodes on the limbs, see Fig. 2. The right hand is marked with the letter RA (right arm, red) and the left hand with the letter LA (left arm, yellow), the RA-LA signal
is marked as Lead I. The third electrode is fixed near the left ankle and is marked with the letter LL (left leg, green). Potential difference LL-RA is marked as Lead II and potential difference LL-LA as Lead III. Electrode N (neutral, black) is connected to the right leg and is not included into the sensing, serves as grounding.
other on the same level on the left rib. Electrodes placed this way directly create a vector through the heart. Methods of obtaining respiratory rate from the ECG: - Method of envelopes - envelopes acquisition of selected characteristics of the ECG recording. RR is the envelope curve connecting all the R oscillations. This curve is calculated by cubic interpolation of R oscillations. - Mean ECG - derived from an average amplitude of the ECG recording. The method captures the mean oscillation of the baseline ECG. The advantage of this method is resistant to interference. The method involves finding the mean valueduring one heart beat (starting just before the P wave and P wave ends before the next contraction the heart). Weak increasing and decreasing the mean value of the selected segment represents breathing.
Fig. 2. Unipolar limb leads according to Einthoven. Lead I (electrodes RA and LA) is used for the measurement. In this lead is the course of electrocardiogram most visible. But the electrodes are not placed on the limbs, but are shifted closer to the heart. They are located under the right and left clavicle about its centre. 3. HEART RATE Heartbeat is a pressure wave that is caused by expulsion of blood from the left ventricle into the aorta (the aorta), from where it is spread to other arteries throughout the body. In medicine a series of these waves corresponds to the heart rhythm and rate. Heart rate is the number of beats (contractions) of the heart in one minute. As the only measured variable accurately reflects the body load.
tN
nB f GEN
The average heart rate has a value of about 75 beats per minute for men and women around 82, but may be lower and may not be a sign of disease. The lower value of the pulse usually occurs in athletes who have a strong heart pump capable of a large amount of blood. The value can then be around 40 beats per minute. When heart rate is below 60 beats per minute, we are talking about the bradycardia. In contrast, when the acceleration of heart rate is above 100 beats per minute, we are talking about the tachycardia. With increased heart rate is impaired oxygen supply to the heart, there is insufficient oxygenation and insufficient heart function, resulting in a higher risk of heart attack. The increase in heart rate occurs in stressful situations, for example, can also be caused by pharmacologically 4. BREATH RATE Respiratory rate is obtained from the ECG, because breathing is closely related to the ECG and affects the ECG recording, e.g. is showed as a change in the amplitude of the ECG recording. ECG recording is sourced using surface electrodes. One electrode is placed on the sternum (breastbone) and the
- Interval method - obtained from the time interval selected characters ECG signal. RR interval is defined by the time period between two consecutive cycles. Changes in RR interval are affected by breathing 5. TEMPERATURE For temperature measurement are used thermistors. There are two types of thermistors - NTC (Negative Temperature Coefficient) and PTC (Positive Temperature Coefficient). NTC whose resistance decreases with increasing temperature is suitable. PTC are used as sensors indicate overtemperature. Linear temperature dependence of the resistance temperature coefficient can be expressed as:
αT R0 1 α Δ β ΔT 2 γ ΔT 3 T 100
where T [K] is the thermodynamic temperature, R0 [Ω] is the resistance at the reference temperature T0, α [K-1] is the temperature coefficient of resistance at temperature T0. The average human body temperature ranges from 35.8 ° C to 37.3 ° C. This temperature ensures the correct functioning of all organs and responses that run through them. From the medical point of view for hypothermia in humans the temperature has to decrease below 35° C. If the temperature exceeds human 37 ° C, these may be overheating, or the defensive reaction of the immune system to infection. 6. ACCELEROMETRY Accelerometry allows the measurement of acceleration using accelerometers. They operate on the determination of a variation of the motion of a body (located in accelerometer) in the acceleration segment. These changes are transferred and measured (e.g. piezoelectric) with an electric output signal. Depending on the number of accelerometers can measure acceleration in one axis in the plane or in space. Three-dimensional acceleration can be determined using three accelerometers placed so that their axes are perpendicular to each other. The actual sensor is integrated micromechanical polysilicon surface structure "floating" on the surface of silicon single crystals. Silicon springs allow movement of the whole
mechanical structure of the single crystal surface, while providing mechanical resistance force caused by acceleration. Bending and deformation of such a structure is converted to a differential change of capacity capacitor, see Fig. 3. It is composed of two fixed plates and plates firmly attached to the deforming beam.
includes all the features that are commonly required in applications for ECG measuring. It can measure up to 12-lead ECG.
Fig. 5. Block diagram. Figure. 3 The principle of the accelerometer sensor. Effects of acceleration changes distance (increases or decreases) by moving capacitor electrodes, which changes the capacity of the sensor depending on the intensity of acceleration. 7. EMBEDDED SENSOR SUBSYSTEM Embedded sensor system collects physiological and mechanical data with built-in sensors. The device includes a sensor system, signal processing and system for display data. Data captured from the body of a measured person are collected in sensor network. The acquired data are transmitted to the vehicle via Bluetooth communication interface; it is used to transmit data over short distances. Data are passed from the vehicle to a web site using databases.
For temperature sensing is chosen sensor Pt 100. The signal from the sensor is then processed using the ADS1247. For the device is selected miniature 3 axis accelerometer LIS331DLH, that has a 16 bit digital output, high resolution and sensitivity. It can be used for low values of gravity acceleration in the LGA16 (Land Grid Array Package). The complete device includes a sensing component and interface IC, which is able to receive information from sensor and provide signal through I2C or serial interface SPI. Therefore it is possible to directly connect the device to any CPU or MCU and information of the accelerations in all directions X, Y and Z are transmitted together via one serial bus.
Fig. 4. Measuring chain. Embedded system consists of the ECG module, from which are indicated heart rate and respiratory rate, temperature sensor and system for determining speed and position of measured person. The block diagram of a measuring chain is on Figure 4. Two electrodes for ECG measurements are placed on the pilot; they are marked with red dots. Sensor for measuring temperature and sensor for measuring acceleration and position is marked with a yellow dot. The device consists of the connection of particular integrated circuits for measuring ECG, temperature, position and acceleration and microprocessor, see block diagram in Fig. 5. The microprocessor communicates with integrated circuits by peripheral interface SPI. The data are then sent via Bluetooth. Terminal equipment ADS1298 is selected for the ECG recording. It is a multi-channel, 24-bit analog to digital deltasigma converter with built-in programmable amplification. It
Fig. 6. Demonstration application on PDA. 4. VISUALIZATION Mobile version of visualization is designed for testing embedded system. This application allows connecting to the sensor system via Bluetooth. One of the implemented versions is an application for PDAs running on Windows Mobile. This application is usable both for displaying sensor data in real time and also can be used to record measured data to internal memory of PDA or to other data medium. Archived data can be also displayed on the PDA device.
Fig. 7. ECG graph in LabView software. Application for processing and visualization of measured data is established in the graphical programming software LabView. It allows viewing incoming data in real time, performing their analysis, such as breathing and heart rate, analysis of power effects on the pilot of vehicle and analysis of the temperature of sensing person. The application can also display historical trends and archived data. Archived data can be processed using other software and tools (e.g. Matlab) too. 8. CONCLUSION The realized prototype of the sensor subsystem is designed especially for use in prototype vehicles Kaipan Voltage. In its current form it is a technological means of demonstrating the possibilities in measuring biotelemetry in vehicles, especially as a tool designed for suggestion for vehicle ergonomics, which leads to optimization of mental and physical load of crew. In the case that the communication interface of the vehicle will be used, the data are matched with the telemetry and transmitted to the storage of the database system based on Oracle tools via GPRS modem. The device is designed to implement itself to the standard gear of the prototype vehicle. It can be modified for use in other areas of human activity, especially where exact information of the physiological condition sensed persons could improve physical performance and avert potential health risks. ACKNOWLEDGEMENTS This research was supported by the project "Comprehensive solutions to electric propulsion units," supported by public funds from MIT in the TIP FR-TI1/223 and by the project SP2012/182, “Control of technological systems with OAZE providing an independent sustainable development of complex systems.” of Student Grant System, VSB-TU Ostrava. REFERENCES Joshi, A., Ravindran, S., Miller, A. (2011). EKG-Based Heart-Rate Monitor Implementation on the LaunchPad Value Line Development Kit Using the MSP430G2452 MCU. Texas Intruments Application Report. Labza, Z., Korpas, D., Penhaker, M. (2008). The measurement and evaluation of the electric parameters of a dual-chamber pacemaker. Lékař a technika, 38, 2, 61-63.