- Email: [email protected]
Non-invasive wearable ECG-patch system for astronauts and patients on Earth
Acta Astronautica xxx (xxxx) xxx–xxx
Contents lists available at ScienceDirect
Acta Astronautica journal homepage: www.elsevier.com/locate/actaastro
Non-invasive wearable ECG-patch system for astronauts and patients on Earth Natalia Glazkovaa,∗, Tatiana Podladchikovaa, Rupert Gerzera, Daria Stepanovaa,b a b
Skolkovo Institute of Science and Technology, Nobelya Ulitsa 3, Moscow, 121205, Russia Moscow Institute of Physics and Technology, Russia
A R T I C LE I N FO
A B S T R A C T
Keywords: Electrocardiogram Vital signs Monitoring Wearable Ecg-patch Human spaceflight
Ambulatory long term cardiac diagnostics is still not optimally solved. We have developed a new system that can overcome this gap in diagnostics. The new system consists of an adhesive patch-like wearable miniaturized device for electrocardiogram (ECG) data acquisition with further processing of acquired data. The new patch-like wearable device is able to record data for up to 7 days and significantly reduces discomfort to the user by its cable-less design, small size and direct attachment to the skin surface. This three lead system also detects ECG waveform morphology. It is aimed to spot heart rate, irregular beat episodes and circadian variations. Such a device has high potential to be used for both aerospace and terrestrial applications.
1. Introduction Many cardiac diseases and abnormalities can be diagnosed by electrocardiogram analysis [1]. The characteristics of the ECG signal components such as QRS complex, P and T waves reflect the clinical status of many heart diseases. Therefore, an acquisition of the waveform and its further analysis are matters of high significance. Within the last decade there were a number of experiments from leading space agencies, involving usage of instrumentation for astronauts vital signs monitoring. Most commonly the used health state monitoring systems were in a strap form (experiment Cardiovector by the Institute of Biomedical Problems (IBMP) of the Russian Academy of Sciences [2–10]), as biometric smartwear with various sensors embedded into clothes and textiles (EveryWear smartshirt kit as part of the ERASMUS experiment by Frances Space Agency [11,12]), or as separate hardware module (Holter Monitor 2 during Expedition 18 on the STS126/Flight ULF-2 [13]). One of the advantages of these devices is that they are proven to operate under extreme space conditions. However, these systems also have drawbacks such as bulkiness. This drawback may cause dislocation during landing and may also hamper movements during performance. On the other hand, in the recent years the technology for non-invasive vital signs monitoring under ambulatory settings improved much further with the development of patch-like biosensors [1,14–16]. Most of these ECG biosensors are single-channel, meaning they could record
∗
only one lead at a time. Single lead devices lack the possibility to indicate the origin of different arrhythmias [17]. The current trends in ECG-related research focus mainly on three aspects: improved instrumentation, big data mining and accuracy of diagnosis and application [18]. The purpose of this study is to develop an improved ECG instrumentation system that could be beneficial for human space exploration and also for similar purposes on Earth. The new system consists of a miniaturized body-worn ECG monitoring device and a novel data processing algorithm. The system records multilead ECG waveform, respiration rate and activity data. This information is then used to detect arrhythmia episodes. The major focus is on the detection and analysis of the following types of heart rhythm disorders: tachycardia, bradycardia, atrial fibrillation [19]. The system enables continuous real-time prolonged monitoring for up to a week. 2. Materials and methods The new system consists of a body-worn miniaturized device, a smartphone gateway and a cloud-based platform. The body-worn miniaturized device, the core component of the system, is a small, lightweight, easy-to-use unit that is worn on the chest along with the respective physiologic sensors. It is capable to record such physiological data as electrocardiogram signal, respiration rate and daily physical activity, as well as to wirelessly stream acquired data to a cloud-based platform for display purposes and further processing. Fig. 1 illustrates the high level system block diagram describing the overall system
Corresponding author. E-mail address: [email protected] (N. Glazkova).
https://doi.org/10.1016/j.actaastro.2019.01.036 Received 30 June 2018; Accepted 27 January 2019 0094-5765/ © 2019 IAA. Published by Elsevier Ltd. All rights reserved.
Please cite this article as: Glazkova, N., Acta Astronautica, https://doi.org/10.1016/j.actaastro.2019.01.036
Acta Astronautica xxx (xxxx) xxx–xxx
N. Glazkova et al.
[22]. As the ECG signal amplifier, the ADS1298 module of Texas Instuments (ADS1298, Texas Instruments, Dallas, TX) is selected for the final design. This 8-channel amplifier with an integrated 24-bit sigmadelta ADC [23] enables prolonged electrocardiogram monitoring with sufficient precision. The design requirements for the microcontroller unit (MCU) are power consumption, memory capacity and cost. An Msp430f261 microcontroller from Texas Instruments was chosen for the final system design. This microcontroller has ultra low power consumption and is equipped with a set of peripheral devices, optimal for this application. The controller architecture in combination with five low-power modes allows to increase the autonomous work time in portable measuring applications. The device is equipped with a powerful 16-bit reduced instruction set computer processor, or RISC-processor [24]. Fig. 1. High level block diagram of the non-invasive wireless wearable system for electrocardiogram monitoring. Physiological data is recorded by the patchlike data acquisition unit. Raw data is wirelessly transmitted via a gateway to the cloud-based server or can be retrieved to the main computer directly from the patch-like device. Raw data processing is done on the server. Healthcare professionals can access the processed information through pre-installed software on the personal computer.
2.2. Components selection and design rationale
2.2.2. Peripherals: accelerometer, memory circuit, data transmission and power management When choosing an accelerometer, the major considerations are acceleration range, sampling rate, power consumption and resolution. A 12-bit chip by Analog Devices is used in the final design. The chip has ultra low power: up to 23 μA in measurement mode and 0.2 μA in standby mode with a supply voltage of 2.6 V. A built-in memory management system with FIFO (first in, first out) technology minimizes the load on the processor. The chip manufacturer also provides algorithms for control of activity/inactivity and fall detection. Flexible interrupt modes minimize the amount of generated data and power consumption. For data storage the device uses both: serial flash memory and a micro-SD card. As the data is collected, it is buffered in the serial flash memory. When the serial flashed memory is loaded, the data is transferred to the micro-SD card and can later be accessed from a computer. Two 128 MB serial flash chips support the standard serial port interface (SPI) and are integrated into the printed circuit board (PCB). Since micro-SD cards have rather high power consumption, its power is controlled by the controller through a switch. The patch also has the ability to transmit information directly through the micro-USB port. To implement data transfer via micro-USB, an FTDI chip was added to the circuit, which converts the universal asynchronous receiver-transmitter (UART) protocol to USB. As for wireless transmission, a Bluetooth Low Energy module from Microchip was chosen. With a footprint of 9 × 11.5 × 2.1 mm it occupies the minimum space on the PCB. Interaction with the device is realized through a standard UART interface. The chip has a fully integrated Bluetooth software package and offers a secure standard certified version with an integrated antenna. At this stage of system configuration, three options for using a memory system are possible: accumulation of data from the ECG and accelerometer in the flash memory and transfer to the SD card in case of its filling; accumulation of data from the ECG and accelerometer in the flash memory and transfer of all information via the micro-USB interface to the computer; data transfer through bluetooth channel. All the elements of electrical circuit described in sections 2.2.1 2.2.2 are powered by a 3.7V Li-Pol battery with the capacity up to 1200 mAh .
2.2.1. Amplifier and microcontroller The bio-electric potential sensed from the body surface is acquired by the silver/silver-chloride (Ag/AgCl) reference electrodes. These signals are of a very low value, from 0.05 mV up to 20 mV [20], and therefore require amplification in order to be sampled by an Analog-toDigital converter (ADC). To remove high frequency noise and baseline variations from the signal, a band pass filter is used. Diagnostic quality electrocardiogram signals require a bandwidth window of 0.05–150 Hz [21]. A minimum of 12-bit ADC resolution is needed for the ECG monitoring applications
2.2.3. Adhesive base The rigid 3D printed case with an assembled PCB (see section 2.2) is connected to a special single-use adhesive base for further attachment to the skin surface. The flexible base is coupled to the rigid case by embedded Ag/AgCl electrodes. A 3M 2477P adhesive tape was chosen as the main material as it provides robust, safe and gentle attachment to the skin. This double-coated Differential Silicone/Gentle acrylic adhesive tape is specially designed for medical and retail lamination applications.
design. The individual patch-like sensor is attached to the chest of the respective subject. The raw data then can be transmitted through the gateway to the cloud-based server, or retrieved to the main computer through the embedded SD-card or USB port. For the ambulatory, preflight and post-flight settings the smartphone is used as a gateway. For the in-flight setting, an additional data-transmitting unit serves as the gateway. The cloud-based platform has a pre-installed software with data processing algorithms. Healthcare professionals can access the data through their PC. Such a system design allows building various configurations and provides flexibility for a number of use-case scenarios. 2.1. System architecture The system consists of data collection and data transmission blocks, memory and power circuits, user interface and a data processing unit. Fig. 2 illustrates the main elements of the system. The data acquisition is done by a low-noise amplifier (see section 2.2.1) through the array of electrodes. A low power microcontroller unit (MCU) (see section 2.2.1) is responsible for the data collection, storage and retrieval through the micro SD card and USB interfaces. The system has two buttons and two LED indicators to show the current status of system. A built-in six degree of freedom inertial measurement unit (6 DOF IMU) detects users movements. Recorded activity information is later correlated with the ECG data to identify potential sources of an arrhythmia episode if one occurs. Data transmission, data collection, memory and user interface system blocks are all actuated by the power management circuit.
2
Acta Astronautica xxx (xxxx) xxx–xxx
N. Glazkova et al.
Fig. 2. Block diagram illustrating the main elements of the device, comprising data collection and data transmission blocks, memory and power circuit, user interface and data processing unit. Table 1 Technical specifications of the developed non-invasive wearable patch-like device for high-quality electrocardiogram recording. Parameter
Value
Physiological measurements
ECG (I, II, V5 leads), heart rate, heart rate variability activity (3-axes acceleration) 8 0.05 − 150 Hz 100 − 1700 24 bit 250 − 500 Hz 200 − 1000 Hz >2 Gb ≥ 1200 mAh >3 days Bio compatible, hypo-allergic ≤ 40 × 40 × 15 mm ≤ 85 g
Number of ECG channels Band-width Gain Ratio ADC Resolution Sampling Frequency Sampling rate of amplifier Memory capacity Battery capacity Monitoring time Adhesive Size of rigid part Weight
2.3. System specifications Selected components described in section 2.2 provide a system with parameters suitable for high quality signal acquisition. Table 1 summarizes the technical specifications of the system. With the 0.05–150 Hz bandwidth, 24-bit ADC resolution, 8 channels configuration and high sampling frequency, the design meets the requirements of the monitoring system. Over 3 Gb of memory storage, together with 1200 mAh battery capacity enable prolonged recording for more than 3 days. The assembled system records the ECG signal in
Fig. 3. Assembled printed circuit board (PCB) of proposed ECG-patch.
various lead selections, as well as the physical activity of the user. Heart rate and heart rate variability are derived from the acquired ECG waveform. Total weight of the current system, including battery, 3D printed case, circuitry board, the adhesive base with embedded gel 3
Acta Astronautica xxx (xxxx) xxx–xxx
N. Glazkova et al.
Fig. 4. (a) Developed ECG-prototype. (b) Prototype on a subject's chest.
Fig. 5. Snapshot of output of console. Fig. 6. ECG waveform obtained by the designed hardware.
significantly improves patients’ comfort compared to a standard Holter monitoring equipment. With the designed hardware we obtained vital signs, including realtime ECG data and real-time mobility data, displayed on the console in Fig. 5. The visual display also includes the hardware setup and telemetry status windows. The user may configure the leads in the corresponding channel selection field. On the basis of visual analysis, it can be seen in Fig. 5, that the specifications of the system are sufficient for providing high-quality recording. The ECG signal of a woman of 24-year old acquired from the assembled prototype with detected RR intervals is also shown in Fig. 6. The filtration of noise intrinsic to a wearable device is based on a smoothing algorithm described in Ref. [25]. Thus, the improved
electrodes, is 85 g. The dimensions of the rigid part are 40 × 40 × 15 mm. Such a relatively small and lightweight solution increases the level of comfort for an individual. 3. Wearable prototype for the ECG data acquisition The assembled system described in previous sections resulted in a prototype of an adhesive patch-like wearable miniaturized device for ECG data acquisition. Fig. 3 illustrates a manufactured PCB, comprising an instrumentation amplifier, a micro-controller, a memory circuit, a data transmission module and a power management circuit. The assembled system is shown in Fig. 4a and its position on the chest is presented in Fig. 4b, respectable. Such a cable-less design 4
Acta Astronautica xxx (xxxx) xxx–xxx
N. Glazkova et al.
instrumentation with high-quality data acquisition along with prolonged ECG monitoring has a high potential to be beneficial for aerospace and terrestrial applications.
1109/EMBC.2013.6611242. [8] P.F. Migeotte, J. Tank, N. Pattyn, I. Funtova, R. Baevsky, X. Neyt, G.K. Prisk, Three dimensional ballistocardiography: methodology and results from microgravity and dry immersion, 2011 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2011, pp. 4271–4274, , https://doi.org/10.1109/ IEMBS.2011.6091060. [9] P.F. Migeotte, S.D. Ridder, J. Tank, N. Pattyn, I. Funtova, R. Baevsky, X. Neyt, G.K. Prisk, Three dimensional ballisto- and seismo-cardiography: Hij wave amplitudes are poorly correlated to maximal systolic force vector, 2012 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2012, pp. 5046–5049. [10] P.F. Migeotte, Q. Delire, J. Tank, I. Funtova, R. Baevsky, X. Neyt, N. Pattyn, 3dballistocardiography in microgravity: comparison with ground based recordings, 2013 35th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBC, 2013, pp. 7012–7016. [11] M. Augelli, Cadmos: the French usoc. from a quarter century history to new prospects, 2018 SpaceOps Conference, 2018, p. 2519. [12] NASA, Human research facility holter monitor (holter). URL http://eea.spaceflight. esa.int/portal/exp/?id=9564. CNES, Everywear - a personal assistant for astronaut (cnes), http://eea.spaceflight. esa.int/portal/exp/?id=9564 [13] NASA, Human research facility holter monitor (holter). https://www.nasa.gov/ mission\_pages/station/research/experiments/614.html. [14] S. Lee, G. Ha, D. Wright, Y. Ma, Highly flexible, wearable, and disposable cardiac biosensors for remote and ambulatory monitoring, npj Dig. Med. 1 (2018) 1–8, https://doi.org/10.1038/s41746-017-0009-x. [15] S. Imani, A. Bandodkar, A. Vinu Mohan, R. Kumar, A wearable chemicalelectrophysiological hybrid biosensing system for real-time health and fitness monitoring, Nat. Commun. 7, 10.1038/ncomms11650. [16] K. Sohn, F. Merchant, O. Sayadi, D. Puppala, A novel point-of-care smartphone based system for monitoring the cardiac and respiratory systems, Sci. Rep. 7, 10. 1038/srep44946. [17] J. Steinberg, N. Varma, I. Cygankiewicz, ISHNE-HRS expert consensus statement on ambulatory ECG and external cardiac monitoring/telemetry, Heart Rhythm J. 14 (2017), https://doi.org/10.1016/j.hrthm.2017.03.038 (2017) e55–e96. [18] X. Yang, G. Liu, Y. Tong, H. Yan, The history, hotspots, and trends of electrocardiogram, J. Geriatr. Cardiol. 12 (2015) 448–456, https://doi.org/10.11909/j. issn.1671-5411.2015.04.018. [19] J. Hall, Textbook of Medical Physiology, twelfth ed., Saunders Elsevier, Philadelphia, PA, 978-1-4160-4574-8, 2011, pp. 143–153 section (Chapter 13): Cardiac Arrhythmias and Their Electrocardiographic Interpretation. [20] H.J. Guyton, C. Arthur, Textbook of Medical Physiology, Elsevier Science, 2015 (Ch. The Normal Electrocardiogram). [21] M.K. Delano, A Long Term Wearable Electrocardiogram (ECG) Measurement System, Master’s thesis Massachusetts Institute of Technology, USA, 2012http:// web.mit.edu/maggied/Public/finalthesisMKD.pdf. [22] Freescale Semiconductor, Inc., Wearable ECG Patch, Rev. 0, 08/2014 (08 2014). [23] Texas Instruments, ADS129x low-power, 8-channel, 24-bit analog front-end for biopotential measurements, Rev. (August 2015) 24–25 01 2010. [24] Texas Instruments, Mixed signal microcontroller, Rev. (December 2012) 15–17 06 2007. [25] T. Podladchikova, R. Van der Linden, A.M. Veronig, Sunspot number second differences as a precursor of the following 11-year sunspot cycle, Astrophys. J. 850 (2017) 81, https://doi.org/10.3847/1538-4357/aa93ef.
4. Discussion and conclusions In this study, we present a novel non-invasive, non-obtrusive and easy-to-use wearable ECG system for long-term ECG monitoring. We have developed a next generation prototype, i.e. a II lead ECG wearable biosensor, using off-the-shelf components only. This novel device is able to extract the ECG waveform in an energy efficient and simple way. The data gathered is stored on the memory card in the format which makes it accessible via a computer. Data visualization was performed through the MATLAB software tool kit. Basic analysis such as RR-peak localization, RR-interval calculation, irregular beat episodes identification was performed. With the proposed configuration of the system using off-the-shelf components, we see the opportunity to use it as a tool for diagnosis support of heart rhythm disorders, cardiovascular syncope and abnormal respiratory rate patterns. The developed device fills the gap between patient comfort and diagnostic value of measurements acquired by a wearable solution. Thia patch-like wearable device provides the opportunity to evaluate the cardiac health state during astronauts stay in space, during launch and landing, pre-flight training periods and post-flight rehabilitation. Besides, with the emergence of commercial spaceflight, medical examination will require a personalized approach. ECG-patch instrumentation solutions could be a part of the medical examination and documentation process of such individuals. The system may as well be applicable in sports medicine and regular clinical diagnostics and health monitoring. In fact, there is an ongoing trend in the development of clinical-grade wearable systems with prolonged monitoring capability for terrestrial applications. With the growth of clinically validated databases, such wearable devices also hold promise for integration into the healthcare system and therefore reshaping the clinical-patient interaction. Acknowledgements The authors are grateful to the Skoltech Translational Research and Innovation Program for the support of this research.
Natalia Glazkova has graduated from the Moscow Aviation Institute (MAI) with a specialist degree in aerospace biomedical life-support engineering. She received a Master degree from the Skolkovo Institute of Science and Technology in Engineering systems. Natalia also completed a year-abroad graduate study in the Department of Aeronautics and Astronautics in the Massachusetts Institute of Technology (MIT). Natalia's scientific interest lies in the field of interdisciplinary research associated with systems engineering of biomedical equipment in different applications.
References [1] E. Fung, M.-R. Jrvelin, R.N. Doshi, J.S. Shinbane, S.K. Carlson, L.P. Grazette, P.M. Chang, R.S. Sangha, H.V. Huikuri, N.S. Peters, Electrocardiographic patch devices and contemporary wireless cardiac monitoring, Front. Physiol. 6 (2015) 149, https://doi.org/10.3389/fphys.2015.00149. [2] R. Baevsky, I. Funtova, E. Luchitskaya, Jens, Microgravity: an ideal environment for cardiac force measuring, Cardiometry 3 (2013) 100–117, https://doi.org/10. 12710/cardiometry.2013.3.100117. [3] I. for Biomedical Problems, Cardiovector experiment. URL https://www.energia. ru/en/iss/researches/human/11.html. [4] Q. Deliere, P.F. Migeotte, X. Neyt, I. Funtova, R.M. Baevsky, J. Tank, N. Pattyn, Cardiovascular changes in parabolic flights assessed by ballistocardiography, 2013 35th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBC), 2013, pp. 3801–3804, , https://doi.org/10.1109/EMBC. 2013.6610372. [5] O.T. Inan, P.F. Migeotte, K.S. Park, M. Etemadi, K. Tavakolian, R. Casanella, J. Zanetti, J. Tank, I. Funtova, G.K. Prisk, M.D. Rienzo, Ballistocardiography and seismocardiography: a review of recent advances, IEEE J. Biomed. Heal. Inform. 19 (4) (2015) 1414–1427, https://doi.org/10.1109/JBHI.2014.2361732. [6] E. Luchitskaya, R. Baevsky, I. Funtova, J. Tank, Space experiment ”cardiovector” as a new step in the development of the method of ballistocardiography, Proceedings of the International Astronautical Congress, vol. 1, IAC, 2013, pp. 52–55. [7] E. Luchitskaya, Q. Deliere, A. Diedrich, N. Pattyn, A. Almorad, L. Beck, P. Gauger, U. Limper, I. Funtova, R.M. Baevsky, P.F. Migeotte, J. Tank, Timing and source of the maximum of the transthoracic impedance cardiogram (dz/dt) in relation to the h-i-j complex of the longitudinal ballistocardiogram under gravity and microgravity conditions, 2013 35th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBC, 2013, pp. 7294–7297, , https://doi.org/10.
5
Acta Astronautica xxx (xxxx) xxx–xxx
N. Glazkova et al. Dr. Tatiana Podladchikova is assistant professor at the Skolkovo Institute of Science and Technology, Russia. Her area of scientific research is solar-terrestrial physics, space weather forecasting for mitigation of space weather hazards, as well as development of advanced data analysis techniques for the extraction of useful knowledge, control and forecasting in interdisciplinary applications (biomedicine, navigation). In 2015 Dr. Podladchikova was awarded with the International Alexander Chizhevsky medal for Space Weather and Space Climate.
Daria Stepanova received her bachelor degree in system control from the Bauman Moscow State Technical University. Then she continued with her masters studies at the Skolkovo Institute of Science and Technology and graduated with a degree in data analysis. Daria completed a year-abroad exchange program in Ecole Polytechnique Federale de Lausanne (EPFL). Additionally Daria graduated from the Moscow Institute of Physics and Technology with a Master degree in mathematical modeling and mathematical physics.
Prof. Dr. Rupert Gerzer is a medical doctor by education, whose scientific interests lie in medicine, life sciences and astronautics. Prior to his position at Skoltech as a Provost, he was Professor and Chairman at the Institute of Aerospace Medicine (Aachen University) and Director of the Institute of Aerospace Medicine, German Aerospace Center DLR (Cologne) Western Europes largest civil institute of aerospace medicine. Prof. Gerzer published more than 250 scientific papers and received the Life Science Award of the International Academy of Astronautics in 2003.
6
Contents lists available at ScienceDirect
Acta Astronautica journal homepage: www.elsevier.com/locate/actaastro
Non-invasive wearable ECG-patch system for astronauts and patients on Earth Natalia Glazkovaa,∗, Tatiana Podladchikovaa, Rupert Gerzera, Daria Stepanovaa,b a b
Skolkovo Institute of Science and Technology, Nobelya Ulitsa 3, Moscow, 121205, Russia Moscow Institute of Physics and Technology, Russia
A R T I C LE I N FO
A B S T R A C T
Keywords: Electrocardiogram Vital signs Monitoring Wearable Ecg-patch Human spaceflight
Ambulatory long term cardiac diagnostics is still not optimally solved. We have developed a new system that can overcome this gap in diagnostics. The new system consists of an adhesive patch-like wearable miniaturized device for electrocardiogram (ECG) data acquisition with further processing of acquired data. The new patch-like wearable device is able to record data for up to 7 days and significantly reduces discomfort to the user by its cable-less design, small size and direct attachment to the skin surface. This three lead system also detects ECG waveform morphology. It is aimed to spot heart rate, irregular beat episodes and circadian variations. Such a device has high potential to be used for both aerospace and terrestrial applications.
1. Introduction Many cardiac diseases and abnormalities can be diagnosed by electrocardiogram analysis [1]. The characteristics of the ECG signal components such as QRS complex, P and T waves reflect the clinical status of many heart diseases. Therefore, an acquisition of the waveform and its further analysis are matters of high significance. Within the last decade there were a number of experiments from leading space agencies, involving usage of instrumentation for astronauts vital signs monitoring. Most commonly the used health state monitoring systems were in a strap form (experiment Cardiovector by the Institute of Biomedical Problems (IBMP) of the Russian Academy of Sciences [2–10]), as biometric smartwear with various sensors embedded into clothes and textiles (EveryWear smartshirt kit as part of the ERASMUS experiment by Frances Space Agency [11,12]), or as separate hardware module (Holter Monitor 2 during Expedition 18 on the STS126/Flight ULF-2 [13]). One of the advantages of these devices is that they are proven to operate under extreme space conditions. However, these systems also have drawbacks such as bulkiness. This drawback may cause dislocation during landing and may also hamper movements during performance. On the other hand, in the recent years the technology for non-invasive vital signs monitoring under ambulatory settings improved much further with the development of patch-like biosensors [1,14–16]. Most of these ECG biosensors are single-channel, meaning they could record
∗
only one lead at a time. Single lead devices lack the possibility to indicate the origin of different arrhythmias [17]. The current trends in ECG-related research focus mainly on three aspects: improved instrumentation, big data mining and accuracy of diagnosis and application [18]. The purpose of this study is to develop an improved ECG instrumentation system that could be beneficial for human space exploration and also for similar purposes on Earth. The new system consists of a miniaturized body-worn ECG monitoring device and a novel data processing algorithm. The system records multilead ECG waveform, respiration rate and activity data. This information is then used to detect arrhythmia episodes. The major focus is on the detection and analysis of the following types of heart rhythm disorders: tachycardia, bradycardia, atrial fibrillation [19]. The system enables continuous real-time prolonged monitoring for up to a week. 2. Materials and methods The new system consists of a body-worn miniaturized device, a smartphone gateway and a cloud-based platform. The body-worn miniaturized device, the core component of the system, is a small, lightweight, easy-to-use unit that is worn on the chest along with the respective physiologic sensors. It is capable to record such physiological data as electrocardiogram signal, respiration rate and daily physical activity, as well as to wirelessly stream acquired data to a cloud-based platform for display purposes and further processing. Fig. 1 illustrates the high level system block diagram describing the overall system
Corresponding author. E-mail address: [email protected] (N. Glazkova).
https://doi.org/10.1016/j.actaastro.2019.01.036 Received 30 June 2018; Accepted 27 January 2019 0094-5765/ © 2019 IAA. Published by Elsevier Ltd. All rights reserved.
Please cite this article as: Glazkova, N., Acta Astronautica, https://doi.org/10.1016/j.actaastro.2019.01.036
Acta Astronautica xxx (xxxx) xxx–xxx
N. Glazkova et al.
[22]. As the ECG signal amplifier, the ADS1298 module of Texas Instuments (ADS1298, Texas Instruments, Dallas, TX) is selected for the final design. This 8-channel amplifier with an integrated 24-bit sigmadelta ADC [23] enables prolonged electrocardiogram monitoring with sufficient precision. The design requirements for the microcontroller unit (MCU) are power consumption, memory capacity and cost. An Msp430f261 microcontroller from Texas Instruments was chosen for the final system design. This microcontroller has ultra low power consumption and is equipped with a set of peripheral devices, optimal for this application. The controller architecture in combination with five low-power modes allows to increase the autonomous work time in portable measuring applications. The device is equipped with a powerful 16-bit reduced instruction set computer processor, or RISC-processor [24]. Fig. 1. High level block diagram of the non-invasive wireless wearable system for electrocardiogram monitoring. Physiological data is recorded by the patchlike data acquisition unit. Raw data is wirelessly transmitted via a gateway to the cloud-based server or can be retrieved to the main computer directly from the patch-like device. Raw data processing is done on the server. Healthcare professionals can access the processed information through pre-installed software on the personal computer.
2.2. Components selection and design rationale
2.2.2. Peripherals: accelerometer, memory circuit, data transmission and power management When choosing an accelerometer, the major considerations are acceleration range, sampling rate, power consumption and resolution. A 12-bit chip by Analog Devices is used in the final design. The chip has ultra low power: up to 23 μA in measurement mode and 0.2 μA in standby mode with a supply voltage of 2.6 V. A built-in memory management system with FIFO (first in, first out) technology minimizes the load on the processor. The chip manufacturer also provides algorithms for control of activity/inactivity and fall detection. Flexible interrupt modes minimize the amount of generated data and power consumption. For data storage the device uses both: serial flash memory and a micro-SD card. As the data is collected, it is buffered in the serial flash memory. When the serial flashed memory is loaded, the data is transferred to the micro-SD card and can later be accessed from a computer. Two 128 MB serial flash chips support the standard serial port interface (SPI) and are integrated into the printed circuit board (PCB). Since micro-SD cards have rather high power consumption, its power is controlled by the controller through a switch. The patch also has the ability to transmit information directly through the micro-USB port. To implement data transfer via micro-USB, an FTDI chip was added to the circuit, which converts the universal asynchronous receiver-transmitter (UART) protocol to USB. As for wireless transmission, a Bluetooth Low Energy module from Microchip was chosen. With a footprint of 9 × 11.5 × 2.1 mm it occupies the minimum space on the PCB. Interaction with the device is realized through a standard UART interface. The chip has a fully integrated Bluetooth software package and offers a secure standard certified version with an integrated antenna. At this stage of system configuration, three options for using a memory system are possible: accumulation of data from the ECG and accelerometer in the flash memory and transfer to the SD card in case of its filling; accumulation of data from the ECG and accelerometer in the flash memory and transfer of all information via the micro-USB interface to the computer; data transfer through bluetooth channel. All the elements of electrical circuit described in sections 2.2.1 2.2.2 are powered by a 3.7V Li-Pol battery with the capacity up to 1200 mAh .
2.2.1. Amplifier and microcontroller The bio-electric potential sensed from the body surface is acquired by the silver/silver-chloride (Ag/AgCl) reference electrodes. These signals are of a very low value, from 0.05 mV up to 20 mV [20], and therefore require amplification in order to be sampled by an Analog-toDigital converter (ADC). To remove high frequency noise and baseline variations from the signal, a band pass filter is used. Diagnostic quality electrocardiogram signals require a bandwidth window of 0.05–150 Hz [21]. A minimum of 12-bit ADC resolution is needed for the ECG monitoring applications
2.2.3. Adhesive base The rigid 3D printed case with an assembled PCB (see section 2.2) is connected to a special single-use adhesive base for further attachment to the skin surface. The flexible base is coupled to the rigid case by embedded Ag/AgCl electrodes. A 3M 2477P adhesive tape was chosen as the main material as it provides robust, safe and gentle attachment to the skin. This double-coated Differential Silicone/Gentle acrylic adhesive tape is specially designed for medical and retail lamination applications.
design. The individual patch-like sensor is attached to the chest of the respective subject. The raw data then can be transmitted through the gateway to the cloud-based server, or retrieved to the main computer through the embedded SD-card or USB port. For the ambulatory, preflight and post-flight settings the smartphone is used as a gateway. For the in-flight setting, an additional data-transmitting unit serves as the gateway. The cloud-based platform has a pre-installed software with data processing algorithms. Healthcare professionals can access the data through their PC. Such a system design allows building various configurations and provides flexibility for a number of use-case scenarios. 2.1. System architecture The system consists of data collection and data transmission blocks, memory and power circuits, user interface and a data processing unit. Fig. 2 illustrates the main elements of the system. The data acquisition is done by a low-noise amplifier (see section 2.2.1) through the array of electrodes. A low power microcontroller unit (MCU) (see section 2.2.1) is responsible for the data collection, storage and retrieval through the micro SD card and USB interfaces. The system has two buttons and two LED indicators to show the current status of system. A built-in six degree of freedom inertial measurement unit (6 DOF IMU) detects users movements. Recorded activity information is later correlated with the ECG data to identify potential sources of an arrhythmia episode if one occurs. Data transmission, data collection, memory and user interface system blocks are all actuated by the power management circuit.
2
Acta Astronautica xxx (xxxx) xxx–xxx
N. Glazkova et al.
Fig. 2. Block diagram illustrating the main elements of the device, comprising data collection and data transmission blocks, memory and power circuit, user interface and data processing unit. Table 1 Technical specifications of the developed non-invasive wearable patch-like device for high-quality electrocardiogram recording. Parameter
Value
Physiological measurements
ECG (I, II, V5 leads), heart rate, heart rate variability activity (3-axes acceleration) 8 0.05 − 150 Hz 100 − 1700 24 bit 250 − 500 Hz 200 − 1000 Hz >2 Gb ≥ 1200 mAh >3 days Bio compatible, hypo-allergic ≤ 40 × 40 × 15 mm ≤ 85 g
Number of ECG channels Band-width Gain Ratio ADC Resolution Sampling Frequency Sampling rate of amplifier Memory capacity Battery capacity Monitoring time Adhesive Size of rigid part Weight
2.3. System specifications Selected components described in section 2.2 provide a system with parameters suitable for high quality signal acquisition. Table 1 summarizes the technical specifications of the system. With the 0.05–150 Hz bandwidth, 24-bit ADC resolution, 8 channels configuration and high sampling frequency, the design meets the requirements of the monitoring system. Over 3 Gb of memory storage, together with 1200 mAh battery capacity enable prolonged recording for more than 3 days. The assembled system records the ECG signal in
Fig. 3. Assembled printed circuit board (PCB) of proposed ECG-patch.
various lead selections, as well as the physical activity of the user. Heart rate and heart rate variability are derived from the acquired ECG waveform. Total weight of the current system, including battery, 3D printed case, circuitry board, the adhesive base with embedded gel 3
Acta Astronautica xxx (xxxx) xxx–xxx
N. Glazkova et al.
Fig. 4. (a) Developed ECG-prototype. (b) Prototype on a subject's chest.
Fig. 5. Snapshot of output of console. Fig. 6. ECG waveform obtained by the designed hardware.
significantly improves patients’ comfort compared to a standard Holter monitoring equipment. With the designed hardware we obtained vital signs, including realtime ECG data and real-time mobility data, displayed on the console in Fig. 5. The visual display also includes the hardware setup and telemetry status windows. The user may configure the leads in the corresponding channel selection field. On the basis of visual analysis, it can be seen in Fig. 5, that the specifications of the system are sufficient for providing high-quality recording. The ECG signal of a woman of 24-year old acquired from the assembled prototype with detected RR intervals is also shown in Fig. 6. The filtration of noise intrinsic to a wearable device is based on a smoothing algorithm described in Ref. [25]. Thus, the improved
electrodes, is 85 g. The dimensions of the rigid part are 40 × 40 × 15 mm. Such a relatively small and lightweight solution increases the level of comfort for an individual. 3. Wearable prototype for the ECG data acquisition The assembled system described in previous sections resulted in a prototype of an adhesive patch-like wearable miniaturized device for ECG data acquisition. Fig. 3 illustrates a manufactured PCB, comprising an instrumentation amplifier, a micro-controller, a memory circuit, a data transmission module and a power management circuit. The assembled system is shown in Fig. 4a and its position on the chest is presented in Fig. 4b, respectable. Such a cable-less design 4
Acta Astronautica xxx (xxxx) xxx–xxx
N. Glazkova et al.
instrumentation with high-quality data acquisition along with prolonged ECG monitoring has a high potential to be beneficial for aerospace and terrestrial applications.
1109/EMBC.2013.6611242. [8] P.F. Migeotte, J. Tank, N. Pattyn, I. Funtova, R. Baevsky, X. Neyt, G.K. Prisk, Three dimensional ballistocardiography: methodology and results from microgravity and dry immersion, 2011 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2011, pp. 4271–4274, , https://doi.org/10.1109/ IEMBS.2011.6091060. [9] P.F. Migeotte, S.D. Ridder, J. Tank, N. Pattyn, I. Funtova, R. Baevsky, X. Neyt, G.K. Prisk, Three dimensional ballisto- and seismo-cardiography: Hij wave amplitudes are poorly correlated to maximal systolic force vector, 2012 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2012, pp. 5046–5049. [10] P.F. Migeotte, Q. Delire, J. Tank, I. Funtova, R. Baevsky, X. Neyt, N. Pattyn, 3dballistocardiography in microgravity: comparison with ground based recordings, 2013 35th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBC, 2013, pp. 7012–7016. [11] M. Augelli, Cadmos: the French usoc. from a quarter century history to new prospects, 2018 SpaceOps Conference, 2018, p. 2519. [12] NASA, Human research facility holter monitor (holter). URL http://eea.spaceflight. esa.int/portal/exp/?id=9564. CNES, Everywear - a personal assistant for astronaut (cnes), http://eea.spaceflight. esa.int/portal/exp/?id=9564 [13] NASA, Human research facility holter monitor (holter). https://www.nasa.gov/ mission\_pages/station/research/experiments/614.html. [14] S. Lee, G. Ha, D. Wright, Y. Ma, Highly flexible, wearable, and disposable cardiac biosensors for remote and ambulatory monitoring, npj Dig. Med. 1 (2018) 1–8, https://doi.org/10.1038/s41746-017-0009-x. [15] S. Imani, A. Bandodkar, A. Vinu Mohan, R. Kumar, A wearable chemicalelectrophysiological hybrid biosensing system for real-time health and fitness monitoring, Nat. Commun. 7, 10.1038/ncomms11650. [16] K. Sohn, F. Merchant, O. Sayadi, D. Puppala, A novel point-of-care smartphone based system for monitoring the cardiac and respiratory systems, Sci. Rep. 7, 10. 1038/srep44946. [17] J. Steinberg, N. Varma, I. Cygankiewicz, ISHNE-HRS expert consensus statement on ambulatory ECG and external cardiac monitoring/telemetry, Heart Rhythm J. 14 (2017), https://doi.org/10.1016/j.hrthm.2017.03.038 (2017) e55–e96. [18] X. Yang, G. Liu, Y. Tong, H. Yan, The history, hotspots, and trends of electrocardiogram, J. Geriatr. Cardiol. 12 (2015) 448–456, https://doi.org/10.11909/j. issn.1671-5411.2015.04.018. [19] J. Hall, Textbook of Medical Physiology, twelfth ed., Saunders Elsevier, Philadelphia, PA, 978-1-4160-4574-8, 2011, pp. 143–153 section (Chapter 13): Cardiac Arrhythmias and Their Electrocardiographic Interpretation. [20] H.J. Guyton, C. Arthur, Textbook of Medical Physiology, Elsevier Science, 2015 (Ch. The Normal Electrocardiogram). [21] M.K. Delano, A Long Term Wearable Electrocardiogram (ECG) Measurement System, Master’s thesis Massachusetts Institute of Technology, USA, 2012http:// web.mit.edu/maggied/Public/finalthesisMKD.pdf. [22] Freescale Semiconductor, Inc., Wearable ECG Patch, Rev. 0, 08/2014 (08 2014). [23] Texas Instruments, ADS129x low-power, 8-channel, 24-bit analog front-end for biopotential measurements, Rev. (August 2015) 24–25 01 2010. [24] Texas Instruments, Mixed signal microcontroller, Rev. (December 2012) 15–17 06 2007. [25] T. Podladchikova, R. Van der Linden, A.M. Veronig, Sunspot number second differences as a precursor of the following 11-year sunspot cycle, Astrophys. J. 850 (2017) 81, https://doi.org/10.3847/1538-4357/aa93ef.
4. Discussion and conclusions In this study, we present a novel non-invasive, non-obtrusive and easy-to-use wearable ECG system for long-term ECG monitoring. We have developed a next generation prototype, i.e. a II lead ECG wearable biosensor, using off-the-shelf components only. This novel device is able to extract the ECG waveform in an energy efficient and simple way. The data gathered is stored on the memory card in the format which makes it accessible via a computer. Data visualization was performed through the MATLAB software tool kit. Basic analysis such as RR-peak localization, RR-interval calculation, irregular beat episodes identification was performed. With the proposed configuration of the system using off-the-shelf components, we see the opportunity to use it as a tool for diagnosis support of heart rhythm disorders, cardiovascular syncope and abnormal respiratory rate patterns. The developed device fills the gap between patient comfort and diagnostic value of measurements acquired by a wearable solution. Thia patch-like wearable device provides the opportunity to evaluate the cardiac health state during astronauts stay in space, during launch and landing, pre-flight training periods and post-flight rehabilitation. Besides, with the emergence of commercial spaceflight, medical examination will require a personalized approach. ECG-patch instrumentation solutions could be a part of the medical examination and documentation process of such individuals. The system may as well be applicable in sports medicine and regular clinical diagnostics and health monitoring. In fact, there is an ongoing trend in the development of clinical-grade wearable systems with prolonged monitoring capability for terrestrial applications. With the growth of clinically validated databases, such wearable devices also hold promise for integration into the healthcare system and therefore reshaping the clinical-patient interaction. Acknowledgements The authors are grateful to the Skoltech Translational Research and Innovation Program for the support of this research.
Natalia Glazkova has graduated from the Moscow Aviation Institute (MAI) with a specialist degree in aerospace biomedical life-support engineering. She received a Master degree from the Skolkovo Institute of Science and Technology in Engineering systems. Natalia also completed a year-abroad graduate study in the Department of Aeronautics and Astronautics in the Massachusetts Institute of Technology (MIT). Natalia's scientific interest lies in the field of interdisciplinary research associated with systems engineering of biomedical equipment in different applications.
References [1] E. Fung, M.-R. Jrvelin, R.N. Doshi, J.S. Shinbane, S.K. Carlson, L.P. Grazette, P.M. Chang, R.S. Sangha, H.V. Huikuri, N.S. Peters, Electrocardiographic patch devices and contemporary wireless cardiac monitoring, Front. Physiol. 6 (2015) 149, https://doi.org/10.3389/fphys.2015.00149. [2] R. Baevsky, I. Funtova, E. Luchitskaya, Jens, Microgravity: an ideal environment for cardiac force measuring, Cardiometry 3 (2013) 100–117, https://doi.org/10. 12710/cardiometry.2013.3.100117. [3] I. for Biomedical Problems, Cardiovector experiment. URL https://www.energia. ru/en/iss/researches/human/11.html. [4] Q. Deliere, P.F. Migeotte, X. Neyt, I. Funtova, R.M. Baevsky, J. Tank, N. Pattyn, Cardiovascular changes in parabolic flights assessed by ballistocardiography, 2013 35th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBC), 2013, pp. 3801–3804, , https://doi.org/10.1109/EMBC. 2013.6610372. [5] O.T. Inan, P.F. Migeotte, K.S. Park, M. Etemadi, K. Tavakolian, R. Casanella, J. Zanetti, J. Tank, I. Funtova, G.K. Prisk, M.D. Rienzo, Ballistocardiography and seismocardiography: a review of recent advances, IEEE J. Biomed. Heal. Inform. 19 (4) (2015) 1414–1427, https://doi.org/10.1109/JBHI.2014.2361732. [6] E. Luchitskaya, R. Baevsky, I. Funtova, J. Tank, Space experiment ”cardiovector” as a new step in the development of the method of ballistocardiography, Proceedings of the International Astronautical Congress, vol. 1, IAC, 2013, pp. 52–55. [7] E. Luchitskaya, Q. Deliere, A. Diedrich, N. Pattyn, A. Almorad, L. Beck, P. Gauger, U. Limper, I. Funtova, R.M. Baevsky, P.F. Migeotte, J. Tank, Timing and source of the maximum of the transthoracic impedance cardiogram (dz/dt) in relation to the h-i-j complex of the longitudinal ballistocardiogram under gravity and microgravity conditions, 2013 35th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBC, 2013, pp. 7294–7297, , https://doi.org/10.
5
Acta Astronautica xxx (xxxx) xxx–xxx
N. Glazkova et al. Dr. Tatiana Podladchikova is assistant professor at the Skolkovo Institute of Science and Technology, Russia. Her area of scientific research is solar-terrestrial physics, space weather forecasting for mitigation of space weather hazards, as well as development of advanced data analysis techniques for the extraction of useful knowledge, control and forecasting in interdisciplinary applications (biomedicine, navigation). In 2015 Dr. Podladchikova was awarded with the International Alexander Chizhevsky medal for Space Weather and Space Climate.
Daria Stepanova received her bachelor degree in system control from the Bauman Moscow State Technical University. Then she continued with her masters studies at the Skolkovo Institute of Science and Technology and graduated with a degree in data analysis. Daria completed a year-abroad exchange program in Ecole Polytechnique Federale de Lausanne (EPFL). Additionally Daria graduated from the Moscow Institute of Physics and Technology with a Master degree in mathematical modeling and mathematical physics.
Prof. Dr. Rupert Gerzer is a medical doctor by education, whose scientific interests lie in medicine, life sciences and astronautics. Prior to his position at Skoltech as a Provost, he was Professor and Chairman at the Institute of Aerospace Medicine (Aachen University) and Director of the Institute of Aerospace Medicine, German Aerospace Center DLR (Cologne) Western Europes largest civil institute of aerospace medicine. Prof. Gerzer published more than 250 scientific papers and received the Life Science Award of the International Academy of Astronautics in 2003.
6