From Institute for Signal Processing Director: Prof. Dr. -Ing. Alfred Mertins Applications of textile based capacitive ECG recordings Dissertation for Fulfillment of Requirements for Doctoral Degree of the University of Luebeck - from the Dept. of Informatics/Technology Submitted by Bhavin Chamadiya Born in Porbandar, India Luebeck, May 2012. 1. Berichterstatter : Prof. Dr. Ulrich G. Hofmann 2. Berichterstatter : Prof. Dr. Hartmut Gehring Tag der mündlichen Prüfung: 24.09.2012 Zum druck genehmigt. Lübeck, den 28.09.2012 Bhavin Chamadiya Doctoral Student Institute for Signal Processing University of Luebeck Ratzeburger Allee 160, 23538, Luebeck Germany To Maa & Bapa (grandma and grandpa) Acknowledgement This doctoral work has been most significant academic challenge for me till now. It would not have finished without the help of some people so I would like to take the opportunity to express my sincere gratitude to some of them here. First and foremost, I am extremely grateful to Mr. Manfred Wagner for giving me this opportunity and to support me throughout the work. He has incubated me fascination and vision for research work as well as non-technical aspects of it. My most sincere gratitude goes to my academic supervisor Prof. rer. Nat. Ulrich G. Hofmann for his encouragement, support, advising and guidance during my entire PhD work. He taught me academic research methodology and scientific writing, what was absolutely essential doing my thesis in Daimler AG, without these, my PhD work would not have been possible. His feedbacks in all my papers and this thesis were thoroughly important and invaluable. A very special thanks to my friend Jörg Mahrle for his advices and translation help and to Mr. Martin Spieth for teaching and sharing with me his vast practical laboratory experience. I would like to thank all my colleagues at Research and Development, Daimler AG, Böblingen, specially Dr. Wolfgang Wondrak, Mr. Rolf Kleinheyer, Mathias Baumann and Ms. Minja Gamerdinger. It has been a great privilege, honor and life changing to spend several years with you guys. I also thank my friend Kunal Mankodiya for his assistance and some interesting interactions during this research work. I owe a lot to my parents and my grandparents, who always encouraged me and supported me unconditionally in every situation of my life. I am very much indebted to my wife, who supported me in every possible manner to see the completion of this work. This moment, I owe great gratitude to Dr. A. P. J. Abdul Kalam and all other heroes who are remarkably inspiring to us in our society and being driven force behind many successes. Abstract The average age of the population is continuously on the rise in several developed countries. This aging population increases the in-advance chronic illnesses and therefore raises the need of permanent health monitoring. One of the major chronic illnesses around the world is in this context cardiovascular diseases. Hence monitoring of heart activity in various environments might prove a beneficial tool to keep track of the state of the heart. The usual way of monitoring the heart, like ECG with wet electrodes with wires and Holter monitoring, are not comfortable at times, even they need special preparation and observation. These conventional methods are even impractical in some environments like wheelchairs (in home and hospital) and automobiles. In this case the possibility of measuring the heart activity without any direct contact to the body may be a useful but an nascent tool. These systems can improve patients’ life greatly in hospital and home by providing free mobility and comfort while being monitored. Measurement in an automobile supports comfort as well as safety features. It can be used to measure the ECG of the driver and consequently enables the possibility to judge driving fitness of the driver, which may help to improve the safety of the occupants. The aim of this study is to show the feasibility of a broader monitoring concept by monitoring contactlessly vital signs with sensors embedded in various environments like Home, Hospital and Automotive. A capacitively (non-contact) coupled ECG (CCECG) system is developed with PCB (stiff) electrodes as pilot work. Subsequently, this system is transformed into a flexible and textile form to enable the possibility of incorporating such systems in various setups. First, the system was implemented by reassembling prior work with a two layer capacitive textile electrode and Starflex PCB structures. A Final version with a three layer capacitive textile electrode and a compact PCB was implemented while trying different capacitive textile electrode designs. Various analog techniques like guarding, shielding, movement compensation were implemented to improve performance of the electronics. Analog and digital signal processing tool was applied to minimize noises and artifacts. The CCECG system was integrated in setups like a car’s, wheel chairs, a clinical bed and a stretcher to analyze the feasibility study and system performance. Some subjects were tested with the setups to gain short term and long term measurements. Standard ECG analysis like QRS-complex detection and heart rate variability (HRV) were performed to assess the quality of the signals in the experimental setups. Integration of the system into an automobile was very crucial as the work was part of a German ministry funded “INSITEX” project. Both the system with two layer and three layer structures were tested in our demonstrator seat in the laboratory. Finally real world tests in an Automobile, Mercedes Benz C-class (W204 Series) were performed by integrating the CCECG system into its car seat. Various measurements were carried out by considering real life aspects like driving in highway or city street surfaces. The influence of car seat functions, like seat movements, heating and ventilation, on the measurements was examined. Measurements were also performed by switching on various car systems, like GPS, radio, and hands-free telephony, to observe their influence on the signal. Lastly, measurements with various climatic clothes like rain jackets, winter jackets and sport coats were carried out on the same subject to find out their effect on the measurements. Contents Contents Acknowledgement Abstract Contents 1 Introduction 1 1.1 Motivation ................................................................................................... 1 1.2 The INSITEX Project .................................................................................. 4 1.3 Scope of the thesis ..................................................................................... 8 2 Theoretical Background ...................................................................................... 11 2.1 Cardio-vascular system ............................................................................ 11 2.1.1 Anatomy of heart ........................................................................... 11 2.1.2 ECG generation from heart ............................................................ 13 2.1.3 Body surface potential mapping ..................................................... 15 2.1.4 Volumetric conduction ................................................................... 16 2.2 Electrocardiography .................................................................................. 20 2.3 Capacitor .................................................................................................. 22 2.3.1 Parallel plate capacitor .................................................................. 23 2.3.2 Capacitor with more dielectric materials ........................................ 25 2.4 Various ECG electrodes ........................................................................... 27 2.4.1 Voltage divider ............................................................................... 27 2.4.2 Wet electrodes ............................................................................... 29 2.4.3 Dry electrodes ................................................................................ 31 2.4.4 Capacitive electrode ...................................................................... 31 2.5 Modeling and Simulation Tools ................................................................ 32 2.5.1 Protel (Altium designer) ................................................................. 32 2.5.2 Cadence Pspice ............................................................................. 33 2.5.3 MATLAB ........................................................................................ 33 2.5.4 Simulink ......................................................................................... 33 2.5.5 LabVIEW ........................................................................................ 33 3 Capacitive Electrocardiography ........................................................................... 37 3.1 State of the art .......................................................................................... 38 3.2 Capacitive Coupling .................................................................................. 39 3.3 Impedance matching and the signal ......................................................... 41 3.3.1 Bandwidth considerations .............................................................. 42 3.3.2 Impedance of the input stage ......................................................... 43 3.3.3 Contact Impedance ........................................................................ 45 i Contents 3.3.4 Ultra High input Impedance Amplifier ............................................ 46 3.4 Signal Conditioning ................................................................................... 49 3.4.1 Baseline and DC removal .............................................................. 49 3.4.2 Differential amplification ................................................................. 49 3.4.3 Anti-aliasing ................................................................................... 50 3.4.4 Digital Signal Processing ............................................................... 50 3.5 Artifacts .................................................................................................... 57 3.5.1 Movement artifacts ........................................................................ 57 3.5.2 Power line and common mode noises ........................................... 62 4 CCECG System Implementation ......................................................................... 70 4.1 Hardware CCECG System ....................................................................... 70 4.1.1 Capacitive electrode ...................................................................... 70 4.1.2 Electronics Unit .............................................................................. 71 4.1.3 PCB CCECG Electrode module ..................................................... 71 4.2 1st Generation Textile CCECG System ..................................................... 74 4.2.1 Textile Capacitive electrode ........................................................... 74 4.2.2 Flexible Electronics Unit (Star-flex) ................................................ 76 4.2.3 1st Generation textile CCECG module ........................................... 77 4.3 2nd Generation Textile CCECG System .................................................... 78 4.3.1 Textile Capacitive electrode ........................................................... 78 4.3.2 Buffer Module ................................................................................ 80 4.3.3 2nd Generation textile CCECG module .......................................... 81 5 Various Measurement Environments .................................................................. 83 5.1 Driving Environment ................................................................................. 83 5.1.1 Textile CCECG Systems in Lab ..................................................... 85 5.1.2 Textile Capacitive ECG system in Car ........................................... 90 5.2 Hospital Environment ............................................................................... 98 5.2.1 Clinical Bed .................................................................................... 98 5.2.2 Stretcher ...................................................................................... 108 5.3 Home environment ................................................................................. 111 5.3.1 Wheel Chair ................................................................................. 112 6 Conclusion and outlook ..................................................................................... 120 6.1 Conclusion .............................................................................................. 121 6.1.1 Driving Environment .................................................................... 122 6.1.2 Hospital Environment ................................................................... 123 6.1.3 Home Environment ...................................................................... 124 6.2 Outlook ................................................................................................... 124 6.2.1 Driving Environment .................................................................... 125 6.2.2 Hospital Environment ................................................................... 125 6.2.3 Home Environment ...................................................................... 126 Publications ….. …………………………………………………………………………...127 List of Abbreviations ............................................................................................... 129 List of Figures ………… .......................................................................................... 131 ii Contents Appendix I : Textile electrodes .......................................................................... 127 I.1 Various versions of the textile electrodes ............................................... 135 Appendix II : Components .................................................................................. 138 Appendix III : Layouts and PCB Designs ............................................................ 139 III. 1 Electrode ................................................................................................ 139 III.1.1 Stiff PCB CCECG electrodes ........................................................ 139 III.2 Electronic circuit ...................................................................................... 140 III.2.1 Pilot Stiff electrodes PCB CCECG System ................................... 140 III.2.2 1st Generation of the textile CCECG System ............................... 141 III.2.2 2nd Generation of the textile CCECG System ............................. 142 III.3 Seat driven circuit .................................................................................... 143 III.3.1 Circuit Schematics ........................................................................ 143 Appendix IV : Simulations ................................................................................... 144 IV.1 Simulink................................................................................................... 144 IV.2 Pspice ..................................................................................................... 145 Appendix V : LabVIEW programming ................................................................. 146 Appendix VI : Biosensor Integrated Steering wheel ............................................ 148 VI.1 Biosensor integrated Steering wheel ....................................................... 148 VI.1.1 Electrocardiography and Electro-dermal Activity ......................... 148 VI.1..2 Pulse oximetry ............................................................................ 150 VI.1.3 Skin temperature ......................................................................... 150 VI.1.4 Sensor integrated Steering wheel ............................................... 151 VI.2 Steering Wheel ........................................................................................ 152 VI.2.1 Reference study .......................................................................... 155 iii Chapter 1: Introduction 1 Introduction 1.1 Motivation D.Kirk’s demographic transition theory is a model to represent demographic changes from high birth rates and death rates to low birth rates and death rates as a nation progresses from a pre-industrialized to an industrialized economic system [1]. Hence it suggests a higher aging society in the developed world than the underdeveloped world. This observation is also evident in present demographic situations in many developed countries, where the aging society is on the rise. Figure 1.1 Current and Projected population of Germany by 2050 [4]. According to a study, between 2004 and 2050 in Europe, the elderly population, aged 65+, will rise sharply by 58 million (77 %) and the fastest growing segment of the population will be the very old (aged 80+) [2]. The population of Germany alone, will be expected to fall by 12 million by 2050, while those who remain will be old, half of the aged will be over 51 [3]. Figure 1.1 graphs current (2010) and projected populations of Germany by 2050 by federal statistical office of Germany (Statistisches Bundesamt) [4]. 1