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PORTABLE TELEMETRY BREATHING AND HEART MONITORING SYSTEM
Swetha Seshu Nagaprasad Ayyagari
B.E., Pune University, India,2007
Pritam Rajendra Chopda
B.E., Pune University, India,2007
PROJECT
Submitted in partial satisfaction of
the requirements for the degrees of
MASTER OF SCIENCE
in
ELECTRICAL AND ELECTRONIC ENGINEERING
at
CALIFORNIA STATE UNIVERSITY, SACRAMENTO
FALL
2011
PORTABLE TELEMETRY BREATHING AND HEART MONITORING SYSTEM
A Project
by
Swetha Seshu Nagaprasad Ayyagari
Pritam Rajendra Chopda
Approved by:
__________________________________, Committee Chair
Warren D. Smith, Ph.D.
__________________________________, Second Reader
B. Preetham Kumar, Ph.D.
____________________________
Date
ii
Students:
Swetha Seshu Nagaprasad Ayyagari
Pritam Rajendra Chopda
I certify that these students have met the requirements for format contained in the University format
manual, and that this project is suitable for shelving in the Library and credit is to be awarded for the
project.
___________________________, Department Chair ___________________
Suresh Vadhva, Ph.D.
Date
Department of Electrical and Electronic Engineering
iii
Abstract
of
PORTABLE TELEMETRY BREATHING AND HEART MONITORING SYSTEM
by
Swetha Seshu Nagaprasad Ayyagari
Pritam Rajendra Chopda
A sudden unexpected death during epilepsy (SUDEP) can occur to an unattended epilepsy
sufferer. The cessation of heart and breathing activity is associated with SUDEP. Therefore, developing
a heart and breathing monitoring system that could alarm when an epilepsy patient experiences cessation
of heart or breathing activity is necessary. This system will assist healthcare providers to respond to the
emergency and prevent sudden death. This collaborative project is to investigate the feasibility of
developing a miniature, unobtrusive, and self-contained module that an epilepsy patient could wear in
bed and a small bedside alarm unit intended to alert healthcare providers to prevent SUDEP. The
wearable unit communicates wirelessly occurrences of breaths and heartbeats to the bedside unit. The
bedside unit alerts upon cessation of heart or breathing activity.
This project assumed that the monitor receives an input voltage from a small strip of
piezoelectric film made of polyvinylidine fluoride (PVDF) attached to the patient’s chest. The PVDF
sensor voltage changes in response both to the chest expansion and contraction of breathing and to the
chest vibrations caused by heartbeats. In the first stage of this project, human subject recordingsof
PVDF, strain-gauge plethysmography (SPG),and photoplethysmography (PPG) signals were analyzedto
determine how to design the signal processing needed to separate out individual breathing and heartbeat
signals. Then, low-power analog, microcontroller, and wireless technologies were used to build a
prototype of the wearable module to separate out the breathing and heartbeat signals, detect individual
breaths and heartbeats, and telemeter the detected breaths and heartbeats to the bedside unit. A
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prototypeof the bedside unit was built using similar technologies to receive the occurrences of heartbeats
and breaths from the wearable module. This unit also calculates heart and breathing rates and
determineswhether or not to alarm if breaths or heartbeats cease or the wireless link fails to function. For
convenience, the wearable module and bedside unit were prototyped using bread-boarded circuitry and
commercial development boards containing the miniature electronic components. Once feasibility is
shown, the wearable module and bedside unit can be compacted by incorporating the miniature
electronic components directly into custom integrated circuits. The performance of the signal processing
algorithm to separate out breathing and heartbeat signals and to detect individual breaths and heartbeats
was tested by using the algorithm to process PVDF recordings from human subjects and comparing the
results with SPG recordings of breaths and PPGrecordings of heartbeats from the same human subjects.
Miss Swetha Seshu Ayyagari designed the hardware for the signal conditioning circuit and the software
for digital signal processing to separate out the breathing and heartbeat signals from the PVDF signal.
Mr. PritamRajendraChopda designed the software to detect individual breaths and heartbeats, transmit
detected breaths and heartbeats to the bedside unit, calculate heart and breathing rate, and alert upon
cessation of heartbeats or breathing or wireless link failure.
Prototypes were successfully built of the wearable module and bedside unit. The prototype
wearable module was capable of processing an incoming PVDF signal, separating out breathing and
heartbeat signals, detecting individual breaths and heartbeats, and wirelessly transmitting them to the
bedside unit. The prototype bedside unit was capable of alarming if breaths or heartbeats stopped or if
the wireless link failed. On six 22-s PVDF recordings, percentage of peaks correctly detectedas breaths
(true positive) is 64%, and the percentage of peaks falsely detectedas breaths (false positive) is 0%. On
six 22-s PVDF recordings,percentage of peaks correctly detected as heartbeats (true positive) is 80%,and
the percentage of peaks falsely detected as heartbeats (false positive) is 4%. No attempt was made in the
prototype system to adapt to changing PVDF signal amplitudes from subject to subject. Such adaptation
is needed before the monitoring system is useful for actual patients. No measurements were
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made of the power consumption of the wearable module electronics. Therefore, at present, battery size to
achieve a given operating time is not known. No measurements were made of whether the wireless link
successfully functions when the wearable module was worn by a sleeping subject changing position in
bed. Such studies need to be done to determine if the monitoring system will work in actual home
settings.
__________________, Committee Chair
Warren D. Smith, Ph.D.
vi
ACKNOWLEDGMENTS
We would like to take this opportunity to thank our families, friends, employers, professors, and
Dr. Warren D. Smith for their continued support and encouragement in completing our education.
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TABLE OF CONTENTS
Page
Acknowledgments ................................................................................................................................. vii
List of Tables ......................................................................................................................................... xi
List of Figures ....................................................................................................................................... xii
Chapter
1. INTRODUCTION ............................................................................................................................. 1
2. BACKGROUND .............................................................................................................................. 3
2.1. Approach ................................................................................................................................. 3
2.2. Review of software used for the development ......................................................................... 3
2.3. Review of wireless protocol .................................................................................................... 4
2.3.1. Wireless Fidelity ............................................................................................................. 4
2.3.2. Bluetooth.......................................................................................................................... 4
2.3.3. ZigBee ............................................................................................................................ 4
2.4. Hardware board review ........................................................................................................... 5
2.4.1. Microcontroller experimenter’s board ............................................................................ 5
2.4.2. ZigBee transceiver .......................................................................................................... 6
2.4.3. Emulation tool ................................................................................................................. 7
2.5. Review of MSP430FG4618 microcontroller and its peripherals ............................................. 8
2.5.1. Memory map ................................................................................................................... 8
2.5.2. Clock module .................................................................................................................. 8
2.5.3. Low power options .......................................................................................................... 9
2.5.4. Timer .............................................................................................................................. 9
2.5.5. USART peripheral interface ........................................................................................... 9
2.5.6. Supply voltage supervisory circuit ................................................................................ 11
2.5.7. Interrupts ....................................................................................................................... 11
2.5.8. LCD controller .............................................................................................................. 12
2.5.9. ADC12 module ............................................................................................................. 12
2.5.10. Hardware multiplier .................................................................................................... 13
3. METHODOLGY ............................................................................................................................ 15
3.1. Development flow ................................................................................................................. 15
3.2. Analysis of PVDF signal ....................................................................................................... 15
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3.3. Design methodology ............................................................................................................. 16
3.3.1. Selection of hardware and wireless protocol ................................................................ 16
3.3.2. Design methodology for hardware ............................................................................... 16
3.3.3. Design methodology for software ................................................................................ 16
3.4. Testing methodology ........................................................................................................... 16
3.4.1. Digital filter testing ...................................................................................................... 16
3.4.2. Extraction and detection of breathing and heartbeats .................................................. 16
3.4.3. Telemetric alert mechanism ......................................................................................... 17
3.4.4. Communication failure ............................................................................................... 17
4. RESULTS ........................................................................................................................................ 18
4.1. Data analysis ......................................................................................................................... 18
4.2. Hardware structure ................................................................................................................ 19
4.3. Signal conditioning circuit..................................................................................................... 31
4.3.1. Amplifier circuit ............................................................................................................ 31
4.3.2. Switched capacitor low-pass anti-aliasing filter ......................................................... 32
4.3.3. Passive low-pass filter ................................................................................................... 32
4.4. Software structure .................................................................................................................. 34
4.5. Software description ............................................................................................................. 35
4.5.1. Configuration of clock ................................................................................................. 35
4.5.2. Configuration of Timer_A ........................................................................................... 37
4.5.3. Configuration of A/D converter ................................................................................... 38
4.5.4. Digital signal processing .............................................................................................. 39
4.5.5. Breath threshold detector ............................................................................................... 39
4.5.6. Heartbeat threshold detector .......................................................................................... 42
4.5.7. Data transmission ......................................................................................................... 46
4.5.8. Supply voltage monitor ................................................................................................ 46
4.5.9. Calculation of breathing and heart rates ...................................................................... 48
4.5.10. Alarm unit .................................................................................................................... 51
4.6. Testing results.. ....................................................................................................................... 51
4.6.1. Signal conditioning circuit ............................................................................................. 51
4.6.2. Signal processing ........................................................................................................... 57
4.6.3. Breath detector test ........................................................................................................ 61
4.6.4. Heartbeat detector test ................................................................................................... 65
5. LIMITATIONS ............................................................................................................................... 72
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6. SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS .................................................. 74
6.1. Summary ................................................................................................................................ 74
6.2. Conclusions ............................................................................................................................ 75
6.3. Recommendations .................................................................................................................. 75
Appendix A.MATLAB code for data analysis of PVDF recordings ..................................................... 77
Appendix B.C program for microcontroller in the wearable module ..................................................... 80
Appendix C.C program for microcontroller in the bedside unit............................................................. 97
Appendix D.MATLAB code for generating the coefficients and plotting the magnitude
response 102
Appendix E.Filter coefficients for the low-pass and band-pass filters ................................................. 103
Appendix F.MATLAB code for testing the digital filters .................................................................... 105
Appendix G. Plots of digital signal processing ................................................................................... 111
References ........................................................................................................................................... 126
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LIST OF TABLES
1. Table 1. Wireless protocol comparison ............................................................................................. 5
2. Table 2.Low power modes ............................................................................................................... 10
3. Table 3.Timer operation modes ....................................................................................................... 10
4. Table 4.A/D converter operation modes .......................................................................................... 12
5. Table 5.Hardware multiplier operation modes ................................................................................. 13
6. Table 6.Hardware multiplier RESHI modes .................................................................................... 13
7. Table 7. Hardware multiplier SUMEXT modes ............................................................................. 14
8. Table 8.Summary of fundamental frequencies and harmonics for Subject 1 ................................... 31
9. Table 9. Time intervals between adjacent peaks of a heartbeat for Subject 1 ................................. 31
10. Table 10.Testing results of switched capacitor low-pass anti-aliasing filter ................................... 57
11. Table 11.Output of low-pass filter for Subject 1 and Subject 2 ...................................................... 61
12. Table 12.Output of band-pass filter for Subject 1 and Subject 2 .................................................... 62
13. Table 13.Results of breathing threshold detector for Subject 1...................................................... 63
14. Table 14. Results of breathing threshold detector for Subject 2.................................................... 63
15. Table 15.Results of breathing threshold detector for Subject 3...................................................... 64
16. Table 16. Results of breathing threshold detector for Subject 4.................................................... 64
17. Table 17.Results of breathing threshold detector for Subject 5...................................................... 64
18. Table 18. Results of breathing threshold detector for Subject 6.................................................... 64
19. Table 19.Summary ofbreathing threshold detector for six subjects .............................................. 65
20. Table 20.Results of heartbeat threshold detector for Subject 1 ..................................................... 66
21. Table 21. Results ofheartbeat threshold detector for Subject 2 .................................................... 67
22. Table 22.Results of heartbeat threshold detector for Subject 3 ..................................................... 68
23. Table 23. Results of heartbeat threshold detector for Subject 4 ................................................... 69
24. Table 24.Results of heartbeat threshold detector for Subject 5 ...................................................... 70
25. Table 25. Results of heartbeat threshold detector for Subject 6 .................................................... 71
26. Table 26.Summary of heartbeat threshold detector for six subjects ............................................... 71
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LIST OF FIGURES
1. Figure 1.MSP430FG4618/F2013 Experimenter’s Board ................................................................... 6
2. Figure 2. CC2500EMK Evaluation Module 2.4 GHz ......................................................................... 7
3. Figure 3. MSP-FET430UIF module .................................................................................................. 7
4. Figure 4. USART master and external slave configuration .............................................................. 11
5. Figure 5. Development flow ............................................................................................................. 15
6. Figure 6. Flowchart for MATLAB program for data analysis ......................................................... 19
7. Figure 7. Time domain plot of PVDF signal for Subject 1 ............................................................. 21
8. Figure 8.Frequency domain plot of PVDF signal for Subject 1 ....................................................... 22
9. Figure 9.Frequency domain plot of SPG signal for Subject 1 .......................................................... 23
10. Figure 10.SPG frequency plot with fundamental frequency and harmonics for Subject 1 ............ 24
11. Figure 11.Frequency domain plot of PPG signal for Subject 1 ...................................................... 25
12. Figure 12.PPG frequency plot with fundamental frequency and harmonics for Subject 1 ............ 26
13. Figure 13.Frequency plot of PVDF signal identifying the peaks for Subject 1.............................. 27
14. Figure 14. Frequency domain plot showing PVDF, PPG, and SPG signals for Subject 1 ............. 28
15. Figure 15. Time domain plot of PVDF signal from 7 s to 10 s corresponding to
one heartbeat for Subject 1. ........................................................................................................... 29
16. Figure 16. Frequency domain plot of PVDF signal in the range 8 Hz to 40 Hz
corresponding to heart signal for Subject 1. .................................................................................. 30
17. Figure 17.Design of non-inverting amplifier circuit using LMC6482 ........................................... 33
18.Figure 18. Circuit schematic of switched capacitor low-pass anti-aliasing filter ............................. 34
19. Figure 19.Circuit schematic of passive low-pass filter .................................................................. 34
20. Figure 20. Flowchart of main program for wearable module’s microcontroller (MCU1) ........... 36
21. Figure 21. Flowchart of main program for bedside unit’s microcontroller (MCU2) ................... 37
22. Figure 22.Method for calculating sample and hold time (tsample) .................................................... 38
23. Figure 23. Design procedure for required digital filter frequency response. ................................. 40
24. Figure 24. Low-pass digital filter frequency response with a cut-off frequency of 0.8 Hz .......... 41
25. Figure 25. Frequency response of band-pass filter with lower cut-off frequency at 8 Hz and
upper cut-off frequency at 40 Hz ............................................................................................. 42
26. Figure 26.Flowchart for digital filter implementation in the microcontroller ................................ 43
27. Figure 27. Flowchart for breath threshold detector ....................................................................... 44
28. Figure 28. Flowchart for heartbeat threshold detector .................................................................. 45
29. Figure 29.Flowchart for data transmission ..................................................................................... 47
30. Figure 30.Flowchart for supply voltage supervisor ........................................................................ 48
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31. Figure 31. Flowchart for the CC2500 interrupt for MCU2 (continued to Figure 33) ................... 49
32. Figure 32.Flowchart for the CC2500 interrupt for MCU2 (continued from Figure 32) ................. 50
33. Figure 33. Flowchart for the alarm unit ....................................................................................... 52
34. Figure 34.Plot verifying input voltage of -20 mV to +20 mV and output voltage
of 0 V to 3 V of amplifier circuit ................................................................................................... 53
35. Figure 35. Plot of closed loop frequency response of amplifier circuit verifying gain of
75 for minimum frequency response of 0 Hz to 50 Hz .......................................................................... 54
36. Figure 36. Input signal (-20 mV to +20 mV) to the amplifier circuit ............................................ 55
37. Figure 37.Output signal (0 V to 3 V) of amplifier circuit. ............................................................. 55
38. Figure 38.Plot of frequency response of passive low-pass filter circuit with output
voltage = 0.024 V at 4.8 kHz for an input voltage of 1 V ...................................................................... 56
39. Figure 39.Signal conditioning circuit implemented on a prototype board ..................................... 56
40. Figure 40. Time domain plot of PVDF signal for Subject 1 ......................................................... 58
41. Figure 41.Time domain plot of SPG signal for Subject 1 .............................................................. 59
42. Figure 42. Time domain plot of PPG signal for Subject 1 ............................................................ 59
43. Figure 43.Time domain plot of breathing signal in the PVDF signal for Subject 1 ....................... 60
44. Figure 44.Time domain plot of heart signal in the PVDF signal for Subject 1 .............................. 60
45. Figure G.1. Time domain plot of PVDF signal for Subject 1 ..................................................... 111
46. Figure G.2. Time domain plot of SPG signal for Subject 1 ........................................................ 111
47. Figure G.3. Time domain plotof PPG signal for Subject 1 ........................................................ 112
48. Figure G.4. Output of the low-pass filter that represents the breathing signal in the PVDF
signal for Subject 1 ................................................................................................. 112
49. Figure G.5.Output of the band-pass filter that represents the heart signal in the PVDF
signal for Subject 1 ................................................................................................. 113
50. Figure G.6. Time domain plot of PVDF signal for Subject 2 ..................................................... 113
51. Figure G.7. Time domain plot of SPG signal for Subject 2 ....................................................... 114
52. Figure G.8. Time domain plotof PPG signal for Subject 2 ........................................................ 114
53. Figure G.9. Output of the low-pass filter that represents the breathing signal in the PVDF
signal for Subject 2 ................................................................................................. 115
54. Figure G.10. Output of the band-pass filter that represents the heart signal in the PVDF
signal for Subject 2 ................................................................................................. 115
55. Figure G.11. Time domain plot of PVDF signal for Subject 3 ................................................... 116
56. Figure G.12. Time domain plot of SPG signal for Subject 3 ..................................................... 116
57. Figure G.13. Time domain plot of PPG signal for Subject 3 ..................................................... 117
58. Figure G.14. Output of the low-pass filter that represents the breathing signal in the PVDF
signal for Subject 3 ................................................................................................. 117
59. Figure G.15. Output of the band-pass filter that represents the heart signal in the PVDF
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signal for Subject 3 ................................................................................................. 118
60. Figure G.16. Time domain plot of PVDF signal for Subject 4 .................................................. 118
61. Figure G.17. Time domain plot of SPG signal for Subject 4 ...................................................... 119
62. Figure G.18. Time domain plot of PPG signal for Subject 4 ..................................................... 119
63. Figure G.19. Output of the low-pass filter that represents the breathing signal in the PVDF
signal for Subject 4 ................................................................................................. 120
64. Figure G.20. Output of the band-pass filter that represents the heart signal in the PVDF
signal for Subject 4 ................................................................................................. 120
65. Figure G.21. Time domain plot of PVDF signal for Subject 5 .................................................. 121
66. Figure G.22. Time domain plot of SPG signal for Subject 5 ..................................................... 121
67. Figure G.23. Time domain plotof PPG signal for Subject 5 ...................................................... 122
68. Figure G.24. Output of the low-pass filter that represents the breathing signal in the PVDF
signal for Subject 5 ................................................................................................. 122
69. Figure G.25. Output of the band-pass filter that represents the heart signal in the PVDF
signal for Subject 5 .................................................................................................. 123
70. Figure G.26. Time domain plot of PVDF signal for Subject 6 ................................................... 123
71. Figure G.27. Time domain plot of SPG signal for Subject 6 ...................................................... 124
72. Figure G.28. Time domain plot of PPG signal for Subject 6 ...................................................... 124
73. Figure G.29. Output of the low-pass filter that represents the breathing signal in the PVDF
signal for Subject 6 .................................................................................................. 125
74. Figure G.30. Output of the band-pass filter that represents the heart signal in the PVDF
signal for Subject 6 .................................................................................................. 125
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