Download Synchronous Pacemakers

Lecture Course
Failure diagnosis for cardiac
pacemakers using Petri nets
Samuel Yang (楊善國)
Professor
National Chin Yi University of Technology
(勤益科技大學機械工程系教授)
Contents
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Introduction
Definition of Reliability
Frequently Used Methods for Failure Analysis
Failure Analysis for pacemakers by Petri Nets
References
Introduction
 A failure is defined as any change in the shape,
size,or material properties of a structure,
machine, or component that renders it unfit to
carry out its specified function adequately.
 For the purpose of reliability assurance, failures
of a system need to be traced and analyzed,
especially for safety devices such as cardiac
pacemakers.
Reliability
Definition:
The probability that an item (a part, a device, a subsystem,
or a system) will carry out its required performance under
specified conditions for a stated time period.
Key factors:
 Specified conditions
 Required performance
 Stated time period
 Probability
Therefore,
Reliability and failure are closely related.
Frequently Used Methods for
Failure Analysis
 Fault Tree Analysis (FTA)
 Failure Modes and Effects Analysis (FMEA)
 Failure Modes, Effects and Criticality
Analysis (FMECA)
 Petri Net Method
Pacemaker
The principal pathologic conditions in which
cardiac pacemakers are applied are known
collectively as heart block (Arrhythmia),
i.e.
the heart of an arrhythmic patient is not
stimulated at a proper rate on its own.
Pacemaker
A cardiac pacemaker is an electric stimulator that produces
periodic pulses that are conducted to electrodes located in the
heart so as to cause it to contract.
 Constant-voltage amplitude pulses are typically in the range of
5.0 to 5.5V with duration of 500 to 600 μs.
 Constant-current amplitude pulses are typically in the range of 8
to 10 mA with pulse durations ranging from 1.0 to 1.2 ms.
 Rates for a synchronous pacemaker range from 70 to 90 beats per
minute (bpm).
Pacemaker
According to the control algorithms,
pacemakers can be classified to:
Asynchronous: Fixed pulse-rate regardless of the body condition
Synchronous: Functioning intermittently as required
1.Demand
2.Atrial
3.Combined
Rate-responsive: Triggered according to the actual demand
Asynchronous Pacemakers
Power
Supply
Oscillator
Pulse Generator
Pulse Output
Circuit
Electrodes
Synchronous Pacemakers
－Demand
Demand: Providing function when it is needed
Power
Supply
Oscillator
Reset
Circuit
Pulse Output
Circuit
Amplifier
Electrodes
Synchronous Pacemakers
－Atrial
Artial
Electrode
V1
Amplifier
Gate
V4
Monostable
Multi-vibrator
500ms delay
Monostable
Multi-vibrator
120ms delay
V2
Monostable
Multi-vibrator
2ms delay
V3
Output
Circuit
Ventricular
Electrode
Synchronous Pacemakers
－Combined
Power
Supply
Reset
Circuit
Amplifer
#1
V3
Atrial
Electrode
V1
Amplifer
#2
Gate
V4
Monostable
Multi-vibrator
500ms delay
Ventricular
Electrode
Pulse Output
Circuit
Oscillator
Monostable
Multi-vibrator
120ms delay
V2
Monostable
Multi-vibrator
2ms delay
Synchronous Pacemakers
－Rate-responsive
Sensor
Controller
Control
Algorithm
Oscillator
Pulse Output
Circuit
Electrodes
Physiological variables and the corresponding
sensors for rate-responsive pacemakers
Physiological Variable
Sensor
Right-ventricle blood temperature
Thermistor
ECG stimulus-to-T-wave interval
ECG electrode
ECG R-wave area
ECG electrode
Blood pH
Electrochemical pH electrode
Rate of change of
right-ventricle pressure
Semiconductor strain-gage
Venous blood oxygen saturation
Optical oximeter
Intracardiac volume changes
Electric-impedence
plethysmography (intracardiac)
Respiratory rate and/or volume
Thoracic electric-impedence
plethysmography
Body vibration
Accelerometer
Basic Symbols of Petri Nets
○ : Place (位置), drawn as a circle, denotes an event
: Immediate transition (立即變遷), drawn as a thin
bar, denotes event transfer with no delay time
: Timed transition (時延變遷), drawn as a thick bar,
denotes event transfer with a period of delay time
: Arc (弧), drawn as an arrow, between places and
transitions
: Token (標記), drawn as a dot, contained in places,
denotes the data
: Inhibitor arc (禁制弧), drawn as a line with a circle
end, between places and transitions
Basic Structures of Logic Relations
for Petri Nets
Logic relation
TRANSFER
AND
OR
Description
If P then Q
If P AND Q then R
Boolean function
Q=P
R=P*Q
TRANSFER AND
TRANSFER OR
INHIBITION
If P OR Q then R
If P then Q AND R
If P then Q OR R
If P AND Q' then R
R=P+Q
Q=R=P
Q+R=P
R=P*Q'
R
Q
Q
R
R
R
Q
R
Petri nets
P
P
Q
P
Q
P
P
P
Q
T12
Ventricular
Electrode
T10
Output
Circuit
T9
T5
V3
B2
M onostable
M ulti-Vibrator
(2ms)
T17=2ms
Oscillator
B1
T8=120ms
V2
M onostable
M ulti-Vibrator
(120ms)
T4
T7
Power
Supply
Reset
Circuit
Gate
B5
T6
V4
T16
Amplifier
#1
T3
Amplifier
#2
M onostable
M ulti-Vibrator
(500ms)
B4
T18=500ms
B3
V1 T2
Atrial
Electrode
T1
Atrial
Contraction
Petri net for
describing
the operation
of a combined
synchronous pacemaker
Marking of a Petri net
A marking (標幟) of a Petri net is defined as:
the number of tokens at each place, denoted
by a column vector M.
Thus vector Mk = (n1, n2, ... nm)T represents
that token numbers of places P1, P2, ... Pm at
state k are n1, n2, ... nm, respectively.
Twelve Checkpoints
CP1: Checkpoint 1, M(CP1)=1 (0) represents that the power-supply is
functioning (not functioning).
CP2: Checkpoint 2, M(CP2)=1 (0) represents that the atrial-electrode is
functioning (not functioning).
CP3: Checkpoint 3, M(CP3)=1 (0) represents that the amplifier#2 is
functioning (not functioning).
CP4: Checkpoint 4, M(CP4)=1 (0) represents that the reset-circuit is
functioning (not functioning).
CP5: Checkpoint 5, M(CP5)=1 (0) represents that the oscillator is
functioning (not functioning).
CP6: Checkpoint 6, M(CP6)=1 (0) represents that the 500ms-delay-vibrator is
functioning (not functioning).
CP7: Checkpoint 7, M(CP7)=1 (0) represents that the gate is at a closed state
(an open state).
CP8: Checkpoint 8, M(CP8)=1 (0) represents that the 120ms-delay-vibrator is
functioning (not functioning).
CP9: Checkpoint 9, M(CP9)=1 (0) represents that the 2ms-delay-vibrator is
functioning (not functioning).
CP10: Checkpoint 10, M(CP10)=1 (0) represents that the output-circuit is
functioning (not functioning).
CP11: Checkpoint 11, M(CP11)=1 (0) represents that the ventricular electrode
is functioning (not functioning).
CP12: Checkpoint 12, M(CP12)=1 (0) represents that the amplifier#1 is
functioning (not functioning).
CP11
T11
CP10
Ventricular
Electrode
CP5
T10
T9
Output
Circuit
CP9
B10
T23
T5
V3
B2
T17=2ms
Monostable
Multi-Vibrator
(2ms)
B1
Oscillator
T8=120ms
CP8
CP1
B9
CP4
V2 T22
T4
B6
B7
Monostable
Multi-Vibrator
(120ms)
CP7
T13
T19
T7
CP3
Power
Supply
Reset
Circuit
CP12
B5
Gate
T6
T3
T16
Amplifier
#1
CP2
CP6
B8
B4
Amplifier
#2
T20
V4
T18=500ms
T2
V1
Monostable
Multi-Vibrator
(500ms)
Atrial
Electrode
T1
Atrial
Contraction
B3
Petri net for
failure diagnosis
of a combined
synchronous
pacemaker
Checking Code
of the Pacemaker
Checking Code of the Petri net
is the marking that is composed of
the token number of the12 check points.
i.e.
Checking Code = (CP1, CP2, ... CP12)T
Transmitter
T99
Remote
Turn-off
Signal
B99
Mixer
T98
T34
T35
B22
T36
B23
T97
T38
B24
B26
Battery
Voltage level
Warning-Value
Comparator
Remote
Turn-on
Signal
Petri net for
the
remote mode
of a combined
synchronous
pacemaker
T62
B25
T96
Battery
Voltage level
Measuring
Circuit
T71
CP7
T81
T61
B15
CP8
T44
T54
B18
CP6
B21
T43
T42
T93
B13
B14
T31
B16
B17
T53
B19
CP3
T33
T37
CP10 CP11 CP12
T52
B20
The transmitter can be triggered
manually or automatically.
T92
=120ms
B12
T91
T00
CP9
T32
CP2
T41
T51
CP4
CP5
Actualization
Steps:
1.Convert Petri nets to a logic circuit
2.Design the resultant circuit by a software
3.Download the designed circuit to an
FPGA (Field Programmable Gate Array)
4.Integrate the logic circuit to a pacemaker
Corresponding Circuits
for Basic Petri Net Symbols
Symbol name
Arc
Petri net
symbol
Immediate
transition
Place
Token
Inhibitor
arc
Timed Transition
T=0
T=t
CLK
D
Q
CP
Q
Vcc
Y
RESET
Circuit
X
Wire
Connection
point
D type
Flip-Flop
+Vcc DC
Signal
Wire with
Inverter
START
DELAY t
OUT
CP11
T11
CP10
Ventricular
Electrode
CP5
T10
T9
Output
Circuit
CP9
B10
T23
T5
V3
B2
T17=2ms
Monostable
Multi-Vibrator
(2ms)
B1
Oscillator
T8=120ms
CP8
CP1
B9
CP4
B7
Monostable
Multi-Vibrator
(120ms)
CP7
T13
T19
T7
CP3
Power
Supply
Reset
Circuit
CP12
CP4
B99
1
1
0
1
0
1
0
0
0
0
1
1
V2 T22
T4
B6
CP2
B5
Gate
T6
T3
T16
Amplifier
#1
CP2
CP6
B8
B4
Amplifier
#2
T20
V4
T18=500ms
T2
V1
Monostable
Multi-Vibrator
(500ms)
Atrial
Electrode
T1
Atrial
Contraction
B3
Truth table for the relations among CP2, CP4, and B99
CP2
CP4
B99
1
1
0
1
0
1
0
0
0
0
1
1
 XOR
Truth table for the relations among CP2, CP5, and B99
CP2
CP5
B99
1
1
1
1
0
0
0
0
1
0
1
0
 XNOR
Logic relation
XOR
Description
XNOR
If X1 not equals to X2 then Y
Boolean function
If X1 equals to X2 then Y
Y=X1*X2+X1*X2
Y=X1*X2+X1*X2
Y
Y
T1
Petri nets
T2
X1
T1
X2
T2
X1
X2
Y
Y
Q
Q
D
CP
D
CP
T
Circuit
T1
T2
Q
D
X1
T1
Q
CP
D
X2
T2
Q
CP
D
CLK
X1
Q
CP
D
X2
CP
CLK
Transmitter
T99
Remote
Turn-off
Signal
B99
Mixer
T98
T34
T35
B22
T36
B23
T97
T38
B24
B26
Battery
Voltage level
Warning-Value
Comparator
Remote
Turn-on
Signal
Petri net for
the
remote mode
of a combined
synchronous
pacemaker
T62
B25
T96
Battery
Voltage level
Measuring
Circuit
T71
CP7
T81
T61
B15
CP8
T44
T54
B18
CP6
B21
T43
T42
T93
B13
B14
T31
B16
B17
T53
B19
CP3
T33
T37
CP10 CP11 CP12
T52
B20
The transmitter can be triggered
manually or automatically.
T92
=120ms
B12
T91
T00
CP9
T32
CP2
T41
T51
CP4
CP5
The Downloaded FPGA
Conclusions
1.The Petri net is a powerful graphical tool for
modeling a dynamic system such as a combined
synchronous pacemaker, which helps the design,
failure diagnosis, and research of control algorithms
of a cardiac pacemaker.
2.This study demonstrates the modeling and failure
diagnosis for the normal mode and remote mode, that
operates manually or automatically, of a combined
synchronous pacemaker by a Petri net approach.
3.The operational status of the pacemaker is clearly visible
from the Petri net model and the health condition is
clear at a glance by the checking code of the pacemaker.
References
1. S. K. Yang, ‘A Petri-net approach to remote diagnosis for failures
of cardiac pacemakers’, Quality and Reliability Engineering
International, 20(8), pp. 761-776, December 2004.
2. Patrick D. T. O’Connor, Practical Reliability Engineering,
4th Ed., John Wiley, Chichester, England, 2002.
3. E. A. Elsayed, Reliability Engineering, Addison Wesley
Longman, Taipei, 1996.
4. Joseph J. Carr and John M. Brown, Introduction to Biomedical
Equipment Technology, 4th Ed., Prentice Hall, New Jersey, 2001.
5. S. K. Yang, Introduction to Reliabilty Engineering, 2nd ed.,
Quan Hua, Taipei, September 2008, ISBN 957-21-4996-2.
(In Chinese and English)
Thank You!
蘇州大學
蘇州大學
蘇州大學
蘇州大學
上海華東理工大學
上海華東理工大學
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