Failure diagnosis for cardiac pacemakers using Petri nets Professor National Chin Yi University of Technology Samuel Yang Lecture Course ( 楊善國 ) ( 勤益科技大學機械工程系教授

Failure diagnosis for cardiac pacemakers using Petri nets

ProfessorNational Chin Yi University of Technology

Samuel YangSamuel Yang

Lecture CourseLecture Course

(楊善國 )

(勤益科技大學機械工程系教授 )

ContentsContents

Introduction Definition of Reliability Frequently Used Methods for Failure Analysis Failure Analysis for pacemakers by Petri Nets References

IntroductionIntroduction

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.

ReliabilityReliability

Specified conditions Required performance Stated time period Probability

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:

Therefore,Reliability and failure are closely related.

Frequently Used Methods for Frequently Used Methods for Failure AnalysisFailure Analysis

Fault Tree Analysis (FTA) Failure Modes and Effects Analysis (FMEA) Failure Modes, Effects and Criticality

Analysis (FMECA) Petri Net Method

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.

PacemakerPacemaker

A cardiac pacemaker is an electric stimulator that producesperiodic pulses that are conducted to electrodes located in theheart 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).

PacemakerPacemaker

Asynchronous: Fixed pulse-rate regardless of the body condition

According to the control algorithms,pacemakers can be classified to:

PacemakerPacemaker

Synchronous: Functioning intermittently as required

1.Demand2.Atrial 3.Combined

Rate-responsive: Triggered according to the actual demand

Asynchronous PacemakersAsynchronous Pacemakers

OscillatorPowerSupply

Pulse Output Circuit

Electrodes

Pulse Generator

Synchronous PacemakersSynchronous Pacemakers －－ Demand Demand

Oscillator Pulse Output Circuit Electrodes

Amplifier ResetCircuit

PowerSupply

Demand: Providing function when it is needed

Synchronous PacemakersSynchronous Pacemakers －－ AtrialAtrial

MonostableMulti-vibrator500ms delay

Ventricular Electrode

Amplifier GateMonostableMulti-vibrator120ms delay

MonostableMulti-vibrator 2ms delay

OutputCircuit

Artial Electrode

V1 V2

V3 V4

Synchronous PacemakersSynchronous Pacemakers －－ CombinedCombined

MonostableMulti-vibrator500ms delay


GateMonostableMulti-vibrator120ms delay

MonostableMulti-vibrator 2ms delay

Atrial Electrode

V1 V2

V3

V4

Oscillator Pulse Output Circuit

ResetCircuit

PowerSupply

Amplifer #2

Amplifer #1

Synchronous PacemakersSynchronous Pacemakers －－ Rate-responsiveRate-responsive

Oscillator Pulse Output Circuit

ElectrodesControllerSensor

Control Algorithm

Physiological Variable

Right-ventricle blood temperature

Sensor

Thermistor

ECG stimulus-to-T-wave interval ECG electrode

ECG R-wave area ECG electrode

Blood pH Electrochemical pH electrode

Rate of change ofright-ventricle pressure

Semiconductor strain-gage

Venous blood oxygen saturation Optical oximeter

Intracardiac volume changes Electric-impedenceplethysmography (intracardiac)

Respiratory rate and/or volume Thoracic electric-impedenceplethysmography

Body vibration Accelerometer

Physiological variables and the corresponding sensors for rate-responsive pacemakers

○ : 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 Symbols of Petri NetsBasic Symbols of Petri Nets

Logic relation

Description If P AND Q then R

Q P

R

Petri nets

P Q

R

OR

If P OR Q then R

Q R

P

If P then Q AND R

P

Q

TRANSFER

If P then Q

P

R

Q

INHIBITION

Q=P Boolean function R=P*Q

AND

R=P+Q Q=R=P

If P AND Q' then R

R=P*Q'

TRANSFER AND

Q R

P

TRANSFER OR

If P then Q OR R

Q+R=P

Basic Structures of Logic RelationsBasic Structures of Logic Relations for Petri Netsfor Petri Nets

Petri net fordescribing

the operationof a combined

synchronous pacemaker Monostable Multi-Vibrator (120ms)

Atrial Contraction

AtrialElectrode

Amplifier #2

Reset Circuit

Oscillator

Output Circuit


T1

T2

T3

T4

T5

T10

Gate

Monostable Multi-Vibrator (2ms)

T8=120ms


T12

V1

V2

V4

T9

V3

Power Supply

T16

Amplifier #1

T17=2ms

T6

T18=500ms

T7

B1

B2

B3

B4

B5

Marking of a Petri netMarking 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.

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).

Twelve Checkpoints


Atrial Contraction

AtrialElectrode

Amplifier #2

Reset Circuit

Oscillator

Output Circuit


T1

T2

T3

T4

T5

T10

Gate


T8=120ms


T11

V1

V2

V4

T9

Power Supply

T16

Amplifier #1

T17=2ms

T6

T18=500ms

T7

CP1

CP5

CP2

CP3

T13

B6

T19

CP4

B7

B8

B2

B1

B3

B4

B5

T20

CP6

CP7

T22

CP8

V3

B10

T23

CP9

CP11

CP10

B9

CP12

Petri net forfailure diagnosis of a combinedsynchronous pacemaker

Checking CodeChecking Codeof the Pacemakerof 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

Remote Turn-off Signal

Remote Turn-on Signal

BatteryVoltage level Measuring Circuit

Battery Voltage level Warning-Value Comparator

T96

T98 T97

T99

T71 T81

T62

T92=120ms

T93

T44 T31 T32 T33

B99

Mixer

T00 T41 T51

T61

T91

CP7 CP8 CP6 CP3 CP10 CP11

CP5CP4CP2CP9

T54

B21

T52T53

T42T43

B19 B20

B12

B13 B14

B15

B16 B17

B18

T34

B22

T36

B24

T38

B26

B25

T37

CP12

T35

B23

Petri net for the

remote modeof a combined synchronous pacemaker

The transmitter can be triggeredmanually or automatically.

ActualizationActualization

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

Steps:

Corresponding CircuitsCorresponding Circuits

for Basic Petri Net Symbols for Basic Petri Net Symbols

Symbol name Arc Immediate transition

T=0Petri net symbol

Circuit

Wire Connection point

Place

D

CP

Q

QCLK

D typeFlip-Flop

Token

Vcc

+Vcc DC Signal

Inhibitor arc

Wire with Inverter

Y

X

Timed Transition

T=t

DELAY t

OUTRESET

START


Atrial Contraction

AtrialElectrode

Amplifier #2

Reset Circuit

Oscillator

Output Circuit


T1

T2

T3

T4

T5

T10

Gate


T8=120ms


T11

V1

V2

V4

T9

Power Supply

T16

Amplifier #1

T17=2ms

T6

T18=500ms

T7

CP1

CP5

CP2

CP3

T13

B6

T19

CP4

B7

B8

B2

B1

B3

B4

B5

T20

CP6

CP7

T22

CP8

V3

B10

T23

CP9

CP11

CP10

B9

CP12

CP2 CP4

1 1

1

1

0

0 0

0

B99

0

1

0

1

Truth table for the relations among CP2, CP4, and B99

Truth table for the relations among CP2, CP5, and B99

CP2 CP4

1 1

1

1

0

0 0

0

B99

0

1

0

1

CP2 CP5

1 1

1

1

0

0 0

0

B99

0

1

0

1

XOR

XNOR

Logic relation

Description

XOR

If X1 not equals to X2 then Y

Boolean function Y=X1*X2+X1*X2

Petri nets

Y

X1

T1

D CP

Q

D CP

Q

Y

X1

Circuit

X2

D CP

Q

X2 CLK

T2

T2 T1

XNOR

If X1 equals to X2 then Y

Y=X1*X2+X1*X2

D CP

Q

D CP

Q

Y

X1

D CP

Q

X2 CLK

T2 T1

T

Y

X1

T1

X2

T2

Transmitter

Remote Turn-off Signal

Remote Turn-on Signal

BatteryVoltage level Measuring Circuit

Battery Voltage level Warning-Value Comparator

T96

T98 T97

T99

T71 T81

T62

T92=120ms

T93

T44 T31 T32 T33

B99

Mixer

T00 T41 T51

T61

T91

CP7 CP8 CP6 CP3 CP10 CP11

CP5CP4CP2CP9

T54

B21

T52T53

T42T43

B19 B20

B12

B13 B14

B15

B16 B17

B18

T34

B22

T36

B24

T38

B26

B25

T37

CP12

T35

B23

Petri net for the

remote modeof a combined synchronous pacemaker

The transmitter can be triggeredmanually or automatically.

The Downloaded FPGAThe Downloaded FPGA

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.

ConclusionsConclusions

ReferencesReferences

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




上海華東理工大學上海華東理工大學




Documents

Failure diagnosis for cardiac pacemakers using Petri nets Professor National Chin Yi University of Technology Samuel Yang Lecture Course ( 楊善國 ) ( 勤益科技大學機械工程系教授