Medical Cyber-Physical Systems · 2019-12-03 · Medical Cyber-Physical Systems Electrophysiology...
Transcript of Medical Cyber-Physical Systems · 2019-12-03 · Medical Cyber-Physical Systems Electrophysiology...
Medical Cyber-Physical Systems
Electrophysiology basics
Lecture 10
Pr inc ip les of Model ing for Cyber-Phys ica l Systems
Instructor: Madhur Behl
Principles of Modeling for CPS – Fall 2018 Madhur Behl [email protected] 1
Many thanks to:Zhihao Jiang,Houssam Abbas, andRahul Mangharam,
For help with preparing this module.
Why explore cardiac modeling?
Cardiac disease is the leading cause of death in the USAround the world, 17.5 million people die of Cardiovascular Diseases (CVD) yearly
That’s an estimated 31% of all deaths
More than 75% of CVD deaths occur in low income and middle income countries
Implanted devices are a leading method of treating some CVDs
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Why study cardiac devices?
These devices are life-critical à must function correctly
Are constrained in their energy consumption à must be low-power
Are implanted in the body à very special design considerations (e.g., materials used, must be ex-plantable…)
Are regulated by the FDA à must follow certain best practices, but also have some inertia
These are life-critical embedded systems
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Its shocking! Cardiac devices can have bugs
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Implantable Cardiac Devices Recalls
• Over 600,000 cardiac medical devices recalled from 1990-2000
– 40% of which were due to software issues
• 2008-12: 15% of all the medical device recalls due to software
Implantable Pacemaker Implantable Cardioverter-Defibrillator (ICD)Principles of Modeling for CPS – Fall 2018 Madhur Behl [email protected] 6
The consequences of incorrect algorithms and implementations
Filmed and shared with patient’s consent
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Closed-Loop Evaluation
Scenario 1
Scenario 2
Scenario 3
Principles of Modeling for CPS – Fall 2018 Madhur Behl [email protected]
Need a model of the heart which can capture the physiological conditions of the heart and respond to pacemaker outputs.
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Model/implement the pacemaker
Check if pacemaker is ‘safe’ for different heart conditions
Let our heart (model) catch the bugs before your heart does
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This Module
Will be challenging:
◦ New domain (electrophysiology)
◦ New tools (Simulink and UPPAAL)
◦ New theory (timed automata)
◦ New concepts (model checking)
Simulink
UPPAAL
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How do we go about understanding the heart?
Understand the electrical system as a circuit?Understand the cellular activity? Understand the molecular activity?What does one heart tell us about other hearts?What does a healthy heart tell us about an unhealthy heart?What is a healthy heart?
What is the purpose of our enquiry?
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Need to understand the domain.
Speak the same language as the domain experts.
Remember….modeling choices and ‘usefulness’ depend on the problem at hand.
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Electrophysiology of the heart
aka ..talking like a cardiologist without attending med schoolPrinciples of Modeling for CPS – Fall 2018 Madhur Behl [email protected] 14
First, let’s examine the human heart
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Circulatory system and heart function
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Vein: towards the heart.Artery: away from the heart
Principles of Modeling for CPS – Fall 2018 Madhur Behl [email protected]
Electrical generation and propagation
Right atrium
Right ventricle
Left atrium
Right ventricle
Sino-atrial (SA) node
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Bradycardia: bradus (slow) + kardia (heart)
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Two leads in heart chambers
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Implantable Pacemaker
Principles of Modeling for CPS – Fall 2018 Madhur Behl [email protected]
Two leads are placed in the right atrium and right ventricleMonitors the local electrical activities of the heart and deliver therapy according to the timing information
Madhur Behl [email protected]
Implantable Pacemaker
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Implantable Pacemaker
A
V
AS
VS
Pacemaker
Pace
Principles of Modeling for CPS – Fall 2018 Madhur Behl [email protected]
Sinoatrial Node“Automaticity”
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RA
RV
LA
LV
+Depolarization-
Bachmann’s bundle
Atrioventricular Node[delay bw Atria & ventricles]
Bundle of His L posterior fascicle
L anteriorfascicle
R bundle
L bundlePurkinje fibers
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Pacemaker cells (naturally pace the atria and ventricles)and
Cardiac myocytes cells (“squeezing” the heart)
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Pacemaker cells – “Automaticity”
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1) Sino-Atrial (SA) node
2) Atrioventricular (AV) node
3) Bundle of His / Purkinje fibers
Pacemaker cells
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mV
(+123) Ca2+
(+67) Na+
(-92) K+ -60
Na+
time
threshold
Na+Ca2+
“Voltage-gated”
-40Na+
K+
+10
-60
Dep
olar
izat
ion
Repo
lari
zatio
n
1 beat
Race to keep pace !
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mV
SA AV BoH
threshold
“Normal Sinus Rhythm”
Race to keep pace !
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Heart Rate (beats/min) 1 beat (sec)SA 60-90 0.66 secAV 40-60 1 sec
BoH 20-30 2 sec
0.66 sec
1 sec
2 sec
Race to keep pace !
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0.66 sec
1 sec
2 sec
Race to keep pace !
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SA AV BoH2cm 1cm
How does SA node control the heart beat ?“Normal Sinus Rhythm”
?
Can this signal arrive before 1 sec ?
0.5 m/sec 2 m/sec
Conduction velocity is very fast !
0.04 sec
0.66 sec0.7 sec+0.1 sec
0.005 sec0.805 sec
0.66 sec
1 sec
2 sec
Race to keep pace !
Principles of Modeling for CPS – Fall 2018 Madhur Behl [email protected] 31
• SA node – Plan A• AV node – Plan B• BoH – Plan C
0.66 sec
1 sec
2 sec
Pacemaker cells (naturally pace the atria and ventricles)and
Cardiac myocytes cells (“squeezing” the heart)
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Cardiac Myocytes – How does the heart squeeze
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mV
time
(+123) Ca2+
(+67) Na+
(-92) K+
K+
-90
Na+
Ca2+
Neighboring cell depolarizes
K+
Na+
-70
+20+5
K+
Ca2+-90
Action Potential - TissueThe elementary signal of the heart
It affects the conduction velocity and signal passage of the tissue.
Closely related to most cardiac diseases.
Madhur Behl [email protected]
APD: Action Potential Duration Functional syncytium
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Cellular Level - Action potentialIons refill
Divided into Effective Refractory Period(ERP) and Relative Refractory Period(RRP) for activation with certain strength
Block Interval during ERP, abnormal new action potential during RRP
Madhur Behl [email protected]
Refractory
ERP RRP
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Refractory
Time
V out
Rest ERP RRP Rest
Refractory
TimeV out
Rest ERP RRP Rest
node
pathnode
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Treating bradycardiaWe want to detect when the atria or the ventricles miss a beat, and pace the chambers when that happens
Start small and simple:◦ We know that usually, the atria contract together, and the ventricles contract together à sense only in right
atrium and ventricles◦ Usually, depolarization is synchronous with contraction à measure the electrical activity as a proxy for the
mechanical activity◦ Usually, depolarization in part of the atrium (or ventricle) is
propagated to the rest of that chamber à measure only inone location of the chamber
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Two leads are placed in the right atrium and right ventricleMonitors the local electrical activities of the heart and deliver therapy according to the timing information
Madhur Behl [email protected]
Implantable Pacemaker
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Timing info for local activation
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Implantable Pacemaker
A
V
AS
VS
Pacemaker
Pace
Principles of Modeling for CPS – Fall 2018 Madhur Behl [email protected]
• Simulink and State-flow tutorials have been posted on the course website. • Not graded. No submission required.
• One week to brush up on Simulink/Stateflow.• Go through the tutorials before the Simulink/Stateflow model walkthrough lecture next week
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Next Lecture:
• Pacemaker operation and heart conditions•Model checking vs Model testing• Heart modeling using timed automata
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