Medical Cyber-Physical Systems

Transcription

1 Medical Cyber-Physical Systems Electrophysiology basics Lecture 10 Principles of Modeling for Cyber-Physical Systems Instructor: Madhur Behl Many thanks to: Zhihao Jiang, Houssam Abbas, and Rahul Mangharam, For help with preparing this module. Principles of Modeling for CPS Fall 2018 Madhur Behl 1

2 Why explore cardiac modeling? Cardiac disease is the leading cause of death in the US Around 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 Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 2

3 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 Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 3

4 Its shocking! Cardiac devices can have bugs Principles of Modeling for CPS Fall 2018 Madhur Behl 4

5 Principles of Modeling for CPS Fall 2018 Madhur Behl 5

6 Implantable Cardiac Devices Recalls Over 600,000 cardiac medical devices recalled from % of which were due to software issues : 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 6

7 The consequences of incorrect algorithms and implementations Filmed and shared with patient s consent Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 7

8 Closed-Loop Evaluation Scenario 1 Scenario 2 Scenario 3 Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 8

9 Need a model of the heart which can capture the physiological conditions of the heart and respond to pacemaker outputs. Model/implement the pacemaker Check if pacemaker is safe for different heart conditions Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 9

10 Let our heart (model) catch the bugs before your heart does Principles of Modeling for CPS Fall 2018 Madhur Behl 10

11 This Module Will be challenging: New domain (electrophysiology) New tools (Simulink and UPPAAL) Simulink New theory (timed automata) New concepts (model checking) UPPAAL Principles of Modeling for CPS Fall 2018 Madhur Behl 11

12 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? Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 12

13 Need to understand the domain. Speak the same language as the domain experts. Remember.modeling choices and usefulness depend on the problem at hand. Principles of Modeling for CPS Fall 2018 Madhur Behl 13

14 Electrophysiology of the heart aka..talking like a cardiologist without attending med school Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 14

15 First, let s examine the human heart Principles of Modeling for CPS Fall

16 Circulatory system and heart function Vein: towards the heart. Artery: away from the heart Principles of Modeling for CPS Fall 2018 Madhur Behl 16

17 Electrical generation and propagation Sino-atrial (SA) node Right atrium Left atrium Right ventricle Right ventricle Principles of Modeling for CPS Fall 2018 Madhur Behl 17

18 Bradycardia: bradus (slow) + kardia (heart) Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 18

19 Implantable Pacemaker Two leads in heart chambers Principles of Modeling for CPS Fall 2018 Madhur Behl 19

20 Implantable Pacemaker Two leads are placed in the right atrium and right ventricle Monitors the local electrical activities of the heart and deliver therapy according to the timing information Madhur Principles Behl of Modeling for CPS Fall

21 Implantable Pacemaker A V Pace AS Pacemaker VS Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 21

22 LA Bachmann s bundle RA Atrioventricular Node [delay bw Atria & ventricles] Sinoatrial Node Automaticity Bundle of His L posterior fascicle L bundle Purkinje fibers LV L anterior fascicle - + Depolarization RV R bundle Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 22

23 Principles of Modeling for CPS Fall 2018 Madhur Behl 23

24 Pacemaker cells (naturally pace the atria and ventricles) and Cardiac myocytes cells ( squeezing the heart) Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 24

25 Pacemaker cells Automaticity 1)Sino-Atrial (SA) node 2)Atrioventricular (AV) node 3) Bundle of His / Purkinje fibers Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 25

26 Pacemaker cells Na + (+123) Ca 2+ (+67) Na + mv Depolarization Repolarization +10 Voltage-gated Ca 2+ Na + time (-92) K threshold Na + 1 beat K + Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 26

27 Race to keep pace! Normal Sinus Rhythm mv SA AV BoH threshold Principles of Modeling for CPS Fall 2018 Madhur Behl 27

28 Race to keep pace! 2 sec 0.66 sec 1 sec Heart Rate (beats/min) 1 beat (sec) SA sec AV sec BoH sec Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 28

29 Race to keep pace! 1 sec 2 sec 0.66 sec Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 29

30 Race to keep pace! 2 sec Conduction velocity is very fast! 0.5 m/sec 2 m/sec SA AV BoH 2cm 1cm 0.66 sec 1 sec Can this signal arrive before 1 sec?? 0.66 sec 0.04 sec 0.7 sec +0.1 sec sec sec How does SA node control the heart beat? Normal Sinus Rhythm Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 30

31 Race to keep pace! 1 sec 2 sec 0.66 sec SA node Plan A AV node Plan B BoH Plan C Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 31

32 Pacemaker cells (naturally pace the atria and ventricles) and Cardiac myocytes cells ( squeezing the heart) Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 32

33 Cardiac Myocytes How does the heart squeeze K + Neighboring cell depolarizes (+123) Ca 2+ Na + Ca 2+ (+67) Na + mv K + Na + time (-92) K K Ca 2+ Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 33

34 Action Potential - Tissue The elementary signal of the heart It affects the conduction velocity and signal passage of the tissue. Closely related to most cardiac diseases. APD: Action Potential Duration Functional syncytium Madhur Principles Behl of Modeling madhur.behl@virginia.edu for CPS Fall

35 Cellular Level - Action potential Ions 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 ERP RRP Refractory Madhur Principles Behl of Modeling madhur.behl@virginia.edu for CPS Fall

36 Refractory V out Time Rest ERP RRP Rest Rest ERP RRP Rest node path node Refractory V out Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 36 Time

37 Treating bradycardia We 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 in one location of the chamber Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 37

38 Implantable Pacemaker Two leads are placed in the right atrium and right ventricle Monitors the local electrical activities of the heart and deliver therapy according to the timing information Madhur Principles Behl of Modeling for CPS Fall

39 Principles of Modeling for CPS Fall 2018 Madhur Behl 39

40 Implantable Pacemaker Timing info for local activation A V Pace AS Pacemaker VS Principles of Modeling for CPS Fall 2018 Madhur Behl madhur.behl@virginia.edu 40

41 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 Principles of Modeling for CPS Fall 2018 Madhur Behl 41

42 Next Lecture: Pacemaker operation and heart conditions Model checking vs Model testing Heart modeling using timed automata Principles of Modeling for CPS Fall 2018 Madhur Behl 42