1 / 36

Intro to some things CRM

Intro to some things CRM. Speaker: Alan Fryer Date: 05-03-06. Goal/Agenda. Present information on pacemakers and ICD’s to give everyone an idea about the technologies involved. Overview of the Heart Information about the technology in pacemakers Pacemaker algorithms

ely
Download Presentation

Intro to some things CRM

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Intro to some things CRM Speaker: Alan Fryer Date: 05-03-06

  2. Goal/Agenda • Present information on pacemakers and ICD’s to give everyone an idea about the technologies involved. • Overview of the Heart • Information about the technology in pacemakers • Pacemaker algorithms • Ventricular only pacemaker • Rate Adaptation 2/ 33

  3. Caveats • Not an expert on everything I am going to talk about. • Whole books exist on these subjects so cannot cover anything in great detail. • Contains opinions that are not necessarily the opinions of others. Disagreement and debate are a natural part of the engineering process. 3/ 33

  4. Hearts Job • Part of the circulatory system. • Pumps: • de-oxygenated blood to the lungs • oxygenated blood to the body 4/ 33

  5. Anatomy of the heart Heart has 4 Chambers. 2 Phase “controlled“ contraction Atrium’s job: Assist in filling the ventricle. Ventricle’s job: move the blood. 5/ 33

  6. How it works • Heart is a muscle but unique • can contract rhythmically and automatically without fatigue. • Made up of cells that rhythmically depolarize and repolarize on their own, or on electrical stimulus. • contract when the depolarize • relax when they repolarize • One cell deplolarizing will cause its neighbors to depolarize in a chain. • Heart also contains specialized cells that form pathways for rapid conduction • Some cells depolarize/repolarize at a more rapid rate than others are on the hearts natural “pacemakers” 6/ 33

  7. Changing potentials for different cells • Shows “action potentials” for various cell types. Sinus node 70 bpm SDD AV node 40-60 bpm SDD PURKINJE fibers 30-40 bpm SDD Myocardial cells <30 bpm 7/ 33

  8. Controlled Contractionby electrical conduction Atrium beats first assisting the ventricle in filling. Ventricle beats. Conduction paths ensure controlled contraction. 8/ 33

  9. PQRST waves • Conduction process visible external to the heart on the ECG. • P is the atrium depolarizing • QRS is the ventricle depolarizing • T is the ventricle re-polarizing • Note: Look how big the QRS complex is. 9/ 33

  10. Heart Control system Adjusts rate and contraction strength to meet the body’s need. 10/ 33

  11. Cardiac Rhythm Management • CRM Devices – Treat conduction problems of the heart. • Bradycardia • Too slow • not synchronized • irregular beating • heart does not rate adapt (chronotropically incompetence) •  treat with a Pacemaker (IPG) to Stimulate the Heart • Tachycardia • Heat beats too fast • irregular beating (at fast rates) •  treat with a Implantable Cardiac Defibrillator (ICD) • Congestive Heart Failure • Heart does not beat efficiently •  treat with Cardiac Resynchronization Therapy Device (3 lead ICD or IPG) 11/ 33

  12. Where do they go? Implanted by the clavicle. Leads go through the veins directly into the right side of the heart. Can also attach leads to the outside of the heart.(epicardial lead) A 3rd lead is also used to stimulate the left side of the heart (Coronary Sinus) for CRT. 12/ 33

  13. Where did they start from Earl Bakken's invented the first wearable, battery-powered, transistorized cardiac pacemaker. 13/ 33

  14. Big Picture Requirements • Lifetime requirements • 10 years, translating to inhibit currents of < 10 uA • Commercial HC11 MCU quotes 25 uA when all clocks are stopped !!! • Size (always pushing for smaller) • 10 cc now (dominated by the battery) • 30 cc now for ICD’s (dominated by battery and caps) • Cost • beginning more cost sensitive, price erosion starting … • volumes are a lot smaller than other industries changing the economics of decisions • safety/reliability • safety critical 14/ 33

  15. Technologies • Multi-chip modules • pushed the manufacturing/packaging industry with regard to miniaturization, now get help from cell phones and digital cameras • Mixed Signal Design • analog design a must for power supplies, switches, signal acquisition, communication circuits, charge pumps, etc. • switched capacitor technology is used throughout the industry. • strong push to digital to take advantage of shrinking process geometries • lots of debate as to the ideal partitioning, and the answer changes with time. • 12 years ago analog required 2 um processes which meant big power hungry digital circuits. 15/ 33

  16. HW / SW in CRM Devices • For at least the last 10 years, all modern CRM devices incorporate some sort of processor • 6502, 6808, 6805, Z80, 8051, HC11 have all been used BUT USUALLY CUSTOMIZED • lower power, lower clock speed ( ~2 Mhz) • reduced number of clock cycles per instruction (8051) • added instructions MUL, DIV, MOVE, etc. • increased address range and added addressing modes • sometimes even added registers (extra index registers) • always have a STOP instruction (stopped > 95 % of the time) • peripherals, IRQ maps, also always custom • most companies have also built custom processors (DSP processors, controllers, Harvard architecture, micro-coded state-machines, you name it) • SW becoming critical path, thus creating sw tool chains makes this expensive. • Different philosophies for HW/SW decomposition • Things we know, put in HW. • Things that take a lot of cpu cycles put in HW • Time critical things, put in HW. • Things you don’t know always go in SW… • Safety critical stuff put in HW (this is changing…) 16/ 33

  17. Applying some of these rules • Features that lean toward HW: • For sensor data: signal acquisition, filtering, auto gain, event detection, feature extraction, waveform recording, waveform compression. • For communications: time division multiplexing of comms. channel, packet transmission, packet reception, primitive command encoding, error detection • For therapy: Bradycardia pacemaker timing, interval measurement, filtering, therapy classification (rate criterions, X of Y, Sudden Onset) • For General use: DMA transfers, timers, signature calculators, time of day • Features that lead towards software: • High level control algorithms like communication protocols, feature control, Progression through Tiered therapies. • New features 17/ 33

  18. RAM / ROM Partitioning • Initially RAM only used for updates late in the development process. Safety demanded code in ROM for fear of corruption. • Now differing opinions: • SW Engineers prefer ram based architectures with minimal code in ROM for safety critical behavior. • HW Engineers prefer as much rom as desired • Factors: • ROM takes up less chip space, meaning you could have more memory for a given chip size. (effects cost, leakage current, etc) • Executing code out of ROM takes less current than out of RAM • Changing ROM means a new part which has significant cost implications for manufacturing and inventory management. • ROM adds time constraints on development to have code early to meet tape-out dates. • RAM can be changed any time allowing new products to be developed without IC turns. 18/ 33

  19. Special Considerations - Clocks • Multiple clocks for low-power operation • CPU clock consumes too much power, so it is off when not use ( 2 Mhz) • Main clock is much slower 32 kHz is used often • clock gating used everywhere • also gate power to blocks as needed 19/ 33

  20. Special Considerations – Charge Pumps • Multiple Battery Types • Battery Voltage vary between 1.6 and 3.4 Volts, impedance can be 1 ohm to > 20 K ohms. • (Nuclear batteries where used in the 70’s but fell out of favor quickly…) • However need to generate: • up to 7.8 V for 2 ms for pacing • Voltage multipliers. • effects IC process choice • > 700 Volts for charging shock electrodes • transformer based pump, also used for charging a flash in a camera and in tasers. • also effects IC process choice 20/ 33

  21. Patient Safety • IPGs and especially ICDs are safety critical • device must be “active” to ensure patient safety • termed as a safety critical device without a static safe state • Also have severe constraints: Size, Cost, Life-time • a safe device that can’t be sold does nobody any good • 2 batteries?, 2*shock caps?, 2 * the leads? • rules out the use of redundancy as a global solution (triple modular redundancy) • not an ideal solution anyway, similar systems tend to fail in similar ways … • Complexity also an important design constraint • Requirements/Design Errors much more likely with increased complexity 21/ 33

  22. Design Process • “Cannot test in quality” means “quality needs to be designed in”. • Safety engineering and risk management are a central part of the design process throughout the product life-cycle. • formal process considering Hazard, Cause, Probability, Severity, Mitigations, Resulting Probability, Resulting Severity • Combined with formal design techniques Req, Des, Verif, Validation, etc. • Medical devices are regulated by the FDA which requires manufactures to follow its Good Manufacturing Practices as well as meet any standards appropriate for the industry. 22/ 33

  23. Modern Pacemaker Safety Architecture • Fault Resolution Lifecycle: • Error Detection • monitors job • Damage Confinement • reset to known minimal state safe state • Error Recovery and continued service • test and try to recover • Fault treatment • record diagnostics, log the failure, communicate it to the physician. 23/ 33

  24. Monitor design crucial • Implemented in HW or Software • Standard protections: • Write Protection, Stack Checks, Illegal Instruction, Reset on Rom Write, Watch Dogs, Key Protection Registers, Range Checks on Parameters, Signature Checks on Data, Algorithm Sanity Checks, Low Voltage, High Current, etc • Therapy Tests: • High Rate Monitor – if the pacemaker ever exceeds the maximum rate, a reset occurs. • Low Rate Monitor - if the pacemaker ever falls below a certain rate, a reset occurs (watch dog can be used for this) 24/ 33

  25. Control System Design • All other factors being equal, complex systems are more likely to fail due to design/requirements errors than simple ones. • Failures can leave systems in unknown states. • Failures should be rare and may be caused by transitory environmental conditions, thus the device should try to recover. • Some failures are correctable (memory corruption). • Therefore: • from reset, start operation in a minimal safe state • Single Chamber Pacemaker • Single Chamber Pacemaker + Fib Detection and Shocking • on passing self tests (consistency checks), recover to full functionality 25/ 33

  26. Start Simple – VVI Back-up Pacemaker Earliest pacemakers just blindly stimulated the ventricle (VOO Mode), here we will stimulate it only when needed. Ventricular Pacing, Ventricular Sensing, Inhibited 26/ 33

  27. VVI Timing Diagram and Rules • wait, if detect nothing, pace • if detect something, restart waiting period • ignore detections that occur within a certain period of a detection/pace • avoids T-wave and other unwanted noise 27/ 33

  28. A VVI Pacemaker Design 28/ 33

  29. VVI Pacemaker Block 29/ 33

  30. VRefractory Block 30/ 33

  31. Simulation Results • The simulation shows the following behavior: • An initial pace occurs which starts a refractory period. • 2 sense events occur and are ignored because they are in the refractory period. • A 3rd sense outside the refractory causes the pacemaker to restart its timing cycle • 3 more paces occur as no more sense events are injected. 31/ 33

  32. What is missing • Real pacemakers have: • more pacing modes (DDD, DDI, DVI, DDD/T, AAI, VDD, etc.) • rate hysteresis to search for the intrinsic rhythm • AV delay adapts to rate, different AV delays for paced vs sensed events • AV delay hysteresis to search for intrinsic events • protection against false senses due to cross talk (safety window) • high rate limiting mechanisms to stop atrial tracking • mode switching for high rates • PVC detection • Far-field avoidance • rate smoothing on rate drops • etc… Gist: Pacemaker timing is a complicated sequence of connected state-machines. 32/ 33

  33. Another Missing Element - Rate Adaptation Sometimes HR does not increase with need or has insufficient dynamic range. • Heart compensates for this by increasing stroke volume. • -> can be bad if allowed to continue over a long time • -> limits as to how well the heart can adapt. • -> not good enough 50% increase in cardiac output vs 200% possible for a normal heart 33/ 33

  34. Rate Adaptive Sensors (part 1) 34/ 33

  35. Part II 35/ 33

  36. Close Loop Stimulation – EXTREMELY SIMPLIFIED • Impedance measurements detect localized changes in geometry of the heart at the site of the lead. • Indirectly measures contractility changes • transform a differential area between the current and reference waveform into a rate 36/ 33

More Related