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Ensuring Patient Safety in Wireless Medical Device Networks

Ensuring Patient Safety in Wireless Medical Device Networks. Presented by: Eric Flickner Chris Hoffman. Speed vs. Safety.

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Ensuring Patient Safety in Wireless Medical Device Networks

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  1. Ensuring Patient Safety in Wireless Medical Device Networks Presented by: Eric Flickner Chris Hoffman

  2. Speed vs. Safety WMDNs provide many alarms and related clinical data that are life-critical. To avoid exposing patients to serious injuries or death, these systems must be protected from data delays, distortions, loss, or other erratic delivery problems.

  3. WDN (Wireless Device Network) • Based upon existing popular IEEE 802.1x technologies • Wi-Fi (IEEE 802.11a/b/g) • Wi-Max (IEEE 802.11n) • Bluetooth (IEEE 802.15.1) • Zigbee (IEEE 802.15.4) • Each of these has their own pros/cons in • Speed, interoperability, security, coexistence, battery life, and building/object penetration

  4. Business Networks • Simple CSM (Collision Sense Method) • Random delay intervals to resequence data • Problems • Unpredictable CSM delay length • Randomization of message transfers • Both are tolerable in this kind of network

  5. Medical Networks • Unpredictable CSM delay length • Ex: delay can exceed max delay allowed in arrhythmia monitoring applications • Causes corruption of real-time patient waveforms leads to misdiagnosis, interfering with therapeutic interventions • Randomization of message transfers • Invalidates intelligent alarm monitoring (IEC/ISO 60601-1-8)

  6. Problems during WMDN Life Cycle • Delayed or lost WMDN data is the major problem • Any change or interference can seriously affect other WMDN during its life cycle • Nonproprietary WMDN verification and validation (V2) techniques do not exist

  7. Problems during WMDN Life Cycle • Absence of industry standards or regulations • Unconstrained mobility of patients and devices • Rapid changes in the underlying wireless network modalities • No single proprietary V2 strategy can assure safe and reliable WMDN systems • Solution: Propose developing a V2 toolkit for use by clinical and biomedical engineering departments to ensure safe and reliable WMDN operation.

  8. Formal Methods • Definition • A notation or technique, based on some mathematical theory, for modeling and analyzing systems. • Advantages • Making sure that it behaves according to specifications • Helps developers identify potential problems or misunderstandings

  9. Petri Nets • A petri net (a.k.a. place/transition net) is one of several mathematical representations of discrete distributed systems. • Graphically depicts the structure of a distributed system as a directed bipartite graph

  10. Petri Nets • States • Ready to accept $$ (Ready) • $$ accepted (Accepted) • Events • Insert coin (Coin) • Soda dispense button (Soda) • Gum dispense button (Gum) • Requirements • Gum costs 1 coin • Soda costs 2 coins • Current state indicates Ready

  11. Healthcare Scenario • For example, suppose a heart alarm goes off while a large image file is being transmitted over the same wireless network. • How will this affect the network’s behavior? • Will the alarm signal reach the station in time? • A formal modeling and analysis technique can answer these questions.

  12. Sample Patient Monitoring System

  13. Sample Patient Monitoring System • 10 patients with heart monitors and pulse oximeters • Heart monitors can generate a low battery alarm • 2 nurses at nurse’s station • Connected via wireless network

  14. Colored Petri Net (CPN) • CPNs trace and control the path and timing of each token (alarm) in the net • CPN ML is a the programming language used to edit, model, simulate, and analyze CPNs

  15. Colored Petri Net (CPN) Model • Red – infrequent heart alarms • Orange – frequent pulse oximetry alarms • Yellow – very infrequent heart monitor battery alarm

  16. Colored Petri Net (CPN) Model

  17. Colored Petri Net (CPN) Model • Pulse oximetry alarms began to queue up, exposing a bottleneck in network • CPN allows priority to be given to individual tokens in a IEEE802.11e-style QoS technique • Critical heart alarm and battery alarms given priority over pulse-oximetry alarms

  18. Conclusions • QoS compliant network equipment necessary for life-critical applications • CPN Tools predict and avoid life-threatening data delays, insufficient bandwidth, and inadequate priority management • Model does not address RF interference

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