ensuring patient safety in wireless medical device networks presented by: eric flickner chris...
TRANSCRIPT
Ensuring Patient Safety in Wireless Medical Device
Networks
Presented by:
Eric Flickner
Chris Hoffman
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.
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
Business Networks
Simple CSM (Collision Sense Method)Random delay intervals to resequence data
ProblemsUnpredictable CSM delay lengthRandomization of message transfers
Both are tolerable in this kind of network
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)
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
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.
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
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
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
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.
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
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
Colored Petri Net (CPN) Model
Red – infrequent heart alarms
Orange – frequent pulse oximetry alarms
Yellow – very infrequent heart monitor battery alarm
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