Transcript Spring 2008 - BME Design Projects

GPS-ENABLED ASTHMA INHALER
Michael Alexander | Joseph Cabelka | Mollie Lange | Peter Ma
BME 402
March 8, 2008
PROJECT SUPPORTERS
Client: David Van Sickle
• PhD, Medical Anthropology
• Population Health Sciences, focus in asthma and allergy
• Epidemic Intelligence Service officer for Centers for
Disease Control
• Special projects with National Asthma Control Program
• Currently at UW as a Health and Society Scholar
Advisor: Professor Mitch Tyler
• Biomedical Engineering
• Orthopedics and Rehabilitation
• UW-CREATe
CONTENT
Problem Statement
Background
Motivation
Design Constraints
Design Solution
Current Progress
Future Work
References
PROBLEM STATEMENT
Create a device capable of:
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Tracking the usage of asthma inhalers
Transferring between medication dispensers
Noting time, date, and location of exacerbations
Wireless transmission of subject data to database
BACKGROUND
• Asthma
– Chronic respiratory disease in which airways are
blocked due to allergy or inflammation
– Over 20 million Americans currently suffer from asthma
• Global Positioning System (GPS)
– First developed for military
– Widely used in communication, recreation, and safety
– Uses signal transmission time to triangulate position
PREVIOUS SEMESTERS
1st Generation:
•Proof of concept
•Not portable
•Manual command prompt
2nd Generation:
•Program PIC chip
•Created PCB
•Power: Cell phone Li-ion battery
•Housing case
THIS SEMESTER
• Goals/Priorities
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Resolve power issues
Packaging (minimize size)
Web integration
Testing
RESOLVING THE POWER ISSUE
• Li-ion Batteries
– Obtained new, high-capacity batteries
• Can be internal or external to casing
• Come with connectors that will make charging simple
• Very low quiescent (non-use) current drain
• Battery life as a function of robustness
– Need to decide how to handle usage issues without
draining battery (more details later)
PACKAGING
• Completed:
– New switch to control circuit
• Considered spring-loaded, momentary, FSR
• Obtained and tested Force-Sensitive
Resistor (next slide)
– Miniaturizing Printed Circuit Boards
• Chose surface-mounted elements to obtain
decrease in surface area, depth; reduces
chance of short circuits
• Rerouted pathways to utilize both sides of
boards
– Made caps w/flat surface to fit medicine
canisters
FORCE-SENSITIVE RESISTORS (FSR)
• Advantages
– Have the ability to set a threshold
that corresponds to desired force
– Minimizes false-positives and
threshold value can be easily
controlled with a voltage divider
– Rounded, non-obtrusive design
• Disadvantages
– Need flat (instead of concave) surface
– Need to test for best sensitivity ratio
FORCE-SENSITIVE RESISTORS (FSR)
• Researched force required for
actuation
– Not perfectly standardized but
average values are available
– Approx force required for
medicine to dispense: ~1500g
– Set threshold resistance based
on documentation for FSR
DEVICE COMPONENTS & TESTING
• Battery
– How long will it last?
• FSR/PIC Chip
– Is it reliable?
• Wear and tear
– Patient use
– Weakest component(s)
• GPS Connection
– Can we always get GPS coordinates?
BATTERY
• Obtain current (I) information
– Quiescent
– Pinging GPS
– Transmitting to website
• Calculate maximum use time
• Finalize program
– Determines how often our device is in each stage
• Suggested battery life
FSR/PIC CHIP
• Will pressing the FSR reliably
activate the device?
– Standard force
• Reliably activate inhaler
– Human finger tests
• Will using a finger distribute force
unevenly enough to not activate
the PIC chip?
WEAR AND TEAR
• Simulate patient use
– Patient usage profiles
– 7 days
• Determine the weakest component of device
• Preliminary test group
– Gather data from user questionnaire
LOCATION TESTING
• Test indoors
– Different floors
– Different buildings
• Test outdoors
– Urban environment
– Rural environment
• Compare GPS output with actual coordinates
• Helps determine how to handle lack of fix
GPS SIGNAL
• Overcoming urban environment
– Need to account for lack of satellite signal inside
most building
– Possibilities:
• Incorporate code to “wake-up” and get GPS coordinates at
set time intervals (dependant on battery). If at time of
patient activation, GPS coordinates cannot be retrieved,
send reserve coordinates
• Send coordinates next time it can get signal
• Send dummy string and ask patient to input location when
they log in online
– Probably will combine all three to make program as
effective as possible
PROGRAMMING
• Multiple Application Handling
– Program distinguishes between single/multiple
ascerbations based upon timing
• GPS Fix Acquisition Profile
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Periodic Fix vs. Push to Fix
Event time vs. fix/database time
Affects position accuracy, validity
Parameters to be determined through testing
PRIVACY ISSUES/IRB
• Robust program – polling frequently
– High poll frequency raises issues of “tracking”
– Reliability may have to be sacrificed to protect patient
privacy
• Patient information online
– Can be set up as normal, blind, or double blind for
studies
– Patients receive ID number based on device given
– Statistics are reported with regard to ID number
REFERENCES
Asthma and Allergy Foundation of America
http://www.aafa.org
American Academy of Allergy Asthma and Immunology
http://www.aaaai.org
Trossen Robotics Community
http://www.trossenrobotics.com
QUESTIONS?
Thank you for your time!
Any questions?