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Pressure Ulcer (Bedsore)
• Tissue damage caused by restricted blood
flow, friction, and shear force.
• Affect ~500,000 people in US hospitals.
When combined with other conditions,
mortality is two to five times higher than
patients without pressure ulcers.
• Prolonged hospital stay up to 5 times longer
than patients without pressure sores.
Stage 2 Pressure Ulcer
Stage 4 Pressure Ulcer[1] http://www.hcup-us.ahrq.gov/reports/statbriefs/sb64.jsp
Pressure Ulcer (Bedsore)
Christopher Reeve died in
2004 from heart failure due to
the septicemia caused by the
pressure ulcer. [2]
[2] http://www.apparelyzed.com/pressuresores.html
Septicemia – A condition in
which the bloodstream is
overwhelmed by bacteria.
Symptoms include organ failure
and blood pressure drop.
Project Summary
• The cushion with automatic distribution of individual air cell
pressure
• Based on the suggestion from Shepherd Spinal Center to
reduce occurrence of pressure ulcers on paraplegic
patients in wheelchairs
• Sponsored by Texas Instruments Analog University
Design Competition
• Expected cost of $2,000.00
Technical Objectives
Proposed Developed
25 Air cushions for even pressure distribution
25 Air cushions with individual cell control
Remap contact pressure distribution on cushion periodically, (25min) as suggested by NPUAP
Timer used to re-adjust pressure every 10 minutes
Portable for use on wheelchair
~ 60 hr battery life using 100Ah lead-acid battery
Small enough to be installed on motorized or unmotorized wheelchair
Easy to UseUI for manual override and data logging
Example System Packaging• System is compact enough to be packaged on motorized and
unmotorized wheelchairs
14”
14”
Project Photo
Air control
block
Air Pump
Pressure
Sensing
Amplifier
Debug Interface
Pressure Cushion
Power
Supply
Pump Driver UI Board
Display
Module
Switch
BoardMSP430F1612
MCU
Valve Selection and Description
Original Valve NOT used
Valve cartridge
Manifold and fitting
Servo motor
• Integrated Air control and Sensor Manifold saves space
and reduces number of electrical components
Pressure Cushion SealingWe welded the channels shut using
a re-flow station from the labOriginal cushion had passages
Interconnecting cells
Sealing Improvisation
Reflow station was used with
small tip @ 200°C and then
passage was clamped shut
until bonded
Pressure Sensing• Freescale MPX2202 Sensors are used to monitor pressure
readings from the individual cushions
• Typical air cell pressure is shown to be about 10-20 psi.
• Set Gain = 100 to read up to 50psi using Texas Instruments
INA333 Precision Instrumentation Amplifiers
• At 10 psi, +/- 20% reading accuracy
• High inaccuracy possibly caused by sensor
grounding issue. Currently troubleshooting to
obtain higher accuracy
Algorithm Description
• Two main state: Manual and Autopilot
• Manual mode
Enable control buttons
Allowing to Inflate /deflate on each cell
• Autopilot mode
Disable control buttons
Load Configuration every period
Control System FlowSTART
Toggle
SW?
Manual Mode
Autopilot
H
L
SW Read
Open valves
Pump ON
Pressure read
Open valves
Pump ON
Pressure Read
User Interface Implementation
• Debug and tracking purpose
• TeraTerm – Terminal emulator
Log and track instructions and data
ASCII data TxD from MSP430
• AVR 8-bit MCU controlled16x2 LCD
Same function as TeraTerm
But simpler for user
Portability and Battery Life• Portability
• Cushion can be installed on the wheelchair seat, with control
elements mounted on the frame
• Device weight is under 20lbs without the 12V battery
• 12V car battery weighs approximately 40 lbs.
• Battery Life
• Current draw with pump ON : 2 – 5 Amps
• Current draw with pump OFF : 40 mA
• Using 100Ah battery, Usage life is expected to be 60 hours
System Performance Testing
• Short Term Testing
• Individual components tested and functioning
• User comfort testing, to be done
• Long Term Testing
• Pressure mapping to test performance of different
operating modes
• Long term efficacy in pressure sore reduction /
prevention
Problems and Solutions Challenges Solutions
Isolating each cushion cell Use glue, and heat gun
Solenoids cost out of budget Team made our own valves using servos from senior labs
Pressure sensors reading Use INA333 to amplify signal
Material limitation to build prototype
Use available wood and parts from lab to build cushion support
Intake air units for each cell Use tire air intake piece and glue it at the bottom of cells
PWM control for servos Use external servo controller
Development CostParts ordered Price
Total amount
sponsored
Total without sponsor
MSP430F1612 (Controller) ($18.87)
MSP-FET43OU64 (Debug) ($149.00)
INA333AIDGKR (Amplifier) ($5.40 x 25)
TMP75 (Temperature) ($1.34)
TLC2558IDW (12bit ADC) $8.38
ROHO Mosaic cushion $97 x 2
Pressure sensors MPX-2202 GP $8.36 x 30
Other Purchased Components $318.44
Other Sponsored Components ($21.03)
Total $926.57 $ 1096.86
Production Run Cost
Production Item Cost
Development Cost per Unit $35.00
Assembly Labor (2 hr) $40.00
Testing Labor (1 hr) $20.00
Customer Support (5 hr) $100.00
Fringe Benefits (30% of Labor) $48.00
Production Equipment ($500,000) $100.00
Material Cost $411.00
Overhead and Sales Expense $943.00
Selling Price $2000.00
Profit Per Unit $303.00
• 5,000 units for 5 years
Recommended Future Work
1.Pump: Select low noise pump, and small in size that can fit in the cushion
package
2.Improve UI display, use touch / tongue control or eye track
3.Cushion material resilient to damage
4.Add moisture and temperature sensors to increase device capability
5.Select light material when designing cushion to reduce weight
6.Add air cooler to the system to keep the skin dry