Multi-Chamber Programmable Air Cushion (MC-PAC) Joli-A Kabamba Masahiro Ohno Scott Paik Joe Suarez

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. Picture courtesy of the National Pressure Ulcer Advisory Panel (NPUAP) Stage 2 Pressure Ulcer Stage 4 Pressure Ulcer [1]

Pressure Ulcer (Bedsore) Christopher Reeve died in 2004 from heart failure due to the septicemia caused by the pressure ulcer. [2] [2] 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 ProposedDeveloped 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 Use UI for manual override and data logging

Example System Packaging System is compact enough to be packaged on motorized and unmotorized wheelchairs 14”

Project Photo Air control block Air Pump Pressure Sensing Amplifier Debug Interface Pressure Cushion Power Supply Pump Driver UI Board Display Module Switch Board MSP430F1612 MCU

MSP430 CPU Peripherals

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

Pump Selection Ryobi portable air compressor

Pressure Cushion Sealing We welded the channels shut using a re-flow station from the lab Original cushion had passages Interconnecting cells

Sealing Improvisation Reflow station was used with small 200°C and then passage was clamped shut until bonded

Pressure Cushion Intakes

Pressure Sensing Freescale MPX2202 Sensors are used to monitor pressure readings from the individual cushions Typical air cell pressure is shown to be about 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 Flow START Toggl e 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

User Interface in Prototype  TeraTerm Console  16x2 LCD AVR controlled

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

Portability and Battery Life 40mA 5 A

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

Manual/ Auto Demo

Problems and Solutions Challenges Solutions Isolating each cushion cellUse glue, and heat gun Solenoids cost out of budgetTeam made our own valves using servos from senior labs Pressure sensors readingUse 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 cellUse tire air intake piece and glue it at the bottom of cells PWM control for servosUse external servo controller

Development Cost Parts orderedPrice 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$8.36 x 30 Other Purchased Components$ Other Sponsored Components($21.03) Total$926.57$

Production Run Cost Production ItemCost Development Cost per Unit$35.00 Assembly Labor (2 hr)$40.00 Testing Labor (1 hr)$20.00 Customer Support (5 hr)$ Fringe Benefits (30% of Labor)$48.00 Production Equipment ($500,000)$ Material Cost$ Overhead and Sales Expense$ Selling Price$ Profit Per Unit$ ,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

Questions?

Appendix 1

Appendix 2