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.

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

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 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 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 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

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 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

Questions?

Appendix 1

Appendix 2