WHEELCHAIR CUSHIONS AND

ISO TESTING Tryksarskonferencen 2011 Denmark

STANDARDIZED TEST RESULTS

ISO 16840-2 WHEELCHAIR CUSHION

TESTS

Load Deflection and Hysteresis

Frictional Properties

Impact Damping

Recovery

Loaded Contour and Overload Deflection

Water Spillage

Biocompatibility

Horizontal Stiffness and Sliding Resistance

TESTS IN PROCESS

Heat and Water Vapor

Changes in Properties with Use

Force Distribution (was pressure mapping)

Envelopment

Adjustability

Instrumented Indenter

Flammability of Wheelchair Cushions

WHEELCHAIR CUSHION MARKET IS RAPIDLY

CHANGING

Standardized Test Methods Manufacturers will be able to claim “test results comply with

ISO 16840”

Performance characteristics will be better defined

It will be difficult unscrupulous persons to skew results

Testing to qualify for reimbursement Required in the US and Germany

Characterization going in the UK

Manufacturers “Designing to Required Tests”

ISO 16840 PROGRESS

Measurement of

Postural Support

Surfaces and Body

Segments

Part 1 Part 2 Part 3 Part 4 Part 5

Draft is nearing completion

For Committee Vote then

Circulation to Member

Countries

Postural Support

Devices, Measurement

Of Static Impact and

Repetitive Load Strength

Technical Report Outlining

Methods for Determining

the Pressure Relief

Characteristics Of Devices

Intended to Manage Tissue

Integrity-Seat Cushions

Approved Standard Approved Standard

7 Parts

Test Methods for

Determining the

Physical

And Mechanical

Characteristics of

Devices

Intended to Manage

Tissue Integrity-Seat

Cushions

Approved Standard

Seating Systems for

Use in Motor Vehicles

Update Requested

ISO 16840 PROPOSED WORK

Test Methods for

Determination of the

Heat and Water Vapor

Dissipating

Characteristics of

Devices Intended

To Manage Tissue

Integrity

Part 7 Part 8

Draft is Ready to be

Submitted

As a Preliminary Work

Item

2 Parts

Changes in

Properties with

Use

Or Product Life of

Devices Intended

To Manage Tissue

Integrity

Draft is being

developed

For Submission

as

Preliminary work

item

Part 9

Flammability Specific to

Wheelchair cushions

Draft method

has been

developed,

tested in

multiple lab

LOAD DEFLECTION AND HYSTERESIS

LOAD DEFLECTION AND HYSTERESIS

Test Concept: Apply increasing and then decreasing

load and measure deflection through out.

Load Deflection and Hysteresis TestApplied Load vs Time

0

250

500

750

1000

0 100 200 300 400 500 600 700 800 900

Time (s)

Load (

N)

LOAD DEFLECTION AND HYSTERESIS AIR

CUSHION

Force Deflection curve

0

100

200

300

400

500

600

700

800

0 10 20 30 40 50 60 70 80 90

Deflection (mm)

Force (

N)

FRICTIONAL PROPERTIES

FRICTION SLED BEING

PULLED ACROSS CUSHION

FRICTION IN TRANSFERRING

IMPACT DAMPING

IMPACT DAMPING INDENTER

IMPACT DAMPENING

Test Concept: Apply a load to the indenter on a

cushion and allow the indenter and cushion to fall

from a 10° angle, measure the vibrations tranfered

through the cushion back to the indenter.

IMPACT DAMPENING TEST RESULTS 45 ILD FOAM

IMPACT DAMPENING REPORTED VALUES

Res1: Mean number of Rebounds greater than 10% of Peak Positive Rebound Acceleration

Res2: Mean of the Peak Rebound (positive) Acceleration relative to the Baseline (negative) Acceleration (Gs)

Res3: Ratio of the of the second rebound relative to the first rebound accelerations (%)

2.67 1.2 45.83%

RECOVERY

RECOVERY

Test Concept: Measure the height of the cushion

unloaded, apply 500N to the indenter on the

cushion for 20 minutes, then unload the cushion an

measure the height

Report the difference between starting and ending

height

RECOVERY RESULTS

Average

Original

Thickness

Ratio of

Thickness at

20 seconds

Post Loading

to Original

Ratio of

Thickness at

1200 seconds

Post Loading

to Original

78.8 mm 0.88 .95

LOADED CONTOUR AND OVERLOAD

DEFLECTION

LOADED CONTOUR FIXTURE

LOADED CONTOUR AND BOTTOMING

Test Concept: Measure the Cushion height, load the

LCJ to 135 N (13.8 kg) and record the cushion

height. Load the indenter to 180 N (18.4 kg),

measure the cushion height.

Point of Interest: Has the cushion stopped deforming

with increase application of load.

LOADED CONTOUR AND BOTTOMING RESULTS

(FICTITIOUS DATA)

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100 120 140 160 180 200

Desirable Cushion

Undesirable Cushion

WATER SPILLAGE

BIOCOMPATIBILITY

Cell Control Bio-compatibility Test

LATERAL STIFFNESS ANNEX C

LATERAL STIFFNESS

Test Concept: Apply a 500 N load to the Indenter on

a test cushion, generate a lateral displacement of 5

mm and hold for 60 seconds. Measure the force

required to maintain the displacement after 60

seconds.

LATERAL STIFFNESS DATA

End Point

SLIDING

RESISTANCE

SLIDING RESISTANCE

Test Concept: Apply a load to the indenter while on

the cushion and then displace the indenter in an

anterior direction, measuring the force required to

generate movement of the indenter on the surface

of the cushion

SLIDING RESISTANCE SAMPLE DATA

End Point

SLIDING RESISTANCE TYPICAL

RESULTS

0

5

10

15

20

25

30

Newtons

Relax Lite Relax Sentinel Relax Air Gel

Contour

Air Cushion Viscous Gel

Cushion

Resistance to Sliding

TC 173 WG 11 CURRENT WORK

Heat and Water Vapor

Changes in Properties with Use

Force Distribution (was pressure mapping)

Envelopment

Adjustability

Instrumented Indenter

Flammability of Wheelchair Cushions

HEAT AND WATER VAPOR

Heat Negatively Impacts Tissue

Raises metabolic demand

Accelerates tissue stress under loading

Moisture Negatively Impacts Tissue

Increases Friction

Causes maceration

IMPACT OF HEAT ON TISSUE

Arrhenius/Brown Model

1.00

1.20

1.40

1.60

1.80

2.00

2.20

2.40

2.60

2.80

3.00

25 26 27 28 29 30 31 32 33 34 35

Temperature C

Reacti

on

Rate

mo

les/

sec X

10

^-1

0

A 5.0 Degree Temperature

decrese yeilds a 38%

reduction in Reaction rate

38% Decrease

SWEAT CONDENSATION ON STONE SITTING

SURFACE

HEAT: TRADITIONAL MATTRESSES (FOAM) ARE

INSULATORS

R value = 9.6

HEAT AND WATER VAPOR TEST

APPARATUS Circulator

maintains body

temperature

Sweating

mechanism creates

water vapor delivery

similar to

transpiration or

imperceptible sweat

No perceptible

sweat deliver

occurs

HRLG/CUSHION ENDOTHERMIC CURVE

Cushion Endothermic Curve, Measured at ITs

20.0

22.0

24.0

26.0

28.0

30.0

32.0

34.0

36.0

38.0

40.0

0 500 1000 1500 2000 2500 3000 3500 4000

Seconds

C

Open Cell Urethane

Air Bladder

Honeycomb

Viscous Fluid

Molded Urethane

PCM

Fluid/Foam Combination

Viscous Fluid, Pouched

Lower buttock interface temperature is desirable, without the extreme of metabolic deficit or tissue damage

Higher buttock interface temperature is undesirable due to increased metabolic stress

DOES CUSHION TYPE IMPACT HEAT

AT THE TISSUE INTERFACE?

IR photos after 1 hour simulated use

DOES CUSHION TYPE IMPACT HEAT

AT THE TISSUE INTERFACE?

IR photos after 1 hour simulated use

DOES CUSHION TYPE IMPACT HEAT

AT THE TISSUE INTERFACE?

IR photos after 1 hour simulated use

DOES CUSHION TYPE IMPACT HEAT

AT THE TISSUE INTERFACE?

IR photos after 1 hour simulated use

WHAT HAPPENED TO PRESSURE

MAPPING?

6 Laboratories performed tests on cushions

shipped from lab to lab

4 of 6 measures varied significantly between labs

Order of results similar

Calibrations were not stable

Manufacturers of Pressure Maps have produced

improved products, but testing has not been

repeated

INSTRUMENTED INDENTER

2005 at meeting in Spain, ROHO offered an R &

D grant to develop the Instrumented indenter

Work was performed in our laboratory

Work was performed in conjunction with Dr.

Stephen Sprigle of Georgia Tech funded by the

Rehabilitation Engineering Research Council

INSTRUMENTED INDENTER

Research and Development over 5 years resulted

in:

Two Methods: Adjustability and envelopment

Highly accurate sensors (expensive)

Repeatable calibration

Fixed shape(s)

Significant Repeatability between labs at 99%

confidence level

LABORATORY TEST DESIRED

49

• Skin Protection (Pressure Management) – Immersion – Magnitude – Envelopment

• Positioning – Stability – Accommodation – Correction – Alignment

• Adjustable / Re-adjustable

– Multiple weights & shapes

– Full or partial

– Discrete or continuous

• Durability/Accelerated

aging – Repetitive Loading – Temperature – UV – Microbial

• Micro-climate – Heat – Moisture

INDENTERS AND LOADS

50

Skin Protection Positioning Loads

• 97 lb load on

indenter

(138.5 lb

individual)

• 116 lb load

on indenter

(165.5 lb

individual)

2-3 shapes and 2 weights per

test

Small indenter

Large indenter

Designed by S.Sprigle

SKIN PROTECTION DIRECT PRESSURE MEASUREMENT

Use of instrumented indenter (pressure sensors

mounted directly to indenter)

Eliminates mat effect (distortion due to tension caused

by mat)

More direct measurement of pressure

Indenter is a model of pelvic area only

51

SKIN PROTECTION TEST APPARATUS

52 One of 18 Sensor Locations

Trochanter locations

Standardized load

IMMERSION

Contact deflection test

Instrumented indenter

Loaded with 97 lbs or 116

lbs

Starting point determined

by sensing point at which

the indenter began to

load (1/2 lb) the cushion

53

ACCOMMODATING VARIOUS SHAPES AND WEIGHTS COMPARING TWO DIFFERENT CONDITIONS (ADJUSTABLE CUSHIONS VS. NON-ADJUSTABLE CUSHIONS)

54

Accommodation of Weights & Sizes

0

20

40

60

80

100

120

140

160

180

200

Right

Lateral

40

Right

Lateral

20

Right

Lateral

5

Right IT Right

Medial

5

Left

Medial

5

Left IT Left

Lateral

5

Left

Lateral

20

Left

Lateral

40

Sensor Location

Dif

fere

nc

e i

n P

res

su

re (

mm

Hg

)

Adjustable Average

Non-Adjustable Average

Overall Average for Cohort

Condition 1:

Small indenter (22cm) high

load (116 lbs)

Condition 2:

Large indenter (25.5cm)

small load (97 lbs)

An ideal

cushion

ENVELOPMENT PRESSURE DISTRIBUTION -VARIOUS CONDITIONS

(SPECIFIC CUSHIONS)

55

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

1 2 3 4

Condition

Vari

an

ce A

cro

ss I

nd

en

ter

Cushion A - Air w Precontour

Cushion B - Foam w Firmness Layer

Overall Average for Cohort

Smaller value variance = more envelopment

Condition 1:

Small indenter (22cm) Small load (97 lbs)

Condition 2:

Small indenter (22cm) Large load (116 lbs)

Condition 3:

Large indenter (25.5cm) Small load (97 lbs)

Condition 4:

Large indenter (25.5cm) Large load (116 lbs)

An ideal cushion

WHEN DOES IT QUIT DOING

WHAT IT WAS DESIGNED TO DO?

TESTS THAT MEASURE DIMENSIONAL

CHANGES

Compression Set

Dimensional

Measurements

User’s Condition

Changes

New vs. Aged Cushions

IDENTIFY INTENDED USE

Wheelchair cushion Exposure Selection Table

Required Minimum Exposures, typical use 1,3,4,5,6,1,7,8,5,10

Intermittent use without incontinence 1,3,4,5,6,1,10,11

Wet Environment (Shower / Toileting) 1,3,4,6,1,7,8,10,3,4,10,

Perspiration (Sport or Hot environment) 1,3,4,5,6,1,7,8,10,11

Incontinence (Faecal and/or Urinary) 1,3,4,5,6,1,5,7,5,8,5,6,1,5,8,5,10

Heavy Use (including outdoor) 1,3,4,5,6,1,7,8,9,10,11,

Extremes of Climate HOT 1,3,4,5,6,1,5,10,3,4,10

COLD 1,3,4,5,6,1,7,8,5,9

Utility (exposed to all environments) 1,3,4,5,6,1,7,8,5,9,10,11

Robust Utility 1,3,4,5,6,1,7,8,5,6,1,7,8,5,9,10,11

Hybrid (minimum plus special case)

Minimum plus MFG special case see annex XX.X or manufacturer method disclosure.

USE

INTENDED

USE TO

OUTLINE

BEST

AGING

CHALLENG

E

Test Number Description

1 Disinfection

2 (alternate) Drop and Settle: Cyclic Loading at Ambient

Temperature

2 Drop and Settle: Cyclic Loading at Elevated

Temperature 50°C

3 Drop and Settle: Cyclic Loading at Elevated

Temperature 70°C

4 Accelerated Shelf Life 70°C

4 A Accelerated Shelf Life 50°C

4 B Rate, Load, Oscillate, Unload and Repeat Cyclic

Loading: Ambient Temperature

4 C Rate, Load, Oscillate, Unload and Repeat Cyclic

Loading: Elevated Temperature

5 Laundering

6 Bacterial Soiling

7 Faecal Incontinence

8 Urinary Incontinence

9 Ultraviolet light Ozone

11 Cold exposure

10 Humidity cycling

CHARACTERIZE PRODUCT PERFORMANCE

PRE AND POST AGING (NOT A CLOSED

LIST)

Instrumented Indenter

Column Buckling

Heat and Humidity

Heated Indenter Compression

Horizontal Stiffness

Impact Damping

Leak Detection

Load deflection and hysteresis

Sliding Resistance

Impact Damping

Antimicrobial Resistance