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