Human and Bench Methods for Measurement of Shear and Performance Characteristics of Devices Intended to Mitigate

Shear

Evan Call, MS, CSM (NRM)

Shear is Both Imparted and Confounded by Friction

Shear Stress/Shear Strain

Image from Edhat.com Image from www2.dickson.edu

What Does Shear Feel Like

• Peanut butter under your tongue

Shear or Deep Tissue Injury

Photo from Woundeducators.com

Shear from Tube Across skin,

Bunching or Rolling Shear Displacement

Tolerance Zone for Shear

0

5000

10000

15000

20000

25000

30000

35000

40000

1 2 3 4 5 6 7 8 9 10 11

Ad

hes

ive

Sh

ear

(PA

)

Dressing Number

Body on Compressible Surface Drives Shear

Modulus Measurement

9

Shear Measurement Tests • L1 to Femoral Epicondyles Sliding Resistance

• Gel Distortion Indenter

• Direct Shear Measurement

• Translational Shear

• Tissue Model Shear

• Cadaver Heel Shear

• Lower extremity indenter shear

• Shear at Force (shear and pressure)

• Shear as a “wear” element

Shear in Humans • Direct measurement

o Molten predia

• Head of bed elevation

• Shear from normal sitting/ laying

• With / Without Dressing comparison

• With / Without Liquicell comparison

o Variable Resistance Elastomer

• Shear in tissues as head of bed is raised

• Shear in tissues as they immerse in a cushion

L1 to Femoral Epicondyle

Shear Modulus in Surfaces and Devices

Work Performed • Work (J) = Max Force (N) x deflection (.150 m)

• The Total work for each mattress tested at displacement intervals

of 50 mm and the 50-150 mm interval is shown below. The error

bars represent the 95th% confidence interval (alpha = 0.05).

Total Work (J)

0.00

2.00

4.00

6.00

8.00

10.00

12.00

IsoFlex Plexus PressurePedic SymmAire TemperPedic

To

tal

Wo

rk (

J)

0-50 mm

50-100 mm

100-150 mm

50-150 mm

Average Force vs Immersion

Average Force (50-150 mm) x Immersion

70.0

75.0

80.0

85.0

90.0

95.0

100.0

105.0

110.0

40.0 60.0 80.0 100.0 120.0 140.0

Immersion (mm)

Avera

ge F

orc

e 5

0-1

50 m

m (

N)

Plexus

IsoFlex

PressurePedic

TemperPedic

SymAire

Plexus, repeat 2

Pexus, Repeat 3

SymAire, repeat 2

SymAire, repeat 3

Slope Slope 1st cm (N/m)

-5.00E-04

0.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

2.50E-03

IsoFlex Plexus PressurePedic SymmAire TemperPedic

Slo

pe (

N/m

) 0-50 mm

50-100 mm

100-150 mm

50-150 mm

•The average slope of the force-displacement curve at 50 mm intervals and the 50-150 mm interval for each mattress is shown below. The error bars represent the 95th% confidence interval (alpha = 0.05).

Friction Shear and Bulk Modulus

17

Gel Indenter with Shear Strain Sensors

Calibration of Shear Indenter

Direct Shear Measurement

Direct Shear Measurent

Shear Translated Through Device

ShearForce Transmitted Through Dressing

• Mepilex® Border Flex

• Mepilex® Border Sacrum

• Optiva Gentle® Border

System to Model Human Shear

System to Model Human Shear

Effect of Dressing on Shear

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0 1 2 3 4

Distance Traveled (cm)

Sh

ear

(N)

With

Dressing

Without

Dressing

Model is Very Close to Human Subjects

Human-bench test comparison

0

1

2

3

4

5

6

7

8

9

Pe

ak

Sh

ea

r (N

)

Human Volunteer

HR-45 Weighted Foam

Sled

Cadaver Friction

Heel Boot Shear

Boot Retention Shear (N)

Friction both Sides, Shear Absorption

More shear stress on patient side due to adhesion

of dressing on skin– injury on removal?

Exterior shear stress is about the same in

dressings

Attempt to measure shear and Normal Force

Shear Reduction

11/17/2014 ESS, Dublin 2013 33

Shear Reduction

11/17/2014 ESS, Dublin 2013 34

Extras – LiquiCell reduces shear

+/-10°rotation

LiquiCell

Basic

+/-1°rotation

LiquiCell

Basic Denim Layer

Peak torque reduced by 25%

Shear Duration Reduced by 8%

Micro-shear events (start, stop, turn) can lead to decubitis

LiquiCell reduces the shear event duration and the peak loads of the shear event

Normal Loading Shear

Torque (twisting) shear test using jeans

Shear on Mattress with Liquicell

AveragePeakForce(N) AverageForce(N)AverageForcePost

Compression

VolunteerWithoutLiquicell

WithLiquicell

WithoutLiquiCell

WithLiquicell

WithoutLiquicell

WithLiquicell

A 8.03±0.62 5.70±0.62 6.55±0.19 4.28±0.70 6.37±1.44 3.10±2.03

B 6.07±0.78 5.14±0.05 5.46±0.81 4.45±0.12 3.05±0.82 4.84±0.31

C 3.94±0.95 3.69±0.55 3.14±0.98 2.87±0.55 3.90±0.33 3.42±0.33

D 6.63±1.32 6.97±1.84 5.49±0.98 6.11±1.53 6.73±0.97 7.19±0.59

E 7.70±2.53 3.70±1.85 6.72±2.23 2.53±1.85 6.59±1.80 1.92±3.59

F 6.58±0.75 5.58±1.65 5.85±0.52 4.60±1.55 5.44±0.77 5.09±1.39

G 4.39±0.96 3.38±0.63 3.67±0.87 2.63±0.59 3.57±0.08 3.18±0.63

H 9.07±2.17 8.34±1.61 7.68±1.47 7.17±1.61 7.21±1.25 6.61±0.38

I 5.90±1.16 4.42±2.15 4.46±1.28 3.07±1.90 2.60±1.60 2.35±1.42

J 5.50±1.41 4.83±1.35 4.32±0.63 3.26±0.79 3.52±0.59 2.85±0.79

AverageA-J 6.38±0.70 5.18±0.69 5.50±0.66 4.24±0.66 5.18±0.66 4.04±0.76

Roller Shear Rig and Result

Roller Shear on Bed

Ultimate Friction: Adhesion

39

Absorb, Displace or Reduce Shear

40

Measuring Shear Between a

Patient and the support

Surface

41

Shear Distortion

42

Shear With and Without Dressing

Single Human Subject 5 Trials Each Condition

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0 1 2 3 4

Shear (N)

Distance Traveled (cm)

Effect of Molnlycke Dressing on Shear Transfered to Underlying Tissue

With Dressing

Without Dressing

Sliding and Shear

44

Resistive Elastometer Skin Shear Test

Shear Conclusions • Shear Measurements are;

o Driven by Friction

o Potentially Confounded by Friction

o Overwhelmed by friction

o Best taken under infinite friction in one plane

• Then static friction

• Then dynamic friction

o In Reference to the Body or the surface it is on

Shear Conclusions • Shear Measurements are;

o Modulus when taken on cushions or beds

o When using a body like indenter

• Immersion and normal force become integral to shear

• Reporting work incorporates these

o Translational shear

• More complex to measure

• More predictive of tissue damage

o More reliable when friction is standardized

References • Brindle CT. Outliers to the Braden Scale: Identifying high-risk ICU patients

and the results of prophylactic dressing use. WCET J. 2010;30:2-8.

• Bots CM, Apotheker BFG. The prevention of heel pressure ulcers using a hydropolymer dressing in surgical patients. J Wound Care. 2004;13:375-378.

• Ashford RL, PodM D, Freear ND, Shippen JM. An in-vitro study of the pressure-relieving properties of four wound dressings for foot ulcers. J Wound Care 2001; 10: 34–8.

• Nakagami G, Sanda H, Chizuko K, Kitagawa A, Tadaka E, Tabata K. Comparison of two pressure ulcer preventative dressings for reducing shear force on the heel. J Wound, Ostomy and Cont Nurs. 2006;33:267272.

• Hall, P. (1983). Prophylactic Use of Op-Site on Pressure Areas. Nurs Focus; 43 (5): 16.

• Callaghan, S., Trapp, M. (1998). Evaluating Two Dressings for the Prevention of Nasal Bridge Pressure Sores. Prof Nurse; 13 (6): 361-364.

• Gefen, A., van Nierop, B. Bader, D., Oomens, C. (2008). Strain-time cell-death threshold for skeletal muscle in a tissue-engineered model system for deep tissue injury. J Biomechanics; 41: 2003-2012.

References • Ohura, N., Ichioka, S., Nakatsuka, T., Shibata, M. (2005). Evaluating

dressing materials for the prevention of shear force in the treatment of pressure ulcers. J wound Care; 14 (9): 401-404.

• Ohura, T., Takahshi, M., Ohura, N. (2008). Influence of External Forces (pressure and shear force) on Superficial Layer and Subcutis of Porcine Skin and Effects of Dressing Materials: Are Dressing Materials Beneficial for Reducing Pressure and Shear Force in Tissues? Wound Repair and Regeneration; 16 (1): 102-107.

• Thomas S. The Role of dressings in the treatment of moisture-related skin damage. World Wide Wounds [Internet] 2008 Mar 5 [cited 2010 Oct 12 1-14 Available from: http://www.worldwidewounds.com/2008/march/Thomas/Maceration-and-the-role-of-dressings.htmlmarch/Thomas[Online]

• Call E, Pedersen J, Bill B, Oberg C, Ferguson-Pell, M. Microclimate impact of Prophylactic Dressings Using In Vitro Body Analog Method. Wounds 2013;25(4):94-103

References • Call, E., Pedersen, J. Bill, B., Black, J., Paulo, A., Brindle, T., Dealey, C.,

Santamaria, Clark, M. Enhancing pressure ulcer prevention using wound dressings: what are the modes of action. International Wound Journal, DOI:10.111/iwj.12123, Accessed on line 30 July 2013.

• Dealey, C., Brindle, T., Black, J., Alves, P., Santamaria, N., Call, E., Clark, M. Challenges in pressure ulcer prevention. International Wound Journal, DOI: 10.111/iwj.12107. Published online 20 Jun 2013.

• Black, J., Alves, P., Brindle, T., Dealey, C., Santamaria, N., Call, E., Clark, M. Use of wound dressings to ehance prevention of pressure ulcers caused by medical devices. International Wound Journal, DOI: 10.111/iwj.12111

• Harada, C., Shigematsu,T., Hagisawa, S. The Effect of 10 Degree Leg Elevation and 30 Degree Head Elevation on Body Displacement and Sacral Interfaxe Pressures Over a 2-hour Period. Wound Care, vol. 29, no. 3, pg 143-148