ANALYSIS OF WHOLE-BODY VIBRATION DURING MANUAL WHEELCHAIR PROPULSION: A COMPARISON OF SEAT CUSHIONS AND BACK SUPPORTS

Carmen P DiGiovine, M.S.

Slide 1
ANALYSIS OF WHOLE-BODY VIBRATION DURING MANUAL WHEELCHAIR PROPULSION: A COMPARISON OF SEAT CUSHIONS AND BACK SUPPORTS

Carmen P DiGiovine, M.S.
5/25/01

Slide 2
Overview

Whole-body vibrations

Seat cushions and back supports

• Unimpaired individuals
  
  • Time domain parameters
    
  • Frequency domain parameters
    
• Manual wheelchair users
  

Slide 3
Introduction

WBV is detrimental to health of humans

Definition of vibrations: ISO 5805

• Single-event shocks
  
• Repeated (repetitive) shocks
  
• Oscillations
  
• Self-Generated vibrations
  

Effects of WBV on unimpaired individuals are well defined

Effects of WBV on MWUs are not well defined

Slide 4
Introduction

Initial analyses of WBV during MWP suggest

• Differences between seating systems
  
• Vibrations exceed recommended levels
  

Paucity of WBV data during MWP

Slide 5
Purpose

Determine Metrics

• Applicable to WBV during MWP
  
• Based on other applications and populations
  

Determine seat cushions and back supports that minimize vibrations

Slide 6
Seating Systems for Wheelchairs

Why is vibration (shock and oscillations) important?

• Elicit response to quick stretch
  
• Elicit a pressure sore
  
• Low Back injuries
  
  • Vibrations from primary activity
    
  • Secondary activities such as transfers and lifts
    

Slide 7
Characterizations of Seated Human Whole-body Vibration

Primary resonance frequency:

• Ranges from 4 to 6 Hz
  
• Centrally located at 5 Hz
  

Secondary resonance frequency

• Ranges from 8 to 13 Hz
  
• Evenly distributed
  

Nonlinearity

Slide 8
Seated WBV: Secondary Injuries

Relatively low loads that are repetitive in nature

High loads (single or Repetitive Events)

Spine Has Memory

• Compromised Spine
  
• Examples
  
  • Transfers
    
  • Lifting Wheelchair into an Automobile
    

Slide 9
METHODS

Individuals without a Disability

• Time Domain Transmissibility
  
• Frequency Domain Transmissibility
  

Individuals with a Disability

• Time and Frequency Domain Transmissibility
  

Slide 10
PARTICIPANTS

Individuals without a disability

10 Total / 3 Female / 7 Male

• Age (yr.): 25.7 ± 4.0 / 27.3 ± 2.9 / 25.0 ± 4.4
  
• Weight (kg): 72.9 ± 15.9 / 55.8 ± 4.8 / 80.2 ± 12.7
  
• Height (cm): 173.9 ± 12.7 / 159 ± 7.1 / 180.0 ± 9.0
  

Slide 11
Participants

Individuals with a disability

32 Total / 10 Female / 22 Male

• Age (yr.): 40.4 ± 8.9 / 38.1 ± 7.2 / 41.5 ± 9.5
  
• Weight (kg): 77.5 ± 16.0 / 61.3 ± 11.2 / 85.3 ± 12.8
  
• Height (cm): 170.2 ± 16.3 / 153.2 ±11.9 / 177.3 ± 11.2
  

Type of Disability

• Spinal Cord Injury: 26
  
• Spina Bifida: 4
  
• Multiple Sclerosis: 2
  

Slide 12
Wheelchairs

11 Quickie 2 or 2HP

4 Invacare Action A4

3 Quickie GP or GPV

14 Other

Slide 13
DATA COLLECTION

Traverse the simulated activities of daily living obstacle course

Self-selected speed

Record the accelerations at the wheelchair / seat cushion interface

3 trials per condition

• 99 trials per individual - Individuals without a disability
  
• 21 trials per individual - Individuals with a disability
  

Slide 14
Seat Cushions

Invacare / PinDot ComfortMate (PDCM)

• Contoured foam
  

Varilite Solo (VS)

• Air Bladder with a foam base
  

Sunrise Medical / Jay Active (JA)

• Viscoelastic Material with a Foam base
  

Roho Low-Profile (RLP)

• Air
  

Slide 15
Seat Cushions

Graphic description: photograph of 4 cushions, Varilite Solo, Jay Active, Roho Low Profile, Pin Dot Comfort Mate.

Slide 16
Back Supports

Nylon Sling Back (SB)

• Nylon Upholstery Only
  

Invacare / PinDot PaxBac (PB)

• Stiff Foam Supplemental Lumbar Support for Nylon Sling Back
  

Sunrise Medical / Jay Active Back (JAB)

• Foam with a Rigid Plastic Base
  

Varilite FastBack (VFB)

• Foam with an Air Bladder Lumbar Support
  

Slide 17
Back Supports

Graphic description: a photograph of 4 back supports, Jay Active Back, Nylon Sling Back, Varilite FastBack, Pin Dot Paxbac.

Slide 18
Simulated Activities of Daily Living Obstacle Course

Graphic description: a photograph of a wheelchair surrounded by surfaces of different textures which impose various vibrations when the chair rides over them.

Slide 19
INSTRUMENTATION

Graphic Description: a photograph of a person in a manual wheelchair during a trial, demonstrating the instrumentation used: a tri-axial accelerometer, an angular rate sensor, a medical grade stainless steel bite-bar, foam dental trays used to protect teeth and a aluminum plate interfaced between seat rails of wheelchair and seat cushion.

Slide 20
Instrumentation

Graphic description: photograph of a wheelchair with the seat removed to view the metal plate that holds the accelerometer.

Slide 21
CALCULATIONS: Time Domain

Vibrational-Dose-Value

Graphic description: mathematical formula for Vibrational-Dose-Value

Transmissibility

Graphic description: mathematical formula for Transmissibility.

Slide 22
CALCULATIONS: FREQUENCY DOMAIN

Unbiased Autocorrelation and Cross-Correlation

74 dB 4-term Blackman-Harris Window

Zero Pad

Estimate of Input and Output autospectral density and cross-spectral density

Estimate of the Transfer Function

Slide 23
Calculations: Frequency Domain

Parameters from Transmissibility

• Single Measures
  
  • Maximum Magnitude (Hmax)
    
  • Frequency Corresponding to the Maximum Magnitude (Fmax)
    
  • Total Power: Area under the Magnitude versus Frequency Curve (Harea)
    
• Repeated Measure: Divide transmissibility into proportional bandwidth increments
  
  • Individuals without a Disability
    
    • 1 to 20 Hz 1/6 Octave Bandwidth
      
    • 20 to 100 Hz 1/3 Octave Bandwidth
      
  • Individuals with a Disability
    
    • 1 to 100 Hz 1/3 Octave Bandwidth
      

Slide 24
Rumble Strip Constant Bandwidth Transmissibility (Vertical)

Graphic description:

Slide 25
Rumble Strip Constant Bandwidth Transmissibility (Vertical)

Graphic description:

Slide 26
Rumble Strip Proportional Bandwidth Transmissibility (Vertical)

Graphic description:

Slide 27
STATISTICS

Individuals without a disability: Randomized Complete Block Design (A, B)

Individuals with a Disability: Balanced Incomplete Block Design (C, D)

Single Measure

• Fixed Effects
  
• Random Effects
  

Repeated Measure (Compound Symmetry)

• Fixed Effects: Center Frequency (Repeated),
  
• Random Effects
  

Slide 28
Results

Individuals without a Disability

• Tw
  
• Hmax, Fmax, Hoct
  
• Hoct
  

Individuals with a Disability

• Tw
  
• Fmax
  
• Hoct
  

Slide 29
Individuals without a Disability: Time Domain

Graphic description:

Slide 30
Rumble Strip Constant Bandwidth Transmissibility (Vertical)

Graphic description:

Slide 31
Individuals without a Disability: Frequency Domain: Hmax

Invacare Action Xtra

• Sig. Diff. among cushions in the fore-to-aft direction when traversing the carpet and dimple strip
  
• Sig. Diff. among cushions in the vertical direction when traversing the medium sinusoidal bump
  
• Sig. Diff. among back supports in the fore-to-aft direction when traversing the curb descent
  
• No significant differences among back supports in the vertical direction
  
• Standard deviation is extremely large
  

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Updated: February 28, 2002