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

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

Slide 2
Overview

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Whole-body vibrations

Seat cushions and back supports

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

Slide 3
Introduction

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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

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Initial analyses of WBV during MWP suggest

  • Differences between seating systems
  • Vibrations exceed recommended levels

Paucity of WBV data during MWP

Slide 5
Purpose

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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

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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

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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

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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

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Individuals without a Disability

  • Time Domain Transmissibility
  • Frequency Domain Transmissibility

Individuals with a Disability

  • Time and Frequency Domain Transmissibility

Slide 10
PARTICIPANTS

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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

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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

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11 Quickie 2 or 2HP

4 Invacare Action A4

3 Quickie GP or GPV

14 Other

Slide 13
DATA COLLECTION

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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

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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

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

Slide 16
Back Supports

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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

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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

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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

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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

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

Slide 21
CALCULATIONS: Time Domain

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Vibrational-Dose-Value

Graphic description: mathematical formula for Vibrational-Dose-Value

Transmissibility

Graphic description: mathematical formula for Transmissibility.

Slide 22
CALCULATIONS: FREQUENCY DOMAIN

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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

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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)

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Graphic description:

Slide 25
Rumble Strip Constant Bandwidth Transmissibility (Vertical)

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Graphic description:

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Rumble Strip Proportional Bandwidth Transmissibility (Vertical)

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Graphic description:

Slide 27
STATISTICS

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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

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Individuals without a Disability

  • Tw
  • Hmax, Fmax, Hoct
  • Hoct

Individuals with a Disability

  • Tw
  • Fmax
  • Hoct

Slide 29
Individuals without a Disability: Time Domain

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Graphic description:

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Rumble Strip Constant Bandwidth Transmissibility (Vertical)

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Graphic description:

Slide 31
Individuals without a Disability: Frequency Domain: Hmax

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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

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Please note: This information is provided a archival information from the Rehabilitation Engineering Research Center on Wheeled Mobility from 1993 to 2002.

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