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

Carmen P DiGiovine, M.S.

(con't.)

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
  

Slide 32
Individual without a Disability: Seat Cushion: Fore-to-aft

Fmax Does not typically reside in frequencies most sensitive to humans (0.63 to 1.6 Hz)

Harea

• No conclusions with regard to Quickie Breezy
  
• JA is worst for Invacare Action Xtra only
  

Hoct

• No conclusions with regard to Quickie Breezy
  
• JA is worst for Invacare Action Xtra only
  
  • No significant differences for Group 2 Obstacles (rumble and dimpl

Slide 33
Individual without a Disability: Seat Cushion: Vertical

Fmax

• Quickie Breezy
  
  • Mean Fmax resides in the frequencies most sensitive to humans (4 to 12.5 Hz)
    
  • JA typically resides outside this range
    
  • significantly different than at least one other cushion for 6 of 9 obstacles and all of the obstacles combined
    
• Invacare Action Xtra
  
  • All cushions typically reside outside range of frequencies most sensitive to humans
    
  • JA is significantly different than at leas one other cushion for 7 of 9 obstacles and all of the obstacles combined
    

Slide 34
Individual without a Disability: Seat cushions: Vertical

Harea

• Quickie Breezy - No significant differences
  
• Invacare Action Xtra - JA had significantly larger results for 3 of 9 obstacles
  

Hoct

• Quickie Breezy - No significant differences
  
• Invacare Action Xtra - JA had significantly larger results for 3 of 9 obstacles
  

Slide 35
Individual without a Disability: Back Support: Fore-to-aft

Fmax

• Does not reside in frequencies most sensitive to humans (0.63 to 1.6 Hz)
  
• Significant differences found for only one obstacle for both Invacare Action Xtra and Quickie Breezy
  

Harea

• Quickie Breezy - SB has significantly smaller results for 4 of 9 obstacles
  
• VFB - VFB has significantly larger results for 2 of 9 obstacles
  

Slide 36
Individual without a Disability: Back Support: Fore-to-aft

Hoct

• Quickie Breezy - SB has significantly smaller results for 6 of 9 obstacles and all of the obstacles combined (Group 1 and 3 obstacles)
  
• Invacare Action Xtra
  
  • PB has significantly larger results for 3 of 9 obstacles and all of the obstacles combined
    
  • VFB has significantly larger results for 2 of 9 obstacles and all of the obstacles combined
    

Slide 37
Individual without a Disability: Back Support: Vertical

Fmax

• Quickie Breezy
  
  • VFB is significantly larger than other BS when examining all of the obstacles combined
    
  • Mean Fmax resides in the frequencies most sensitive to humans (4 to 12.5 Hz)
    
• Invacare Action Xtra
  
  • Significant differences exist for 3 of 9 obstacles, but results are inconsistent
    
  • Mean Fmax typically reside outside the frequencies most sensitive to humans (4 to 12.5 Hz)
    

Slide 38
Individual without a Disability: Back Support: Vertical

Harea

• Significant differences exist for only one obstacle when considering the Quickie Breezy and no obstacles when considering the Invacare Action Xtra
  

Hoct

• No differences exist among back supports for either wheelchair
  

Slide 39
Individuals with a Disability

Time Domain: Tw

Frequency Domain

• Single Measure: Fmax
  
• Repeated Measures: Hoct
  

Slide 40
Individuals with a Disability: Results: Seat Cushions

Fore-to-Aft

• Tw
  
  • JA is significantly smaller than the PDCM and the VS for all of the obstacles combined
    
  • RLP is significantly smaller than the VS for all of the obstacles combined
    
• Fmax - Mean Fmax always reside outside the frequencies most sensitive to humans
  
• Hoct - Significant differences exist for 3 of the nine obstacles but the differences are not consistent
  

Slide 41
Individuals with a Disability: Results: Seat Cushions

Vertical

• Tw - Significant differences exist for only of the nine obstacles
  
• Fmax
  
  • Significant differences among seat cushions do not exist
    
  • Mean Fmax reside in region most sensitive to humans for rumble strip and dimple strip
    
• Hoct - JA is significantly larger than PDCM and RLP for all of the obstacles combined
  

Slide 42
Individuals with a Disability: Results: Back Supports

Fore-to-aft

• Tw
  
  • VFB is significantly larger than all other back supports for curb descent, rumble strip and all of the obstacles combined
    
  • VFB is significantly larger than SB and PB for the dimple strip
    
• Fmax
  
  • Mean Fmax always reside outside the frequencies most sensitive to humans
    
  • Significant differences exist for only of the nine obstacles
    
• Hoct - Significant differences among back supports do not exist
  

Slide 43
Individuals with a Disability: Results: Back Supports

Vertical

• Tw - Significant differences among back supports do not exist
  
• Fmax
  
  • Mean Fmax reside in region most sensitive to humans for rumble strip and dimple strip
    
  • Significant differences among back supports only exist for medium sinusoidal bump
    
• Hoct - Significant differences among back supports do not exist
  

Slide 44
Individuals without a Disability: Discussion

Weighted Vibrational-Dose-Value

Invacare Action Xtra

• Best
  
  • Seat Cushion: VS
    
  • Back Support: VFB followed closely by JAB
    
• Worst
  
  • Seat Cushion: RLP
    
  • Back Support: SB
    

Slide 45
Individuals without a Disability: Seat Cushion

Fore-to-Aft

• The JA is the worst cushion
  
• Wheelchair Dependence
  
• Effect of cushion in the Fore-to-Aft direction is larger than originally anticipated
  
  • Fore-to-Aft Vibrations are larger than originally thought
    
  • Shear between the body and the cushion is significant enough to transmit vibrations
    
  • Important for minimizing the chances of pressure sores occurring due to sheer stress.
    

Slide 46
Individuals without a Disability: Seat Cushion

Vertical

• Wheelchair Dependence
  
• Conflicting conclusions
  
  • Based on Fmax the JA is the best seat cushion when considering the Quickie Breezy only
    
  • Based on Harea and Hoct JA is the worst seat cushion when considering the Invacare Action Xtra only
    

Slide 47
Individuals without a Disability: Back Support

Fore-to-Aft

• Best back support is the SB
  
• Worst back support dependent on wheelchair
  
  • Quickie Breezy: JAB
    
  • Invacare Action Xtra: VFB
    

Vertical

• No conclusions can be made
  

Slide 48
Individuals with a Disability: Seat Cushions

Fore-to-aft

• Conflicting results depending on the type of measure
  
  • Time domain transmissibility: JA is the Best
    
  • Frequency Domain (Hoct): JA is the worst
    

Vertical

• No Conclusions can be made
  

Slide 49
Individuals with a Disability: Back Supports

Fore-to-aft

• VFB is the worst back support
  

Vertical

• No conclusions can be made
  

Slide 50
Limitations

Control of propulsion speed

Assumption that head and seat plate remain level for individuals without a disability

Individual seating systems were not examined

An accelerometer was not used at the wheelchair/back support interface

Individual with a disability used his/her own wheehchair

Slide 51
Future Investigations

Due to apparent dependence on wheelchair, investigate role of wheelchair and wheelchair related components

Examine parameters other than transmissibility such as VDV at the seat for wheelchair or VDV at bite-bar for seating system

Examine seating systems in a more controlled setting

• Hybrid III test dummy
  
• Standardized Testing equipment
  

Slide 52
CONCLUSION

Relevant parameters

• Tw, Fmax, Hoct
  

Difficult to recommend a single cushion and/or back support for all cushions

Other components associated with wheelchairs may have a greater effect

• Frame design
  
• Frame Materials
  
• Casters and Wheels
  
• Shock absorption systems
  

Clinical Relevance: Focus on other aspects of seating system

Slide 53
Seating Systems for Wheelchairs

Seating System Recommendations (Minkel, 2000, Hastings, 2000, Trefler et al., 1993)

• Skin Protection / Prevent pressure sores
  
• Promote independent mobility
  
• Enhance functional skills (e.g. transfers, ADL)
  
• Inhibit the response or reactivity to quick stretch
  
• Inhibit abnormal tone
  
• Comfort
  
• Positioning (i.e. prevent / accommodate deformity)
  

Do not consider the effects of whole-body vibration except Cooper (1998); does not suggest which cushion will be the best.

Slide 54
Seated Whole-body Vibration of Unimpaired Individuals

High risk: spine (low-back pain, early degeneration of the spine and herniated disc) and peripheral nervous system

Lower risk: digestive system, peripheral veins, female reproductive system, vestibular system

Interference with vision and manual control performance

Slide 55
Seated Whole-body Vibration of Unimpaired Individuals

Role of muscles

• Fatigue will put spine at increased risk
  
• Muscle response 180
  

Memory of spine: increased risk of injury for activities that normally would not cause injury

Slide 56
Factors Related to WBV

Degraded Comfort

• Back Pain
  

Interference with Activities

• Fine Motor Control
• Manual Wheelchair Propulsion
  

Impaired Health

• Increased Susceptibility to Pressure Sores and Secondary Injuries
  

Perception of Low-Magnitude Vibration

Motion Sickness

Slide 57
Individuals without a Disability: Time domain

Graphic description:

Slide 58
Individuals without a Disability: Frequency Domain

Quickie Breezy

• No significant differences among cushions in fore-to-aft and vertical directions
• No significant differences among back supports in the vertical direction
• Significant differences among back supports in the fore-to-aft direction when traversing the medium sinusoidal bump
• Standard deviation is extremely large
  

Slide 59
Individuals without a Disability: Frequency Domain

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
  

Slide 60
Individuals without a Disability: T

VS is the Best

• Interaction of Air Bladder and Foam Bas
• Air Bladder secures buttocks within cushion
  

RLP is the Worst with PDCM deserving mention

• Air or foam by themselves tend to transmit vibrations from wheelchair to user
  

Limited to Invacare Action Wheelchair

Slide 61
Individuals without a Disability: T

VFB is the Best

• Air bladder maximizes contact area
• Air / Foam combination
• Postural Position of Individual
  • Relaxed body tends to absorb less vibration
    

SB is the Worst

• Materials are not conducive to absorbing vibration
• Poor Postural Position
  • Tense muscles in order to compensate for lack of support

Limited to Invacare Action Wheelchair

Slide 62
Individuals without a Disability

Single Measures

• Hmax Maximum transmissibility an individual experiences in any one frequency. Do not use in final analysis
• Fmax Frequency corresponding to Hmax. Estimate of Primary Resonance Frequency
• Harea Power of the vibrations transmitted to the individual
  

Repeated Measure

• Hoct Power of the vibration transmitted to the interval within a given frequency interval
  

The End

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Updated: February 28, 2002