RESNA 27th International Annual Confence
Revaluation of the Vibration Exposure Power Wheelchair Users Experience When Driving Over Selected Sidewalk Surfaces
The purpose of this research was to determine the levels of vibration that a person driving an electric powered wheelchair are exposed to when driving over six different sidewalk surfaces. Testing was conducted in the spring of 2002 and summer of 2003 to determine if environmental factors increase the vibration levels experienced by power wheelchair users. Ten non-wheelchair users were asked to drive an electric powered wheelchair over six sidewalk surfaces a total of three times each at 1 m/s and 2 m/s. Vibrational Dose Values (VDV) was used as a measurement of the severity of the amount of whole body vibration experienced. For seat VDVs, results showed that significantly lower values were found in the second year compared to the first year as well as across surfaces.
Power wheelchairs, Sidewalk surfaces, Vibration
Throughout the course of their daily routine, power wheelchair users often encounter driving surfaces that are rough and uneven. These irregular surfaces can cause vibrations on the wheelchair and in turn, the wheelchair user, which through extended exposure can cause low-back pain, disc degeneration and other harmful effects to the body (1). To date, little research has been conducted to assess the vibrations experienced by power wheelchair users (2). In response to the lack of evidence, a study was conducted in 2002 to evaluate the amount of vibration both manual and power wheelchairs users are subjected to when driving over various pavement surfaces (3-4). These results demonstrated that five of the six newly installed outdoor surfaces tested met the standards for whole-body vibration measurement developed by the International Standards Organization (ISO) and the American National Standards Institute. To further evaluate these sidewalk surfaces and determine if environmental factors, such as weather related wear, over the course of one-year affect the vibration levels, testing was repeated.
The purpose of this research study was to determine the levels of vibration that a person driving an electric powered wheelchair is exposed to when driving over six different sidewalk surfaces. This study was previously conducted in the spring of 2002 and was replicated in the summer of 2003 to determine if environmental factors, such as weather related wear, increase the vibration levels experienced by power wheelchair users. It was anticipated that there would be no significant differences between the vibrational dose values (VDV) recorded in 2002 and 2003.
In the summer of 2003, we repeated an evaluation of six different types of sidewalk surfaces initially conducted in the spring of 2002. The outdoor sidewalk surfaces are located in Pittsburgh Pennsylvania and have been maintained by research staff. All the sidewalk surfaces are contiguous and are approximately 4 feet wide and 25 feet long. Surface 1 was a poured concrete sidewalk with a brush finish to represent the norm. Surfaces 2, 3, and 4 were made from interlocking concrete pavers placed in a 90 degree herringbone pattern. The beveled edges of the concrete blocks used for surfaces 2-4 varied (squared edges, 3.2 m (1/8”) beveled edges, and 6.4 mm (1/4”) beveled edges, respectively.) Surfaces 5 and 6 were constructed of fired clay bricks placed in a 45 degree herringbone pattern with squared edges.
All ten participants provided written informed consent prior to participating in the study. Half of the participants were from the original 2002 sample and the other five participants were matched by gender, height ( " 2 inches) and weight ( " 5lbs) to the previous participants. Five men and five women were in the study sample. The mean ± SD age of the 2002 participants was 32.5 ± 10.0 years, and the range was 23 to 55 years. The mean ± SD age of the 2003 participants was 30.7 ± 11.6 years, and the range was 21 to 56 years.
The participants were ten non-wheelchair users asked to drive a power wheelchair (Quickie P200, Sunrise Medical Ltd.) over the six sidewalk surfaces a total of three times each at two speeds (1 m/s and 2 m/s) for a total of 360 trials (360 = 10 participants x 6 surfaces x 3 repetitions x 2 speeds). Speed was verified for each trial using a stopwatch over a known distance. Trials were considered acceptable when the time was within 0.1 s of the target time. Tri-axial accelerations were collected at the footrests and seat. A custom data-collection program was used to interface with a data acquisition card. The acceleration data were calibrated and converted for analysis in custom software written using Matlab.
A mixed model repeated measure was completed on the data, using seat VDV as the dependant variable, and surface (6 repeated levels), year (2 levels), and speed (2 levels) as the independent factors. A Bonferroni post hoc analysis was completed if the surface factor was significant. Two separate models were created, one for foot vibrational dose values and one for seat vibrational dose values. Alpha was set a priori at 0.05.
Vibrational Dose Values (VDV) is a measurement of the severity of the amount of whole body vibration experienced. The greater the vibrational dose values, the greater risk of discomfort, pain, and injury (5). In accordance with the ISO 2631 standard, the VDV was calculated by taking the total amount of vibrations experienced for each trial to the forth power, and then taking the fourth root of the sum (6).
For seat VDVs, results showed that significantly lower values were found in the second year compared to the first year as well as across surfaces. The post-hoc analysis showed that surface four was significantly higher than the other surfaces. For the foot VDVs, differences between years were barely significant (p=0.048), although differences across surfaces were significant. As with the seat, surface four had the highest VDVs. Figures 1 and 2, show the distribution of the average values for each of the surfaces, for each of the years.
In comparing the results of testing in 2002 and fifteen months later in 2003, it was demonstrated consistently that four out of the five surfaces are acceptable as pedestrian access routes for wheelchairs users when compared to the standard concrete surface (Surface 1). Surface 4 has the greatest beveled edge (¼ inch), which explains why this surface produced the greatest amount of vibration at the seat and footrest among the 6 surfaces tested and should not be used. Surface 2 has a squared edge and demonstrated the least amount of vibration at both the seat and footrest among all surfaces, including the concrete surface used as the gold standard. The probable cause of this finding is due to the front casters “catching” the breaks or cracks between the concrete sections causing increased vibration levels. Because the front casters are smaller in diameter and loaded with less effective mass, they detect more subtle changes in the surface profile than at the seat, this also explains why the VDVs at the footrest are higher and the VDVs at the seat are lower in year two compared to year one.
Further testing of these and additional surfaces is warranted. Although these sidewalk surfaces have been exposed to Pittsburgh's climate over at least 1-year, these surfaces do not sustain continuous use, which could affect the quality of the surfaces.
Funding was provided by the VA Rehabilitation Research and Development Service, Veterans Health Administration, U.S. Department of Veterans Affairs (F2181C), and the U.S. Department of Education, National Institute on Disability and Rehabilitation Research (NIDRR) Rehabilitation Engineering Research Center on Wheeled Mobility (H133E990001).
Annmarie R. Kelleher, OTR/L
VA Pittsburgh Healthcare System, 151R-1
Human Engineering Research Laboratories
7180 Highland Drive, Pittsburgh, Pennsylvania 15206
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