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MEASURING VIBRATION EXPOSURE TO WHEELCHAIR USERS IN THE
COMMUNITY.
Yasmin Garcia BSa,b, Jonathan Pearlman PhDa,b, Steve Hayashi BSa,b, Juan J. Vazquez MSa,b, Rory A. Cooper PhDa,b, aHuman Engineering Research Laboratories, Department of Veterans Affairs, Pittsburgh, PA; bDepartment of Rehabilitation Science and Technology, University of Pittsburgh, Pittsburgh, PA; cDepartment of Physical Medicine and Rehabilitation, University of Pittsburgh, Pittsburgh, PA; ABSTRACT
In order to investigate vibration exposure to WC users, instrumentation has been developed Several laboratory studies among and a series of studies have been performed wheelchair (WC) users have suggested that WC [7-9]. The results suggest that hazardous levels users may be exposed to unhealthy levels of of vibration are present during certain WC Whole Body Vibration (WBV), a risk factor of propulsion or driving tasks. Nonetheless these spinal pain. To demonstrate this conclusively, studies have only collected data in short- long-duration community-based measurements duration in-lab or community-based trials. of WBV must be recorded. In this study, we While these studies provide an important describe the development of a vibration snapshot of the WBV exposure, because of their datalogger system to collect up to 14 days of short duration and in many cases a simulated environment, they do not provide conclusive evidence of hazardous levels of WBV exposure KEYWORDS
DESIGN OBJECTIVE
The purpose of this study is to develop non- BACKGROUND
invasive instrumentation to collect vibration exposure over extended periods (more than 2 There is a high prevalence of neck and back weeks) to accurately record the WBV exposure pain reported by wheelchair (WC) users [1]. A levels that WC users are subjected to during study carried out by Boninger and Siddall [1-2] found that around 60% of the WC users in their study complained about pain. They also found METHODS/APPROACH
that 60% of the subjects visited the doctor because of the pain and 40% of them had to limit their daily activities. Prolonged exposure to vibrations has been linked to injuries in Based on current standards and literature to nearly every body organ [3], with the most measure and assess WBV exposure to seated pronounced effects being on the spine [3-5]. As individuals, the following design criteria for a a result, the research in the field has led the vibration datalogger was established (Table 1.) International Standards Organization (ISO) to Electronic Design develop a standard for assessing translational (WBV) [6]. Although most of the studies low power microcontroller (Texas Instruments conducted about WBV have focused on vehicle operators, hazardous levels of vibration accelerometers (Analog Devices ADXL335), and exposure can occur in many circumstances and two AA alkaline batteries, was designed and to other populations which would arguably lead to similar health problems. For instance, studies Table 1: Vibration datalogger (VDL) design
carried out have confirmed that WC users are exposed to dangerous levels of vibration [7-8]. Need Design
requirements
Statement
Requirement Specification
WC has been unoccupied for more than 4 seconds. The On/Off switch design was tested using different types of WC cushions proof the switch´s reliability on different conditions such as weights, materials and base supports (rigid Diode) that indicate 1) whether there is a person seated on the WC, and 2) if there is a Software code was written in C language. The VDL system performs 4 essential tasks: detects if there if a memory card inserted in the VDL and checks whether or not there is space in the memory to store new data. If there is enough space, a new file will be created for writing. These following steps are executed every time the VDL is turned on: check sear sensor status to identify if there is a person seated on the WC, acquires analog data from the 3 accelerometers at 60Hz sampling rate and converts it to digital data, and writes data packaging, and a prototype of the circuit-board Premium 2009 (Figure 1) and prototyped in a The microcontroller was selected because of 1:1 scale using selective laser sintering (SLS) its low energy consumption (365 μA when to evaluate the feasibility of the design. The active and 0.5 μA during “stand-by” mode); VDL packagings consist in one main box that contains the electronics, one small packaging that contains the foot-rest sensor and two were chosen because their small dimensions covers for the back-rest and seat sensors. (20x20 mm in the evaluation board), low power consumption (350 μA), excellent temperature The back-rest and seat sensor’s covers were stability, linearity and effective application for designed using different types and sizes of Circuit-board and sensor’s packages were whether the WC is occupied of not. Its design tested to be water proof by using humidity incorporates two interlink FSR (Force Sensor stones and placing the boxes below the faucet. Resistor) on a voltage divider configuration that are mounted on top of the WC seat. The On/Off switch activates the “stand-by” mode when the 1 Based on research monitoring during community-based trials, a representative sample of activities can be captured over a 2 week time-period [11]. circular panel connectors to reinforce sensors’ connections to the main board and protect laboratory by attaching them on four WC and asking students, faculty and staff to use the WC during a day while logging their activity (each time they moved from their desk, got out of the WC, or did a weight-shift) Data collected from the VDLs were compared with the person´s log successfully. After a few software corrections, the VDL showed to work appropriately and the 20 VDLs were programmed. An additional test was carried out on nine WC users in an IRB- Figure 1: VDL computer design in SolidWorks. Figures a)
approved study who were asked to have the and b) show the VDL enclosure; figure c) shows a transparent isometric view of the VDL enclosure with the period. All the VDLs were able to collect main circuit board inside; figure d) shows the VDL tap vibration data for more than 2 weeks. Figure 2 designed to facilitate access to memory card; figure e) illustrates a snapshot of 2-days vibration data shows the main circuit board of the VDL; and figures f) show the enclosure for the footrest sensor. showing the RMS (root-mean-square) value estimated for each minute set data. Blank VDL’s mounting was selected from segments in the image represent periods of commercial fastener-mount cable holders. time when the wheelchair was unoccupied. These holders have different bundle sizes showed to be easy to attach to the VDL case RMS acceleration for each minute of a 2-days vibration data set and flexible to setup in different configurations. The foot-rest sensor case was designed to be attached to the foot-rest tube with Velcro® strap. VDLs and sensors cases were tested on different WC configurations (i.e. rigid and diameters) to ensure the packages can be 20 circuit-boards of the main electronics were fabricated by a third party company. Previous to the fabrication of the whole 20 set of VDLs, two samples of the circuit-board were provided by the company in order to verify the Figure 2: Vibration data collected on WC users.
functionality of the instrumentation. Once the Blue dots represent RMS acceleration data point for a electronic was improved and the errors were specific time; blank regions are periods of time when corrected, 20 circuit boards were approved to acceleration data were not collected because the wheelchair fabrication. VDL’s packages and sensor RESULTS/RESOLUTION
stereolithography (SLA). Flexible covers for the back-rest and seat sensors were fabricated with 3mm water proof neoprene and Velcro® straps. collect vibration data at the back-rest, seat and All sensors and On/Off switch (FSR and foot-rest surfaces of the WC. The VDL case and accelerometers) were connected to the main sensors can be attached to different WC circuit board using 24 AWG wires, plastic sleeve designs (rigid and folding frames) without to organize and protect wires, and water proof (transfers on and off the WC, moving around, ACKNOWLEDGEMENTS
folding and storing the WC). In addition, the VDL material and water-proof design of the This material is based upon work supported in cases covers and wire connectors are strong part by the Office of Research and enough to resist daily WC riding. The VDL Development, Rehabilitation Research & mounting system allows easily attaching and Development Service, Department of Veterans removing the VDL from the WC. Figure 3 shows Affairs, Grant# B6789C and Grant# B6673M; a WC with the VDL and sensors on it. In by Department of Veterans Affairs, VISN 4 addition, the VDL can acquire 2DOF CPPF; and by CONACyT scholarship register acceleration data from the accelerometers at #212007. 60Hz and store it on a 2Gb flash memory card for future use. The system power supply (AA represent the views of the Department of alkaline batteries) provides enough energy to Veterans Affairs or the United States collect data from 6 the channels (3 Government. accelerometers and 2DOF each) over 2-weeks Thanks are extended to the Human Engineering period of time. Finally, the VDL On/Off switch Research Lab shop staff. The team also thanks enables the system to stop acquiring data when the support of WC users for contributions to the the user is not in the WC, this prevents the system evaluation. collection of spurious data and save energy and Yasmin Garcia BS, University of Pittsburgh, Human Engineering Research Laboratories, Pittsburgh, PA, 15206, EMAIL: yag18@pitt.edu REFERENCES
[1] P. J. Siddall, et al., "A longitudinal study of the prevalence and characteristics of pain in the first 5 years following spinal cord injury," Pain, vol. 103, pp. 249-57, Jun 2003. [2] M. L. Boninger, et al., "Investigating neck pain in wheelchair users," Am J Phys Med Rehabil, vol. 82, pp. 197-202, Mar 2003. [3] H. Seidel and R. Heide, "Long-term effects of whole-body vibration: a critical survey of the literature," Int Arch Occup Environ Health, vol. 58, pp. 1-26, 1986. [4] S. Lings and C. Leboeuf-Yde, "Whole-body vibration and low back pain: a systematic, critical review of the epidemiological literature 1992-1999," Int Arch Occup Environ Health, vol. 73, pp. 290-7, Jul 2000. [5] M. Bovenzi and C. T. Hulshof, "An updated review of epidemiologic studies on the relationship between exposure to whole-body vibration and low back pain (1986-1997)," Int Arch Occup Environ Health, vol. 72, pp. Figure 3: VDL and sensors attached on a WC.
[6] I. S. O. ISO, "Mechanical Vibration and Shock-- Evaluation of human exposure to whole-body vibrations (2631-1 )," International Standards Organization1997. DISCUSSION/OUTCOMES/PERFORMANCE
[7] D. P. VanSickle, et al., "Analysis of vibrations induced during wheelchair propulsion," J Rehabil Res Dev, vol. 38, The VDL developed in this study was shown [8] D. P. VanSickle, et al., "Road loads acting on manual to be effective to measure long-duration wheelchairs," Rehabilitation Engineering, IEEE Transactions vibration data collected at all interface locations between the user and seat. The design allows [9] R. A. Cooper, et al., "Seat and footrest shocks and vibrations in manual wheelchairs with and without the system to be mounted on a wide range of suspension," Arch Phys Med Rehabil, vol. 84, pp. 96-102, manual WCs and to be easily manipulated by the WC user or the research staff. Data [10] M. J. Griffin and J. Erdreich, "Handbook of Human Vibration," The Journal of the Acoustical Society of collection of users in the community is ongoing, and publication of the WBV exposure levels in [11] M. L. Tolerico, et al., "Assessing mobility characteristics the community is forthcoming. and activity levels of manual wheelchair users," J Rehabil Res Dev, vol. 44, pp. 561-71, 2007.

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