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-
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 . 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
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 , 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) . 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 .
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
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,
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: email@example.com
 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.
 M. L. Boninger, et al., "Investigating neck pain in
wheelchair users," Am J Phys Med Rehabil, vol. 82, pp. 197-202, Mar 2003.
 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.
 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.
 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.
 I. S. O. ISO, "Mechanical Vibration and Shock-- Evaluation
of human exposure to whole-body vibrations (2631-1 )," International Standards Organization1997.
 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
 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
 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  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  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.
ME RESEARCH MEDICAL RESEARCH: SEEKING OBJECTIVITY IN ME STUDIES .2 REFUTING MISCONCEPTIONS .2 LESSONS FROM MS, GWS, RED AND PPV RESEARCH .3 PROBLEMS WITH DEFINITIONS .4 PROBLEMS WITH RESEARCH METHODS .5 RESEARCH SUPPORTS BIOLOGICAL EVIDENCE OF ME UNIQUENESS .6 RESEARCH: ME VS. CLINICAL DEPRESSION .7 RESEARCH: ME BIOLOGY VS. HEALTHY STATES.9 IMMUNOLOGY .9 VIROLOGY
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