November 2002

Delving into Design

By Pascal Malassigné, MID, IDSA; Audrey L. Nelson, RN, PhD; Robert P. Jensen; Mark Cors; Thomas L. Amerson, PhD, CPE; and Leah P. McLellan, PhD

There are more than 220,000 individuals with spinal cord injury (SCI) in the United States today.¹ The majority of these individuals need to use a commode-shower wheelchair for toileting and showering. A survey of 147 veterans with SCI was conducted to evaluate existing commode-shower wheelchairs, and findings revealed numerous safety-related problems with existing models.

METHOD

Before beginning the design process, we evaluated existing wheelchairs with patients and caregivers. From this evaluation, functional and performance criteria were established to develop new wheelchair prototypes for clinical evaluation at two Veterans Administration (VA) Medical Centers. Typical of many such projects, an iterative process of prototype development and clinical evaluation was used to develop the new wheelchairs. Responses received from patients and caregivers were incorporated into the next prototype until the new wheelchairs were completed.

Figure 1. The VA folding commode chair

Figure 2. The VA advanced commode shower chair

SAFETY AND PERFORMANCE CRITERIA

The wheelchairs were designed based on the following safety and performance criteria:

• Overall chair safety: must not contribute to the development of pressure ulcers, or cause injuries to patients because of falls while transferring or bending forward to wash the feet.
• Positioning over a toilet: must fit properly over a toilet bowl to prevent fecal matter from falling on the floor.
• Seat design: must be designed for under-seat hand access from three sides, be waterproof, provide full thigh support, and be cushioned to avoid skin pressure.
• Seating position: must be sloped 4° to 5Þ toward the back to hold the user safely in place.
• Armrests: must swing out of the way for transfers, provide a resting place for the forearms, and support the user’s body weight while hooking under or lifting themselves or repositioning their body.
• Hand access to the perianal area: must provide unrestricted under-seat hand access to the perianal area from at least three positions (right, left, and front).
• Caregiver friendly: must provide for unrestricted hand access to the perianal area of the patient. The footrests must adjust easily for users of varying height.
• Durability rustproofing: must survive long-term use in wet environments.
• Propulsion pushrims: must be appropriately sized for optimum hand positioning, be coated with nonslippery material to assist propelling in wet environments.
• Static stability: must be designed for a minimum tip angle of 20° in forward, rearward, and sideways tipping.
• Design of two versions: rigid and folding for independent use, and rigid and folding wheelchairs for assisted care.

The project began with the design of adjustable wheelchair frames, in order to establish the proper relationship between the seat, toilet bowl, and bathroom wall. With the frame geometry established, the other aspects of the folding and rigid wheelchairs development followed.

The design development process is presented using American National Standards Institute-Rehabilitation Engineering and Assistive Technology Society of North America (ANSI/RESNA) Wheelchair (WC) Standards nomenclature.

BODY SUPPORT

WC-00 defines the body support system as “those parts of the wheelchair which directly support or contain the body of the user.” This includes seat design, and several rectangular seats of various dimensions and hole opening were developed and evaluated with a pressure-mapping system. From these various designs, a new “C” shape seat was created, allowing hand access in three positions (front, left, and right side). This seat measures 49 x 54 cm and incorporates front “wings” projecting on the sides to facilitate side transfers.

In developing seat cushioning, we evaluated various foam densities with a pressure mapping system. Using established maximum acceptable pressures for persons with SCI, testing involved recording the amount of pressure being exerted on the surface of the seat by patients. The results indicated that low-pressure readings were dependent not only on the amount of padding but also in using a softer density of foam Indentation Force Deflection (IFD 55) under the ischial tuberosities (around the periphery of the inner seat area) versus a harder density foam (110 IFD) for the rest of the seat.

Lockable pivoting and swing-away armrests, capable of holding patients weighing upward of 100 kg, were also designed. In the locked position, users can latch under them and pull up without fear of unlocking them. A lever release mechanism was developed to lock and unlock the armrests. For added comfort, long armrest pads are used to provide increased resting surface area for the arms and elbows.

FOOTRESTS

Footrest design was also important. Development started with designs that held the entire foot. The new design is a footrest with a deep heel cup, contoured to fit the bottom of the foot. To avoid potential ankle injuries, all edges are rounded and smooth. A hole is included for water drainage when showering.

The ability to adjust footrests in order to match the user’s height is critical in establishing a good seating position, yet footrests typically require the use of tools for adjustment. In developing the new footrests, a lever handle was selected that would easily lock or unlock the footrests to raise or lower them along the footrest posts.

It is not uncommon for users to fall out of the chair while trying to reach their feet during showering. Discussions with users about showering in a chair revealed that lifting the leg over a bathtub ledge or a raised surface was a safer alternative than trying to reach down. This was the inspiration for a new footlift that allows the safe cleaning of feet and legs.

The footlift is a hinged mechanism that hangs in front of the frame when not in use. To use the footlift, the user swings it up into position and manually brings each foot up into the heel cup.

DRIVING WHEELS AND PUSHRIMS

WC-00 defines the driving wheel of a wheelchair as “a wheel that is connected to the driving system and when in contact with the underlay develops the propelling force.” Typical commode-shower chairs are equipped with 61-cm-diameter wheels and 1.9-cm-diameter metal pushrims.

In the driving wheel selection process for self-propelled wheelchairs, 55-cm-diameter wheels, instead of the customary 61-cm wheels, were chosen for clinical evaluation. While the standard wheel size provides easier hand access to the pushrims, it also creates problems by butting against the bathroom wall before centering over the toilet. The decision to use smaller wheels solved problems with access over the toilet as well as for transfers. For assisted care wheelchairs, for patients who need caregiver assistance, wheels of 32.5-cm diameter were selected.

To develop new pushrims, we used ergonomic data on the dimensions of the hand. The goal was to increase the surface area for the hands when grasping the pushrims. A test mock-up was built, made of curved PVC tubing and mounted to the wheel of a wheelchair, with three different diameters: 2.7, 3.5, and 4.2 cm, all larger than the typical diameter of 1.9 cm. It was then possible to compare one pushrim size to another. Ten veterans with SCI participated in a preference study of the three diameters. The 3.5-cm size was preferred and was produced in aluminum and coated with rubber. These larger than typical pushrims were mounted on the new wheelchair prototypes. The rubber coating further enhanced grasping ability and was greatly appreciated in clinical evaluations conducted in wet environments.

WC-00 defines the caster wheel of a wheelchair as “a wheel that can pivot but is not intended to govern the driving direction.” Standard 15-cm caster wheels were used on all the chair prototypes, with the stems mounted inside the frame to protect the bearings from rusting. After 12 months of clinical evaluation in active hospital settings, no rust was detected on any of the prototypes.

As for the parking brake, WC-00 defines it as “the braking system that is intended for keeping the wheelchair stationary on sloping ground whether or not the wheelchair is occupied.” Lever-type parking brakes were selected for all wheelchair prototypes. Clinical evaluation indicated complete user satisfaction with these brakes.

FRAMES AND STATIC STABILITY TESTING

WC-00 defines a wheelchair frame as follows: “The frame unites and supports the other parts of the wheelchair. Seat-frame-backrest could form, or be combined into, one unit or consist of separate parts.” Design of new frames started with development of an adjustable chair frame to establish the proper relationship between the seat, toilet bowl, and wall. From there, rigid and folding wheelchair frames were developed.

The frames were tested for static stability according to WC-01: determination of static stability for forward, rearward and sideways tipping. Static stability was measured when the wheelchair was positioned on a platform with a 75-kg and a 100-kg subject. The platform was tilted up-slope and down-slope, and tipping was achieved when the front or rear wheels of the chair lifted off the platform. Frame configurations were modified until a minimum 20° tipping angle was established. The prototype evaluation involved focus group discussions and questionnaires designed for patients and caregivers. The questions related to the wheelchair’s features regarding toileting and showering, seating, transferring, folding and unfolding, and other issues.

RESULTS

The new wheelchairs were found to fit conveniently in shower stalls and over toilets, and to improve showering and toileting via the many places available to hold onto. The wheelchairs were also found to hold users in an appropriate position and to provide a wide, comfortable seat.

Stability: Both patients and caregivers considered the wheelchairs to be stable while in use and for transferring. The brakes were found to be easily activated and effective in holding the wheelchairs in place.

Backrest: Both patients and caregivers reported that the backrest was comfortable and that it provided sufficient space to wash the back.

Seating comfort: Patients responded that the seat was comfortable and not too firm. Both patients and caregivers were able to reach under the seat easily. They found the opening of the seat to be an adequate size and the seat cover material not overly slippery when wet. The patients felt secure and did not feel that they were falling into the seat opening.

Armrests: They were found to be strong, and to have comfortable pads and curved ends that helped grasping. Footrests: The footrests were found to hold the patients’ feet properly and safely in place, and to be easily adjustable by caregivers.

Footlift: The footlift did not interfere with patient transfer. Both patients and caregivers found the footlift made washing of feet easy and caused no discomfort or loss of balance.

Pushrims: The new pushrims received positive responses for their gripping effectiveness when wet, and for their larger-than-standard size.

REFERENCE

1. Stover S, DeLisa J, Whiteneck G. Spinal Cord Injury: Clinical Outcomes from the Model Systems. Gaithersburg, Md: Aspen; 1995.

Pascal Malassigné, MID, IDSA, is a professor of industrial design, Milwaukee Institute of Art & Design and research industrial designer, Milwaukee VA Medical Center (VAMC). He is a Fellow member of the Industrial Designers Society of America (IDSA) and president of IDSA’s Design Foundation.

Audrey L .Nelson, RN, PhD, is associate chief of nursing service for research, at James A. Haley Veterans Hospital, Tampa, Fla.

Robert P. Jensen is an industrial designer, Department of Physical Medicine & Rehabilitation at Medical College of Wisconsin, Milwaukee.

Mark Cors is a graduate student at the Institute of Design of the Illinois Institute of Technology in Chicago.

Thomas L. Amerson, PhD, CPE, is a statistician and human factors consultant in Gales Ferry, Conn.

Leah P. McLellan, PhD, is an epidemiologist, Baltimore VAMC.

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