MECHANICAL DESIGN REPORT

Mechanical Design Report: 'Tilt Wheelchair System'

Table of Contents

Introduction3

Literature Review5

Worldwide Need for Pediatric Wheelchairs7

Unique Needs of Pediatric Wheelchair Users9

Physical growth and change9

Mobility10

Self-sufficiency of child11

Comfort and enjoyment12

Seating13

Transportation of wheelchair and child15

Consequences of inadequate pediatric wheelchairs16

Performance Criteria19

Hardware20

Methods23

Subjects23

Instrumentation24

Protocol25

First Visit26

Midstudy Visit26

Final Visit27

Data Analysis and Reduction27

Wheelchair Occupancy27

Characteristics of Usage Patterns28

Statistical Analysis29

Results30

Demographics30

Wheelchair Data30

Wheelchair Occupancy30

Seating Function Usage31

Characteristics32

Survey Results32

Discussion33

Conclusions39

References40

Mechanical Design Report: 'Tilt Wheelchair System'

Introduction

Prescribing seating for individuals who use wheelchairs primarily for mobility often entails considering posture, comfort, function, and pressure management. Power wheelchairs with self-actuated seating functions, such as tilt-in-space, backrest recline, and seat elevation, are usually prescribed by clinicians to facilitate posture change and/or assist activities of daily living (ADL) for persons with a high-level spinal cord injury (SCI) who have impaired sensation and are unable to adjust postures independently or for those with neuromotor impairments who are unable to use a standard wheelchair seat (Kernozek & Wilder, 2002: 868).

Previous research that evaluated the effectiveness of tilt-in-space and backrest recline functions was largely conducted in laboratory settings. Studies have been conducted to examine seat pressures at different angles of tilt-in-space and backrest recline. Researchers found that tilt-in-space significantly reduced static seating pressure, a key component in pressure ulcer development, and that combining tilt-in-space with backrest recline reduced pressure more than tilt-in-space alone (Stinson & Porter-Armstrong, 2003: 504). In addition, almost all the previous laboratorybased studies suggested that persons use large tilt-inspace and recline angles to effectively manage pressure to reduce the risk of skin breakdown. The study concluded that the biggest reduction in maximum pressure at the ischial tuberosities was found at 45° of tilt-inspace and 120° of backrest recline and that an effective weight shift could be achieved only when tilt-in-space is >15°. As for the time required for pressure relief, Coggrave and Rose described measuring transcutaneous oxygen tension to effectively determine when pressure relief becomes adequate. They measured the time taken for subjects to return their tissue oxygen to unloaded levels and found that brief pressure lifts for 15 to 30 seconds did not relieve pressure for most people, while longer lifts for an average of 111 seconds were required to return tissue oxygen to unloaded levels.

In addition to facilitating appropriate pressure management, tilt-in-space and backrest recline may also improve seating comfort. Although comfort is difficult to define and measure, it is a very real concern in seating (Koo & bMak, 1996: 40). Feelings of discomfort among wheelchair users can have serious consequences, including equipment abandonment, decreased satisfaction, and an inability to function throughout the day. Previous studies have shown that high peak pressures at the body-seat interface correlated with seating discomfort. Qualitative research has also been undertaken with respect to seating and comfort. A Wheelchair Seating Discomfort Assessment Tool (a survey questionnaire) was developed to quantify seating discomfort in wheelchair users who have intact sensation in the buttocks.

Rehabilitation Engineering and Assistive Technology Society of North America (RESNA) recently published a position paper on the application of seat-elevating devices for wheelchair users for whom seat elevation is considered medically ...