Clifford E. Brubaker

Reduction of sitting pressures with custom contoured cushions.

Previous research indicated that matching a cushion to the shape of the buttocks results in less tissue distortion and lower interface pressures. A system was developed to measure body contours and fabricate a cushion to match the measured contour. This project fabricated contoured foam cushions for 11 persons with spinal cord lesions (C5-L3). Mean pressures were compared on two flat and two contoured foams with different degrees of stiffness. Deflection characteristics on flat foam were compared to deflection on contoured foam in order to analyze loading differences. Material studies were determined by examining the load-deflection curves for flat foams of 1-, 2-, and 3-inch thicknesses. It was found that sitting on contoured foam resulted in a lower pressure distribution than sitting on flat foam (p less than 0.05), and sitting on a soft foam (ILD = 45) resulted in a lower pressure distribution than sitting on a stiffer foam (ILD = 55) (p less than 0.05). Results of the deflection measurements and compression tests were used to explain the loading differences at the seat interface of flat and contoured cushions. Loaded contoured foam demonstrated increased enveloping of the buttocks, decreased foam compression, and a more uniform pressure distribution. These attributes are typical of a safer sitting surface and may indicate less tissue distortion.

A system for the analysis of seat support surfaces using surface shape control and simultaneous measurement of applied pressures

A system for the design and analysis of seat support and buttock tissue interfaces has been developed. It has the ability to control the seating surface shape while measuring the pressure applied to the buttocks by the surface. Pressures are measured over an 11 x 12 rectangular array of support elements using silicon pressure sensors mounted in a swiveling head atop each support element. Control of surface shape is mediated by selective linear translation of the support elements along their respective vertical axes. Closed-loop control of the system allows for the dynamic formulation of a support surface on the basis of programmable criteria. The system is intended to function as a research tool to facilitate the study of the relationships between support surface shape and interface pressure, and support surface shape and soft tissue distortion. The purpose of this paper is to present the system instrumentation and the rationale behind its design and development. The paper also presents the results of several tests to evaluate the accuracy and performance of the system. This evaluation included a pilot study on 10 able-bodied subjects. The results of these system evaluations indicate that the system is capable of making repeatable and precise measurements of pressure and surface element position and can formulate support surface shapes that satisfy specified optimization criteria.

Electromyographic investigation of extensor activity in cerebral-palsied children in different seating positions.

This study was designed to determine whether tonic myoelectric activity of low‐back extensors of spastic cerebral‐palsied children changed in response to changes in seating position, and if so, which position was coincident with the least extensor activity. Using two pairs of surface electrodes, the electrical activity of the lumbar erector spinae muscles was monitored in seven combinations of backrest inclinations (75o, 90o, 105o and 120o) and seat surface elevations (0o and 15o degrees). Off‐line analysis of action potential counts per second of recorded electromyographic signals showed that electrical activity was least when the seat surface elevation was 0o and the backrest inclination 7o. The results showed that differences existed in the activity of the low‐back extensors in the seating positions that were assessed.

Biomechanics and the wheelchair

Wheelchair biomechanics involves the study of how a wheelchair user imparts power to the wheels to achieve mobility. Because a wheelchair can coast, power input need not be continuous, but each power strike can be followed by a period of recovery, with the stroking frequency depending on user preferences and the coasting characteristics of the wheelchair. The latter is described in terms of rolling resistance, wind resistance and the slope of the surface. From these three factors the power required to propel the wheelchair is determined, and must be matched by the power output of the user. The efficiency of propulsion is the ratio of this power output to the metabolic cost and is typically in the order of 5% in normal use. The features required in a wheelchair depend upon user characteristics and intended activities. The ideal wheelchair for an individual will have the features that closely match these characteristics and activities. Thus prescription is not just choosing a wheelchair, but choosing the components of the wheelchair that best serve the intended purpose. In this paper, each component is examined for available options and how these options effect the performance of the wheelchair for the individual. The components include wheels, tyres, castors, frames, bearings, materials, construction details, seats, backrests, armrests, foot and legrests, headrests, wheel locks, running brakes, handrims, levers, accessories, adjustments and detachable parts. Each component is considered in relation to performance characteristics including rolling resistance, versatility, weight, comfort, stability, maneouvrability, transfer, stowage, durability and maintenance. Where they exist, wheelchair standards are referred to as a source of information regarding these characteristics.

Factors affecting seat contour characteristics

This project focused on identifying the influence of subject characteristics and foam properties on seat contours in order to explain the load transfer between the buttocks and cushion. Seat contours were recorded for 17 people (11 spinal cord injured and six able-bodied individuals). Contour characteristics were represented by maximum contour depth, surface area, and displaced volume. Subject characteristics were represented as intertrochanteric distance, body weight, and lower extremity muscle tone. Two foams with different degrees of stiffness (45- and 55-pound indentation load deflection [ILD]) were studied. Multiple regression equations were calculated for each of the three contour characteristics by entering in all three subject attributes. While the equations differ, all six exhibited a significant Multiple R (range: 0.79 to 0.92). Each subject characteristic was a significant predictor of at least one contour trait (p less than 0.05). The major difference between the two cushions was the predictive ability of muscle tone. For the stiffer HR55 foam, muscle tone was the strongest predictor of all contour characteristics. Therefore, some conclusions can be drawn concerning the relationship between foam stiffness, tone, and resulting seat contours. These relationships help define the differences in load transfer as subject and cushion characteristics vary and are important in the design of contoured foam for use as wheelchair cushions.

A manufacturing system for contoured foam cushions

The design, application and evaluation of a specialized, personal computer-based manufacturing system for contouring foam cushions is presented. The topics discussed include both the hardware configuration and the software design. The target applications of this device are local or centralized fabrication of custom-contoured seat cushions. Although the technologies used for the development and implementation of this system are not new, using a personal-computer-based (PC) controller in place of a stand-alone numerically controlled (NC) motion controller significantly reduced the cost associated with this component. Further reductions in cost resulted from an optimization of the mechanical configuration for the dedicated task of carving foam cushions.

Design of a computer-controlled seating surface for research applications

The design of a system to facilitate investigations of the loading of the human body on a seat surface and the ongoing evaluation of a prototype system are presented. Knowledge and understanding of the effect of support surface shape on load distribution at the body and seat interface are vital components of an automated seat contour design and fabrication system. The need for a research tool that allows for control of surface shape with simultaneous measurement of the interface forces is of considerable importance to current research in the area of custom and specialized seating. The computer-aided seating system (CASS) presented allows for development of surface control algorithms based on force feedback that are not possible using currently available contour sensing and evaluation devices. Additionally, the contour-controlled force feedback system will facilitate the study of tissue distortion at the loaded seat interface. Such information about how the body distorts under load can be directly applied to passive custom seating systems, assist in clinical seat contour design and benefit designs on noncustom wheelchair cushions. The specification, design and testing of a prototype of the CASS is described. >

A New Approach To Seat Contour Design

Optimal control techniques have been applied to the problem of forming a seat contour. An algorithm has been developed for implementation on a closed loop active contour measurement device. The active device will consist of an array of positioning probes equipped with forcc sensors cor fccdback. With a patient seated on the array, the algorithm is designed to find a seat contour which optimally satisfies the given performance indcx. The performance index used for the algorithm presented is based on the magnitude of the force exertcd normal to the surface of the contour. A dctailed description of the algorithm is presented.

Engineering in Rehabilitation: A Brief History of Engineering Contributions to the Science, Art and Practice of Rehabilitation

It seems appropriate to begin by acknowledging that the evolution of a field or discipline is subject to invention and discovery but, perhaps, even more so to political and social forces. It is also worth noting that advances proceed erratically for these same reasons. This is certainly the case for Engineering and its sub-disciplines of Bioengineering and Rehabilitation Engineering. Hopefully this will become evident in the following discourse.Copyright

Analysis of muscular load sharing in wheelchair propulsion cycles

Results are presented on the musculoskeletal system modeling and validation phase of a broader research program which is directed toward the development of a simulation system for the total wheelchair propulsion system. The modeling and validation process itself consists of four areas of research: (i) the determination of architectural models for the selected upper-extremity muscles, (ii) the physical tests and experimental acquisition of kinematic, force and muscle activation (EMG) data for a range of wheelchair propulsion cycles and subjects, (iii) the development of a spatial musculoskeletal model including load-sharing algorithms, and (iv) the determination of qualitative and quantitative correlations between the model analysis results and the experimental data, to be used to refine iteratively the model details and the load-sharing algorithms.<<ETX>>