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Biomedical subjects

C E Brubaker

Publications and source records attributed to C E Brubaker.

15 recordsLinked to original sources
PubMed1996

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.

Back↗
PubMed1996

Seat cushion design for elderly wheelchair users based on minimization of soft tissue deformation using stiffness and pressure measurements.

A method for designing seat support surfaces using interface pressure and soft tissue stiffness criteria was evaluated. An algorithm designed to drive a rigid support surface on a programmable seating system to a shape for which the externally applied pressure is inversely related to the measured stiffness of adjacent soft tissue was evaluated on 30 elderly subjects (age 65 years or older). The resulting support surface shapes were transferred to compliant foam cushions and evaluated using interface pressure measurements. Pressure and stiffness measurements on the seating system indicated the surface shape control algorithm met the desired programmed criteria by achieving an inverse relationship between pressure and stiffness, as it converged to an "optimal" support surface shape. Evaluation of interface pressures on the compliant foam cushions showed that the pressure distributions on the cushions contoured to the optimal surface shapes were more uniform and had lower values than distributions on flat foam cushions and foam cushions contoured to shapes measured using state-of-the-art load-deflection devices. The results suggest that support surfaces designed using tissue stiffness as a criteria can provide loading conditions intended to minimize relative deformation and, thus, stress in load-bearing soft tissue.

Aged↗
PubMed1993

Seat support surface optimization using force feedback.

The development, implementation and evaluation of an algorithm designed to find optimal seat support surfaces is presented. The algorithm has been developed and implemented on an active contour measurement device. The device consists of an array of positioning elements equipped with force sensors for feedback. With a patient seated on the array, the algorithm is designed to find a seat contour that optimally satisfies given performance criteria. The performance criteria are based on measured stiffness of the soft tissues. A theoretical development of the algorithm is presented along with the modifications made to the algorithm during implementation. The results from several tests using man-made test bodies and a prototype contour gage are presented to verify the algorithm's performance.

Algorithms↗
PubMed1992

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.

Computer-Aided Design↗
PubMed1992

Biomechanics of wheelchair propulsion as a function of seat position and user-to-chair interface.

This study investigated the biomechanics of lever and hand-rim propulsion and the effects of seat position on propulsion mechanics. Nine able-bodied and six paraplegic spinal cord injured persons participated. Subjects performed hand-rim and lever propulsion on a wheelchair test simulator at a speed and load of 3km/hr and 7.5 watts/side, respectively. A 2 x 3 matrix of randomized seat positions was used. Three-dimensional motion measures of the trunk, shoulder, elbow, and wrist were collected over four-second sample periods for each seat position. Hub torque and stroke arc measurements were determined. Upper extremity motions were significantly different (p less than .05) for the two methods of propulsion. Hand-rim propulsion required less elbow motion, greater shoulder extension, less shoulder rotation and less arm abduction than lever propulsion. Both methods of propulsion required a substantial amount of internal rotation at the shoulder. Seat position changes had a greater effect on joint motion ranges when hand-rim propulsion was performed. No significant differences (p greater than .05) were found for trunk motion for the treatments. The findings provide additional information for development of a model for the optimization of wheelchair propulsion.

Adult↗
PubMed1991

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.

Biomechanical Phenomena↗
PubMed1990

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.

Equipment Design↗
PubMed1990

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.

Biomechanical Phenomena↗
PubMed1986

Lever drive system for wheelchairs.

The various stages of development of a lever drive system are described. The use of both roller and friction clutches are discussed and the means for controlling forward, reverse, and braking are included. The current system allows good maneuverability without requiring hand skills and may be effective for quadriplegics.

Humans↗
PubMed1986

Effects of side slope on wheelchair performance.

Compensation for the downhill turning moment of a wheelchair on a 2-degree side slope results in retarding force approximately equal to the rolling drag of a wheelchair on a level surface. The total drag force on the wheelchair while transversing a sloping surface is, therefore, roughly double the rolling drag. In contrast, the net energy cost of propulsion on this side slope is only 30 percent greater than for a level surface. Side slope propulsion is managed by "dragging" the uphill rim while pushing the downhill rim. Although this results in increased mechanical efficiency through greater use of a smaller muscle mass, it is more difficult and tiring for the wheelchair user.

Humans↗
PubMed1986

Wheelchair prescription: an analysis of factors that affect mobility and performance.

Clearly, all considerations for wheelchair performance and their applicability to optimization of mobility are related to user position relative to the main wheel axis. It is also obvious that wheelchair performance is enhanced by a center of gravity position rearward of that which is characteristic of the generic wheelchair. The only obvious features of the generic wheelchair are excessive static stability and limitation of body motion. Perhaps at this stage the reader may be ready to accept some of the arguments presented above, but have reservations about prescribing a less stable wheelchair for the more severely disabled (e.g., quadraplegics). Consider that the reduction of rolling resistance, decrease in downhill turning tendancy, and required turning force would likely be even more important to the user with marginal physical capacity. This would appear as an attractive trade for reduction in static stability. The number of factors unfavorably affected by increased static stability would suggest the use of an anti-tipping device rather than designed static stability if this is thought to be an important consideration.

Gravitation↗
PubMed1983

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 (75 degrees, 90 degrees, 105 degrees and 120 degrees) and seat surface elevations (0 degrees and 15 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 0 degrees and the backrest inclination 75 degrees. The results showed that differences existed in the activity of the low-back extensors in the seating positions that were assessed.

Action Potentials↗
PubMed1972

Running mechanics.

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Athletic Injuries↗
PubMedDate not supplied

Injuries to runners.

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Athletic Injuries↗