Predictors of pressure ulcer incidence following traumatic spinal cord injury: a secondary analysis of a prospective longitudinal study.

STUDY DESIGN: Secondary analysis of data from a prospective cohort study. OBJECTIVES: The objective of this study was to identify the medical and demographic factors associated with the development of pressure ulcers during acute-care hospitalization and inpatient rehabilitation following acute spinal cord injury. SETTING: The study was carried out at acute hospitalization, inpatient rehabilitation and outpatient rehabilitation sites at a university medical center in the United States. METHODS: Adults with acute traumatic spinal cord injury (n=104) were recruited within 24-72 h of admission to the hospital. Pressure ulcer incidence was recorded. RESULTS: Thirty-nine participants out of 104 (37.5%) developed at least one pressure ulcer during acute-care hospitalization and inpatient rehabilitation. Univariate logistic regression analyses revealed significant association of pressure ulcer incidence for those with pneumonia and mechanical ventilation (P=0.01) and higher injury severity (ASIA A) (P=0.01). Multiple logistic regression showed that the odds of formation of a first pressure ulcer in participants with ASIA A was 4.5 times greater than that for participants with ASIA B, CI (1-20.65), P=0.05, and 4.6 times greater than that for participants with ASIA C, CI (1.3-16.63), P=0.01. CONCLUSION: Among individuals with acute traumatic SCI, those with high-injury severity were at an increased risk to develop pressure ulcers. Pneumonia was noted to be associated with the formation of pressure ulcers.

Comparison of skin perfusion response with alternating and constant pressures in people with spinal cord injury.

STUDY DESIGN: Two-way factorial mixed design, the between-subjects factor as the spinal cord injury (SCI) status (SCI and non-SCI) and the within-subjects factor as the pressure pattern (alternating and constant pressures). OBJECTIVES: To compare the effects of alternating and constant pressures on weight-bearing tissue perfusion in people with SCI, with application for improving alternating pressure support surface usage. SETTING: University research laboratory. SUBJECTS: A total of 28 participants were studied, 7 participants with cervical injury, 7 participants with injury below T6 and 14 healthy controls. METHODS: Sacral skin perfusion was continuously measured using laser Doppler flowmetry under 10 min preloading, 20 min loading (alternating or constant pressures) and 10 min postloading. Alternating pressure was applied with low-interface pressure at 0 mm Hg and high-interface pressure at 60 mm Hg with a cycle time of 5 min; constant pressure was applied with interface pressure at 30 mm Hg. RESULTS: The results showed that pressure pattern affects skin perfusion responses in weight-bearing tissues (P < 0.01). Alternating pressure stimulates an increase in skin perfusion (1.21 ± 0.08 au) as compared with constant pressure (0.74 ± 0.07 au) in people with SCI (P < 0.01). There was no overall difference in the skin perfusion responses of patients with SCI as compared with non-SCI patients (P > 0.05). CONCLUSION: This study has shown that alternating pressure enhances the skin perfusion of weight-bearing tissues as compared with constant pressure in people with SCI. The protocol tested in this study may be used to guide the selection of parameters of commercial alternating pressure support surfaces for preventing pressure ulcers in people with SCI.

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.

A steering linkage for short wheelbase vehicles: design and evaluation in a wheelchair power base--a technical note.

An Ackerman steering linkage for short wheelbase, four-wheel vehicles has been developed. The linkage coordinates the steering angle of each wheel through a range of 180 degrees with minimal misalignment between wheels. Control of steering angles is accomplished using a single linear actuator. Control complexity is lower compared to four-wheel systems using individually controlled steering actuators for each wheel. A prototype linkage that provides a minimum turning radius while maintaining maximum stability has been developed and evaluated for a power wheelchair base. The single-actuator linkage is well suited for this application, due to the cost-sensitive nature of wheelchair products.

A compound sensor for biomechanical analyses of buttock soft tissue in vivo.

A sensor for in vivo biomechanical characterization of buttock soft tissue has been developed and evaluated. The sensor measures interface pressure, applied force, tilt, and rotation angle of the sensor head, and the thicknesses of multiple soft tissue layers. A composite ultrasonic transducer using a 1-3 ceramic-polymer structure was developed for the sensor. The sensor can identify subcutaneous soft tissue interfaces 5 to 65 mm below the skin surface with a 0.26-mm axial resolution, pressure over the range of 0 to 68 kPa, and force over the range of 0 to 3.6 kg. Our purpose for developing the sensor was to study the biomechanical characteristics of buttock soft tissues. Successful identification of distinguishing characteristics in persons with a susceptibility to pressure ulcers may result in the development of a risk assessment tool based on tissue characterization.

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.

A force feedback joystick and control algorithm for wheelchair obstacle avoidance.

Many powered wheelchair users have difficulty manoeuvring in confined spaces. Common tasks such as traversing through doorways, turning around in halls or travelling on a straight path are complicated by an inability to accurately and reliably control the wheelchair with a joystick or other common input device, or by a sensory impairment that prevents the user from receiving feedback from the environment. An active joystick with force feedback to indicate obstacles in the environment has been developed. Two force feedback schemes designed to assist a powered wheelchair user have been developed and implemented using the active joystick. The development of the joystick and associated control algorithms are described.

Consumer participation in identifying research and development priorities for power wheelchair input devices and controllers.

A focus group comprised of persons who use power wheelchairs and professionals working in the field were asked to participate in a brainstorming session to determine priorities for the development and application of power mobility input devices and control concepts. The group consensus was that durability and reliability are the most important criteria. Essentially, the expectation is that a power wheelchair must work everyday in the way a person needs it and wants it. At the same time, there is a desire to enhance and advance the features of input devices and control systems. Many would say these changes constitute designing "smarter" power wheelchairs, such as systems that can independently detect obstacles and can provide users with more feedback. This paper presents the rationale behind forming this focus group and details of the results of a brainstorming session where ideas were generated and prioritized. The five most important issues as determined by the group are discussed in depth.

Seat cushion optimization: a comparison of interface pressure and tissue stiffness characteristics for spinal cord injured and elderly patients.

OBJECTIVE: A method for designing tissue deformation minimizing seat surfaces was evaluated. Pressure and stiffness criteria were used to optimize surface shape. The method's efficacy for patients with spinal cord injuries (SCI) and a comparison of cushion performance and interface characteristics with a group of 30 elderly patients are presented. DESIGN: Repeated measures, prospective study. SETTING: University medical center. PATIENTS: SCI (n=12), elderly (age 65 + years) [n=30]. INTERVENTIONS: One flat and two custom foam seat cushions. MAIN OUTCOME MEASURES: Interface pressure measured using a pressure sensing pad; tissue stiffness and pressure recorded on a rigid programmable seat surface. RESULTS: Pressure distributions on contoured cushions for the SCI group contained lower values than distributions on flat cushions. A comparison of the pressure data between the elderly and SCI showed that significant differences exist between interface characteristics. The SCI group had higher peak interface pressures for all cushions tested. Tissue stiffness measurements were similar for each group. CONCLUSIONS: Results showed improved effectiveness of custom contoured foam seat cushions versus flat foam cushions. The results suggest that pressure distributions for SCI are more sensitive to support cushion characteristics than for the elderly. Further research is needed to determine the extent of the difference between the populations represented by these groups.

Computer design and fabrication of custom-contoured seating.

This article describes the development of a computer-controlled system for measuring anatomical contours and forces at the interface with seat surfaces. The system was designed to eliminate the cause of pressure sores, which are a major problem for wheelchair-bound individuals. A parallel and compatible system also has been developed for the rapid, precise, and cost-effective fabrication of custom-contoured seat cushions and other body supports from a range of open- and closed-cell foam materials.

A method for custom-contoured cushion design using interface pressure measurements.

The interface pressure distributions between flat foam cushions and the buttocks of seated test subjects were compared to custom-contoured cushion surface shapes generated with a seated-buttock contour gauge. Our hypothesis was that pressure measurements could be used to generate a contour equivalent to that obtained with a force-deflection contour gauge. The study was performed in a university medical center using spinal cord injured (SCI) (12) and elderly (30) test subjects. Interface pressure was measured using a pressure mapping pad. Contour shape was measured using an electronic force-deflection contour gauge. Pressure and contour information were reduced prior to analysis using singular value decomposition. Polynomial regressions were performed on the values in the first singular vectors of the corresponding pressure and contour decompositions. Relationships best described by cubic polynomials were detected between pressure and contour shape suggesting that interface pressure predicts optimal contour shape.

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.

Determination of generic body-seat interface shapes by cluster analysis.

The purpose of this study was to determine typical or generic shape patterns of the buttock-seat interface for elderly wheelchair users. The group of subjects was composed of 30 elderly people (aged 65 or older) and the shapes of the body-seat interface were measured by the electronic shape sensor (ESS). By analyzing the dissimilarity in geometrical shape descriptors or parameters, four distinct generic shapes were identified by means of the cluster analysis method. The results suggest that the generic shapes were mainly characterized by the lateral symmetry of the shapes. The determination of elderly people's seat interface shapes into distinct clusters may lead to a more comprehensive understanding of the seat support interface and more effective seat cushion designs.

A randomized control trial to evaluate pressure-reducing seat cushions for elderly wheelchair users.

OBJECTIVE: To determine if the use of pressure-reducing wheelchair cushions for elderly nursing home resident wheelchair users who are at high risk for developing sitting-acquired pressure ulcers would result in a lower incidence rate of pressure ulcers, a greater number of days until ulceration, and lower peak interface pressures compared with the use of convoluted foam cushions over a 12-month period. To determine the feasibility of conducting a subsequent full-scale definitive trial to evaluate the use of pressure-reducing seat cushions for elderly nursing home resident wheelchair users. DESIGN: Randomized control trial SETTING: 2200-bed skilled nursing facilities (1 suburban and 1 urban academic medical center) PATIENTS: 32 male and female at-risk nursing home residents who were wheelchair users > or = 65 years of age. Participants had Braden Scale scores < or = 18, Braden Activity and Mobilitysubscale scores < or = 5, no sitting surface pressure ulcers, and a daily wheelchair sitting tolerance of more than 6 hours. All met criteria for using the ETAC Twin wheelchair. INTERVENTIONS: Seating evaluation with pressure-mapping and subsequent seating prescription. Subjects were assigned to either a foam (n=17) or pressure-reducing cushion (n=15) group and weekly assessments of skin and pressure ulcer risk were made. MAIN OUTCOME MEASURES: Incidence of pressure ulcers, days to ulceration, and peak interface pressure. MAIN RESULTS: At a 95% confidence interval, a 2-tailed analysis showed no differences between the FOAM and pressure-reducing cushion groups for pressure ulcer incidence, total days to pressure ulcer, or initial peak interface pressure. Pressure-reducing cushions were more effective in preventing sitting-acquired (ischial) pressure ulcers (P<.005). Higher interface pressures were associated with a higher incidence of pressure ulcers (P<.001). CONCLUSIONS: A definitive randomized control multicenter cushion trial is feasible with a sample size of 50 to 100 per study group. In the definitive trial, the definition of sitting-acquired pressure ulcers should be limited to lesions occurring over the ischial tuberosities.

The relationship between pressure ulcer incidence and buttock-seat cushion interface pressure in at-risk elderly wheelchair users.

OBJECTIVE: To investigate the relation between pressure ulcer incidence and buttock-wheelchair seat cushion interface pressure measurements. DESIGN: Secondary analysis of data from a randomized clinical trial. SETTING: Skilled nursing facility. PATIENTS: Thirty-two elderly patients (age, > or = 65 yr), with Braden score < or = 18 and Braden mobility and activity subscale score < or = 5, who used wheelchairs > or = 6 hr/d, were free of existing sitting-induced pressure ulcers, and weighed < or = 250 lb. INTERVENTIONS: Generic foam seat cushion or pressure-reducing seat cushion. MAIN OUTCOME MEASURES: The incidence of sitting-induced pressure ulcers over a 1- to 12-month period was compared with pressure measured between patients' buttocks and wheelchair seat cushions. A flexible pad with a 15 x 15 pressure sensor array was used to measure interface pressure. RESULTS: Interface pressure measured on wheelchair seat cushions was higher (p < or = .01 for both peak pressure and average of highest 4 pressures) for patients who developed sitting-acquired pressure ulcers compared with those patients who did not. CONCLUSIONS: Results indicated that higher interface pressure measurements are associated with a higher incidence of sitting-acquired pressure ulcers for high-risk elderly people who use wheelchairs.

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.

Orbital metastases: echographic findings our experience.

In this paper the authors examine the echographic findings in 20 patients with metastatic and secondary tumors of the orbit observed at the University Eye Clinic of Ferrara (Italy) between January 1985 and August 1995. The aim of this study is to identify some typical echographic characteristics in these forms and to underline the diagnostic role of orbital echography.