Body-seat Interface Research Articles

PRESSURE DISTRIBUTION ON WHEELCHAIR CUSHIONS IN STATIC SITTING AND DURING MANUAL PROPULSION

Quantification of biomechanical parameters by describing interactions between a wheelchair user and his cushion is important to prevent pressure sores in a better way and to match the needs of the subjects in terms of comfort and mobility. This paper presents the method and the results of a biomechanical analysis through the pressure maps at the body–seat interface of a antidecubitus wheelchair cushion on a group of eight patients (affected by SCI or Multiple Sclerosis) during autonomous wheelchair propulsion. In general, our results confirm that mobility is an important factor for ulcer prevention because passing from the static sitting posture to propulsion the mean pressure decreases and there is a redistribution of the load at lower pressure values. Moreover this represents a useful approach for the customized choice and adaptation of the antidecubitus aids.

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.

Effect of seated posture on interface pressure in children who are able-bodied and who have myelomeningocele

Purpose : The objective of this study was to investigate the relationship between sitting position and interface pressure distribution in seated children. Method : Fifteen able-bodied children and 15 children with myelomeningocele complete paraplegia, aged 7 to 18 years were included in the study. The body-seat interface pressure was measured with the QA pressure measurement system. Four sitting positions typically used to reduce body-seat interface pressure position (recline, tilt, combined and lean forward) were compared to a neutral position. Results : Test/re-test Pearson correlation coefficients were greater than 0.94 for maximum pressure and greater than 0.88 for mean pressure at all test positions ( p < 0.0001) and, for the risk area (defined as the percentage of sensors which recorded pressures greater than 40 mm Hg.) varied from 0.62 to 0.85 ( p < 0.0005). Maximum pressures for the myelomeningocele group were significantly higher than those recorded for ablebodied subjects in the neutral, combined and lean forward positions ( p < 0.001). For the able-bodied subjects, maximum pressures at the combined ( p < 0.001), tilt ( p < 0.05) and lean forward ( p < 0.0001) positions were significantly lower than those measured at the neutral position. For the myelomeningocele subjects, maximum pressure at all tested positions was significantly lower than at the neutral position ( p < 0.05). Conclusions : The results point to the importance of measuring body-seat interface pressure for each wheelchair user and of using the information to customize wheelchair utilization.

Comparative effects of posture on pressure and shear at the body-seat interface.

This study considers the effects of seated posture and body orientation on the pressure-distribution and surface shear (tangential) forces acting at the body-seat interface. Nine postures typically assumed by wheel-chair users were studied. Comparisons were made within and between two study groups, made up of 12 subjects with spinal cord injuries (SCI) and 10 nondisabled subjects. Both interface pressure and the surface shear were measured simultaneously in each of nine reproducible, seated postures. The same seat cushion was used for all trials. The Oxford Pressure Monitor, a pneumatic cell device, was used to measure and record the interface pressures. Instrumentation for measuring and recording the surface shear force was constructed specifically for the study. Analysis consisted of statistically comparing changes in pressure values and shear forces derived from eight sitting postures with reference to values recorded in a defined neutral sitting posture. The pressure-distribution findings suggest that in the postures studied SCI subjects have maximum pressures that are higher than nondisabled subjects in all postures, ranging from 6% to 46% depending on the posture. Maximum pressures can be reduced by postural changes: forward flexion to 50 degrees, -9%; backrest recline to 120 degrees, -12%; and, full body tilt, -11%. On average, the SCI group members have peak pressure gradients (PPG) that are 1.5 to 2.5 greater than the nondisabled group. The maximum reduction in PPG occurred at backrest recline of 120 degrees, -18%. Tangential shear force acts at the body-seat interface in all nine postures studied. Extrapolation of results suggests that full-body tilt to approximately 25 degrees reduces the surface shear force to near zero. In contrast, a backrest-only recline of 20 degrees causes a 25% increase in the surface shear force. These results suggest that caution must be taken when using nondisabled subjects as surrogates for people with SCI because of the inherent differences between the groups. Also, researchers and clinicians should recognize that posture and body orientation in space are additional variables that can have a profound effect on the interaction between a seated person and his or her supporting surface.