Reduction of sitting pressures with custom contoured cushions

The clinical effectiveness of custom-contoured seating for wheelchair users with neuromuscular disorders: a scoping review

Despite its widespread use, the clinical effectiveness of custom-contoured wheelchair seating for individuals with neuromuscular disorders remains unclear. A scoping review was conducted using PubMed, Scopus, and Web of Knowledge databases in November 2021 and updated April 2022. A total of 17 full text articles were included. Discussion themes were grouped based on three outcomes of interest: (1) posture and musculoskeletal deformity, (2) quantitative measures of body structures and functions, and (3) qualitative perceptions, opinions, and quality of life indicators. This review highlighted the lack of literature exploring the impact of custom-contoured seating on cardiopulmonary function, pressure injury management, and upper limb function; although, there was no indication that risk is increased compared to alternative seating and it performed well in terms of perceived user satisfaction, comfort, and function. The findings also demonstrated immediate benefits to postural alignment, although, the longitudinal effect on progression of musculoskeletal deformity compared to alternative seating is more ambiguous. This review aimed to scope the evidence-base for custom-contoured seating for wheelchair users with neuromuscular disorders to synthesize information from the existing literature, inform current practice, and identify knowledge gaps for further experimental investigation.

The Soft Prefabricated Orthopedic Insole Decreases Plantar Pressure during Uphill Walking with Heavy Load Carriage

This study aimed to investigate the effect of varying the hardness of prefabricated orthopedic insoles on plantar pressure and muscle fatigue during uphill walking with a heavy backpack. Fifteen healthy male recreational athletes (age: 20.4 ± 1.0 years, height: 176.9 ± 5.7 cm, weight: 76.5 ± 9.0 kg) wore prefabricated orthopedic insoles with foot arch support; a heel cup with medium (MI), hard (HI), and soft (SI) relative hardnesses; and flat insoles (FI). They performed treadmill walking on uphill gradients with 25 kg backpacks. The plantar pressure and surface electromyographic activity were recorded separately, in 30 s and 6 min uphill treadmill walking trials, respectively. The HI, MI, and SI significantly decreased peak plantar pressure in the lateral heel compared to FI. The MI and SI significantly decreased the peak plantar pressure in the fifth metatarsal compared to FI. The MI significantly reduced the pressure–time integral in the lateral heel compared to FI. The HI significantly increased the peak plantar pressure and pressure–time integral in the toes compared to other insoles, and decreased the contact area in the metatarsal compared to SI. In conclusion, a prefabricated orthopedic insole made of soft material at the fore- and rearfoot, with midfoot arch support and a heel cup, may augment the advantages of plantar pressure distribution during uphill weighted walking.

Risk factors for pressure ulcer recurrence following surgical reconstruction: A cross-sectional retrospective analysis

Many studies on the recurrence of pressure ulcers after surgical reconstruction have focused on surgical techniques and socioeconomic factors. Herein, we aimed to identify the risk factors of the associated comorbidities for pressure ulcer recurrence. We enrolled 147 patients who underwent pressure ulcer reconstruction and were followed up for more than three years. The recurrence of pressure ulcers was defined as recurrent pressure ulcers with stage 3/4 pressure ulcers. We reviewed and analyzed systematic records of medical histories, including sex, age, associated comorbidities such as spinal cord injury (SCI), diabetes mellitus (DM), coronary artery disease, cerebral vascular accident, end-stage renal disease, scoliosis, dementia, Parkinson's disease, psychosis, autoimmune diseases, hip surgery, and locations of the primary pressure ulcer. Patients with recurrent pressure ulcers were younger than those without. Patients with SCI and scoliosis had higher odds, while those with Parkinson's disease had lower odds of recurrence of pressure ulcers than those without these comorbidities. Moreover, the decision tree algorithm identified that SCI, DM, and age < 34 years could be risk factor classifiers for predicting recurrent pressure ulcers. This study demonstrated that age and SCI are the two most important risk factors associated with recurrent pressure ulcers following surgical reconstruction.

The influence of a contoured seating base on pressure distribution and discomfort

PURPOSE

This research paper examines how contouring of a wheelchair seating base can help prevent pressure sores by distributing pressure over the buttocks. Contouring wheelchair cushioning is already done to some extent and has proved to be beneficial for pressure distribution. We researched the effect of contouring the seating base, and whether contouring the seating base affects effectiveness in pressure distribution and perceived discomfort.

MATERIALS & METHODS

13 healthy participants performed a within-subject experiment with three differently contoured seating bases. Perceived comfort and seating pressure were measured for each condition.

RESULTS

Results indicate that a more contoured base is positive for both comfort and increased pressure distribution.

CONCLUSIONS

Contoured seating bases can provide increased comfort and improved pressure distribution over flat seating bases. Future research should examine the effect of contouring on stability, as well as compare the effects of contoured seating bases and contoured cushions.Implications for rehabilitationWe evaluated the comfort and pressure characteristics of three differently contoured hard seating bases for a wheelchair. The outcomes of the research shows that providing increased contour to seatings could be beneficial to reduce pressure peaks in the buttocks.Contour in the seating is conventionally created by shaping the cushions, this research shows the possibility of using a hard base underneath a cushion to create the desired contour.

Insoles of uniform softer material reduced plantar pressure compared to dual-material insoles during regular and loaded gait

There is limited evidence on the efficacy of insole materials to reduce plantar pressure during regular walking and loaded walking. In-shoe plantar pressures and subjective footwear comfort were recorded in twenty healthy participants at a self-selected treadmill walking speed in six conditions: two commercial insoles or no insole, and with or without carrying a load in a backpack. A single-material insole, comprised of polyurethane, had reduced density and compressive stiffness compared to a dual-material insole with added viscoelastic material in rearfoot and forefoot regions. Load carriage increased peak pressure across the foot. Both insoles reduced plantar pressure in the rearfoot. Yet, the softer single-material insole also attenuated forefoot pressure and loaded walking did not appear to cause bottoming-out of the polyurethane. Plantar pressure changes did not affect perceived footwear comfort. The softer single-material insole was more effective in reducing plantar pressure, further research would confirm if this influences injury prevalence.

Contact Area Effects on Discomfort

Most “ergonomic” products attempt to adopt a uniform force distribution strategy to improve comfort. The rationale being that force distribution over a large area reduces pressure and thereby enhances user comfort. However, sensory literature alludes to the concept of spatial summation, i.e. greater sensation by stimulating a larger surface area. Hence spatial summation would tend to suggest a greater discomfort when forces are applied over large surface areas. This study reports the effect of surface area on maximum discomfort causing pressure or maximum pressure tolerance (MPT). Two circular probes of different cross sectional area were used to stimulate the skin surface. The mean MPT with a probe of 5mm diameter was 3.3 times higher than the MPT with a probe of 13mm diameter. These findings suggest the following:

• Perceived discomfort and contact area seem to have a “U-relationship” above a critical force value. Traditional thinking of distributing forces is successful only in the first half of the U-curve or with forces below the critical value. The section with the monotonically increasing relationship between discomfort and contact area (i.e., second half of U) may not be seen at very low forces or forces below the critical value. • “High” pressures in concentrated areas may cause less discomfort than “moderate” pressures over a larger area. • The critical or threshold pressure to induce discomfort is force and contact area dependent.

Discomfort of seated persons exposed to low frequency lateral and roll oscillation: effect of seat cushion

The discomfort caused by lateral oscillation, roll oscillation, and fully roll-compensated lateral oscillation has been investigated at frequencies between 0.25 and 1.0 Hz when sitting on a rigid seat and when sitting on a compliant cushion, both without a backrest. Judgements of vibration discomfort and the transmission of lateral and roll oscillation through the seat cushion were obtained with 20 subjects. Relative to the rigid seat, the cushion increased lateral acceleration and roll oscillation at the lower frequencies and also increased discomfort during lateral oscillation (at frequencies less than 0.63 Hz), roll oscillation (at frequencies less than 0.4 Hz), and fully roll-compensated lateral oscillation (at frequencies between 0.315 and 0.5 Hz). The root-sums-of-squares of the frequency-weighted lateral and roll acceleration at the seat surface predicted the greater vibration discomfort when sitting on the cushion. The frequency-dependence of the predicted discomfort may be improved by adjusting the frequency weighting for roll acceleration at frequencies between 0.25 and 1.0 Hz.

Objective classification of vehicle seat discomfort

The objective of this study was to identify how physiological measures relate to self-reported vehicle seating discomfort. Twelve subjects of varied anthropometric characteristics were enrolled in the study. Subjects sat in two seats over a 2-h period and were evaluated via three physiological measures (near-infrared spectroscopy, electromyography and pressure mapping) yielding six testing sessions. Subjective discomfort surveys were recorded before and after each session for nine regions of the body. Conditional classification discomfort models were developed through dichotomised physiological responses and anthropometry to predict subjective discomfort in specific body locations. Models revealed that subjects taller than 171 cm with reduced blood oxygenation in the biceps femoris or constant, low-level muscle activity in the trapezius tended to report discomfort in the lower extremities or neck, respectively. Subjects weighing less than 58 kg with reduced blood oxygenation in the biceps femoris or unevenly distributed pressure patterns tended to report discomfort in the buttocks. The sensitivities and specificities of cross-validated models ranged between 0.69 and 1.00.

The effect of seat shape on the risk of pressure ulcers using discomfort and interface pressure measurements

BACKGROUND

It is clinically known that shape is important when selecting or designing a wheelchair support surface for the prevention of pressure ulcers (a £ 2 billion annual cost to the National Health Service, UK); however, the effect of different levels of shape contouring has not been adequately studied.

OBJECTIVES

To investigate the effect of seat shape on the risk of pressure ulcers using discomfort and interface pressure measurements.

STUDY DESIGN

Randomised, repeated trial.

METHODS

Thirty able-bodied participants sat with restricted movement for 30 min in three sessions to evaluate two cushion shapes against a flat baseline surface. Visual Analog Scaling and pressure mapping were used to measure surrogates for pressure ulcer risk, discomfort and interface pressures, respectively.

RESULTS

Linear regression revealed a reduction in discomfort (p < 0.05) on the custom contoured shapes. Interface pressures measured were also lower (p < 0.05) on the custom contoured shapes, and a negative Pearson's correlation (p < 0.05) indicated an association between smaller hip widths and increased discomfort for the commercially shaped cushion.

CONCLUSIONS

The results of this study confirm that custom contoured shapes were effective at reducing pressure ulcer surrogate measures in the participants of this study and therefore suggests that the contribution of a cushion's three-dimensional contours on pressure ulcer risk should be further researched.

CLINICAL RELEVANCE

The measurement of seat shape, discomfort and interface pressure in surrogate participants can help inform the design of wheelchair seating for individuals who are insensate or otherwise at risk of developing pressure ulcers. This knowledge can now be implemented using modern three-dimensional shape acquisition, analysis and fabrication technologies.

An alternating pressure sequence proposal for an air-cell cushion for preventing pressure ulcers

The distribution and release of pressure on ischial regions are two important parameters for evaluating the effectiveness of a cushion; especially the release of pressure over time on ischial tuberosities, which is significant for preventing pressure ulcers. The aim of this work is to evaluate the effect on interface pressure through the application of a proposed alternating pressure sequence for an air-cell cushion. Six healthy volunteers were asked to sit on the air cell cushion, in static and alternating modes, as well as on a typical foam cushion for 12 minutes. Interface pressure was monitored with a matrix sensor system. Interface pressure values on ischial tuberosities, user contact area and pressure distribution were analyzed. Results showed that IP on IT tends to increase in both foam and static cushions, while in alternating cushion IP on IT tends to decrease. User contact area was significantly larger in alternating cushion than in static or foam cushions. Moreover, there is a better pressure re-distribution with alternating cushion than with the other cushions. The goal of the alternating sequence is to redistribute pressure and stimulate the ischial regions in order to promote blood flow and prevent pressure occurring in wheelchair users.

A NEW CUSTOM-CONTOURED CUSHION SYSTEM BASED ON FINITE ELEMENT MODELING PREDICTION

High internal stress in the deep tissues adjacent to bony prominences can cause deep tissue injuries. Therefore, internal stress in the soft tissue should be considered when the performance of anti-decubitus cushions is evaluated during cushion design. This paper reports on a custom-contoured cushion (CCC) system incorporated with a three-dimensional (3D) slice subject-specific finite element (FE) model to investigate the internal stress distribution in the soft tissues. This stress distribution was used to transform the interface pressure into the carving depth of the fabricated cushions based on the biomechanical characteristics of the cushion materials. The internal stress in the soft tissues was investigated using an FE model of buttocks and cushion made from three cushion materials. The cushion design was optimized according to the properties of the material. The simulated interface stress between the buttocks and the cushion (18 kPa) was consistent with the measured interface pressure of the CCC (17.1 kPa). The 3D FE model predicted the internal stress and displacement of the soft tissues and cushion. Additionally, it efficiently optimized the selection of cushion material. Fifty subjects (25 subjects with spinal cord injuries (SCI) and 25 healthy subjects) were recruited to investigate the interface pressure and perform subjective comfort evaluation. The CCC decreased the interface pressure under the buttocks and simultaneously increased the subjective comfort and stability. The effectiveness of the cushion materials was predicted by the CCC system, which also validated the clinical performance of decreasing interface pressure.

DEVELOPMENT OF A PROTOTYPING SYSTEM FOR CUSTOM-CONTOURED FOAM CUSHION USING THE PRESSURE MAPPING METHOD

For people with limited mobility such as wheelchair users, prevention of pressure sore is an important health care issue. To relieve pressure at buttocks, foam cushion enveloping specific contour matching with an individual's buttocks has commonly been employed. This paper presents a prototyping system that generates custom-contoured foam cushion using the pressure distribution at the buttock–cushion interface. Based on the load–deformation characteristics of the foam material, this pressure distribution is converted into the corresponding deformation of the foam. A surface smoothing process approximates all discrete data points into a bi-cubic surface. ASCII NC codes are then generated for CNC fabrication of the cushion with the desired surface contour. This study integrates commercially available products into a fully automated system and can be readily implemented by seat/wheelchair cushion manufacturers.

Association of race, socioeconomic status, and health care access with pressure ulcers after spinal cord injury

OBJECTIVE

To assess the associations of race and socioeconomic status (SES) with pressure ulcers (PUs) after accounting for health care access among persons with spinal cord injury (SCI).

DESIGN

Cross-sectional.

SETTING

Large specialty hospital in the southeastern United States.

PARTICIPANTS

Persons with traumatic SCI who (1) had residual effects from their injury, (2) were 18 years or older at the time of the survey, and (3) were a year or more postinjury at the time of survey (N=2549).

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Outcomes were measured by a mail-in survey: having a current PU (yes vs no), having a PU in the past year with or without reduced sitting time (no PU, no reduced sitting time, month or less, ≥5wk), and having at least 1 PU surgery since SCI onset (yes vs no).

RESULTS

Of participants, 39.3% reported a PU in the past year, 19.9% had a current PU, and 21.9% reported having had surgery for a PU since their SCI onset. While race was preliminarily associated with each PU outcome, it became nonsignificant after controlling for SES and health care access. In each analysis, household income was significantly associated with PU outcomes after controlling for demographic and injury factors and remained significant after accounting for the health care access factors. Persons with lower income had higher odds of each PU outcome. Health care access was not consistently related to PU outcomes.

CONCLUSIONS

Even after accounting for health care access, household income, a measure of SES, remained significantly associated with PU outcomes after SCI; however, race became nonsignificant.

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.

Settling down time following initial sitting and its relationship with comfort and discomfort

This study examined the subjective rating of wheelchair comfort and discomfort (numerical rating scale questionnaire) and the duration of objective in-chair movement reduction "settling down time" following initial contact with the seating surface. Healthy young subjects (n = 22) sat for 5 min on contoured foam or wood cushion surfaces fitted to otherwise identical wheelchairs. Force sensing resistors attached to each quadrant of the sitting interface measured the relative movements of the subjects over time. A significant correlation was found between settling down time (SDT) and reported leg/feet discomfort (p = 0.003; correlation co-efficient = 0.44); and a significant negative correlation was found between SDT and overall comfort (p = 0.015; correlation co-efficient = -0.36). When comparing cushion surfaces: SDT was significantly longer (p < 0.0001) for subjects sitting on wood (5.8 s) compared to contoured foam (3.9 s); Leg/feet discomfort was significant higher (p = 0.007) for subjects sitting on wood (1.1 out of 10) compared to contoured foam (0.3 out of 10); Overall discomfort was significant higher (p = 0.009) for subjects sitting on wood (1.3 out of 10) compared to contoured foam (0.5 out of 10); Comfort was significantly lower (p = 0.001) for subjects sitting on wood (6.5 out of 10) compared to contoured foam (8.3 out of 10); Support was significantly lower (p = 0.001) for subjects sitting on wood (6.4 out of 10) compared to contoured foam (8 out of 10). The results of this study suggest that the shape and firmness of the surface at the buttock-wheelchair interface can affect a subject's SDT following initial contact with the seat as well as their perception of comfort and discomfort. In addition, there appears to be a relationship between longer SDT's and increased discomfort ratings, and shorter SDT's and increased comfort ratings. Therefore, testing for SDT's may be useful in the indirect objective assessment of wheelchair cushions and possibly other types of seating surfaces with design differences that aim to improve comfort and minimize discomfort.

Quality-of-life technology for people with spinal cord injuries

Technology plays a critical role in promoting well-being, activity, and participation for individuals with spinal cord injury (SCI). As technology has improved, so has the realm of possibilities open to people with SCI. School, work, travel, and leisure activities are all facilitated by technology. Advances in materials have made wheelchairs lighter, and developments in design have made wheelchairs that fit individual needs. Software has made computer interfaces adaptive and in some case intelligent, through learning the user's behavior and optimizing its structure. As participatory action design and aware systems take greater hold, transformational change is likely to take place in the technology available to people with SCI.

Load redistribution in variable position wheelchairs in people with spinal cord injury

BACKGROUND/OBJECTIVE

Tilt and recline variable position seating systems are most commonly used for pressure relief to decrease potential for skin breakdown. This study provides quantitative information on the magnitudes of loading on the seat and back during phases of tilt, recline, and standing. The objective of this study was to show that the amount of force reduction at the seat would differ across these 3 methods within their respective clinical ranges.

PARTICIPANTS

Six able-bodied (AB) subjects (2 men, 4 women) with a median age of 25 years, and 10 subjects (8 men, 2 women) with spinal cord injury (SCI) with a median age of 35.5 years.

METHODS

Subjects sat on a power wheelchair with Tekscan pressure mats placed underneath a foam backrest and cushion. Data were collected at 5 positions for each method. Order of position and method tested were randomized. Linear regressions were used to calculate the relationships of normalized seat and backrest forces to seat and backrest angles for each chair configuration.

RESULTS

Normalized seat loads had strong linear relationships with the angles of change in tilt, recline, and standing for both groups. Maximum decreases in seat load occurred at full standing and full recline in the SCI subjects and in full standing in the AB subjects. Loads linearly increased on the back during tilt and recline and linearly decreased during standing for both groups.

CONCLUSIONS

Standing and recline offered similar seat load reductions at their respective terminal positions. Standing also reduced loading on the backrest. Recognizing that each method had clinical benefits and drawbacks, the results of this study indicate that tilt, recline, and standing systems should be considered as a means of weight shifting for wheelchair users.

Effects of backrest design on biomechanics and comfort during seated work

The purpose of this study was to examine the effects of backrest configuration on seatpan and backrest pressure, spinal posture, and comfort. Thirty volunteers (15 male, 15 female) typed a standardized text passage while seated at a computer workstation in five backrest configurations: chair only, chair with a supplementary backrest, and with each of three lumbar pad thicknesses. Pressure, lumbar and cervical angles were collected during 15-min trials. Subjective data were collected during each trial and at the end of the entire protocol. The addition of a supplementary backrest to a standard chair reduced peak and average pressure on the back by 35% and 20%, respectively (P<0.02). Lumbar lordosis was observed only when lumbar pads were used, being greatest with the large pad. Participants preferred backrest configurations that had lower pressure on the back and less lordotic lumbar posture (backrest only or 3 cm lumbar pad), regardless of anthropometrics. Comfort was rated highest in conditions that would not necessarily be considered biomechanically ideal. Further delineation between specific comfort and objective seating variables is required to effectively reduce and prevent low back pain.

Seated buttock contours: a pilot study of Australian senior high-school students

Both posture and comfort of a chair are influenced by the contour and characteristics of the seat. Knowledge of seat contours of a student population could thus be useful in the design of school chairs. This study investigated seated buttock contours of senior high-school students in order to determine: (a) their general characteristics, (b) the effect of gender and sitting posture and (c) the relationship between the contours and selected anthropometric variables (stature and mass). A contour measurement device was developed and used to measure buttock contours in five sitting postures (typing, sitting up, sitting back, slumping and writing). Buttock contours were quantified by constructing anterior-posterior (AP) and lateral profiles from which six discrete profile dimension measurements were made. AP and lateral profiles were found to have a consistent shape across all participants. Five out of six profile dimensions were significantly different between genders, with just one significantly different between sitting postures (typing and sitting back). Correlations between anthropometric measures and profile dimensions were relatively low (r < 0.34) with no clear patterns evident. Overall results of this study suggest that buttock contours are influenced by gender to a greater extent than sitting posture.

Using Support Surfaces to Manage Tissue Integrity

PURPOSE

To provide the clinician with an overview of support surfaces used to manage tissue integrity as well as a review of how pressure ulcers develop.

TARGET AUDIENCE

This continuing education activity is intended for physicians and nurses with an interest in understanding how available support surfaces can impact the development and treatment of pressure ulcers.

OBJECTIVES

After reading the article and taking the test, the participant should be able to:

Modeling the human body/seat system in a vibration environment

The vibration environment is a common man-made artificial surrounding with which humans have a limited tolerance to cope due to their body dynamics. This research studied the dynamic characteristics of a seated human body/seat system in a vibration environment. The main result is a multi degrees of freedom lumped parameter model that synthesizes two basic dynamics: (i) global human dynamics, the apparent mass phenomenon, including a systematic set of the model parameters for simulating various conditions like body posture, backrest, footrest, muscle tension, and vibration directions, and (ii) the local human dynamics, represented by the human pelvis/vibrating seat contact, using a cushioning interface. The model and its selected parameters successfully described the main effects of the apparent mass phenomenon compared to experimental data documented in the literature. The model provided an analytical tool for human body dynamics research. It also enabled a primary tool for seat and cushioning design. The model was further used to develop design guidelines for a composite cushion using the principle of quasi-uniform body/seat contact force distribution. In terms of evenly distributing the contact forces, the best result for the different materials and cushion geometries simulated in the current study was achieved using a two layer shaped geometry cushion built from three materials. Combining the geometry and the mechanical characteristics of a structure under large deformation into a lumped parameter model enables successful analysis of the human/seat interface system and provides practical results for body protection in dynamic environment.

Pressure distribution at the seating interface of custom-molded wheelchair seats: effect of various materials

OBJECTIVE

To identify which of 4 materials has the most favorable pressure distribution when used in custom-molded seats (CMSs) to assist clinicians in providing appropriate seating for wheelchair-bound individuals who are prone to develop pressure ulcers.

DESIGN

Repeated-interface pressure measurements for all materials, followed by statistical analysis.

SETTING

The general community and referral centers.

PARTICIPANTS

Seven subjects, 5 with cerebral palsy, 1 with Schilder's disease, and 1 with postmeningitis effects. All subjects were seated in a CMS and had spinal deformities.

INTERVENTIONS

Viscoelastic polyurethane foams (Pudgee, Sunmate) and gels (Floam trade mark, Jay) were used as inserts in the CMSs. Evazote foam was used as a control material.

MAIN OUTCOME MEASURES

Pressure readings were taken at the seat interface with pneumatic pressure sensors and the Talley Pressure Monitor. Peak pressure readings, mean pressure ratio, and peak pressure ratio for the different materials were compared.

RESULTS

Foams, Sunmate in particular, produced lower peak-interface pressures and also showed better pressure distribution than did gels.

CONCLUSION

Foams are the preferred insert material with CMSs when increased tissue breakdown risk is present.

Buttock and back pressure distribution tests on seats of mobile agricultural machinery

Multidisciplinary effort is usually required in the evaluation of comfort problems in the working environment of mobile agricultural machinery workers. Comfort can be partly assessed from the study of the pressure distribution of the human-seat interface. Four combine foam seats and a new air-based seat were compared with regards to static buttocks and back support pressures. Within and between subject variability and the issue of measurement repeatability were addressed. Significant differences were found in the maximum pressure profiles of the four seating systems with seats 2 and 3 performing better than seat I (seat 4 showed no significant difference when compared to the other seats). There is an almost linear relationship between mean pressure and body mass index. In all cases the air seating system performed better with regards to the static pressure gradients.

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 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 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.

Evaluation of a simple approach to modify the supporting property of seating foam cushion for pressure relief

To provide pressure relief at the high pressure areas of the buttocks, small holes were drilled on the polyurethane (PU) foam cushion under the ischial tuberosities areas. This modification was done to locally lower the supporting property of the cushion. This approach could be easily implemented in the clinical setting. Measurements of interfacial pressures at the ischial tuberosities on such modified cushions for eight nondisabled subjects showed an average pressure 25% lower than those measured on foam cushions without modification (p < 0.01). The maximum pressure was 30% lower after modification (p < 0.01) The peak pressure gradient also showed a 38% decrease on modified foam compared to those measured on unmodified foam cushions (p < 0.01). Simple hole drilling could potentially provide an effective approach to enhance the pressure-relief characteristics of foam cushions.

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.

Pressure ulcers: a review

This article reviews the etiology, pathology, description, risk factors, prevention, medical and surgical management, and complications of pressure ulcers. Pressure ulcers, which develop primarily from pressure and shear, are also known as decubitus ulcers, bed sores, and pressure sores. They continue to occur in hospitals, nursing homes, and among disabled persons in the community. Estimates of the prevalence of pressure ulcers in hospitalized patients range from 3% to 14% and up to 25% in nursing homes. Persons with spinal cord injury and the elderly are two groups at high risk. The most common sites of development are the sacrum, ischium, trochanters, and about the ankles and heels. Areas of ongoing research such as electrical stimulation and growth factors are discussed.

Seating and wheeled mobility in the disabled elderly population

Elderly persons constitute the largest among the populations regularly using wheelchairs. This is a review of the few studies specifically concerned with seating for the elderly; it identifies current problems, particularly in the seating for aged people who are in long-term care facilities. This review describes ways of matching currently available seating technology with the needs of disabled elderly persons. Two major barriers to greater use of newer seating technology are (1) the high cost of durable medical equipment and (2) the failure of most clinicians and institutional administrators to recognize the importance of posture and comfort to provide functional independence in wheelchair users. This review discusses seating for four groups of elderly persons: (1) the nonmobile, dependents who may be safety risks and are without energy or ability to wheel or walk by themselves; (2) mobile nonambulatory; and (3) ambulatory, but with special wheelchair needs. Research is needed in wheeled mobility in a number of areas: better matching of mobility to function, cheaper and more effective cushions, more modular seating systems, and better lifting and transfer devices. The American National Standards Institute in cooperation with Rehabilitation Engineering Society of North America has recently recommended standards for wheelchair performance that may be legislated in the next few years.