David Brienza, Ph.D.

Patricia Karg, M.S.

Research and development in the field of specialized seating has focused on many areas and questions over its short 30-year history. However, no area has been studied more intensely than the area of pressure ulcer etiology and prevention. Publications focusing on the still prevalent problem of pressure ulcers have and continue to dominate the literature.

Positioning, especially as related to function, has also received significant attention by researchers an product developers. An overview of past, present and future research is perhaps best organized by categorizing the research and development efforts with respect to the research questions and clinical needs that they address. A majority of the efforts aim to answer one or more of the following research questions concerning wheelchair seating:

What intrinsic and extrinsic factors effect pressure ulcer development?

What strategies are effective for reducing risk of pressure ulcer development?

What methods and technology are available to assess pressure ulcer risk and seating system efficacy?

What is the relationship between posture and positioning to pressure ulcer risk?

How does posture affect function?

What are the long term effects of particular seating interventions?

What are effective methods of consumer education?

A summary of research and development is divided into the following broad categories:

Pressure Ulcer Etiology

The effects of pressure

The relationship between posture and pressure

Pressure Ulcer Prevention

Product developments

Determining support surface efficacy (e.g., measuring pressure)

Postural Control

Development of contoured seating systems

Positioning for function and analysis of function

The publications discussed during the presentation are listed among others in the partially annotated bibliography included at the end of this section. Although the list is not complete, it represents many of the most important studies conducted in this field.

Current research and future directions:

What is left do? (Unanswered research questions)

What effect does externally applied pressure ulcer development?

Which support surfaces and contours work well and why?

What effect has "aggressive" seating intervention had on retention of postural deformities?

How can seating technology be improved so that it is less expensive, more readily available and more effective?

What outcome measures accurately assess the degree of success or failure of seating interventions?

How do we involve consumers in the process of decision making and follow up so that they are better prepared?

What level of professional training is necessary for service providers?

Which service models are most effective and when?

How can clinical guidelines be developed and validated by?

Bader DL: The recovery characteristics of soft tissues following repeated loading J rehabil Res Dev 1990, 27:141-150.

Tissue recovery repeated comprehensive loading was examined at the sacrum and ischial tuberoses. Transcutaneous gas tension was used as a measure of tissue viability. Normal subjects exhibited rapid and complete tissue recovery to unloaded values. Disabled subjects often demonstrated impaired and delayed tissue recovery.

Bar CA: Evaluation of cushions using dynamic pressure measurement. [Review] Prosthetics & Orthotics International 1991 15(3):323-40.

In this study a dynamic pressure monitoring system was used to obtain pressure-time profiles for 25 spinal cord injured subjects. Each subject tested three types of cushion (Foam, Gel (Aberdeen) and Roho) for two hours each during which outine activities were performed. Results obtained were broadly comparable with previous studies. Average pressures were: Foam 87.6 mmHg (11.6 kPa); Gel 68.6 mmHg (9 kPa) and Roho 54.6 mmHg (6.7 kPa). Pressure-time histograms are presented for three subjects for each cushion. These show inter-subject variability on the same cushion as well as intra-subject variability on different cushions.

Barbenel JC: Pressure management. [Review] prosthetics & Orthotics International. 1991, 15(3):225-31.

The relationship between the magnitude of pressure and its duration; the temperature and humidity at the interface; and the physiological effects that this has on the microcirculation and lymphatic drainage are discussed in this article. It is suggested that a rationale for the prevention of pressure sores includes the limitation of the duration of pressure applied to the skin surface and the reduction of the peak pressures particularly at vulnerable sites.

Barnett RI, Ablarde JA, Skin Vascular Reaction to Short Duration of Normal Seating, Archives of Physical Medicine and Rehabilitation Volume 76, pp. 533-540, 1995

Thermographic and visual techniques are used to compare skin reaction to short durations of sitting (5, 10 and 15 minutes sessions) on a hard surface. Four normal, 1 subject with paraplegia and one subject with cerebral palsy were evaluated . A characteristic hyperemic skin response was detected in which the time required for recovery to baseline temperature and the time to peak temperature increase was related to the sitting duration.

Bennet L, Kavner D, Lee DW, Trainor FA: Shear vs Pressure as causative factors in skin, blood flow occlusion. Arch Phys Med Rehabil 1979; 60:309-314.

Bennet L Lee: Paraplegic pressure sore frequency versus circulation measurements J rehabil Res Dev 1990; 27:115-126.

Paraplegic subjects were examined to determine the association of pressure sore history with respect to ankle pressure rations and buttock skin circulation measurements. No significant relationships were found between ankle pressure rations and history of pressure ulcers. A relationship was found between skin circulation measurements and pressure sore history.

Brienza D.M., K.-C. Chung, C.E. Brubaker and J.J. Kwaitkowski, "Design of a Computer-Controlled Seating Device for Research Applications," IEEE Transactions on Rehabilitation Engineering, Vol. 1, pp. 63-67, March, 1993.

Brienza, D.M., R.M. I¤igo, K.-C. Chung and C.E. Brubaker, "Seat Contour Optimization," IEEE Transactions on Biomedical Engineering, Vol. 40, No. 1, pp. 95-104, January, 1993.

Brienza DM, Chung KC, Brubaker CE, Wang J, Krg PE and Lin CT, A System for the Analysis of Seat Support Surfaces Using Surface Shape Control and Simultaneous Measurement of Applied Pressures, IEEE Transactions on Rehabilitation Engineering, Volume 4, No. 2 pp. 103-113, 1996;

This paper presents the design and characterization of a system to study the relationships between seat support surface shape, interface pressure and tissue deformation. Characteristics of the system are given. Results from a pilot experiment with 10 able-bodied test subjects show that the system is capable of achieving support surfaces based on programmable criteria.

Curtis KA Kindlin CM Reich KM White DE: Functional reach in wheelchair users: the effect of trunk and lower extremity stabilization. Arch Phys Med Rehabil 1995 76:360-367.

Chow, W.W. and Odell, E.I.: "Deformation and Stresses in Soft Body Tissues of a Sitting Person," ASME J. Biomechanical Engineering, 100: 79-87, 1978.

Daniel, R. Priest D., Wheatly D: Etiologic factors in pressure sores: An Experimental model. Arch Phys med Rehabil 1983 62(10):492-498.

Showed that in normal, intact pigs, the pressure duration thresholds to produce skin damage were 800mmHg for 8 hours or 200 mmHg for 17 hours, where as in paraplegic pigs the pressure duration threshold was significantly reduced, suggesting an increased sensitivity to pressure. This suggests that pressure alone is not the sole factor causing increased risk among SCI patients.

Ferguson-Pell, M.W.: "Seat Cushion Selection," J. Rehabil. R&D Clinical Supplement, 2:49-74 1990.

Ferguson-Pell M, Cardi M D: Prototype Development And Comparative Evaluation Of Wheelchair Pressure Mapping System. Assistive Technology. 1993, 5:78-91.

Commercially available seat support interface pressure measurement systems were evaluated. Results indicate that some mapping systems produce relatively large errors caused by hystersis, hammocking and creep. Guidelines for the interpretation of pressure measurements are discussed.

Frantz RA, Xakellis G: Characteristics of skin blood flow rochanter under constant, prolonged pressure. Am J Phys Med Rehabil 1989, 68:272-276.

Blood flow over the trochanter was measured over a prolonged period using Doppler flow meter. Blood flow was monitored while subjects lay in supine positions. The rate of flow under loading showed a gradual increase from preload. After the load was removed, a marked increase in flow occurred that failed to reach preload levels within 30 minutes.

Garber SL Krouskop: Wheelchair cushion modification and its effect in pressure Am J Phys Med Rehabil 1984, 65(10):579-83.

Garber SL: Wheelchair Cushions: a historical review Am J occupational Thpy 1985 39(7):453-9.

Hagisawa S, Ferguson-Pell M, Cardi M, Miller D: Assessment of Skin Blood Content and Oxygenation In Spinal Cord Injured Subjects During Reactive Hyperemia. Journal of Rehabilitation Research and Development. 1994, 31:1-14.

Reactive hypermia response was measured in 10 SCI subjects and 10 AB subjects using reflectance spectrophotometry. Results indicate that the reactive hyperemia response was "not substantially different" in the SCI group compared to the AB group but that reflow rate after load release was slower in the SCI group.

Hobson DA: Comparative effects of posture on pressure and shear at the body-seat interface J Rehabil Res Dev 1992 29(4):21-31.

Changes is pressure and shear force were measured for different postures for 10 able-bodied subjects and 12 SCI subjects. Maximum pressures were reduced by approximately 10% through postural changes in anteroposterior and mediolateral directions on the order of 30ø from upright. Shear force was reduced to zero or increased by 25% by similar postural changes. This information is important in determining optimal postures for preventing pressure sores.

Kadaba, M.D., Ferguson-Pell. M.W., Palmieri, V. And Cochran, GVB: "Ultrasound Mapping of the Buttock-Cushion Interface Contour," Arch. Phys. Med. Rehab., 65:467-468, 1984.

Koo TK, Mak A, Lee YL: Posture effect on Seating interface Biomechanics - Comparison Between 2 Seating Cushions, Archives of Physical Medicine and Rehabilitation Volume 77, pp. 40-47, 1996.

The effect of cushion type (Roho and flat polyurethane foam), subject group (normal and SCI),and posture (forward leaning, trunk-bent-right, trunk-bent-left, slumped, upright midline and upright) on pressure under the ischial tuberosities and on pelvic tilt are investigated. The Roho cushion was found to provide lower pressures but higher pelvic tilting, particularly for the SCI group. Posture was found to have a significant effect on pressure.

Kosiak, M.: "Etiology of Decubitus Ulcers," Arch. Phys. Med. Rehab., 42: 19-29, 1961.

Krouskop, T.A., Nobel, P.C., Garber, S.I. and Spencer, W.A.: "The Effectiveness of Preventative Management in Reducing the Occurrence of Pressure Sores," Journal of Rehab. R & D, Vol. 20, No.1, July 1983.

Krouskop, T.A., D.R. Dougherty and R.S. Vinson, "A Pulsed Doppler Ultrasonic System for Making Non-invasive Measurements of the mechanical Properties of Soft Tissue," J. Rehab. R & D 24(2), pp. 1-8, 1987.

Levine, S.P. and Kett, R.L.: "Electric Muscle Stimulation for Pressure Sore Prevention: Tissue Shape Variation," Arch. Phys. Med. Rehab., 71:210-215, 1990.

This study measured changes in buttock tissue shape at the seating interface produced by electric muscle stimulation of the gluteus maximus of able-bodied subjects. Ultrasonic imaging of the seat interface is described under three conditions: buttocks suspended, external loading with no muscle stimulation, and external loading with muscle stimulation. Results show that electric muscle stimulation produces changes in the shape of the loaded buttocks to match more closely the shape of the suspended buttocks.

Levine, SP, Kett, RL, Cederna PS, Bowers, LD, Brooks, SV: Electrical muscle stimulation for pressure variation at the seating interface. J Rehabil Res Dev 1989, 26:1-8.

Electric muscle stimulation was investigated as a method for pressure sore prevention. Bilateral stimulation of the gluteus maximus was performed on three able bodied subjects and one subject with injured spinal chord. The results indicated that electric muscle stimulation produces load redistribution over the seating surface.

Levine, S.P., M. S. Kett and M.W. Ferguson-Pell, "Tissue Shape and Deformation Versus Pressure as a Characterization of the Seating Interface," Assistive Technology, 2:93-99, 1990.

Mason A R, Siddiqui F H, Biundo J: Enhancing host resistance to pressure ulcers: a new approach to prevention. [Review]. Preventive Medicine 1993, 22:433-50.

A literature review n intrinsic factors affecting the susceptibility to pressure ulcers in the spinal cord injured and elderly population. Studies on electrical stimulation of tissues to increase cutaneous blood flow and analysis of blood flow are covered in the review.

Mawson A R, Siddiqui F H, Connolly B J, Sharp C J, Summer W R Biundo J: Sacral transcutaneous oxygen tension levels in the spinal cord injured: risk factors for pressure ulcers?. Archives of Physical Medicine & Rehabilitation 1993, 74:745-51.

Sacral transcutaneous oxygen tension levels were measured in 21 SCI subjects and 11 AB subjects while lying prone and supine on egg-crate mattresses. The results showed that oxygen tension levels for SCI subjects were significantly lower than those of AB subjects while unloaded, had more variability than AB subjects while loaded, and appeared to stabilize at lower levels after supination.

Polliack A, Taylor R, Bader D: Analysis Of Sweat During Soft Tissue Breakdown Following Pressure Ischemia, Journal of Rehabilitation Research and Development.1993, 30:250-259.

Sweat during soft tissue breakdown was analyzed for 11 AB subjects. Results show pressure ischemia produced increased concentrations of lactate, chloride, urea, and urate associated with decreased sweat rate.

Pope P Bowers C Booth E: Postural control in sitting the SAM system: Evaluation of use after three years. Dev Med and Child Neurology 1994, 36:241-252

Pressure Ulcers in Adults: Prediction and Prevention. 1992, AHCPR document, Publication No. 92-0047.

Final report from the Agency for Health Care Policy and Research pressure ulcer guideline panel. The report includes sections on patient risk assessment, care for unbroken skin, recommendations for support surfaces and pressure reduct ion methods, and education in the prevention of pressure ulcers.

Reddy, N.P., V. Palmieri and G. V. B. Cochran, "Evaluation of Transducer Performance for Buttock-Cushion Interface Pressure Measurements," J Rehab R&D, Vol 21, No. 1 pp. 43-50, 1984.

Reddy, N.P., V. Palmieri and G. V. B. Cochran, "Subcutaneous Interstitial Fluid Pressure During External Loading," Am, J. Physiol., Vol. 240, pp. 327-329, 1982.

Redford J B: Seating and wheeled mobility in the disabled elderly population. [Review]. Archives of Physical Medicine & Rehabilitation 1993, 74:877-85.

A review article focusing on seating and wheeled mobility needs for the disabled elderly population. A summary of available technologies is presented.

Reswick, J.B. and Roger, J.: Annual Report of Progress, Rehabilitation Engineering Center, Rancho Los Amigos Hospital, 1975.

Rosenthal MJ, Felton RM, Hileman DL, Lee M, Navach JH, A Wheelchair Cushion to redistribute Sites of Sitting Pressure, Archives of Physical Medicine and Rehabilitation Volume 77, pp. 278-282, 1996.

Presents the evaluation of an experimental seat cushion designed to redistribute pressure away from critical areas the body and seat interface. Cushion performance is compared to three commercially available seat cushions. The results indicate that the seat achieved the goal of reducing pressure in the specified regions and that the pressures in these regions was lower than on the commercially available cushions.

Sacks, AH: Theoretical prediction of a time-at-pressure curve for avoiding pressure sores, J Rehabil Res Dev 1989, 26:27-34.

A theoretical development of a pressure versus time curve for the onset of pressure ulcers is presented. Current theory agrees with available experimental data from studies and may be effective in predicting the pressures that can be safely tolerated by specific individuals.

Schubert V, Perbeck L, Schubert P A: Skin microcirculatory and thermal changes in elderly subjects with early stage of pressure sores. Clinical Physiology 1994, 14.:1-13.

Skin microcirculation and temperature were evaluated in 12 elderly subjects with stage I pressure ulcers and compared to that of 10 elderly subjects without pressure ulcers. The methods included measurement of total skin microcirculation using laser doppler fluxmetry, nutritive transport of small solutes using a fluorescein flowmetry technique, and skin temperature measurement with a thermoelement. Microcirculation was found to increase in the sore area, and, contrary to previous studies, no increase in skin surface temperature was found in the sore area.

Shaw G C: Seat Cushion Comparison For Nursing Home Wheelchair Users. Assistive Technology, 1993, 5:2:92-105.

Peak seating pressures were measured on 21 elderly wheelchair user while sitting on commercially available gel/foam seat cushions and eggcrate foam cushions. The results did not show a significant difference in peal pressure between the two types of cushions.

Sprigle, S.H., K.-C. Chung and C.E. Brubaker, "Factors Affecting Seat Contour Characteristics," J. Of Rehab. R&D, Vol. 27, No. 2 pp. 127-134, 1990.

Relationships between the physical characteristics of able-bodied subjects and of subjects with spinal cord injuries and seat contours were identified. Muscle tone was a stronger predictor of seat contour characteristics than either body mass or pelvic width.

Sprigle, S.H., T. Faisant and K.-C. Chung, "Clinical Evaluation of Custom Contoured Cushions for the Spinal Cord Injured," Arch. Of Phys. Med. and Rehab., 71(9):655-658, 1990.

Sprigle S, Schuch J Z, : Using Seat Contour Measurements During Seating Evaluations Of Individuals With SCI. Assistive Technology. 1993, 5.1:24-35.

A method for the application of foam deflection measurements to seat loading and postural assessment is presented as an alternative to interface pressure measurements. Case studies demonstrating the methods use to evaluate pelvic tilt, pelvic obliquity, and areas of high loading are presented.

Taylor R P, Polliack A A, Bader D L: The analysis of metabolites in human sweat: analytical methods and potential application to investigation of pressure ischaemia of soft tissues. Annals of Clinical Biochemistry 1994, 31:18-24.

A technique for the collection of sweat from a loaded skin and support surface interface is presented. Samples were collected from 11 AB subjects and analyzed to test feasibility of the technique.

Todd BA Thacker: Three-dimensional computer model of the human buttocks in vivo J rehabil Res Dev 1994 31(2):111-119.

Willis J, Pressure-relief seating. Professional Nurse 1995 Aug. 10:713-4, 718-21.

There is a vast array of pressure relief seating products available to consumers. Many users of these products and professionals recommending the products are confused by conflicting, and in many cases, unsubstantiated claims by manufacturers on the performance of the cushion. This article reviews a large sample of cushions available in the UK and demonstrates the need for structured comparative analysis and clinical trials of pressure relief seating devices.

Xakellis G C: Guidelines for the prediction and prevention of pressure ulcers. The Agency for Health Care Policy and Research. Journal of the American Board of Family Practice 1993, 6:269-78.

An overview of the AHCPR pressure ulcer guideline panel. Recent statistics on prevalence and incidence of pressure ulcers, methodology for guideline development, and summary of guideline on prediction and prevention of pressure ulcers are presented.