Patent Application
20120037169
Decubitus ulcers (also known as pressure ulcers) afflict many people. Those who spend long periods of time on support surfaces such as wheelchairs and beds are particularly vulnerable.
The sitting position of a wheelchair user focuses significant loads on a small area; namely, the buttocks and surrounding areas. Carlson J M, Payette M J, Vervena L P, “Seating orthosis design for prevention of decubitus ulcers,” J Prosth & Orth, Spring 1995; 7(2): 51-60. Wheelchair users often sit for prolonged periods; moreover, the physiology of many wheelchair users (e.g., geriatric or paraplegic) makes them more prone to ulcer formation. Bennett L, Kavner D, Lee B Y, Trainor F S, Lewis J M, “Skin stress and blood flow in sitting paraplegic patients,” Arch Phys Med Rehabil., April 1984; 65(4):186-90. With regard to people with spinal cord injury (SCI)—most of whom use wheelchairs—between a third and a half develop ulcers within five years after the injury. Five to seven percent of people with SCI eventually require hospitalization due to decubitus ulcers and seven to eight percent eventually die of complications from ulcers. Agram L, Gefen A, “Pressure ulcers and deep tissue injury: a bioengineering perspective,” Journal of Wound Care, Vol. 16, Iss. 8, 1 Sep. 2007, pp 336-342.
Overall, the incidence rates for all kinds of decubitus ulcers range from 0.4% to 38% in acute care, 2.2% to 23.9% in long-term care, to 0% to 17% in home care. More than 2.5 million pressure ulcers are treated each year in the United States. Estimates put United States expenditures on the treatment of decubitus ulcers as high as $11 billion. Reddy M, Gill S S, Rochon P A, “Preventing pressure ulcers: a systematic review,” JAMA, 23 Aug. 2006; 296(8): 974-84.
Most decubitus ulcers form over weightbearing bony prominences. In seating, the most frequently involved areas are over the sacrum, coccyx, ischial tuberosities and greater trochanters. Carlson et al., Spring 1995. For people in beds, other involved areas can include those over the back of the heels, the back of the head, the elbows, and the shoulder blades, for example.
Two forms of external loading play a role in the formation of decubitus ulcers: pressure and shear. Friction forces act parallel (or tangential) to the skin surface and produce shear strains within the skin and underlying tissue. Both pressure and shear harm skin. Carlson et al., Spring 1995.
For many years, care providers focused predominantly on alleviating pressure when evaluating support surfaces and wheelchair cushions. Reducing pressure is accomplished by redistributing the overall contact pressure. Carlson et al., Spring 1995. This commonly involves off-loading pressure from a vulnerable area to a less vulnerable area.
Like pressure, shear is also reduced by lowering peak pressure because shear is caused by two phenomena: pressure and friction. In the context of seat cushions and other support surfaces, there are several reasons to focus on shear reduction. First, in relative terms, shear is more destructive of tissue integrity than pressure. Bennett et al., April 1984. Second, in some instances, it may be easier to manage friction and shear than it is to manage pressure. Third, most efforts to control peak pressure involve foam materials that can accelerate ulcer formation by impeding heat dissipation and evaporation.
An apparatus is disclosed for placement on a support surface between the support surface and a living being, wherein the living being has a bony prominence. The apparatus comprises a first zone having a first coefficient of friction, the first zone being configured for positioning proximate the bony prominence. A second zone is adjacent the first zone, the second zone having a second coefficient of friction higher than the first coefficient of friction. The second zone is configured for positioning remote from the bony prominence.
A method of preventing or healing decubitus ulcers comprises positioning the bony prominence over the first zone and positioning an area remote from the bony prominence over the second zone.
The disclosed subject matter will be further explained with reference to the attached figures, wherein like structure or system elements are referred to by like reference numerals throughout the several views.
The present disclosure presents an apparatus and method for preventing the formation of decubitus ulcers by managing shear forces. The present disclosure relates to a cover for a support surface such as a seat cushion or a bed mattress, said cover having zones of low friction and higher friction. The cover is constructed such that zones of low friction are positioned proximate tissue that is vulnerable to the formation of decubitus ulcers. Zones of higher friction are positioned proximate less vulnerable tissue; these higher friction zones help to provide support for a living being such as a person.
Shear can be mitigated by increasing the “slipperiness” (i.e., reducing the coefficient of friction (COF)) in an interface between the skin and the support surface.
If we define:
Managing friction and shear does not simply mean attempting to eliminate all friction. Friction may be essential for proper positioning of a person or retention of a person on a support surface. For example, there is often a tendency for a seated person to slide forward in a chair. Without friction, the person could even slide out of the chair or wheelchair. Similarly, for a bed, it may not be desirable that the entire bearing surface be low friction. This may be especially true of areas near the lateral sides of the bed, where too little friction could cause a person to slide out of the bed. Therefore, having a higher friction zone in particular locations on a support surface may be beneficial.
The present disclosure presents a way to manage friction and shear by controlling the COF of an interface between the skin and a surface supporting a human body (or other living being). This allows for the management of friction and shear without changing the structure of the underlying support device. In an exemplary embodiment, an apparatus such as a cover for a support surface is secured to the support surface rather than to a part of the body. The apparatus can cover all or a portion of a support surface. The apparatus has one or more zones of low friction on a support surface so that vulnerable parts of the body can be subjected to lower friction and shear loads. The apparatus also has one or more zones of higher friction on a support surface so that less vulnerable parts of the body can be subjected to higher friction and shear loads; additionally or alternatively, the zones of higher friction on a support surface can be used for beneficial purposes such as the positioning of a person on the support surface or the retention of the person in a desired position.
An exemplary embodiment of a cover 100 for a seat cushion 101, the cover 100 incorporating first zones of low friction 112 and second zones of higher friction 113, is shown in
As mentioned above, most decubitus ulcers form over weight-bearing bony prominences of people who spend long periods of time sitting or lying down. In seating, the most frequently involved areas are tissue over the coccyx 103, ischial tuberosities 104a, 104b and greater trochanters 105a, 105b, as illustrated in lower body 111 of
Some areas of the body in contact with the seat cushion 101 can better withstand the effects friction and shear. Generally, these are areas more remote from bony prominences 103, 104a, 104b, 105a, 105b such as parts of the gluteal regions 106a, 106b and the undersides of the thighs 107a, 107b.
For purposes of support surface design for seated persons 108, therefore, the area of greatest concern for decubitus ulcer formation can be identified. If one were to draw a dotted line around these bony prominences 103, 104a, 104b, 105a, 105b, as shown in
The design of the seat cushion cover 100 can take into account the susceptibility of various regions of the body to skin trauma. The seat cushion cover 100 can have zones of low friction 112 and zones of higher friction 113. The low friction zones 112 of the seat cushion cover 100 can be positioned proximate the primary area of tissue vulnerability 109. Thus, when the person 108 is sitting on the seat cushion 101, the low friction zone 112 can be positioned proximate the bony prominences such as the ischial tuberosities 104a, 104b, the coccyx 103, and the greater trochanters 105a, 105b.
On the other hand, the higher friction zones 113 can be positioned proximate parts of the body more distant from bony prominences 103, 104a, 104b, 105a, 105b and therefore less vulnerable to skin trauma—such as parts of the gluteal regions 106a, 106b and the undersides of the thighs 107a, 107b. Areas more remote from bony prominences 103, 104a, 104b, 105a, 105b are less susceptible to the formation of decubitus ulcers because more tissue can dissipate shear forces. Areas remote from bony prominences 103, 104a, 104b, 105a, 105b can serve to support the seated person 108 and to keep the seated person 108 well-positioned in the wheelchair 110 and on the cushion 101. For example, friction against the undersides of the thighs 107a, 107b can prevent the seated person 108 from sliding forward on the cushion 101. With regard to the higher friction zone 113 in the front part 121 of the cushion 101, this can serve as a less slippery location on which to place a hand (or place a transfer board) when the seated person 108 re-positions herself or himself or transfers into or out of the wheelchair 110.
The low friction zone 112 can be created in a variety of ways. One way is to create the zone 112 from a material having a slippery surface. One such material is a film made of polytetrafluoroethylene (PTFE) or other similar material. Films such as those made of PTFE can form interfaces with other materials (such as clothing, skin, etc.) with extremely low COF's. In an exemplary embodiment, the film is cut into the shape of the low friction zone 112 and attached to the top 118 of the cover 100. In this way the slippery surface of the low friction zone 112 is exposed and can therefore form an interface with the clothing or skin of the seated person 108.
However, polymer films such as those made from PTFE can have potential disadvantages. Films made from materials such as PTFE generally lack elasticity and breathability. The lack of elasticity can be particularly problematic in a cover 100 for a seat cushion 101 because tension loads in a cover material can transfer to a bony prominence. Fabrics can also be utilized for the low friction zone 112. However, many fabrics with low COFs do not exhibit much elasticity.
Another way to create the low friction zone 112 can be to employ a layered fabric construction.
In the illustrated example, a first ply 114 having a top major surface A and a bottom major surface B forms the top layer of construction 117. The second ply 115 has a top major surface C and bottom major surface D. Each of the first ply 114 and second ply 115 exhibits anisotropy, wherein there is a different physical property of the material when measured along different axes in a plane of the material corresponding to the orientation of a major surface. Each of the first ply 114 and the second ply 115 has a relatively shiny major surface. In the illustrated embodiment, the bottom major surface B of the first ply 114 and the top major surface C of the second ply 115 are the relatively shiny major surfaces of each layer. The first and second plies 114, 115 are arranged as shown: the bottom major surface B of the first ply 114 and the top major surface C of the second ply 115 contact each other to form an interface in construction 117. At this interface, the first and second plies 114, 115 move relatively freely in relation to each other, with low friction therebetween. Thus, the interface has a low COF.
Many different fabrics can be used to form the two-ply construction 117. One suitable fabric for both plies 114, 115 is Style 480 Spandex distributed by Cooper Fabrics of Norwood, Mass. This is a three-bar tricot fabric consisting of 85% 40-denier semi-dull nylon and 15% 140-denier spandex. To form the interface 117, the plies 114, 115 are oriented with each other in the following way: sides B and C face each other as mentioned above. When using this particular kind of fabric, sides B and C are shinier than sides A or D. In other words, the shiny sides of the two plies 114, 115 face each other.
Second, the length L1 of the first ply 114 and the length L2 of the second ply 115 are arranged so they are not parallel and are preferably substantially perpendicular, as shown in
The length directions L1 and L2 of the plies 114, 115 do not have to be arranged precisely perpendicular. In addition, when in use, the plies 114, 115 will slide out of a perpendicular relationship. However, the closer the lengths L1 and L2 of the plies 114, 115 remain perpendicular to one another, the lower the COF of the interface 117 will be.
The first ply 114 can be a layer cut or fabricated generally in the shape of the low friction zone 112 shown in
A cover 100 using the Style 480 fabric demonstrates excellent elastic deformation characteristics. A single ply of the fabric that can be used in the higher friction zones 113 can stretch 270% in the L1 direction and 90% in the W1 direction. The two-ply combination construction 117 that can be used in the low friction zone 112 would demonstrate lower stretch capabilities. For example, stretch in the L1 direction of the first ply 114 would be limited by the stretch of second ply 115 in the W2 direction, i.e., limited to a stretch of 90%.
The elasticity of the cover 100 can be enhanced in a variety of ways. First, an elastic seam can join the first ply 114 and second ply 115 at the perimeter 116 of the first ply 114. Examples of stitches for an elastic seam include a three-step zig-zag also known as a multi-step zig-zag (such as that made on a Singer Tradition sewing machine with a stitch length setting of two and one half); single-step zig-zag; overlock (serger); and cover stitch. Using an elastic stitch can help prevent the seam from restricting the stretch of the cover 100. Moreover, use of a three-step zig-zag or multi-step zig-zag stitch can also prevent a sewn seam from bunching. Preventing bunching can be desirable both aesthetically and for the comfort of the seated person 108.
Second, the L2 direction of the second ply 115 of the cover 100 can be oriented from side-to-side of the seat cushion 101 rather than front-to-back. This can maximize the elasticity of the cover 100 in the side-to-side direction of the seat cushion 101. Since the greater trochanters 105a, 105b will likely be positioned near the sides 119 of the of the seat cushion 101, it is the side-to-side direction that may be in most need of additional elasticity to avoid “tenting” of the cover 100 over the greater trochanters 105a, 105b.
Another exemplary embodiment of a cover 200 for a seat cushion 201 is illustrated in
One way to construct the cover 200 is to first make the entire cover 200 out of the two-ply fabric construction 117 described above. Then, holes are cut in the first ply 114 in the oval shapes 235 at the locations shown in
Another exemplary embodiment of a cover 300 for a seat cushion 301 is shown in
Yet another exemplary cover 400 for a seat cushion 401 is shown in
Friction appliment 438 can be used to create zones with differing COF. In the higher friction zone 413, a friction appliment 438 can be a series of round dots, approximately 1/16″ in diameter, evenly spaced in a rectangular pattern at approximately 8 dots per linear inch, approximately 64 dots per square inch and lightly screen printed to create an opaque deposit of ink approximately 0.004 inches thick on Style 480 Spandex from Cooper Fabric. Changing the friction appliment 438 diameter, spacing, application thickness or material properties can alter a zone's COF. For example, a zone of intermediate friction could be created by altering the application of the friction appliment 438. A friction appliment 438 can also be used on a cover for another type of support surface, such as a bed mattress.
A sewn seam can be used to attach the first ply 414 to the second ply 415 at a perimeter 436. Some types of sewn seams can reduce elasticity in a cover 400. For this reason many wheelchair users 108 prefer a cover 400 without sewn seams in areas needing the greatest elasticity. By using a friction appliment 438 to create higher friction zone 413 and omitting the use of friction appliment 438 to create lower friction zone 412, no seams are required at the perimeter 416 between the higher friction zone 413 and the lower friction zone 412. Thus, other seams may be easily positioned away from areas of the cover 400 that may come in contact with vulnerable tissue.
Another cover 500 for a seat cushion 101 is shown in
In yet another exemplary embodiment, friction appliment 536 is applied within friction appliment zone 537 to cover 500 on a side of cover 500 that will be in contact with the seated person 108. Accordingly, the friction appliment 536 can help prevent the seated person 108 from sliding with respect to cover 500. In an exemplary embodiment, friction appliment zone 537 is remote from vulnerable tissue. A friction appliment could also be used on a cover for other types of support surfaces such as a bed mattress.
An exemplary embodiment of a bed cover 600 is shown in
The cover 600 can generally be constructed in the same way as the seat cushion covers 100, 200, 300, 400, 500 described above, though there may be some differences. The cover 600 is sized and constructed to fit onto a standard mattress 601 used in a hospital, long-term care facility, or a home. A portion of the cover 600 can be a low friction zone 612, which can have the shape 635. This shape 635 circumscribes contact areas 625 for bony prominences such as the occipital bone 626; the shoulder blades 627a, 627b; the elbows 628a, 628b; the hands 629a, 629b; the lower part of the spinous process 631; and the heels of the feet 630a, 630b, as shown in
The higher friction zone 613 along the lateral sides of the bed can prevent a person from sliding out of the bed. It can also allow a visitor or a caregiver, for example, to sit on the side of the bed without sliding off. The higher friction zone 613 along the lateral sides also allows for the secure positioning of transfer boards on the side of the bed. Finally, the higher friction zone 613 on the sides 619, head 621, and foot 622 of the mattress 601 can help secure top sheets or blankets tucked underneath the mattress 601.
Another exemplary embodiment of a cover 700 is shown in
The disclosed support surface cover is used on a wheelchair or chair cushion or a bed mattress in exemplary embodiments. The cover need not extend completely over or conceal a support surface. The support surface cover could, for example, be merely placed upon a support surface without a means of fixable attachment. On the other hand, a support surface cover could also be fixably attached to a support surface.
Many other configurations for seat cushion covers and support surface covers with low friction and higher friction zones are conceivable. Zones of various dimensions, shapes, and locations can be employed. For example, the low friction zone of a seat cover could make up the back two-thirds, the back half, or the back one-third of the seat cushion (not shown). For other people or for animals other than humans, different areas of vulnerability than those depicted above may exist. In such instances, zones of low friction and higher friction can be formed to meet the needs of the person or animal being supported. These variations and many others are within the scope of this disclosure.
The present disclosure should not be considered limited to the particular examples described above. For example, while suitable sizes, materials, fasteners, and the like have been disclosed in the above discussion, it should be appreciated that these are provided by way of example and not of limitation, as a number of other sizes, materials, fasteners, and so forth may be used without departing from the invention. Various modifications as well as numerous structures to which the present disclosure may be applicable will be readily apparent to those of skill in the art to which the present disclosure is directed upon review of the present specification. The claims, which arise from this application, are intended to cover such modifications and structures. In addition, any feature disclosed with respect to one embodiment may be incorporated in another embodiment, and vice-versa.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
This Application is a Section 371 National Stage Application of International Application No. PCT/US2009/057991 filed Sep. 23, 2009 and published as WO 2010/039524 A2 on Apr. 8, 2010, the content of which is hereby incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2010/031695 | 4/20/2010 | WO | 00 | 9/29/2011 |
| Number | Date | Country | |
|---|---|---|---|
| 61171863 | Apr 2009 | US |
