Abstract:
A foam core cushion mattress assembly provides semi-independent foam pillars on the upper surface of the mattress. The mattress may be unitary, or comprise multiple cushioning components, possibly base, body support and foot cushions. The body support cushion is constructed from a flat, rectangular solid, foam element whose upper surface is cut into an array of rectangular solid pillars, preferably by a hot wire cutting method. The array of rectangular solid pillars is grouped into a central array comprising pillars with generally square top surfaces and edge rows of rectangular solid pillars having rectangular top surfaces. The depth of the hot wire cuts into the surface of the body support cushion is preferably approximately one-half the overall thickness of the body support cushion or approximately three fourths of the length of the shortest face of the pillar. A zippered fabric cover removeably envelops the assembled cushioning components. The resultant structure defines a plurality of semi-independently compressible pillars that support a reclining, or supine patient. The pillars may also be cut into the top and bottom surfaces of the cushion for enhanced pressure relieving effects. Methods of manufacture, and treatment and alleviation of decubitus ulcer formation are also presented.

Description:
RELATED APPLICATION INFORMATION 
   This application is a continuation in part of co-pending and commonly assigned application for Pat. Ser. No. 09/522,145 filed Mar. 9, 2000 entitled “MATTRESS WITH SEMI INDEPENDENT PRESSURE RELEIVING PILLARS.” 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to mattresses for use in association with beds and other support platforms. The present invention relates more specifically to a foam containing mattress assembly having a pressure relieving structure comprising semi-independent foam pillars, on either one, or two surfaces of such a mattress, a method of manufacture thereof, and a method of treating decubitus ulcers therewith. 
   2. Description of the Related Art 
   Patients and other persons restricted to bed for extended periods incur the risk of decubitus ulcers formation. Decubitus ulcers (also referred to as bed sores, pressure sores or pressure ulcers) are formed due to an interruption of blood flow in the capillaries below skin tissue due to pressure against the skin. The highest risk areas for such ulcer formation are those areas where there exists a bony prominence, which tends to shut down capillaries sandwiched between the bony prominence and the underlying support surface. When considering the redistribution of body weight and the formation of decubitus ulcers, historically, the trochanter (hip) and the heels are the body sites of greatest concern because these are the areas most frequently involved in decubitus ulcer formations that afflict bedridden or immobile patients. 
   Generally, as is well known in the art, blood flows through the capillaries at an approximate pressure of 32 millimeters of mercury (mm Hg). This pressure can be somewhat lower for elderly individuals or individuals in poor health or with nutritional deficiencies. Once the net external pressure on a capillary exceeds its internal blood pressure, occlusion occurs, preventing the afflicted capillaries from supplying oxygen and nutrition to the skin in close proximity thereto. Tissue trauma may then set in with the resultant tissue decay and ulcer formation. Movement of the afflicted individual into different positions generally helps in restoring blood circulation into the effected areas. However, such movement is, either not always possible or is in some instances neglected. 
   Additionally, even shorter bed rest periods by healthy individuals on a mattress that neither relieves nor reduces the pressure exerted on the user is likely to be considered uncomfortable. Conversely, a mattress that provides insufficient firmness or support is also likely to be uncomfortable. 
   In attempting to avoid the problem of decubitus ulcers in bedridden individuals and to provide greater user comfort to those spending substantial amounts of time in bed, a variety of techniques and devices have been used in the past. For instance, air mattress overlays, air mattresses (static and dynamic), water mattress overlays, water mattresses, gel-like overlays, specialty care beds, foam overlays and various types of other mattresses have been introduced in an attempt to avoid the above noted problems with decubitus ulcers and general user discomfort. Some relatively expensive motorized and/or dynamic devices have been quite successful in solving these problems. However, their cost and relative complexity drastically reduce the breadth of market to which such devices can be effectively offered. 
   Therefore prior to the filing of the parent application cited above, no non mechanized device has been wholly successful in meeting these needs, at a cost which, in view of government cutbacks in such programs as Medicare, and stringent, possibly draconian, cost restrictions, would make such devices readily accessible. 
   Recently, applicant has filed the above identified parent application for letters patent for a novel and unique device that meets the above identified goals in a surprising and unexpected manner. After this filing was made, applicant has further defined and refined this invention, as described below. The meeting of the needs stated above, in a reasonably economical fashion, is the goal of the present invention. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention provides a non-mechanized mattress assembly that possesses a plurality of semi-independent foam pillars comprising an upper portion of the mattress. This mattress assembly may be fabricated from a single piece of deformable material, such as foam, or, in the presently preferred embodiment, comprises a plurality of core components, for example, a foam base, a foam body support cushion, and a foot cushion insert, which are placed in a contiguous operatively coactive manner. In a multiple component embodiment, these components may be held in place by appropriate contouring of their structures, may be bonded together, or may be fixedly attached in any other suitable manner as is presently known in the art, so as to fix their relative orientation. 
   In addition to the embodiment described above, where the upper surface is composed of such semi-independent pillars, applicant has also devised an embodiment containing two arrays of pillars. In addition to the upper patient surface pillar array described above, a second array of pillars is incorporated into the bottom surface of the body support cushion. 
   Once so placed, or assembled, or in the single component embodiment, after fabrication, a removable fabric cover envelops this mattress core assembly. The enveloping must be sufficiently loose so as to not create meaningful tension on the top surface of the mattress. Most usually, the completed mattress core is generally rectangular in shape. 
   In the multiple component embodiments, the base component supports the other elements of the mattress core, and, therefore has the same lateral and longitudinal dimensions, as does the entire assembled mattress core. The overall height of the covered mattress assembly, in either the single component, or the multiple component embodiments will generally approximate the thickness of a present day medical mattress, from about 5 to about 7 inches. The height (or depth) of the base generally ranges from about 1 to about 2 inches, except as may be necessitated by any applicable contouring requirements. The base is less deformable than is either the body support cushion or the foot support insert. The base is generally symmetrical, during the process of placing the components into alignment, one of the short edges of the base is designated as the top edge of the base, and thereby also of the assembled mattress core. 
   The body support cushion component is made from a rectangular solid foam element whose upper surface is cut into a plurality of solid pillars, which are most commonly arranged in some systematic manner, here defined as arrays. In addition, as stated above, pillars may also be cut into the lower surface of this cushion, thereby providing a cushion with opposed pillar arrays. 
   This cushion is longitudinally symmetrical about its central longitudinal axis. In the presently preferred embodiment, the rectangular solid pillars are grouped into a central array comprising pillars with generally square top surfaces, and edge rows of rectangular solid pillars having rectangular top faces. 
   Making repeated cuts into the top of the body cushion creates these pillars. Similarly making repeated cuts into the bottom of the body cushion creates those pillars. These cuts may be made by heated wires, saws, or other cutting method now known, or which becomes known in the future, to those having ordinary skill in the art. 
   In the single pillar array embodiment, the depth of the cuts into the surface of the body support cushion is preferably approximately 50% of the shortest dimension of the face of the pillar to approximately 150% of the longest dimension of the face of the pillar, or roughly one third to two thirds the overall thickness of the body support cushion, in the multi component embodiment. 
   In the double pillar array embodiment, that is, where arrays of pillars exist in both the top and the bottom surfaces of the body support cushion, the depth of the cuts is somewhat different. In this embodiment, there is an uncut central zone intermediate the top pillars and the bottom pillars. Given present limitations in the durability of foam materials in the preferred ranges of density and IFD, substantially cubical pillars with an about 20% uncut intermediate level is the presently preferred configuration. However, if, for some reason the uncut region is not in the middle of the body support cushion, cut depths similar to those described above could well be used. 
   The foot cushion insert, if employed, in the multi component embodiment, is a generally trapezoidal geometric solid comprised of polyurethane foam, or other suitable material, which could include air, or other fluid. This trapezoid is oriented so that its thickness is greater in that portion proximate to the body support cushion, and lesser in that portion remote from the body support cushion, thereby resulting in the insert having a thick edge and a thin edge, and a downward slope from the direction of the designated top edge of the mattress, to the designated bottom edge of the mattress. 
   Viewed from the top, the trapezoid is substantially rectangular in shape. The insert is, most usually, more easily deformable than both the base and the body support cushion. The same slope will generally be fabricated into the single component embodiment, in the same relative location. 
   The multiple component embodiment of the present invention is assembled in the following manner. The base is placed in the desired orientation. The body support cushion is aligned so that the top edge of the cushion is in registry with the selected top edge of the base. The foot insert is then placed so that the thick edge of the insert abuts the bottom edge of the body support cushion, the thin edge of the insert is in registry with the bottom edge of the base, and the sides of the assembled cushion are in substantial registry with the sides of the base. The base, body support cushion, and insert, are then secured in position. Two easy methods of securing the body support cushion to the base are through either lamination, or through a relatively rigid perimeter framing. 
   A zippered fabric cover then removeably envelops the assembled mattress core. The resultant structure defines a plurality of semi-independently compressible pillars that provide appropriate support to the upper portion of a person in a supine, or reclining position on the mattress, and an inclined uniform surface that supports the feet and connective portions of the person in question. 
   An object of the present invention is to provide a non-mechanized pressure-reducing mattress that provides therapeutic benefits to a person confined thereto for a substantial period. 
   Another object of the present invention is to provide a mattress, which prevents or minimizes capillary damage to those who are confined thereto. 
   A further object of the present invention is to provide a reasonably economical pressure-relieving mattress that provides therapeutic benefits to a mammal confined thereto for a substantial period. 
   Yet another object of the present invention is to provide a relatively lightweight pressure-relieving mattress. 
   A still further object of the present invention is to provide a mattress that is easy and relatively affordable to manufacture. 
   Still another object of the present invention is to provide a method of alleviating or minimizing the occurrence of decubitus ulcers on a person confined to a bed for a significant period of time, by the use of the semi-independent pillar containing mattress disclosed herein. 
   A yet further object of the present invention is to provide a decubitus preventing or alleviating mattress containing semi-independent pressure relieving pillars which is more economical than those of equal efficacy known to the prior art. 
   An even yet further object of the present invention is to provide a decubitus preventing or alleviating mattress containing semi-independent pressure relieving pillars which is more economical than those of equal efficacy known to the prior art where these pillars are provided in both the top and bottom surfaces of the mattress. 

   
     These and still further objects as shall hereinafter appear are readily fulfilled by the novel pressure relieving mattress of the present invention in a remarkably unexpected manner as will be readily discerned from the following detailed description of an exemplary embodiment thereof especially when read in conjunction with the accompanying drawings in which like parts bear like numerals throughout the several views. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
       FIG. 1  is an exploded perspective view of the cushioning components of the mattress of the present invention. 
       FIG. 2   a  is a top plan view of the body support cushion component of the present invention. 
       FIG. 2   b  is a side view of the body support cushion component of the present invention. 
       FIG. 2   c  is an end view of the body support cushion component of the present invention. 
       FIG. 2   d  is a detailed view of a cut made into the body support cushion component of the present invention. 
       FIG. 3   a  is a detailed top plan view of the central pillars of the body support cushion component of the present invention. 
       FIG. 3   b  is a detailed cross-sectional view of a number of the central pillars in the body support cushion component of the present invention. 
       FIG. 4   a  is a top plan view of the foot cushion insert component of the present invention. 
       FIG. 4   b  is an end view of the foot cushion insert component of the present invention. 
       FIG. 4   c  is a side view of the foot cushion insert component of the present invention. 
       FIG. 5   a  is an exploded view of the upper and lower components of a cover appropriate for use in conjunction with the present invention. 
       FIG. 5   b  is an assembled view of the cover shown in  FIG. 5   a.    
       FIG. 6  is a view of a body support cushion having two sets of pillars. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The cushioning components of the first embodiment  10  are displayed in an exploded view shown in FIG.  1 . The three basic components of mattress assembly  11  include foam base  12 , foam body support cushion  14 , and foot cushion insert  16 . 
   Foam base  12  is a substantially rectangular solid structure having end walls  18  sidewalls  20 , surfaces  22 , and body  23 . The dimensions of foam base  12  viewed from above may be similar to those of any standard mattress, particularly medical mattresses, but are preferably approximately 35 inches wide by 80 inches long. The thickness of foam base  12  may vary according to the needs of the application and would range anywhere from about one inch to about two inches, or even more than two inches. In addition, the choice of foam material for base  12  permits variations in the overall resiliency of the mattress. In the preferred embodiment, foam base  12  is presently preferably constructed from a polyurethane core material having 1.8 lb. per cubic foot density and 33 lb. IFD (Indention Force Deflection). However any suitable similar foam presently used in this field of endeavor may be used within the spirit of the present invention. 
   Foot insert cushion  16  comprises a generally trapezoidal solid having thick end wall  24 , thin end wall  25 , top surface  26 , and sidewalls  28 . In the preferred embodiment, foot cushion  16  is constructed from a polyurethane viscoelastil foam core material having 3.8 lb. density and 10 lb. IFD. However, any material possessing the desired softness and deformability characteristics may be employed within the spirit of the present invention. As viewed in  FIG. 1  cushion  16 , when viewed from either the top or the bottom, is generally rectangular in shape. 
   As shown in  FIG. 2  the detailed structure of foam body support cushion  14  is described below. Body support cushion  14  is a generally rectangular solid foam element having top surface  30 , bottom surface  32 , body  34 , side walls  36 , top end wall  38 , and bottom end wall  39 . 
   Body  34  is cut, into a plurality of foam pillars including central pillars  40 , and edge pillars  42 . The cuts into body  34  which define pillars  40 ,  42  begin at the top of surface  30  of body  34 , and extend approximately ½ of the way from top surface  30  towards bottom surface  32 . The degree of independence of the pillars depends, at least in part, upon the depths of the cuts used to create these pillars. Plainly if the cuts extend 100% of the way through body  34 , the pillars would be substantially 100% independent. Equally plainly, if the cuts extend a miniscule percentage of the way through body  34 , the pillars would be substantially dependent such that compression or movement of one pillar is readily transmitted to the adjacent pillar. Therefore, a cut that extends part way into body  34  from top surface  30  provides pillars  40 ,  42 , with a limited amount of independence. 
   Applicant believes, but does not desire to be bound by, that the independence of such pillars is also related to the relationship between the dimension of the face of a pillar,  40 ,  42 , having the smallest value, and the depth of such a cut. Applicant believes that in certain circumstances, the depth of the cuts could range from about one sixth to about five sixths of the depth of the body cushion  14 , and that more optimally, the depth of the cuts could range from about 25% to about 75% of the depth of body cushion  14 , or also about 50% of to approximately 100% or more, of the face dimension noted above. 
   As shown in  FIG. 6  the cuts can be made from either top surface  30  or bottom surface  32 , into body  34 . The total depth of the cuts into body  34  is primarily determined by the need to assure a reasonable durability of body cushion  14 . Presently, the preferred embodiment of cushion  14  is to have 2 inch square, substantially cubical pillars cut into both the top surface  30  and bottom surface  32  of body  34 . Body  34  can also be subdivided into horizontal strata. Cut strata  38 , are those strata of body  34  into which cuts are made. Uncut strata  39  are those strata of body  34  into which cuts are not made. If cuts are made into both the top surface  30  and bottom surface  32  of cushion  14 , then the uncut region of body  34  comprises uncut strata  39 . These uncut strata  39  would then have a thickness of approximately 2 inches. 
   In the presently preferred embodiments pillars  40  are substantially square, while pillars  42  are substantially rectangular. Pillars  42  are adjacent sidewalls  36 , while pillars  40  are not adjacent to the longitudinal sidewalls  36 . In the preferred embodiment, body support cushion  14  is constructed from a polyurethane core material having 1.8 lb. density per cubic foot, and 21 lb. IFD. This provides a softer top layer compared to the firmer under layer comprising foam base  12 . However many such foams are currently available, and could well be used within the spirit of the present invention. 
   As shown in  FIG. 1 , each of the three cushioning components of foam mattress assembly  11  are secured one to another in a manner sufficient to prevent layer shifting between the components, after they have been placed in the proper arrangement. Thick end wall  24  of insert  16  is placed in intimate contact with bottom end wall  39  of body support cushion  14 . In the presently preferred embodiment, this configuration has the result of causing the top surface  26  of foot insert  16  to slope downward away from body cushion  14 . Body support cushion  14  and insert  16  are both placed atop foam base  12 , while the intimate contact between walls  29  and  39  is either maintained or reestablished prior to securing theses components in place. 
   Such securing could be accomplished in a variety of manners well known in the art. For example the cushioning components could be contoured so as to allow for a force fit intimate contact between components. In the presently preferred embodiment, the cushioning components could also be bonded together in the proper configuration. 
   This bonding would typically take the form of an adhesive agent that does not alter the foam core shape or the cushioning performance of the foam components. In addition, the bonding agent should not emit appreciable odors after curing and no bonding agent residue should extend beyond the outer edges of the foam core components. A variety of bonding agents known in the industry are suitable for assembling the mattress core  11  in the manner described. 
   Reference is now made to  FIG. 2  for a detailed description of the structure of body support cushion  14  of the present invention. As presently preferred by applicant, the pillars in the top and bottom surfaces of cushion  14  are substantially identical.  FIG. 2   a  is a top plan view showing the array of foam pillars exposed on top surface  30  of body support cushion  14 . In this view the array of central support pillars  40  is seen  3  intermediate edge row pillars  42 . In this view it can also be seen that central support pillars  40  have a generally square upper surface, while edge row support pillars  42  have a generally rectangular upper surface. The larger top surfaces afforded edge row pillars  42  provide enclosing support to the patient positioned within a central area of the mattress. The larger pillars  42  at the longitudinal edges of the mattress incorporated within the present embodiment  10  tend to contain the patient within the central portion of the mattress over the smaller square-faced central foam pillars  40 . 
   The dimensions of pillars  42  are now believed to be primarily determined by the operational requirements of the manufacturing process. The combination of the mattress width and length, and the desire to have cuts on readily reproducible depths and spacings, within the parameters needed to assure patient care, are paramount. In use, 2 inches cut spacings and depths are therefore used for the central pillars  40 , though other spacings would likely also be suitable. Equally, if hard metric spacings and dimensions were used, 5 cm would likely be an equally satisfactory spacing and depth dimension. The operative requirement is to avoid edge pillars  42  which are smaller than the central pillars  40 . 
   In the presently preferred embodiment, the array of central support pillars  40  positioned along the center of support cushion  14  comprises  32  columns by  14  rows for a total of  448  discrete support pillars. The two sets of edge row pillars  42  which border central support pillars  40 , each comprise  32  discrete support pillars. Central support pillars  40  present 2 inch by 2-inch top surfaces in the preferred embodiment as described in more detail below; edge row pillars  42  present 2 inch by 3.5 inch top surfaces. These dimensions provide overall dimensions of approximately 35 inches by 64 inches for body support cushion  14 . Variations are possible in the overall size of support cushion  14  by adding or removing rows of central support pillars  40  to vary the width of embodiment  10 , and/or by adding or removing columns of central support pillars  40  bounded by edge row pillars  42  to vary the length thereof. As is referenced elsewhere herein, the size of the pillars  40  from the plan view may vary to some degree, although approximately two inches by two inches plus or minus about a half inch is preferred, though central pillars ranging from about 1 inch square to about 4 inches square could be used in various applications of the present invention, particularly if the mattress thickness is increased, for example to possibly 9 inches for a home health care product, or even possibly to as much as 12 inches for a hyperbaric mattress. 
   While there is no requirement that the pillars in the top and bottom surfaces be in registry, or even be equal in shape or size, such congruity is likely to provide operational efficiencies, and is therefore presently preferred. One manner wherein the top and bottom surface pillar array embodiment differs from the top surface only pillar array, is the increased importance of lateral support to the bottom surface of cushion  14 , in order to maximize the durability of the embodiment  10 . As discussed above, this can be enhanced through lamination of cushion  14  to the base, or by the provision of a perimeter support, not shown. 
     FIG. 2   b  is a side view of the structure of body support cushion  14  of the present invention showing the manner in which the array of central support pillars  40  are cut into top surface  30  of body support cushion  14 . The dashed line in  FIG. 2   b  indicates the approximate depth to which the cuts in top surface  30  are made into the solid rectangular body structure  34  of support cushion  14 . An exemplary row of foam pillars  40  is displayed. 
     FIG. 2   c  is an end view of support cushion  14  of the present invention showing a complete column of pillars comprising central support foam pillars  40 , and two of edge row pillars  42 . This dashed line also indicates the approximate depth of the cuts made in order to form the semi-independent foam pillars  40 . 
     FIG. 2   d  is a detail of section A shown in  FIG. 2   c , disclosing the manner in which slot  50  is made in the top surface  30  of body support cushion  14 . The method of using a hot wire or an array of hot wires to make cuts into foam solids is well known in the art. The process includes heating a wire, typically with electrical current, and forcing the hot wire into a foam element in a manner that cuts a void of relatively narrow width into the foam core. In the present invention the array of cuts necessary to create the array of semi-independent foam pillars could be accomplished with a predefined array of hot wires or a movable hot wire that cuts in sequence each of the necessary slots in the top surface of the foam support cushion. 
   Although certain aspects of the present invention can be appreciated while still using a saw-cut, or even laser cut foam, the hot wire cutting technique is presently most preferred. One of the important advantages of utilizing hot wire cuts as opposed to cuts made with a saw, for the purpose of creating the slots  50  in the surface of the mattress, relates to the resultant structure walls of the foam pillars  40 ,  42 . A saw cut generally leaves the walls of the foam pillars more jagged, or open-celled, for most types of foam. 
   A hot wire cut will slightly sear (melt) and partially seal the walls of the foam pillars in the process of cutting the slot into the top surface of the foam core. In the preferred embodiment of the present invention, the most preferred width of the slot cut in this manner is between approximately {fraction (1/16)}″ and approximately ⅛″, though wider cuts could be used if desire. The slightly seared walls of the foam pillars that result from this process have a smoother surface than those that might result from cutting with a saw. Applicant believes that this smoother surface reduces the coefficient of friction between adjacent pillars  40 ,  42  and permits greater independent movement of one pillar of foam with respect to adjacent pillars. 
   Applicant does not desire to be bound by this theory; however, saw cut structures of this geometry are thought to have an increased frictional coefficient between the walls of adjacent pillars. The present invention overcomes problems associated with this increased friction by utilizing a hot wire method for cutting the slots that create foam pillars  40 ,  42 . Other cutting techniques that produce a smoother cut than a saw may be utilized in alternate embodiments. 
   The hot wire cutting process is also believed to obtain another unobvious benefit. Leaving the heated wire in place at the bottom of each slot for some interval after the time necessary to complete cutting the slot in question can incrementally increase the width of the slot at that location. This is believed to be particularly beneficial in the present invention in that the increased width in the base of the slots is believed to distribute the foam stress that would otherwise be concentrated at the bottom of each slot, which reduces the likelihood of tearing or other damage to the pillars. This should add to the durability of a mattress embodying the present invention. 
   Reference is now made to  FIG. 3   a  for a detailed view and description of the structure of foam pillar components  40  of the present invention.  FIG. 3   a  is a plan view of the surface of body support cushion  14  showing the full upper, or lower, surface of one foam pillar  40 , and a partial view of eight adjacent foam pillars. In the preferred embodiment of the present invention, the exposed surface of these central foam support pillars is substantially square in geometry. 
   Dimension a shown in  FIG. 3   a , comprises a fraction of the length of embodiment  10 , and is therefore approximately equal to dimension b, which comprises a fraction of the width of embodiment  10 . As indicated above, the width of slots  50  cut into upper surface  30  of body support cushion  14  is approximately {fraction (1/16)}″-⅛″ in the preferred embodiment. Applicant believes that slots that are substantially larger than ⅛″ may decrease the amount of the patient interface surface, and thereby increases the amount of interface pressure. Dimension a and dimension b in the preferred embodiment, that is for a medical mattress having the dimensions discussed above, are approximately 2″ each, thereby providing a 2″×2″ square exposed surface for each foam pillar  40 . 
     FIG. 3   b  is a partial cross-sectional detailed view of body support cushion  14 , again showing one complete foam pillar  40 . In this view, the depth of slots  50 , disclosed in the preferred embodiment shown as dimension c, is approximately 2″. This is an appropriate depth for an overall thickness of body support cushion  14  having dimension d, which in the preferred embodiment is approximately 6″. Preferably, the dimension c, should be from about 50% of the smaller of dimensions a and b to about 150% of the larger of dimensions a and b, obtain optimum pressure relief. This would hold true for the multiple component embodiment, as well as the single component embodiment of the present invention. 
   A variety of dimensions are possible for those dimensions a and b shown in  FIG. 3   a , and those dimensions c and d shown in  FIG. 3   b . Applicant believes that the a:b ratio for central pillars  40  could range from about 1.5:1 to about 0.67:1 without materially affecting the efficacy of the present invention. Similarly the nominal a:b ratio for the edge pillars is approximately 0.56:1. Applicant believes that this could range from about 0.8:1 to about 0.28:1. 
   Applicant also believes that a graduated ratio, particularly where the a:b ratio is greatest about the longitudinal axis of the mattress assembly  11  could be employed, to provide even greater lateral support to the occupant of the embodiment  10 . Plainly, the inverse of the a:b ratio could also be used within the spirit of the present invention. 
   In addition various shaped pillars could be employed if desired. For example, if the slots  50  were made with an array of wires, and the body cushion  14  were subjected to lateral compression during the cutting process, then the slots  50  would be in a curvilinear configuration. Further, the wires or wire array could be arranged to obtain almost any desired shape slots  50  and pillars  40 ,  42 . For instance, rather than the one-eighth inch slot with an enlarged radius at its lower end (caused by leaving the hot wire in place), each slot could be shaped in teardrop fashion by moving the hot-wire through a tear-drop path during the cutting operation. 
   Slots could also be cut in a two-step process, which process is presently preferred. In this process, a set of wires is arranged in a parallel array. The wires are heated. The heated wires cut the first set of slots. The relative orientation between the mattress component being cut, and the wires, is shifted by approximately 90 degrees, and the second set of slots are then also cut by the same heated wire array. 
   Reference is now made to  FIGS. 4   a - 4   c  for a description of the structure and geometry of the foot cushion component  16  of the present invention. In  FIG. 4   a , top surface  26  of foot cushion  16  is displayed. The dimensions of insert  16  are defined primarily by the width of the assembled foam mattress, which, in the preferred embodiment, is approximately 35″. The short dimension of the upper surface  26  of foot cushion  16  is approximately 16″ but is sloped as described in more detail below. 
   Foot cushion  16  is a generally rectangular foam solid who&#39;s top surface  26  that inclines downward from thick end wall  24  towards thin enwall  25 , which comprises the outward edge the insert. This downward inclination provides what has been found to be an appropriate pressure relief for the heels of a patient positioned on the mattress  11  of the present embodiment  10 . The thickness of the foot cushion at its thickest dimension, the edge of thick end wall  24  where it abuts support cushion  14 , is approximately the same as the thickness of body support cushion  14 . 
     FIG. 4   b  is an end view of foot cushion component  16  of the present invention showing thin end wall  25  and sloping upper surface  26 . Thin end wall  25  has a thickness approximately one-half that of the thickness of foot cushion  16  where it meets with support cushion  14 , at thick end wall  24 , as previously discussed. This provides adequate inclination to upper surface  26  for insert  16  as described above. 
     FIG. 4   c  is a side view of foot cushion  16  showing in detail the inclined upper surface  26  sloping downward toward thin end wall  24 . While this inclined surface has been shown to have beneficial pressure relieving characteristics, it is of course possible to simplify the structure further by using a rectangular foam core with an orthogonal top surface. 
   Reference is now made briefly to  FIGS. 5   a  and  5   b , which disclose the structure of an appropriate fabric cover  60  for enveloping the mattress assembly  11  of the present invention. The cover shown in  FIGS. 5   a  and  5   b  is well known in the art and is marketed in conjunction with various mattresses under the trademark THERAREST® manufactured and sold by Kinetic Concepts, Inc. of San Antonio, Tex., the applicant, and assignee of the present invention. 
   The basic structure of the fabric cover  60  comprises two components; a lower component  61  is matched with and mated to an upper component  62 . Lower component  61  comprises a bottom cover material  64  having sidewalls  66 ,  68 ,  70 , and  72 . In the preferred embodiment, bottom cover material  64  is manufactured from a laminated vinyl fabric material, possibly double laminated vinyl material, and has surface dimensions generally equal to those dimensions for the foam mattress, namely 35″×80″. Lower component  61  also contains a plurality of lifting straps  74  that are attached, possibly by stitching, on to the fabric of lower component  60  and facilitate the movement and positioning of the assembled and enclosed mattress. Upper component  62  comprises top cover material  76  and sidewalls  78 ,  80 ,  82 , and  84 . In a preferred embodiment, top cover material ( 76 ) is manufactured from a poly/nylon denim fabric and is sewn in the configuration shown in  FIG. 5   a.    
   Upper component  62  is permanently and fixedly attached to lower component  61  along a “non-zipper” side of the enclosure  88  (best seen in  FIG. 5   b ). This side thereby becomes a “hinge” side of the enclosure and permits the assembled cover to encompass the assembled foam cushion components mating zipper components  90  sewn on to upper cover component  62  and lower cover component  61  provide means for repeatedly opening and closing the cover. 
     FIG. 5   b  also shows the assembled mattress cover with top cover material  76  exposed as indicated. As mentioned above, zipper  90  is shown positioned around approximately three-fourths of the perimeter of the cover to provide closure to the fabric material around the foam components described above. The fabric should have no tension on the surface upon which the patient is intended to rest, so as not to interfere with the therapeutic action of the present invention. 
   In the interest of more clearly explaining the present invention, and without limiting it in any way, applicant offers the following examples. 
   EXAMPLE 1 
   A piece of foam approximately 35″×64″×5″ deep, having the proper characteristics is selected. The following steps are performed upon the foam: 
   1. Place foam flat on cutting surface. 
   2. Align foam to be parallel with cutting wires so that the foam is centered along the width of wires. 
   3. Lower the hot cutting wires 2″ into the foam; these wires are preheated to a suitable temperature by electric current. 
   4. If desired leave the heated wires in place momentarily after the desired depth has been reached. 
   5. Raise the cutting wires out of the foam. 
   6. Rotate the foam 90 degrees and repeat steps 1-5. 
   The cut foam is now a body support cushion, and assembled as part of a completed mattress embodying the present invention. 
   EXAMPLE 2 
   A piece of foam is treated in accordance with Example 1. This piece of foam is then rotated so that the cut side is downward. The following steps are then performed upon the foam:
         1. Place foam flat on cutting surface.   2. Align foam to be parallel with cutting wires so that the foam is centered along the width of wires.   3. Lower the hot cutting wires 2″ into the foam; these wires are preheated to a suitable temperature by electric current.   4. If desired leave the heated wires in place momentarily after the desired depth has been reached.   5. Raise the cutting wires out of the foam.   6. Rotate the foam 90 degrees and repeat steps 1-4.
 
The cut foam is now a body support cushion having two opposed arrays of semi-independent pillars. It may now be assembled as part of a completed mattress embodying the present invention.
       

   From the foregoing, it is readily apparent that a new and useful embodiment of the present invention has been herein described and illustrated which fulfills all of the aforestated objects in a remarkably unexpected fashion. It is of course understood that such modifications, alterations and adaptations as may readily occur to the artisan confronted with this disclosure are intended within the spirit of this disclosure, which is limited only by the scope of the claims appended hereto.