CA1301377C - Multi-section mattress overlay for systematized pressure dispersion - Google Patents

Abstract

ABSTRACT OF THE INVENTION
A polyurethane foam mattress overlay has several sections defined in a relatively flat support surface thereof. The sections are longitudinally disposed so as to correspond with different parts of a user's body.
Each such section has predetermined support characteristics which are selected in relationship with such characteristics for the other sections so as to define systematized support. Specific numerical ranges and interrelationships for such sections are disclosed.
A plurality of projections are formed in each surface section. In general, the cross-sectional area of such projections at the overlay support surface or at a given depth therefrom is the same within each section, but differs from one section to another. Separation distances between such projections may also vary with the respective sections. In such manner, tailored support characteristics in respective sections provide engineered support for all parts of a user's body.
Further, side edges of the projections may be bevelled and/or include a radius of curvature to enhance independent action of the projections. Also, channels for dissipating heat and moisture may be provided, and have characteristics which vary with the different support sections. Further disclosed is an effectiveness index which takes into consideration the thickness, indentation load deflection (i.e.
stiffness), and density of a given pad.

Description

~L30~3~77 Title: MULTI-SECTION MATTRESS OVERLAY FOR
SYSTEMATIZED PRESSURE DISPERSION
BACKGROUND OF THE INVENTION
This invention concerns mattress pads or overlays in general, and in particular a mattress pad having a variety of features for providing sectioned support areas collectively functioning as a coordinated system for improved pressure dispersion for all parts of a user's body.
Decubitus ulcers, also known as bed sores, are a significant concern for bed-ridden patients. The problem of prolonged pressure on natural bony projections of a patient (such as the scapula, sacrum, and trochanter) is compounded in acute care settings where the patient cannot be frequently turned or moved.
It is relatively common practice in hospitals in the United States for a 1exible polyurethane foam mattress overlay to be used to supplement the mattresses of acute care patients. The goal generally is to provide at least some relief from bed sores during their immobilizatian. Simple convoluted foam pads, readily produced with known machinery, are typical of mattress overlays in present use.
A major thrust in recent hospital care practices has included higher-developed cost consciousness. To reduce costs, a trend has developed whereby,convoluted foam pads are provided with relative taller conical peaks and thinner bases so that the pad may be produced with less foam (and hence be more cheaply provided).
Many of such convoluted foam pads typlcally provide uniform instead of differentiated support across their ~3~37~
entire patient support surface. Accordingly, effective pressure distribution for the prevention of decubitus ulcers is not optimized for all parts of a patient's body.
Other forms of cushions or pads are known. For example, Berman ~U.S. Patent 2,638,156) discloses a seat-type cushion having a substantially flat support surface, but utilizing density variations for different segments thereof to variably support the ischial tuberosites of a user's pelvis. Variations in density rnay be obtained in alternative ways, but particularly include the production of channels and cavities through the cushion (i.e., the removal of material). Rogers (U.S. Patent 3,885,2S7) also varies support provided with a defined section of a pad by varying the amount of material removed from around projections formed thereby. However, the cross-sectional area of the external support surface of each projection is maintained constant over an entire block of his invention. Furthermore, the generally to substantially reduced cross-sectional area of such projections beneath the upward external support surface thereof can cause such projections to buckle, twist, and/or become unusually compressed, during load bearing, with possible unintended modification of the support action offered thereby.
Thompson (U.S. Patent 4,110,881) discloses a process for fabricating a mattress including the making of slots of varying depth and/or spacing therein so as to alter the support provided thereby. Removal of material is not ordinarily significant nor a design parameter. Instead, slicing is effected to provide a foamed material mattress which mimics the function of "inner spring" mattresses.
In addition to such cutting (i.e. slicing) and ~3013~7 'J
coring (i.e. producing cavities) other processing of foam products may be effected. For example, Spann (U.S.
Patent 4,573,456) discloses air channels which may be formed in a foam block for dissipating heat and moisture away from a person utilizing a product made from such foam block. And, though not in all circumstances analogous to foam pads, other types of mattress supplements are generally known. For example, Douglas (U.S. Patent 4,279,044) discloses a fluid support system with automatic valving for distributing the body weight of a patient received thereon.
SUMM~RY OF THE PRESENT INVENTION
This invention seeks to provide an improved mattress overlay or pad with coordinated support characteristics which optimize support for all parts of a patient's body. Support provided by various sections of the mattress overlay is preferably selected in accordance with the support provided by the other sections.
Therefore, the present invention further seeks to establish a relationship among the support characteristics of the various sections suppoxting different parts of a patient's body so that optimi~ed support may be provided for such patient. Such relationship may be expressed in different ways in accordance with this invention, e.g. a range of support characteristics for each of the respective pad sections.
Typical convoluted foam mattress overlays do not provide as favourable pressure dispersion for all parts of a patient's body to prevent decubitus ulcers as does a flat foam pad. Thus, it is another present object to provide an effective engineered pad which has an essentially flat support surface.
It is a further goal to provide particular predetermined and different support for different parts 3~13~7 of a patient's body in order to most effectively minimize or disperse pressures applied thereto. In accordance with this invention, the general mid-section of a patient's body, the scapula, the sacrum (with the patient in a supine position), and the trochanter (with the patient in a lateral position), are all provided with support geometry which is different from that provided for the head and heels of the patient. Generally, such is achieved by providing a relatively flat foam mattress overlay having a coordinated system design for optimum support of the overall body.
Still further, the present invention seeks to provide an engineered polyurethane mattress overlay which recognizes that adjusting support for a patient's head or foot areas affects the support and pressure dispersion provided to the torso or mid-area of the patient (the reverse affect also being true). Therefore, a further aspect of this invention is to provide an engineered polyurethane mattress overlay which has at least two or more separate support sections which function as an inter-related system (i.e.~ in a systematized relationship).
Further still this invention seeks to provide a mattress overlay having interface pressures among support sections thereof (i.e. interface of such sections and a user's body) which are relatively independent of a user's body build. It is a further aspect of this invention to provide a mattress overlay which is effective in supporting all parts of a patient's body in all positions thereof.
Generally, it is recognized by this invention that at least three characteristics of pads made from foamed materials (such as foamed polyurethane) contribute to the effectiveness of the resulting pad used for supporting patients. Such characteristics are:
(1) thickness of the foam pad;

(2) indentation load deflection (ILD) of the resulting pad (defined for purposes of this disclosure as the number of pounds of pressure needed to push a 50 square inch circular plate into a pad so as to deflect such pad a given percentage distance of its non-loaded thickness); and ` ''.~:

~3~L3~7 , (3) density (i.e. weight per cubic foot) of the material comprising the pad.
Further still, this invention seeks to provide an engineered mattress overlay which effectively mixes and selects the foregoing characteristics of foam materials (i.e. thickness, ILD, and density) to provide a pad which optimiæes pressure dispersion for all parts of a patient's body, generally without regard to the nature of the prone position assumed by the patient (i.e. supine or lateral) or the body build of the patient. It is also an object to devise and provide effectiveness ratings and the like which take into account the inter-relationship of all such three characteristics.
The invention in one aspect provides a mattress pad for providing systematized pressure dispersion for a person reclined thereon, comprising a main body of resilient material having a predetermined thickness and predetermined density, an upper support surface, defined by the main body, for receipt of a person thereon, and a plurality of parallel lon~itudinal and parallel transverse cuts ~ormed in the main body to a given depth thereof, and defining a plurality o~ rectangular-shaped elements. A plurality of sections are d~fined in the body, with each respective section including at least two adjacent transverse rows o~ the rectangular-shaped elements, and having predetermined support characteristics and element cross-sections which are generally constant over the respective section but which differ among the sections. The support characteristics are selected with determined relationships therebetween, and having 25% ILD characteristics generally in a range from about 17 pounds to about 26 pounds, where 25~ ILD
stands for 25% indentation load deflection as defined by the number of pounds of pressure required to push a 50 square inch circular plate into the main body so as to compress same by 25~ of its predetermined thickness, so as to form a support system for dispersing pressure in a desired manner for all parts o~ a person reclined thereon for optimized prevention of decubitus ulcers.

~3~377 The invention also provides a multi-section mattress overlay for supporting in a systematized manner all parts of a patlent received thereon for optimized prevention of decubitus ulcers, the mattress overlay comprising a generally rectangular body of foam material having a predetermined density and thickness, and defining an essentially flat support surface for receiving a patient in a substantially longitudinal, prone position thereon. At least three longitudinally-spaced sections are formed in the support surface for ; consecutively head, mid-section, and feet areas generally of the patient, each of the sections having at least one uniform, predetermined load-bearing characteristic which is selected with respect to that of each other section for establishing the systematized support provided by the overlay. Grid-shaped cuts are formed in the support surface of the body so as to define a plurality of substantially rectangular projections therein, the cross-sectional area of the projections being constant over a given section but varying with the three sections so as to determine the load-bearing characteristics thereof.
The head and feet areas each have 25% ILD characteristics in a range from about 17 pounds to about 22 pounds, and the mid-section area has a 25% ILD characteristic in a range from about 21 pounds to about 26 pounds, where 25%
ILD stands for 25% indentation load deflection, which is defined by the number of pounds of pressure re~uired to push a 50 square inch circular plate into said body of foam material so as to compress same by 25% of its predetermined thickness.
Still another aspect of the invention provides a process for manufacturing a pad comprising a mattress overlay with systematized features for supporting a person, comprising providing a generally rectangular ~3~L37~

member of resilient material having a substantially predetermined uniform thickness and predetermined uniform density, and with a support surface formed on one side of the members, the surface defining three longitudinal areas therein generally for operative association with the head, mid-section and feet, respectively, of a person, forming the head and feet areas so that each have 25% ILD characteristics in a range from about 17 pounds to about 22 pounds, and forming the mid-section area so that it has a 25% ILD characteristic in a range from about 21 pounds to about 26 pounds wherein 25% ILD
stands for 25% indentation load deflection, which is defined by the number of pounds of pressure required to push a 50 square inch circular plate into the polyurethane member so as to compress same by 25% of its predetermined thickness, and wherein the process further includes selecting the predetermined thickness to fall generally within a range of from about two inches to about four inches, and selecting the predetermined unifoI~ density such that the square root of the product of the ILD and the predetermined uniform density falls generally within a range of from about 5.7 to about 9.3, whenever Il,D is expressed in pounds, and density is expressed in pounds per cubic root, whereby a desired effectiveness rating for the pad is obtained for optimizing the preventi.on of decubitus ulcers.
The invention still further provides a method of making a mattress pad for providing systematized pressure dispersion for a person reclined thereon, comprising providing a main body of resilient material having a predetermined thickness and predetermined density, and an upper support surface defined by the main body, for receipt of a person thereon, making a plurality of parallel longitudinal and parallel transverse cuts in ., ~3~L377 the main body to a given depth thereof, for defining a plurality of rectangular-shaped elements, defining a plurality of sectlons in the body, with each respective section including at least two adjacent transverse rows of the rectangular-shaped elements, and having predetermined support characteristics and element cross-sections which are generally constant over the respective section but which differ among the sections. The support characteristics are selected with determined relationships therebetween, and having 25% ILD
characteristics generally in a range from about 17 pounds to about 26 pounds, where 25% ILD stands for 25%
indentation load deflection as defined by the number of pounds of pressure required to push a S0 square inch circular plate into the main body so as to compress same by 25% of its predetermined thickness, so as to form a support system for dispersing pressure in a desired manner for all parts of a person reclined thereon for optimized prevention of decubitus ulcers.
Numerous variations of and modifications to the presently disclosed embodiments and respective features thereof will occur to one of ordinary skill in the art.
All such variations, and e~uivalent substitutions therefor, are intended to be included within the scope and spirit of this invention by virtue of present reference thereto.
BRIEF DESCRIPTION OF THE DRAWINGS
A full and enabling disclosure of the present invention, including the best mode thereof, may be understood upon studying the following detailed specification, in conjunction with the appended figures, in which:
; Figure 1 illustrates an end plan view of an exemplary mattress overlay constructed in accordance with this invention;
Figure 2 is an enlarged, partial illustration of the right hand corner of Figure 1;
Figures 3 and 4 are top and side plan views, respectively, of the exemplary embodiment of Figure 1;

~''r' ~ 8a ~3~37~7 Figures 5 and 6 are enlarged side and perspective views, respectively, of a portion of the Figure 4 illustration; and Figure 7 is a nomograph in accordance with features of this invention illustrating relative effectiveness ratings in reducing the risk of decubitus ulcers for various pad embodiments of different thickness, ILD, and density combinations.
Repeat use of the same reference characters throughout the present specification and drawings is intended to indicate same or analogous elements or features of the present invention, with the exception of the numbers on the graph lines of Figure 7 which are not intended as reference characters. In most instances, dotted line representations are intended to illustrate alternative features of the embodiment presently shown, unless otherwise indicated.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the figures, a mattress pad 10 includes a main body 20 comprised of resilient material. A variety of resilient materials may be used, with foam polyurethane preferred. Pad 10 is ~enerally rectangular and provided with a predetermined thickness, typically in a range of about 2 to 4 inches.
The exact rectangular dimensions may also vary, but approximately 34 inches wide by about 74 inches long is preferred for the exemplary embodiment presently illustrated.
Pad 10 has a defined upper support surface 30 which is essentially flat. Surface 30 may longitudinally be divided into a plurality of sections (at least two, and preferably three), each having predetermined support characteristics which are generally constant over their respective sections, but which may typically differ among such sections. Figures 3 and 4 generally show ~3~3~77 three such sections, 40, 50, and 60. Initially main body 20 comprises uniform resilient material. Sections 40, S0, and 60 may be formed by variously adapting upper support surface 30 to tailor the support characteristics thereof. While the respective longitudinal lengths of sections 40, 50, and 60 may ; vary, in one preferred embodiment section 40 is about 16 inches long, section 50 is about 36 inches long, and section 60 is about 21 inches long.
l~ ~ne preferred method of adapting such sections for particular support characteristics is to make a plurality of cuts through or form separations in main body 20. Such cuts (discussed in greater detail below) may be variously placed in virtually any displacement in body 20 and in a variety of relationships to surface 30, but rectangular patterns (particularly as illustrated by Figure 3) are preferred for ease of manufacture and effectiveness in selectively altering support characteristics of main body 20. In accordance with broader aspects of this invention, whenever a main body 20 of a pre~etermined thickness and uniform density is initially provided, a desired indentation ; load defleation (ILD) may be established in sections 40, S0, and 60 by changing from one section to another the disposition and nature (eg. the spacing and number) of the plurallty of parallel longitudinal and parallel transverse cuts in such main body.
Providing two sets of parallel cuts disposed so as to intersect one another at 90 angles (as in present Figure 3) defines independent rectangular-shaped elements or projections, up-turned sides of which form support surface 30. A plurality of such projections are formed in each of the various sections, with at least two transverse rows of such projections preferred in each respective section. In one preferred ~3(~377 embodiment, projections 42 and 62, formed respectively in sections 40 and 60, may be approximately 1 by 2 inches, and have a thickness (i.e. height) of approximately 1.5 inches (whenever a three inch main body 20 is initiall~ provided). Projections 52 in such preferred embodiment may comprise approximately 2 inches by 2 inches, with all projections from the ~- different sections having substantially identical heights~
As generally lllustrated by the figures, projections in accordance with this invention are substantially rectangular-shaped in cross-section, both in the plane of support surface 30 and at various depths therebelow. In general, the cross-sectional area of the rectangular-shaped elements is greater beneath the plane of surface 30, than in such plane.
This is due to bevelled surfaces of such projections, discussed below in greater detail with reference to Figures 5 and 6.
Referring in particular to Figures 2, 5, and 6, as a further optional feature of this invention channels may be formed in main body 20 at the base of projections 42, 52, and 62. SUCh channels may assume various shapes and forms, but a generally circular cross-section is preferred for combined effectiveness of their dissipation function and ease of fabrication.
The channels intersect with the separations (or cuts) which define adjacent projections, and thereby receive heat and moisture from a patient or person resting on pad 10 for generally dissipating excesses of same.
Excess heat and moisture may also enter such channels by filtering through the body of pad 10. By either manner, dissipation removes air from around the user so as to carry off excess heat and moisture, thereby enhancing the comfort provided by the mattress pad.
` 11 .

~3~)3L;377 Further, the channels cooperate with the cuts to promote independent action of the individual projections responsive to loads placed thereon. Also, the channels may alternatively be formed at the bottom of longitudinal cuts, lateral cuts, or virtually any eombination of both (including all of both as shown by the present figures~. While permitting independent action, the substantially rectangular nature of the present projections preserves a desirable up/down compression action. Instead of being easily twisted or contorted during loading, the present projections move substantially straight up and down due to cooperation with the respective presence of adjacent rectangularly-shaped projeetions.
Figure 2 illustrates generally circular channels 64 having generally all the same diameter 66, preferably in the range of 0.5 eentimeters. Channels 64 run longitudinally along the entire length of pad 10 as do the longitudinal euts 70 with whieh they are assoeiated. In general, actual lateral separation due to cuts 70 between adjaeent projeetions will be preferably about zero. Also, it is preferred that the lateral spaeing between longitudinal cuts 70 be substanti.ally eonstant over the entire lateral width of pad 10.
The longitudinal spaeing of lateral cuts made in pad 10 is generally constant in a given section but varies from one section 40, 50, or 60 to another.
~imilarly, the eross-sectional areas of projections 42, 52, and 62 are generally constant (at given depths thereof) in their respective sections, but differ from one section to the next. Furthermore, the longitudinal separation distance between adjacent projections and the diameter of circular channels associated therewith also typically varies from one section to another while ~3t~L37~

being generally constant in a given section.
Alternatively, the longitudinal spacing of cuts in body 20 could be held constant over the entire pad 10, and the lateral spacing varied in each respective support section thereof for adjusting their respective load-bearing characteristics.
; Figure 5 shows two dotted lines 80 and 82 for illustration purposes only which demonstrate that circular channels 44 ~associated with section 40) have a generally larger constant diameter than the generally constant diameter of circular channels 54 (associated with section 50). The diameter of circular channels 54 preferably falls in a range from about 0.5 centimeters to about 0.8 centimeters, while that of channels 44 preferably fall in a higher range from about 1.0 to about 1.2 centimeters. Circular channels 68 (Figure 4), associated with lateral cuts formed in section 60, typically have diameters of approximately the same size as those of circular channels 44.
As illustrated particularly by present Fi~ures 5 and 6, lateral cuts made across the width of main body 20 preferably provide some finite longitudinal separation distance between adjacent projections, instead of generally providing virtually no separation distance as do longitudinal cuts 70. While variations may be practiced in accordance with this invention, a ~; longitudinal separation distance of approximately 0.4 . centimeters between adjacent projections 42 is ; preferably formed by cuts 46 made therebetween.
Longitudinal separations between adjacent projections 62 are preferably but not limited to distances similar to those between adjacent projections 42.
Projections 52 generally need not be appreciably separated, but a separation distance of approximately one-half that produced with cuts 46 (i.e., 0.2 37~
centimeters) is preferred. Dotted lines 56 in Figures 5 and 6 represent such 0.2 centimeter preferred separation distance, while solid lines 58 illustrate an alternative embodiment of separation representing virtually no (i.e. zero) separation distance.
All of the foregoing variations in slot spacing, projection separation distances, and channel diameters, contribute to the inter-related systematized adaptation of sections 40, 50, and 60 for dispersing pressure from a user reclining on pad 10.
While the present invention generally utilizes a relatively flat support surface 30 instead of a convoluted support surface, each of projections 42, 52, and 62 may be further provided with bevelled edges which enhance independent action thereof. For example, bevelled edges 90 (Figures 5 and 6) rnay be selectively used on any or all of the projection edges laterally formed on upper support surface 30. Likewise, bevelled edges 92 (shown in dotted line in Figure 6) may be provided in association with the longitudinal cuts defined in upper support surface 30 for providing further independent action between adjacent projections. Lateral bevelled edges gO and longitudinal bevelled edges 92 may be optionally ~Ised with any or all of projections 42, 52, and 62.
Furthermore, any o either type of bevelled edges (90 or 92) may be generally straight-lined, as illustrated, or alternatively provided generally with a radius of curvature such as illustrated by such sides 94 of Figure 5. More rounded sides 94 further enhance independent movement of associated projec~ions without adversely affecting other beneficial features and aspects of this invention.
While the foregoing describes in detail various structural aspects of the present invention which may : . .

~.3~3~7 be observed from a visual inspection thereof, further features of this invention concern support characteristics of pad 10 not immediately discernible.
Support characteristics defined by sections 40, 50, and 60 of upper support surface 30 may be varied so as to define a system of patient support for optimized pressure dispersion. Adjusting the support provided in any one of sections 40, 50, and 60 affects the patient support and dispersion of pressure in each of the other sections. Such is particularly the case whenever a subject patient is supported in a prone position (either supine or lateral) over all three support sections of upper support surface 30.
It is thus one further aspect of this invention that the support provided by each section should be selected so as to define an interface relationship among all three sections, which results in a system of support for a patient, and hence optimized pressure dispersion. The three separate sections 40, 50, and 60, with their particularly selected support characteristics, collectively function as a system to achieve such optimized dispersion of pressure for all parts of a user's body in generally all positions thereof.
2S Assuming that section 40 is disposed adjacent a patient's head, section 50 would generally support the scapula, torso, sacrum, and trochanter sections of an ad~lt user of pad 10, while section 60 would support the lower legs, feet, and heels of such patient. In 30` such configuration, a range of support characteristics may be stated wherein such optimized pressure dispersion may be provided. Alternatively, the orientation of a user on pad 10 may be changed so that section 40 is associated with the user's feet and section 60 associated with the head, while section 50 ~3~3~
of course continues to be associated generally with the user's mid-section.
An indentation load deflection (ILD) characteristic may be defined as the number of pounds of pressure needed to push a 50 square inch circular plate into a pad a given percentage deflection thereof. For example, a 25% ILD of 30 pounds would mean that 30 pounds of pressure is required to push a 50 square inch circular plate into a four inch pad a distance of 1 inch (i.e. 25% of the original, unloaded thickness).
Using a main body 20 of given thickness and density (which is assumed initially constant over such body), controlled and described variations in the ILD
characteristics of selectively defined sections may be achieved by forming cuts in such sections 40, 50, and 60. In general, for a given cut size and depth, selection in the spacing of such cuts permits selection of the ILD characteristic in a given section.
Generally, it is preferred that an ILD
characteristic in the range of 17 to 22 pounds be provided in each of sections 40 and 60 (at 25%
compression), while seation 50 is preferably provided with a 25~ ILD in the range of 21 to 26 pounds.
Sections 40 and 60 are not limited to having the same ILD characteristics even though they generally preferably share the same range of such. Such ILD
characteristics are preferably formed in a main body member 20 initially having an uncut, uniform (i.e.
constant) ILD characteristic of 30 pounds for 25~ ILD.
Of course, a variety of initial characteristics and modifying cuts may be practiced to achieve the above-stated ranges or their equivalents.
}3y providing pads with a systematized support profile of ILD's in the preferred ranges stated above, average pressure readings at various points on a ~3~:~377 person's body (such as heels, scapula, sacrum, trochanter) can be reduced by as much as 25 to almost 50~ from average pressure readings for the same points taken for convoluted foam overlays. In fact, convoluted pads in general have reduced ILD support characteristics in comparison with support pads having relatively flat support surfaces, and may have effectiveness as much as 50% less than such flat support surfaces. In general, whenever a relatively flat, sectioned support surface in accordance with the present invention is provided with a relationship of support characteristics for its sections, the engineered support for all parts of the user's body (and in virtually all positions thereof) surpasses support by convoluted foam overlays, as well as jell and water overlays, or even air-filled overlays presently available.
While various features of this invention have been described with reference to ILD characteristics alone, further definition of an optimal set of foam properties may be obtained from considering Il.D and density support characteristics together in a multi-variable approach. A range of optimized performance can be obtained whenever all three basic characteristics of the foam material utilized (i.e., thickness, density, and ILD) are collectively adjusted and inter-related.
Using a calculation of the square root of the product of ILD times density (where ILD is given in pounds and density is given in pounds per cubic foot), an optimized range for best performance numerically falls in a range of about 5.7 to about 6.9 for approximately a 4 inch thickness of foam, and in the range of about 7.5 to 9.3 for approximately a 2 inch thickness of foam.
Of course, it is possible to calculate such . .
,': ;

~3~L3~7 , . . ~
arbitrary numerical numbers with alternative expressions than those presently stated. For example, instead of calculating the square root of the product of the given ILD and density for a particular embodiment ~as done above), the product of the ILD and the square root of the density may be a preferable calculation in a given circumstance~ In general, either expression accurately predicts the combined influence of the two variables (ILD and density) upon the effectiveness of particular embodiments.
Further, in accordance with features presently disclosed, all three variables of thickness, ILD and density may be judged on an effectiveness scale hereinafter arbitrarily referred to as the Span Index.
Figure 7 illustrates a nomograph which represents the complex relationship among such three characteristics and an effectiveness rating (Span Index number).
In brief summary, the Span index predicts the performance (i.e. effectiveness) of a particular substantially flat polyurethane foam mattress af given thickness, ILD, and density characteristics for reducing the risk of decubitus ulcers for relatively immo~ile patients using such mattress. In general, the higher the Span index rating, the more effective the given mattress will likely be in reducing the incidence of such ulcers.
Referring to Figure 7, three vertical columns are established with a given, specifically determined relationship therebetween. Each column has discrete markings, but expresses continuously variable information between such discrete markings. In general, columns A and B are linear, while column C is non-linear generally as marked thereon. Column A is generally the thickness of a particular pad embodiment, expressed in inches. Column B is the square root of ~3~1L377 the product of a given ILD and density for a particular pad embodiment.
Column C is the Span Index, which is a compilation of ratings for various combinations of the ; 5 aforementioned characteristics in reducing the risk of decubitus ulcers. To determine the Span index for a given combination of characteristics, the particular appropriate numbers are located in Columns A and B and ~oined by a straight line. Where the continuation of lo such line intersects Column C determines the Span index for that given embodiment.
For example, lines 100 and 110 demonstrate the resulting Span index for the two extremes stated above with respect to the preferred range for the combined ILD and density characteristics for a pad oE
approximately 4 inch thickness. In other words, line 100 connects a 4 inch indication on Column A and a 5.7 indication on Column B for a resulting Span index of about 50 (a relatively high rating). Similarly, ].ine 110 is directed to the same thickness but a Column B
characteristi.c of about 6.9, again resulting in a Span index of about 50~ It should be apparent from Figure 7 that other 4 i.nch embodiments falling within the stated preferred range of 5.7 to 6.9 will have an even higher Span index.
Line 120, on the other hand, demonstrates the foregoing general statement that generally lower Span index numbers have relatively reduced effectiveness.
Line 120 connects a Column A two inch indication with a Column B combined ILD/density characteristic of 7.5 (one extreme of the preferred range stated above). The resulting Span index number falls below 14 (a relatively low number). As is evident from the Figure 7 nomograph, in general a two inch thick pad with a given combined ILD/density characteristic of 7.5 can be ~3~3~7 improved with respect to preventing the risk of decubitus ulcers by increasing its thickness.
In general, development and disclosure of the Span Index permits direct comparison of the effectiveness of different mattresses in reducing the risk of decubitus ulcers~ The Span Index provides an absolute number which obtains meaning when compared with other absolute rating numbers, in a manner analogous to APR
(annualized percentage rates) ratings for loan interest rates.
While the Figure 7 nomograph is particularly established for support pads having generally flat support surfaces, both the general Span Index concept and the specific Figure 7 nomograph may be adapted for different basic types of pads. For example, convoluted pads may be judged directly on the graph of Figure 7 simply by dividing the appropriate ILD and density data product by one halE before taking its square root. The resulting calculation is then used in conjunction with Column B as in previous examples. The appropriate pad thickness i.s entered on Column A, and intersection in Column C of the resulting straight line running from Columns A and B predicts the eEfectiveness of that particular generally convoluted pad.
While particular embodiments and exemplary constructions have been discussed in detail above, numerous modifications and variations to this invention will occur to one of ordinary skill in the art. All such variations (for example, including substitution of 3~ various materials, use of characteristics within and without stated ranges, and other alternatives, substitutions, and equivalents) come within the spirit and scope of the present invention. Further, language used above directed to the exemplary embodiments is ; descriptive and exemplary only, and not language of limitation, which appears only in the appended claims.
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Claims (63)

1. A mattress pad for providing systematized pressure dispersion for a person reclined thereon, comprising:
a main body of resilient material having a predetermined thickness and predetermined density;
an upper support surface, defined by said main body, for receipt of a person thereon;
a plurality of parallel longitudinal and parallel transverse cuts formed in said main body to a given depth thereof, and defining a plurality of rectangular-shaped elements;
a plurality of sections defined in said body, with each respective section including at least two adjacent transverse rows of said rectangular-shaped elements, and having predetermined support characteristics and element cross-sections which are generally constant over the respective section but which differ among said sections; wherein said support characteristics are selected with determined relationships therebetween, and having 25% ILD
characteristics generally in a range from about 17 pounds to about 26 pounds, where 25% ILD stands for 25%
indentation load deflection as defined by the number of pounds of pressure required to push a 50 square inch circular plate into said main body so as to compress same by 25% of its predetermined thickness, so as to form a support system for dispersing pressure in a desired manner for all parts of a person reclined thereon for optimized prevention of decubitus ulcers.

2. A pad as in claim 1, wherein:
said body is comprised of foamed material and is substantially rectangular, approximately 34 inches wide by 74 inches long, and with a thickness in a range from about 2 inches to about 4 inches.

3. A pad as in claim 1, wherein said sections are longitudinally spaced on said support surface, and generally correspond to the upper, middle, and lower portions of a person longitudinally reclined on said support surface so as to define upper, middle, and lower sections, respectively.

4. A pad as in claim 1, wherein the number and spacing of said cuts is constant for a given section but varies among said sections so as to selectively establish the cross-sectional area of rectangular-shaped elements defined therein.

5. A pad as in claim 1, further comprising at least one channel defined in said body adjacent the bottom of said cuts, said channel providing means for dissipating heat and moisture from a person received on said pad.

6. A pad as in claim 3, wherein the cross-sectional area of elements defined in said middle section is approximately twice that of elements defined in other sections of said body of resilient material.

7. A pad as in claim 6, wherein the cross-sectional area of projections defined in said middle section is approximately 4 square inches.

8. A pad as in claim 5, wherein:
said elements have no appreciable lateral separation distances with respect to one another; and said pad includes a plurality of channels such as said at least one channel thereof, said channels being associated with said longitudinal cuts, having generally circular cross-sections, and having respective diameters approximately in a range from about 0.5 centimeters to about 0.8 centimeters.

9. A pad as in claim 5, wherein:
said pad has a plurality of channels such as said at least one channel thereof;
said transverse cuts defined in said upper and lower sections provide longitudinal separation distances between adjacent elements of approximately 0.4 centimeters, and have associated channels which are generally circular in cross-section with diameters approximately in a range from about 1.0 centimeters to about 1.2 centimeters; and said transverse cuts defined in said middle section provide longitudinal separation distances between adjacent elements which are approximately one half separation distances provided in said other sections, and which have associated channels with diameters of approximately 0.7 centimeters.

10. A pad as in claim 3, wherein:
said upper section extends longitudinally about 16 inches, and is adapted for support of the head area of a person;
said middle section extends longitudinally about 36 inches, and is adapted for support of the scapula, torso, sacrum, and trochanter areas of a person;
said lower section extends longitudinally about 21 inches, and is adapted for support of the lower leg, foot, and heel areas of a person; and wherein said pad provides coordinated sectionalized support which is relatively independent of a user's body build.

11. A pad as in claim 1, wherein said rectangular-shaped elements are each substantially rectangular in the plane of said upper support surface, and each have at least two bevelled sides intersecting with said support surface.

12. A pad as in claim 11, wherein:
said bevelled sides of said elements have a given radius of curvature; and said elements each have a rectangular cross-section beneath said upper support surface which is generally larger than the respective rectangular cross-sections thereof in said upper support surface plane.

13. A multi-section mattress overlay for supporting in a systematized manner all parts of a patient received thereon for optimized prevention of decubitus ulcers, said mattress overlay comprising:
a generally rectangular body of foam material having a predetermined density and thickness, and defining an essentially flat support surface for receiving a patient in a substantially longitudinal, prone position thereon;
at least three longitudinally-spaced sections formed in said support surface for consecutively head, mid-section, and feet areas generally of the patient, each of said sections having at least one uniform, predetermined load-bearing characteristic which is selected with respect to that of each other section for establishing the systematized support provided by said overlay; and grid-shaped cuts formed in said support surface of said body so as to define a plurality of substantially rectangular projections therein, the cross-sectional area of said projections being constant over a given section but varying with said three sections so as to determine said load-bearing characteristics thereof;
wherein said head and feet areas each have 25%
ILD characteristics in a range from about 17 pounds to about 22 pounds, and said mid-section area has a 25% ILD
characteristic in a range from about 21 pounds to about 26 pounds; where 25% ILD stands for 25% indentation load deflection, which is defined by the number of pounds of pressure required to push a 50 square inch circular plate into said body of foam material so as to compress same by 25% of its predetermined thickness.

14. An overlay as in claim 13, further comprising:
generally circular cross-section channels formed at the bottom of said cuts for dissipating heat and moisture from patients received on said overlay; and wherein said channels formed longitudinally in said overlay all have substantially the same diameter, while the diameters of channels formed laterally in said overlay are constant in a given section but vary among said three sections.

15. An overlay as in claim 14, wherein:
said foam material comprises foamed polyurethane;
said cuts and said channels formed therewith extend approximately half way through the thickness of said body; and said projections have bevelled upper edges, and are separated along said cuts by different distances which are generally constant in a given section but which vary among said three sections;
wherein such separations in conjunction with said bevelled edges, which each have respective radius of curvature, permit relatively independent compression of adjacent projections in response to appropriate loading, without excessive frictional interaction between adjacent of said projections.

16. A pad as in claim 1, wherein:
said resilient material comprises foamed polyurethane; and further wherein said predetermined thickness of said main body is approximately 4 inches, and the density of said main body is selected such that the square root of the product of said ILD and said density falls within a range of about 5.7 to 6.9, whenever ILD is expressed in pounds and density is expressed in pounds per cubic foot.

17. A pad as in claim 1, wherein:
said resilient material comprises foamed polyurethane; and further wherein said predetermined thickness of said main body is approximately 2 inches, and the density of said main body is selected such that the square root of the product of said ILD and said density falls within a range of about 7.5 to 9.3, whenever ILD is expressed in pounds and density is expressed in pounds per cubic foot.

18. An overlay as in claim 13, wherein:
said plurality of projections defined in said support surface provides independently-reactive support and collectively forms a relatively flat surface defined as said support surface for supporting a person; and said overlay further includes circular cross-section channels formed between adjacent bases of said projections, said channels providing for air-carried dissipation of heat and moisture from a person supported on said overlay; and wherein said projections have cross-sectional areas and spacing therebetween which is generally constant for a given section but which varies with said three sections.

19. An overlay as in claim 13, wherein said rectangular body is approximately four inches thick and has a relatively high Span Index effectiveness rating, with the density of said body being selected such that the square root of the product of said ILD and said density falls within a range of about 5.7 to about 6.9, whenever ILD is expressed in pounds and density is expressed in pounds per cubic foot.

20. An overlay as in claim 13, wherein said rectangular body is approximately two inches thick and has a relatively low Span Index effectiveness rating, with the density of said body being selected such that the square root of the product of said ILD and said density falls within a range of about 7.5 to about 9.3, whenever ILD is expressed in pounds and density is expressed in pounds per cubic foot.

21. A process for manufacturing a pad comprising a mattress overlay with systematized features for supporting a person, comprising:
providing a generally rectangular member of resilient material having a substantially predetermined uniform thickness and predetermined uniform density; and with a support surface formed on one side of said member, said surface defining three longitudinal areas therein generally for operative association with the head, mid-section and feet, respectively, of a person;
forming said head and feet areas so that each have 25% ILD characteristics in a range from about 17 pounds to about 22 pounds, and forming said mid-section area so that it has a 25% ILD characteristic in a range from about 21 pounds to about 26 pounds;
wherein 25% ILD stands for 25 percent indentation load deflection, which is defined by the number of pounds of pressure required to push a 50 square inch circular plate into said polyurethane member so as to compress same by 25% of its predetermined thickness;
and wherein said process further includes selecting said predetermined thickness to fall generally within a range of from about two inches to about four inches, and selecting said predetermined uniform density such that the square root of the product of the ILD and said predetermined uniform density falls generally within a range of from about 5.7 to about 9.3, whenever ILD is expressed in pounds, and density is expressed in pounds per cubic foot, whereby a desired effectiveness rating for said pad is obtained for optimizing the prevention of decubitus ulcers.

22. A pad as in claim 3, wherein said upper and lower sections have 25% ILD characteristics generally in a range from about 17 pounds to about 22 pounds, and said middle section has a 25% ILD characteristic generally in a range from about 21 pounds to about 26 pounds.

23. A pad as in claim 1, wherein said predetermined thickness is selected to fall generally in a range of from about 2 inches to about 4 inches, and said predetermined density is selected such that the square root of the product of the ILD and said predetermined density falls generally within a range of from about 5.7 to about 9.3, whenever ILD is expressed in pounds and density is expressed in pounds per cubic foot.

24. A method of making a mattress pad for providing systematized pressure dispersion for a person reclined thereon, comprising:
providing a main body of resilient material having a predetermined thickness and predetermined density; and an upper support surface, defined by said main body, for receipt of a person thereon;
making a plurality of parallel longitudinal and parallel transverse cuts in said main body to a given depth thereof, for defining a plurality of rectangular-shaped elements;

defining a plurality of sections in said body, with each respective section including at least two adjacent transverse rows of said rectangular-shaped elements, and having predeter-mined support characteristics and element cross-sections which are generally constant over the respective section but which differ among said sections; wherein said support characteristics are selected with determined relationships therebetween, and having 25% ILD characteristics generally in a range from about 17 pounds to about 26 pounds, where 25% ILD stands for 25% indentation load deflection as defined by the number of pounds of pressure required to push 50 square inch circular plate into said main body so as to compress same by 25% of its predetermined thickness, so as to form a support system for dispersing pressure in a desired manner for all parts of a person reclined thereon for optimized prevention of decubitus ulcers.

25. A method as in claim 24, including forming said body of foamed material and substantially rectangular, approximately 34 inches wide by 74 inches long, and with a thickness in a range from about 2 inches to about 4 inches.

26. A method as in claim 24, including defining said sections longitudinally spaced on said support surface, for generally corresponding to the upper, middle, and lower portions of a person longitudinally reclined on said support surface so as to define upper, middle, and lower sections, respectively.

27. A method as in claim 26, wherein the cross-sectional area of elements defined in said middle section is formed approximately twice that of elements defined in other sections of said body of resilient material.

28. A method as in claim 27, wherein the cross-sectional area of projections defined in said middle section is approximately 4 square inches.

29. A method as in claim 26, wherein:
said upper section is defined to extend longitudinally about 16 inches, and is adapted for support of the head area of a person;
said middle section is defined to extend longitudinally about 36 inches, and is adapted for support of the scapula, torso, sacrum, and trochanter areas of a person;
said lower section is defined to extend longitudinally about 21 inches, and is adapted for support of the lower leg, foot, and heel areas of a person; and wherein said pad provides coordinated sectionalized support which is relatively independent of a user's body build.

30. A method as in claim 26, wherein said upper and lower sections are defined so as to each have 25% ILD characteristics generally in a range from about 17 pounds to about 22 pounds, and said middle section is defined so as to have a 25% ILD charac-teristic generally in a range from about 21 pounds to about 26 pounds.

31. A method as in claim 24, wherein the number and spacing of said cuts is constant for a given section but varies among said sections so as to selectively establish the cross-sectional area of rectangular-shaped elements defined therein.

32. A method as in claim 24, further including forming at least one channel in said body adjacent the bottom of said cuts, said channel providing means for dissipating heat and moisture from a person received on said pad.

33. A method as in claim 32, wherein:

said elements are defined with no appreciable lateral separation distances with respect to one another; and said pad includes a plurality of channels formed therein such as said at least one channel thereof, said channels being associated with said longitudinal cuts, having generally circular cross-sections, and having respective diameters approximately in a range from about 0.5 centimeters to about 0.8 centimeters.

34. A method as in claim 32, wherein:
said pad has a plurality of channels formed therein such as said at least one channel thereof;
said transverse cuts are defined in said upper and lower sections so as to provide longitudinal separation distances between adjacent elements of approximately 0.4 centimeters, and have associated channels which are generally circular in cross section with diameters approximately in a range from about 1.0 centimeters to about 1.2 centimeters; and said transverse cuts are defined in said middle section so as to provide longitudinal separation distances between adjacent elements which are approximately one half separation distances provided in said other sections, and which have associated channels with diameters of approximately 0.7 centimeters.

35. A method as in claim 24, wherein said rectangular-shaped elements are each formed substantially rectangular in the plane of said upper support surface, and each have at least two bevelled sides intersecting with said support surface.

36. A method as in claim 35, wherein:
said bevelled sides of said elements have a given radius of curvature; and said elements each have a rectangular cross-section beneath said upper support surface which is generally larger than the respective rectangular cross-sections thereof in said upper support surface plane.

37. A method as in claim 24, wherein:
said resilient material comprises foamed polyurethane; and further wherein said predetermined thickness of said main body is approximately 4 inches, and the density of said main body is selected such that the square root of the product of said ILD and said density falls within a range of about 5.7 to 6.9, whenever ILD is expressed in pounds and density is expressed in pounds per cubic foot.

38. A method as in claim 24, wherein:
said resilient material comprises foamed polyurethane; and further wherein said predetermined thickness of said main body is approximately 2 inches, and the density of said main body is selected such that the square root of the product of said ILD and said density falls within a range of about 7.5 to 9.3, whenever ILD is expressed in pounds and density is expressed in pounds per cubic foot.

39. A method as in claim 24, wherein said predetermined thickness is selected to fall generally in a range of from about two inches to four inches, and said predetermined density is selected such that the square root of the product of the ILD and said predetermined density falls generally within a range of from about 5.7 to about 9.3, whenever ILD is expressed in pounds, and density is expressed in pounds per cubic foot.

40. A method of making a multi-section mattress overlay for supporting in a systematized manner all parts of a patient received thereon for optimized prevention of decubitus ulcers, said method including:
providing a generally rectangular body of foam material having a predetermined density and thickness, and defining an essentially flat support surface for receiving a patient in a substantially longitudinal, prone position thereon;
forming at least three longitudinally-spaced sections in said support surface for consecutively head, mid-section, and feet areas generally of the patient, each of said sections having at least one uniform, predetermined load-bearing characteristic which is selected with respect to that of each other section for establishing the systematized support provided by said overlay;
and making grid-shaped cuts in said support surface of said body so as to define a plurality of substantially rectangular projec-tions therein, the cross-sectional area of said projections being constant over a given section but varying with said three sec-tions so as to determine said load-bearing characteristics thereof;
wherein said head and feet areas are formed so that each have 25% ILD characteristics in a range from about 17 pounds to about 22 pounds, and said mid-section area is formed so as to have a 25% ILD characteristic in a range from about 21 pounds to about 26 pounds; where 25% ILD stands for 25% indentation load deflection, which is defined by the number of pounds of pressure required to push a 50 square inch circular plate into said body of foam material so as to compress same by 25% of its predeter-mined thickness.

41. A method as in claim 40, further comprising:
forming generally circular cross-section channels at the bottom of said cuts for dissipating heat and moisture from patients received on said overlay; and wherein said channels that are formed longitudingally in said overlay all have substantially the same diameter, while the diameters of channels that are formed laterally in said overlay are constant in a given section but vary among said three sections.

42. A method as in claim 41, wherein:
said foam material comprises foamed polyurethane;
said cuts and said channels are formed therewith so as to extend approximately half way through the thickness of said body;
and said projections are provided with bevelled upper edges, and are separated along said cuts by different distances which are generally constant in a given section but which vary among said three sections;
wherein such separations in conjunction with said bevelled edges, which each have respective radius of curvature, permit relatively independent compression of adjacent projections in response to appropriate loading, without excessive frictional interaction between adjacent of said projections.

43. A method as in claim 40, wherein:
said plurality of projections is defined in said support surface so as to provide independently-reactive support and to collectively form a relatively flat surface defined as said support surface for supporting a person; and said method further includes forming circular cross-section channels between adjacent bases of said projections, said channels providing for air-carried dissipation of heat and moisture from a person supported on said overlay: and wherein said projections have cross-sectional areas and spacing therebetween which is generally constant for a given section but which varies with said three sections.

44. A method as in claim 40, wherein said rectangular body is approximately four inches thick and has a relatively high Span Index effectiveness rating, with the density of said body being selected such that the square root of the product of said ILD and said density falls within a range of about 5.7 to about 6.9, whenever ILD is expressed in pounds and density is expressed in pounds per cubic foot.

45. A method as in claim 40, wherein said rectangular body is approximately two inches thick and has a relatively low Span Index effectiveness rating, with the density of said body being selected such that the square root of the product of said ILD and said density falls within a range of about 7.5 to about 9.3, whenever ILD is expressed in pounds and density is expressed in pounds per cubic foot.

46. A mattress pad for providing systematized pressure dispersion for a person reclined thereon, comprising:
a main body of resilient foamed material;
an upper support surface, defined by said main body, for receipt of a person thereon;
a plurality of parallel longitudinal and parallel transverse cuts formed in said main body, and defining a plurality of rectangular-shaped elements;
a plurality of sections defined in said body, with each respective section including at least two adjacent transverse rows of said rectangular-shaped elements, and having predetermined support characteristics and element cross-sections which are generally constant over the respective section but which differ among said sections: wherein said support characteristics are selected with determined relationships therebetween as set forth in Fig. 7 so as to form a support for dispersing pressure in a desired manner with a relatively high Span Index effectiveness rating for all parts of a person reclined thereon; and wherein said support characteristics include thickness of said main body;
indentation load deflection of said main body, defined as the number of pounds of pressure needed to push a 50 square inch circular plate into said main body an amount adequate to deflect such a body a given percentage distance of its non-loaded thickness; and density of said resilient foamed material comprising said main body.

47. A pad as in claim 46, wherein:
said body is comprised of foamed material and is substantially rectangular, approximately 34 inches wide by 74 inches long, and with a width in a range from about 2 inches to about 4 inches.

48. A pad as in claim 46, wherein said sections are longitudinally spaced on said support surface, and generally correspond to the upper, middle, and lower portions of a person longitudinally reclined on said support surface so as to define upper, middle, and lower sections, respectively.

49. A pad as in claim 48, wherein the cross-sectional area of elements defined in said middle section is approximately twice that of elements defined in other sections of said body of resilient material.

50. A pad as in claim 49, wherein the cross-sectional area of projections defined in said middle section is approximately 4 square inches.

51. A pad as in claim 48, wherein:
said upper section extends longitudinally about 16 inches, and is adapted for support of the head area of a person;
said middle section extends longitudinally about 36 inches, and is adapted for support of the scapula, torso, sacrum, and trochanter areas of a person;
said lower section extends longitudinally about 21 inches, and is adapted for support of the lower leg, foot, and heel areas of a person; and wherein said pad provides coordinated sectionalized support which is relatively independent of a user's body build.

52. A pad as in claim 48, wherein the cross-sectional spacing of said cuts is constant for a given section but varies among said sections so as to selectively establish the cross-sectional area of rectangular-shaped elements defined therein.

53. A pad as in claim 46, further comprising at least one channel defined in said body adjacent the bottom of said cuts, said channel providing means for dissipating heat and moisture from a person received on said pad.

54. A pad as in claim 52, wherein:
said elements have no appreciable lateral separation distances with respect to one another; and said pad includes a plurality of channels such as said at least one channel thereof, said channels being associated with said longitudinal cuts, generally circular cross-section, and having a diameter approximately in a range from about 0.5 centimeters to about 0.8 centimeters.

55. A pad as in claim 53, wherein:
said pad has a plurality of channels such as said at least one channel thereof;
said transverse cuts defined in said upper and lower sections provide longitudinal separation distances between adjacent elements of approximately 0.4 centimeters, and have associated channels which are of generally circular cross-section with diameters approximately in a range from about 1.0 centimeters to about 1.2 centimeters; and said transverse cuts defined in said middle section provide longitudinal separation distances between adjacent elements which are approximately one half separation distances provided in said other sections, and which have associated channels with diameters of approximately 0.7 centimeters.

56. A pad as in claim 46, wherein said rectangular-shaped elements are each substantially rectangular in the plane of said upper support surface, and each have at least two bevelled sides intersecting with said support surface.

57. A pad as in claim 56, wherein:
said bevelled sides of said elements have a given radius of curvature; and said elements each have a rectangular cross-section beneath said upper support surface which is generally larger than the respective rectangular cross-sections thereof in said upper support surface plane.

58. A pad with systematized features for supporting a person, comprising:
a rectangular member comprising an integral body of resilient foamed material having a predetermined thickness in a range of from about two inches to about four inches and having a predetermined uniform density;
and a support surface formed on one side of said member, said surface defining three longitudinal areas therein generally for operative association with the head, mid-section, and feet respectively, of a person;
said head and feet areas each having 25% ILD
characteristics in a range from about 17 pounds to about 22 pounds, and said mid-section area having a 25% ILD
characteristic in a range from about 21 pounds to about 26 pounds;
wherein 25% ILD stands for 25% indentation load deflection, which is defined by the number of pounds of pressure required to push a 50 square inch circular plate into said rectangular member so as to compress same by 25% of its predetermined thickness; and wherein said predetermined thickness is selected in conjunction with the square root of the product of the ILD and the predetermined material density so as to obtain a relatively high Span Index effectiveness rating for said pad, as set forth by the Fig. 7 nomographic representation of the complex relationship among thickness, ILD, and density characteristics.

59. A pad as in claim 58, wherein:
said rectangular member comprises foamed polyurethane; and further wherein said predetermined thickness of said member is approximately 4 inches, and the density of said member is selected such that the square root of the product of said ILD and said density falls within a range of about 5.7 to 6.9, whenever ILD is expressed in pounds and density is expressed in pounds per cubic foot.

60. A pad as in claim 58, wherein:
said rectangular member comprises foamed polyurethane; and further wherein said predetermined thickness of said member is approximately 2 inches, and the density of said member is selected such that the square root of the product of said ILD and said density falls within a range of about 7.5 to 9.3, whenever ILD is expressed in pounds and density is expressed in pounds per cubic foot.

61. A pad as in claim 58, further comprising:
a plurality of projections defined in said support surface for providing independently-reactive support and for collectively forming said support surface as relatively flat for supporting a person; and circular cross-section channels formed between adjacent bases of said projections, said channels providing for air-carried dissipation of heat and moisture from a person supported on said pad; and wherein said projections have cross-sectional areas and spacing therebetween which is generally constant for a given section but which varies with said three sections.

62. A pad as in claim 58, wherein said member is approximately four inches thick and has a relatively high Span Index effectiveness rating, with the density of said member being selected such that the square root of the product of said ILD and said density falls within a range of about 5.7 to about 6.9, whenever ILD is expressed in pounds and density is expressed in pounds per cubic foot.

63. A pad as in claim 58, wherein said member is approximately two inches thick and has a relatively low Span Index effectiveness rating, with the density of said member being selected such that the square root of the product of said ILD and said density falls within a range of about 7.5 to about 9.3, whenever ILD is expressed in pounds and density is expressed in pounds per cubic foot.