Patent Publication Number: US-6212718-B1

Title: Air-over-foam mattress

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     This application claims the benefit of U.S. provisional application Serial No. 60/080,087 filed Mar. 31, 1998, now expired and U.S. provisional application Serial No. 60/105,374 filed Oct. 23, 1998, now expired. 
    
    
     The present invention relates to a mattress and particularly, to a mattress for use on a hospital bed. More particularly, the present invention relates to a hospital mattress having air bladders for supporting a bedridden patient requiring long term care. 
     Mattresses that include air bladders to support bedridden patients in hospitals are known in the art. Such mattresses typically include apparatus for inflating the air bladders to predetermined pressure levels and for maintaining and adjusting the pressure in the air bladders after inflation. See, for example, U.S. Pat. Nos. 5,594,963 to Berkowitz; 5,542,136 to Tappel; 5,325,551 to Tappel et al.; and 4,638,519 to Hess. See also, U.S. Pat. Nos. 5,586,346 to Stacy et al.; 5,182,826 to Thomas et al.; and 5,051,673 to Goodwin, the assignee of each of these patents being the assignee of the present invention. 
     It is desirable for the interface pressure between a patient and the mattress supporting the patient to be evenly distributed over the mattress so as to minimize the formation of pressure ulcers. Some hospital mattresses include a plurality of side-by-side elements, such as foam blocks or air bladders, that vary in firmness depending upon the portion of the patient to be supported by the respective element. It is desirable for the friction between the side-by-side elements to be minimized so that each element compresses and expands individually without interference from adjacent elements. 
     According to the present invention, a mattress structure includes a plurality of side-by-side lower support elements and a layer of material underlying the lower support elements. The mattress structure further includes a plurality of side-by-side upper support elements overlying and supported by the lower support elements. In addition, the mattress structure includes a plurality of tethers. Each tether connects a respective one of the upper support elements to the layer of material and each tether extends between a respective pair of the lower support elements. 
     In illustrated embodiments, the upper support elements are air bladders and the lower support elements are foam blocks. The mattress structure further includes a plurality of sleeves made of a shear material with a low coefficient of friction. Each lower support element is received in an interior region of the respective sleeve. Each tether is also made of a shear material with a low coefficient of friction. In addition, each tether extends between a respective pair of the sleeves. Each sleeve is anchored to the layer of material so that longitudinal shifting of the lower support elements relative to the layer of underlying material is prevented. Receipt of the tethers between respective sleeves and the associated lower support elements prevents longitudinal shifting of the upper support elements. 
     Also according to the present invention, a modular mattress system includes a mattress having a plurality of inflatable air bladder sets. The modular mattress system further includes an air bladder inflation system having a compressor and a plurality of pressure sensors. Each pressure sensor is responsive to the pressure in an associated air bladder set. The air bladder inflation system further includes a bladder set selector that receives a pressure signal from each of the pressure sensors. The bladder set selector is responsive to only one pressure signal at a time. 
     The bladder set selector fluidly couples a selected one of the air bladder sets to the compressor and operates the compressor to increase the pressure in the selected air bladder set if the respective pressure sensor indicates that the pressure in the selected air bladder set is below a predetermined level. The bladder set selector couples the selected air bladder set to the atmosphere to allow fluid to bleed from the selected air bladder set to the atmosphere if the respective pressure sensor indicates that the pressure in the selected air bladder set is above a predetermined level. Each of the unselected air bladder sets remain fluidly decoupled from the compressor and fluidly decoupled from the atmosphere. The bladder set selector selects each of the air bladder sets in a cyclical manner. 
     In illustrated embodiments, the bladder set selector includes a manifold having a main passage coupled to the compressor and coupled to the atmosphere at a vent port. The manifold includes a plurality of bladder passages coupled to the main passage at respective bladder ports and coupled to respective air bladder sets. A vent valve is movable to open and close the vent port. A plurality of bladder valves are movable to open and close respective bladder ports. A plurality of actuators are coupled to respective bladder valves and the vent valve. The bladder set selector includes a microprocessor that receives signals from the pressure sensors and sends signals to the actuators. In illustrated embodiments, the actuators are stepper motors and the microprocessor sends signals to each stepper motor to open the associated valve one step at a time until the desired pressure is achieved in the respective air bladder set. When the desired pressure is achieved, the microprocessor sends signals to quickly close the opened valve. 
     Further according to the present invention, the mattress structure includes a cover enclosing the plurality support elements. The cover includes a bottom surface and a strap having two spaced apart free ends and a middle portion between the free ends connected to the lower outer surface. The support elements are configured to allow the mattress structure to be folded so that the free ends of the strap may be coupled together. 
     In the illustrated embodiment, the apparatus includes a buckle having a first buckle half and a second buckle half. The first and second buckle halves are attached to the strap. The first buckle half is coupled to the strap for movement relative to the second buckle half to adjust an effective length of the strap. Also in the illustrated embodiment, an anti-skid pad is coupled to the bottom surface of the mattress. 
     Still further according to the present invention, a connector apparatus is configured to couple a mattress including a plurality of inflatable air bladders to an air bladder inflation system including an air supply. The connector apparatus includes a first set of connectors coupled to the air supply. The first set of connectors is coupled to a first body portion. The apparatus also includes a plurality of air supply tubes, at least one air supply tube being coupled to each of the plurality of air bladders, and a second set of connectors coupled to the air supply tubes. The second set of connectors are coupled to a second body portion. The first and second sets of connectors are in alignment with each other to permit substantially simultaneous coupling of the first and second sets of connectors. 
     In the illustrated embodiment, the air bladder inflation system also includes a plurality of pressure sensors. Each pressure sensor is responsive to the pressure in an associated air bladder. The connector apparatus includes a third set of connectors coupled to the pressure sensors. The third set of connectors is coupled to the first body portion. The apparatus also includes a plurality of pressure tubes, at least one pressure tube being coupled to each of the plurality of air bladders, and a fourth set of connectors coupled to the pressure tubes. The fourth set of connectors is coupled to the second body portion. The third and fourth sets of connectors are also in alignment with each other to permit substantially simultaneous coupling of both the first set of connectors with the second set of connectors and the third set of connectors with the forth set of connectors. 
     Also in the illustrated embodiment, the air bladder inflation system further includes a manifold having a main passage coupled to the air supply and coupled to the atmosphere at a vent port. The manifold includes a plurality of bladder passages coupled to the main passage at respective bladder ports and coupled to the first set of connectors. A vent valve is movable to open and close the vent port, and a plurality of bladder valves are movable to open and close respective bladder ports. A plurality of actuators are coupled to respective bladder valves and the vent valve. 
     Also in the illustrated embodiment, a latch configured to secure the first and second bodies together. The latch is illustratively coupled to one of the sets of connectors. The illustrated air bladder inflation system includes a housing surrounding the air supply and the plurality of pressure sensors. The first body portion is illustratively coupled to the housing. Also illustratively, the first and second sets of connectors are unequally spaced on the first body portion and the third and fourth sets of connectors are unequally spaced on the second body portion so that the connectors can only being coupled together in a single orientation. 
     Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The detailed description particularly refers to the accompanying figures in which: 
     FIG. 1 is a perspective view of a mattress according to the present invention showing top and bottom mattress covers zipped together to enclose other mattress components; 
     FIG. 2 is an exploded perspective view of the mattress of FIG. 1, with portions broken away showing the top cover unzipped and separated away from the bottom cover to expose the other mattress components which include an inner shear cover beneath the top cover, an air-over-foam core structure beneath the inner shear cover, an optional foam base beneath the air-over-foam mattress structure, the optional foam base including an air tube pass-through aperture, and a protective sleeve extending downwardly from the bottom cover to protect air tubes that pass therethrough; 
     FIG. 3 is a bottom plan view of the air-over-foam core structure of the mattress of FIG. 1, with portions broken away, showing a plurality of air tubes routed to various zones of the mattress; 
     FIG. 4 is a side elevation view of the air-over-foam core structure of FIG. 2 showing a plurality of transversely extending foam blocks with square cross section arranged in side-by-side relation between head and foot ends of the mattress and a plurality of cylindrical air bladders supported by the plurality of foam blocks; 
     FIG. 5 is a perspective view of a portion of the air-over-foam core structure of FIG. 4, with portions broken away, showing a bottom layer of material, a plurality of square-shaped sleeves anchored to the layer of material, a portion of one of the plurality of foam blocks arranged for insertion into one of the square-shaped sleeves, and the plurality of air bladders including a longitudinally extending header bladder and a plurality of transversely extending bladders fluidly coupled to the header bladder, each transversely extending air bladder being tethered to the bottom layer of material; 
     FIG. 6 is a diagrammatic view of an air pressure system that is coupleable to the mattress of FIG.  1  and that is operable to control and adjust pressure in the plurality of air bladders, the air pressure system including user inputs outside and above a dotted line which represents a housing, a microprocessor that receives signals from the user inputs, a manifold, four valves situated in respective manifold passages, a stepper motor coupled to each valve and coupled to the microprocessor, a compressor coupled to the manifold, the manifold being fluidly coupled to three mattress zones shown beneath the housing, and three pressure sensors coupled to respective mattress zones and coupled to the microprocessor through respective analog-to-digital converters; 
     FIG. 7 is a perspective view of the air pressure system of FIG. 6 mounted to an end board of a hospital bed showing three heel-relief knobs on a front panel of the housing, a main power switch on a side panel of the housing, and a weight range selector on a top panel of the housing; 
     FIG. 8 is a diagrammatic view of the manifold of FIG. 6 showing passages formed in the manifold and showing each valve including a tapered tip that seats against a respective nozzle port of the manifold; 
     FIG. 9 a  is a first portion of a flow diagram showing some of the steps performed by the air pressure system of FIG. 6; 
     FIG. 9 b  is a second portion of a flow diagram showing some of the steps performed by the air pressure system of FIG. 6; 
     FIG. 10 is a diagrammatic view of a portion of an alternative embodiment air pressure system that is coupleable to the mattress of FIG.  1  and that is operable to control and adjust pressure in the plurality of air bladders, the alternative embodiment air pressure system including a manifold, four valves situated in respective manifold passages, a stepper motor coupled to each valve, a compressor coupled to the manifold, the manifold being fluidly coupled to three mattress zones shown beneath the manifold, and a single pressure sensor coupled to the manifold; 
     FIG. 11 a  is a first portion of a flow diagram showing some of the steps performed by the air pressure system containing the components of FIG. 10; 
     FIG. 11 b  is a second portion of a flow diagram showing some of the steps performed by the air pressure system containing the components of FIG. 10; 
     FIG. 12 is a bottom plan view of a first alternative embodiment core structure according to the present invention, with portions broken away, showing air tubes routed to a plurality of air bladders that are supported on large foam blocks; 
     FIG. 13 is side elevation view of the first alternative embodiment core structure of FIG. 12, with portions broken away, showing the plurality of air bladders subdivided into four zones and the large foam blocks subdivided into three zones; 
     FIG. 14 is a bottom plan view of a second alternative embodiment core structure according to the present invention, with portions broken away, showing air tubes routed in an alternative pattern to a plurality of air bladders to provide the second alternative embodiment core structure with a heel relief section; 
     FIG. 15 is a side elevation view of a third alternative embodiment core structure according to the present invention, with portions broken away, showing a plurality of foam blocks at the head, seat, and thigh sections, a plurality of air bladders supported over the foam blocks at the head, seat, and thigh sections, and a double layer of air bladders at the foot section to provide the third alternative embodiment core structure with a heel relief section; 
     FIG. 16 is a flow diagram showing some of the steps performed by an air pressure system including a max inflate button in processing a main control algorithm; 
     FIG. 17 a  is a first portion of a flow diagram showing some of the steps performed by an inflation subroutine associated with the main control algorithm of FIG. 16; 
     FIG. 17 b  is a second portion of a flow diagram showing some additional steps performed by an inflation subroutine associated with the main control algorithm of FIG. 16; 
     FIG. 18 a  is a first portion of a flow diagram showing some of the steps performed by a deflation subroutine associated with the main control algorithm of FIG. 16; 
     FIG. 18 b  is a second portion of a flow diagram showing some additional steps performed by a deflation subroutine associated with the main control algorithm of FIG. 16; 
     FIG. 19 is a bottom plan view of the mattress of FIG. 1 showing two transport straps each having spaced apart ends, a central portion attached to the bottom cover of the mattress, and cooperating buckle halves, and an anti-skid pad attached to the bottom cover of the mattress and also showing the protective sleeve extending from the bottom mattress cover; 
     FIG. 20 is a perspective view of the mattress core of FIG. 1 showing the mattress being folded at two points in preparation for transport or storage; 
     FIG. 21 is a perspective view of the mattress of FIG. 20 showing the mattress completely folded for transport or storage and the cooperating buckle halves on each transport strap coupled together; 
     FIG. 22 is a partial front plan view of a controller quick disconnect showing a controller unit having six male connector portions and a controller tube connector having six female connector portions in fluid communication with six tubes with the male and female connector portions each secured within a male connector housing and a female connector housing respectively which properly position the twelve connector portions for simultaneous coupling and decoupling to form six connectors; 
     FIG. 23 is a partial front plan view of the controller quick disconnect of FIG. 22 with the female connector housing rotated 180 degrees so that the female connector portions no longer align with the male connector portions prohibiting simultaneous coupling; 
     FIG. 24 is a top plan view of the female connector housing of FIG. 22 showing the six female connector portions; 
     FIG. 25 is an exploded view of the male housing connector of FIG. 22 showing the six male connector portions and an electrical wiring pass through; and 
     FIG. 26 is a bottom plan view with portions broken away of an alternative embodiment air-over-foam core structure showing the six air passage tubes formed into a tube ribbon over a substantial portion of their lengths with the individual tubes being separated near the point of connection to a connector housing and at the opposite end for communication with the various air bladders. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     A mattress structure  30  in accordance with the present invention includes a mattress cover  32  having a top cover  34  and a bottom cover  36  connected to top cover  34  by a zipper  38  as shown in FIG.  1 . Top cover  34  includes an upwardly facing sleeping surface  40  configured to support a patient. Top cover  34  cooperates with bottom cover  36  to provide mattress cover  32  with an interior region  42  as shown in FIG.  2 . Mattress structure  30  includes a core structure  44  and an inner shear cover  46  each of which are received in interior region  42  of cover  32 . In illustrated embodiments, mattress structure  30  also includes a foam base  48  received in interior region  42  along with core structure  44  and inner shear cover  46 . In other embodiments, mattress structure  30  does not include foam base  48 . 
     Mattress structure  30  includes longitudinally extending, transversely spaced-apart sides  31  and transversely extending, longitudinally spaced-apart ends  33  as shown in FIG.  1 . Sides  31  of mattress structure  30  are longer than ends  33  of mattress structure  30 . Thus, mattress structure  30  is rectangular in shape. However, the teachings of the present invention may be used with mattress structures having other shapes. 
     Core structure  44  includes a plurality of lower support elements  50  and a plurality of upper support elements  52  that are supported by lower support elements  50  as shown in FIGS. 2 and 4. In illustrated embodiments, lower support elements  50  are transversely extending foam blocks and upper support elements are somewhat cylindrically-shaped air bladders. Hereinafter, the lower support elements  50  are referred to as foam blocks  50  and the upper support elements  52  are referred to as air bladders  52 . Core structure  44  further includes a layer of material  54  that underlies foam blocks  50 . Foam blocks  50  and air bladders  52  are secured to layer of material  54  as described below in detail with reference to FIG.  5 . Securing foam blocks  50  and air bladders  52  to layer of material  54  allows core structure  44  to be moved as a single unit with foam blocks  50  and air bladders  52  remaining held in the proper positions relative to one another and relative to layer of material  54 . 
     Shear cover  46  includes a top panel  56 , perimetral side panels  58  extending downwardly from top panel  56 , and a fitted portion  60  appended to side panels  58  and extending at least partially beneath top panel  56 . Top panel  56  cooperates with side panels  58  and fitted portion  60  to define an interior region  62  which receives core structure  44 . Fitted portion  60  includes an inner perimetral edge  64  defining an opening  66  beneath top panel  56  allowing for movement of core structure  44  into and out of interior region  62  of shear cover  46 . In illustrated embodiments, inner perimetral edge  64  of fitted portion  60  is provided with either an elastic band  68  or draw string or other suitable structure for drawing opening  66  of fitted portion  60  closed to facilitate wrapping shear cover  46  snugly around core structure  44 . 
     Inner shear cover  46  is made from a material having a low coefficient of friction such as “parachute” material or any other material that will allow top cover  34  to slide relative to core structure  44 . In the illustrative embodiment, inner shear cover  46  may be made from nylon rip stop 30 denier, style #66938 or 1.5 mil polyurethane material. Mattress cover  32  can be made from any of a number of materials, but, in illustrated embodiments, top cover  34  is made from DARTEX™ TC-23/PO-93 urethane coated nylon fabric which allows for wipe-down cleaning and bottom cover  36  is made from STAPH-CHEK® or WEBLON® reinforced vinyl laminate. 
     Mattress structure  30  may be used with a bed or table including an articulating deck (not shown) having pivotable head, seat, thigh, and leg sections. As the deck articulates, mattress structure  30  bends along with the deck sections. Top cover  34  frictionally engages a user lying on sleep surface  40  so that, when mattress structure  30  bends during articulation of the deck, top cover  34  tends to move with the user rather than moving with core structure  44 . Thus, providing shear cover  46  between top cover  34  and core structure  44  minimizes the rubbing of mattress structure  30  against the user during articulation of the deck. 
     An anti-skid pad  35  is RF welded, stitched, bonded, or otherwise appropriately attached to central region  37  of bottom cover  36  as shown, for example, in FIG.  19 . Anti-skid pad  35  frictionally engages the bed or table (not shown) on which mattress structure  30  is used to inhibit movement of mattress structure  30  relative to the bed or table, especially during articulation of the deck. In the illustrated embodiment, anti-skid pad  35  is made from textured rubber but may be made from other materials which would increase the frictional forces between the mattress structure  30  and the bed or table. 
     Mattress structure  30  also includes transport straps  39  and buckles  41  coupled to transport straps  39 . Transport straps  39  are attached to bottom cover  36 , as shown, for example, in FIG.  19 . Each transport strap  39  includes a first end  43 , a spaced apart second end  45 , a central portion  47 , a first free portion  49  extending between first end  43  and central portion  47 , and a second free portion  51  extending between second end  45  and central portion  47 . Buckles  41  include a first buckle half  53  and a second buckle half  55  which may be selectively coupled to, and decoupled from first buckle half  53 . In the illustrated embodiment, first buckle half  53  is attached to first end  43  of transport strap  39  and second buckle half  55  is attached to second free portion  51  of transport strap  39  to slide between second end  45  and central portion  47  of transport strap  39  to adjust the effective length of transport strap  39 . In the illustrated embodiment, central portions  47  of two transport straps  39  are single stitch sewn to the central region  37  of bottom cover  36 , as shown, for example, in FIG.  19 . 
     Air-over-foam mattresses are not required for all patients at all times during their stay at a care facility so it is envisioned that facilities will rent air-over-foam mattresses from supply houses on an as needed basis or that facilities will purchase air-over-foam mattresses and store them until needed. The foam block and bladder construction of mattress structure  30  facilitates folding mattress structure  30  for shipping or storage, as shown, for example, in FIGS. 20 and 21. The plurality of laterally extending foam blocks  50  in mattress structure  30  define fold locations between each adjacent foam block  50 , thus mattress structure  30  may be folded in many different ways. The illustrated embodiment of mattress structure  30  is preferably folded so that foot zone  136  will lie on top of seat and thigh zones  132 ,  134  and back zone  130  will lie on top of the foot zone  136 , as shown, for example, in FIG.  21 . This allows air tubes  92  to be wrapped around end  33  of foot zone  136  so that they are not exposed when mattress structure  30  is folded for transport or storage, as shown, for example, in FIGS. 20 and 21. 
     Prior to folding mattress structure  30 , air tubes  92  should be disconnected from housing  172  of air pressure system  170  and housing  172  should be placed on top of seat and thigh zones  132 ,  134  of mattress structure  30 , as shown, for example, in FIG.  21 . Thus after folding mattress structure  30 , housing  172  will be protectively encased between seat and thigh zones  132 ,  134  and foot zone  136  so that foam blocks  50  of the mattress structure  30  will act as protective packing material for the housing  172 . 
     In illustrated embodiments, air bladders  52  of core structure  44  include a pair of back section header bladders  70 , a pair of seat section header bladders  72 , a pair of thigh section header bladders  74 , and a pair of foot section header bladders  76 . Header bladders  70 ,  72 ,  74 ,  76  extend longitudinally relative to mattress structure  30  and are arranged in end-to-end relation along respective sides  31  of core structure  44  as shown best in FIG.  2 . Header bladders  70 ,  72 ,  74 ,  76  each include a cylindrical portion  78  and a pair of end portions  80 , as shown best in FIGS. 2 and 5. The rest of the plurality of air bladders  52  extend transversely between respective header bladders  70 ,  72 ,  74 ,  76  and are arranged in side-by-side relation between ends  33  of core structure  44 . Each of the transversely extending air bladders  52  includes a cylindrical portion  82  and a pair of end portions  84 , as also shown best in FIGS. 2 and 5. 
     Each end portion  84  of the transversely extending air bladders  52  is attached to respective cylindrical portions  78  of the associated header bladder  70 ,  72 ,  74 ,  76 , for example, by radio frequency (RF) welding. A fluid port  86  is formed through each end portion  84  and through the respective cylindrical portion  78  of the associated header bladder  70 ,  72 ,  74 ,  76  so that an interior region  88  of each header bladder  70 ,  72 ,  74 ,  76  is in fluid communication with an interior region  90  of each of the transversely extending air bladders  52  attached thereto as shown in FIG.  5 . Fluid ports  86  are formed in the regions where header bladders  70 ,  72 ,  74 ,  76  and the transversely extending air bladders  52  are attached together so that an air-tight seal is formed around the periphery of each fluid port  86 . 
     Header bladders  70 ,  72 ,  74 ,  76  and the transversely extending air bladders  52  associated therewith are sized so as to be supported by the respective deck sections of the articulating deck with which mattress structure  30  is used. Thus, back section header bladders  70  and the associated transversely extending air bladders  52  provide mattress structure  30  with a back zone  130 , shown in FIG. 4, which is supported by the underlying foam blocks  50  and the back section of the articulating deck. Similarly, seat, thigh, and foot section header bladders  72 ,  74 ,  76  and the associated transversely extending air bladders  52  provide mattress structure  30  with seat, thigh, and foot zones  132 ,  134 ,  136 , respectively, which are supported by respective underlying foam blocks  50  and the seat, thigh, and foot sections, respectively, of the articulating deck. 
     Mattress structure  30  includes a plurality of air tubes  92  that are routed to each of header bladders  70 ,  72 ,  74 ,  76  as shown best in FIG.  3 . Foam base  48  is formed to include an aperture  94  as shown in FIG.  2 . Bottom cover  36  includes a bottom sheet  95  that is formed to include an aperture  96 . Bottom cover  36  also includes a protective sleeve  98  appended to bottom sheet  95  adjacent to aperture  96  and extending downwardly therefrom. Aperture  96  and sleeve  98  are aligned with aperture  94  allowing tubes  92  to be routed from interior region  42  of mattress structure  30  to the region outside of mattress structure  30 . Protective sleeve  98  protects tubes  92  from being contacted and possibly damaged by components of the bed which support mattress structure  30  as the deck sections of the bed articulate. 
     Core structure  44  includes layer of material  54  to which foam blocks  50  and air bladders  52  are secured as previously described and as shown in FIG.  5 . Core structure  44  includes a plurality of square-shaped sleeves  100 , each of which includes an interior region  112  and each of which are anchored to layer of material  54  by, for example, RF welding. Each sleeve  100  includes open ends  110  that allow foam blocks  50  to be inserted into interior region  112  of the respective sleeve  100 . Each foam block  50  includes a top surface  114 , a bottom surface  116 , a pair of side surfaces  118  extending between top and bottom surfaces  114 ,  116 , and a pair of end surfaces  120  extending between top and bottom surfaces  114 ,  116 . Each sleeve  100  includes a top panel  122 , a bottom panel  124 , and a pair of side panels  126  extending between top and bottom panels  122 ,  124 . 
     Sleeves  100  are sized so that foam blocks  50  fit snugly within interior region  112 . Thus, top panel  122 , bottom panel  124 , and side panels  126  of sleeves  100  engage top surface  114 , bottom surface  116 , and side surfaces  118  of foam blocks  50 , respectively. Engagement between panels  122 ,  124 ,  126  and surfaces  114 ,  116 ,  118  causes foam blocks  50  to resist transverse shifting within sleeves  100 . In addition, securing sleeves  100  to layer of material  54  prevents longitudinal shifting of foam blocks  50 . Thus, sleeves  100  hold foam blocks  50  in their respective positions relative to layer of material  54 . In illustrated embodiments, the length of foam blocks  50  is such that foam blocks  50  extend substantially between sides  31  of mattress structure  30  and the length of each sleeve is substantially equivalent to the length of foam blocks  50  so that sleeves  100  completely surround surfaces  114 ,  116 ,  118  and so that end surfaces  120  of foam blocks  50  are aligned with open ends  110  of sleeves  100 . Each sleeve  100  is made from a material having a low coefficient of friction, such as urethane coated nylon twill, to provide foam blocks  50  with an anti-friction shear coating. Layer of material  54  is also made from a material having a low coefficient of friction. 
     Although sleeves  100  completely surround surfaces  114 ,  116 ,  118  of foam blocks  50 , it is within the scope of the invention as presently perceived for core structure  44  to include sleeves that are U-shaped having a top panel and a pair of side panels that extend downwardly from the top panel to attach to layer of material  54  so that bottom surfaces  116  of foam blocks  50  engage layer of material  54 . In addition, although each sleeve  100  includes two open ends  110 , it is within the scope of the invention as presently perceived for core structure  44  to include sleeves having only one open end. 
     Core structure  44  includes a plurality of tethers  128  that connect respective transversely extending air bladders  52  to layer of material  54  as shown in FIG.  5 . Tethers  128  extend downwardly from air bladders  52  between side panels  126  of respective pairs of sleeves  100  and attach to layer of material  54  by, for example, RF welding. In illustrated embodiments, tethers  128  are formed integrally with transversely extending air bladders  52 . However, it is within the scope of the invention as presently perceived for tethers  128  to be separate pieces that attach to air bladders  52  as well as to layer of material  54 . The majority of transversely extending air bladders  52  are arranged above foam blocks  50  so that approximately half of each transversely extending air bladder  52  is supported by the respective underlying foam block  50  as shown, for example, in FIG.  4 . However, the foam blocks  50  at ends  33  of mattress structure  30  are slightly larger in cross section than the other foam blocks  50  so that the transversely extending air bladders  52  at ends  33  of mattress structure are supported by these slightly larger foam blocks  50  as also shown in FIG.  4 . In addition, the air bladders  52  at ends  33  of mattress structure  30  do not have tethers  128  extending therefrom but instead, rely on the attachment to respective header bladders  70 ,  76  for proper positioning. 
     In illustrated embodiments, each tether  128  is a contiguous sheet of material that extends the full transverse length of the respective transversely extending air bladder  52 . However, it is within the scope of the invention as presently perceived for tethers  128  to be shorter in length or to comprise several smaller sheets or strands that extend between a respective air bladder  52  and layer of material  54 . Each tether  128  is sized so as to be substantially pulled taut when the respective underlying pair of foam blocks  50  are uncompressed as shown in FIG.  5 . Thus, each tether  128  extends in a vertical reference plane  127  defined between respective pairs of adjacent foam blocks  50  and each tether  128  is positioned to lie vertically beneath a transverse central axis  129  of the associated air bladder  52  as also shown in FIG.  5 . 
     Each tether  128  is made of an anti-friction shear material having a low coefficient of friction, such as urethane coated nylon twill, and each pair of adjacent sleeves  100  contacts the tether  128  positioned therebetween as shown in FIG.  5 . Because sleeves  100  and tethers  128  are all made of an anti-friction shear material having a low coefficient of friction, as described above, the foam blocks  50  and associated sleeves  100  are able to compress and uncompress with a minimal amount of friction being created by tethers  128 . In addition, air bladders  52  are made of an anti-friction shear material having a low coefficient of friction which allows air bladders  52  to compress and uncompress with a minimal amount of friction therebetween. The minimal amount of friction between sleeves  100  and tethers  128  allows each foam block  50  to compress and uncompress individually with minimal interference from adjacent foam blocks  50 . Similarly, the minimal amount of friction between air bladders  52  allows each air bladder  52  to compress and uncompress individually with minimal interference from adjacent air bladders  52 . 
     The firmness and support characteristics provided by each foam block  50  depend in part upon the indention load deflection (ILD) of the foam from which each foam block is made. The ILD is a well-known industry-accepted index indicating the “firmness” of material such as urethane foam and other foam rubber materials. The ILD correlates to the amount of force required to compress a piece of foam by twenty-five per cent with an industry standard indenter having a specified area. It is within the scope of the invention as presently perceived to provide core structure  44  in which each foam block  50  has the same ILD or to provide core structure  44  in which the ILD of at least one foam block  50  is different from the ILD of at least one other foam block  50 . For example, the ILD&#39;s of the foam blocks  50  which support air bladders  52  of respective back, seat, thigh, and foot zones  130 ,  132 ,  134 ,  136  may vary from one another. In addition, it is within the scope of the present invention for each foam block  50  to be comprised of portions having varying ILD&#39;s. For example, in one illustrated embodiment, core structure  44  is provided with foam blocks  50  each having firm end portions  138  with an ILD of about forty-four and a soft middle portion  140  with an ILD of about seventeen as shown in FIG.  5 . Firm end portions  138  are sized so as to support the respective overlying header bladders  70 ,  72 ,  74 ,  76  to provide mattress structure  30  with more firmness along sides  31  thereof. End portions  138  are bonded to respective middle portions  140  with an adhesive such  30  as, for example, an acetone heptane and resin base spray. 
     Mattress structure  30  includes a plurality of air tubes  92  that are routed to each header bladder  70 ,  72 ,  74 ,  76  as previously described. Tubes  92  include a first zone tube set  142 , a second zone tube set  144 , and a third zone tube set  146  as shown in FIG.  3 . First zone tube set  142  includes a pressure tube  148  that fluidly couples to one of the back section header bladders  70  and to one of the thigh section header bladders  74 . First zone tube set  142  also includes a sensor tube  150  that fluidly couples to the other of the back section header bladders  70 . Pressure tube  148  and sensor tube  150  each couple to a single, dual-passage tube connector  152 . Second zone tube set  144  includes a pressure tube  154  that fluidly couples to one of the seat section header bladders  72  and a sensor tube  156  that fluidly couples to the other of the seat section header bladders  72 . Pressure tube  154  and sensor tube  156  each couple to a single, dual-passage tube connector  158 . Third zone tube set  146  includes a pressure tube  160  that fluidly couples to one of the foot section header bladders  76  and a sensor tube  162  that fluidly couples to the other of the foot section header bladders  76 . Pressure tube  160  and sensor tube  162  each couple to a single, dual-passage tube connector  164 . Layer of material  54  is formed to include a plurality of small slits  166  which define a plurality of pass-through bands  168 . Air tubes  92  are routed through slits  166  so that pass-through bands  168  secure air tubes  92  to core structure  44  in the desired routing pattern as shown in FIG.  3 . 
     Because one of the back section header bladders  70  and one of the thigh section header bladders  74  are each fluidly coupled to pressure tube  148 , back zone  130  and thigh zone  134  provide mattress structure  30  with a first mattress zone  131  as shown diagrammatically in FIG.  6 . Seat zone  132  provides mattress structure  30  with a second mattress zone, hereinafter referred to as either second mattress zone  132  or seat zone  132 . In addition, foot zone  136  provides mattress structure  30  with a third mattress zone, hereinafter referred to as either third mattress zone  136  or foot zone  136 . 
     An air pressure system  170 , shown diagrammatically in FIG. 6, couples to air tubes  92  and operates to pressurize first, second, and third mattress zones  131 ,  132 ,  136 . Air pressure system  170  includes a housing  172  that encases the other components of system  170 . Air pressure system  170  includes a compressor  174  that operates through a manifold  176  to pressurize mattress zones  131 ,  132 ,  136 . Air pressure system  170  also includes first, second, and third pressure sensors  178 ,  180 ,  182  that sense pressure in first, second, and third mattress zones  131 ,  132 ,  136 , respectively. Air pressure system  170  includes a microprocessor  184  that provides a control signal to compressor  174  on a control line  186 . Each pressure sensor  178 ,  180 ,  182  is coupled electrically to a respective analog-to-digital converter  188  via a respective analog signal line  190  and each analog-to-digital converter  188  provides an input signal to microprocessor  184  via a respective digital signal line  192 . 
     Manifold  176  is formed to include a main passage  194  with an inlet  196  as shown in FIGS. 6 and 8. Compressor  174  includes an outlet  198  that couples to inlet  196  of main passage  194  via a pneumatic hose  200 . Manifold  176  is also formed to include a first passage  210  fluidly coupled to main passage  194  at a first port  212 , a second passage  214  fluidly coupled to main passage  194  at a second port  216 , a third passage  218  fluidly coupled to main passage  194  at a third port  220 , and a vent passage  222  fluidly coupled to main passage  194  at a vent port  224  as shown best in FIG.  8 . Manifold  176  includes a bottom surface  226  having a first exit port  228  at which first passage  210  terminates, a second exit port  230  at which second passage  214  terminates, a third exit port  232  at which third passage  218  terminates, and a vent exit port  234  at which vent passage  222  terminates as also shown best in FIG.  8 . 
     First passage  210  is fluidly coupled to pressure tube  148  via a first connector hose  236 , shown in FIG. 6, that extends from first exit port  228  to dual-passage connector  152 . Similarly, second passage  214  is fluidly coupled to pressure tube  154  via a second connector hose  238  that extends from second exit port  230  to dual-passage connector  158  and third passage  218  is fluidly coupled to pressure tube  160  via a third connector hose  240  that extends from third exit port  232  to dual-passage connector  164 . In addition, vent passage  222  is fluidly coupled to the atmosphere by a vent hose  242  that extends from vent exit port  234  to an outlet aperture (not shown) formed in housing  172 . First pressure sensor  178  is fluidly coupled to sensor tube  150  via a fourth connector hose  244 , shown in FIG. 6, that is routed to dual-passage connector  152  alongside first connector hose  236 . Similarly, second pressure sensor  180  is fluidly coupled to sensor tube  156  via a fifth connector hose  246  that is routed to dual-passage connector  158  alongside second connector hose  238  and third pressure sensor  182  is fluidly coupled to sensor tube  162  via a sixth connector hose  248  that is routed to dual-passage connector  164  alongside third connector hose  240 . 
     Although hoses  236 ,  238 ,  240 ,  244 ,  246 ,  248  are shown diagrammatically in FIG. 6 as being continuous hoses that extend from either manifold  176  or pressure sensors  178 ,  180 ,  182  to respective mattress zones  131 ,  132 ,  136 , it should be understood that hoses  236 ,  238 ,  240 ,  244 ,  246 ,  248  are subdivided into segments that connect together with connectors that are like dual-passage connectors  152 ,  158 ,  164  or that mate with dual-passage connectors  152 ,  158 ,  164 . For example, in illustrated embodiments, a set of dual-passage connectors like dual-passage connectors  152 ,  158 ,  164  are provided at a bottom panel  250  of housing  172  and a first portion of hoses  236 ,  238 ,  240 ,  244 ,  246 ,  248  extend from either manifold  176  or pressure sensors  178 ,  180 ,  182  to the set of dual-passage connectors that are like dual-passage connectors  152 ,  158 ,  164 . In addition, a second portion of hoses  236 ,  238 ,  240 ,  244 ,  246 ,  248  extend from the set of dual-passage connectors at bottom panel  250  of housing  172  to dual-passage connectors  152 ,  158 ,  164 . Both ends of the second portion of hoses  236 ,  238 ,  240 ,  244 ,  246 ,  248  are provided with dual-passage connectors that are configured to mate with dual-passage connectors  152 ,  158 ,  164 . 
     Air pressure system  170  includes a first valve  252 , a second valve  254 , a third valve  256 , and a vent valve  258  that are situated in passages  210 ,  214 ,  218 ,  222 , respectively, of manifold  176 , as shown in FIGS. 6 and 8. Valves  252 ,  254 ,  256 ,  258  are each moveable to block and unblock the flow of air through passages  210 ,  214 ,  218 ,  222 , respectively. Each valve  252 ,  254 ,  256 ,  258  includes a tapered tip  260  as shown in FIG.  8 . In addition, first passage  210  includes a first nozzle port  262  and tapered tip  260  of first valve  252  seats against first nozzle port  262  to block the flow of air through first passage  210 . Similarly, second passage  214 , third passage  218 , and vent passage  222  include a second nozzle port  264 , a third nozzle port  266 , and a vent nozzle port  268 , respectively, against which tapered tips  260  of valves  254 ,  256 ,  258  seat. The amount that tapered tips  260  are moved away from respective nozzle ports  262 ,  264 ,  266 ,  268  determines the volume of air that flows through the respective nozzle port  262 ,  264 ,  266 ,  268  at any particular pressure as is well-known in the art. 
     Air pressure system  170  includes first, second, third, and vent actuators  270 ,  272 ,  274 ,  276  that are coupled mechanically to respective valves  252 ,  254 ,  256 ,  258  as shown in FIGS. 6 and 8. In one illustrated embodiment actuators  270 ,  272 ,  274 ,  276  are each Model No. 26461-12-006 stepper motors manufactured by Haydon Switch and Instruments, Inc. of Waterbury, Conn. and having ratings of 12 V DC and 3.4 W. Each actuator  270 ,  272 ,  274 ,  276  is coupled electrically to microprocessor  184  and receives control signals therefrom via respective signal lines  278 . A main power switch  280  is mounted to housing  172  and is coupled to microprocessor  184  via a power line  282 . Switch  280  is movable between an ON position in which power is provided from an external power source (not shown) to operate air pressure system  170  and an OFF position in which power is decoupled from air pressure system  170 . 
     Air pressure system  170  includes a weight range selector  284  having a button (not shown) that is pressed to select the weight range of the patient supported by mattress structure  30 . Weight range selector  284  is provided with a label  286  having indicia (not shown) specifying the available weight ranges from which to select and a set of LED&#39;s  288  that light up to indicate which of the weight ranges is selected currently. The selected weight range is communicated to microprocessor  184  via a data line  290 . Air pressure system  170  further includes a run-time meter  292  that is used to track overall run time of air pressure system  170  to provide information for service and maintenance tracking. 
     Housing  172 , shown best in FIG. 7, includes a front panel  296 , a pair of side panels  298 , a back panel (not shown), and a top panel  300 . Knobs  294  are mounted to front panel  296 , run-time meter is mounted to the back panel, and weight range selector  284  is mounted to top panel  300 . A carrying handle  310  is mounted to housing  172  and is movable between a storage position, shown in FIG. 7, and an upright carrying position (not shown). In addition, a mounting hook  312  is mounted to housing  172  and is movable between a retracted position (not shown) in which a bight portion  314  of hook  312  is adjacent to the back panel of housing  172  and an extended position, shown in FIG. 7, in which bight portion  314  is spaced apart from the back panel of housing  172 , allowing hook  312  to be used to mount air pressure system  170  to another structure such as, for example, a foot board  316  of a hospital bed (not shown). 
     Microprocessor  184  is operated by a software program that is written so that only one of valves  252 ,  254 ,  256  is opened at a time. In addition, the software is written so that air pressure system  170  monitors and, if necessary, adjusts the pressure in each of mattress zones  131 ,  132 ,  136  in a cyclical manner. If microprocessor  184  determines that one of mattress zones  131 ,  132 ,  136  is below the desired pressure, based on information received from the associated pressure sensor  178 ,  180 ,  182 , microprocessor  184  sends a signal on the respective signal line  278  to operate the respective actuator  270 ,  272 ,  274  to open the associated valve  252 ,  254 ,  256  while simultaneously sending a signal on control line  186  to run compressor  174  so that the respective mattress zone  131 ,  132 ,  136  is further inflated. If microprocessor  184  determines that one of mattress zones  131 ,  132 ,  136  is above the desired pressure, based on information received from the associated pressure sensor  178 ,  180 ,  182 , microprocessor  184  sends a signal on the respective signal line  278  to operate the respective actuator  270 ,  272 ,  274  to open the associated valve  252 ,  254 ,  256  and to operate actuator  276  to open vent valve  258  while simultaneously sending a signal on control line  186  to keep the compressor  174  from running so that the respective mattress zone  131 ,  132 ,  136  is deflated. 
     Core structure  44  includes a plurality of vent valves  318 , shown in FIGS. 3 and 4, that are each manually opened to fluidly couple a respective one of each of header bladders  70 ,  72 ,  74 ,  76  to the atmosphere which results in rapid deflation of all air bladders  52 . In illustrated embodiments, vent valves  318  are VARILITE® release valves, Model No. 04227, and hat flanges Model No. 04226. 
     An alternative embodiment of air-over-foam core  844  for mattress structure  830  is substantially similar to air-over-foam core  44  for mattress structure  30  but does not include vent valves  318 . Since alternate embodiment mattress structure  830  is similar to mattress structure  30 , like reference numerals are used for like components. Mattress structure  830  includes a plurality of air tubes  892  that are routed to each header bladder  70 ,  72 ,  74 ,  76  as previously described. Tubes  892  include a first zone tube set  942 , a second zone tube set  944 , and a third zone tube set  946  as shown in FIG.  3 . First zone tube set  942  includes a pressure tube  948  that fluidly couples to one of the back section header bladders  70  and to one of the thigh section header bladders  74 . First zone tube set  942  also includes a sensor tube  950  that fluidly couples to the other of the back section header bladders  70 . Second zone tube set  944  includes a pressure tube  954  that fluidly couples to one of the seat section header bladders  72  and a sensor tube  956  that fluidly couples to the other of the seat section header bladders  72 . Third zone tube set  946  includes a pressure tube  960  that fluidly couples to one of the foot section header bladders  76  and a sensor tube  962  that fluidly couples to the other of the foot section header bladders  76 . Pressure tube  948 , sensor tube  950 , pressure tube  954 , sensor tube  956 , pressure tube  960  and sensor tube  962  are each RF welded or otherwise coupled longitudinally to each other to form a substantially flat multi-lumen tube ribbon  949  extending from interior region  42  of mattress structure  830  to near attachment end of each tube  892 . Near attachment end of each tube  892 , the tubes  892  forming tube ribbon  949  are separated to allow each tube  892  to be connected to a separate single passage tube connector  951  as shown, for example, in FIGS. 22,  23 , and  26 . 
     Tubes  892  connect to air pressure system  170 , shown diagrammatically in FIG. 6, which operates to pressurize first, second, and third mattress zones  131 ,  132 ,  136 , as previously described. First passage  210  is fluidly coupled to pressure tube  948  via a first connector hose  236  that extends from first exit port  228  to single-passage connector  952 . Similarly, second passage  214  is fluidly coupled to pressure tube  954  via a second connector hose  238  that extends from second exit port  230  to single-passage connector  958  and third passage  218  is fluidly coupled to pressure tube  960  via a third connector hose  240  that extends from third exit port  232  to single-passage connector  964 . In addition, vent passage  222  is fluidly coupled to the atmosphere by a vent hose  242  that extends from vent exit port  234  to an outlet aperture (not shown) formed in housing  172 . First pressure sensor  178  is fluidly coupled to sensor tube  950  via a fourth connector hose  244 , shown in FIG. 6, that is routed to single-passage connector  953  alongside first connector hose  236 . Similarly, second pressure sensor  180  is fluidly coupled to sensor tube  956  via a fifth connector hose  246  that is routed to single-passage connector  959  alongside second connector hose  238  and third pressure sensor  182  is fluidly coupled to sensor tube  962  via a sixth connector hose  248  that is routed to single-passage connector  965  alongside third connector hose  240 . 
     Although hoses  236 ,  238 ,  240 ,  244 ,  246 ,  248  are shown diagrammatically in FIG. 6 as being continuous hoses that extend from either manifold  176  or pressure sensors  178 ,  180 ,  182  to respective mattress zones  131 ,  132 ,  136 , it should be understood that hoses  236 ,  238 ,  240 ,  244 ,  246 ,  248  may be subdivided into segments that connect together with connectors that are like single-passage connectors  952 ,  953 ,  958 ,  959 ,  964 ,  965 . For example, in illustrated embodiments, a set of male portions of single-passage connectors  952 ,  953 ,  958 ,  959 ,  964 ,  965  are provided at a bottom panel  250  of housing  172  and a first portion of hoses  236 ,  238 ,  240 ,  244 ,  246 ,  248  extend from either manifold  176  or pressure sensors  178 ,  180 ,  182  to the set of male portions of single-passage connectors  952 ,  958 ,  964 . In addition, a second portion of hoses  236 ,  238 ,  240 ,  244 ,  246 ,  248  extend from the set of female portions of single-passage connectors  952 ,  953 ,  958 ,  959 ,  964 ,  965  at bottom panel  250  of housing  172 . In the illustrated embodiment, the second portion of hoses  236 ,  238 ,  240 ,  244 ,  246 ,  248  includes tubes  892 . 
     To facilitate rapid connection of hoses  236 ,  238 ,  240 ,  246 ,  248  to tubes  948 ,  950 ,  954 ,  956 ,  960 ,  962 , the male portions of single passage connectors  952 ,  953 ,  958 ,  959 ,  964 ,  965  are held in specific positions in a male connector housing  961  and the female portions of single passage connectors  952 ,  953 ,  958 ,  959 ,  964 ,  965  are held in a cooperating specific orientation in female connector housing  963  forming a quick-disconnect assembly  947 , as shown for example in FIGS. 22-25. Male connector housing  961  is attached to the bottom panel  250  of housing  172  of air pressure system  170  and internally connected to hoses  236 ,  238 ,  240 ,  244 ,  246 ,  248 . Female connector housing  963  is coupled to attachment ends of tubes  948 ,  950 ,  954 ,  956 ,  960 ,  962 . 
     In the illustrated embodiment, female portions of connectors  953 ,  959 ,  965 , coupled to the three sensor tubes  950 ,  956 ,  962 , are aligned longitudinally with respect to each other and are off-set laterally from female portions of connectors  952 ,  958 ,  964 , coupled to the three pressure tubes  948 ,  954 ,  960 , which are aligned longitudinally with respect to each other, as shown for example in FIG.  22 . Female portions of sensor connectors  953  and  959  are longitudinally displaced from each other by a displacement  967  as are female portions of pressure connectors  952  and  958 . Female portions of sensor connectors  959  and  965  are longitudinally displace from each other by a displacement  969  as are female portions of pressure connectors  958  and  964 . Likewise male portions of connectors  953 ,  959 ,  965 , coupled to the three sensor hoses  244 ,  246 ,  248 , are aligned longitudinally with respect to each other and are off-set laterally from male portions of connectors  952 ,  958 ,  964 , coupled to the three pressure hoses  236 ,  238 ,  240 , which are aligned longitudinally with respect to each other, as shown, for example, in FIG.  22 . Male portions of sensor connectors  953  and  959  are longitudinally displaced from each other by a displacement  967  as are male portions of pressure connectors  952  and  958 . Male portions of sensor connectors  959  and  965  are longitudinally displace from each other by a displacement  969  as are male portions of pressure connectors  958  and  964 . Displacement  967  differs from displacement  969  so that the male and female portions of all six connectors  952 ,  953 ,  958 ,  959 ,  964 ,  965  can be simultaneously coupled only when oriented so that cooperating tubes and hoses mate. 
     In the illustrated embodiments the male portions of connectors  952 ,  953 ,  958 ,  959 ,  964 ,  965  are male portions of single passage connectors available from Colder Products Corporation As part number PMCX 42-03. Female portions of connectors  952 ,  958 ,  959 ,  964  are female portions of single passage connectors available from Colder Products Corporation as part number PMCX 16-04-NC. 
     The female portions of the two front end connectors  953 ,  965  include a latching mechanism  971  including a spring  973  which urges a latch plate  975  (“the snap-fit hardware”) into channel  977  of male connector portion to secure the connectors in a connected state (not shown). Latch plate  975  includes and actuator  981  against which spring  973  pushes to bias the plate  975  in the channel engaging position. By concurrently pushing on both actuators  981  to compress springs  973 , a user can position latch plates  975  so that they do not engage channels  977  facilitating decoupling of male and female portions of connectors  952 ,  953 ,  958 ,  959 ,  964 ,  965 . In the illustrated embodiment female portions of connectors  953 ,  965  are available from Colder Products Corporation as part number PMCX 16-04. Both connectors  953  and  965  are sensor connectors and thus are positioned on the ends of the front row of connectors in the female connector housing  963  facilitating access to the actuators  981  by a health care provider. The snap-fit hardware also provides a visual indicator of the proper orientation of the female connector housing  963  aiding in quickly orienting the housing  963  for connection to the male connector housing  961 . When the male portion of each connector  952 ,  953 ,  958 ,  959 ,  964 ,  965  is properly seated in the female portion of connector  952 ,  953 ,  958 ,  959 ,  964 ,  965  the snap-fit hardware produces an audible click. Thus the illustrated embodiment provides a quick-connect/quick-disconnect between the mattress structure and the air supply. 
     The quick-connect/quick-disconnect between mattress and air supply allows for rapid deflation of the air bladders without the need for additional vent valves  318 . In the illustrated embodiment disconnection of the female connector housing  963  from the male connector housing  961  immediately vents first zone tube set  942  to the atmosphere through tubes  948  and  950 , second zone tube set  944  to the atmosphere through tubes  954  and  956 , and third zone tube set  946  to the atmosphere through tubes  960  and  962 . While described as elements of mattress structure  830  used in conjunction with air supply  170 , it should be understood that tube ribbon  949 , male connector housing  961  and female connector housing  963  are easily adaptable for use with any of the disclosed mattress structures or air supplies. 
     It is within the scope of the invention as presently perceived for microprocessor  184  of air pressure system  170  to execute any one of a number of air pressure control algorithms to control the air pressure within zones  131 ,  132 ,  136 . For example, a block diagram of one algorithm that may be executed by microprocessor  184  to control the air pressure within zones  131 ,  132 ,  136  is shown in FIGS. 9 a  and  9   b  and a set of block diagrams of another algorithm that may be executed by microprocessor  184  to control the air pressure within zones  131 ,  132 ,  136  is shown in FIGS. 16,  17   a ,  17   b ,  18   a , and  18   b.    
     FIGS. 9 a  and  9   b  show a flow chart of the steps performed by microprocessor  184  of air pressure system  170  as one possible software program is executed as previously mentioned. The first step performed by microprocessor  184  is to send signals on lines  278  to actuators  270 ,  272 ,  274 ,  276  to close all of valves  252 ,  254 ,  256 ,  258  as indicated at block  320  of FIG. 9 a . In addition, compressor  174  is off when microprocessor  184  first begins executing the software program. The next step performed by microprocessor  184  is to select the initial mattress zone to be monitored for possible pressure adjustment as indicated at block  322 . The initial zone can be any one of mattress zones  131 ,  132 ,  136 , but typically, the initial zone is programmed to be mattress zone  131 . After the initial zone has been selected, microprocessor  184  reads the weight range selected by the user with weight range selector  284  as indicated at block  324 . 
     After reading the selected weight range, microprocessor  184  determines whether the selected weight range has been changed as indicated at block  326  of FIG. 9 a . If the selected weight range has been changed, microprocessor  184  will re-establish a pressure set point and the tolerances above and below the set point as indicated at block  328 . It should be understood that when the software program is executed the first time after air pressure system  170  is powered up, the selected weight range will be considered to be a new weight range by microprocessor  184 . 
     The set points are the target pressures to be maintained in each of mattress zones  131 ,  132 ,  136  based on the weight range selected by the user and the tolerances are the ranges above and below the target pressure that are considered to be adequate for patient support. For example, when a heavy person is supported on mattress structure  30 , a higher weight range should be selected with selector  284  so that relatively high pressure set points and associated tolerances are established for each of mattress zones  131 ,  132 ,  136  and when a light person is supported on mattress structure  30 , a lower weight range should be selected with selector  284  so that relatively low pressure set points and associated tolerances are established for each of mattress zones  131 ,  132 ,  136 . It is within the scope of the invention as presently perceived for the set points established for each mattress zone  131 ,  132 ,  136  to be different than the set points established for each of the other mattress zones  131 ,  132 ,  136  and it is also within the scope of the invention as presently perceived for the set points established for two or more of mattress zones  131 ,  132 ,  136  to be substantially equivalent. 
     After the pressure set points and tolerances are re-established at block  328  or if the selected weight range has not been changed as determined at block  326 , microprocessor  184  reads the value of the pressure in the selected mattress zone  131 ,  132 ,  136  which is communicated to microprocessor  184  from the associated pressure sensor  178 ,  180 ,  182  as indicated at block  330  of FIG. 9 a . After reading the pressure of the selected mattress zone  131 ,  132 ,  136 , microprocessor  184  determines whether the selected mattress zone  131 ,  132 ,  136  needs inflation as indicated at block  332 . Microprocessor  184  makes the determination at block  332  by comparing the value of pressure read at block  330  with a low-limit pressure which is calculated based on the set point and tolerance established at block  328 . If the pressure in the selected mattress zone  131 ,  132 ,  136  is below the low-limit pressure, then the selected mattress zone  131 ,  132 ,  136  needs inflation. 
     If microprocessor  184  determines at block  332  that the selected mattress zone  131 ,  132 ,  136  needs inflation, microprocessor  184  then sends a signal on one of signal lines  278  to actuate the actuator  270 ,  272 ,  274  associated with the selected mattress zone  131 ,  132 ,  136  to open the respective valve  252 ,  254 ,  256  by one step as indicated at block  334 . After the valve  252 ,  254 ,  256  associated with the selected mattress zone  131 ,  132 ,  136  is opened by one step at block  334 , microprocessor  184  then sends a signal on line  186  to run compressor  174  as indicated at block  336 . Compressor  174  is run for a predetermined delay period, as indicated at block  338 , and then microprocessor  184  sends a signal on line  186  to stop running compressor  174  as indicated at block  340 . After compressor  174  is turned off at block  340 , microprocessor  184  takes another pressure reading from the pressure sensor  178 ,  180 ,  182  associated with the selected mattress zone  131 ,  132 ,  136  as indicated at block  330 . 
     After microprocessor  184  takes another pressure reading at block  330 , microprocessor then determines whether further inflation of the selected mattress zone  131 ,  132 ,  136  is needed as indicated at block  332 . If inflation is still needed, microprocessor then loops through blocks  334 ,  336 ,  338 ,  340  and back to block  330 . Microprocessor  184  will loop through blocks  330 ,  334 ,  336 ,  338 ,  340  as many times as required until the selected mattress zone  131 ,  136  no longer needs inflation. Each time microprocessor  184  loops through blocks  330 ,  334 ,  336 ,  338 ,  390 , the valve  252 ,  254 ,  256  associated with the selected mattress zone  131 ,  132 ,  136  is opened by one additional step. Thus, if the selected mattress zone  131 ,  132 ,  136  needs a small amount of inflation, the associated valve  252 ,  254 ,  256  will be stepped open by a small amount and if the selected mattress zone  131 ,  132 ,  136  needs a large amount of inflation, the associated valve  252 ,  254 ,  256  will be stepped open by a large amount. This “step-measure” process results in controlled inflation of the selected mattress zone  131 ,  132 ,  136 . 
     If microprocessor  184  determines at block  332  that the selected mattress zone  131 ,  132 ,  136  does not need inflation, microprocessor  184  then determines if the valve  252 ,  254 ,  256  associated with the selected mattress zone  131 ,  132 ,  136  is open as indicated at block  342 . If the valve  252 ,  254 ,  256  associated with the selected mattress zone  131 ,  132 ,  136  is open, which will be the case if microprocessor  184  has looped through blocks  334 ,  336 ,  338 ,  340  one or more times, then microprocessor  184  sends a signal on the appropriate signal line  278  to the actuator  270 ,  272 ,  274  associated with the selected mattress zone  131 ,  132 ,  136  to close the respective valve  252 ,  254 ,  256  at a fast rate. 
     After the valve  252 ,  254 ,  256  associated with the selected mattress zone  131 ,  132 ,  136  is closed at block  344  or if microprocessor  184  determines at block  342  that the valve  252 ,  254 ,  256  associated with the selected mattress zone  131 ,  132 ,  136  is not open, microprocessor  184  reads the value of the pressure in the selected mattress zone  131 ,  132 ,  136  which is communicated to microprocessor  184  from the associated pressure sensor  178 ,  180 ,  182  as indicated at block  346  of FIG. 9 b . After reading the pressure of the selected mattress zone  131 ,  132 ,  136 , microprocessor  184  determines whether the selected mattress zone  131 ,  132 ,  136  needs deflation as indicated at block  348 . Microprocessor  184  makes the determination at block  348  by comparing the value of pressure read at block  346  with a high-limit pressure which is calculated based on the set point and tolerance established at block  328 . If the pressure in the selected mattress zone  131 ,  132 ,  136  is above the high-limit pressure, then the selected mattress zone  131 ,  132 ,  136  needs deflation. 
     If microprocessor  184  determines at block  348  that the selected mattress zone  131 ,  132 ,  136  needs deflation, microprocessor  184  then sends a signal on one of signal lines  278  to actuate the actuator  270 ,  272 ,  274  associated with the selected mattress zone  131 ,  132 ,  136  to open the respective valve  252 ,  254 ,  256  by one step as indicated at block  350 . After the valve  252 ,  254 ,  256  associated with the selected mattress zone  131 ,  132 ,  136  is opened by one step at block  334 , microprocessor  184  then sends a signal on the appropriate line  278  to vent actuator  276  to open vent valve  258  by one step as indicated at block  352 . After the valve  252 ,  254 ,  256  associated with the selected mattress zone  131 ,  132 ,  136  is stepped open and after vent valve  258  is stepped open, microprocessor  184  takes another pressure reading as indicated at block  346 . 
     After microprocessor  184  takes another pressure reading at block  346 , microprocessor  184  then determines whether further deflation is needed as indicated at block  348 . If deflation is still needed, microprocessor  184  then loops through blocks  350 ,  352  and back to block  346 . Microprocessor  184  loops through blocks  346 ,  348 ,  350 ,  352  as many times as required until the selected mattress zone  131 ,  136  no longer needs deflation. Each time microprocessor  184  loops through blocks  346 ,  348 ,  350 ,  352 , the valve  252 ,  254 ,  256  associated with the selected mattress zone  131 ,  132 ,  136  and vent valve  258  are both opened by one additional step. Thus, if the selected mattress zone  131 ,  132 ,  136  needs a small amount of deflation, the associated valve  252 ,  254 ,  256  and vent valve  258  will both be stepped open by a small amount and, if the selected mattress zone  131 ,  132 ,  136  needs a large amount of deflation, the associated valve  252 ,  254 ,  256  and vent valve  258  will both be stepped open by a large amount. This “step measure” process results in controlled deflation of the selected mattress zone  131 ,  132 ,  136 . 
     If microprocessor  184  determines at block  348  that the selected mattress zone  131 ,  132 ,  136  does not need deflation, microprocessor  184  then determines if the valve  252 ,  254 ,  256  associated with the selected mattress zone  131 ,  132 ,  136  is open as indicated at block  354 . If the valve  252 ,  254 ,  256  associated with the selected mattress zone  131 ,  132 ,  136  is open, which will be the case if microprocessor  184  has looped through blocks  350 ,  352  one or more times, microprocessor  184  sends a signal on the appropriate signal line  278  to the actuator  270 ,  272 ,  274  associated with the selected mattress zone  131 ,  132 ,  136  to close the respective valve  252 ,  254 ,  256  at a fast rate as indicated at block  356 . 
     After the valve  252 ,  254 ,  256  associated with the selected mattress zone  131 ,  132 ,  136  has been closed at a fast rate or if the valve  252 ,  254 ,  256  associated with the selected mattress zone  131 ,  132 ,  136  is not open, microprocessor  184  determines whether vent valve  258  is open as indicated at block  358  of FIG. 9 b . If vent valve  258  is open, which will be the case if microprocessor  184  has looped through blocks  350 ,  352  one or more times, microprocessor  184  sends a signal on the appropriate signal line  278  to actuator  276  to close vent valve  258  at a fast rate as indicated at block  360 . After vent valve  258  has been closed at a fast rate or if vent valve  258  is not open, microprocessor  184  then selects the next mattress zone  131 ,  132 ,  136  as indicated at block  362 . The next mattress zone  131 ,  132 ,  136  selected at block  362  can be either of the two mattress zones  131 ,  132 ,  136  that were not selected previously. For example, if mattress zone  131  was the mattress zone selected initially, then either of mattress zones  132 ,  136  can be the next selected mattress zone. After the next mattress zone  131 ,  132 ,  136  is selected, microprocessor  184  loops through the software program again, beginning with block  324  of FIG. 9 a.    
     Thus, mattress structure  30  includes air bladders  52  that are grouped into sets comprising mattress zones  131 ,  132 ,  136  and air pressure system  170  includes microprocessor  184 , manifold  174 , actuators  270 ,  272 ,  274 ,  276 , and valves  252 ,  254 ,  256 ,  258  that comprise a bladder set selector. The air bladder sets comprising zones  131 ,  132 ,  136  are selected in a cyclical manner and the bladder set selector operates to fluidly couple the selected bladder set to either the atmosphere, if the selected bladder set needs deflation, or to the compressor, if the selected bladder set needs inflation. The unselected bladder sets remain fluidly decoupled from the compressor and fluidly decoupled from the atmosphere. 
     A portion  370  of an alternative embodiment air pressure system which can be used to adjust the pressure in mattress zones  131 ,  132 ,  136  is shown in FIG.  10 . The alternative embodiment air pressure system is similar to air pressure system  170  and therefore, like reference numerals are used for like components. For example, portion  370  of the alternative embodiment air pressure system includes compressor  174  that receives control signals on control line  186  from a microprocessor (not shown) that is substantially similar to microprocessor  184  of air pressure system  170 . Portion  370  includes a manifold  376  having a main passage  394  with an inlet  396  and an outlet  397  as shown in FIG.  10 . Compressor  174  includes an outlet  198  that couples to inlet  396  of manifold  376  via a pneumatic hose  200 . 
     Manifold  376  is formed to include a first passage  410  fluidly coupled to main passage  394  at a first port  412 , a second passage  414  fluidly coupled to main passage  394  at a second port  416 , a third passage  418  fluidly coupled to main passage  394  at a third port  420 , and a vent passage  422  fluidly coupled to main passage  394  at a vent port  424  as shown in FIG.  10 . Manifold  376  includes a bottom surface  426  having a first exit port  428  at which first passage  410  terminates, a second exit port  430  at which second passage  414  terminates, a third exit port  432  at which third passage  418  terminates, and a vent exit port  434  at which vent passage  422  terminates as also shown in FIG.  10 . 
     First passage  410  is fluidly coupled to first mattress zone  131  via a first connector hose  436  that extends from first exit port  428  to a single-passage connector (not shown) associated with first mattress zone  131 . Similarly, second passage  414  is fluidly coupled to second mattress zone  132  via a second connector hose  438  that extends from second exit port  430  to a single-passage connector (not shown) associated with second mattress zone  132  and third passage  418  is fluidly coupled to third mattress zone  136  via a third connector hose  440  that extends from third exit port  432  to a single-passage connector (not shown) associated with third mattress zone  136 . In addition, vent passage  422  is fluidly coupled to the atmosphere by a vent hose  242  that extends from vent exit port  434  to an outlet aperture (not shown) formed in a housing (not shown) that contains portion  370  of the alternative embodiment air pressure system. 
     Although hoses  436 ,  438 ,  440  are shown diagrammatically in FIG. 10 as being continuous hoses that extend from manifold  376  to respective mattress zones  131 ,  132 ,  136 , it should be understood that hoses  436 ,  438 ,  440  could be subdivided into segments as was the case with hoses  236 ,  238 ,  240 ,  244 ,  246 ,  248  of air pressure system  170 . For example, each of hoses  436 ,  438 ,  440  preferably includes first and second portions that connect together with respective single passage connectors (not shown). 
     Portion  370  of the alternative embodiment air pressure system includes a first valve  452 , a second valve  454 , a third valve  456 , and a vent valve  458  that are situated in passages  410 ,  414 ,  418 ,  422 , respectively, as shown in FIG.  10 . Valves  452 ,  454 ,  456 ,  458  are each moveable to block and unblock the flow of air through passages  410 ,  414 ,  418 ,  422 , respectively. Portion  370  of the alternative embodiment air pressure system also includes first, second, third, and vent actuators  470 ,  472 ,  474 ,  476  that are coupled mechanically to respective valves  452 ,  454 ,  456 ,  458  as shown in FIG.  10 . In addition, each actuator  470 ,  472 ,  474 ,  476  is coupled electrically to the microprocessor of the alternative embodiment air pressure system and receives control signals therefrom via respective signal lines  478 . Actuators  470 ,  472 ,  474 ,  476  and valves  452 ,  454 ,  456 ,  458  of portion  370  are substantially similar to actuators  270 ,  272 ,  274 ,  276  and valves  252 ,  254 ,  256 ,  258  of air pressure system  170 . 
     Portion  370  of the alternative embodiment air pressure system includes a single pressure sensor  442  that fluidly communicates with main passage  394  via a sensor connector hose  444  that extends from outlet  397  of manifold  376  to pressure sensor  442  as shown in FIG.  10 . Pressure sensor  442  communicates pressure data on an analog signal line  446  to the microprocessor of the alternative embodiment air pressure system through an analog-to-digital converter (not shown) that is substantially similar to the analog-to-digital converters  188  of air pressure system  170 . When compressor  174  is in the off state and when one of valves  452 ,  454 ,  456  is opened, pressure sensor  442  is in fluid communication with the mattress zone  131 ,  132 ,  136  associated with the opened valve  452 ,  454 ,  456  and is, therefore, able to sense the pressure of the mattress zone  131 ,  132 ,  136  associated with the opened valve  452 ,  454 ,  456 . 
     The microprocessor of the alternative embodiment air pressure system, hereinafter referred to as microprocessor  184  is operated by a software program that is written so that only one of valves  452 ,  454 ,  456  is opened at a time. In addition, the software program is written so that the alternative embodiment air pressure system monitors and, if necessary, adjusts the pressure in each of mattress zones  131 ,  132 ,  136  in a cyclical manner. Microprocessor  184  sends a signal on one of lines  478  to open a selected one of valves  452 ,  454 ,  456  so that pressure sensor  442  can read the pressure of a selected mattress zone  131 ,  132 ,  136 . If microprocessor  184  determines that one of mattress zones  131 ,  132 ,  136  is below the desired pressure, based on information received from pressure sensor  442 , microprocessor  184  sends a signal on the respective signal line  478  to operate the respective actuator  470 ,  472 ,  474  to step open the associated valve  452 ,  454 ,  456  while simultaneously sending a signal on control line  186  to run compressor  174  so that the respective mattress zone  131 ,  132 ,  136  is further inflated. If microprocessor  184  determines that one of mattress zones  131 ,  132 ,  136  is above the desired pressure, based on information received from pressure sensor  442 , microprocessor  184  sends a signal on the respective signal line  478  to operate the respective actuator  470 ,  472 ,  474  to step open the associated valve  452 ,  454 ,  456  and to operate actuator  476  to step open vent valve  458  while simultaneously sending a signal on control line  186  to keep the compressor  174  from running so that the respective mattress zone  131 ,  132 ,  136  is deflated. 
     FIGS. 11 a  and  11   b  show a flow chart of the steps performed by microprocessor  184  of the alternative embodiment air pressure system as the software program is executed. The first step performed by microprocessor  184  is to send signals on lines  478  to actuators  470 ,  472 ,  474 ,  476  to close all of valves  452 ,  454 ,  456 ,  458  as indicated at block  480  of FIG. 11 a . In addition, compressor  174  is off when microprocessor  184  first begins executing the software program. The next step performed by microprocessor  184  is to select the initial mattress zone to be monitored for possible pressure adjustment as indicated at block  482 . The initial zone can be any one of mattress zones  131 ,  132 ,  136 , but typically, the initial zone is programmed to be mattress zone  131 . After the initial mattress zone  131 ,  132 ,  136  has been selected, microprocessor  184  reads the weight range selected by the user with a weight range selector of the alternative embodiment air pressure system as indicated at block  484 . 
     After reading the selected weight range, microprocessor  184  determines whether the selected weight range has been changed as indicated at block  486  of FIG. 11 a.  If the selected weight range has been changed, microprocessor  184  will re-establish a pressure set point and the tolerances above and below the set point as indicated at block  488 . It should be understood that when the software program is executed the first time after the alternative embodiment air pressure system is powered up, the selected weight range will be considered to be a new weight range by microprocessor  184 . 
     After the pressure set points and tolerances are re-established at block  488  or if the selected weight range has not been changed as determined at block  486 , microprocessor  184  sends a signal on the appropriate signal line  478  to the respective actuator  470 ,  472 ,  474  to open the valve  452 ,  454 ,  456  associated with the selected mattress zone  131 ,  132 ,  136  by one step as indicated at block  490 . After the valve  452 ,  454 ,  456  associated with the selected mattress zone  131 ,  132 ,  136  is opened by one step, microprocessor  184  reads the value of the pressure in the selected mattress zone  131 ,  132 ,  136  which is communicated to microprocessor  184  from pressure sensor  442  as indicated at block  492  of FIG. 11 a. After reading the pressure of the selected mattress zone  131 ,  132 ,  136 , microprocessor  184  determines whether the selected mattress zone  131 ,  132 ,  136  needs inflation as indicated at block  494 . Microprocessor  184  makes the determination at block  494  by comparing the value of pressure read at block  492  with a low-limit pressure which is calculated based on the set point and tolerance established at block  488 . If the pressure in the selected mattress zone  131 ,  132 ,  136  is below the low-limit pressure, then the selected mattress zone  131 ,  132 ,  136  needs inflation. 
     If microprocessor  184  determines at block  492  that the selected mattress zone  131 ,  132 ,  136  needs inflation, microprocessor  184  then sends a signal on one of signal lines  478  to actuate the actuator  470 ,  472 ,  474  associated with the selected mattress zone  131 ,  132 ,  136  to open the respective valve  452 ,  454 ,  456  by one additional step as indicated at block  496 . After the valve  452 ,  454 ,  456  associated with the selected mattress zone  131 ,  132 ,  136  is opened by an additional step at block  496 , microprocessor  184  then sends a signal on line  186  to run compressor  174  as indicated at block  498 . Compressor  174  is run for a predetermined delay period, as indicated at block  500 , and then microprocessor  184  sends a signal on line  186  to stop running compressor  174  as indicated at block  510 . After compressor  174  is turned off at block  510 , microprocessor  184  takes another pressure reading from pressure sensor  442  as indicated at block  492 . 
     After microprocessor  184  takes another pressure reading at block  492 , microprocessor then determines whether further inflation of the selected mattress zone  131 ,  132 ,  136  is needed as indicated at block  494 . If inflation is still needed, microprocessor  182  then loops through blocks  496 ,  498 ,  500 ,  510  and back to block  492 . Microprocessor  184  will loop through blocks  492 ,  494 ,  496 ,  498 ,  500 ,  510  as many times as required until the selected mattress zone  131 ,  136  no longer needs inflation. Each time microprocessor  184  loops through blocks  492 ,  494 ,  496 ,  498 ,  500 ,  510 , the valve  452 ,  454 ,  456  associated with the selected mattress zone  131 ,  132 ,  136  is opened by one additional step. Thus, if the selected mattress zone  131 ,  132 ,  136  needs a small amount of inflation, the associated valve  452 ,  454 ,  456  will be stepped open by a small amount and if the selected mattress zone  131 ,  132 ,  136  needs a large amount of inflation, the associated valve  452 ,  454 ,  456  will be stepped open by a large amount. This “step-measure” process results in controlled inflation of the selected mattress zone  131 ,  132 ,  136 . 
     If microprocessor  184  determines at block  494  that the selected mattress zone  131 ,  132 ,  136  does not need inflation, microprocessor  184  then reads the value of the pressure in the selected mattress zone  131 ,  132 ,  136  which is communicated to microprocessor  184  from pressure sensor  442  as indicated at block  512  of FIG. 11 b . After reading the pressure of the selected mattress zone  131 ,  132 ,  136 , microprocessor  184  determines whether the selected mattress zone  131 ,  132 ,  136  needs deflation as indicated at block  514 . Microprocessor  184  makes the determination at block  514  by comparing the value of pressure read at block  512  with a high-limit pressure which is calculated based on the set point and tolerance established at block  488 . If the pressure in the selected mattress zone  131 ,  132 ,  136  is above the high-limit pressure, then the selected mattress zone  131 ,  132 ,  136  needs deflation. 
     If microprocessor  184  determines at block  514  that the selected mattress zone  131 ,  132 ,  136  needs deflation, microprocessor  184  then sends a signal on one of signal lines  478  to actuate the actuator  470 ,  472 ,  474  associated with the selected mattress zone  131 ,  132 ,  136  to open the respective valve  452 ,  454 ,  456  by one additional step as indicated at block  516 . After the valve  452 ,  454 ,  456  associated with the selected mattress zone  131 ,  132 ,  136  is opened by one additional step at block  516 , microprocessor  184  then sends a signal on the appropriate line  278  to vent actuator  476  to open vent valve  458  by one step as indicated at block  518 . After the valve  452 ,  454 ,  456  associated with the selected mattress zone  131 ,  132 ,  136  is stepped open and after vent valve  458  is stepped open, microprocessor  184  takes another pressure reading as indicated at block  512 . 
     After microprocessor  184  takes another pressure reading at block  512 , microprocessor  184  then determines whether further deflation is needed as indicated at block  514 . If deflation is still needed, microprocessor  184  then loops through blocks  516 ,  518  and back to block  512 . Microprocessor  184  loops through blocks  512 ,  514 ,  516 ,  518  as many times as required until the selected mattress zone  131 ,  136  no longer needs deflation. Each time microprocessor  184  loops through blocks  512 ,  514 ,  516 ,  518 , the valve  452 ,  454 ,  456  associated with the selected mattress zone  131 ,  132 ,  136  and the vent valve  458  are both opened by one additional step. Thus, if the selected mattress zone  131 ,  132 ,  136  needs a small amount of deflation, the associated valve  452 ,  454 ,  456  and vent valve  458  will both be stepped open by a small amount and, if the selected mattress zone  131 ,  132 ,  136  needs a large amount of deflation, the associated valve  452 ,  454 ,  456  and vent valve  458  will both be stepped open by a large amount. This “step measure” process results in controlled deflation of the selected mattress zone  131 ,  132 ,  136 . 
     If microprocessor  184  determines at block  514  that the selected mattress zone  131 ,  132 ,  136  does not need deflation, microprocessor  184  then determines if vent valve  458  is open as indicated at block  520 . If vent valve  458  is open, which will be the case if microprocessor  184  has looped through blocks  516 ,  518  one or more times, microprocessor  184  sends a signal on the appropriate signal line  278  to the actuator  476  to close vent valve  458  at a fast rate as indicated at block  522 . 
     After vent valve  458  is closed at a fast rate at block  522  or if vent valve  458  is not open, as determined at block  520 , microprocessor  184  sends a signal on one of signal lines  478  to the appropriate actuator  470 ,  472 ,  474  to close the valve  452 ,  454 ,  456  associated with the selected mattress zone  131 ,  132 ,  136  at a fast rate as indicated at block  524 . After the valve  452 ,  454 ,  456  associated with the selected mattress zone  131 ,  132 ,  136  is closed at a fast rate, microprocessor  184  then selects the next mattress zone  131 ,  132 ,  136  as indicated at block  526 . The next mattress zone  131 ,  132 ,  136  selected at block  526  can be either of the two mattress zones  131 ,  132 ,  136  that were not selected previously. For example, if mattress zone  131  was the mattress zone selected initially, then either of mattress zones  132 ,  136  can be the next selected mattress zone. After the next mattress zone  131 ,  132 ,  136  is selected, microprocessor  184  loops through the software program again, beginning with block  484  of FIG. 11 a.    
     Although air pressure system  170  and the alternative embodiment air pressure system including portion  370  have been described above as being used with core structure  44  of mattress structure  30  to control the pressure in air bladders  52 , it is within the scope of the invention as presently perceived for air pressure system  170  and the alternative embodiment air pressure system including portion  370  to be used with other types of core structures. For example, air pressure system  170  can be used with a first alternative embodiment core structure  544  which is shown in FIGS. 12 and 13. 
     Core structure  544  includes a plurality of lower support elements  550  and a plurality of upper support elements  552  that are supported by lower support elements  550  as shown best in FIG.  13 . Lower support elements  550  are large foam blocks and upper support elements  552  are somewhat cylindrically-shaped air bladders. Hereinafter, the lower support elements  550  are referred to as foam blocks  550  and the upper support elements  552  are referred to as air bladders  552 . Core structure  544  further includes a layer of material  554  that underlies foam blocks  550 . Core structure  544  includes a set of straps that are used to secure air bladders  552  and foam blocks  550  to layer of material  554 . Securing foam blocks  550  and air bladders  552  to layer of material  554  allows core structure  544  to be moved as a single unit with foam blocks  550  and air bladders  552  remaining held in the proper positions relative to one another and relative to layer of material  554 . Straps  542  may include hook and loop fasteners (not shown) that attach to hook and loop fasteners (not shown) secured to layer of material  554  or straps  542  may include free ends (not shown) with other types of connectors, such as buckles or snaps that allow the free ends of straps  542  to connect together. 
     Air bladders  552  of core structure  544  include a pair of back section header bladders  570 , a pair of seat section header bladders  572 , a pair of thigh section header bladders  574 , and a pair of foot section header bladders  576  as shown in FIGS. 12 and 13. The rest of the plurality of air bladders  552  extend transversely between respective header bladders  570 ,  572 ,  574 ,  576  and are arranged in side-by-side relation between ends  533  of core structure  544 . Each of the transversely extending air bladders  552  is attached to respective header bladders  570 ,  572 ,  574 ,  576  in a manner substantially similar to the manner in which transversely extending bladders  52  of core structure  44  attach to header bladders  70 ,  72 ,  74 ,  76  as described above with reference to FIG.  5 . 
     Core structure  544  may be included in a mattress structure used with a bed or table including an articulating deck (not shown) having pivotable head, seat, thigh, and leg sections. Header bladders  570 ,  572 ,  574 ,  576  and the transversely extending air bladders  552  associated therewith are sized so as to be supported by the respective deck sections of the articulating deck with which core structure  544  is used. Thus, back section header bladders  570  and the associated transversely extending air bladders  552  provide core structure  544  with a back zone  530 , shown in FIG. 13, which is supported by the underlying foam block  550  and the back section of the articulating deck. Similarly, seat, thigh, and foot header bladders  572 ,  574 ,  576  and the associated transversely extending air bladders  552  provide core structure  544  with seat, thigh, and foot zones  532 ,  534 ,  536 , respectively, which are supported by respective underlying foam blocks  550  and the seat, thigh, and foot sections, respectively, of the articulating deck. 
     The firmness and support characteristics provided by each foam block  550  depend in part upon the indention load deflection (ILD) of the foam from which each foam block is made. The ILD is a well-known industry-accepted index indicating the “firmness” of material as was described previously with reference to mattress structure  30 . It is within the scope of the invention as presently perceived to provide core structure  544  in which each foam block  550  has the same ILD or to provide core structure  544  in which the ILD of at least one foam block  550  is different from the ILD of at least one other foam block  550 . In addition, it is within the scope of the present invention for each foam block  550  to be comprised of portions having varying ILD&#39;s. For example, core structure  544  may be provided with foam blocks  550  each having firm end portions  538  with an ILD of about forty-four and a soft middle portion  540  with an ILD of about seventeen as shown in FIG.  12 . Firm end portions  538  are sized so as to support the respective overlying header bladders  570 ,  572 ,  574 ,  576  to provide core structure  544  with more firmness along sides  531  thereof. 
     Core structure  544  includes a plurality of air tubes  556  that are routed to each of header bladders  570 ,  572 ,  574 ,  576  as shown best in FIG.  12 . Tubes  556  include a first zone tube set  558 , a second zone tube set  560 , and a third zone tube set  562 . First zone tube set  558  includes a pressure tube  564  that fluidly couples to one of the back section header bladders  570  and to one of the thigh section header bladders  574 . First zone tube set  558  also includes a sensor tube  566  that fluidly couples to the other of the back section header bladders  570 . Pressure tube  564  and sensor tube  566  each couple to a single, dual-passage tube connector  568  shown in FIG.  13 . Second zone tube set  560  includes a pressure tube  578  that fluidly couples to one of the seat section header bladders  572  and a sensor tube  580  that fluidly couples to the other of the seat section header bladders  572 . Pressure tube  578  and sensor tube  580  each couple to a single, dual-passage tube connector  582 . Third zone tube set  562  includes a pressure tube  584  that fluidly couples to one of the foot section header bladders  576  and a sensor tube  586  that fluidly couples to the other of the foot section header bladders  576 . Pressure tube  584  and sensor tube  586  each couple to a single, dual-passage tube connector  588 . Foam blocks  550  are each formed with passages and slits that allow respective air tubes  556  to be routed therethrough to connect with respective header bladders  570 ,  572 ,  574 ,  576 . Routing air tubes  556  through foam blocks  550  in this manner helps to secure air bladders  552  in the proper position relative to foam blocks  550 . 
     Although air pressure system  170  includes manifold  176  with four valves  252 ,  254 ,  256 ,  258  coupled thereto and although portion  370  of the alternative embodiment air pressure system includes manifold  376  with four valves  452 ,  454 ,  456 ,  458  coupled thereto, it is with the scope of the invention as presently perceived to provide an air pressure system with more or less valves and corresponding passages in the respective manifold so as to allow the pressures in the air bladders of more or less mattress zones, respectively, to be controlled. For example, an air pressure system having a manifold with more valves and passages than manifolds  176 ,  376  can be used with a second alternative embodiment core structure  644  shown in FIG.  14 . 
     Core structure  644  includes a plurality of lower support elements  650  and a plurality of upper support elements  652  that are supported by lower support elements  650 . Lower support elements  650  are foam blocks and upper support elements  652  are somewhat cylindrically-shaped air bladders. Hereinafter, the lower support elements  650  are referred to as foam blocks  650  and the upper support elements  652  are referred to as air bladders  652 . Core structure  644  further includes a layer of material  654  that underlies foam blocks  650 . Core structure  644  includes a plurality of sleeves  610  that are anchored to layer of material  654  and that are configured to receive foam blocks  650  in a manner substantially similar to the manner in which sleeves  100  are configured to receive foam blocks  50  as described above with reference to core structure  44 . In addition, core structure  644  includes a plurality of tethers  612  that connect transversely extending air bladders  652  to layer of material  654  in a manner substantially similar to the manner in which tethers  128  connect air bladders  52  to layer of material  54  as also described above with reference to core structure  44 . 
     Air bladders  652  of core structure  644  include a pair of back section header bladders  670 , a pair of seat section header bladders  672 , a pair of thigh section header bladders  674 , and a pair of foot section header bladders  676  as shown in FIG.  14 . The rest of the plurality of air bladders  652  extend transversely between respective header bladders  670 ,  672 ,  674 ,  676  and are arranged in side-by-side relation between ends  633  of core structure  644 . The transversely extending air bladders  652  positioned to lie between header bladders  670 ,  672 ,  674  are attached thereto in a manner substantially similar to the manner in which transversely extending bladders  52  of core structure  44  attach to header bladders  70 ,  72 ,  74 ,  76  as described above with reference to FIG.  5 . The manner in which the transversely extending air bladders  652  positioned to lie between header bladders  676  are attached thereto is described below in more detail. 
     Core structure  644  may be included in a mattress structure used with a bed or table including an articulating deck (not shown) having pivotable head, seat, thigh, and leg sections. Header bladders  670 ,  672 ,  674 ,  676  and the transversely extending air bladders  652  associated therewith are sized so as to be supported by the respective deck sections of the articulating deck with which core structure  644  is used. Thus, back section header bladders  670  and the associated transversely extending air bladders  652  provide core structure  644  with a back zone  630 , shown in FIG. 14, which is supported by the underlying foam block  650  and the back section of the articulating deck. Similarly, seat, thigh, and foot header bladders  672 ,  674 ,  676  and the associated transversely extending air bladders  652  provide core structure  644  with seat, thigh, and foot zones  632 ,  634 ,  636 , respectively, which are supported by respective underlying foam blocks  650  and the seat, thigh, and foot sections, respectively, of the articulating deck. 
     The firmness and support characteristics provided by each foam block  650  depend in part upon the indention load deflection (ILD) of the foam from which each foam block is made. The ILD is a well-known industry-accepted index as previously described. It is within the scope of the invention as presently perceived to provide core structure  644  in which each foam block  650  has the same ILD or to provide core structure  644  in which the ILD of at least one foam block  650  is different from the ILD of at least one other foam block  650 . In addition, it is within the scope of the present invention for each foam block  650  to be comprised of portions having varying ILD&#39;s. For example, core structure  644  may be provided with foam blocks  650  each having firm end portions  638  with an ILD of about forty-four and a soft middle portion  640  with an ILD of about seventeen as shown in FIG.  14 . Firm end portions  638  are sized so as to support the respective overlying header bladders  670 ,  672 ,  674 ,  676  to provide core structure  644  with more firmness along sides  631  thereof. 
     Core structure  644  includes a plurality of air tubes  656  that are routed to each of header bladders  670 ,  672 ,  674 ,  676  as shown in FIG.  14 . Core structure  644  also includes a plurality of heel-relief tubes  658  that are routed to designated transversely extending air bladders  652  associated with foot zone  636 . Tubes  656  include a first zone tube set  660 , a second zone tube set  662 , and a third zone tube set  664 . Core structure  644  includes a tube storage housing  700  having a compartment (not shown) in which end portions (not shown) of tubes  656 ,  658  are stored after tubes  656 ,  658  are coiled up when disconnected from the respective air pressure system that controls the air pressure of air bladders  652 . Layer of material  654  is formed to include a plurality of small slits  710  which define a plurality of pass-through bands  712 . Tubes  656 ,  658  are routed through slits  710  so that pass-through bands  712  secure tubes  656 ,  658  to layer of material  654  in the desired routing pattern as shown in FIG.  14 . 
     First zone tube set  660  includes a pressure tube  678  that fluidly couples to one of the back section header bladders  670  and to one of the thigh section header bladders  674 . First zone tube set  660  also includes a sensor tube  680  that fluidly couples to the other of the back section header bladders  670 . Pressure tube  678  and sensor tube  680  each couple to a single, dual-passage tube connector (not shown). Second zone tube set  662  includes a pressure tube  682  that fluidly couples to one of the seat section header bladders  672  and a sensor tube  684  that fluidly couples to the other of the seat section header bladders  672 . Pressure tube  682  and sensor tube  684  each couple to a single, dual-passage tube connector (not shown). Third zone tube set  664  includes a pressure tube  686  that fluidly couples to one of the foot section header bladders  676  and a sensor tube  688  that fluidly couples to the other of the foot section header bladders  676 . Pressure tube  686  and sensor tube  688  each couple to a single, dual-passage tube connector (not shown). 
     Both header bladders  676  of foot zone  636  are attached to the transversely extending air bladder  652  which is adjacent to thigh section  634 , for example, by RF welding as shown in FIG. 14. A fluid port  690  is formed at the area of attachment so that header bladders  676  are each fluidly coupled to the transversely extending air bladder  652  adjacent to thigh zone  634 . The other transversely extending air bladders  652  of foot zone  636  are grouped into pairs and the air bladders  652  of each pair are fluidly coupled together by respective connector tubes  692 . Each connector tube  692  is positioned to lie in an interior region  694  of the respective header bladder  676  as shown in FIG.  14 . In addition, each connector tube  692  is configured to isolate the respective grouped pairs of air bladders  652  from the pressure established in header bladders  676 . 
     Heel-relief tubes  658  include a short-heel tube  666  that fluidly couples to the grouped pair of air bladders  652  positioned closest to thigh zone  634 , a tall-heel tube that fluidly couples to the grouped pair of air bladders  652  positioned at end  633  of core structure  644 , and a medium-heel tube  667  that fluidly couples to the grouped pair of air bladders  652  positioned between the grouped pairs of air bladders  652  associated with tubes  666 ,  668 . The air pressure in each pair of the three grouped pairs of air bladders  652  between header bladders  676  is controlled separately from the air pressure in each of the other grouped pairs of air bladders  652 . Thus, core structure  644  is provided with a short heel-relief zone  694 , a medium heel-relief zone  696 , and a tall heel-relief zone  698  as shown in FIG.  14 . 
     Air tubes  660 ,  662 ,  664  are each “dual tube” tube sets  660 ,  662 ,  664  and heel relief tubes  658  are each “single tube” tubes  666 ,  667 ,  668 . Thus, an air pressure system having a portion that is like air pressure system  170  and having a portion that is like the alternative embodiment air pressure system including portion  370  may be used to control the pressure in air bladders  652  of core structure  644 . The air pressure system used to control the pressure in air bladders  652  of core structure  644  should be configured so that the air bladders  652  of one of heel-relief zones  694 ,  696 ,  698  can be deflated while the air bladders  652  of the other heel-relief zones  694 ,  696 ,  698  remain inflated. In use, the heel-relief zone  694 ,  696 ,  698  to be deflated is the one that underlies the heels of a patient supported by core structure  644 . Deflating the heel-relief zone  694 ,  696 ,  698  that underlies the heels of the patient minimizes or eliminates the interface pressure between the heels of the patient and core structure  644 . 
     The air pressure system associated with core structure  644  includes controls such as, for example, knobs or switches (not shown). Each of the knobs or switches is associated with a respective one of heel-relief zones  694 ,  696 ,  698  and is movable from a first position in which the associated heel-relief zone  694 ,  696 ,  698  is inflated to a normal operating pressure and a second position in which the associated heel-relief zone  694 ,  696 ,  698  is either maintained at a pressure below the normal operating pressure or vented to the atmosphere. It should be understood that other types of controls can be used in lieu of the knobs or switches and that such controls can be accessible on panels of a housing, such as panels  296 ,  298 ,  300  of housing  172  of air pressure system  170 . 
     Although the above-described core structures  44 ,  544 ,  644 ,  844  each include air bladders  52 ,  552 ,  652 ,  52  respectively, that are supported by foam blocks  50 ,  550 ,  650 ,  50  respectively, it is within the scope of the invention as presently perceived for one or more portions of a core structure to include a lower layer of air bladders that support an upper layer of air bladders. For example, a fourth alternative embodiment core structure  744  having such an arrangement is shown in FIG.  15 . 
     Core structure  744  includes a plurality of lower support elements  750  and a plurality of upper support elements  752  that are supported by lower support elements  750 . Some of lower support elements  750  are foam blocks, hereinafter referred to as foam blocks  750 , and some of lower support elements  750  are air bladders, hereinafter referred to as air bladders  751 . All of the upper support elements  752  are somewhat cylindrically-shaped air bladders, hereinafter referred to as air bladders  752 . Core structure  744  further includes a layer of material  754  that underlies foam blocks  750  and air bladders  751 . Core structure  744  includes a plurality of sleeves  720  that are anchored to layer of material  754  and that are configured to receive foam blocks  750  in a manner substantially similar to the manner in which sleeves  100  are configured to receive foam blocks  50  as described above with reference to core structure  44 . In addition, core structure  744  includes a plurality of tethers  722  that connect a majority of the transversely extending air bladders  752  to layer of material  754  in a manner substantially similar to the manner in which tethers  128  connect air bladders  52  to layer of material  54  as also described above with reference to core structure  44 . Air bladders  751  are attached to layer of material  754  and air bladders  752  are attached to air bladders  751 , for example, by RF welding. 
     Air bladders  752  of core structure  744  include a pair of back section header bladders  770 , a pair of seat section header bladders  772 , a pair of thigh section header bladders  774 , and a pair of upper foot section header bladders  776 . The rest of the plurality of air bladders  752  extend transversely between respective header bladders  770 ,  772 ,  774 ,  776  and are arranged in side-by-side relation between ends  733  of core structure  744 . Air bladders  751  of core structure  744  include a pair of lower foot section header bladders  777  positioned to lie underneath header bladders  776  as shown in FIG.  15 . The rest of air bladders  751  are arranged in side-by-side relation between header bladders  777 . The transversely extending air bladders  751 ,  752  positioned to lie between header bladders  770 ,  772 ,  774 ,  776 ,  777  are attached thereto in a manner substantially similar to the manner in which transversely extending bladders  52  of core structure  44  attach to header bladders  70 ,  72 ,  74 ,  76  as described above with reference to FIG.  5 . 
     Core structure  744  may be included in a mattress structure used with a bed or table including an articulating deck (not shown) having pivotable head, seat, thigh, and leg sections. Header bladders  770 ,  772 ,  774 ,  776 ,  777  and the transversely extending air bladders  751 ,  752  associated therewith are sized so as to be supported by the respective deck sections of the articulating deck with which core structure  744  is used. Thus, back section header bladders  770  and the associated transversely extending air bladders  752  provide core structure  744  with a back zone  730 , shown in FIG. 15, which is supported by the underlying foam blocks  750  and the back section of the articulating deck. Similarly, seat and thigh section header bladders  772 ,  774  and the associated transversely extending air bladders  752  provide core structure  744  with seat and thigh zones  732 ,  734  respectively, which are supported by respective underlying foam blocks  750  and the seat and thigh sections, respectively, of the articulating deck. In addition, upper foot section header bladders  776  and the associated transversely extending air bladders  752  provide core structure  744  with a foot zone  736  which is supported by underlying air bladders  751  and the foot section of the articulating deck. 
     The firmness and support characteristics provided by each foam block  750  depend in part upon the indention load deflection (ILD) of the foam from which each foam block is made as previously described. It is within the scope of the invention as presently perceived to provide core structure  744  in which each foam block  750  has the same ILD or to provide core structure  744  in which the ILD of at least one foam block  750  is different from the ILD of at least one other foam block  750 . In addition, it is within the scope of the present invention for each foam block  750  to be comprised of portions having varying ILD&#39;s. 
     Core structure  744  includes a plurality of air tubes  756  that are routed to each of header bladders  770 ,  772 ,  774 ,  777 . Tubes  756  include a first zone tube set  760 , a second zone tube set  762 , and a third zone tube set  764 . First zone tube set  760  includes a pressure tube (not shown) that fluidly couples to one of the back section header bladders  770  and to one of the thigh section header bladders  774 . First zone tube set  760  also includes a sensor tube (not shown) that fluidly couples to the other of the back section header bladders  770 . The pressure tube and the sensor tube of first zone tube set  760  each couple to a single, dual-passage tube connector  778 . Second zone tube set  762  includes a pressure tube (not shown) that fluidly couples to one of the seat section header bladders  772  and a sensor tube (not shown) that fluidly couples to the other of the seat section header bladders  772 . The pressure tube and the sensor tube of second zone tube set  762  each couple to a single, dual-passage tube connector  780 . Third zone tube set  764  includes a pressure tube (not shown) that fluidly couples to one of the lower foot section header bladders  777  and a sensor tube (not shown) that fluidly couples to the other of the lower foot section header bladders  777 . The pressure tube and the sensor tube of third zone tube set  764  each couple to a single, dual-passage tube connector  782 . 
     Air bladders  751 ,  752  of foot section  736  are fluidly coupled together so that substantially the same air pressure is established in each of air bladders  751 ,  752  of foot section  736 . Air bladders  751 ,  752  of foot section  736  can be deflated by varying amounts to provide core structure  744  with a varying amount of heel relief. When air bladders  751 ,  752  of foot section  736  are deflated, the interface pressure between the heels of a patient support and core structure  744  is reduced. In illustrated embodiments, the air pressure system coupled to core structure  744  includes a control, such as a knob, a switch, or a button, that is engageable to operate the air pressure system in a “normal” mode having foot section  736  inflated to a normal operating pressure and a “heel-relief” mode in which the pressure in air bladders  751 ,  752  of foot zone  736  is maintained below the normal operating pressure of foot zone  736 . Deflating foot zone  736  below the normal operating pressure minimizes or eliminates the interface pressure between the heels of the patient and core structure  744 . 
     The transversely extending air bladder  752  of thigh zone  734  that is closest to foot zone  736  is not tethered to layer of material  754  and the foam block  750  adjacent to foot zone  736  is slightly larger than the other foam blocks  750  so that the air bladder  752  of thigh zone  734  closest to foot zone  736  is supported thereon as shown in FIG.  15 . In addition, the foam block at end  733  of core structure  744  beneath back zone  730  is slightly smaller than the other foam blocks  750  and includes and inclined portion  740  that helps to prevent air bladders  752  from shifting beyond end  733  of the underlying foam blocks. 
     Air pressure systems associated with any of the above-described core structures  44 ,  544 ,  644 ,  744 , may include a “max inflate” control, such as a knob, a switch, or a button. The max inflate control is engageable to cause all of the air bladders of the associated core structure  44 ,  544 ,  644 ,  744  to inflate to a maximum pressure, such as, for example, twenty-six inches of water. When the max inflate control is actuated, the control algorithm of the air pressure system is executed in the same manner as when the max inflate control is not actuated, but the pressure set point in each mattress zone of the associated core structure  44 ,  544 ,  644 ,  744  is set to a predetermined maximum level. Inflating the air bladders of each mattress zone to a maximum level increases the firmness of the patient-support surface which is desirable, for example, during transfer of the patient from the mattress to another patient-support device. 
     FIGS. 16,  17   a ,  17   b ,  18   a , and  18   b  show flow charts of one possible software program that microprocessor  184  of an air pressure system similar to air pressure system  170 , but including a max inflate button, may execute to control the inflation and deflation of air bladders of an associated core structure, such as core structure  44 . FIG. 16 shows a flow chart of a main program  790 . Main program  790  begins at block  792  when the associated air pressure system, hereinafter referred to as system  170 , is powered on initially or is reset at any time during execution. After system  170  is powered on or reset, microprocessor  184  sends a signal to ensure that the associated compressor is turned off as indicated at block  794  of FIG.  16 . Microprocessor  184  then resets an alarm system timer as indicated at block  796 . 
     An alarm (not shown) is controlled by the alarm system timer, which is reset each time a complete pass is made through main program  790 . If system  170  is unable to make a complete pass through main program  790  in a predetermined time period, such as, for example, fifteen minutes, a soft reset is performed by the software. System  170  is then given an additional period of time, such as, for example, fifteen minutes, to make a complete pass through main program  170 . If system  170  is still unable to make a complete pass through main program  170 , all zone valves are opened, the compressor is turned of; audible and visual alarms are activated, and system operation is halted. 
     After microprocessor  184  resets the alarm system timer at block  796  of FIG. 16, microprocessor  184  restores the last patient level settings as indicated at block  798  and then calculates the zone tolerance limits as indicated at block  800 . Next, microprocessor  184  sends appropriate signals to close all valves as indicated at block  810  of FIG.  16 . After all valves are closed by microprocessor  184 , an inflation subroutine is executed by microprocessor  184  as indicated at block  812  and then a deflation subroutine is executed as indicated at block  814 . Inflation subroutine  812 , which is discussed in detail below with reference to FIGS. 17 a  and  17   b,  causes the air bladders of the associated core structure to be inflated to the proper levels and the deflation subroutine  814 , which is discussed in detail below with reference to FIGS. 18 a  and  18   b , causes the air bladders of the associated core structure to be deflated to the proper levels. After each of subroutines  812 ,  814  is executed, microprocessor  184  resets the alarm system timer as indicated at block  816 . 
     After microprocessor  184  resets the alarm system timer at block  816 , main program  790  loops through blocks  812 ,  814  again to run the inflation and deflation subroutines again. During normal operation, microprocessor  184  will execute main program  790  so as to loop continuously through blocks  812 ,  814 ,  816  until system  170  is powered down or until an interrupt occurs. One interrupt that may occur during execution of main program  790  is a patient weight range interrupt as indicated at block  818 . A patient weight range interrupt occurs when a caregiver inputs new data with an associated weight range selector, such as weight range selector  284 . After interrupt  818  occurs, the air bladder pressures and tolerances are recalculated and main program  790  then resumes normal execution. Another interrupt that may occur during normal execution of main program  790  is a max inflate interrupt as indicated at block  820 . A max inflate interrupt occurs when the caregiver presses the max inflate button to fully inflate the air bladders as previously described. 
     Although each of interrupts  818 ,  820  is indicated in FIG. 16 by phantom arrows that connect to the remainder of main program  790  between block  792  and block  794 , it should be understood that interrupts  818 ,  820  may occur at any point during the execution of main program  790 . After the execution of an associated interrupt subroutine (not shown), main program  790  resumes normal execution at the point where the interrupt  818 ,  820  occurred. 
     During execution of inflation subroutine  812 , microprocessor  184  first retriggers a watchdog timer as indicated at block  822  of FIG. 17 a . The watchdog timer provides a hardware reset to system  170  causing main program  170  to jump to block  792  if the watchdog timer is not retriggered by the software within a predetermined time period, such as, for example, six-hundred milliseconds. 
     After the watchdog timer is retriggered at block  822 , microprocessor  184  reads the pressure sensor associated with the first mattress zone, thereby measuring the pressure in the first mattress zone as indicated at block  824 . Microprocessor  184  then determines at block  826  whether the pressure in the first mattress zone is below the lower limit. If the first mattress zone is not below the lower limit, microprocessor  184  sends a signal to close the valve associated with the first mattress zone as indicated at block  828  of FIG. 17 a . If the first mattress zone is below the lower limit, microprocessor  184  first sends a signal to close the vent valve as indicated at block  830 , then sends a signal to open the valve associated with the first mattress zone as indicated at block  832 , and next sends a signal to turn the compressor on as indicated at block  834  so that the compressor operates to inflate the first mattress zone. 
     After execution of the program steps associated with either block  828  or block  834 , microprocessor  184  reads the pressure sensor associated with the second mattress zone, thereby measuring the pressure in the second mattress zone as indicated at block  836 . Microprocessor  184  then determines at block  838  whether the pressure in the second mattress zone is below the lower limit. If the second mattress zone is not below the lower limit, microprocessor  184  sends a signal to close the valve associated with the second mattress zone as indicated at block  840  of FIG. 17 a . If the second mattress zone is below the lower limit, microprocessor  184  first sends a signal to close the vent valve as indicated at block  842 , then sends a signal to open the valve associated with the second mattress zone as indicated at block  844 , and next sends a signal to turn the compressor on as indicated at block  846  so that the compressor operates to inflate the second mattress zone. 
     After execution of the program steps associated with either block  840  or block  846 , microprocessor  184  reads the pressure sensor associated with the third mattress zone, thereby measuring the pressure in the third mattress zone as indicated at block  848  of FIG. 17 b . Microprocessor  184  then determines at block  850  whether the pressure in the third mattress zone is below the lower limit. If the third mattress zone is not below the lower limit, microprocessor  184  sends a signal to close the valve associated with the third mattress zone as indicated at block  852  of FIG. 17 b . If the third mattress zone is below the lower limit, microprocessor  184  first sends a signal to close the vent valve as indicated at block  854 , then sends a signal to open the valve associated with the third mattress zone as indicated at block  856 , and next sends a signal to turn the compressor on as indicated at block  858  so that the compressor operates to inflate the second mattress zone. 
     After execution of the program steps associated with either block  852  or block  858 , microprocessor  184  checks to see if the valves associated with respective first, second, and third mattress zones are closed as indicated at blocks  860 ,  862 ,  864 , respectively, as shown in FIG. 17 b . If any of the valves associated with the first, second, and third mattress zones are not closed, which means that at least one of the mattress zones required inflation during the execution of inflation subroutine  812 , microprocessor returns to block  822  of FIG. 17 a  and loops back through inflation subroutine  812  again. If all of the valves associated with the first, second, and third mattress zones are closed, which means that none of the mattress zones require inflation during the execution of inflation subroutine  812 , microprocessor  184  sends a signal to turn the compressor off as indicated at block  866  and then returns to main program  790  as indicated at block  868 . 
     During execution of deflation subroutine  814 , microprocessor  184  first retriggers the watchdog timer as indicated at block  870  of FIG. 18 a . After the watchdog timer is retriggered at block  870 , microprocessor  184  reads the pressure sensor associated with the first mattress zone, thereby measuring the pressure in the first mattress zone as indicated at block  872 . Microprocessor  184  then determines at block  874  whether the pressure in the first mattress zone is over the upper limit. If the first mattress zone is not above the upper limit, microprocessor  184  sends a signal to close the valve associated with the first mattress zone as indicated at block  876  of FIG. 18 a . If the first mattress zone is above the upper limit, microprocessor  184  first sends a signal to open the valve associated with the first mattress zone as indicated at block  878  and then sends a signal to open the vent valve as indicated at block  880  so that air in the first mattress zone bleeds to the atmosphere. 
     After execution of the program steps associated with either block  876  or block  880 , microprocessor  184  reads the pressure sensor associated with the second mattress zone, thereby measuring the pressure in the second mattress zone as indicated at block  882 . Microprocessor  184  then determines at block  884  whether the pressure in the second mattress zone is above the upper limit. If the second mattress zone is not above the upper limit, microprocessor  184  sends a signal to close the valve associated with the second mattress zone as indicated at block  886  of FIG. 18 a . If the second mattress zone is above the upper limit, microprocessor  184  first sends a signal to open the valve associated with the second mattress zone as indicated at block  888  and then sends a signal to open the vent valve as indicated at block  890  so that air in the second mattress zone bleeds to the atmosphere. 
     After execution of the program steps associated with either block  886  or block  890 , microprocessor  184  reads the pressure sensor associated with the third mattress zone, thereby measuring the pressure in the third mattress zone as indicated at block  892  of FIG. 18 b . Microprocessor  184  then determines at block  894  whether the pressure in the third mattress zone is above the upper limit. If the third mattress zone is not above the upper limit, microprocessor  184  sends a signal to close the valve associated with the third mattress zone as indicated at block  896  of FIG. 18 b . If the third mattress zone is above the upper limit, microprocessor  184  first sends a signal to open the valve associated with the third mattress zone as indicated at block  898  and then sends a signal to open the vent valve as indicated at block  900  so that air in the third mattress zone bleeds to the atmosphere. 
     After execution of the program steps associated with either block  896  or block  900 , microprocessor  184  checks to see if the valves associated with respective first, second, and third mattress zones are closed as indicated at blocks  910 ,  912 ,  914 , respectively, as shown in FIG. 18 b . If any of the valves associated with the first, second, and third mattress zones are not closed, which means that at least one of the mattress zones required deflation during the execution of deflation subroutine  814 , microprocessor returns to block  870  of FIG. 18 a  and loops back through deflation subroutine  814  again. If all of the valves associated with the first, second, and third mattress zones are closed, which means that none of the mattress zones require deflation during the execution of deflation subroutine  814 , microprocessor  184  returns to main program  790  as indicated at block  916 . 
     Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.