GB2090734A - Improvements in alternating pressure beds - Google Patents

Abstract

An alternating pressure bed is composed of an envelope in which are formed pockets extending right across the working surface of the bed. A separate inflatable liner is a snug fit in each pocket and can be individually replaced at will. Alternate liners are cyclically inflated in opposite phase by link pipes, each of which is rendered captive across the mouth of the intervening pocket by being threaded through either a non-inflatable lug constituting an extension of the blank end of each liner, or a duct formed along the margin of the envelope itself. The link pipes thus perform the dual function of inflating the liners and of tethering them to the envelope against migration from the pockets. The boundaries of the pockets and of the liners may be sinuous to increase the captivity of the liners and to reduce "bottoming" during use of the bed. Selected linears have an insert layer of a highly heat-absorbent substance held snugly against the top wall. Such liners can be substituted for ordinary linears to support parts of a patient's body such as heels, hips, shoulders, etc. which are particularly susceptible to the development of bed sores in order to lower skin temperature at those parts. <IMAGE>

Description

SPECIFICATION Improvements in alternating pressure beds This invention relates to alternating pressure beds commonly known as ripple beds (which term includes both mattresses and cushions) - which consist of a relatively large number of alternately inflatable and deflatable cells extending between opposite boundaries of the working surface of a supplementary "mattress" to be laid over the normal bed mattress or other suitable support. Each cell is rhythmically alternately inflated and deflated, in antiphase with its neighbour on each side, between set values of high and low pressure through a respective one of two pipe systems each of which links one set of alternate cells to one of two ports of an inflate/deflate pump in which the fluid pressure varies cyclically in phase opposition to that in the other port.When a patient rests on such a mattress the physical support for the body changes location rhythmically, giving the impression of wave action albeit with a periodicity of the order of 30 to 40 minutes - and plays a major role in the prevention of bed sores which are known to be encouraged by continuous pressure on a localised area of the body such as occurs when a patient lies on a normal inert mattress.

'Ripple bed' is a Registered Trade Mark.

In one known form of ripple bed the working surface consists of a series of parallel, substantially identical, sealed bags or cells formed by transversely seaming at regular intervals two PVC or like sheets of a length appropriate to the size of mattress or cushion required. Alternate cells are pneumatically (or hydraulically) linked by respective common pipe systems in two interleaved sets, and cells of each set are coupled in parallel to the respective outlet port of a pump which rhythmically reverses the fluid flow in the ports alternately from high to low pressure in antiphase.

A major drawback of such a construction is that if a cell is punctured, or develops a defect, which causes a significant pressure fluid leak, the whole mattress has to be scrapped because of the difficulty of effecting a reliable repair. The minute "pinholes" which are prone to form at random in PVC sheeting are tolerable in a pneumatic inflation system because of the dynamic nature of the inflation cycle.

The pump can automatically make up small losses of air, but larger leaks due, for example, to double penetration by a safety pin, cannot be automatically compensated.

In another prior construction, each cell is separate and made in the form of a centrally "waisted" or dumb-bellshaped inflatable bag of a length equal to the width of the mattress and which is inserted through a loop on a plane carrier or backing sheet so as to be held relatively tightly at the "waist". The cells are pneumatically coupled in parallel, in two groups or sets of alternate neighbours, to the ports of a pump for cyclic inflation and deflation in rhythmically alternating sequence. In an alternative construction, the separate cells are each individually attached at each end to a backing sheet by snap fasteners such as press-studs. The cells in this alternative construction can be cylindrical.

An advantage of each of the above constructions is that each cell can be separately replaced if punctured. But in the "waisted" design each cell exhibits a lack of positional restraint during handling, due to the single central anchorage of each cell by its waist. This makes the mattress unwieldy to move, due to the disorientation of the cells when the carrier or backing sheet is picked up. In the alternative design, cell orientation is more positive.Both designs, however, suffer from the further defect that they are prone to "bottoming" - i.e. the fluctuating pressure cushion support for parts of the body such as hips or shoulders can be easily displaced - due to the facility with which adjacent cells can be pushed apart; the "waisted" design already presents a positive gap between each pair of cells at their waist and the end-located cell design leaves the intermediate portions of a cell laterally unrestrained.

The present invention aims at minimising all the aforesaid defects. First, each alternately inflatable and deflatable cell is formed as a separate liner which can be removed and replaced individually when punctured or otherwise rendered unusable.

Second, the liners are housed in full-length open pockets formed in a 2-ply main carrier or envelope of sheet material of a size to fit the normal bed, with provision for releasably securing at least its ends - as by "tucking in" plain sheet extensions beneath an undermattress, or by a system of lacing through eyeiets along one or more edges of the envelope, or otherwise. Over the working surface part of the carrier or envelope the two plies are seamed together at regular intervals to form transverse pockets each open, at least one end, and into each of which can be inserted one individual liner which, when inflated, is a snug fit within the pocket. One or each of the liner protrudes from the respective open end of the pocket.

Each liner is formed at one end with the necessary pressure fluid - usually air - connections to a pipe system linking it to its alternate or next-but-one neighbours (or, in the case of the end liner of a set, to one alternate-neighbour in one direction and, in the other, to either the pump or to a blanking plug or equivalent fluid-tight closure). The other end of the liner is seamed or blanked off in a manner which allows it to be inflated and deflated like a balloon by way of the aforesaid end connections.

An obvious problem arises in the prevention of endwise migration of each liner within its pocket as a result of the dynamic motion of the mattress and of the body of a patient lying thereon. Ease of interchangeability of liners requires that the number of separate operations involved in each change to be kept to a minimum. It is necessary that, on insertion of a liner into its pocket, a releasable connection to its link pipe system must be made; and on removal of the liner from its pocket, these connections must be broken. The link pipes therefore remain with, and effectively constitute a permanent part of, the main carrier or envelope of the mattress, and can be used to perform the dual function of pneumatic or hydraulic inflation and deflation and of tether of the liner by positive interference between a link pipe and the envelope to render it captive in its pocket.The pneumatic or hydraulic function is performed by any conventional releasable coupling with the pressure fluid connections of the liner at its one projecting end - for example, by the push fit engagement of each pipe end with a nipple or socket. The mechanical interlock or tether function can be achieved in alternative ways.

Thus, in one way, the blank end of each liner is designed to incorporate an integral non-inflatable extension or lug, and each pocket is open at both ends so that this non-inflatable extension can also protrude therefrom to form a support or anchor extending across the major part of the width of the liner for carrying the interconnecting pipe which links the inflate/deflate connections on the immediate neighbouring liners. The lug or other form of support is preferably formed as a transverse tube or tunnel through which the respective link pipe interconnecting the immediately adjacent liners can be passed.If this tunnel extends for substantially the full width of the liner, this link pipe is shielded for most of its length between successive liners in a set from accidental contact by the hands of a nurse or orderly during normal bed-making activities such as the tucking in of sheets and blankets along the sides of the mattress to which the transverse pockets are open. At the same time, the link pipe constitutes a mechanical bar spanning the adjacent end of the pocket, thus positively interfering with migration of the liner out of its pocket in one direction. Migration in the opposite direction is similarly subject to interference between the ends of the seams which bound the pocket and the link pipes which couple the liner to its neighbour in its own set. Each liner is thus tethered to the envelope at both ends.

Another way of tethering a liner in its pocket involves the use of two sheets of unequal width to make the main carrier or envelope. The sheets are overlaid symmetrically and seamed transversely to form the open-ended transverse pockets, as described above. This leaves a plain flap of the wider sheet along each edge to which the pockets are open. Each flap is then folded over towards the pockets and seamed to produce a tubular marginal duct which is of an internal diameter to allow the link pipes of the various liners to be inserted thereinto.

The marginal ducts are gapped opposite each seam between pockets, or twice opposite each alternate pocket, and the link pipe between each pair of liners in a set is threded through the section of the adjacent duct which spans the mouth of the intervening pocket. In this way, each liner is intimately and positively tethered to the envelope.

It will be understood that in the above alternative arrangements the liners are inserted into their pockets in alternately reversed attitudes. That is to say, if the assembled mattress is observed from one edge parallel to the transverse pockets, the liners are inserted thereinto so that their inflate/deflate connections protrude alternately right-handed and lefthanded. Should it be desired that all the liners lie in their pockets in the same handed attitude, the latter alternative construction can be modified so that the narrower sheet is overlaid on the wider assymetric ally, and the residual margin of the wider sheet is folded lengthwise, and longitudinally seamed to form two parallel marginal ducts, each accommodat ing the link pipes of a respective set of alternate liners.In this form, the pockets themselves can be blind at their ends remote from the ducted margin of the envelope, thus permitting the envelope to be formed by making an asymmetric lengthwise fold in a double-width sheet.

The phenomenon known as "bottoming" is the localised absence or loss of adequate fluid pressure to support a part of the patient's body. Insofar as this is due to the minimum pressure on the deflation part of the pressure change cycle being too low, the phenomenon can usually be corrected by adjustment of a control on the pump to ensure that adequate pressure is available to provide universal fluid pressure support. Sometimes, however, it is caused by the physical separation of adjacent cells, which in turn can be due to straight line divisions between adjacent pockets which give rise to a "hinge" action in the mattress.This can be combated, according to another feature of the invention by curving the boundaries of the pockets, and correspondingly curving the liners, sufficiently to combat the tendency for a liner to flatten at low pressure over a sufficient area to allow, say, a hip or a shoulder joint to become supported solely by the usually relatively hard base on which the ripple mattress is placed. Thus, if the curvature of the boundaries of each pocket is sufficiently pronounced - especially if a reverse curvature contour is adopted - an overlapping or interleaved chevron-like effect can be achieved in which the supportive action of one liner "intrudes", as it were, into the sphere of influence of an adjacent liner. At the same time, a reverse curvature contour of the liners and pockets for example, two reversals of curvature - opposes the tendency of the liners to migrate out of their pockets.However, there are limits to the radius of curvature which can be adopted, these limits being imposed by the liability of the inflatable liner or the pocket to pucker or crease or form a blister at the maximum working pressure.

Bed sores tend to be more prevalent in patients who, through illness or infirmity, are substantially immobile. While their onset is to be prevented if at all possible, their severity once formed is mainly due to the activities of bacteria which enter the lesion and not only exacerbate the condition of the entry site but also tend to spread their influence to other sites beyond it. A major factor in bacteria activity is temperature; if the skin temperature at a lesion is artificially lowered, the rate of degeneration and the speed of dissemination of the condition are reduced.

In its conventional form of sets of air bags filled with air at ambient temperature, a ripple bed can do nothing to halt or slow down bacterial activity once a lesion has occurred. It is a further object of the present invention to provide a relatively simple and effective means for combating this state of affairs.

According to the present invention, therefore, the inflatable cells of a ripple bed mattress or cushion are formed by separate liners each of which is a close sliding fit in an elongated pocket formed in an envelope of the required overall dimensions for the mattress or cushion, and is rendered captive by the positive interference between the envelope and the pipes which link alternate liners in sets for simulataneous cyclic alternate inflation and deflation, the link pipes being directly engaged with adjacent portions of the envelope so that no liner can migrate out of its pocket under the joint or several actions of the inflate/deflate cycle and the movements of the patient's body. At least one end of each pocket is open for the insertion or withdrawal of a liner.

Conveniently, each pocket is open to its full width at both ends.

Advantageously, each liner has an integral noninflatable lug projecting from its blank end and adapted to embrace the pipe linking the immediately adjacent liners.

Preferably, each liner has a tubular neck or socket at the end opposite the blank and into which the stem of a tubular T-piece is sealed. The cross-arm of the "T" terminates in nipples for fluid-tight connection to respective link pipes.

In order to promote local reduction of skin-temperature, the invention includes the provision of a special inflatable liner having a layer of a highly heat-absorbent substance inserted therein so asto lie snugly against the upper surface of the liner when inflated in order that heat from the zone of the body supported thereby can be extracted and the skin temperature lowered. Such a liner has the same external shape, dimensions and pneumatic connections as an ordinary liner with which it is precisely interchangeable in a ripple bed. Thus, if a supine patient begins to develop bed sores - the most regularly vulnerable points are the heels, the elbows, the hips and the shoulder blades - each liner supporting an affected zone can be quickly and simply replaced by a heat-absorbent liner.When the patient recovers, or is transferred, the special liner or liners can be removed and replaced by an ordinary inflatable liner or liners.

Optionally, each heat absorbent liner is physically distinguishable from an ordinary liner - for example, by means of a colour code, or a special surface texture.

It is desirable that the layer of heat-absorbent material can be encapsulated in a sealed bag of a material identical with or physically and chemically compatibie with the material or a liner itself so that it can be heat-sealed to the fabric of a liner during manufacture. The sealed bag forms a compartment in intimate contact with the top side of the liner, and contains a substance such as SCMC (Sodium carboxymethyl cellulose) in gel form.

Conveniently, the sealed bag forms a compartment of about the same length as the liner but only about one third the width thereof so as to concentrate the heat-absorbent substance along the crest of the special liner when inflated. Alternatively, the highly heat-absorbent substance may be distributed in several compartments arranged in a pattern such as to ensure that highly heat-absorbent substance is always available at the point or points of contact between the patient and the liner and cannot be displaced by localised pressure. For example, the area of the top of the liner over which the substance is distributed by the bag may be subdivided into three or six zones - say, three full-length compart ments without transverse subdivision, or with one central transverse direction - and the bag is corres pondingly seamed.All such sub-divisions are de signed to prevent or reduce displacement of the highly heat-absorbent substance when the liner is subjected to especially concentrated pressure such as occurs art a patient's heels.

Depending on the quantity and composition of the highly heat-absorbent substance, it may be deemed medically expedient to provide a measure of thermal insulation between the patient and the bag contain ing the substance in order to control the rate of heat loss from the patient's skin. Such insulation may be in the form of a pad or layer of a foamed plastics material which may be either built into the top surface of the bag prior to its insertion into a liner or placed between the bag and the top ply or lamina of the liner during manufacture of the liner.

Where the liner must be capable of being inserted -into its pocket either side up, a duplicate cooling insert is mounted on the opposite side.

One or each margin of the envelope at right angles to the line of the pockets may be defined by a tubular duct adapted to accommodate sections of respective link pipe systems.

Where only one margin of the envelope is so defined, it is preferably bounded by two parallel tubular ducts, and the envelope may be formed by folding a substantially doublewidth sheet lengthwise on a line offset from the longitudinal centreline of the sheet so that the narrower portion overlies the wider portion asymmetrically. The overlaid portions are transversely seamed to form the pockets, and the plain residual flap along the free margin of the wider portion of the asymmetrically folded sheet is itself folded back towards the pockets and seamed leng thwise to form one - or optionally two - tubular ducts to accommodate the respective linkpipe systems, and is suitably apertured for the insertion of the successive sections of link pipe interconnecting alternate liners.

Practical embodiments of the present invention will now be described, by way of illustration only, with reference to the accompanying drawings in which: Figure 1 is a fragmentary part-sectional plan view of a first form of ripple bed according to the invention; Figure 2 is a section on the line ll-ll of Figure 1; Figure 3 is a scrap view of a detail at one end of a liner; Figure 4 is a scrap view of a detail at the other end of a liner; Figure 5 is a modified design of the detail shown in Figure 3; Figure 6 is a view similar to Figure 1 of a second form of ripple bed according to the invention; Figure 7 is a fragmentary part-sectional plan view of a third form of ripple bed according to the invention; Figure 8 is a section on the line VIII-VIII of Figure 7; Figure 9 is an enlarged scrap view of part of Figure 7;; Figure 10 is a view similar to Figure 9 showing a further modification; Figure 1 lisa fragmentary plan view of the underside of the top ply or lamina of a liner having a bag containing a highly heat-absorbent substance superimposed thereon preparatory to the assembly of the remaining components of a liner and the final heat-sealing thereof to produce a finished special liner; Figure 12 is a stylised exploded sectional view, taken on the line XII-XII of Figure 11, through a finished special liner, and Figure 13 is a fragmentary longitudinal section on the line Xlil-Xlil of Figure 11.

Referring first to Figures 1 - 4, the ripple bed shown consists of an envelope formed by two heavy-gauge plasticised PVC sheets 10, 12 which are seamed together transversely at regular intervals along their lengths by curvilinear seams 14to form wavy pockets. The number of pockets is determined by the length of the working surface of the bed. At least one of the sheets 10, 12 is conveniently longer than the working surface (shown terminating at one end on the line s-S) to provide free ends 16 which can be tucked beneath a conventional sprung or stuffed bed mattress. The contour of each seam 14 is a reverse curve consisting of three arcs 18,20,22.

The centres of the outer arcs 18,20 lie on the opposite side of the seam 14 to that on which the centre of the middle arc 22 lies, and the radius of all three is the same. As shown, the seams 14 terminate at each edge in a straight section, but there is no particular reason why the outer arcs 18, 22 should not continue to the edges of the sheets 10,12 or meet still further reverse-curved arcs which run to the edges of the envelope. A liner 24 of flexible inflatable material such as plasticised PVC is shaped along each longer side, when deflated, to the same contour and radii as the wavy boundaries of a pocket, and can be pulled into or out of the pocket as required. The deviations of each arc 18,20,22 from the straight line joining the ends of each seam 14, however, is insufficient to resist migration of a liner 24 out of its pocket due to the normal restlessness of a patient.The liners 24 are thus rendered substantially captive in the envelope 10, 12 but are free to be withdrawn in the event of damage or failure necessitating replacement.

Each liner 24 has a lug or tab 26 at one end and a generally similar but non-inflatable lug or tab 28 at the other end. The liner and its lugs or tabs are dimensioned so that in use each lug 26, 28 protrudes from the respective open mouth of its pocket. The lug 26 contains a cavity 30 communicating at its central part with the interior of the liner 24. Lateral branches 32, 34 open through the side edges of the lug to form inflate/deflate ports by which the interior of the liner 24 can be interconnected with its companion alternate liners on the same side of the pump, indicated schematically at 36. The manner of interconnection is shown as short sections of flexible pipe 38 which are push fit on unions or nipples 40 heat-sealed into the ports 32,34.

Each section of pipe 38 linking a pair of alternate liners 24 is passed through a tunnel 42 in the non-inflatable lug 28 which constitutes an extension of the blank or closed end of the respective intervening liner 24. The link pipe 38 spans the full width of the pocket housing the liner carrying the lug which embraces the pipe, so that the pipe 38 forms a positive interlock with the envelope if the liner in spite of its sinuous shape - still tends to migrate out of the opposite end of the pocket. Migration of the liner 24 in the opposite direction is likewise positively prevented by interference between the link pipe or pipes and the fabric of the envelope. A liner 24 is thus positively held captive in its pocket by the interference of its own and its immediate neighbour's link pipes 38 with the envelope 10,12.

To construct a ripple bed according to the present invention, a liner 24 is inserted into each pocket, successive liners being reversed end for end relative to the preceding one so that each edge of the finished article presents alternate lugs 26, 28. The two sets of alternate liners 24 are linked by the respective sections of pipe 38, and one end of each link pipe system is connected to a respective port of the pump 36, the final liner port 34 on each side being piugged. When the pump is started, one port inflates one set of liners 24 while the other port deflates the other set. After a few strokes of the pump, the bed settles down to rhythmic inflation and deflation of each liner in phase opposition to its immediate neighbours.Under no-load conditions, the maximum operating flow pressure is about 1.5 p.s.i. (42 in. water gauge); the maximum is about 0.65 p.s.i. (18 in.w.g.), and the average working pressure is 1.0 p.s.i. (28 in. w.g.).

If one liner 24 is punctured or otherwise rendered unserviceable, the connections of the link pipes 38 at each lug 26,28 are broken so that the damaged liner 24 can be withdrawn from its pocket and a replacement inserted. During this operation, both the old and new liners are in the collapsed state, making removal and insertion relatively easy. After the new liner 24 has been inserted in its pocket, it is coupled to its link pipe system and the bed reinflated to its working pressure.

The sizes of the liners 24 and their pockets in a ripple bed according to the present invention may be varied to suit different requirements, such as the adaptation of the design to wheelchairs or reclining chairs, or to mattresses for children's cots. In one working embodiment of the present invention for normal adult use, the length of each pocket is 321/2 in. and the width of each liner 24, measured flat, is 51/2 in.

The radius of each arc 18, 20, 22 is carefully chosen in relation to the flexibility and elasticicity of the materials used and the working pressure at which they will be called upon to operate. In the particular working embodiment referred to above using heavygauge platicised PVC for the liners 24, the radius and length of the three liner arcs corresponding to the three arcs 18, 20,22 in the seam 14 give an offset at the crest of the arc 20 from the tangent to the arcs 18, 20 of 1 inch in a chordal length of 14 inches. This parameter has proved successful in avoiding both bottoming and creasing, puckering or localised blister or "goitres" in the liner or the envelope at working pressure. It may not be the only solution to both problems, and there may be merit increasing the offset provided the 14-inch chordal length is correspondingly adjusted.Similarly, the straight ends of the seams 14 may be replaced by continuations of the arcs 18 and 20. The number of "humps" 22 may also be increased, each liner 24 being correspondingly shaped.

The curvature of the seams at the ends of each liner 24 is also important. At the junction of the port cavity 30 and the interior of the liner 24 it has been found advantageous to adopt a fairly large arc 44 and to leave a generally triangular non-inflatable web 46 of material between the outside of each seam and the adjacent port 32 or 34. The analytical criteria are not at present codified, and optimum dimensions are best determined empirically. However, a modifiction of the design of the lug 25 shown in Figure 5 has advantages in respect of improved fluid-tightness of the seal between the nipples 40 and the liner.

Referring to Figure 5, the two nipples 40 constitute the cross-arm of a tubular T-piece 140, the stem or shank of which is sealed into a short nozzle tube 142 by means of a conventional clip 144. The nozzle tube 142 is itself sealed into a tubular neck 130 which replaces the port cavity 30 of Figure 3, and resembles the conventional neck of a toy balloon. The non-inflatable web 46 of Figure 3 is now replaced by a much larger web 146 which reinforces the whole of the end of the liner 24.This modification has been found to have certain advantages over the design of Figure 3; (a) there is only one seal - at the neck 130 between the nipples 40 and the liner 24; (b) the single seal at the neck 130 is easily reinforced by a conventional mechanical clip 144 because it is accessible for such treatment, whereas the ports 32,34 of Figure 3 are not; (c) the increased size of the non-inflatable webs 146 renders the modified design Iessvulnerableto creases or "goitres" than that of Figure 3; (d) the nipples 40 are more easily accessible for releasable connection of the link pipes 38 when a liner 24 has to be replaced.

Insertion of the liners 24 into their pockets in the envelope 10, 12 can be achieved without the use of special tools if a new or replacement liner 24 is rolled up about its long axis, inserted into the pocket, and flattened or inflated after insertion. Withdrawal in the deflated state is relatively easy.

The use of lugsortabs28to act as holders for link pipe sections 38 serves the dual purpose of keeping the edges of the ripple bed tidy and also of providing a positive bar to any significant migration of a liner from its pocket in either direction. However, the lugs or tabs 28 at the blank ends of the liners can be dispersed with if desired, but preferably by adopting the modified design of Figures 7 - 9 or Figure 10 described below.

Figure 6 shows another modified design of ripple bed in which the pocket seams 114 and liners 124 are straight, and the only restraint on endwise migration of the liners from their pockets is provided by the interference between the link pipes 38 and the envelope 10, 12 at the boundaries of the pockets.

This is illustrated purely schematically in Figure 6 by the distortions from the straight of the link pipes 38.

Thus, the liner in the position marked A is beginning to migrate to the right. The liners at B are beginning to migrate to the left, while the liner at C has migrated to the left to its maximum allowable extent.

The liner 124 at A has begun to pull the link pipes 38 at both ends out of line, and soon the left-hand pipe 38Awhich is confined in the tunnel through the lug 28A will engage the edge of the respective pocket mouth adjacent the left-hand ends of the definitive seams 114 at the points marked D. Similarly, the link pipes 38B along the right-hand edge of the ripple bed which are confined in the lugs 28B will be pulled by the respective liners at B into contact with the mouths of their respective pockets at the points marked E.

The limiting condition is illustrated by the liner at C where the right-hand link pipes 38C have been pulled taut into positive contact with the roots of the mouth of the respective pockets at the points marked F. At the same time, of course, the left-hand link pipe 38' which is confined in the lug 28C has been pulled taut on the respective nipples of the T-piece 140 in the adjacent liners against the restraint exerted by the link pipes 38B confined in the respective lugs 28B. Thus, both link pipe systems cooperate with the envelope 10, 12 to restrain migration of the liners 124 from their pockets in either direction.

Figures 7 - 9 illustrate a further modified construction of ripple bed according to the invention. In this modification, the lower sheet 10 of the pair which form the envelope 10, 12 is narrower than the upper sheet 12, and the latter is placed symmetrically on the former before the seams 14 are made. The excess width of the lower sheet 10 is chosen so that the plain margin down each side of the sheet 10 can be rolled or folded over to meet the longitudinal edge of the sheet 12, and a longitudinal seam is made at 48 to form a hollow tubular duct 50 extending at least for the length of the working surface of the bed.In Figure 7, each duct is shown as terminating at 52 a short distance beyond the end edge of the overlying envelope sheet 12 so that the "tuck-in" (or other form of anchorage) flap 16, is the same width as the sheet 12 and plain-edged, but this is entireiy optional. There is no particular reason why the duct 50 along each side of the sheet 10 should not continue for the full length of the sheet.

Each duct 50 is formed with pairs of apertures at 54 on either side of the centreline of each alternate pocket and close to the respective seams 14, the pockets selected for the location of each pair of apertures 54 in one duct 50 alternating with those selected for the location of the pairs of apertures in the other duct. Each duct 50 is sufficiently larger in section than the diameter of a link pipe 38 to permit the insertion of such pipes through the aperture 54 so that the link pipes 38 emerge from the duct 50 close to the nipples 40 or T-piece 140. Thus, each duct 50 houses a respective link pipe system associated with one of the inflate/deflate ports of the pump 36. In this way, every liner 24 is positively tethered to the ripple bed by its link pipes 38 which are trapped in the respective duct 50.Migration of the liners 24 is thus closely controlled, and at the same time the extension lugs 28 at the blank ends of the liners are rendered superfluous. However, if it is desired to retain the lugs 28, each duct may be apertured opposite every pocket so that the link pipes 38 can be passed through the tunnels 42 in the lugs 28.

The foregoing modification has certain advantages. In the first place, the longitudinal edges of the bed are reinforced by the ducts 50. Secondly, the link pipes 38 are almost totally concealed within the ducts 50 so that they are even less vulnerable to accidental disconnection from the liners 24 during making of a bed. Thirdly, engagement of the pipes 38 with the envelope 10, 12 is even more positive leading to enhanced restraint against migration for each linen At the same time, the number of operations involved in releasing a damaged liner 24 for replacement and the introduction of a new liner are reduced to a minimum, viz: the breaking and remaking of two push fit connections at a pair of nipples 40, reducing the time for which the ripple bed needs to be out of service.In addition, a slightly cheaper design of liner 24 is rendered possible by the (optional) omission of the lug 28 atthe blank end.

Figure 10 illustrates a still further modified construction according to the present invention. This modification is a development of the design of Figures 7 - 9 except that only one longitudinal edge of the envelope 10,12 is bounded buy a duct 60. This duct is at least large enough to house two sets of link pipes 38 which emerge from the interior thereof opposite the mouth of each pocket associated with the respective set of liners 24. As a simple but practical economy, only one aperture 64 is provided for this purpose in the duct 60, and this is located opposite the end of each seam 14. Through each aperture 64 pass two link pipes 38 in mutually opposite senses.

The same positive tether action is achieved by this modification as by the preceding one (Figures 7 - 9), except that it is provided along one longitudinal margin of the envelope 10, 12. The design, however, permits a particular, and particularly economic, method of construction to be adopted. Thus, an envelope 10, 12 according to the modification of Figure 10 can be made from a single sheet of heat-sealable material, such as PVC, which is sub stantially twice as wide as either sheet in the design according to Figures 1 - 4. This sheet is first folded lengthwise asymmetrically about a longitudinal fold line which is offset laterally from the longitudinal centreline of the sheet. The amount of offset is approximately equal to the width of the duct 60.This produces two plies 10, 12, the latter overlying the former two provide a working surface of the reqired width, and also leaves a plain residual flap on the wider portion of twice the width of the marginal duct 60. This flap is then folded up to meet the free edge of the upper narrower ply and is seamed lengthwise at 58 to form a duct 60.

Simultaneously, or separately, the asymmetrically folded plies 10,12 are transversely seamed at regular intervals 14to form the pockets for insertion of the liners 24. These seams 14 need not extend right to the line of the asymmetric fold, thus leaving a continuous hollow zone running along the line of the fold to constitute a counterpart to the duct 60 except that it is not defined by a counterpart to the seam 58. All the pockets are therefore blind at their one ends remote from the duct 60, so that all the liners are inserted thereinto in the same "hand", as shown in Figure 10.

In this modification, migration of any liner 24 in the direction away from the duct 60 is positively prevented by the blind end of the respective pocket.

Migration in the opposite direction is prevented, as in the design of Figures 7 - 9, by the positive interference of the link pipes 38 with the material of the envelope at the apertures 64.

Figures 11 - 13 illustrate a modified design of liner 224 which is specially designed for the localised cooling of the skin on particular parts of a patient's body where bed sores have developed or which are prone to the development of bed sores. Each special skin-cooling liner 224 has an insert 70 comprising two sheets 72,74 (Figure 12) of a flexible and relatively inextensible material, such as that used for the envelope 10, 12 and the liners 24 or 124, which are seamed together at 76 (Figure 11) to form a central longitudinal bag or compartment 78. The seams 76 are offset mutually inwards at 76a to define a neck 77 opening into the bag or compartment 78 for the insertion of a substance 80 (Figures 12 and 13) such as an aqueous solution of SCMC (sodium carboxymethyl cellulose) which has a high heat absorbency and is used here in the form of a gel.Other substances having similar characteristics of high specific heat and gel-like viscosity may be substituted, it being understood that the substance chosen must be chemically inert in the environment in which it will be used. After the insertion of the heat-absorbent substance 80 into the compartment 78, the neck 77 is sealed at 79.

The insert 70 thus prepared is then built in to the special liner 224 in the following way. As in the cases of the liners 24 and 124 described above, the "carcase" or outer skin of the liner 224 is made up from a pair of identical blanks or panels 25,25' (Figures 12 and 13) which are exactly superimposed and seam-weided together around their peripheries to form a necked inflatable sac. One such blank 25, which will constitute the top wall of the liner, is shown in Figure 11, the symmetrically arranged dotted lines 27 indicating the sites for the subsequent seam welds which will unite the panel or blank 25 to its bottom wall fellow 25' (Figures 12 and 13).

Onto the top wall blank 25 is placed the preformed insert 70. The insert is shown in Figure 11 as having a rectangular profile with its ends approximately coincident with the ends of the straight side edges of the blank 25. The choice of this particular length of insert is purely practical, since it represents the normal maximum length of the top wall of the liner 224 which is operative to actually underlie a patient's body. Theoretically, there is no fundamental reason why the side edges of the insert 70 should not follow the complete contour of the inflatable sac.

Once placed in position on the top wall blank 25 the insert 70 is ready to be incorporated in the special cooling liner 224. If no other component is to be incorporated, the end edges of the insert must first be seam welded at71 to the top wall blank 25 so as to ensure that, when the other (bottom wall) blank 25' is superimposed and the seam welds 27 are made to complete the liner, the insert 70 is completely sealed round its entire periphery to the top wall blank 25 and the two components - blank 25 and insert 70 - become a fully integrated unit so that no air can percolate between them during the inflation/ deflation cycle to cause sagging of the cooling bag or compartment 78 out of contact with the top wall of the liner 224.The resultant externally visible transverse weld lines 71 across the top wall of the liner act as a marker to identify the correct attitude of the liner 224 when it is introduced into its appropriate pocket in the envelope 10,12. Other means of identification of the top wall of the liner can also be adopted as preferred.

The construction illustrated in Figures 12 and 13 differs from that just described in that the end seams 71 are omitted and the insert 70 is sandwiched between the top wall blank 25 and a membrane 82 shaped and dimensioned identically to the blank.

This membrane 82 is impervious to air and, if made of PVC sheet, preferably comprises two relatively thin sheets loosely superposed so that the almost inevitable pinholes through which air can seep are less likely to coincide, and the unpunctured surface of one sheet acts as a seal to block a pinhole in the other. The membrane 82 can in fact be a duplicate blank 25. In any case, the material of the membrane 82 must be capable of being heat-sealed (or otherwise bonded in air-tightfashion if heat-sealing is not adopted) to the blanks 25,25' forming the top and bottom walls of the liner 224 and the insert 70.

When all the components shown in Figures 12 and 13 of the special skin-cooling liner 224 are assembled for the final peripheral seals 27 to be made, the inflation nozzle tube 142 is sealed between the membrane 82 and the bottom wall blank 25' so that the air pressure within the inflatable sac of the liner 224 presses the cooling compartment 78 snugly against the top wall 25 of the liner 224.

In a further modification (not illustrated) a cooling insert 70 is applied to both top and bottom walls 25, 25'. In spite of the extra complexity of manufacture and the extra weight which this entails, it will normally be found beneficial when, as shown in Figure la a replacement liner must be capable of insertion into either end of the pocket and the sinuous curvature requires that the liner be turned over when its attitude is reversed. Thus, irrespective of the "hand" of the regular liner 24to be replaced, the "double-sided" modification of cooling liner 224 will always be able to be introduced into the vacant pocket so as to present a high heat-absorbent surface to the patient's body.

Special skin-cooling liners 224 are intended for emergency use as temporary replacements in any ripple bed where medical circumstances require or justify localised artifical reduction of skin temperature. Each skin-cooling special liner shown in Figures 11 - 13 is identical in shape and overall dimensions, and has the same external connections 140 to the inflate/deflate link pipe systems 38, as the ordinary or regular simple "air-bag" design of liner 24 or 124 as described above with reference to Figures 1 - 10 of the drawings.It can thus be interchanged at will with a regular liner where required, but since the circumstances of the individual patients will usually vary, due to differences in stature and physique and in locations of affected areas of skin; and because of the higher cost of special liners 224 compared with their regular counterparts 24 or 124, only a small stock of special liners will normally be carried by a hospital and will be removed from a ripple bed and replaced by regular liners when they are no longer required by the patient.

To facilitate identification of the top skin-cooling wall 25 of a liner 224, all blanks 25 can be of a special colour or surface texture, or bear some other means of identification - especially when their substitution for regular liners 24 or 124 is likely to occur in the dark.

In all modifications of the present invention, the end liner 24 of each set remote from the pump has one nipple 40 blanked off, while the end liner of each set adjacent the pump has one nipple directly connected to a respective port of the pump. Sundry details such as the particular form of connection between a link pipe 38 and the inflate/deflate union on a liner can be a matter of choice having regard to the need for fluid-tightness during operation of the bed and simplicity of detachment and re-attachment for the pupose of changing a liner.

Although the working fluid will normally be air, any pneumatic or hydraulic fluid can be used according to preference. Thus, water may be used instead of air.

For hospital use, or wherever sterile conditions must be preserved, at least the envelope 10, 12 will be made of hospital quality sanitised PVC which has undergone an anti-bacteria treatment. The use of such material for the liners 24 is optional. Other materials which satisfy particular working conditions may, of course, be substituted.

Claims (17)

1. A ripple bed wherein each separate cell comprises one of a plurality of similar parallel pockets in a flexible envelope, each pocket extending between opposite boundaries of a working surface of the bed and having at least one open end; and a fluidimpervious inflatable liner of a length substantially equal to the length of the pocket and adapted to be introduced into or withdrawn from the pocket at will and to be a snug fit therein; and wherein each liner has a union for releasable fluid-tight connection thereof to a pipe system linking the liner with each alternate neighbour and one of the two alternating pressure ports of the cyclic inflation/deflation pump; and both pipe systems are physically engageable with a part of the envelope adjacent each liner so as to render it captive in its pocket against endwise migration during operation of the mattress.

2. A ripple bed according to claim 1 wherein each pocket is open to its full width at both ends.

3. A ripple bed according to claim 2 wherein each liner has an integral non-inflatable lug projecting from its blank end and adapted to embrace the pipe linking the immediately adjacent liners.

4. A ripple bed according to claim 1,2 or 3 wherein each liner has a tubular neck or socket at the inflate/deflate end into which the stem of a tubular T-piece is sealed, the cross arm of the T terminating in nipples for fluid-tight connection to respective link pipes.

5. A ripple bed according to claim 1 or 2 wherein each edge of the envelope transverse to the axes of the pockets is defined by a continuous tubular duct of an internal diameter greater than the external diameter of a link pipe, and each link pipe is located for part of its length within the appropriate duct and emerge through apertures in the wall of the duct adjacent its connections with respective liners.

6. A ripple bed according to claim 5 wherein each duct bridges the mouths of the successive pockets which open towards that edge of the mattress, and the apertures in each duct for the passage of link pipes are located opposite respective alternate pockets housing a respective set of liners for simultaneous inflation, the aperture locations in each duct thus alternating with those in the other duct.

7. A bed according to any preceding claim wherein each pocket is symmetrical about the longitudinal centre line of the envelope.

8. A ripple bed according to claim 1 or 2 wherein one edge of the envelope transverse to the axes of the pockets is defined by a tubular duct of an internal diameter to accommodate two link pipes side by side, and having apertures of a size to permit simultaneous passage therethrough of two link pipes and located adjacent the ends of the seams defining the pockets.

9. A ripple bed according to claim 8 wherein the tubular duct is divided lengthwise into two similar ducts, each accommodating the link pipes of a respective set of liners.

10. A ripple bed according to claim 8 or 9 wherein the envelope consists of a single flexible sheet of approximately double the intended width of the working surface of the bed which is folded lengthwise asymmetrically so that the narrower portion overlies the wider to leave a residual margin al flap of a width greater than double the diameter of a link pipe, the overlying folded portions being transversely seamed to form blind pockets open only towards the flap while the latter is seamed lengthwise to form a duct or ducts for accommodat ing all the link pipes.

11. A liner for a ripple bed according to claim 1 or 2 comprising an elongated inflatable body of a size and shape to fit snugly into a pocket of the envelope of the bed and having means at one end for connection to an inflate/deflate pipe system, and at the other end for embracing the inflate/deflate pipe connected to an adajcent liner whereby the liner is tethered in its pocket.

12. A liner for a ripple bed according to claim 1 or 2 comprising an inflatable carcase and an insert therein which encapsulates a highly heat-absorbent substance and locates it snugly against the top wall of the liner.

13. A liner according to claim 12 comprising a pair of identically shaped and dimensioned blanks which are sealed to each other in fluid-tight manner around their peripheries, save for an inflation neck; and the insert is sealed at least to the blank constituting the top wall of the liner so as to prevent inflation fluid from percolating between the said top wall blank and the insert.

14. A liner according to claim 13 wherein the insert has a compartment of approximately the same length as the operative body-supporting length of the liner but a width less than that of the liner whereby the skin-cooling effect of the liner is localised along a zone of the top wall of the liner.

15. A liner according to claim 12 wherein the insert is sandwiched between the top wall of the liner and a membrane impervious to the inflation fluid which is substantially co-extensive with and sealed in fluid-tight manner to the top wall.

16. A ripple bed substantially as hereinbefore described with reference to Figures 1 - 4; Figures 5 and 6, Figures 7 - 9 and Figure 10 of the accompanying drawings.

17. A mattress according to claim 1 including a liner having an insert therein which encapsulates a highly heat-absorbent substance substantially as described with reference to Figures 11 - 13 of the accompanying drawings.

17. A ripple bed according to claim 16 including a liner having an insert therein which encapsulates a highly heat-absorbent substance substantially as described with reference to Figures 11 - 13 of the accompanying drawings.

New claims or ammendments to claims filed on 25 January 1982 Superseded claims All claims New or amended claims:

1. An alternating pressure mattress or cushion wherein each cell consists of a pocket and an individually removable inflatable liner therein, the pockets being formed in an envelope extending over substantially the full width of the working surface and consisting of upper and lower sheets which are joined at regular intervals along the length of the working surface by transverse seams; and each liner is restrained against axial migration from its respective pocket by the interengagement of a link pipe for inflating a respective set of alternate liners with the material of the envelope at or adjacent an open end of the pocket.

2. A mattress according to claim 1 wherein each transverse seam in the envelope is identically curved to form sinuous pockets and each liner is shaped to the same contour so that when inflated it is a snug fit within any pocket.

3. A mattress according to claim 1 or 2 wherein a portion of each link pipe between consecutive liners in its set is held captive either by an appendage on the intervening liner or by a part of the envelope.

4. A mattress according to claim 1, 2 or 3 wherein each liner is necked at its inflation end and the stem of a tubular T-piece is sealed into the neck and clamped in fluid-tight manner, the cross bar of the T terminating in nipples for the fluid-tight releasable connection of respective sections of the appropriate link pipe system.

5. A mattress according to claim 1,2,3or4 wherein each pocket is open at each end to the full width between transverse seams, and each liner has an integral non-inflatable lug projecting from its blank end and adapted to positively engage the pipe linking the immediately adjacent liners.

6. A mattress according to claim 1,2,3 or4 wherein each edge of the envelope transverse to the axes of the pockets is defined by a continuous tubular duct of an internal diameter greater than the external diameter of a link pipe, and each link pipe is located for part of its length within the appropriate duct and emerges through apertures in the wall of the duct adjacent its connections with respective liners.

7. A mattress according to claim 6 wherein each duct bridges the mouths of the successive pockets which open towards that edge of the mattress, and the apertures in each duct for the passage of the link pipes are located opposite respective alternate pockets housing a respective set of liners for simultaneous inflation, the aperture locations in each duct thus alternating with those in the other duct.

8. A mattress according to claim 1,2,3 or 4 wherein one edge of the envelope transverse to the axes of the pockets is defined by a tubular duct of an internal diameterto accommodate two link pipes side by side, and having apertures of a size to permit a simultaneous passage therethrough of two link pipes and located adjacent the ends of the seams defining the pockets.

9. A mattress according to claim 8 wherein the tubular duct is divided lengthwise into two similar ducts, each accommodating the link pipes of a respective set of liners.

10. A mattress according to claim 8 or 9 wherein the envelope consists of a single flexible sheet of approximately double the intended width of the working surface of the bed which is folded lengthwise asymmetrically so that the narrower portion overlies the wider to leave a residual marginal flap of a width greater than double the diameter of a link pipe, the overlying portions being transversely seamed to form blind pockets open only towards the flap while the latter is folded over and seamed lengthwise to form a duct or ducts for accommodating all the link pipes.

11. A liner for a mattress as claimed in any preceding claim comprising an inflatable carcase and an insert therein located snugly against that portion of the internal wall of the carcase which will be uppermost when inserted into a pocket in an envelope, and a highly heat-absorbent substance encapsulated within said insert.

12. A liner according to claim 11 comprising a pair of identically shaped and dimensioned blanks which are sealed to each other around their peripheries save for an inflation aperture at one end, and a capsule containing a highly heat-absorbent substance sealed to the internal wall of at least that blank which will constitute the top wall of the liner when in use.

13. A liner according to claim 11 or 12 wherein the insert is of a length equal to the operative length of the liner but narrower than the liner so as to localise the cooling effect of the heat-absorbent substance on a patient's skin.

14. A liner according to claim 11,12 or 13 wherein the insert is sandwiched between a wall of the liner and a membrane impervious to the inflation fluid and substantially co-extensive with and sealed in a fluid-tight manner to the wall of the liner.

15. A liner according to any claims 11 - 14 having two inserts located on opposite walls.

16. A mattress substantially as hereinbefore described with reference to Figures 1 - 4; Figures 5 and 6; Figures 7 - 9, or Figure 10 of the accompanying drawings.