US 3678520 A
An air cell for use in an alternating pressure pad has a tube with its wall of flexible sheet material and at least the outermost half of the length of that tube, considered in the direction outwardly longitudinally from the longitudinal center of the tube, having its width increasing towards the remote end of the tube, a preferred form having the tube composed of two similar frusto-conical portions joined at their smaller ends.
Description (OCR text may contain errors)
[451 July 25, 1972 United States Patent Evans References Cited UNITED STATES PATENTS Ronal J m Peter E B y H 2,719,986 Rand England FOREI N PATE S  Assignee: Talley Surgical Instruments Limited, Hert- G NT OR APPLICATIONS fordshire, England Dec. 14, 1970 996,959 12/195] 959,103 5/1964 GreatBritainWM  Filed:
Primary liraminer-Casmir A. N unberg Attorney-William Anthony Drucker  Appl No.:
ABSTRACT  Foreign Application Priority Data An air cell for use in an alternating pressure pad has a tube with its wall of flexible sheet material and at least the outermost half of the length of that tube, considered in the direction outwardly longitudinally from the longitudinal center of the tube, having its width increasing towards the remote end of the tube, a preferred form having the tube composed of two similar frustoconical portions joined at their smaller ends.
8 Claims, 9 Drawing Figures PATENTED JUL25 I972 sum 1 or 3 lNVE NToR- IQbNnL) I P Evmvs mam] JUL25 1912 3,578,529
sum 2 or 3 FIG. 2a
2 II II Pwvmp I EVH S ALTERNATING PRESSURE PADS FOR BED PATIENTS This invention relates to alternating pressure pads for bed patients, as used for example for the prevention of bed sores and other conditions arising from restricted circulation of the blood. Such pads comprise essentially a number of sets of collapsible air cells which together provide a surface for supporting the patient, the arrangement being that from time to time some of the cells are inflated and others are deflated, with the result that the patient is supported by pressure exerted at different areas of the body at different times, and no one area of the body remains permanently under pressure. A convenient construction already commercially available in the United Kingdom has the cells in the form of substantially cylindrical tubes made of flexible plastics material and each fed with air, and exhausted, through header pipes connected at one end, the tubes being each positioned loosely within an open-ended cylindrical pocket of flexible plastics material serving to retain the assembly of tubes in position.
It has been found that, using cylindrical air tubes, there is a danger that a patient may simply roll off the pad or mattress sideways, particularly in the case of subnormal patients.
it has also been found that, as patients vary widely in their width across the body and also in their weight, it is desirable to provide such pads or mattresses in which the support given by the air tubes is provided over a suitable width of the pad, and is also proportionate to the weight of the patient. Hitherto, this has necessitated the production of at least two types of pad, i.e. a pad having a large number of tubes of relatively small diameter, for use with patients of small size and weight, and a pad, having a lesser number of tubes of greater diameter for use with patients of greater size and weight.
The object of the present invention is to provide an improvement in the nature of the air tubes which results in the pad automatically assuming, under loading, a shape tending to prevent the patient rolling to either side of the pad, and which permits a single type of pad to be equally suitable for both small and light patients, and large and heavy patients.
According to the present invention an air cell for use in an alternating pressure pad comprises a tube having its wall of flexible sheet material, at least the outermost half of the length of said tube, considered in the direction outwardly longitudinally from the longitudinal center of the tube, having its width increasing towards the remote end of the tube.
The portion of increasing width may most conveniently be frusto-conical, and in a preferred construction of the tube it is composed of two similar frusto-conical portions joined at their smaller ends. in other form, the tube is composed of an inter mediate portion, which may conveniently be cylindrical, and two similar frusto-conical portions each joined at its smaller end to a respective end of the intermediate portion.
Two results are obtained from the construction of the invention. Firstly, as each tube is wider, i.e. higher, at its ends as compared with centrally, there is provided a natural rim or barrier tending to keep the patient on the central area and preventing rolling off the pad laterally. Moreover, when the weight of the patient is applied to the pad, the tubes bend under the load until their lower longitudinal face is presented flat against the underlying support, whereby the upper longitudinal edge is presented at a doubly-steep angle and the rim or barrier effect becomes more pronounced.
Secondly, the assemblyof tubes forming the pad are all of the narrow center and wide ends shape, so that when viewed in plan, the central area of the pad has relatively narrow tubes widely spaced, whereas the lateral areas of the pad have relatively wider tubes more narrowly spaced. Accordingly, when a small (narrow bodied) patient is placed on the pad, the body is supported by smaller tube portions at wider spacing, which is the desirable arrangement for a light body. When a heavier (wide bodied) patient is placed on the pad, the body is then supported largely at the sides by the wider tube portions of smaller spacing, which is the desirable arrangement for a heavy body. The width and spacing of the end portions of the tubes varies progressively towards the lateral edges, so that there is obtained automatically a selfproportionating supporting effect, according to the width and weight of the patient, without requiring any change in the shaping or degree of inflation of the tubes. As a result, a single production model of pad can be used for patients of all sizes and weights.
A further advantage is gained that, as the central portion of the pad consists of portions of tube which are of smaller diameter and which are relatively widely spaced, there is considerably less pressure exerted at the central area, and the spinal cord area of the patient is accordingly subjected to less upward pressure than the more lateral portions of the body.
Where the air tubes are each positioned loosely in a tubular pocket, to retain them in assembly, the further advantage is gained that each tube, being at some point along each end portion of a greater diameter than the pocket in which it is positioned, automatically settles itself symmetrically into the pocket and remains tightly gripped to prevent any rolling or longitudinal movement with respect to the pocket.
Whilst the tubes are substantially cylindrical at their center at the narrowest point, they become gradually more oval in the direction towards their two ends. For example, in the case of a practical embodiment in which the center portion is approximately three inches in circumference, the ends are approximately four inches high but about seven and one-half inches wide, i.e. somewhat'pillow shaped. This shape is a distinct advantage in the use of the pad, because it is found that, with patients who are nursed in a sitting position on such pads, i.e. having separate air tubes contained in retainer pockets, the tubes may tend to roll under the patient's body,
because of the angle assumed by the body. This action can be damaging to the patients skin because it causes the exertion on the skin of a shearing force due to the weight on the sacram area. Such shearing force, exerted on the skin, is one of the major causes of pressure sores. However, the somewhat oval shape adopted by the tubes described above discourages any tendency for such rolling to occur in the manner described. Moreover, the shape adopted by the tube, upon inflation, is substantially wrinkle-free, so that stress on the material is reduced.
Each cell may be fed with air by connecting it at one end to a header tube, and in a convenient arrangement a series of the cells are disposed in spaced parallel position and each connected at one end to a common header tube. in an alternating pressure pad, two such series of air cells may be disposed with the cells of the two series interdigitated, and means may be provided for supplying air to and exhausting air from the series of cells, such that the two series of cells are inflated and deflected alternately.
Apparatus for use in making the air cell may comprise two mould electrodes defining between them a cavity having the shape of the tube to be formed, means for introducing air between two sheets of heat-scalable plastics material disposed between said mould electrodes so as to cause the sheets each to conform to the shape of a respective mould electrode, means for moving the electrodes together so as to clamp the two sheets peripherally, and means for applying R.F. energy to the two mould electrodes so as to seal the sheets together where they are clamped peripherally. A symmetrical half portion of the cavity may be included in each of the mould electrodes, or the entire mould cavity may be included in one mould electrode whereas the other mould electrode is plane.
A method of making the air cell comprises the steps of disposing two sheets of heat-scalable plastics material between two mould electrodes defining between them a cavity having the shape of the tube to be formed, introducing air between the two sheets so as to cause them each to conform to the shape of a respective mould electrode, moving the mould electrodes together so as to clamp the two sheets peripherally, and applying R.F. energy to the two mould electrodes so as to seal the sheets together where they are clamped peripherally.
In order that the nature of the invention may be readily ascertained, an embodiment of alternating pressure pad incorporating the improved tube, some constructions of tube, and apparatus and a method for the manufacture of such tubes, are hereinafter particularly described with reference to the accompanying drawings, wherein:
FIG. I is a plan view of an embodiment of alternating pressure pad;
FIGS. 2a and 2b show a first form of tube respectively in unloaded and loaded condition;
FIG. 3 shows a second form of tube;
FIG. 4 shows in central vertical longitudinal section a fonn of mould for making the tube of FIGS. 2a and 2b, the mould being shown at a first stage of the production;
FIG. 4a is a central vertical transverse section of the mould of FIG. 4, in a second stage of the production;
FIG. 5 shows, in central vertical longitudinal section, a modification of the mould of FIG. 4;
FIG. 6 is a plan view of another embodiment of alternating pressure pad;
FIG. 7 is a partial section taken on the line VII-VII of FIG. 6.
The alternating pressure pad shown in FIG. I has two interdigitated series of tubes la, la, la and lb, lb, lb arranged in parallel position transversely of the pad, the tubes of each series being connected together and the two series being alternately inflated and deflated. The tubes of each series are connected together, all at the same end, by respective flexible header pipes 2 coupled to a rotary valve 3 having a connection to a pump 4, and an exhaust 5. The tubes are arranged each in an individual cylindrical tubular pocket 6 formed by securing a sheet 7 at intervals to a base sheet 8 of the pad, whereby each tube is held in proper position in relation to the others. Individual tubes can be disconnected and changed on site. The entire assembly of tubes, in their pockets, is covered by a loose top cover 9 which is held in place, at the head and foot of the pad, by conventional fasteners 10 such as press studs.
Referring to FIG. 2a, each air tube Ia and Ibis composed of two similar symmetrical frusto-conical portions 11 connected at their smaller ends at the longitudinal center point of the tube. By way of example, for a total tube length end-to-end of about thirty to thirtysix inches, the smallest diameter would be about three inches at the center point and about five inches at the extreme ends. As the tube portions are frusto-conicaL' the longitudinal seams on them are linear and accordingly there is no wrinkling of the material when inflated, and fatiguing of the material is avoided.
FIG. 2b shows how, when the weight of a patient is applied in the direction of the arrows, the tube adopts a linear base line and the upper surface becomes more steeply inclined so as to tend to keep the patient in a central position.
FIG. 3 shows a tube having two frusto-conical portions 12, and an intermediate cylindrical portion 13.
The tubes may be made of any convenient flexible sheet material but preferred materials for the purpose are rubbercoated canvas, seamed by hand or machine, or plastics material such as polyvinylchloride, which may be high-frequency welded.
Where welded plastics material is used, the entire tube may be formed in a single welding operation to form a tear-weld about the necessary double-conical contour, whereafter the finished tube is stripped from the surrounding waste. In a preferred method of forming the tube from plastics material,
see FIGS. 4 and 40, there is used a welding machine which has a pair of mould-like electrodes 14, 15 which between them define a cavity 16 having the shape of the eventual tube. Two flat sheets 17, I8 of material are placed between the mould electrodes 14, I5, and the electrodes are closed together into the position of FIG. 4, but not sufficiently to grip the sheets immovably. Air is then blown into the space between the sheets, in the direction of the arrow in FIG. 4, to cause them to be inflated to the internal shape of the mould cavity 16. The electrodes 14, 15 are then brought firmly together, as in FIG. 4a, to grip the two sheets tightly about the desired contour,
whereafter R.F. energ is a lied to the electrod heat-seal at 19 about the COBIEOUI. The material is n ch bi hfgly sealed when in its inflated condition, and remains relatively stress-free. In a modification, seen in FIG. 5, the mould electrodes 20, 21 are shaped such that the bottom electrode 2] has a plane face, and the whole of the cavity 22 is contained within the electrode 20, the bottom sheet 23 of plastics material is retained flat, andthe upper sheet 24 is blown to the shape of the mould by air introduced in the direction of the arrow, a seal is formed along the base of the eventual tube as described in relation to FIG. 4a. A multiple cavity mould-electrode may be used, e.g. having say four cavities each provided with means for injecting air between the upper and lower sheets placed between the upper and lower electrodes.
FIGS. 6 and 7 show another embodiment of alternating pressure pad, seen in deflated condition. A base sheet 25 has on it two interdigitated series of tubes 26 each of which is formed by two similar frusto-conical portions joined at their smaller ends. Each tube is attached to the base sheet by a fastener 27, to permit easy replacement.
On top of the two of tubes 26 there are provided three parallel retainer strips 28 of flexible material which are secured, e.g. welded, to the base sheet 25 between each neighboring pair of tubes, so as to form pockets in which the tubes are engaged. At the ends of the base sheet it has fasteners 29 by means of which a cover sheet 30 is secured in position.
The two series of tubes 26 are connected by T-junctions 31 to respective header tubes 32 and 33 which are coupled to a rotary valve 34 having an inlet 35 from a pump 36, and an exhaust 37.
1. An air cell, for use in plural assembly in an alternating pressure pad, comprising a discrete elongated tube of flexible sheet material, the wall of said tube being varied, in its peripheral dimension measured in a plane normal to the median longitudinal axis of the tube, at points along the length of the tube such that at least the outermost half of the length of the tube, considered in the direction outwardly longitudinally from the longitudinal center of the tube, increases in both width and height towards the remote end of the tube.
2. An air cell, as claimed in claim I, wherein the portion of increasing width and height is frustoconical.
3. An air cell, as claimed in claim 2, wherein the tube is composed of two similar frusto-conical portions joined at their smaller ends.
4. An air cell, as claimed in claim 2, wherein the tube is composed of an intermediate cylindrical portion, and two similar frusto-conical portions each joined at its smaller end to a respective end of the cylindrical portion.
5. An air cell, as claimed in claim 1, connected at one of its ends to a header tube.
6. For use in an alternating pressure pad, a series of air cells as claimed in claim I, disposed in spaced parallel position and each connected at one end to a common header tube.
7. An alternating pressure pad comprising two series of air cells as claimed in claim 6 disposed with the cells of the two series interdigitated.
8. In combination, an alternating pressure pad as claimed in claim 7, and means for supplying air to and exhausting air from the series of cells, such that the two series of cells are inflated and deflated alternately.