PATIENT SUPPORT MATTRESS

Abstract: A patient support mattress (1) comprises a substantially flat body contact surface formed from a plurality of discrete fluid filled sections (2). The number of sections per unit area of body contact surface is varied at different portions thereof in accordance with the loading characteristic of a body part to be supported there.

Description: PATIENT SUPPORT MATTRESS The present invention relates to patient support mattresses of the static pressure, alternating pressure and low air loss type. Alternating pressure type air beds are to be found described in GB-A-1595417. Briefly this document describes an air bed for patient support, for example in a burns unit or in geriatric care, which comprises a plurality of overlying flexible pressure resistant tubes which are inflated and deflated in an alternating cycle over about 5 to 10 minutes. The purpose of this is to reduce the period of time that an immobile body tissue carries weight which could shut off or reduce blood flow. Thus every five minutes or so every skin tissue is unstressed by weight and hence where blood flow is weak the capillary system can operate to oxygenate the unstressed tissue. The effect of this is for example to greatly assist the prevention and healing of bed (pressure) sores. There are a number of different developments of this type in use, all of which have as a goal the reduction of point loading of particular parts of the body on an alternating basis. As will be apparent bony prominences such as the sacrum are particularly prone to cause problems with tissue perfusion in semi-immobile geriatric patients, or those who have undergone significant surgery. One example of an air bed of this type is in the marketplace under the trade mark "Pegasus". Another approach to this problem has been the use of the low air loss bed concept, for example, that marketed under the trade mark "Mediscus". in this arrangement, the patient is in effect supported on air contained in a plurality of water proof, but water-vapour permeable, air sacs. Air is caused to flow through the air sacs at about 140 m 3 /hr. The plurality of sacs are arranged in, for example, four groups of five sacs, and each is adjusted to a pressure suitable for support of a part of the patient's body. Again the air sacs used are essentially flexible although they are made of a material which allows for a degree of resilience. In another type of fluid filled mattress, a static pressure air filled mattress is provided. The mattress is valved so that the pressure can be adjusted to a desired value when the patient is in situ on the mattress. With these prior art mattresses, their design has been based on an assumption that the loading applied to the mattress by the different limbs of the body is relatively uniform. However, in practice, the different weights and configurations of each limb that may come into contact with the mattress mean that the prior art mattresses are unable to accurately match the loading requirements so as to minimise the risk of, for example, bed sores developing. It is therefore an object of the present invention to alleviate these problems associated with the prior art mattresses. According to an aspect of the present invention there is provided a patient support mattress comprising a substantially flat body contact surface formed from a plurality of discrete fluid filled sections; characterised in that the number of sections per unit area of body contact surface is varied at different portions thereof in accordance with the loading characteristic of a body part to be supported there. Preferably, the number of sections per unit area of body contact surface is varied at different positions along the length of the mattress. In preferred embodiments, the number of sections per unit area of body contact surface is relatively increased for portions supporting body parts such as limbs having smaller contact areas and/or smaller radius of curvature. Thus, for limbs such as elbows and heels, the number of sections per unit area of body contact surface is relatively increased, whereas for limbs such as the trochanter (the hip area) or the sacrum (the lower back area) , the number of sections per unit area of body contact surface may be relatively decreased. The interaction between the various forces resulting from the respective contact surfaces of the sections with each other and those of the limbs of a patient is highly complex and a theoretical basis for the behaviour of the present invention has not been established at the present time. In experimental studies however the arrangement of the present invention has been found to afford improved pressure signatures over conventional arrangements. Preferably, each fluid filled section has an arcuate cross- section at the body contact surface, the sections which in use are for supporting body parts having smaller contact areas, having smaller effective radii. The radius of such arcuate cross-sectioned sections is preferably made to correspond closely with the radius of curvature of the body part to be supported thereby. Conveniently, each fluid filled section is filled with a gas, liquid, gel or low friction powder and is connected to a source of pressurization. The fluid filled sections may optionally be connected to a means for alteration of their internal pressure on a cyclical basis. In preferred embodiments, the body contact surface comprises a plurality of adjacent tubes, each arranged at right angles to a longitudinal direction of the mattress. The upper arcuate surfaces of such tubes are therefore presented to the patient, although alternative non-arcuate tubular shapes may be used where suitable. Whilst any suitable arrangement for providing variable numbers of fluid filled sections per unit area of body contact surface may of course be used, conveniently, portions of the mattress having a higher relative number of sections per unit area of body contact surface comprise at least one bifurcated or trifurcated tube. In preferred embodiments, each tube comprises an elongated sac having a substantially arcuate body contact part, a lower support surface and an intermediate section which is not substantially longitudinally extensible. In preferred embodiments, a plurality of discrete transverse supports are provided between internal sides of the intermediate section. These limit the deformation of the body contact part and lower support surface. Preferably, at least the body contact part of each sac is pleated or ruffled along its length. In this way, the mattress is particularly directed to alleviating hammocking. Whilst pleating is conveniently disposed perpendicular to the length of the sac, it may of course, also be longitudinal of its axial length, or angled to the axis of the sac. The term pleated as used herein includes the term ruffled. In low air loss beds, adjacent air sacs are not subject to alternating pressure. In such cases, sacs in accordance with the present invention may still be used. Particularly suited to such an embodiment are effectively single celled elongate air sacs provided with upper body contact and lower support, surfaces, especially those in which the upper contact surface is in cross-section bifurcated or trifurcated. In a preferred embodiments, the pleat/ruffle ratio of the body contact part is between 1:1.57 to 1:2.5. Although generally planar, the lower support surface may be pleated along its length, and in a preferred embodiment is pleated only over a central section of about to V4 the axial length. The pleat/ruffle ratio of the lower support surface may be 1:2.0 to 1:3.0, preferably about 1:2.5. The sides of the intermediate section may provide a continuous or partially discontinuous member to which the pleats of the body contact part may be secured. Alternatively or additionally, a non-extensible member may be provided in the form of a string or cord. It is preferable that such a non- extensible member, when used, should be positioned within the sac as far as possible from the body contact surface to avoid uncomfortable contact with the patient. Conveniently, the body contact part of each sac is orientated such that its vertical axis is normal to the body contact surface of the mattress. The sacs may thus be arranged so that the sides thereof are also generally normal to the body contact surface of the mattress. In this manner, the centre of body contact part arcuate surface is presented for first contact with a body part of a patient. In preferred embodiments, one or more sacs are arranged so that the vertical axis of their body contact part is inclined with respect to the body contact surface of the mattress. Such sacs may be provided at a portion of the body support surface where a patient is likely to load the mattress when seated. The vertical axis is conveniently inclined at a 45° in such sacs. Preferably, each sac is formed of a pressure retaining flexible material adapted to be air filled under pressure. The material may be arranged to seep air. Each sac is preferably provided with areas for retaining the same in position, for example, a reinforced ring through which a securing cord may pass. Each sac may be fabricated from any flexible and/or resilient material, for example, polyurethane or PVC or a fabric supported polyurethane. The pleats may be stuck and/or sewn or vacuum formed and then welded as appropriate. In an alternative method of manufacture, the pleats or ruffles may be formed by causing relative expansion of the body contact part or relative reduction in axial length of the intermediate section, when an intermediate section is used. In the case of a single sac, the sac may be formed as a preform and inserted into a heated mould. The preformed sac is filled with air or an inert gas and heat is then applied differentially such that the body contact part is heated to a significantly higher value than the support surface. With the positive air pressure within the formed sac but with the support surface retained by the mould, and since the temperature of the body contact part is locally raised above the thermoplastic threshold of the material used, the body contact part will deform non-elastically to form pleats and/or ruffles. Alternatively and/or additionally vacuum forming may be used to achieve this end. A cover for a mattress may be provided, the cover comprising a central ruffled/pleated section for receiving a patient. The invention will now be described by way of illustration only with reference to the accompanying drawings wherein:- Figure 1 shows a perspective view of a section of a mattress of the present invention; Figure 2 shows a side cross-sectional view of the mattress of Figure 1; Figures 3 to 5 show side cross-sectional views of alternative embodiments of the present invention; and Figure 6 shows a cover for use with the mattress of Figure 1. Referring to Figure 1, this shows a mattress 1 made up of a plurality of tubular members or sacs 2, formed from a flexible and/or resilient material, for example, polyurethane or PVC or a fabric supported polyurethane. The tubular members are arranged to lie adjacent one another in abutting relationship. Each tubular member comprises an arcuate body contact part 5, and intermediate section 6 and a support surface 7. The tubular members are housed at each of their ends in a discrete box section 3, such box sections ensuring the general shape of the mattress in maintained. The box sections may be formed from fabric or any alternative suitable material. The tubular members 2 are arranged to be air filled, although alternative fillers may comprise any suitable gas, liquid, gel or low friction powder. They are connected to a means for alteration of their internal pressure on a cyclical basis (not shown) . As shown in Figures 1 and 2, the mattress has a body contact surface formed by the upper portions of the tubular members 2. This surface is itself divided into different longitudinal areas, shown generally as D, N, and S, although it will be appreciated that longitudinally or transversely separated areas may be provided. In area D, the foot or heel area, the body contact part 5 of the tubular members 2 is bifurcated so that in effect each tubular member in this area presents two initial contact points or areas 15. The "ear" portions thus formed may be ruffled or pleated in their longitudinal direction or not depending upon the eventual use thereof. As shown, two "ear" portions are formed from a single tubular member by tensioning a central area of the body contact part using a cord 17 attached to a button 18 supported by a transverse support 4. Of course alternative suitable arrangements may be used. In any event, varying the number of sections per unit area of body contact surface may be by any suitable arrangement, as for example shown in Figures 3 to 5. For example, the difference in numbers of sections per unit area of body contact surface may be provided simply by having different sized tubular members 2. Alternative arrangements for supporting the tubular members 2 are also indicated in Figures 3 to 5. Furthermore, "bubble pad" arrangements may be used particularly for areas of the mattress where the number of sections per unit area is relatively high. In "bubble pad" arrangements each tubular member is configured into a series of connected circular portions, that become hump-like when inflated. The arcuate side profiles or adjacent such tubes are arranged to interfit. Referring to Figures 1 and 2, in area N, the abdomen area, the tubular members are not bifurcated so that only a single initial contact point or area 15 is presented for each tubular member. As shown particularly in Figure 2, in area S, the sacral area, the tubular members 2 are inclined with respect to the body contact surface at 45°. The body contact part 5 of each sac is thus orientated such that its vertical or major axis is inclined with respect to the body contact surface of the mattress. When therefore a patient is seated on the mattress. probably with the area of the mattress supporting the patient's back being inclined with respect to the body support surface, the tubular members 2 in area S are directed specifically for dealing with the load characteristics presented by the sacral ischial region of the patient. For further support of the patient, the mattress extends with upright tubular members 2 associated with area N of the mattress. In order to support the inclined tubular members, straps 16 are used at strategic places. A plurality of transverse supports 4 are provided between the sides of the intermediate section. These limit the arcuate deformation of the body contact surface and the support surface. Further support 4' may be provided to enhance this effect, particularly of the support surface. At least the body contact part 5 of each tubular member is pleated or ruffled along its length. In this way, the mattress is particularly directed to alleviating hammocking. The pleating 8 is shown disposed generally perpendicular to the length of the tubular members, but of course, may also be longitudinal of its axial length, or angled to its axis. The term pleated as used herein includes the term ruffled. The pleats may be stuck and/or sewn or vacuum formed and then welded as appropriate. In an alternative method of manufacture, the pleats or ruffles may be formed by causing relative expansion of the body contact portion or relative reduction in axial length of the intermediate section when the intermediate section is used. In the case of a single sac, the sac may be formed as a preform and inserted into a heated mould. The preformed sac is filled with air or an inert gas and heat is then applied differentially such that the body contact part is heated to a significantly higher value than the support surface. With the positive air pressure within the formed sac but with the support surface retained by the mould, and since the temperature of the body contact part is locally raised above the thermoplastic threshold of the material used, the body contact part will deform non-elastically to form pleats and/or ruffles. Alternatively or additionally vacuum forming may be used. The intermediate section 6 is continuous or at least partially discontinuous and provides a member to which the pleats may be secured. Alternatively or additionally, a non-extensible member may be provided in the form of a string or cord (not shown) . Such a non-extensible member when used should be positioned as far as possible from the body contact surface to avoid uncomfortable contact with the patient. Such a string or cord should terminate in shaped end plates which allow the same to exert a longitudinal compressive force. Where transverse members 4 are provided to restrict the deformation of the arcuate body contact part 5 and support surface 7, the pleat/ruffle ratio of the upper body contact parts is between 1:1.57 to 1:2.5. The support portion may be pleated along its length, but is preferably pleated only over a central section of about to 1 4 the axial length. The pleat/ruffle ratio of the support portion is 1:2.0 to 1:3.0, preferably about 1:2.5. As shown in Figure 2, each sac is preferably provided with areas for retaining the same in position, for example, a reinforced ring 10 through which a securing cord 11 may pass. The cords 11 are attached to battens 12 through a wedge shaped supporting foam structure 14. As shown in Figure 6, a cover 19 may be provided which includes a ruffled centre section 20 on which a patient will predominantly lie. The ruffled section assists to improve the pressure signature for a patient lying thereon. The cover may be used with conventional mattresses. Example 1 In order to compare the pressure signatures achievable by standard commercial air beds, an air bed substantially as shown in Figure 1 (the invention) was tested against a standard foam NHS mattress, a "Pegasus" Air Mattress and a "Nimbus 2" Air Mattress. This was effected by positioning a pressure pad at the sacrum, the ischial protuberance, the heel and the trochanter of a series of healthy volunteers and measuring maximum and minimum pressure values in each case and averaging the same. The minus percentage values are therefore particularly desirable since they indicate the percentage improvement over standard values. In this example, the "Oxford Pressure Monitor Mark II" was used for all readings. This determines the interface pressure for observation of the pressure flow characteristics of small pulses of air. The positioning of the centers were as follows:- Semi-recumbent - right heel, left heel, sacrum, left ischial tuberosity, right ischial tuberosity. Side Lyinσ - left trochanter. The heels and the ischial/sacral region are chosen for investigation as they represent a comparatively light yet bony area in the case of the heel whereas the sacrum/ischial tuberosities when semi-recumbent have an area which has considerable loading over a much larger surface. Therefore in making measurements at these sites, the performance of the mattress to a variety of loading patents can be assessed. The trochanter is chosen and is often considered one of the most difficult areas in which to achieve satisfactory pressure relief. The subjects used in this evaluation were all members of Salisbury Hospital Retirement Fellowship and hence have an average age of over 70 years. All are ambulant and in good health. None have any current sores or a history of pressure sores. During the tests they all wear standard night wear or loose fitting underclothes. A single sheet is placed over each mattress. It is not tucked in but left to lie loose, all wrinkles being smoothed out. For the measurements on the sacrum, ischials and heels, the back rest is left at 45° and the mattress is placed over the top of the back rest. Two pillows are used to support the head. For the measurement on the trochanter, the beds are flat with the subjects' heads being supported on two pillows. Both hip and knee angles are at 60° by using specially constructed foam templates. The 3*4 sensor arrays are taped to the skin over the sacrum and over both ischials with the subject standing with the hips flexed at 45° in a similar position to that which they will adopt on the bed during the tests. Care is taken to ensure that there is no tape across the surface of any of the pressure elements. The subject is then carefully transferred onto the bed and the bed is checked to ensure none of the sensors are creased or folded. If any problem is found, the sensor is then inspected and any creases removed and the pressure is remeasured. The subject then remains stationary on the bed for two complete cycles so the bed can adjust to the weight of the subject. The readings are then taken in two complete cycles for the sacrum and one complete cycle for the ischial tuberosities. The maximum, minimum and average pressures measured over one or two cycles is then printed out using a programming facility. Foot blocks are adjusted to ensure that the patient does not slide down the bed during tests. Pressures are measured on the heels using individual cells connected to a standardized computer. One sensor is taped to each heel over the point of maximum pressure and the heel is positioned on the ridge of the mattress with the foot held vertically. The block or board used to prevent the subject from slipping down the bed in the sacral readings is not used as false readings can occur due to some pressure being taken on the soles of the feet. However, the block or board is used as an indicator to observe if the subject slips down the bed. Readings on both heels simultaneously on two complete cycles. Again the maximum, minimum and average pressures are recorded. The head is supported on two pillows and the subject is left in the position of two complete cycles during which time measurements are taken to ensure the sensor is lying correctly before the actual readings are taken again over two cycles. Maximum, minimum and average pressure readings are then recorded. The ten volunteers who participated in the study had an average age of 67 years and an average weight of 60.9 kg and an average height of 1.64 m. For each given subject, the maximum pressure measured on each location on each mattress was noted. This maximum pressure and the corresponding minimum and average pressures for the same sensor were then used to calculate a mean average pressures and examined deviations for all subjects on that mattress. The results obtained in that way were shown in Table I. TABLE I AREA STANDARD AVERAGE MAXIMUM MINIMUM NHS PRESSURE PRESSURE PRESSURE CONTRACT MATTRESS SACRUM Mean 74 39 61 27 St.Dev. 17 18 16 13 Conf. Int. % Pressure -48% -18% -64% ISCHIALS Mean 54 41 61 25 St.Dev. 16 13 14 11 Conf. Int. % Pressure -24% +13% -54% TROCH. Mean 99 43 65 20 St.Dev. 24 10 18 8 Conf. Int. % Pressure -57% -34% -80% HEELS, FULL CELL Mean 112 74 115 24 St.Dev. 23 14 21 9 Conf. Int. % Pressure -34% +3% -79% HEELS, HALF CELL Mean 113 29 58 10 St.Dev. 15 29 37 21 Conf. Int. % Pressure -74% -49% -91% AVERAGE PERCENT PRESSURE -41% -9% -69% FULL CELL AVERAGE PERCENT PRESSURE -51% -22% -72% HALF CELL The results presented above have been obtained using the protocol described above and developed from the Department of Health Mattress evaluation project. As such, these readings are directly comparable with those published in the Department of Health Publication PS4 to be published shortly. It can be seen that the results of the product are impressive especially after the large cells on the heels were replaced with cells of half of the width. The initial reading on the first two volunteers showed that some design modifications were needed to improve the performance of the mattress in the sacral/pelvic area when the subject was in a semi-recumbent position. Hence the readings presented here on the sacrum and ischials are only on eight subjects not on ten. There are six sets of readings on the large heel cells and four sets of readings on the half sized heel cells which are shown to make a substantial improvement. As both heels are measured the statistical analysis was undertaken with twelve and eight readings of full and half heels respectively. The readings on this product compare very well with market leaders which are measured as part of the Department of Health Trial. These were shown in Table II below. TABLE II The average pressure reduction figures over all sites on the two market leaders were then compared with the inventive system below:- TABLE III 1st Tech (large heel 1st Tech (small Pegasus λ Nimbus B cells) heel cells) Ave -41% -51% -30% -35% Max -9% -22% +30% +10% Min -69% -72% -69% -62% Negative pressures correspond to a reduction in pressure and positive values and relate to an increase in pressure compared to the standard hospital mattress values of which are given in Table I. As can be seen, the air mattress in accordance with the present invention provides improved comparative pressure signatures throughout the range of pressures points. This is particularly so with reference to the heel area shown as "D" in Figure 2 which shows a higher average value for the heel area. It will be understood that the embodiments illustrated show applications of the invention in certain forms only for the purposes of illustration. In practice, the invention may be applied to many different configurations, the detailed embodiments being straight forward for those skilled in the art to implement. For example, foregoing arrangements have been described with reference to inflatable air tubes or sacs, but it will be appreciated that static fluid filled sacs equally benefit from the alleviation of the sores as described. The invention provides therefore a novel patient support mattress.

Claims: CLAIMS : 1. A patient support mattress comprising a substantially flat body contact surface formed from a plurality of discrete fluid filled sections; characterised in that the number of sections per unit area of body contact surface is varied at different portions thereof in accordance with the loading characteristic of a body part to be supported there. 2. A mattress according to claim 1, wherein the number of sections per unit area of body contact surface is varied at different portions along the length of the mattress. 3. A mattress according to claim 1 or 2, wherein the number of sections per unit area of body contact surface is relatively increased for portions supporting body parts having smaller contact areas for smaller radii of curvature. 4. A mattress according to any preceding claim, wherein each fluid filled section has a arcuate cross-section, the sections which in use are for supporting body parts having smaller contact areas, having smaller effective radii. 5. A mattress as claimed in claim 4 wherein the radius of the section is made to correspond closely with the radius of a body part to be supported there. 6. A mattress according to any preceding claim, wherein the fluid filled sections are filled with a gas, liquid, gel or low friction powder and connected to a source of pressurization. 7. A mattress according to any preceding claim, wherein the fluid filled sections are connected to a means for alternating of their internal pressure on a cyclical basis. 8. A mattress according to any preceding claim, wherein the body contact surface comprises a plurality of tubes arranged at right angles to a longitudinal direction of the mattress. 9. A mattress according to any preceding claim, wherein a body contact surface of the mattress having a higher relative number of sections per unit area of body contact surface comprises at least one bifurcated or trifurcated tube. 10. A mattress according to claim 8 or 9, wherein each tube comprises an elongated sac having an arcuate body contact part, a support surface and a substantially non-extensible intermediate section. 11. A mattress according to claim 10, wherein one or more tubes are arranged so that their body contact part is orientated such that its vertical axis is inclined with respect to the body contact surface. 12. A mattress according to claim 10 or 11, wherein a plurality of transverse supports are provided between sides of the intermediate section. 13. A mattress according to any one of claims 10 to 12, wherein at least the body contact part of each tube is pleated or ruffled along its length. 14. A mattress according to any of claims 8 to 13, wherein each tube is formed of a pressure retaining flexible material adapted to be fluid filled under pressure. 15. A mattress according to any of claim 8 to 13 wherein each tube is formed of a flexible material which seeps air.

Inventors: WELCH ROBERT DUDLEY, WELCH, ROBERT, DUDLEY
Applicants: WELCH ROBERT DUDLEY, WELCH, ROBERT, DUDLEY
Application year: 1996
Main classification: A47C27
IPC codes: A61G7