Patent ID: 12239592

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the present invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the present invention to the skilled person.

FIG.1illustrates a patient transfer mattress100having a lateral (x) and a longitudinal (y) extension, wherein the mattress100can be arranged in a resting configuration and in a lifting configuration; the mattress100comprising a main mattress section101and a bottom mattress section103; the bottom mattress section103having a smaller lateral (x) extension than the main mattress section101, wherein the main mattress section101comprises a first set of lifting straps105arranged along a first lateral edge106of the main mattress section101and a second set of lifting straps107arranged opposite of the first set of lifting straps105along a second lateral edge108of the main mattress section101, wherein the bottom mattress section103comprises at least one first lower lifting strap109arranged on a first lateral edge110of the bottom mattress section103opposite of at least one second lower lifting strap111arranged on a second lateral edge112of the bottom mattress section103; the lifting straps (105,107,109,111) being configured to be connected to a patient lifting device, wherein the bottom mattress section103comprises a sealed compartment of air104and is configured to cover the thighs of a patient in the lifting configuration.

As used herein, the term “patient transfer mattress” refers to a support mattress or an overlay designed to be placed directly on top of an existing surface, such as a bed. The patient transfer mattress may be used to offload pressure both during lifting of a patient (in the lifting configuration) and when the patient is lying down (in the resting configuration).

As used herein, the term “sealed compartment of air” means a compartment pre-inflated with air. The material of the compartment enclosing the air may be any kind of air leakage tight material.

As illustrated inFIG.1a, the main mattress section may comprise a sealed compartment of air102. This compartment of air may be referred to as a first sealed air compartment, and the sealed air compartment of the bottom mattress section103may be referred to as a second sealed compartment of air104. The sealed compartments of air102and104are illustrated with dotted lines inFIG.1a.

The pre-inflated mattress has various advantages compared to inflatable mattresses existing on the market. The fact that the mattress is pre-inflated relieves the burden for caregivers to deal with an additional step of inflating or deflating the mattress during lifting.

The size of the second sealed air compartment104may correspond to at least 80%, preferably at least 90% of the size of the bottom mattress section103.

In other words, substantially the entire bottom mattress section103encloses an air compartment, and allows for an improved bolstering and cushioning effect during lifting.

The air filling degree of the sealed air compartment104may be from 20 to 70%, preferably from 30 to 60%.

Preferably, the mattress does not provide significant elevation of the thighs, but should be allowed to provide cushioning and allowing air to reposition and flow “freely” within the sealed air compartment104.

As used herein, the term “resting configuration” means the configuration wherein the mattress lays substantially flat on a support surface. In this configuration, the bottom mattress section may or may not be arranged to cover the thighs of the patient. For example, if the patient has been positioned on the bed during a long period, it may be beneficial to fold the bottom mattress section in an area above the thighs, preferably under the sacrum of the patient to provide offloading and re-distribution of pressure in this area instead.

As used herein, the term “lifting configuration” means the configuration wherein the mattress is adapted to be lifted and attached to a lifting device. In this configuration, the bottom mattress section is arranged to cover the thighs of a patient to be lifted. The mattress should not exceed the folds of the knees, as this may result in that the folds of the knees may be bent in the wrong direction.

In the lifting configuration, the bottom mattress section103may be folded such that the second sealed compartment of air104forms at least two overlying air compartments (as best illustrated inFIGS.2band2c).

The main mattress section101is generally rectangular in shape and is adapted to cover at least the sacrum, pelvis and spine of a patient. The main mattress section103is defined by two opposing lateral edges106and108extending between opposing longitudinal edges122and123. The lower longitudinal edge123corresponds to the interface113between the main mattress section101and the bottom mattress section103.

The lateral (x) extension of the main mattress section; i.e. the width, w1, of the main mattress may be from 70 to 110 cm, e.g. from 80 to 100 cm.

The longitudinal (y) extension of the main mattress section; i.e. the length,11, of the main mattress section may be from 100 to 130 cm, e.g. from 105 to 120 cm.

The bottom mattress section103is generally rectangular or square shaped and is adapted to cover the thighs and the folds of the knees of a patient. The bottom mattress section103is defined by two lateral edges110and112extending between opposing longitudinal edges126and123. The lowermost longitudinal edge126also constitutes the peripheral edge of the mattress100. The upper longitudinal edge corresponds to the lower longitudinal edge123of the main mattress section.

The lateral (x) extension of the bottom mattress section; i.e. the width, w2of the bottom mattress section may be from 60 to 100, e.g. from 75 to 90 cm.

The longitudinal (y) extension of the bottom mattress section; i.e. the length,12, of the bottom mattress section may be from 25 cm to 60 cm, e.g. from 30 to 45 cm.

The main mattress section101and the bottom mattress section103may either be formed from the same material or from different materials.

The bottom mattress section103comprises at least one first lower lifting strap109arranged on the first lateral edge110of the bottom mattress section103opposite of at least one second lower lifting strap111arranged on the second lateral edge112of the bottom mattress section103.

Each of the lower lifting straps109,111may comprise at least a first114and a second115attachment means configured to attach the lifting straps to the bottom mattress section103.

As used herein “attachment means” refers to the means or points of attachment of the lifting straps109,111to the bottom mattress section103(or, in embodiments, to the main mattress section101). The attachment means may be secured to the bottom mattress by any mode of attachment, e.g. stitching, welding etc.

The lifting straps are typically arranged at the bottom part of the bottom mattress section103; i.e. close to the peripheral edge126of the bottom mattress section103(i.e. the lowermost peripheral edge of the mattress100).

The attachment means114,115may be arranged at a distance, d1, from each other, wherein the distance, d1, corresponds to the minimum length by which the bottom mattress section103is folded in the lifting configuration.

The distance, d1, may be from 7 to 13 cm, e.g. from 8 to 10 cm.

The two attachment means facilitates the folding of the bottom mattress section103into two overlying air compartments and the bottom mattress section103is preferably folded at least a length corresponding to the distance between the two attachment means. Depending on the length of the patient, the “folding distance” of the bottom mattress section may be larger. Typically, the folds of the knees of a patient serve as the guideline as to where the folding line should be.

During lifting, the lower lifting straps109and111enclose the air in the lowermost compartment and prevents it from slipping out. Thereby, an improved cushioning effect is achieved by means of the air compartments formed in the bottom mattress section103.

The lower lifting straps109,111may be arranged at a distance, d2, from the interface113between the main mattress section101and the bottom mattress section103, wherein the distance, d2, is larger than the distance d1.

The distance, d2, may be at least 12 cm. For example, the distance, d2may be from 12 to 35 cm. In embodiments, where the lifting strap(s) comprises two attachment means, the distance, d2, is measured from the center point of two neighbouring attachment means.

This arrangement enables folding of the bottom mattress section103while still keeping part of the bottom mattress section103substantially unfolded.

The first and second sets of lifting straps105,107preferably comprise at least three lifting straps120. As illustrated inFIGS.1aand1b, four lifting straps120are arranged on each lateral edge106,108of the main mattress section101. Four lifting straps are preferred for an even distribution of load during lifting.

Each of the lifting straps120may include a strap portion that forms one or several gripping loops127in the lifting strap120. The gripping loops are used to secure the lifting straps to a lifting device. This allows for flexibility in terms of the length of the straps when attaching to a lifting device, and particularly allows the mattress to be used to support a patient in a generally seated position.

The lifting straps120may be configured to be attached to a variety of different lifting devices. The lifting straps may or may not be all of the same length. The lifting straps may be configured to engage with a lifting device so that the patient is lifted in supine position. Preferably, the lifting straps are configured to engage with a lifting device so that the patient is lifted in a seated position.

The lifting straps120may have a length of from 30 to 50 cm. The lifting straps may also be adjustable in length.

As illustrated inFIG.1, the lifting straps120extend perpendicular to the lateral edges106,108of the main mattress section101.

The lifting straps120of the main mattress section101are arranged such that the distance, d3, between a first lifting strap120and a neighbouring lifting strap120′ is from 8 to 20 cm, such as from 10 to 16 cm.

The distance, d3, between the lifting straps should not be too large as this may yield undesired pressure points for a patient being lifted, particularly if the patient is heavy or obese. Preferably, the distance, d3, between the lifting straps120does not exceed 20 cm to obtain an even distribution of load. The distance, d3, is measured from the center point of two neighbouring lifting straps120.

Each of the lifting straps120of the first105and the second107sets of lifting straps may comprise at least two attachment means121. This further improves the load distribution of a patient being lifted and prevents “protruding” body parts from falling out in the areas between the lifting straps.

The attachment means121are similar to the attachment means114,115, for the lower lifting straps and may be secured to the mattress by any mode of attachment such as stitching, welding etc.

In embodiments, additional handles may be secured between the attachment means121of the lifting straps120. The handles may be located on the underside of the mattress100, illustrated by128inFIG.1b. The handles128may serve to move and reposition the mattress100and the patient. The handles128may be formed from bands extending between the attachment points. This offers the caregivers a variety of options for gripping locations when moving a patient.

To optimize the load distribution and prevent pressure peaks, the distance, d4, between each attachment means121of the lifting straps120,120′ of the main mattress section101is substantially equal along the length of the lateral edges106,108of the main mattress section101. Preferably, the distance, d4is from 8 to 18 cm, e.g. from 10 to 14 cm.

As illustrated inFIG.1, the mattress100comprises two side mattress sections124; each side mattress section124extending from each lateral edge106,108of the main mattress section101.

The side mattress section124may extend at an angle of 30 to 60 degrees from the main mattress section101in order not to completely enclose and “bury” the patient.

The main mattress section101has a first longitudinal edge122and a second longitudinal edge123; the bottom mattress section103extending from the second longitudinal edge123, and wherein the mattress100comprises a head mattress section125extending from the first longitudinal edge122of the main mattress section101.

The head mattress section125may be sized and shaped so as to extend across a patient's upper torso at least from shoulder to shoulder and from the base of the spine to the top of the head. Alternatively, the head mattress section125covers the neck and the head of the patient only.

The head mattress section125provides support for the head of the patient during lifting. The head mattress section may or may not be formed integral with the main mattress section101. It may be formed from the same material as the main mattress section101, or from a different material, such as a material that provides comfort to the head during lifting.

Lifting straps129may be provided on the head mattress section125.

As illustrated inFIG.1a, the first102and the second104sealed compartments of air are configured to overlap in an area of the main mattress section101.

The main mattress section101may comprise an upper portion116and a lower portion117, wherein the first compartment of air102and the second compartment of air104are arranged to overlap at least in an area of the lower portion117of the main mattress section101.

As used herein, the term “upper portion of the main mattress section” means a portion of the main mattress section corresponding to 50% of the extension of the main mattress section in the longitudinal (y) direction, extending from the first longitudinal edge122to a center point of the main mattress101.

Accordingly, the term “lower portion of the main mattress section” means a portion of the main mattress section corresponding to 50% of the extension of the main mattress section in the longitudinal (y) direction, extending from the second longitudinal edge123to a center point of the main mattress101.

The dotted lines inFIG.1aillustrates the area of overlap between the first102and second104air compartments.

The overlapping air compartments102and104are preferably arranged in an area of the mattress100intended to be placed slightly below the sacrum area of the patient. When the patient is lifted, this has an offloading effect on the sacrum, which is an area of particular concern for pressure ulcer prevention. By supporting and lifting the upper thighs, a rotation of the pelvis is generated, which creates a changed angle of the coccyx bone. The sacrum is offloaded both due to the bolstering effect of the folded bottom mattress section103and due to the air compartment102.

The offloading of pressure during lifting and the bolstering and cushioning effect provided by a mattress100of the present disclosure, makes the mattress useful not only for transferring a patient from one surface or bed to another, also for the purpose of providing an alternative position in a patient repositioning schedule.

In embodiments, the size of the first sealed air compartment102corresponds to at least 70% of the size of the main mattress section101.

The lateral (x) extension of the first sealed air compartment102in the lower portion117of the main mattress section101may be smaller than the lateral (x) extension of the upper portion116of the main mattress section101, as illustrated inFIG.1a.

This configuration allows for advantages both when the patient is lying down, and is being lifted. The configuration allows the air to be pushed in the direction of the back of the patient, which enhances the bolstering effect of the lower back, the sacrum as well as the thighs of the patient. Air fills up the voids between the body and the mattress, which generates a more even support and contact over the patient body. An improved pressure redistribution effect is thereby achieved, since an even pressure over a larger surface area is generated.

In embodiments, the first compartment of air102and the second compartment of air104are unattached to each other.

In embodiments, the mattress100comprises a top layer118and a bottom layer119, wherein the first compartment of air102is attached to the top layer118and the second compartment of air104is attached to the bottom layer119.

As used herein the term “top layer” means the layer in contact with the patient during use. The top layer may be formed by one single layer covering all sections of the mattress, or it may comprise several layers sewn or sealed together. For example, the bottom mattress section may comprise a top layer being different from the top layer of the side or head mattress section.

The top layer118may be formed from a variety of materials and may also include multiple layers. The top layer118may comprise a softer material providing comfort to the patient. The top layer118may be formed from a material having a higher coefficient of friction than the bottom layer119in order to inhibit undesired slipping of the patient during lifting. For example, the top layer118may be comprise e.g. cotton, microfiber or other textiles.

The bottom layer119may be formed from a material having a low friction to facilitate sliding of the mattress100on a bed or support surface. The bottom layer119may for example be formed from a synthetic material, such as plastic, vinyl or the like.

The term “low friction” is a relative term that refers to the relative frictional forces generated when two surfaces are tested under similar conditions.

During manufacture of the mattress of the present disclosure, the first compartment of air102may first be attached to the top layer118; i.e. sewn or sealed to an underside of the top layer (facing the interior of the mattress). The second compartment of air104may subsequently be attached to the bottom layer119of the mattress. Thereafter, the top layer118and the bottom layer119may be attached to each other, e.g. by sewing or sealing the outermost edges of the mattress100. This way the air compartments102and104will partially overlap, but will remain unattached to each other.

As illustrated inFIG.1b, the bottom layer119of the mattress100may comprise markings130to guide a caregiver to correctly position the patient on a hospital bed after the patient has been lifted, and is to be positioned on a bed or support surface.

If a hospital bed with an adjustable “head section” is utilized, the horizontally extending line of the mattress markings130is preferably arranged at the position of the bed, where the bend of the bed is located. This facilitates a correct positioning of a patient of the bed when a patient has been lifted and is to be re-positioned on the hospital bed (seeFIG.2d).

Markings may also be provided on the top layer118of the mattress. For example, such markings may be arranged to guide a caregiver on how to correctly position the patient on the mattress, both for the purposes of lifting the patient correctly, but also for the purpose of yielding an optimal pressure off-loading effect when a patient is lying down.

According to another aspect, the present disclosure relates to a method for lifting and/or transferring a patient.

With reference toFIG.2a-c, the method comprisesa) providing a patient transfer mattress200having a lateral (x) and a longitudinal (y) extension and comprising a main mattress section201and a bottom mattress section203; the bottom mattress section203having a smaller lateral (x) extension than the main mattress section201, wherein the main mattress section201comprises a first set of lifting straps205arranged along a first lateral edge of the main mattress section201and a second set of lifting straps207arranged opposite of the first set of lifting straps205along a second lateral edge of the main mattress section201, wherein the bottom mattress section203comprises at least one first lower lifting strap209arranged on a first lateral edge of the bottom mattress section203opposite of at least a second lower lifting strap211arranged on a second lateral edge (not shown) of the bottom mattress section203; wherein the bottom mattress section203comprises a sealed compartment of air,b) positioning a patient231on the mattress200such that the sealed compartment of air of the bottom mattress section203is arranged to cover the thighs of the patient231c) connecting the lifting straps205,207,209and211to a patient lift system233d) lifting and/or transferring the patient231.

As illustrated inFIG.2, the method comprises folding of the bottom mattress section203such that the sealed compartment of air204forms at least two overlying air compartments232(see the partial view inFIG.2billustrating the folding of the bottom mattress section)

The lift system233may be arranged over the patient231prior to lifting. Each of the lifting straps is engaged with the patient lift system233. Gripping loops may be used to engage the mattress200with the lift233. Depending on the size of the patient to be lifted, and on the position of the patient233during lifting, the gripping loops provides for a situation and patient adapted lifting.

After the lifting straps have been arranged on the lift233, the lift233may be activated and the patient231may be lifted from the bed234and raised to the position as illustrated inFIG.2a.

In step b), the bottom mattress section203may be folded along a folding line which corresponds to the lower thighs and/or the folds of the knees235of the patient231.

As best illustrated inFIG.2c, a bolstering and cushioning effect is achieved in the area of the lower thighs and the folds of the knees235.

In another aspect of the present disclosure, the method as described hereinbefore constitutes a step in a patient repositioning and/or turning schedule.

Thus, there is provided a method for repositioning a patient comprising at least one step of lifting a patient with a mattress as described hereinabove or comprising a method for lifting a patient as described hereinabove.

The transfer mattress of the present disclosure may be used as a pressure off-loading mattress for a patient in both a lying and a lifting configuration. In other words, after the patient has been lifted or transferred, there is no need to replace the mattress of the present disclosure with another, different pressure off-loading mattress.

The lifting configuration of the mattress of the present disclosure has a pressure off-loading effect on the patient. A patient at risk of developing pressure ulcers must be repositioned and turned at regular intervals and such repositioning, and turning schedules are frequently utilized in care facilities and hospitals. The method described could form a step within such a repositioning schedule.

FIG.2dillustrates a patient231that has been repositioned (but not lifted). The patient231is lying sideways on the bed234. The dotted lines236of the bed234illustrate the “bend” of the bed; i.e. where the head of the bed can be elevated. After a patient has been lifted (as illustrated inFIG.2a) and the patient is to be repositioned in bed, the markings230of the bottom layer of the mattress200serve to guide the caregivers to correctly position the patient on the bed (i.e. corresponding to the bend236of the bed234where the head section can be elevated).

It should be noted that terms, definitions and embodiments of the first aspect of the present disclosure apply mutatis mutandis to the other aspects of the present disclosure, and vice versa.

Example 1: Evaluation of the Pressure Distribution Effect

To evaluate the effect of a patient transfer mattress according to the present disclosure, three separate patient transfer mattresses were evaluated.

Mattress A was a transfer mattress according to the present disclosure as defined in claim1, and illustrated inFIG.1. Mattress A comprised a top layer, a bottom layer and two respective sealed compartments of air; i.e. a first sealed compartment of air comprised in the main mattress section and a second sealed compartment of air comprised in the bottom mattress section, as illustrated inFIG.1a.

Mattress B was a transfer mattress with the same construction as Mattress A, but differed with respect to the presence of air. No air was present in the bottom mattress section or in any other portion of the mattress.

Mattress C was a commercially available transfer sheet, Solo RepoSheet®, from Hill-Rom.

The mattresses were tested to evaluate the interface pressure and surface area subject to pressure above different critical thresholds when a subject has been suspended.

Three different test subjects were included in the tests:

TABLE 1Subjects testedHeight (cm)Weight (kg)BMIGenderSubject 11685519.5FemaleSubject 21757524.5FemaleSubject 31668029FemaleAverage170 ± 570 ± 1324 ± 5Female
Test Set-Up

The mattresses (A-C) and the subjects were attached to a lift (VEGA505EE) provided with a bar from Handicare (Slingbar L). The test duration was five minutes. A pressure mat (XSensor LX100:40:40.02) was used to register the interface pressure during the entire test period. The pressure mat was arranged to register the interface pressure in an area covering the sacrum and the thighs (covering the thighs all the way to the knee folds).

First, the subject was in a flat supine position on a bed (Enterprise 500), then the bed was raised such that the head-of-bed (HOB) angle was 30 degrees, and the knees were bended as well. The subject was then lifted until totally suspended; i.e. freely hanging in the air. The test was repeated three times, one test for each mattress; i.e. the total test time for each subject was 20 minutes. Data was recorded directly from the pressure mat and the calibration of the pressure mat was controlled. The pressure data extracted from the pressure mat was made after the patient had been suspended for about one minute.

Pressure Re-Distribution Effect: Surface Area Evaluation

The pressure redistribution effect of the mattresses was evaluated by the pressure mat registration of the surface area (cm2) above a pressure threshold of 40 mm Hg, and, of 60 mm Hg, respectively.

FIG.3illustrates the surface area for pressures above 40 mm Hg for three subjects for Mattress A, and Mattress B, respectively. As illustrated in this figure, Mattress A yields a significantly smaller area of higher pressures than Mattress B.

FIG.4illustrates the pressure mat recordings of 5-80 mm Hg for subject2when lifted with Mattress A (FIG.4a) and Mattress B (FIG.4b). The darker sections in this figure illustrate the areas of the subject exposed to higher amounts of pressure. As can be seen, the areas exposed to the highest amounts of pressure are the knee folds, and the sacral buttocks.

FIG.5illustrates the surface area for pressures above 60 mm Hg for Mattress A, and Mattress C, respectively. As illustrated in this figure, Mattress C yields a significantly higher surface area of high pressures for all subjects compared to Mattress A.

In addition toFIG.5that illustrates surface area for pressure above 60 mmHg, the average surface area above pressure thresholds up to 200 mm Hg was evaluated, and is illustrated inFIG.6. As can be seen, Mattress C has a large surface with stresses all the way up to 200 mm Hg. In contrast, the surface area recorded for Mattress A was small for pressures above 60 mm Hg. This is due to the pressure offloading effect of Mattress A, i.e. the ability of the mattress to distribute the body load more evenly over the entire mattress surface. With a larger surface area that evenly supports the body, the body load per area unit, i.e. pressure, will be smaller and less harmful. InFIG.6the large area with lower pressure (<40 mm Hg) for Mattress A illustrates this.

To summarize, these results illustrate that even during short durations of lifts, the patient may be exposed to high pressures which eventually may lead to the formation of pressure ulcers. This is demonstrated by the surface area recordings of Mattress B, and C, respectively. However, when a mattress according to the present invention is used (Mattress A) for lifting a subject, an enhanced pressure redistribution and pressure offloading effect is achieved.

Example 2: Evaluation of Critical Stresses in the Soft Tissue by FE Modelling

Finite Element (FE) Modelling

The mechanisms leading to pressure ulcers are not fully understood. Pressure sensing mats can give information on pressure present at the mattress under the skin surface but does not inform on the behavior inside the soft tissues. An increased stress and/or strain in the soft tissue can generate increased discomfort, or even pain. Therefore, the Finite Element (FE) method offers a great alternative to study deep tissue response.

The FE method is a numerical and computational technique used to solve multiphysics problems by solving partial differential equations upon different types of discretizations. The FE method subdivides a large problem or large 3D model into smaller parts, called finite elements. The analyses are performed within each element, and the assembly gives a solution to the entire problem.

The workflow for a FE analysis can be explained as follows: creation of a 3D model constituted of finite elements, definition of the material properties of the model, definition of the boundary conditions and loadings to apply to the model according to the problem, computational solving of the problem, and analysis of the results through visualization and calculations.

Finite Element (FE) Settings and Anatomical Model

In order to understand the effect of the patient transfer mattress according to the present invention, finite Element (FE) models of a full body model and of a patient transfer mattress according to the present disclosure were created, and analyses were performed to study the effect of pressure and stresses in the deep tissue layers. The volunteer was a non-smoker healthy adult male of 31 years at the time of the study (length: 177 cm, weight: 85 kg).

The FE models were prepared in prepared in ANSA 19.1.1 and META 19.1.1 (BETA CAE) and the analysis performed in ABAQUS 2019x (DASSAULT SYSTEM). The human body model was based on segmentation from MRI data from the Virtual Population 3.0.

The soft tissues were represented as non-linear materials. The muscles were lumped together as one material, the fat and the skin were lumped together as one compressive material, tensile properties of the skin were represented with a shell, the bones as rigid body. The main joints (i.e. two knee joints, two hip joints and one neck/skull joint) were modelled to enable a realistic movement of a human body. The spine was modelled with intervertebral discs.

The deformation of the soft tissue caused by compression from the body weight was used to validate the material properties in the FE model with ABAQUS14.0(DASSAULT SYSTEM). The validation was carried out by comparing the thickness of the soft tissues before and after compression between the model and the MRI data.

The evaluation of the soft tissue was performed by first simulating a clinical setting where a patient is lying on a mattress. A soft mattress (30 kPa) was added under the pelvis and the equivalent of the body weight was applied to induce contact and compression of the pelvis on the mattress. Next, the evaluation of the body position was performed by comparing the body position of a healthy subject hanging in the patient transfer mattress with the body position in the FE model when simulating the patient hanging in a patient transfer mattress according to the present disclosure.

Patient mattresses A and B (as described in Example 1) were used in the experiments. Accordingly, Mattress A represented a patient transfer mattress according to the present disclosure. Mattress A comprised a top layer, a bottom layer and two respective sealed compartments of air; i.e. a first sealed compartment of air comprised in the main mattress section and a second sealed compartment of air comprised in the bottom mattress section, as illustrated inFIG.1a. Each sealed air compartment was modeled as a single fluid cavity with holes. Mattress B had the same construction and same shape as Mattress A, but did not comprise any air comprised within the sealed (air) compartments. This patient mattress corresponds to a prior art mattress. The distribution of the lifting straps were the same for both mattresses (corresponding to the illustration inFIGS.1aand1b).

Both mattresses A and B were simulated with the second sealed compartment in a folded configuration during lifting of the patient; i.e. the folded compartment was the edge of the mattress and positioned just above the knee fold of a patient.

The movement of the straps was made in two steps. First, two pairs of top straps were moved to a hanger bar positioned 530 mm from the bed surface in the level of the navel area. This was done to straighten it up in a more seated position. Second, the remaining four pairs of straps were moved to the hanger bar.

The results hereinbelow show different stresses for the last stage in the FE simulation; i.e. in the lifting configuration when the body is hanging in the air. These results were observed on all the soft tissue layers together. Table 2 below presents the stresses evaluated.

To calculate the volume of tissue under stress, all tissue elements of certain tissue volume were observed. After deciding the range of critical stresses, it was possible to isolate the elements which were above that critical stress and then compare the results for Mattress A, and Mattress B, respectively. The volume calculation was based on stresses in each element. The following stresses were investigated:

TABLE 2Soft tissue and simulated stressesSoft tissueDefinition ofStresses investigated (inlayersurfaces observedlifting configuration)Soft tissueSkin, fat and muscleVon Mises stresses (VMS)Shear stresses (XY, XZ, YZ)

The “Von Mises stresses”, VMS (MPa) origin from the von Mises criterion, also known as the maximum distortion strain energy criterion. It is a quantitative criterion widely used in engineering. A stress measure that takes into account all stresses experienced by a continuum element. The Strain Energy Density is separated into different components in order to isolate the hydrostatic stresses and the deviatoric stresses. The deviatoric stresses are represented by the VMS, and combine stresses in different directions into an equivalent stress that will take into account normal stresses, shear stresses and distortion.

The Von Mises Stresses (VMS) are defined in the Distorsion Energy Theory and represent a common criterion widely used in engineering. The VMS can be defined as:
σVM=√{square root over (½[(σxx−σyy)2+(σyy−σzz)2+(σzz−σxx)1]+3(τxy2+τyz2+τzx2))}

“Shear stresses” in different planes (MPa) cause deformation of a material by slippage along a plane or planes parallel to the imposed stress. It arises from the shear force, the component of force vector parallel to the material cross section. The reason for introducing them as a measure is an experienced feeling of shearing in soft tissues in contact with the mattress edge during hanging/lifting in the mattress.

Shear stresses are stresses parallel to the plane and can be expressed as:
τ=Fp/A, whereinτ=shear stress (MPa)Fp=parallel component force (N)A=area (mm2)

There are no known values of critical stresses, as it varies between individuals, due to their physiological parameters, health, age and with the duration of exposure to the stresses. Therefore, the evaluation of the effect of the mattresses relies on qualitative values.

The critical value of stresses correspond to about 1 kg for 10 cm2(around 10 kPa), except for the shear stresses, where a lower value of the critical stresses was used, corresponding to about 100 g for 10 cm2(around 1 kPa), as the stresses are applied parallel to the muscle fibers and therefore against a more natural compressive behavior.

Results

The patient transfer mattresses A and B were evaluated by their ability to reduce stresses in soft tissue. The performance of the mattresses was evaluated by their ability to reduce the volume of tissue under critical stresses. The performances of the mattress of the present disclosure; i.e. Mattress A would therefore be defined as the percentage reduction of volume of tissue under critical stress when compared to the product without air; i.e. Mattress B:
Reduction (%)=((Vno air−Vair)/Vno air)×100, whereinthe reduction (%)=percentage reduction of volume of tissue under critical stress,Vno air=volume of tissue under critical stress in Mattress BVair=volume of tissue under critical stress in Mattress A

FIG.7illustrates the volume for critical stress evaluation, defined by two cross sections, y1 and y2. Both mattresses were investigated in the same volume of tissue; i.e. in the area just above the knee fold. The area measured is referred to as the “knee fold region” in table 3 below, although the evaluation is actually performed in the region just above the knee fold, where the edge of the mattresses is arranged. For both mattresses, measurements were made with y1=575 mm and y2=650 mm.

Next, a larger area, covering also the thighs of the patient (from the knees to the hips), was analyzed. In this evaluation, y1 was 575 mm and y2 was 925 mm for both mattresses. The area measured is referred to as “the thigh region” in table 3 below.

Table 3 below illustrates the volume of soft tissue under critical VMS stresses; i.e. the volume that exceeds the 0.01 MPa threshold, and the percentage of improvement in stress reduction by Mattress A.

TABLE 3Volume of soft tissue with critical Von Misesstresses in knee fold and thigh regionsImprovement byMattress AMattress BMattress AVolume of soft tissue72503640480%elements under criticalstresses in knee foldregion (mm3)Volume of soft tissue395244688616%elements under criticalstresses in thigh region(mm3)

Next, the volume of elements under critical shear stresses in the soft tissue was compared between Mattress A and Mattress B. The area above the knee fold was investigated (i.e. y1 was 575 mm and y2 was 650 mm for both mattresses). The volume of elements that exceeds the critical shear stresses (±0.001 MPa) threshold was investigated in three different planes; i.e. the XY plane, the XZ plane, and the YZ plane. The results are shown in table 4 below.

TABLE 4Volume of soft tissue elements under critical shear stressesImprovement byMattress AMattress BMattress AVolume of soft tissue92644486779%elements under criticalXY shear stresses (mm3)Volume of soft tissue399838825955%elements under criticalXZ shear stresses (mm3)Volume of soft tissue285785515548%elements under criticalYZ shear stresses (mm3)Total volume of soft7782518828159%tissue elements undercritical shear stresses(mm3)

As demonstrated in tables 3 and 4, a mattress according to the present disclosure significantly reduces critical Von Mises stresses and shear stresses in the soft tissue. This is particularly the case in the area just above the knee fold, which is regarded as a critical area for the creation of harmful pressure points during lifting.

In addition, the results from the FE modelling indicated that the simulated body laying on Mattress A had a contact area of 240350 mm2. The corresponding area for Mattress B was 197366 mm2. This represents an increase in 22%. These results indicate that Mattress A yields an improved weight distribution, and can also relieve the sacral buttocks to a greater extent.

Even though the present disclosure has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art.

Variations to the disclosed embodiments can be understood and effected by the skilled addressee in practicing the present disclosure, from a study of the drawings, the disclosure, and the appended claims. Furthermore, in the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality.