EP0712306B1 - Fluidity of particles in an enclosure - Google Patents

Description

Background of the invention:

This invention consists of a bead-filled mattress placed in a supporting structure, designed to prevent bed sores in bed-ridden patients. Various patents exist in this area. The following list is an extract and is not exhaustive.

US-A-4577358 describes a bean bag body support for use with medical and dental patients. Baffles and cups are used to discourage displacement of filler material.

CA-A-934078 covers a positioning aid designed for immobilising a part of a medical patients body. Form stability is achieved by evacuating air from the bag.

FR-A-1488290 is similar to CA-A-934078 but uses a high level of filling to prevent migration of filler material.

WO 0381 uses the fluid bed principle to enhance mobility and reflow of filler material.
None of the above inventions achieves the desired effect or balance of fluidity and stability required to offer relief to (mostly) bed-ridden patients prone to bed-sores.
The problem to prevent bed sores is one of pressure distribution and avoiding shear forces.
Mattresses with elastic behaviour like polyether have poor performance both in distributing pressure in the body tissue and avoiding shear on the skin. Waterbeds have good pressure distribution but induce shear foreces on the skin.
The fluid bed solution is a good one but is noisy and difficult to handle both for patient and staff.
The original bean bag gives good support in the beginning but shows signs of campacting resulting in poor adaptation to body movements and migration of filler material to the extremes of the mattress.
US-A-4213213 describes an airtight enclosure filled with beads to be used in a chair for supporting purposes. This uses inflation for modelling and subsequent deflation for support.

Detailed description.

The invention consists of three elements:

1. A sealed bag partially filled with e.g. polystryrene beads.

2. A contoured flexible support with inclined walls wich serve as enclosure for the loosely filled bag.

3. A system for regulating the amount of air in the bag.

Common knowledge says that bigger particles show better flow behaviour than small ones. E.g. corn and plastic pallets show flow behaviour in silo's while flour and pigments do not so. Contrary to this it has been demonstrated that small hard spherical particles provide optimum fluidity. Remaining friction between particles gives a sense of stability whilst lying on the mattress. Particles with a bulk density in exess of 1000 gr/l require airflow to provide the necessary fluidity, whilst particles with a bulk density less than 100 gr/l are displaced by the weight of the body. A useful equilibrium has been found using particles of less than 1 mm diameter and a bulk density of 200 gr/l.

Use of a relatively large bag, filled to a low degree has been found to reduce shear forces acting on the skin and provide exellent pressure distribution. The bag is made of non-elastic material also to prevent shear. Wrinkels in the fabric have contrary to general belief in this field no adverse effect on the patient.

Containing the bag in a flexible support structure with inclined walls has also been found to improve the characteristics of stability and fluidity, whilst reducing the amount of filler material required. Alternatively the filler material can be placed directly in the supporting tub, the top surface being sealed with an interchangeable sheet. In all cases use of thin pliable fabric is giving the best results.

Use of vapour permeable sheets keeps contamination from the mattress in case of incontinence.
It has been found that regulation of the amount of air wich is in the bag together with the filler material offers the only means of counteracting the effects of compaction resulting in reduction of the fluidity of the filler material occurring with the passage of time. Addition of approximately one litre of air into a bag wich has been in use for some time reinstates it to its original condition. The air wich has been introduced disappears rapidly when a pervious material like cotton is used, whearas an airtight bag, although solving this problem, does not absorb body perspiration. The best compromise would seem to be a vapour permeable material such as tenting fabric or goretex, where introduction of air at a rate of about one litre per hour is sufficient. Furthermore, ventilation of filler material can be achieved by providing an air outlet also.

In the cases of treatment of patients, changing sheets, patients wishing to sit upright, coming out of bed etc. extra support is obtained by eliminating the same amount of a few litres of air from the bag wich introduces just the amount of rigidity necessary without growing to stiff or hard.

Claims (2)

1. A supporting device for a bed-ridden person for preventing bed-sores, said device comprising a flexible support base having in its upper surface a recess of V-shaped cross section extending centrally across the base, and a closed loosely-filled bag of beads located in said recess, the inclined walls of said recess serving to confine said bag of beads.
2. A supporting device for a bed-ridden person for preventing bed-sores, said device comprising a flexible support base having in its upper surface a recess of V-shaped cross section extending centrally across the base, said recess being filled with beads, and an interchangeable sheet located on the top surface of the beads, whereby the beads are confined by the inclined walls of the recess and the interchangeable sheet.

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