Beds – Mattress – Having confined gas
Patent
1997-11-07
1999-10-26
Trettel, Michael
Beds
Mattress
Having confined gas
5712, 5713, A61G 7057
Patent
active
059705485
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to sacs for 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.sup.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.
All these mattress types suffer to a greater or lesser extent from the problem of "hammocking". Hammocking is the effect which takes place when the weight of a human body is transferred to pressure bearing flexible contact faces such as tubes. The effect of point loading on such tubes is to cause local stretching (to an extent) such that a portion at least of the loading is accepted, not by the pressurised air, but by the stretching of the material of the tube. This causes localised pressures to rise and induces shear forces between the skin and the material, and hence increases the loading of certain areas of the skin adjacent for example a bony prominence. These arrangements therefore can be improved such that the weight transfer is nearer to the ideal, in that the whole weight of the patient's body is borne by a fluid (i.e. the pressure exerted over a section of a patient's body is more equalised whatever the body shape).
The Applicant has now discovered that the above ideal can be more nearly approached by arranging that the body contact surface is provided with a pleated or ruffled contact surface, particularly one in which the longitudinal length of the sac is maintained by a longitudinally extending substantially non-extensible member. This allows body prominences to sink into the surface material with much reduced hammocking thereby more readily transferring the patient's weight to the fluid and so tending to equalize pressure relative to adjacent skin portions.
Accordingly support sacs for use in the foregoing mattress types can be improved in performance by the arrangement of the present invention. The invention also provides that the fluid may be any suitable gas, vapour, liquid or gel or a mixture thereof, so long as it fulfils the requirements of the alleviation of hammocking.
Accordin
REFERENCES:
patent: 3780388 (1973-12-01), Thomas et al.
patent: 5704084 (1998-01-01), Evans et al.
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