GB2237208A - Heating and humidifying respiratory gas - Google Patents

Abstract

Breathing apparatus, in particular a face mask incorporates a regenerator matrix 7 of foam or packed filamentary material, which recovers heat and moisture from exhaled breath and restores the heat and moisture to inhaled breath. The mask has a resilient moulded plastics or rubber or covered foam facepiece, 1, held in place by a strap and with a perforated plastics or metal grill 5 over a matrix body 7 which may be a knitted mesh of aluminium wire or synthetic resin material such as ptfe, nylon or methyl methacrylate which may be hydrophilic. <IMAGE>

Description

DEVICE This invention relates to breathing apparatus.

Persons working in very cold conditions, for example in the Arctic and Antarctic regions, at high altitudes, deep sea divers in helium-rich atmospheres, and so on, are subject to rapid loss of body heat, which may lead to hypothermia. A major cause of loss of body heat is breathing, since the exhaled breath carries heat with it.

Similarly, in situations in which the air temperature is high, for example in deserts, and in manufacturing plant for example foundsries, potteries, glassworks, the inhalation of air can carry excessive amounts of heat into the body causing discomfort or even injury.

The exhaled breath also carries #moisture with it, which can lead to dehydration, especially where the air temperature is high but also in very cold conditions.

An object of this invention is to provide breathing apparatus which can enable the user to breathe without losing all of the body heat carried by the exhaled breath.

Another object of this invention is to provide breathing apparatus which can enable the user to breath comfortably in conditions of high temperature and/or low humidity.

According to one aspect of the present invention breathing apparatus comprises means defining a path for exhaled and inhaled breath, and at least one pervious regenerator body of porous or closely packed eg knitted filamentary heat-storing material in the path of the breath.

The arrangement is such that in cold conditions, heat carried by the user' S breath is absorbed by the regenerator body during exhalation, and heat is recovered from the regenerator during inhalation.

Consequently, the net heat loss through exhalation is reduced, and inhaled breath is warmed.

The regenerator material preferably is such that it also serves to trap moisture from the exhaled breath and add trapped moisture to inhaled breath.

Ideally, the mask, and in particular the regenerator material, should act as though it were an extension of the upper respiratory tract, in respect of heat and moisture recovery. The material to be used should therefore be chosen to emulate, as closely as is practicable, the humidifying and heating effects of the upper respiratory tract.

According to another aspect of the present invention, breathing apparatus comprises means defining a path for exhaled and inhaled breath, and at least one pervious body of porous or closely packed eg knitted filamentary water-absorbent material in the path of the breath.

In one preferred embodiment, the water-absorbent material is arranged and adapted to absorb water by immersion.

Such apparatus can enable the user to breath in conditions of low humidity with reduced loss of moisture from the body. In the preferred embodiment, the said body of material is pre-soaked in water and acts as a reservoir, releasing the stored water slowly while the breathing apparatus is being used. In conditions with high temperatures, this can produce a cooling effect on the inhaled breath, substantially greater than that which can be achieved by a regenerator body which has not been pre-soaked. Loss of body moisture can be substantially eliminated while the breathing apparatus is being used.

Whether the material is intended to be pre-soaked in water, or whether it is merely to absorb moisture from the exhaled breath and restore it to inhaled breath, it is preferably such as to collect and store water at the molecular level. Suitable materials include hydrophilic polymers (inherently hydrophilic, or with coatings or additives of hydrophilic material) in porous or filamentary form, and aluminium wire with porous anodizing.

The material for thermal and/or moisture-buffering can for example be in the form of a foam, or filamentary.

Knitted fibres or wires are particularly simple and effective and can easily be configured to desired shapes and sizes.

However filamentary materials in other forms, for example felted and non-woven structures, can be used.

The filament is preferably pre-crimped before being knitted.

The filament may have a circular or other rounded cross section, but it has been found that the effectiveness of the material in retaining heat and or moisture is enhanced if the filament has a flattened cross section, for example a rectangular or square cross section.

The filament thickness or diameter is typically of the order of 0. 15 mm.

To enhance the moisture-retaining performance of the material, it is preferred to use a material which is inherently hydrophilic or has a hydrophilic coating.

Anodized aluminium and various polymer materials are suitable in this respect.

A body of filamentary material may be made by bundling or pressing together one or more layers of knitted filament, in an ordered or disordered arrangement.

The filamentary material may for example be made of metal wire, e. g. aluminium, monel, nickel, copper, stainless steel. The metal can be treated or coated to provide desired surface properties eg hydrophilia.

One suitable material is knitted metal wire mesh, in particular of aluminium. Aluminium has a number of advantages. It is effectively inert and non-corrodable, and it can readily be anodized to different colours and to provide special surface properties e.g. hydrophilia.

It has a relatively high specific heat and conductivity and therefore high heat absorption and retention.

Plastics filaments can also be used in the manufacture of the regenerator and can have better properties than metals. In particular their thermal storage capacity is higher, and they can be made to have more desirable qualities than metals. Suitable materials include polymer meshes (knitted, felted, woven or non-woven) and foams.

Particularly preferred materials comprise copolymers and composite polymers.

In the case of plastics regenerators, the desired qualities are preferably achieved by copolymerisation but can be introduced by the use of fillers and additives. Qualities such as thermal storage and conductivity, physical strength, elasticity, wetability and water permeability and take up are all desirable and can be achieved in ths way. Resistance to the invasion and multiplication of microorganisms is achieved by the addition of particles of appropriate substances, for example an iodoform compound.

Plastics regenerators are bulkier than metal regenerators, and a nylon knitted mesh would take up approximately twice the volume of an equivalent metal one.

A thermoplastic material modified by additives can be formed into a filament and a knitted mesh produced.

Several layers of a fine mesh netting is also suitable. If a thermosetting plastic is used then more sophisticated manufacturing processes are required.

Materials such as methyl methacrylate copolymerised to make it hydrophilic is nearly ideal, however it is difficult to produce cheaply as a filament or a mesh.

One method of production of a suitable foam is a sacrificial moulding process. The positive consists of a shaped coalescence of particles. Interstitial spaces are then filled with the prepared monomer. After polymerisation is complete the positive is melted or dissolved away. Suitable materials for the positive are sugar, salt or wax.

Particularly suitable materials are: A. Poly methyl methacrylate copolymerised with a hydrogel, prepared as a foam by sacrificial moulding.

B. PTFE or nylon incorporating or supporting additives, eg particulate additives, to impart hydrophilic and/or fungistatic and/or bacteriostatic qualities, in the form of filaments woven, knitted or felted.

The hydrophilic nature of the special polymers which can be used, in particular those mentioned above, can provide improved operation, in that the regenerator can be charged with water before use and the enhanced retention of water provided by such materials allows sustained release of water to the surface of the material, providing cooling of the inhaled breath for a period of time. For example, if the regenerator material is incorporated in a mask, the mask can be simply kept normally immersed in water, and picked out for use in hot conditions.

The present breathing device may be in the form of, or be incorporated in, a mask, which may cover the whole face or only the mouth and nostrils. The invention is applicable, for example, to breathing circuits, anaesthetic masks, and so on. Alternatively, the breathing device may be designed to be held in the mouth, with the filamentary body inside or outside the mouth.

Suitable mask housing materials include high performance synthetic rubbers and resins. The material used must be capable of retaining flexibility at low temperatures. A good example of this is silicone rubber. Semi-rigid closed cell foams are also suitable especially where weight is important. It is preferable that part of the mask in contact with the face be of a suitable foam or fabric covered foam. For use in low-temperature environments, this part of the mask may be of material particularly adapted to remain flexible and comfortable when in contact with the skin for long periods at low-temperature.

There are conflicting requirements of rigidity and flexibility in an orinasal mask and a solution is to make an area of rigid material in the centre of an otherwise flexible mask. The rigid central part can be the housing of the mesh body (removable or otherwise).

Knitted metal or plastics mesh is a particularly suitable material because the knitted structure provides a flexibility not possessed by other forms of filamentary matrix, for example woven metal mesh. The flexibility of the knitted mesh enables it to be deformed or shaped so as to use most efficiently the space available. For example, the body of knitted mesh may become part of the shape or structure of the mask or other breathing device. This material is relatively cheap and therefore, for some applications, can be regarded as disposable. This is particularly advantageous in the case of anaesthetic masks.

The invention will be further described with reference to the accompanying drawing, which shows schematically, in cross-section, a mask embodying the invention.

The mask illustrated comprises a face piece or housing 1, shaped to cover the mouth and nostrils of the user.

This face piece is provided with a strap or straps, by which it can be held in place on the head of the user.

The straps may be mounted directly onto a rigid part of the mask to distribute the load and thus prevent the tension in the strap from distorting the mask.

The face piece is made of any suitable impervious material having an appropriate combination of strength and lightness. It may for example be of moulded plastics material or high-performance rubber e.g. a silicone rubber, or of moulded plastics foam material with a non-permeable skin or covering, or it may be of moulded rigid material provided with a lining or rim of softer material for example plastics foam. The face piece, or at least its rim, is desirably deformable so that it can be made to fit closely and comfortably against the face of the user without significant leakage at the edges.

In the front of the face piece is a circular opening, covered by a perforated wind shield or grill 5 made for example of moulded plastics material or thin metal.

Behind this grill is a regenerator matrix 7 of suitable material as set forth above. This matrix may be integrated with the face piece, for example by having the face piece moulded around the edges of the matrix, or by means of a seal and/or mounting means provided in the face piece. Alternatively, the matrix may be removable from the face piece, for example being held in place in the face piece by the grill 5. The grill serves to protect the matrix, e. g. against strong wind, snow and rain.

In use, the wearer of the mask exhales and inhales continuously through the matrix. An appreciable amount of the heat in the breath will be absorbed by the matrix during each exhalation, and at least part of this stored heat will be recovered by the next inhalation. As a result, the wearer will actually lose only a small proportion of the heat normally lost from the body during breathing, thereby preserving body heat, particularly in very cold conditions. Similarly, the matrix will conserve body moisture, and will help to prevent dehydration particularly in very cold or very dry conditions. The matrix thus acts as a regenerator for heat and moisture.

The illustrated mask is to be held in place by a strap.

Alternatively, a sufficiently light mask can be held in place by a scarf, or other item of clothing for example a Balaclava helmet, or may be incorporated in an item of headgear or clothing. A low-cost light-weight mask can be made for example by molding the face piece in plastics foam and fitting a knitted matrix, e. g.

directly into the foam mouldi#ng, possibly omitting the grill in front of the matrix. Such a mask can be inherently flexible, making it easy to put in a pocket and easy to wear under a scarf or Balaclava helmet.

The face piece can for example be moulded of brightly coloured material or provided with a coloured skin or coating. The matrix material can be coloured for example by anodizing in the case of an aluminium matrix, or by coating.

If a combined form of mask and goggles or visor is used then the dead space can be minimised by means of a divider or separate section. This would also prevent misting of the eyepiece or lenses taking place.

The function of the mask can be altered by replacing the matrix element with one to perform another function as needed. Alternatively filtering or similar can be added to the existing function.

Water build up in the mask can be taken care of by incorporating a cavity in the lower part of the mask.

Alternatively the water can be allowed to drain out of the regenerator. The problem of condensation is not seen to be sufficiently important to warrant a valve drainage system.

An added advantage of using hydrophilic materials is that there is less condensate to dispose of.

Further material may be deposited on the knitted mesh matrix to build up a more solid structure, if required.

Adequate porosity must of course be preserved.

It may be noted that the matrix material used can be similar to material used in the regenerators of Stirling cycle engines; An important factor is that the matrix must provide a minimum path length, if it is to operate effectively, and its minimum path length is believed to be of the order of 6 mm.

Claims (15)

1. Breathing apparatus comprising means defining a path for exhaled and inhaled breath, and at least. one pervious regenerator body of porous or closely packed filamentary heat-storing material in the path of the breath.

2. Breathing apparatus as claimed in Claim 1 in which the regenerator body is adapted to trap moisture from exhaled breath and restore trapped moisture to inhaled breath.

3. Breathing apparatus comprising means defining a path for exhaled and inhaled breath, and at least one pervious body of porous or closely packed eg knitted filamentary water-absorbent material in the path of the breath.

4. Breathing apparatus as claimed in Claim 1, 2 or 3 in which the regenerator body is composed of filamentary material.

5. Breathing apparatus as claimed in Claim 4 in which the filamentary material is Knitted.

6. Breathing apparatus as claimed in Claim 4 or 5 in which the filamentary material is metal wire.

7. Breathing apparatus as claimed in Claim 6 in which the filamentary material is anodized aluminium wire.

8. Breathing apparatus as claimed in Claim 1, 2, 3 or 4 in which the said body is composed of synthetic resin material.

9. Breathing apparatus as claimed in Claim 8 in which the synthetic resin material is modified to have hydrophilic properties.

10. Breathing apparatus as claimed in Claim 8 in which the regenerator is composed of hydrophilic methyl methacrylate.

11. Breathing apparatus as claimed in Claim 8 or 9 in which the said body is composed of PTFE or nylon filaments.

12. Breathing apparatus as claimed in Claim 11 in which the said filaments incorporate or support hydrophilic material.

13. Breathing apparatus as claimed in any preceding claim in the form of face mask.

14. Breathing apparatus substantially as herein described with reference to the accompanying drawing.

15. A method of using breathing apparatus as claimed in Claim 13 or 14 in which the said body comprises hydrophilic material, wherein the mask is immersed in water whereby the said body absorbs water, and thereafter the mask is worn by a user, the absorbed water cooling and/or adding absorbed water to the inhaled breath.