IES67150B2 - Filter units - Google Patents

Abstract

Filter units for filtering bacteria and other particles from exhales breath are needed to protect lung function testing apparatus from contamination. The construction according to the invention provides very low pressure drop units consisting of a pair of mating housing halves (1,2) with a sheet of filter material sandwiched between them. By design of the axial cross-sectional area profile through the unit, from an inlet port (7) to an exit port (7), performance may be improved .

Description

FILTER WITS This invention relates to filter units , particularly those used in lung function test equipment or other equipment designed for use with a mouthpiece.

It has been common knowledge for a long time that infection can spread from one person to another by exhalation of material from an infected person and its inspiration by a previously uninfected person. The old adage coughs and sneezes spread diseases has some basis in real life.

This phenomenon is clearly one which must be taken into account in the design and use of any apparatus which is to be used by a person where the person exhales into the apparatus,, particularly because exhalation can easily be followed by inhalation,, even against the conscious wishes of the person exhaling. Thus,, for example, lung function testing apparatus which is designed for use with a % succession of patients needs to be protected against contamination from each patient and thereby prevented * from infecting subsequent patients. The easiest way of achieving thisf and which has been widely adopted in - 2 S677SG practice, is to provide that the patient has a disposable mouthpiece (or a single use mouthpiece which may be recycled following cleaning and sterilisation) and a filter associated with the mouthpiece with the object trapping material exhaled and preventing its reinhalation.

United States patent specification 5230727 describes such a device and in particular discloses a filter consisting of a replaceable filter disc which fits into a housing having an inlet and an outlet. The housing may be disassembled to change the filter and the portion constituting a mouthpiece and replace them with fresh clean sterile ones.

As is disclosed in specification 5230727, the filter material for certain applications, notably lung function testing, needs to have a very low impedance to air flowing through it, in order that it does not affect the measurements being made. Such materials are available in commerce, but they are very expensive. It is accordingly desirable to use them as efficiently as possible.

We have now found that by careful design it is possible to produce filter units which are simple to manufacture, effective in use, and which maximise the useabilitv of expensive filter material.

In accordance with a first feature of the present invention there is provided a filter assembly for use in apparatus adapted to have exhaled breath passed through it which consists of a housing having a pair of members which may be mated together with interposition of a piece of filter material and which may thereafter be separated « 30 - 3 to release the filter material, the configuration of such housing member being such as to provide a chamber, a planar wall of which is constituted by the filter material itself and which has, generally opposite the filter material, an open inlet/outlet port, the crosssectional area of the chamber in planes parallel to the filter material in each case increasing gradually from the port to the filter material, and the filter material being of generally square shape and held in position by co-acting formations on the housing members when mated.

Preferably the co-acting portions are constituted by oppositely arranged lands each located substantially half way along one side of the substantially square section chamber.

Preferably the two mating housing members are identical, each being formed with means capable of clipping onto appropriately configured portions of an identical housing member.

By making the cross-sectional area in planes parallel to the filter material increase gently, substantially improved evenness of flow is secured. The maximum crosssectional area may not be equal to the area of the filter material, but is preferably less by the areas of the formations designed to hold between them the filter material.

By using substantially square pieces of filter material, substantially improved usage of that material may be achieved. The material may be cut into squares with no wastage whatever, though it is generally convenient to cut the material into squares with slightly rounded corners, but the amount of waste caused by the loss of the small four pointed star shapes is trivial compared with the loss of material from three pointed star shapes if a close packed array of circles is cut from a web of filter material, and of course in the latter case there may be substantial further waste at each edge of such a web.

The invention is illustrated by way of example with reference to the accompanying drawings in which; Figure 1 shows in perspective view one form of filter unit in accordance with the present invention, assembled; Figure 2 shows an alternative form of filter unit (with the filter itself removed for clarity) in disassembled fashion; Figure 3 is a plan view of a further embodiment, and Figure 4 is a partial sectional view on an enlarged scale of the part of the housing denoted 4-4 on Figure 3.

Referring first to Figure 1 this shows a perspective view of two clipped together identical plastics housing members 1 and 2. As can be seen, each member has a generally flat rim 3 with on two opposite edges a plastics sprung tab 4. The tabs are configured to spring over the edge of flange 3 of a like housing member» Internally of the flange 3 there is a generally hollow section 5 which is connected via a shoulder 6 to an outlet or inlet tube 7» Tube 7 may be used as a - 5 “ mouthpiece or be provided with a disposable mouthpiece on the one hand, while the other tube 7 of the assembly shown in Figure 1 is e-g- connected to an inlet tube of lung function monitoring apparatus.

Not visible in Figure 1 is a generally rectangular piece of thin filter material which is held between the two housing parts 1 and 2- As can be seen, the hollow space formed by chamber 5 has four cylindrical surfaced portions 8 the section of the flange 3 adjacent to which constitutes a gripping jaw for the internally located generally square piece filter material- A suitable filter material is commercially available in various grades under the designation FILTRETE from 3M Corporation- Grades of base weight 100 to 150 gsm have given good results .

Figure 2 shows a similar pair of housing parts but separated one from another- In this embodiment, each of the clips consists of a projecting tag 12 having an aperture 14 in it which when the two portions are assembled together engages over a ramped bead 16Internal moulded walls 17 co-act to hold a generally square piece of filter material in place- The filter material should of course be of sufficient size to cover the whole of the facing surfaces of the two housing components which can be assembled together i.e™ the filter material must be substantially of the same shape and size as the mating edges 18 of the two housing members» In the embodiment shown in Figure 3, the housing unit is again a hollow moulded plastics body having on two of its side a pair of holes 20 and on the other two sides a pair of hooks 22 each of which has an end which may be latched over a ledge internally of aperture 20. The general configuration, save for the clips 22 and apertures 20, is substantially that of Figure 1. In the cross-section shown in Figure 4, the filter element 23 may be seen held half way along each edge by the juxtaposition of flat wall sections 28 and 29.

By forming the housing members of appropriate resilient plastics material, for example polypropylene, they may be easily clipped together or unclipped one from another to release the square of filter material 23 disposed between them. Manufacture from such plastics material also enables easy sterilisation and reuse of the housing portion. Dependent upon the degree of risk and the precautions adopted, one or both housing portions can be removed from the lung function testing apparatus after each patient has been tested, and in either case the interposed piece of filter material is simply discarded.

Claims (4)

1» A filter assembly for use in apparatus adapted to have exhaled breath passed through it which consists of a housing having a pair of members which may be mated together with interposition of a piece of filter material and which may thereafter be separated to release the filter material, the configuration of such housing member being such as to provide a chamber, a planar wall of which is constituted by the filter material itself and which has, generally opposite the filter material, an open inlet/outlet port, the cross-sectional area of the chamber in planes parallel to the filter material in each case increasing gradually from the port to the filter material, and the filter material being of generally square shape and held in position by coacting formations on the housing members when mated.

2. A filter assembly according to Claim 1 wherein the co-acting portions are constituted by oppositely arranged lands each located substantially half way along one side of the substantially square section chamber.

3. A filter assembly according to Claims 1 or 2 wherein the two mating housing members are identical, each being formed with means capable of clipping onto appropriately configured portions of an identical housing member.

4. A filter assembly substantially as hereinbefore described with reference to the accompanying drawings.