WO2003105938A1

WO2003105938A1 - A device for the exchange of heat and moisture between inhalation and exhalation air flows

Info

Publication number: WO2003105938A1
Application number: PCT/SE2003/000317
Authority: WO
Inventors: Carl-Eric Lindholm; Lars WENSTRÖM
Original assignee: Medical Products Octagon Ab
Priority date: 2002-02-27
Filing date: 2003-02-26
Publication date: 2003-12-24
Also published as: SE0201858L; SE0201858D0; AU2003217098A1

Abstract

A device for exchanging heat and moisture between the flows of respiration air to and from a patient that breaths spontaneously, said device including a body (20) comprised of air-permeable material and having a good heat and moisture exchanging capacity, wherein the body is adapted to screen a passageway (10, 11, 30, 40, 60) for the throughflow of said respiratory air. The passageway is screened by a filter (22) that is chosen to allow air to pass through at a resistance that is lower than 0.2 kPa.s.l^-l and to prevent the passage of at least 95 % of any viruses or bacteria present in the flow of respiratory air.

Description

A DEVICE FOR THE EXCHANGE OF HEAT AND MOISTURE BETWEEN INHALATION AND EXHALATION AIR FLOWS

The present invention relates to a device of the kind defined in the preamble of the accompanying Claim 1 for the exchange of heat and moisture between respiratory air flows to and from a patient who breaths spontaneously.

It is sometimes necessary to support breathing of a patient with the aid of a respirator or some like apparatus. In such cases the patient is often connected to the respirator by means of a tracheostomy tube or tracheal tube. When the respirator can be disconnected, the tube is usually left in the patient for a given length of time over which the patient breaths naturally. There is normally connected to the exposed outer end of the tube an "artificial nose" in the form of an air flow passageway which is screened by an air-permeable body that functions as a moisture and heat exchanger between the inhalation and exhalation air flows through the passageway and also to restrict the passage of small particles, such as dust to some extent. Such known "artificial noses" consist of a plastic foam body that includes large open cells or a body that includes a large number of mutually parallel through passing passages formed from paper, corrugated board or some like material.

On other occasions a device of this kind may be connected to a breathing mask placed around the patient's nose and possibly also around his/her mouth.

The subject of the invention is thus an "artificial nose" which is connected to the airways of a patient and which includes a body that functions as a heat exchanger and a moisture exchanger. The artificial nose is constructed to enable it to be used by patients that can breath naturally; the inventive device shall not be confused with filter devices that are used together with respirators.

US- A-5042468 discloses a device of the kind that includes a "filter" which although being able to prevent dust and bacteria from entering the airways of a patient functions primarily to receive moisture and heat (warmth) from the patient's expiration air and to return the moisture and the warmth to the following flow of inhalation air. The filter does not afford any acceptable separation of viruses or bacteria from the air flow. US-A-5848590 discloses a filter of the kind concerned which is adapted to emulate the resistance offered in the airways in the case of normal spontaneous respiration. The filter does not provide a barrier against bacteria and viruses, since it is constructed to shunt a momentarily elevated flow of expiration air past the actual filter, for instance when the patient coughs.

US-A-5666950 discloses a similar circumstance, where the penetration of small particles (smaller than 3 μm) from the surroundings into the patient's airways shall correspond to those particle sizes allowed by the human nose, which means that over 50% of viruses and bacteria are able to pass through this known filter. Moreover, the air resistance afforded by the "filter" shall be at least 0.2 IcPa.s.l^"1 and preferably about 0.7 IcPa.s.l^"1 so as to provide a throughflow resistance that is considered desirable.

US-A-5606966 also relates to a filter of the kind in question that emulate7 the ability of the human nose to filter out airborne material. Moreover, the filter device according to US-A-

5606966 has a throughflow area of about 2cm.

One problem with devices of the aforedescribed kind is that patients fitted with the artificial nose are liable to be infected with disease generating agents, such as viruses, bacteria and like agents, from other patients, hospital personnel, contaminated surfaces, contaminated air and other ambient agents, and that small particles, such as dust particles, are able to pass through the artificial nose. Another problem is that patients to whom such an artificial nose is applied can infect other patients , personnel, surfaces and other things in the surroundings with disease generating agents, such as bacteria, viruses and other contagia, carried by the patient. Furthemiore, there is a risk of cross-transference of bacteria from the airways of a patient to sores on the patient, for example.

Accordingly, an object of the present invention is to provide a device of the aforesaid kind that will offer a solution to such problems.

This object is achieved by means of the present invention. The invention is defined in the accompanying independent main claim. Further embodiments of the invention will be apparent from the accompanying dependent claims.

The invention is based on the concept of screening the air throughflow passageway of the device with a proper filter that is adapted to allow air to pass through with a flow resistance that is lower than 0.2 IcPa.s.l^"1 and preferably higher than 0.05 IcPa.s. l^"1 but that will prevent the passage of more than about 5% and preferably more than 0.1% of any viruses and bacteria carried by the respiratory air. In order to achieve such a low throughflow resistance, it is necessary that the virus and bacteria filter of the inventive device has an area that is larger than 15 cm² and preferably about 20 cm² or larger. The filter may have the form of a thin filter layer that is both flexible and moldable and that has the general form of thin fabric. The filter layer may particularly have the form of fibre cloth or fibre wool matting, for instance of the kind marketed by 3M under the tradename FILTRETE TM, type G-GS-GSB and often used for the separation of particles in electrostatic filters.

In particularly preferred embodiments of the invention, the filter shall offer a throughflow resistance that is lower than 0.19 or 0.18 IcPa.s.l^"

A device constructed in accordance with the invention can be produced at low cost and provides an effective means of reducing the extent of so-called nosocomial infections or diseases (infections acquired during hospitalization) The problems caused by nosocomial infections and diseases are enormous and cause much human suffering besides incurring costs in the order of billions of Swedish Crowns. A British led investigation found that about 50.000 patients suffer nosocomial infections and diseases each year in Great Britain. The aim of the present invention is reduce the extent of such complications, which are often serious due to the fact that they are associated with bacteria that are resistant to many antibiotics.

In one embodiment of the invention, the passageway may comprise an air line that includes a T-branch pipe which has two mutually facing legs that are substantially filled by said bodies, wherein a virus/T)acteria filter layer is placed on each of those ends of said bodies that are exposed at the mouths of said legs, wherein the third leg of the T-tube provides a connector for detachable connection to a connecting line, such as a tracheostomy tube or tracheal tube. Application of the virus/bacteria filter layer on two opposite end surfaces of the body 20 enables each filter layer to be given a relatively small area, so that the body diameter can be minimised to the values that minimise the amount of space needed to accommodate the device. In preferred embodiments of the invention the virus/bacteria filter shall have an effective area of at least 15 cm and preferably 20 cm , so as to enable a total throughflow resistance of less than 0.2 IcPa.s.l^"1 to be achieved in respect of said device. The body 20 itself has a much lower throughflow resistance than the virus/bacteria filter. By way of an alternative, when it is necessary to reduce the accommodation space the filter layer may be pleated and therewith made smaller whilst still providing the area required with regard to the air flow.

In the case of another embodiment the passageway may be formed by a tracheostoma in the absence of a tracheostomy tube. In such a case, the passageway may be covered by the body, which, in turn, is screened by a bacteria/virus filter. The virus/bacteria filter may, of course, be placed at other positions in the device, the important thing being that the virus/bacteria filter screens the passageway through which the respiratory air passes forwards and backwards. Because the virus/bacteria filter can represent a relatively high flow resistance, it may, in certain embodiments, be desirable to increase the effective throughflow area of the filter by appropriate covering of the filter layer.

In the case of the embodiment in which the line includes a T-tube whose inwardly facing legs are substantially filled with the moisture/heat exchanging body, the legs containing the body may have a generally larger cross-sectional area than the third leg, so as to minimise the resistance to air flow through the body and through the virus/bacteria filter layers.

The bacteria/virus layer that screens the passageway may, of course, have the form of a bag that connects sealingly to one part of the device which can be connected to another part of the device, such as a tracheostomy tube or a tracheal tube for instance.

The line associated with the device may, of course, include a so-called speech valve, i.e. a valve which is normally open but which can be caused to screen the line manually. Such valves are beneficial with respect to patients that have a tracheostomy tube; the patient may either have lost his/her voice or has been fitted with a cannula for other reasons but is able to breath naturally. In other cases in which the passageway is defined by a tracheostoma the patient may be provided between trachea and oesophagus with a valve through which air can be forced up into pharynx or throat of the patient, by holding a finger over the stoma when breathing out. Alternatively, the device may, of course, include a speech valve that will automatically shut off the flow of air out through the stoma and through the device, at least to some extent, in the exhalation phase of the patient, so that the exhalation air will be driven through said overflow valve situated between trachea and oesophagus.

The invention will now be described by way of example with reference to the accompanying drawing, in which

Figure 1 is a schematic axially sectioned view of a device constructed in accordance with the invention;

Figure 2 illustrates schematically and in perspective another embodiment of an inventive device;

Figure 3 illustrates a further embodiment of an inventive device;

Figure 4 illustrates still a further embodiment of an inventive device; and

Figure 5 illustrates a device which corresponds to the device shown in Fig. 1 and which includes a speech valve.

Shown in Figure 1 is a T-shaped tubular element 1 which includes two mutually axially and inwardly facing tubular legs 10 and a third leg 11 which extends at right angles to the legs 10 at a midway point therebetween such as to provide a branch line. The tubular legs 10 are completely filled with a tubular body 20 comprised of an open cell plastic foam, wherein the body 20 has exposed end surfaces 21 at the ends of the legs 10. The exposed end surfaces 21 of the body 20 are covered by a virus/bacteria filter 22 which functions essentially to prevent the passage of microorganisms, such as viruses and bacteria.

The body 20 is chosen to form a heat exchanger and moisture exchanger in respect of respiratory air as it passes through the third leg 11 on its way to and from the patient, via the body 20 and the filters 22. The third tubular leg 11 provides a connector that can be connected to a tube 30, which may have the form of a typical tracheal tube or tracheostomy tube, one end of which can be connected to the connector 11.

As will be evident from Fig. 1, a virus/bacteria filter 22' may be fitted to screen the connector 11 and/or a virus/bacteria filter 22" may be fitted to screen the throughpassing passageway of the tube 30, provided that the filter area can be maintained by pleating the filter or in some similar fashion, or when their are available filters that have a very low resistance to the passage of air per unit of surface area.

Figure 2 illustrates a generally T-shaped tubular element 1 that forms an air through- passage line which is screened by the body 20 and which, in this case, is fully covered by a bag 22'" comprised of flexible sheet material and forming a virus/bacteria filter.

Figure 3 sows a variant of the inventive device. This variant includes an air throughflow line 40 which has a longitudinal section 41 that accommodates a body 20 which functions to screen the air throughflow passageway of the line 40. The passageway is also screened by a filter 22, preferably by a filter 22 on each end of the body 20. Also shown in Fig. 3 is a water delivery line 44 which opens into the body 20 and delivers water thereto. The outer end of the line 40 is connected to an air source 45 from which air is supplied to a breathing mask 47, shown fitted over the nose of a patient, through the line 40. Air is delivered to the mask 47 at an overpressure in the order of 5 - 10 cm water. The patient is also able to breathe naturally, tlirough his/her mouth. The device illustrated in Fig. 3 can be used conveniently in the treatment of patients suffering from sleep anpnoea, wherewith the filter is beneficial and wherewith the supply of water to the body 20 can conveniently ensure that the air delivered to the mask 47 is liquid saturated; patients who suffer from this ailment have serious problems with dryness in the nose and throat if no liquid saturated air is administered.

Fig. 4 is a highly schematic illustration of a section through a patient's neck and shows a tracheostoma 60 that forms an air passageway that connects the trachea to the surroundings. Placed over the stoma is a body 20 which is covered with a filter 22 so that air which flows in and out via the patient's trachea and stoma will also pass tlirough the filter 22 and the body 20. The embodiment shown in Fig. 4 also includes a valve 63 connected between the trachea 60 and the oesophagus (gullet) 68. Although the valve 63 is normally closed, it will open in response to a high pressure in the trachea 60. The patient can himself place a finger over the stoma 60 (over the filter 22 and the body 20) so that the air pressurised in the exhalation phase is able to pass out in the direction of arrow 63.

Although not shown in detail, a speech valve can be fitted in connection with the filter arrangement 20 - 22 for interrupting automatically the flow of air out through the stoma 60 in the exhalation phase, at least to some extent.

Figure 5 illustrates schematically a speech valve applied in the type of device shown in Fig. 1. It will be seen that the junction between the connector or pipe 11 and the legs 10 forms a valve seat 71 around the mouth of the connector 11. A valve plate 72 can be moved readily between a position in which it seals against the seat 71 and a position in which it is withdrawn into the interior of the tubular legs 10 (in a corresponding recess in the body 20). The valve plate 72 is carried by a shaft or stem 73 which extends out of the device, via a seal 74, and carries an actuator button 76. Situated between the legs 10 and the button 76 is a spring 77 which normally holds the plate 72 away from the seat 71. The speech valve functions to redirect the expiration air in a selective manner for a known purpose.

The body 20 may be comprised of an open-cell plastic foam or have corrugated board structure that includes a large number of mutually parallel channels that are delimited by paper walls.

In the case of preferred embodiments, the area of the filter layer 22 that is through-passed by the air is at least 15 cm² or larger, and preferably about 20 cm² or larger. The filter arrangement shall have in its entirety a throughflow resistance that is lower than 0.2 kPa.s.l^"1 (1 = litre). A low throughflow resistance is important with regard to patients that have a poor respiration ability.

The filter layer 22 is chosen to have the capacity to prevent more than 95% and ideally more than 99.9% of microorganisms, such as viruses and bacteria, present in the respiratory air from penetrating the filter and the heat exchanging and moisture exchanging body 20. A suitable filter material is a fibre cloth, which is often used for the separation of particles in electrostatic filters and which is marketed by 3M under the trade name FILTRETE TM, type G-GS-GSB, for example.

The filter 22 is chosen to extract from the air any particles that are at least larger than 3 μm, preferably larger than 2 μm, and more preferably particles that are larger than 1 μm, and still more preferably particles that are larger than 0.1 μm. This will enable the filter to extract viruses and bacteria of corresponding sizes, and also other particles.

Claims

1. A device for exchanging heat and moisture between the flows of respiratory air to and from a patient that breaths spontaneously, said device including a body (20) comprised of air-permeable material and having a good heat and moisture exchanging capacity, wherein the body (20) is adapted to screen a passageway (10, 11, 30, 40, 60) for the throughflow of said respiratory air, characterised in that the passageway is screened by a filter (22) that is chosen to allow air to pass through at a resistance that is lower than 0.2 kPa.s.l^"1 and to prevent the passage of at least 95% of any viruses or bacteria present in the flow of respiratory air.

2. A device according to Claim 1 , characterised in that the passageway is formed by a tubular line, and in that at least a part of said body is received in said line.

3. A device according to Claim 1 or 2, characterised in that the filter (22) is mounted in the close proximity of the body (20) and preferably in contact with said body.

4. A device according to any one of Claims 1 - 3, characterised in that the filter (22) forms an outer layer on the exposed surface of the body (20) that faces away from the patient.

5. A device according to any one of Claims 1 - 4, characterised in that the line includes an adjustable valve for temporary screening of said passageway.

6. A device according to any one of Claims 1 - 5, characterised in that the line includes a tracheal tube or a tracheostomy tube; and in that the tube is preferably releasably attached to other parts of the device.

7. A device according to any one of Claims 1 - 6, characterised in that the filter (22) is disposed in the tube (30).

8. A device according to any one of Claims 1 - 7, characterised in that the line has the form of a T-shaped element (1) which includes two legs (10) which face inwardly towards each other and which are filled substantially by said body (20); in that a filter (22) is placed on and over each of the exposed ends (21) of the body (20); and in that the third leg (11) of the T-shaped element (1) is adapted for releasable sealed connection to a connection line, such as a tracheostomy tube or a tracheal tube (30).

9. A device according to any one of Claims 1 - 8, characterised in that said line has an inlet connection (44) for the supply of liquid to the body (20).

10. A device according to Claim 9, characterised in that said line includes an end section in the form of a breathing mask (47).

11. A device according to any one of Claims 2 - 10, characterised in that said line includes a housing in which the body is received; and in that the housing (1) is surrounded by a casing (22 " ') of filter material, preferably in the form of a sealed, flexible bag comprised of sheet-like filter material.

12. A device according to any one of Claims 1 - 11, characterised in that the filter (22) is chosen to offer an air resistance that is greater than 0.05 IcPa.s.l^"1 and preferably lower than 0.19 kPa.s.l^"1.

13. A device according to any one of Claims 1 - 12, characterised in that the filter (22) is chosen to block the passage of at least 95% and preferably at least 99.9% of any viruses or bacteria present in the respiratory air.

14. A device according to any one of Claims 1 - 13, characterised in that the filter (22) is chosen to have an effective area of at least 15 cm² and preferably of at least 20 cm².

15. A device according to 13, characterised in that the filter (22) is chosen to extract from the respiratory air at least 95% and preferably at least 99.9% of any airborne particles that are larger than 3 μm, preferably larger than 1 μm, and still more preferably larger than 0.1 μm.