GB2062470A - Spirometers - Google Patents

Abstract

A mouthpiece for the inlet tube of a spirometer is formed to engage the inlet end of the tube and has a radially extending part or parts for preventing reverse fitting. An apertured valve seating has a valve diaphragm of flexible material for obstructing the return flow of air to the patient's mouth. The seating may have a projecting rim for engagement with the peripheral region of the diaphragm, and the diaphragm is preferably mounted so that it is planar on first engagement therewith. A ring may be arranged to be contacted by the diaphragm after initial bulging by back-pressure. Further deformation of the diaphragm is thereby controlled so that its peripheral region remains in engagement with the rim. <IMAGE>

Description

SPECIFICATION Spirometers Spirometers by which the pattern of exhalation by a patient can be recorded are used as a diagnostic aid in clinical practice. It is usual, for hygenic reasons, to provide a spirometer with a disposable mouthpiece eg. of cardboard. This arrangement does not however eliminate the possibility of the patient inhaling, from the apparatus, air which is contaminated by matter from previous tests on other patients.

The present invention provides an inlet tube for a spirometer, said tube being fitted with a mouthpiece formed to engage the tube at the in let end thereof, an apertured valve seating part carried by the mouthpiece and being formed to extend across the bore of the tube, a valve diaphragm formed of flexible material, said diaphragm being operable to obstruct a return flow of air blown through the mouthpiece and a radially extending part or parts for preventing reverse fitting of the mouthpiece to the tube.

The radially extending part may simply be a flange. In a more elaborate arrangement the flange has a sleeve part for engagement with the exterior of the tube, the flange extends inwardly from the sleeve part and the valve seating part is carried by the inner periphery of the flange.

In a preferred arrangement the seating part has an axially projecting circular rim for engagement with the peripheral region of the diaphragm. A major part of the force produced on the diaphragm by a (potential) reverse flow of air is carried by the rim to give an efficient sealing effect at low back-pressure with a diaphragm of economic construction.

Conveniently the seating part has a central mounting for mounting the diaphragm by its centre, said mounting being carried by spokes.

Best sealing results are obtained by mounting the diaphragm centrally at an axial position such that on its initial engagement with the circular rim produced by said return flow of air, said diaphragm is in a substantially un-distorted configuration. With a diaphragm of the most economic form ie. a planar form, this arrangement involves having the centre of the diaphragm mounted in the plane of the rim.

Provision is required for maintaining an adequate sealing action for the increased back-pressures which develop after the initial sealing action and such relatively high back-pressures as may be produced by the patient sucking. For this purpose the seating part may be provided with an inner ring part mounted co-axially with the rim in an axially recessed position with the diaphragm deformable to engage the ring part after said initial engagement with the circular rim. With this arrangement, the efficient sealing action of the circular rim for low backpressures is maintained. As the pressure increases, the diaphragm bulges. Such bulging action is limited by contact of the diaphragm with the inner ring.

Such further bulging action between the periphery and the inner ring, and between the inner ring and the centre of the diaphragm, as may occur produces far less disturbance of the sealing action than does free bulging. By assisting the sealing action, the provision of the inner ring reduces the constructional requirements of the diaphragm and makes it possible to form the diaphragm from flexible resinous sheeting, eg. plasticised polyvinyl chloride sheeting.

It is satisfactory to cut the diaphragm from resinous sheeting of the quality supplied in the form of rolls.

In use the diaphragm is warmed by the patient's breath and when cut as aforesaid many forms of the sheeting tend to curl. For this reason the diaphragm is preferably oriented so that the potentially concave face of the sheeting is the face which engages the seating.

The inner ring, in promoting the sealing action of a diaphragm of low rigidity, also results in minimising the flow resistance of an exhalation into the spirometer. The inner ring itself can be discontinuous in form thus reducing its own flow resistance. By giving the spokes, aforesaid, a laminar configuration and orienting them with their edges facing the diaphragm, the flow resistance attributable to the spokes is reduced. Not only is the area of the spokes across the direction of flow minimised but the laminar form tends to reduce turbulence and the flow-resistance attributable thereto.

Having an even number of spokes is desirably avoided. It is found that with two or four spokes there is a tendency to induce a folding action of the diaphragm. An odd number, three spokes being the most convenient, gives best results.

The following description, in which reference is made to the accompanying drawings is given in orderto illustrate the invention.

In the drawings: Fig. 1 is a cross section showing the general arrangement of a first embodiment of the inlet tube in association with a spirometer, Fig. 2 is a cross section showing part of the embodiment 1 in further detail, Fig. 3 shows part of the embodiment in plan, Fig. 4 shows a second embodiment partly in elevation and partly in axial cross-section, Fig. 5 is an underneath plan of part of the embodiment of Fig. 4, Fig. 6 is a cross section taken along line VI-VI of Fig. 5, and Figs. 7A, B & Care diagrammatic cross-sections showing the diaphragm of the embodiment of Figs.

4 to 6, its associated parts and its response to pressure Fig. 1 shows the known arrangement of a flexible tube 1 connected with a bellows-type spirometer shown diagrammatically at 2 and having a fitting 3 for receiving the end of a disposable cardboard tube 4.

In accordance with the invention, the tube 4 is fitted with a mouthpiece 5 (shown in further detail in Figs. 2 and 3) having a valve diaphragm 6 on the spirometer-side of a seating 7. Seating 7 is mounted in a recessed position within a sleeve part 8 which slides over the exterior of tube 4. Sleeve part 8 terminates in a radially inwardly projecting flange 9 the inner periphery of which carries an inner sleeve part 10 which engages the interior of tube 4 and carries seating 7. The sleeve parts 8 and 10, the flange 9 and seating 7 are formed in a single piece from aluminium or a thermoplastic resin.

On the spirometer side, seating part 7 has a projecting circular rim 11 for engagement with the periphery of diaphragm 6. A central hole 12 serves for mounting the diaphragm by a rivet (13 in Fig. 1).

Apertures 14 in seating 7 admit air to flex the diaphragm 6 away from seating 7 when the patient exhales for a test. Return flow from tube 1 is prevented by sealing contact of diaphragm 6 with rim 11. Parts 15 of the seating 7 prevent major distortion of the diaphragm.

Mouthpiece 7, like the tube 5, is an expendable accessory. Its design is comfortable for the patient (edges 16 and 17 are rounded), and flange 9 (and in the case shown, also sleeve 8) prevents reverse fitting to tube 4.

The embodiment of Figs. 4to 7C has a simple flange 91 for engagement with the end of cylindrical cardboard tube 4 (internal diameter 28mm) when the inner sleeve part 10' is fully inserted. Flange 9' projects radially outwardly beyond tube 4 as shown in Fig. 4. End 18 of tube 4 has a firm mating fit within the fitting 3 shown in Fig. 1 and reverse-fitting is prevented by projection 9'.

The inner end of sleeve part 10', ie. that end which fits within tube 4, is formed with a convergent portion 19 which terminates in a circular rim 20 projecting in the axial directions of sleeve part 10' and tube 4. Internally, the inner end of the sleeve part has three radial spokes 21 of laminar cross-section which locate a central mounting 22 for a circular diaphragm 23 cut from plasticised polyvinylchloride sheeting of thickness 0.25mm. As shown in Fig. 6 the mounting is generally tapered to receive a circular hole 24 punched through the centre of the diaphragm. The diaphragm is retained by subsequent forming the mounting to a mushroom shape 25 as shown in Figs.

7A, 78 and 7C and also, in broken lines, in Fig. 6.

Spokes 21 have their major and minor dimensions of cross-sections oriented in the axial direction (Fig.

6) and the circumferential direction (Fig. 5) respectively. In this way, their flow resistance is minimised and they also act to smooth-out turbulence.

On their edges facing the diaphragm, the spokes carry a concentric ring 26.

Inner sleeve part 10' with its flange 9' its rim 20, the spokes 21, ring 26, mounting 22 for the diaphragm and a central boss 27 are formed as an integral injection moulding of a thermoplastic resin, eg. polystyrene, polyethylene, polypropylene or polyvinyl chloride. Part 28 (Fig. 6) which is of conical form as far as the diaphragm mounting 22 serves as the resin entry from the moulding tool. The flow of resin to form the sleeve part 10' and parts 91, 19, 21 and 26 is from resin entry part 28 via spokes 21.

Having the spokes in the laminarform described instead of merely with a lesser dimension in the axial direction of the sleeve part which is sufficient to support the boss 27 provides an adequate flow of resin in the moulding operation besides smoothing turbulence and giving a low resistance to the exhalation of the patient. This applies even though only three spokes are provided for the reason aforesaid.

Ring 26 is an incomplete ring with gaps 29 (Fig. 5).

These gaps which do not interfere in any significant way with the action required of the ring, are found to lead to reliable formation of the ring in the moulding operation.

The exhalation flow of a patient through tube 4 into a spirometer, flexes the diaphragm away from rim 20 giving a negligible flow resistance.

When the pressure on the spirometer side of the diaphragm is greater than or equal to that within the sleeve part 101, the peripheral region of the diaphragm engages the rim 20. The force on the diaphragm is opposed by reaction with rim 20 and central mounting 22. Rim 20 has a radius of curvature of only 0.2mm and provides a substantially gas-tight seal (Fig. 7A). Further increase of the pressure causes the diaphragm to bulge, Fig. 7B, with the force still opposed as before. The flexibility of the diaphragm is such that the bulging as the pressure increases substantially would drag the peripheral region clear of rim 20. Before this can happen, the bulging diaphragm engages ring 21. Subsequent bulging is then over two separate concentric parts of the diaphragm as shown in exaggerated form in Fig.

7C causing subsequent radial contraction to be at a reduced rate so that the edge 30 of the diaphragm remains outwardly of the rim 20.

Having the rim 20 formed on convergent portion 19 of sleeve 10' enables the diaphragm to have an adequate diameter without contacting the interior of tube 4.

Figs. 7A, B & C have an enlarged scale in the direction of flow for clarity of illustration.

The economic arrangement whereby a mouthpiece with an internal non-return valve rapidly responsive to back pressure is provided in the form of a simple diaphragm, a single piece moulding and a simple tube, preferably of cardboard, enables the mouthpiece to be discarded after a single use. The problem of achieving effective sterilisation for re-use is avoided.

Claims (17)

1. An inlet tube for a spirometer, said tube being fitted with a mouthpiece formed to engage the tube at the inlet end thereof, an apertured valve seating part carried by the mouthpiece and being formed to extend across the bore of the tube, a valve diaphragm formed of flexible material, said diaphragm being operable to obstruct a return flow of air blown through the mouthpiece and a radially extending part or parts for preventing reverse fitting of the mouthpiece to the tube.

2. An inlet tube according to claim 1 in which the radially extending part is a flange.

3. An inlet tube according to claim 2 in which the mouthpiece has a sleeve part for engagement with the exterior of the tube, the flange extends inwardly from the sleeve part and the valve seating part is carried by the inner periphery of the flange.

4. An inlet tube according to any one of claims 1 to 3 in which the seating part has an axially projecting rim for engagement with the peripheral region of the diaphragm.

5. An inlet tube according to claim 4 in which the seating part has a central mounting for mounting the diaphragm by its centre, said mounting being car ried by spokes.

6. An inlet tube according to either of claims 4 or Sin which the diaphragm is centrally mounted at an axial position such that on its initial engagement with the circular rim produced by said return flow of air, said diaphragm is in a substantially un-distorted configuration.

7. An inlet tube according to claim 6 in which the seating part has an inner ring part mounted coaxially with the rim in an axially recessed position and the diaphragm is deformable to engage the ring part after said initial engagement with the circular rim.

8. An inlet tube according to claim 7 in which the diaphragm is formed from flexible resinous sheeting.

9. An inlet tube according to either of claims 7 or 8 in which the diaphragm is formed from flexible plasticised polyvinyl chloride sheeting.

10. An inlet tube according to either of claims 8 or 9 in which the sheeting is cut from a supply of the sheeting provided in the form of a roll and the diaphragm is oriented so that the potentially concave face of the sheeting is the face which engages the seating.

11. An inlet tube according to any one of claims 7 to 10 in which the inner ring part is discontinuous.

12. An inlet tube according to any one of claims 5 to 11 in which the spokes are of laminar configuration and are oriented with their edges facing the diaphragm.

13. An inlet tube according to any one of claims 5 to 12 in which the spokes are three in number.

14. An inlet value arrangement for use with an inlet tube of a spirometer responsive to the exhalation flow of breath gases from a patient, said arrangement comprising (a) a mouthpiece for operative engagement with said tube to receive, and admit to said tube, an exhalation flow of breath gases from the patient, (b) within said mouthpiece and integrally formed therewith a valve seating part in the form of an axially projecting rim, a central boss, spokes mounting said boss and, on said boss, a diaphragm-mounting projection, and (c) a circular diaphragm of flexible sheet material, said diaphragm being dimensioned to provide a peripheral region for engagement with said rim, and being formed with a central aperture, said central aperture being positioned over said projection and said projection being thermally upset to form a retaining head for said diaphragm, said diaphragm having an axial location within said mouthpiece such that on first engagement of the peripheral region of said diaphragm with said rim produced by a return flow of breath gases, said diaphragm has a substantially planar configuration and a ring member carried by said spokes, said ring member being positioned to be engaged by said diaphragm after said diaphragm has engaged said rim and is deformed from said planar configuration by said pressure of said return flow.

15. An arrangement according to claim 14 in which said ring member is in the form of arcuate projections extending from said spokes, said arcuate projections having terminal ends spaced circularly apart to define gaps in said ring member.

16. An inlet valve arrangement for a spirometer substantially as hereinbefore described and illustrated by reference to the accompanying drawings.

17. A spirometer having an inlet tube and in association therewith a set of interchangeable mouthpieces formed as defined in any one of claims