PEAK-FLOW METER

Abstract: An air-flow valve (1) having associated therewith at least one movable blade (13) means for detecting air-flow thereabout, which valve (1) includes at least one air-directing aperture (5), said aperture being adapted to alter the direction of air-flow incident on said valve (1) from a first direction tangential to a second altered direction, which second altered direction is perpendicular or at least towards the planar surface of said blade (13) means; whereby said direction-altered air-flow provides a force which causes said blade means (13) to move.

Description: PEAK-FLOW METER Field of the Invention This invention relates to the field of apparatus for measuring lung function. Background to the Invention During normal adult respiration, the amount of air inspired or expired per breath (tidal air) is approximately 500ml. After a normal tidal expiration, a further volume of air (the expiratory reserve-volume) can be expired - approximately 750-1000ml in adults. Vital capacity is the maximum volume of air which can be expelled from the lungs by a forceful effort, following a deliberate inhalation of the maximum volume possible. This vital capacity is normally of the order of 4.8 litres in men and 3.2 litres in women, but can be substantially reduced in asthmatics and people with other bronchial problems. The vital capacity and/or the ability to exhale thus provides a good indication of a subject's lung function. Several devices exist which monitor a subject's ability to exhale, thus providing an indication of lung function. These devices employ a number of different methods which either directly or indirectly provide a measurement of expiratory volume; tidal reserve or more preferably vital capacity. For example, a subject may be asked to blow into a calibrated tube containing a spring-loaded device, for example a piston, which is moved along a calibrated scale according to the force provided by the exhaled air. The inertia of the spring-loaded device will affect the sensitivity of the equipment and may require that, for a valid measurement, a degree of force is needed which a severe asthmatic, or otherwise respiratory-impaired individual, cannot provide. An alternative method involves the use of a device containing a hot wire. Exhaled air passes over the hot wire, cooling it and a measure of the degree of cooling thus provides an indication of lung function. Again the device may not be sensitive enough for some subjects. In addition the difficulty in accurately measuring the degree of cooling further affects the sensitivity. A further method involves the use of rotating blades or a turbine. Exhaled air causes the blades to rotate and this motion is detected and translated into an indication of lung function. The device is generally arranged so that the exhaled air impinges on the edges of the blades (i.e perpendicular to their mounting) and, again, the inertia of the device will affect its sensitivity, particularly in subjects with poor lung function. It is, therefore, an object of the present invention to provide a reliable and easily adapted device which is more sensitive than the prior art for measuring lung function. Summary of the Invention In its broadest aspect, the invention concerns the advantageous manipulation or redirection of an air-flow. According to a first aspect of the present invention there is therefore provided an air-flow valve having associated therewith at least one movable blade means for detecting air-flow thereabout, which valve includes at least one air-directing aperture, said aperture being adapted to alter the direction of air-flow incident on said valve from a first direction tangential to a second altered direction, which second altered direction is perpendicular or at least towards the planar surface of said blade means; whereby said direction- altered air-flow provides a force which causes said blade means to move. Preferably, at least a part of said air-flow valve which is in the region of said blade means is substantially transparent. This is favoured because a motion detecting means which relies on the transmission and detection of an infra¬ red or light beam can be used with said valve. In a preferred embodiment, said blade means moves ideally in a rotary fashion or at least through a predetermined arc, which arc is at least in part in the path of said beam. Preferably, a plurality of air-directing apertures are provided about the perimeter of said valve. More preferably still, said apertures are equispaced. Preferably said valve is elongate or tube shaped. Preferably, said first direction is substantially parallel to the longitudinal axis of said valve and said second direction is in a plane substantially perpendicular to said first direction. In a preferred form, said valve is further provided with a plurality of fins substantially adjacent each of said air-directing apertures. In a further preferred form, said valve is further provided with a plurality of air-flow guides substantially adjacent each of said air-directing apertures, which air-flow guides are adapted to facilitate the change in air-flow direction from said first direction to said second direction. The air-flow valve of the invention is ideally suited for use in an air-flow measuring device, which device comprises a number of components which may be detachable. Similarly, said valve may be made from a number of detachable components thus facilitating cleaning. According to a second aspect of the present invention, there is therefore provided a device for measuring air-flow comprising: an air inlet; an air-flow valve substantially as described above, on which air from said air inlet impinges; one or more optical transducers adapted to monitor the movement of said blade means; processing means for determining a required parameter from the output(s) of said optical transducer(s); and display means for visually representing said required parameter. Preferably the device is arranged so that movement of the blade means of said valve affects said transducers, ideally interfering with or interrupting an infra-red or light beam. Preferably further still said inlet includes a mouthpiece ideally including an elastomeric means so that variable mouthpieces can be attached to the device. Or, alternatively said inlet includes a releasable mouthpiece. Brief Description of the Drawings A particular embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings wherein: Figure 1 shows two perspective views of the air-directing valve; Figure 2 shows a top view of the air-directing valve; Figure 3 shows a plan view of the air-directing valve; Figure 4 shows a side sectional view of the air-directing valve; Figure 5 shows sectional, side and end views of a mouthpiece; Figure 6 shows two perspective views of the mouthpiece extension; Figure 7 shows a perspective view of the device for measuring air-flow; Figure 8 shows a side sectional view of the device; Figure 9 shows a top view of the device; Figure 10 is a schematic representation of the optical transducer, processing and display means. Figure 11 shows a top view of an air-directing valve having fins 16; Figure 12 shows a side sectional view of the air-directing valve of Figure 11; Figure 13 is a perspective view of insert 18; Figure 14 is a cross-sectional view of a guide 19; Figure 15 is a side perspective view of a peak-flow meter incorporating insert 18. Description of the Preferred Embodiment Referring to Figure 1 the air-flow valve 1 consists of a disc-shaped (or alternatively barrel-shaped) body 2 with an upstanding portion 3 of smaller diameter at its centre. The outer part of the upstanding portion has a conical cap 4. Figures 1-3 show the positioning of a series of equispaced apertures 5 around the inner part or perimeter of the upstanding portion 3. Apertures 5 are elongate in cross-section as shown in Figures 2 and 3 and ideally also angled so as to efficiently direct air-flow. In an a preferred form (Figures 11 and 12), apertures 5 are extended by means of upstanding fins or flaps 16 glued in place, or integrally formed along one edge of each aperture 5. The fins may extend all the way to the rim 17 of body 2. Figure 4 shows the provision of a blade support 6 depending inwardly from the inside of the apex of conical cap 4. Figure 5 shows a mouthpiece 7 consisting of a funnel-shaped portion 8 integral with a narrowed portion 9 whose cross-sectional shape can be seen in the lowermost view in Figure 5. Figure 6 shows a mouthpiece extension 10. Figures 7-9 show an assembled device for measuring air-flow. The air-flow 1 is releasably fitted inside mouthpiece 7 and this assembly is then releasably and frictionally attached to a casing 8 by a connector 9. Connector 9 is hollow and comprises a tubular portion 9A and a disc-shaped mating portion 9B. Portion 9A is sized and shaped so as to frictionally fit a semi-circular recess provided on the upper side of casing 8. Part way along portion 9B there is provided a transverse blade mounting means 21. Casing 8 consists of two mouldings, upper moulding 10 and lower moulding 11, which releasably fit together to define a hollow casing within which replaceable batteries 20 and electronics are housed. A transparent display panel 12 is provided on the upper moulding 10 of casing 8 as shown in Figure 9. A rectangular blade 13 is attached between blade support 6 and the blade mounting means 21 of connector 9. Alternatively, blade 13 can be integrally formed with its shaft and can have self-lubricating bearings. The blade can be any preferred shape for example a rectangular shape and it is mounted so that it is free to rotate within the air-flow valve 1. However, the position of the blade is such that when the valve 1 and mouthpiece 7 are mounted on casing 8, via connector 9, the blade is located between an emitter 14 and detector 15. In use, a subject blows into mouthpiece 7, the exhaled air travelling in the direction of the arrows in Figure 9. The orientation of apertures 5 cause the air to be re-directed into the area enclosed by upstanding portion 3, and so impinge on the blade 13, causing it to rotate. The air-flow therefore is caused to divert through essentially 90° and so travel towards the upstanding or planar surface of blade 13. An infra-red emitting diode 14 is positioned within casing 8 such that its infrared beam is received by an infrared sensor 15. The path of the beam is intercepted by blade 13 (a sufficient portion of valve 1 and connector 9 needs to be transparent to permit this, alternatively, suitably placed holes are provided in valve 1 and connector 9) and the periodic interruption of the infra-red beam is used to determine the frequency of rotation of the blade 13. Microprocessor IC1 (shown in Figure 10) is used to process the output of the infra-red sensor 15 in order to drive a LCD which displays a representation of the volume of air exhaled by the subject. Appendix 1 provides suggested component values and further details of the components to be used. A further embodiment of the invention is shown in Figures 13, 14 and 15. In that embodiment an insert 18 is provided (either attached or integrally- formed) between the upstanding portion 3 and the rim 17 of valve body 2. The insert 18 is provided with air-flow guides 19 which correspond to the apertures 5 of the air-flow valve. These guides 19 serve to assist in the smooth air-flow between the first (incident) direction through 90° to the second direction (towards the planar surface of blade 13). The curved shape of the guides 19 (see Figure 14 for a cross-sectional view) is, in this embodiment, preferable to causing the incident air-flow to change sharply from the first direction to the second, as is the case when insert 18 is not used. This embodiment (with insert 18 in place) is particularly effective when the incident air-flow rate is low. The air-flow valve of the invention thus provides a means of increasing the sensitivity of a respiratory device by simply making maximum use of expired air. Re-direction of air-flow is employed in order to reduce inefficiency of existing systems. Appendix 1 Typical values are given, exact values will depend upon such things as LED, PEC and resonator used. Rl 56K 5% exact value will depend on LED/Photocell characteristics R2 10K 5% exact value will depend on LED/Photocell characteristics R3 100K 5% R4 100K 5% R5 100K 5% R6 100K 5% R7 lOOK 5% Cl 0.1 MFD Ceramic C2 33 PFD Ceramic exact value to suit resonator used C3 33 PFD Ceramic exact value to suit resonator used XI MHz Resonator IC1 PIC16C54 512 Byte OTP Microprocessor LED1 Infrared Emitting Diode PEC1 Infrared Sensor Display Custom Triplexed Display SW1 Technical Notes on Components 1. LED Infrared emitting diode. No special characteristics but to keep current consumption down a narrow angle high efficiency type preferred. 2. PEC No special characteristics but to match the wavelength emitted by the LED. 3. DISPLAY The display character height to be 6 mm Temperature range -5C to +40C Connection method to be most economical overall digit multiplexed with 3 backplanes Viewing angle perpendicular to display face Polarizer to built into display All segments 'a' will be commoned, all segments 'b' commoned etc. Those segments that cannot be commoned within the display will be interconnected externally on the PCB. The rms voltage ratio between a segment being on or off is 1.73.

Claims: CLA1MS 1. An air-flow valve having associated therewith at least one movable blade means for detecting air-flow thereabout, which valve includes at least one air-directing aperture, said aperture being adapted to alter the direction of air-flow incident on said valve from a first direction tangential to a second altered direction, which second altered direction is perpendicular or at least towards the planar surface of said blade means; whereby said direction-altered air-flow provides a force which causes said blade means to move. 2. An air-flow valve according to Claim 1 wherein at least part of said air-flow valve which is in the region of said blade means is substantially transparent. 3. An air-flow valve according to Claim 2 wherein said blade means moves at least through a predetermined arc, which arc is at least in part in the path of said beam. 4. An air-flow valve according to any of the preceding claims wherein said blade means moves in a rotary fashion. 5. An air-flow valve according to any of the preceding claims wherein a plurality of air-directing apertures are provided about the perimeter of said valve. 6. An air-flow valve according to Claim 5 wherein said apertures are equispaced. 7. An air-flow valve according to any of the preceding claims wherein said valve is elongate or tube shaped. 8. An air-flow valve wherein said first direction is substantially parallel to the longitudinal axis of said valve and said second direction is in a plane substantially perpendicular to said first direction. 9. An air-flow valve according to any of claims 5-8 wherein said valve is further provided with a plurality of fins substantially adjacent each of said air-directing apertures. 10. An air-flow valve according to any of claims 5-8 wherein said valve is further provided with a plurality of air-flow guides substantially adjacent each of said air-directing apertures, which air-flow guides are adapted to facilitate the change in air-flow direction from said first direction to said second direction. 11. An air-flow valve according to any of the preceding claims wherein said valve comprises a number of detachable components thus facilitating cleaning. 12. An air-flow valve according to any of the preceding claims wherein said valve is adapted for use in an air-flow measuring device, which device comprises a number of components which may be detachable. 13. A device for measuring air-flow comprising: an air inlet; an air-flow valve substantially as described above, on which air from said air inlet impinges; one or more optical transducers adapted to monitor the movement of said blade means; processing means for determining a required perameter from the output(s) of said optical transducer(2); and display means for visually representing said required perameters. 14. A device according to Claim 14 wherein said device is arranged so that movement of the blade means of said valve affects said transducers, ideally interfering or interrupting an infra-red or light beam. 15. A device according to Claim 14 or Claim 15 wherein said inlet includes a mouthpiece ideally including an elastomeric means so that variable mouth pieces can be attached to the device. 16. A device according to Claim 14 or Claim 15 wherein said inlet includes a releasable mouthpiece.

Inventors: FORD THOMAS MCDONALD, FORD, THOMAS, MCDONALD
Applicants: FORD THOMAS MCDONALD, SOVEREIGN SURGICAL LTD, FORD, THOMAS, MCDONALD, SOVEREIGN SURGICAL LIMITED
Application year: 1995
Main classification: A61B5
IPC codes: A61B5