GB2104385A - Respiratory test device - Google Patents

Abstract

A device for testing a patient's breathing rate has a pair of tubular members 11 and 12. One of the members 12 is formed with a set of leakage ports 17. The other, 11, slides inside or outside the first to govern the number of ports communicating with the atmosphere. One of the tubular members is fitted with a transducer, eg. a whistle 23, which responds when the flow rate reaches a given level. By suitable dimensioning of the ports, the number exposed can be given a linear relationship with the flow rate. Having the transducer response adjustable significantly improves the accuracy in absolute terms. <IMAGE>

Description

SPECIFICATION Respiratory test device The present invention relates to respiratory-test devices of the type which provides an output signal when the respiratory flow of a patient, on exhalation or inhalation reaches or exceeds a predetermined value.

In accordance with the present invention, there is provided a respiratory-test device which comprises a pair of tubular members, the first of said tubular members having connected with one end thereof a transducer responsive to produce an output signal only when gaseous flow through said transducer is at least at a predetermined rate, either of said tubular members being formed with a set of leakage ports for communication with the atmosphere spaced apart in its axial direction and either of said tubular members having an inner surface which engages the outer surface of the other tubular member in a sliding relationship, the arrangement being such that the ports of said set are opened progressively to atmosphere by sliding one member relative to the other in said sliding relationship.

The device is used by the patient blowing or sucking air through the first tubular member. In both cases, part of the flow passes through the opened port or ports and the remainder through the transducer. The number of ports opened determines the exhalation or inhalation rate required to produce the output signal. To determine the patient's maximum expiratory or inspiratory flow rate the maximum number of open ports with which the output signal is given can be found by simple manipulation, if necessary during a series of attempts. Exercises requiring inspiration or expiration at a given rate may be performed with the device preset as required.

Conveniently the first tubular member is the one formed with the set of leakage ports. With this arrangement, the other tubular member can be no more than a plain tube formed, for example, by cutting-off an appropriate length from a supply of tubing. In a preferred arrangement, the first tubular member has its outer surface in engagement with the inner surface of the other tubular member.

The ports may be so dimensioned that the number of ports arranged to provide communication with the atmosphere, by positioning the first and second tubular members relative to one another, has a linear stepwise relationship with the total flow (including flow to or from atmosphere, required to cause response of said transducer). Having such a linear relationship renders the performance of the device simple to understand and convenient to use.

The type of transducer employed depends upon the intended application of the device.

Transducers having an electrical, pneumatic or mechanical output may be provided for actuating automatic equipment, eg., equipment which responds only when the output reaches a required level. For most purposes, including self-testing by the patient, the transducer may be a whistle which sounds when the predetermined rate aforesaid is reached or exceeded.

The linear relationship is obtained over a limited range with ports of constant size. A wider range is achieved without sacrifice of linearity by providing further ports of different sizes as will be s;;own by way of example in the description of preferred embodiments given hereinafter. For a wide-range device the total area of the ports providing communication with the atmosphere is not a linear function of the corresponding flow rate except over a restricted range.

It is found that the accuracy of callibration obtained, is such that inevitable variations of response over a supply of whistles is significant. For this reason the response of a whistle used as the transducer is, in a preferred form of the device made adjustable.

According to a preferred arrangement the whistle is rotatably mounted and is formed with an eccentrically positioned entrance port for communication with the interior of the first tubular member via a port formed in an adjacent wall which otherwise closes the whistle from communication with the interior of the first tubular member. By rotating the whistle the overlap between the two ports may be adjusted, eg. by the manufacturer, to set its response to flow, as required.

Both tubular members are readily formed from cheap material, for example from cardboard, or thermoplastic, tubular stock. Together with a transducer in the form of a whistle of econimic construction they yield a cheaply manufactured device suitable for once-only use or for issue to individual patients. For simplicity in use, the ports are preferably formed in a substantially constant circumferential position. Compactness of construction and an even centre-to-centre spacing of the ports may be achieved by forming the ports to a constant dimension in the axial direction. With this arrangement, the areas of the ports are varied, as required, by varying their dimensions in the circumferential direction.

Having a constant axial spacing, leaves material of constant width between the ports. This width contributes to the strength of the tubular member in which the ports are formed, and in practice facilitates compact design of the member and its construction from cheap material.

The following description of a preferred embodiment of the device, in which description reference is made to the accompanying drawing Is given in order to illustrate the invention. In the dravving: Figure 1 is an exploded elevation of the embodiment, Figure 2 is a cross section taken at ll--ll of Fig. 1, Figure 3 is a cross section of the transducer (a whistle and its mounting) taken at lll---lll of Fig. 1.

Figure 4 shows an internal component in perspective, and Figure 5 shows part of Fig. 3 on an enlarged scale.

The embodiment has a tubular member 11, 75mm in length, which has a sliding fit over a longer tubular member 12 of length 133mm. Both tubular members are formed of cardboard tubing of the helically wound type, the wall thicknesses being 1.25mm and 0.7mm respectively.

Member 12 is formed with a row of eight leakage ports as shown. These ports are centred about a substantially constant circumferential position and are equally spaced apart. They are labelled 1 to 8 as shown by a strip of paper 13. glued in position, which extends away from an edge 14 and around member 12 to terminate in edge 15 (Fig. 2) near the opposite sides of the ports. It is indicated at 16 that the numbers 1 to 8 denote flow rates of from 1 to 8 litres per second. Between the ports the residual cardboard of member 12 forms bridges, such as bridge 17, which join together the cardboard across the row In a robust manner.

The labelling, 1 to 8 of the ports as seen to the left thereof in Fig. 1 is accompanied by further labelling in litres per minute (ie. 60 to 480 litres per minute) near their right. This is not seen in Fig. 1 because of the circular cross-section of member 12.

A component 18, shown in Fig. 4 is adhesively secured within member 12. It has a cylindrical wall 19 projecting from an integral disc part 20 formed with circular aperture 21 formed excentrically. The positions of disc part 20 and the open end 22 are shown at 20' and 22' in Fig. 1. A cylindrical whistle chamber 23. having an entrance port 21 a fills the end portion of member 12 between end 24 thereof and component 18.

Whistle chamber 23, shown in cross-section In Fig. 3, has a pair of moulded mating parts 25 and 26 secured together at 27 to define a cavity 28. Circular end 29 of part 25 is formed with the port 21 a. Circular end 30 of part 26 is formed with a central aperture 31 into which is force-fitted a tubular, injection moulded, polyethylene whistle body 32 having an integral outer flange 33 surrounding an open end 35.

Midway along the length of its otherwise generally cylindrical bore, the whistle body 32 is formed internally with a section 37 of reduced diameter in which is located an integrally formed longitudinal partition 38 carried by a segmental support 39. Partition 38 carries an aluminium reed 40 which is held in position by an aluminium pressing 41, of arcuate cross-section, shaped at its ends 42 and 43 to permit restricted gaseous flow through spaces 44 and 45. Reed 45 vibrates to produce an acoustic signal when the rate of this flow is at or above a minimum value. The pressure differential required to provide this value is set by adjusting the overlap between ports 21 and 21 a as a step in the assembly of the device.

To use the device, tubular member 11 is slid with respect to member 12, so as to position end 36 that the port corresponding with the required rate of flow is exposed. For example, when the required rate is 5 litres per second, the ports labelled 1, 2, 3, 4 8 5 are exposed and those labelled 6, 7 8 8 are covered by member 11. The patient sucks or blows through open end 37.

The major part of the flow leaks from or to atmosphere through the exposed port or ports. Only if the rate of flow reaches the required rate does the pressure differential at the whistle rise sufficiently to produce an audible signal.

The eight ports enable the device to be set for as many as eight different flow rates having equal increments therebetween. This is achieved by appropriate dimensioning of the ports. In practice their appropriate sizes are determined by experiment. Once these sizes have been established, the ports may be formed by a single punching tool. The production of such a tool for repeated use with the preferred constructional material for the tubular member, cardboard, is a simple matter.

In the example shown in the drawing, member 12 has an internal diameter of 27mm. Each port has a width of 4.8mm, and the bridging material left between the ports a width of 2.9mm.

The ports have semi-circular ends and parallel sides therebetween. Their overall end-to-end sizes as measured straight, rather than in a circular manner, and flow rate callibration are substantially as follows: Port Labelled Flow rate (litres/sec.) Size,mm. (litres/min) 1 7.7 60 2 8.4 120 3 8.8 180 4 8.8 240 5 8.8 300 6 8.9 360 7 10.0 420 8 11.5 480 In the embodiment described with reference to the drawings, the tubular member 11 is slid over the whistle to uncover the ports. An alternative arrangement is to form the ports in the reverse order and uncover them by sliding member 11 in the opposite direction, over end 37 if member 11 fits the exterior of member 12 or through end 37 if member 11 fits the interior of member 12. The ports may be formed in member 11 if this member is to slide over or through end 20.

A ninth port may be provided in order to extend the range to 9 libres per second. For this purpose, the row is commenced nearer to end 37 of tubular member 12. Members 11 may be provided in increased lengths to accommodate the additional port, but this is not essential.

In a modified form of the device, tubular member 12 has a length of 140mm and an internal diameter of 26mm. This decrease from 27mm gives an increased wall thickness and added strength. Eight ports are provided, each with a width of 4.8mm, together with an additional (ninth) port of width 5.5mm. The sizes of the ports-measured straight-and flow rate callibration are substantially as follows: Port Labelled Flow Rate (litres/sec) Size,mm. (litres/min) ; 1 7.75 60 2 8.75 120 3 8.75 180 4 8.75 240 5 8.75 300 6 8.75 360 7 10.2 420 8 11.5 480 9 14.7 540 It will be understood that various departures may be made from the embodiment described, by way of example, without departing from the ambit of the invention.

Claims (11)

1. An exhalation-test device which comprises a pair of tubular members having connected with one end thereof a transducer responsive to produce an output signal only when gaseous flow from the tubular member outwardly through said transducer is at least at a predetermined rate, either of said tubular members being formed with a set of leakage ports, for communication with the atmosphere spaced apart in its axial direction and either of said tubular members having an inner surface which engages the outer surface of the other tubular member in a sliding relationship, the arrangement being such that the ports of said set are opened progressively to atmosphere by sliding one member relative to the other in said sliding relationship.

2. A device according to claim 1 in which the first tubular member is the one formed with said set of leakage ports.

3. A device according to either of claims 1 or 2 in which the first tubular member has its outer surface in said engagement with the inner surface of the other tubular member.

4. A device according to any one of claims 1 to 3 in which the ports of said set are located in a substantially constant circumferential position.

5. A device according to any one of claims 1 to 4 in which the ports of said set are so dimensioned that the number of ports arranged to leak to atmosphere by positioning the first and second tubular members relative to one another has a linear relationship with the total flow required to cause response of said transducer.

6. A device according ot any one of claims 1 to 5 in which said transducer is a whistle.

7. A device according to claim 6 in which said whistle is rotatably mounted and is formed with an eccentrically positioned entrance port for communication with the interior of the first tubular member via a port formed in an adjacent wall which otherwise closes the whistle from communication with the interior of the first tubular member.

8. A device according to claim 7 in which said whistle is in the form of a chamber having two end closures, one of said closures being formed with said entrance port, and the other having an exit in the form of said exit piece being formed with a bore at least part of which is non-cylindrical and is accessible from the exterior of the chamber.

9. A device according to claim 8 in which said bore is occupied by a metal reed.

10. A device according to any one of claims 1 to 9 in which at least one of said tubular members is formed of cardboard tubing.

11. An exhalation test device, substantially as hereinbefore described and illustrated by reference to the accompanying drawings.