MXPA97009084A - Device for periodically verifying a max flow - Google Patents

Abstract

Portable devices for periodic verification of the maximum expiratory flow rate (PEFR) are known, and use whistles or tabs that are triggered by threshold in order to return the PEFR. This invention provides a periodic PEFR verification device that includes a threshold-activated tongue (16) located in an outlet formed in a body. The body comprises the plates of the input and output body (12, 14) which are interengagable with one another in a plurality of rotational positions of the plates one with respect to the other. A vent opening (26) extends axially along the length of the outlet plate (14). The entrance panel (12) includes a buccal part (18) that extends inside a cylindrical occluder (20), the upper edge (20.1) of which is spirally shaped. When the plates are interconnected, the occluder (20) extends. inside the exit plate, to occlude the ventilation to a greater or lesser degree, depending on the rotational position of the plates (12, 14), whereby a greater or lesser proportion of the flow is directed through the tongue assembly (16) the body plates (12, 14) which are insurable to each other to adjust the size of the ventilation outlet, normally in accordance with a predetermined treatment protocol

Description

DEVICE FOR PERIODICALLY VERIFYING A MAXIMUM FLOW FIELD OF THE INVENTION This invention relates to a device for periodically checking the flow, mainly a device for periodically checking the maximum expiratory flow.

BACKGROUND OF THE INVENTION The maximum expiratory flow rate (PEFR) is a measure of a person's lung function, which can be easily and precisely determined by various devices. The PEFR home verification has gained acceptance as a means to periodically verify asthma states. This can be periodically verified reliably by cooperative subjects without the assistance of technically skilled personnel and, since its original definition in 1959 (Wright BM, McKerrow CB: forced expiratory flow velocity, maximum as a measure of ventilatory capacity (Maximun forced expiratory flow rate as a measure of ventiiatcry capacity) - British REF: 26301 Medicine, 2, 1041 - 1959) this has found wide application. A number of portable PEFR measuring devices are currently commercially available. These vary in portability, graduation, cost and work, essentially, on two different principles. The first involves the displacement of a spring-loaded piston, the total displacement of which depends on the pressure arising from the generated flow and the area of a ventilation located behind the piston. The second class of devices uses whistles or tabs that are normally activated by a threshold, in order to register the PEFR. The first class of devices includes well-known devices such as the Wright Peak Flow Meter and the Vitalograph Pulmonary Monitor. One of the first devices of the second type is described in British Patent No. 1,018,387 - De Bono, an evaluation of which is reported in The Lancet, July 31, 1965, 212 - Colley JRT, Holland WW. The devices of the second class include a whistle of maximum flow, a first prototype of which is described in Annals of Allergy, 47, August 1981 - 95 to 98 - Chiara onte LT, Prabhu SL: maximum flow whistle: preliminary report - and a last form which is described in Annals of Allergy, March 52, 1984, 155 to 158 - Chiaramonte LT, Goldstein S, Rockwell W: Report of a newly redesigned maximum flow whistle. This device also forms the subject of interest of U.S. Patent No. 4,421,120-Edwards. Another such device is described in U.S. Patent No. 5,357,975-Kraemer, which describes a whistle with a sound generator designed and constructed using the general characteristics of wind instruments. This device uses electronic equipment to measure time and sound, in order to evaluate the flow volume curve of the subject. The De Bono whistle consists of a plastic tube with a whistle-type whistle on one end. A disposable cardboard mouthpiece fits over the other end and an exhaust hole is formed below one side of the tube, the size of the hole is adjusted by moving the mouthpiece. A critical level of air flow through the whistle is necessary to produce sound, and the disposable mouth piece is progressively removed to increase the size of the exhaust port, whereby a progressively higher air flow rate is required with the order to produce a whistle. This device suffers from the disadvantages that the whistle loses its intensity and its sharpness at low flow rates. In addition, the exhaust air flow and any expiratory asthmatic fucks produced by the subject tend to quench or imitate the whistle. The Edwards maximum flow whistle uses a threshold-activated tongue to record the maximum flow at which the tongue sounds only at the openings are equal to or less than the maximum flow of the subject. The ventilation opening is determined by adjusting a rotatable closure plate, before being used, at a known "critical" level of a maximum flow predicted for the subject. The subject is then required to blow through the device, widening the opening with each successive expiratory effort, until the whistle no longer sounds. The last position of the closing plate to which the whistle can be heard gives the maximum flow value. The devices of De Bono and Kraemer suffer from the disadvantage that their sound generators do not have a clearly determinable threshold.

BRIEF DESCRIPTION OF THE INVENTION According to this invention, a periodic flow verification device comprises a signal generator that is adapted to generate a signal in dependence upon achieving a predetermined volumetric flow rate of the fluid through the signal generator; the signal generator is located in a fluid flow passage extending between an inlet and a ventilation outlet formed in a body, the size of the ventilation outlet is variable to vary the characteristics of the passage to the flow resistance of the fluid, and the variation of the ventilation outlet that is adjustable to a predetermined variation of the size of the ventilation outlet. The size of the ventilation outlet is preferably variable and adjustable in increments. In the preferred form of the invention, the sound generator is constituted by a tongue located in an outlet formed in the body, the tongue being activated by threshold, since it is adapted to generate sound depending on the achievement of a volumetric flow rate predetermined fluid through the tongue, and the fluid flow velocity, which is predeterminable by the adjustment of the vent outlet. The tongue and the ventilation outlets are preferably separate outlets formed in the body, and the outlet of the tongue may be conveniently shaped to expand outwardly toward the atmosphere, in a horn-like manner, thereby improving substantially the signal to noise ratio of the device. The static and dynamic flow thresholds of the sound generator or the tongue are preferably close to each other in value, to minimize the generation of false positive sound due to pulse-like flow patterns, such as may occur during flow explosive as opposed to the soft expiratory flow through the device. In order to further improve the signal to noise ratio of the device, the dominant frequency of the sound generator is adjusted within the largest area of human audible sensitivity, preferably between 800 Hertz and 2000 Hertz, and conveniently at approximately 1000 Hertz. It is possible to minimize the generation of erroneous sound due to large fluctuations in flow, such as the explosive flow as opposed to the smooth expiratory flow through the device, simply by shifting the sound generator relative to the flow path of the flow. main fluid through the body. This is best accomplished by placing the sound generator downstream of a transverse barrier extending through the flow path. The signal to noise ratio of the device can be improved even if the body is adapted to form a resonance chamber for the sound generator. For this purpose, the body can be shaped in the form of a substantially bulbous resonance chamber. In a form of the invention which is suitable for manufacturing in injection molded plastics, the device may comprise a plurality of outer body plates which are interengagable to define the body, the outlet being formed in an outer body sheet and another of the outer plates of the body is provided with an occluder for the exit, the outer plates are movable relative to one another so that the occluder occludes the outlet to a greater or lesser degree, depending on the relative positions of the outer plates, with which varies the size of the ventilation outlet and the relatively movable outer plates that are at least partially insurable to each other, to adjust the ventilation outlet to a predetermined variation of the size of the ventilation outlet. In this form of the invention, the body can comprise exterior body panels, inlet and outlet, which are interengagable with one another in a plurality of positions in which the outer plates are rotated relative to one another, the outer exit plate being constituted by an external wall enclosing a resonance chamber formed with the opening of ventilation and the entrance plate that is constituted by a buccal piece that extends inside a cylindrical occluder that is adapted for the placement inside the exit plate and the upper edge of which is spirally shaped, the ventilation opening in the exit plate extends axially along the length of the exit plate and the occluder that is adapted, when the plates are intercoupled, to extend inside the exit plate, to occlude the ventilation to a greater or lesser degree depending on the rotation of the plates one in relation to the other.

The outer plates of the body, inlet and outlet, can be conveniently formed with complementary coupling formations, by means of which the two plates can be held together, the coupling formations being constituted by an inwardly directed flange formed on a coupling end of an outer wall of the outlet plate and an undercut groove, directed in an outward direction formed on a flange extending peripherally around the outside of the outlet plate, the flange and the coupling end of the plate. The inlet and the notch and the flange are of suitable dimensions so that the inlet and outlet plates are firmly secured to one another with the flange engaging within the undercut groove. The outlet can be defined by curved portions inwardly of the outer wall of the outlet plate, the flange being formed on the entrance plate with a coupling ring formed with outwardly directed slits, which are formed in addition to the base ends of the outlet plate. the walls defining the ventilation outlet, the base ends of the curved walls are interconnectable with the slits in the coupling ring, whereby the entrance plate to the exit plate is secured in a predetermined rotational position. The outwardly directed slits may be suitably adapted to define relatively small increments of rotation. In this form of the invention, the occluder can be provided with a stop formation which is positioned to engage against the curved walls at the maximum rotational positions of the entrance plate relative to the exit plate. While the following description is directed to a device for periodically checking the flow, which is designed for use as a maximum expiratory flow checker, the device can be adapted for bidirectional fluid flow if the sound generator is intended to generate sounds in any direction of flow through the sound generator. A bidirectional tab could be an example of such a sound generator.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings Figure 1 is an exploded, perspective view of the periodic verification device according to the invention, observed from the output end of the device; Figure 2 is an exploded perspective view of the device of Figure 1, seen from the input end of the device; Figure 3 is a diagrammatic section on a line 3-3 in Figure 2; Figure 4 is an isometric view of the tongue assembly of the periodic verification device according to the invention; Figure 5 is a diagrammatic section on a line 5-5 in Figure 4; Figure 6 is a diagrammatic section on a line 6-6 in Figure 5; Figure 7 is a side elevational view (partially in section) of the device according to the invention; and Figure 8 is an extreme elevation view (partially in section) of the device according to the invention.

DESCRIPTION OF THE MODALITIES OF THE INVENTION The periodic verification device of the invention is not a flow meter in the sense that it does not measure the absolute flow through the device. Rather, this is a device designed to periodically check the maximum expiratory flow rate (PEFR) of a person. This is done by periodically verifying the achievement, or otherwise of a predetermined threshold PEFR, by the subject. In this sense, the verifier or monitor of this invention is a threshold verifier, since it verifies periodically the PEFR achieved by the subject, in comparison to a diagnostic threshold. The predetermined PEFR is a diagnostic threshold that will depend on the treatment protocol prescribed for the subject, after the measurement of the anticipated or predicted PEFR of the subject. With reference to Figure 3, it can be seen that the verifier 10 of the invention comprises a pair of interengaging outer plates 12, 14 and a sound generator constituted by a tongue assembly 16. The plate 12 is essentially an entrance plate and the plate 14 is an exit plate, which are joined together in the manner described below with reference to Figures 7 and 8. In practice, the subject sucks as much as possible and then it blows out or expires through the cylindrical tube that constitutes the mouthpiece 18 in the entrance, and the entrance plate 12. The subject is normally instructed not to cough or allow explosive expiratory flow, such as spitting , coughing or interrupted flow resulting from obstructions with the tongue of the mouthpiece, but as will be seen below, the verification device 10 of the invention is designed to minimize possible inaccuracies arising from such explosive expiratory flow. The outlet plate 14 is constituted by an external plate 24 enclosing a resonance chamber 46 formed with a ventilation opening 26 extending axially along the length of the outlet plate 14. A central housing 22 for mounting of tab 16, extends axially within resonance chamber 46.

The plates 12, 14 are designed for interconnection with each other (by means of inter-coupling fastening formations, which will be described in more detail below, and the tongue assembly 16 is designed for placement within the housing 22 in The horn piece 18 extends within a cylindrical occluder 20, the upper edge of which is spirally cut in. When the plates 12, 14 are joined, the occluder 20 extends into the outlet plate 14, to occlude the ventilation 26 to a greater or lesser degree, depending on the location of the upper edge of the occluder 20, relative to the ventilation 26, which in turn depends on the relative degree of rotation of the plates 12, 14 a in relation to the other, when the subject blows through the buccal part 18 and the exit plate 14, a portion of the flow expired by the subject will escape through the vent 26, and a portion of the This will be directed through the tongue assembly 16. By rotating the entrance plate 12 relative to the exit plate 14, the spiral occluder 20 occludes the ventilation opening 26 to a greater or lesser degree, thereby it determines the degree to which the expired flow will be directed through the tab assembly 16. If sufficient flow is directed through the tab assembly 16, it will generate sound. With reference to Figures 4, 5 and 6, it can be seen that the tongue assembly consists of a pair of diffuser plates 28, 30, each occluding the opposite halves of the ends of a tubular housing 32. A tongue bed 34 it extends axially between the diffuser plates 28, 30; the bed 34 of the tongue is formed with an opening 36 within which a tongue 38, elastically deformable, is fitted by engagement of the fixed end 40 of the tongue 38 within the bed 34 of the tongue. The tongue assembly 16 is not linear (a linear whistle being one which will produce, for example, twice the sound intensity for a double in the flow velocity), and the length, shape and mass of the tongue will be they choose to produce a sound within the frequency range in which the human ear is most sensitive. The tongue 38 is adapted to produce sound with a tone or frequency of about 1000 Hertz. While the tongue 38 is not linear, the device 10 can, in effect, be "linearized" by the proper design of the spiral occluder.

More importantly, the tongue assembly 16 provides a quick and clear start of the sound when its flow threshold is exceeded. In this respect it can be seen as an analog to digital device which is either "on" or "off" with nothing inside. For this purpose, the tongue assembly 16 is manufactured to exact tolerances to ensure minimum variation from unit to unit, so that each tongue 38 is activated at the same flow threshold. This eliminates the need to calibrate each verification device 10. In addition, the tab 38 is shaped to ensure that the static and dynamic flow thresholds of the tab assembly 16 are close to each other to minimize erroneous sound generation due to fluctuations large in the flow, as may occur during explosive expiration, as opposed to the soft expiratory flow, through the device 10. With reference to Figure 3, the tongue assembly 16 is pressed into the housing 22 extending below the interior of the outlet plate 14, the outer shape of the tongue assembly 16 and the internal shape of the housing 22 are complementary frusto-conical. The entrance end of the tongue assembly 16 is open towards the inside of the entrance end 42 of the housing 22, and the exit end of the tongue assembly opens outwardly toward the atmosphere inside the horn-shaped mouth 48 or horn of the housing 22. The mouth 48 in the shape of a horn or horn improves the hearing capacity of the device 10 as does the exit plate 14, which forms a resonance cavity 46 around the housing 22. The entrance end 42 of the housing 22 is formed with a transversely extending barrier 44 (which can be observed more clearly in Figure 2). The barrier 44 acts as a low pass filter and helps to prevent the tongue 38 from being activated by the subject using explosive expiratory flow or pulse-like techniques, in order to obtain an overly optimistic result from a test. The entry and exit plates 12, 14 are formed with complementary coupling formations by means of which the two parts 12, 14 can be held together. As can be seen from Figures 3 and 7, the coupling formations are constituted by an inwardly directed rim 54, formed on a coupling end 52 of the outer wall 24 of the outlet plate 14, and an undercut groove. 56 directed outwards, formed on a flange 58 extending peripherally around the outside of the tubular mouthpiece 18. The rim 54 and the coupling end 52 of the entry plate 14, as well as the notch 56 and the flange 58, they are of suitable dimensions so that the entry and exit plates 12, 14 are held together with the rim 54, engaging within the undercut sample 56. Referring now to Figures 1, 2 and 8, it can be seen that the edges of the vent opening 26 are defined by portions 50 curved inwardly of the outer wall 24 of the outlet plate 14. The ventilation walls 50 are curved and aerodynamically shaped, to minimize the noise resulting from the air escaping from the vent 26. The flange 58 is formed with a coupling ring 60, notched, the notches from which, directed outwards, are formed complementary to the base ends 62 of the curved walls 50, defining the ventilation 26. During the interengagement of the entry and exit plates 12, 14, the practitioner will be required to align the base ends 62 of the curved walls 50.1, 50.2, with the slits in the coupling ring 60, thereby the entrance plate 12 is secured to the exit plate 14, in a predetermined rotational position. The combination of the engagement of the notch 56 and the flange 58 of the body plates 12, 14 with the slit coupling ring 60, and the base ends 62 of the walls 50, results in the positive securing of the plates 12, 14 of the body, which the subject will only alter with difficulty. By securing the entrance plate 12 to the exit plate 14 in a predetermined rotational position, the spiral occluder 20 is secured in a particular position relative to the ventilation 26, whereby the effective ventilation opening is determined. As stated above, the ventilation opening will be determined by the treatment protocol. The advantage of the coupling ring 60, notched, is that it allows adjustment of the periodical verification device 10 of the invention, in small increments. The occluder 20 is provided with a stop formation 64 which is positioned to engage against the curved walls 50 at the maximum rotational positions of the entrance plate 12 relative to the exit plate 14. At one end, the stop 64 will engage or will be trapped within the curved wall 50.1 in the maximum "closed" position of the periodic checking device 10, in which position the spirally cut upper surface 20.1 of the occluder is as close to the upper end of the vent 26 as rotation allows of the entrance plate 12 relative to the exit plate 14. At the other rotational end, the stop 64 will be trapped inside the curved wall 50.2 in the maximum "open" position of the periodic verification device 10, in which position the upper surface 20.1 spirally cut, of the occluder, is as close to the lower end of the vent 26 as the relative rotation of the plates 12, 14 allows. In use, the physician will determine the subject's diagnostic threshold, after which the physician will assemble the device 10 or instruct the subject regarding the assembly of the device 10, by coupling the entrance and exit plates 10, 12, one to the other with the occluder 20 located in the position determined by the treatment protocol of the subject. To assist in such an assembly, appropriate markings may be made on one or more of the occluder 20, the flange 58 and the exit plate 14. For example, coupling marks may be molded on the outer wall of the occluder 20, and on one or both of the curved ventilation walls 50. Alternatively, such markings can be molded into the outer surface of the wall 24 of the exit plate 14 and the front surface of the flange 58. The appropriate markings will then have to be coupled accordingly. with the treatment protocol. The marks can take the form of values of the speed of flow. The subject is merely asked to implement the domestic verification regime - the subject will be told when the flow should be measured and how the periodic verification device should be used. The dominant frequency of the tongue 38 is well within the most sensitive auditory range of the human ear, and it has a relatively high signal-to-noise ratio, as a result of the round surfaces of the device, the large resonance chamber and the housing in horn shape for tongue assembly 16. To improve the signal-to-noise ratio even further, the subject will be advised to turn the ventilation opening in a downward direction away from the ear during use. The outer wall 24 of the outlet plate 14 can be formed with holding formations to facilitate such anchoring, and also to minimize the risk of the subject accidentally occluding the ventilation 26 by hand. If required, the device 10 can be predesigned for use by children or adults. In the first case, the size of the ventilation 26 may be predetermined to allow maximum flows of up to 450 liter / minute, whereas in the latter case, the size of the ventilation may be predetermined to allow maximum flows of up to 800 liters / minute . The invention thus provides a method for periodically checking the maximum exhalation flow velocity of a subject, using a device of the invention, which method is characterized in that the subject exhales within the entrance of a device in which the exit opening ventilation has been preset to correspond to the predicted value of the maximum exhalation flow velocity, which the subject must achieve, for example, by the physician adjusting the relative rotational positions of the two entry and exit plates; and the subject verifies whether the signal generating device is actuated, indicating that the subject has achieved the maximum, predicted, exhalation flow rate, or if the signal generating device has not been activated, indicating that the subject has failed to achieve the maximum exhalation flow rate, predicted, and remedial action is required, for example to take medication or to visit the doctor.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following:

Claims (13)

1. A device for periodic verification of the flow, comprising a threshold activated sound generator, which is adapted to generate an audible signal in dependence on the achievement of a predetermined volumetric flow velocity of the fluid through the sound generator, the sound generator is located in a fluid passage extending between an inlet and a vent outlet formed in a body, the size of the vent outlet is variable to vary the resistance characteristics of the fluid flow of the fluid flow passage, characterized by the provision of means for adjusting and fixing the ventilation outlet to a predetermined variation of the size of the ventilation outlet.

2. A device for the verification of the flow according to claim 1, characterized in that the sound generator is located at a separate output of the sound generator, formed in the body, whose sound generator output is in fluid communication with the sound passage. flow of fluid that extends between the inlet and the outlet of ventilation, the sound generator being displaced with respect to the fluid flow path that extends between the inlet and outlet of the sound generator, by the provision of a barrier of fluid impervious protection, located upstream of the sound generator in the fluid flow path that extends between the input and output of the sound generator.

3. A flow verification device according to claim 1 or 2, characterized in that the output of the sound generator is shaped to expand outward into the atmosphere in a horn-like manner.

4. A device for the verification of the flow according to any of the previous claims, characterized in that the body is shaped to form a substantially bulbous resonance chamber for the sound generator.

5. A flow verification device according to any of the preceding claims, characterized in that the body comprises a plurality of body covers or plates that are interengagable to define the body, the ventilation outlet is formed in a body plate, and the Another of the body plates is provided with an occluder for the ventilation outlet, the plates are movable relative to one another so that the occluder occludes the ventilation outlet, to a greater or lesser degree, depending on the relative positions of the ventilator. the sheets, whereby the size of the ventilation outlet and the relatively movable sheets which are at least partially insurable to each other are varied to adjust the ventilation outlet to a predetermined variation of the size of the ventilation outlet.

6. A flow verification device according to claim 5, characterized by the provision of plates of the input and output body that are interengagable with each other in a plurality of positions in which the plates are rotated one relative to the other. the other, the exit plate is constituted by an external wall that encloses a resonance chamber formed with the ventilation opening, and the entrance panel is constituted by a buccal part that extends inside the occluder, which is cylindrical and adapted for positioning inside the exit plate and the upper edge from which it is spirally shaped, the ventilation opening in the outlet plate extends axially along the length of the exit plate, and the occluder is adapted, When the sheets are intercoupled, to extend inside the exit plate to occlude the ventilation to a greater or lesser degree depending on the rotation of the plates one in relation to the other.

7. A device for the verification of the flow according to claim 6, characterized in that the body plates, inlet and outlet are formed with complementary coupling formations, by means of which the two sheets can be held together, the coupling formations being constituted by an inwardly directed flange formed on a coupling end of an external wall of the outlet plate, and an undercut groove directed outward, formed on a flange extending peripherally around the outside of the entrance plate, the flange and the coupling end of the entrance plate and the notch and the flange, are suitable dimensions for the entry and exit plates to be held together with the flange, engaging within the undercut groove.

8. A device for the verification of the flow according to claim 7, characterized in that the ventilation outlet is defined by curved portions inward of the outer wall of the outlet plate, the flange being formed on the entrance plate with a ring of formed coupling with outwardly directed slits, which are formed in addition to the ends of the walls, defining the ventilation outlet, the ends and the curved walls which are interengagable with the slits in the coupling ring, thereby ensuring the entrance plate to the exit plate in a predetermined rotational position.

9. A flow verification device according to claim 8, characterized in that the outwardly directed slits are adapted to define relatively small rotation increments.

10. A flow verification device according to claim 8 or 9 characterized in that the occluder is provided with a stop formation which is positioned to engage against the curved walls at the maximum rotational positions of the entrance plate with respect to the sheet of exit.

11. A device for the verification of the flow according to any of the preceding claims, characterized in that the sound generator is a tongue that is adapted to have static and dynamic flow thresholds that are close to each other in value.

12. A device for flow verification, characterized in that it is substantially as described in this specification with reference to the accompanying drawings.

13. A method for periodically checking the maximum exhalation flow velocity of a subject, using a device according to any of the preceding claims, characterized in that the subject exhales inside the entrance of a device, in which the opening of the exit of ventilation has been preset to correspond with the predicted value of the maximum exhalation flow velocity which the subject must achieve; and the subject verifies where the sound generating device is operated, indicating that the subject has achieved the predicted maximum exhalation flow rate, or if the sound generating device has not been triggered, indicating that the subject has failed to achieve maximum predicted exhalation flow rate, and remedial action is required. SUMMARY OF THE INVENTION Portable devices for periodic verification of the maximum expiratory flow rate (PEFR) are known, and use whistles or tabs that are triggered by threshold in order to register the PEFR. This invention provides a periodic PEFR verification device that includes a threshold-activated tongue (16) located in an outlet formed in a body. The body comprises the plates of the input and output body (12, 14) which are interengagable with one another in a plurality of rotational positions of the plates one with respect to the other. A vent opening (26) extends axially along the length of the outlet plate (14). The entrance plate (12) includes a buccal part (18) that extends inside a cylindrical occluder (20), the upper edge (20.1) of which is spirally shaped. When the sheets are interengaged, the occluder (20) extends inside the exit plate, to occlude the ventilation to a greater or lesser degree, depending on the rotational position of the plates (12, 14), with which it is directed a greater or lesser proportion of the flow through the tongue assembly (16). The body plates (12, 14) which are insurable to each other to adjust the size of the ventilation outlet, usually in accordance with a predetermined treatment protocol.