Bidirectional flow meter for an MDI device and an MDI device containing such a bidirectional flow meter
The present invention relates to a bidirectional flow meter for an MDI device, which device has a flow channel and first and second pressure tap points arranged in the flow channel.
The invention further relates to an MDI device comprising such a bidirectional flow meter.
The number of chronic respiratory diseases is increasing worldwide. Certain types of disease, such as asthma or chronic obstructive pulmonary disease (COPD), cannot be cured, but the medical condition of the patients can be maintained with adequate drug dosing. An effective means of targeted drug treatment of the respiratory system is inhaled drug delivery, for which mainly metered dose aerosols, also known as MDI (Metered Dose Inhaler) devices, are used. The peculiarity of MDI devices is that achieving the desired effect requires attention and practice from the user, as 10-40% of the inhaled dose reaches the patient's lungs only, depending on the type of aerosol and the way of inhalation. Therefore, it is important to check the correctness and regularity of medication intake, which can be done, for example, with various sensors built into the MDI device.
For MDIs, regular and correct intake can be monitored from several perspectives. For example, an accelerometer can be used to determine if the patient has shaken the device before use. A sensor can be used to measure that the patient has actually inhaled the product and not just blown it into the air. All of these features are of great help to the physician in tracking the patient’s condition, defining and reviewing their treatment plan. A more advanced way to monitor medication use when in addition to the use (as an event) and the correctness (shaking and blowing into the mouth), the quality of suction is also measured, and try to estimate how much of the inhaled drug has reached the patient’s lungs. To do this, the flow velocity (or volume flow) of the air drawn in through the MDI device and the corresponding time of drug activation must be determined. The delivery efficiency will be greatest if the volume flow at the time of activation is within the range specified by the product manufacturer.
There are several ways for measuring the intake air velocity profile when using an inhaled drug. In one example, a spirometer is placed in front of the product outlet and the patient draws in the medication through it while the spirometer measures the velocity of the air. The disadvantage of this is that the outlet of the device is moved further away from the patient's mouth, so the efficiency of inhalation deteriorates and the dosage will not be ideal. Alternatively, the spirometer is located on the inlet of the inhaler. To do this, however, the connection must be properly sealed and the spirometer must be positioned so as not to interfere with the use of the drug. On the one hand, this is difficult to do in practice, and on the other hand, the installation of the spirometer changes the operating parameters of the inhaler.
The most efficient way to measure the volume flow through the inhaler is to integrate an air velocity meter into the inhaler. Such a solution is described, for example, in U.S. Pat. No. 2017/0290527, in which a measuring module comprising a pressure sensor and associated electronics is connected to the upper inlet portion of the inhaler by means of a hook. The capillary tube of the pressure sensor is hung in a cylindrical shell-shaped channel between the housing of the inhaler and the canister containing the active ingredient, thus measuring the air flow there. In this case, the patient can use the device as before, there are no extra instructions to follow, nothing to connect, no position to hold, and so on. The disadvantage of the above solution is that it can only measure the volume flow for suction.
In addition to determining the inspiratory air velocity profile, by measuring the expiratory air velocity profile (especially by determining the peak expiratory value), direct information about the patient's current condition can be obtained, which can further increase the efficiency of drug administration. However, a problem in designing such a bidirectional flow device is that the flow velocities (or pressure ranges) that can be measured during inspiration and exhalation differ significantly. This is because the drug should not be inhaled very vigorously, while must exhale with full force to reach the expiratory peak. The expiratory flow rate can be up to four times that measured at inhalation. Since the differential pressure range required for the joint measurement of the two flows is difficult to measure with a single system, providing the required measurement accuracy, in the currently known solutions, the airflows generated during exhalation and inhalation are measured in two separate channels with two different sensors. Such a solution is described, for example, in US 2009/0270752. The disadvantage of this arrangement is that it is complex and, due to its size, cannot be integrated with existing MDI devices.
It has been found that the measurement of expiratory and inspiratory volume flow can be performed in a compact and simple manner by measuring the difference in pressure before and after a constriction arranged in the flow path, i.e. by using differential pressure measurement.
It has also been recognized that classical, symmetrical constriction or flange designs are out of the question due to volume flows of different magnitudes in each direction, as in the case of a measuring system optimized for inhalation, a much larger volume flow during exhalation would result in a large pressure difference, exceeding the measuring limit. In addition, a symmetrical constriction design would not be suitable for determining the direction of flow, since changing the direction of flow would not change the relation of the resulting pressures.
It has also been found that the expiratory pressure difference measured before and after the constriction can be reduced, and even the relation of the measured pressures can be reversed by means of an asymmetric flow channel in which the exhaled flow through the constriction detaches from the wall of the flow channel, thereby proceeding at a high speed. That is, in the case of exhalation, the pressure difference between a small overpressure before the constriction and a high velocity (i.e., lower pressure) core due to detachment after the constriction are measured. At the same time, the asymmetrical design of the flow channel ensures that, in the case of inhalation, a well-conditioned flow is formed for accurate measurement, i.e. the measuring points are not in a detachment zone (with highly fluctuating quantities).
It is an object of the present invention to provide a bidirectional flow meter which is free from the disadvantages of the prior art, i.e. which allows the magnitude and direction of volume flows of different magnitudes passing through the MDI device from two directions to be determined and which device can be integrated with existing MDI devices.
It is a further object of the invention to provide an MDI device which is free from the disadvantages of the prior art, i.e. comprising a bidirectional flow meter according to the invention.
According to the invention, this object is achieved by means of a bidirectional flow meter according to claim 1 .
The object is further achieved according to the invention by means of an MDI device according to claim 14.
The object is achieved by providing a flow meter having a flow channel and first and second pressure tap points arranged in the flow channel. The flow channel comprises a first channel part delimited by first walls and a second channel part delimited by second walls, said channel parts are separated by a constriction, wherein said first channel part widens in a direction leading away from the constriction. The first walls are configured to separate an outlet flow entering from the second channel part into the first channel part from the first walls and to guide an inlet flow entering from the first channel part into the second channel part, and said second walls are configured to guide the outlet flow. The essence of the solution is that the second pressure tap point is arranged in the second channel part and the first pressure tap point is arranged in the first channel part in the vicinity of the constriction, along the detaching (i.e. separated) outlet flow. The advantage of the bidirectional flow meter according to the invention is that the outlet and inlet flows can be measured with a single flow channel and the same sensors, i.e. it is not necessary to use two separate channels and different sensors for each channel for the outlet and inlet flows.
Further preferred embodiments of the invention are defined in the dependent claims. Further details of the invention will be described with reference to the accompanying drawings. In the drawing is
Figure 1 a is a schematic front view of an exemplary embodiment of a bidirectional flow meter according to the invention;
Figure 1 b is a schematic front view of another exemplary embodiment of a bidirectional flow meter according to the invention;
Figure 2 is a schematic perspective view of the embodiment of the bidirectional flow meter according to the invention shown in Figure 1 a;
Figure 3a is a simulated view of streamlines of an outlet flow passing through the bidirectional flow meter according to Figure 1 b, mounted on the MDI device;
Figure 3b is a simulated view of streamlines of an inlet flow passing through the bidirectional flow meter according to Figure 1 b, mounted on the MDI device;
Figure 4 is a schematic perspective view of a bidirectional flow meter according to the invention in a state mounted on an MDI device;
Figure 5 shows the pressure difference measured between the pressure tap points as a function of the volume flow in the case of inhalation and exhalation.
Figure 1 a is a front view of an exemplary embodiment of a bidirectional flow meter 10 according to the present invention for an MDI device 100. The device 10 has flow channel 20 along a longitudinal axis T and first and second pressure tap points 31 , 32 arranged in the flow channel 20. The first and second pressure tap points 31 , 32 are areas formed in the flow channel 20 to which a manometer can be connected (not shown in the figures). The manometer used can be any known commercially available pressure gauge; for example, a digital manometer measuring indirectly or directly, such as a piezoresistive pressure gauge, which converts the pressure change into a digital signal and which, due to its size and measurement accuracy, is suitable for use in the MDI device 100 as is known to those skilled in the art. By means of the first and second pressure tap points 31 , 32, the static pressure at the given point and therefore the difference between the pressures measured at the pressure tap points 31 , 32 can be determined. For the sake of clarity, it is noted that in the present description, pressure is to be understood as meaning the static pressure of the flow.
In the context of the present invention, a flow channel 20 is an open space bounded by side walls for guiding airflow along the longitudinal axis T, which by its shape changes the velocity or pressure conditions of the air flowing therethrough along the flow channel 20. The flow channel 20 comprises a first channel part 21 delimited by first walls 41 and a second channel part 22 delimited by second walls 42, wherein said channel parts 21 , 22 are separated by a constriction 25. In other words, the constriction 25 divides the flow channel 20 into first and second channel parts 21 , 22. The constriction 25 is the smallest cross-sectional portion of the first channel part 21 and the flow channel 20 perpendicular to the longitudinal axis T, as shown in Figure 1a. It should be noted, however, that embodiments are conceivable in which the second channel part 22 of the flow channel 20 has a constant cross- section equal to the cross-section of the constriction 25 (see, e.g., Figure 1 b). The first walls 41 and the second walls 42 form opposite pairs, the respective members of which pairs meet at the constriction 25, i.e. the respective first and second walls 41 , 42 meet on either side of the constriction 25. The walls 41 , 42 are rigid in terms of flow through the flow channel 20 and have a fixed position relative to each other, i.e. the flow does not change their shape and position. The walls 41 , 42 can be made of, for example, plastic, metal, or any other known material of proper strength. The first and second channel parts 21 , 22 are defined by the first and second walls 41 , 42, respectively, that is, in the context of the present invention, the first channel part 21 means the space between the first walls 41 and the second channel part 22 means the space between the second walls 42.
In a preferred embodiment, the first and second walls 41 , 42 are planar surfaces, and the flow meter 10 includes a deflector plate 40 delimiting the flow channel 20 in a plane perpendicular to the planar surfaces of the first and second walls 41 , 42. Thus, in this embodiment, the flow channel 20 is enclosed by the deflector plate 40 and the walls 41 , 42 such that the flow channel 20 is open on the side opposite the deflector plate 40 (see Figure 2). The height of the first and second walls perpendicular to the deflector plate is, for example, between 2 and 8 mm.
Note that the flow through the flow channel 20 is substantially parallel to the plane of the deflector plate 40. In a preferred embodiment, the first and second walls 41 , 42 are formed as opposite sides of two deflector elements 45 fixed to the deflector plate 40. The deflector elements 45 can be solid or hollow in design, and made of plastic, for example. In an exemplary embodiment, the surface of the deflector elements 45 in contact with the deflector plate 40 is triangular, i.e., they form a triangular-based column as shown in Figure 2. The deflector element 45 can be attached to the deflector plate 40 in a known manner (e.g. by gluing or welding), but optionally the deflector plate 40 and the deflector elements 45 can also be formed as a single element, for example by injection molding.
The first channel part 21 according to the invention widens in a direction leading away from the constriction 25, i.e. the distance, taken perpendicular to the longitudinal axis T, between the first walls 41 increases in a direction leading away from the constriction 25 along the longitudinal axis T, as shown, for example, in Figures 1 a and 1 b. The first walls 41 delimiting the first channel part 21 are preferably planar surfaces, the angle formed by the planar surfaces, i.e. the opening angle of the first channel part 21 is at least 15 degrees. Embodiments are also possible in which the first walls 41 are curved (not shown in the figures), so that the distance between the walls 41 increases non-linearly as it moves away from the constriction 25 along the longitudinal axis T. The first walls 41 are configured to separate an outlet flow entering from the second channel part 22 into the first channel part 21 from the first walls 41 and to guide an inlet flow entering from the first channel part 21 into the second channel part 22. In the context of the present invention, the flow separation (or detachment) means that the flow entering the first channel part 21 through the constriction 25 does not widen and extend along the first walls 41 , but retaining its original direction and velocity in the space after the constriction 25, spreading like an air column along a longitudinal axis T, as shown, for example, in Figure 3a. Flow detachment occurs in channels that expand in the direction of flow. The minimum opening angle value above which flow detachment is certain to occur can be determined as a function of the Reynolds number, as is known to those skilled in the art for diffusers. In contrast, during guiding the flow, the flow travels along the walls 41 follows the shape of the first channel part 21 in the direction of the constriction 25, during which its velocity increases and its pressure decreases due to the continuously narrowing cross-section, as shown in Fig. 3b. It is noted that with respect to inlet flow, the channel part 21 behaves as a known confuser of venturi tubes.
The second walls 42 of the present invention are configured to guide the outlet flow. In the exemplary embodiment shown in Fig. 1 a the second channel part 22 widens in a direction leading away from the constriction 25 such that the second walls 42 delimiting the second channel part 22 are planar surfaces and the angle (opening angle) formed by said planar surfaces is smaller than the angle formed by the planar surfaces of the first walls 41 . That is, the distance between the second walls 42 measured perpendicular to the longitudinal axis T increases along the longitudinal axis T in a direction leading away from the constriction 25, but the opening angle is preferably smaller than the opening angle of the first channel part 21 . The outlet flow does not separate from the walls 42 due to the narrowing cross section of the channel part 22 and the increase in velocity. In another possible embodiment, the opening angle of the channel part 22 is zero, i.e. the second walls 42 are arranged parallel to each other (see Fig. 1 b). In this case, essentially neither the outlet nor the inlet flow separates from the wall of the channel part 22, but proceeds laminarly.
In the flow meter 10 according to the invention, the second pressure tap point 32 is arranged in the second channel part 22 and the first pressure tap point 31 is arranged in the first channel part 21 , in the vicinity of the constriction 25, along the separated outlet flow. The pressure tap points 31 , 32 are arranged along the longitudinal axis T so as to be in contact with the air flow through the flow channel 20, thereby being capable of sampling the static pressure at that point. In a preferred embodiment, the first and second pressure tap points 31 , 32 are on the deflector plate 40 in its plane, as shown, for example, in Fig. 2. For a given volume flow and flow channel 20 design, the magnitude and sign of the pressure difference measured between the pressure tap points 31 , 32 depends on the distance of the pressure tap points 31 , 32 from the constriction 25. In the case of inlet flow, the pressure measured at the first pressure tap point 31 will always be higher than the pressure measured at the second pressure tap point 32, i.e. the pressure difference will have a positive sign. In the case of an outlet flow, an overpressure relative to the atmospheric pressure is generated in the second channel part 22. The air flowing through the channel part 22 gradually accelerates along the channel part 22, as a result of which its pressure gradually decreases (possibly falling below atmospheric pressure). The outlet flow reaches its maximum velocity near the constriction 25, i.e. it will have the lowest static pressure here. The outlet flow leaving the constriction 25 continues in the first channel part 21 , detached from the walls 41 , so that its velocity does not decrease and its pressure does not increase significantly compared to the velocity or pressure at the constriction 25. Therefore, in the case of an outlet flow, the pressure measured at the first pressure tap point 31 , i.e. at the detached flow, will be lower than the pressure measured at the second pressure tap point 32, so that the sign of the pressure difference will be negative. The direction of the flow can thus be determined from the sign of the measured pressure difference. As the velocity of the detached flow decreases as the distance from the constriction 25 increases and its pressure increases, as well as the undesired pressure fluctuations in the detached flow increase, the pressure tap point 31 should be located as close as possible to the constriction 25. Therefore, in an exemplary embodiment, the first pressure tap point 31 is arranged at a distance of up to 5 mm from the constriction 25 along the separated outlet flow.
Outer flow channels increase the cross section for the outlet flow, so that the flow rate in the flow channel 20 in the case of exhale can be reduced, which reduces the pressure difference between the pressure tap points 31 , 32, which can be advantageous for the measuring range. Therefore, in a preferred embodiment, the flow meter 10 comprises outer flow channels 28 enclosing the flow channel 20 on two sides, which outer flow channels 28 are delimited by third walls 43 of the deflector elements 45 opposite the first and second walls 41 , 42 and by outer walls 44. That is, the respective outer flow channel 28 is defined by the third wall 43 of the respective deflector element 45 and the outer wall 44. In a possible embodiment, the height of the outer walls 44 and the first and second walls 41 , 42 perpendicular to the deflector plate 40 is substantially equal to each other, as shown in Fig. 2. The outer and third walls 44, 43 are preferably planar surfaces, and the outer flow channels 28 are tapered in the direction of the outlet flow. The advantage of this tapered design is that the orderliness of the flow passing through is improved, so that less flow-inhibiting turbulences occur, and the flow cross-section does not increase significantly for the inlet flow, i.e. most of the flow continues to pass through the flow channel 20 and not through the outer channels 28. The outer flow channels 28 narrowing in the direction of the outlet flow can be formed, for example, according to the arrangement shown in Figures 1 a or 1 b, i.e. by means of triangular column shaped deflector elements 45 and outer walls 44 arranged perpendicular to the deflector plate 40 and arranged parallel to each other.
By means of the flow meter 10 according to the invention, the volume flow passing directly through the flow channel 20 can be measured. To determine the volume flow through the MDI device 100, the flow meter 10 must be placed in the path of the air flow through the MDI device 100. The volume flow through the MDI device 100 can be calculated by knowing the volume flow measured by the flow meter 10, as it is apparent to those skilled in the art. Since it is intended that the flow meter 10 of the present invention can be used with existing MDI devices 100 of known design, and that the flow meter 10 interfere as little as possible with the normal operation of the MDI device 100, in the embodiment shown in Figure 4, the flow meter 10 includes a collar 50 that mounts to the inlet of the MDI device 100 and fits around the circumference of the inlet. The collar 50 may be made of, for example, plastic or metal, and is preferably releasably attached to the inlet of the MDI device 100. The collar 50 is preferably hollow in design, which allows, for example, the compact placement of manometers or other components (e.g. electronics, power supply, etc.) belonging to the pressure tap points 31 , 32.
The invention further relates to an MDI device 100 comprising a bidirectional flow meter 10 according to the invention.
In the following, the operation of the flow meter 10 according to the invention will be briefly described with reference to Figures 1 b, 3a, 3b and 5. In the exemplary embodiment of the flow meter 10 shown in Figure 1 b, the walls 42 of the second channel part 22 are arranged in parallel, 2.8 mm apart. The length of the channel part 22 is approximately 4.5 mm. The distance between the center of the second pressure tap point 32 and the constriction 25 along the longitudinal axis T is 2 mm, and the distance between the first and second pressure tap points 31 , 32 is 4.2 mm. The opening angle of the first channel part 21 is 90 degrees and its length along the longitudinal axis T is 4 mm.
The flow meter 10 is secured to the inlet of the MDI device 100 by means of the collar 50 as shown in Fig. 4. When the MDI device 100 is being sucked, the inlet flow shown in Figure 3b is formed in the flow channel 20. The stream lines illustrate the flow path and velocity at a flow rate of 150 l/min. It can be seen that in this embodiment, in case of inlet flow, an ordered flow is formed in both channel parts 21 , 22, which follows the walls 41 , 42. Due to the narrowing cross section of the first channel part 21 , the flow velocity increases and the static pressure decreases towards the constriction 25 according to Bernoulli's law. Thus, the pressure measured at the pressure tap point 31 will be higher than the pressure measured at the pressure tap point 32, i.e. the sign of the pressure difference will be positive. The outlet flow developed during exhalation in the flow meter 10 mounted on the MDI device 100 is illustrated in Fig. 3a at a flow rate of 150 I / min. It can be seen that in the case of an outlet flow, an ordered flow is formed in the channel part 22, which follows the wall 42. The velocity of the air along the channel part 22 increases continuously and the pressure decreases continuously. The flow entering the channel part 21 does not follow the walls 41 , i.e. it does not widen, but continues in its direction and speed, thus creating a small pressure difference between the pressure tap points 31, 32. The pressure in the vicinity of the constriction 25 does not increase significantly, the pressure measured at the pressure tap point 31 will thus be lower than the pressure measured at the pressure tap point 32, and the sign of the pressure difference will be negative. Fig. 5 shows the pressure difference measured between the pressure tap points 31 , 32 as a function of the volume flow for both the outlet flow (dashed line) and the inlet flow (solid line). It can be seen that a given volume flow value has twice the pressure difference during suction as when blowing out. All this means that the measuring range when blowing is twice as large as when suction. This makes it possible to accurately measure the inlet flow and the outlet flow having a several times higher mass flow, using a single device.
Various modification to the above disclosed embodiment will be apparent to a person skilled in the art without departing from the scope of protection determined by the attached claims.