Patent Application
20180066968
This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to French Patent Application No. 1658167 filed Sep. 2, 2016, the entire contents of which are incorporated herein by reference.
The present invention relates to a fluidic oscillation flowmeter usable in oxygen therapy, to a device intended for monitoring oxygen therapy and equipped with such a fluidic oscillation flowmeter, and to associated oxygen therapy equipment.
In the context of oxygen therapy provided to a patient at home, a monitoring device is normally used which is inserted between the gas source, typically a source of oxygen, and the patient, in such a way as to permit monitoring of the oxygen consumed by the patient and to ensure that the latter is indeed observing his or her treatment. Such a device may be equipped with a communication module for remote transmission of data, for example to a remote server.
Thus, WO-A-2009/136101 describes a device for monitoring oxygen therapy of a patient being treated at home by administration of oxygen, said device comprising a casing with a conduit passing through it, one or more pressure sensors, a microprocessor, a memory, a battery for providing electric current, and a radiofrequency antenna.
EP-A-2670463 proposes a similar device additionally including an accelerometer for monitoring the variable oxygen requirements of the patient depending on the patient's physical activity, in particular normal or sustained activity, low activity or rest, or sleep for example.
Moreover, EP-A-2506766 discloses a device for monitoring the respiration of a patient, comprising a differential pressure sensor arranged on a gas conduit additionally comprising an internal configuration of the Venturi type. This device is principally intended for the detection of apnoea or hypopnea in a patient treated by continuous positive airway pressure.
In addition, EP-A-2017586 proposes a device for monitoring the respiration of a patient under normal ventilation or continuous positive airway pressure. It comprises a gas conduit equipped with a diameter-reducing element generating a pressure drop, and a differential pressure sensor for determining the pressure and the flow rate of the gas.
However, these known devices are not ideal since they are in some cases bulky, consume a lot of energy, are sensitive to drift of the sensors, are imprecise in estimating the volume of gas supplied to the patient, especially in the case of low flow rates, or are sensitive to the pressure variations of the source, etc.
In view of this, the problem addressed is to be able to improve the determination of the flow rate of the gas administered to the patient and which preferably has low electricity consumption and is compact, that is to say miniaturized, and inexpensive.
The solution of the invention is therefore a fluidic oscillation flowmeter which is usable in oxygen therapy and which in particular is intended to form part of a device for monitoring a patient, comprising:
characterized in that:
Choosing an upper limit of the depth h0 of the connection conduit at 6.5 times the width l0 is associated, firstly, with the existence of a minimum speed limitation in the connection conduit, starting from which the pressure oscillations begin to take effect in the oscillation chamber. Secondly, for a given flow rate, the greater the height h0 of the connection conduit, the lower the speed inside. Consequently, the amplitude of variation of the pressure at the sensors (which is proportional to the speed in the connection conduit squared) becomes ever smaller and the measurement ever more sensitive to noise. Under these conditions, the quality of the measurement will therefore tend to deteriorate. It is therefore preferable to limit the height h0 to the abovementioned values in order to avoid or minimize this phenomenon.
Depending on the circumstances, the invention can comprises one or more of the following technical features:
The invention relates to a device for monitoring oxygen therapy, said device comprising a fluidic oscillation flowmeter according to the invention.
Moreover, the invention also relates to oxygen therapy equipment comprising:
The invention will now be better understood from the following detailed description, given by way of non-limiting illustration, with reference to the attached figures among which:
The reflux element 21 is sandwiched between two parallel walls 28, 29 delimiting the oscillation chamber 2 at the top and bottom respectively (
A connection conduit 3 fluidically connects the stabilization chamber 1 to the oscillation chamber 2, such that the gas entering the stabilization chamber 1 passes through the latter and then feeds the oscillation chamber 2. The connection conduit 3 opens into the latter in line with, that is to say facing or opposite, the reflux element 21 of semi-cylindrical shape, and this generates an oscillation of the flow and formation of vortices in the two aforementioned zones Z1 and Z2.
As will be seen, there is in fact a plane of symmetry P separating the whole system, in particular the connection conduit 3, the stabilization chamber 1, the flow-stabilizing element 11, the fluidic oscillation chamber 2 and the reflux element 21, into two equal and symmetrical parts with respect to this plane of symmetry P.
Such a configuration is known and described in the publication: Yves Le Guer; Jet confiné, dispersions fluide-particules et mélange chaotique; Engineering Sciences; Université de Pau et des Pays de l'Adour; 2005, and in the document WO 93/22627. According to said document, the depth of the channel feeding the oscillation chamber is 70 mm and its width is 10 mm.
However, such an architecture is not sufficient, especially if the positioning of the pressure taps of the flowmeter is not chosen with care. Indeed, if the pressure taps are poorly positioned, a flowmeter equipped with such a system will not be efficient enough.
In other words, it has been found that certain dimensions are particularly important and have to be respected in order to obtain an effective and precise flowmeter, in particular the positioning of the pressure taps and the dimensions (h0, l0) of the connection conduit 3 fluidically connecting the stabilization chamber 1 to the oscillation chamber 2.
Thus, during tests carried out in the context of the present invention, it was shown that, in order to ensure efficient measurement of the variation of the gas pressure, as a function of time, in the reflux chamber 2 in which the gaseous flux oscillates to form gaseous vortices in the zones Z1, Z2, the measurement site of the pressure sensors or microphones must be chosen with precision, namely the two measurement orifices 24, 25 to which the pressure sensors or microphones (not shown) are connected.
According to the invention, the two measurement orifices 24, 25 must be arranged, in the ceiling 28 (or in the floor 29) of the reflux chamber 2, that is to say approximately above the zones Z1, Z2 where the vortices form, and especially symmetrically with respect to the plane of symmetry P of the flowmeter, imperatively with a distance d between them (measured between the axes or centers of the measurement orifices) of between 0.5 and 15 mm (cf.
The two measurement orifices 24, 25, preferably connected to microphones, are situated on an axis perpendicular to the plane of symmetry P, preferably in the zone Z3 shown by broken lines in
Indeed, the principle of a fluidic oscillation flowmeter as described in the abovementioned publications does not permit an efficient flowmeter to be obtained unless the positioning of the two measurement orifices 24, 25 is chosen with care.
Indeed, the positioning of the two measurement orifices 24, 25 with respect to each other, and with respect to other elements of the geometry of the flowmeter system, plays an important role in the perception of the oscillation frequency of the pressure of the vortex and consequently influences the precision of the calculation of the flow rate based on the pressure values measured by these sensors.
It is thus also essential to specifically dimension the connection conduit 3 which conveys the gas flow into the reflux chamber 2 where the two measurement orifices 24, 25 are situated and connected preferably to microphones (not shown), as is explained below.
It must be emphasized that the two measurement orifices 24, 25 are preferably closed by a fluidically leaktight membrane so as to ensure the correct function of the microphones. Indeed, the pressure in the oscillation chamber 2 is transmitted to the sensors or to the microphones via the two orifices 24, 25 and through the membranes which cover these two orifices 24, 25. The membrane preferably has a very small thickness in the area of the sensors 24 and 25, typically of the order of about 50 to 500 μm; elsewhere, its thickness can be between 1 and 2 mm, or even more.
Indeed, the gas flow circulates in the direction of the arrows (=>) shown in
Within the stabilization chamber 1, the flow is subjected to stabilization by the flow-stabilizing element 11, which has a cross section approaching that of a triangle with its base oriented opposite the mouth of the inlet channel 4, hence facing the first inlet orifice 12. In fact, the cross section of the flow-stabilizing element 11 is slightly concave as it approaches the inlet 13 of the conduit 3.
The gas flow goes round the flow-stabilizing element 11 by flowing through the passages 15 formed on each side of the latter. The passages 15 are in fact delimited by the outer surface of the flow-stabilizing element 11 and by the inner peripheral wall 14 of the stabilization chamber 1. In other words, the flow-stabilizing element 11 is spaced apart from the peripheral wall 14 of the stabilization chamber 1 in such a way as to create passages 15 for the gas around said flow-stabilizing element 11.
The gas flow then leaves the stabilization chamber 1 via the first outlet orifice 13 and is conveyed through the connection conduit 3 which fluidically connects the first outlet orifice 13 of the stabilization chamber 1 to the second inlet orifice 23 of the oscillation chamber 2.
The first and second inlet orifices 12, 13 and the first and second outlet orifices 13, 26 are arranged symmetrically with respect to the plane of symmetry P, as can be seen in
According to the present invention, in order to be able to ensure effective measurements, the connection conduit 3 also has to be configured and dimensioned in a specific way. Thus, according to the invention, the connection conduit 3 is of rectangular cross section, that is to say it has the general shape of a parallelepiped with a width l0 and a height h0 such that: 6.5·l0≧h0≧3·l0, where the width l0 is for example 0.5 to 1.5 mm, more preferably between 0.8 and 1.3 mm; this is illustrated in
In other words, by choosing a connection conduit 3 whose width is small in relation to its height, it will be possible to obtain a two-dimensional laminar flow with a sufficiently high speed, which will favor its oscillation in the reflux chamber 2.
Moreover, it is also preferable to observe a length L0 of the connection conduit 3 in relation to its width l0, such that 2·l0≦L0≦10·l0, preferably with: 3·l0≦L0≦7·l0.
Generally, as illustrated in
The gas then continues its travel through the oscillation chamber 2 before leaving the latter through a gas evacuation conduit 27, which is fluidically connected to the second gas outlet orifice 26 of the oscillation chamber 2.
It will thus be understood that, starting from a speed symmetrical in two dimensions, a vortex is created whose location (zones Z1 and Z2) will oscillate with a frequency proportional to the value of the flow rate of the fluid that circulates there. By placing microphones or pressure measurement members/sensors outside the path of the fluid, that is to say above zones Z1, Z2 where the vortices form, it is possible to measure the presence or absence of a drop in pressure of the gas.
With the flowmeter of the invention, the flow rate of the circulating gas can be measured in a non-intrusive, miniaturized and inexpensive manner, with a pressure drop that is limited by comparison with a flowmeter having a throttle.
The whole system is accommodated in a casing shown in
Moreover, control means 35 such as an electronic card with microprocessor, for example a microcontroller, are connected electrically to the pressure sensors or microphones in such a way as to collect and exploit the pressure measurements by extracting their oscillation frequency and then deducing therefrom a gas flow rate, as is illustrated in
A control and processor module 35, such as an electronic card, is connected electrically to the sensors 31, 32 and to the flowmeter 33 in such a way as to recover and process the measurements carried out by the sensors 31, 32 and the flowmeter 33. An energy source, such as an electric battery or a cell, is able to supply electric current to the control and processor module 35.
In order to show the importance of the correct positioning of the measurement orifices 24, 25 according to the present invention, simulation tests have been carried out as explained below.
The geometry of the chosen flowmeter (cf.
Several virtual measurement orifices OM1 to OM4 were positioned in order to evaluate the impact of their placement/positioning in terms of amplitude and frequency of the associated pressure signal. The positioning of the measurement orifices 24, 25 (designated OM1 to OM4 in
After several tests of the positioning of the orifices OM1 to OM4 (cf. table above), it was noted that the pressure measurement allowing the gas flow rate to be deduced is not correct when the position of the acoustic measurements is not chosen with care.
Indeed, the tests demonstrated that the measurement orifices 24, 25, connected to the sensors, should be positioned symmetrically with respect to the plane P and at a distance d between the axes of the measurement taps of between 0.5 and 15 mm in order to guarantee quality measurements. The best results are obtained with a distance d between the axes of the measurement taps of between 1 and 10 mm, preferably between 1 and 6 mm, typically of the order of 3 to 5 mm.
Advantageously, their position is chosen preferably in the zone Z3 of
These results are shown in
Similarly,
In
In
In conclusion, the two measurement orifices connected to the pressure sensors or microphones have to be placed in the zone Z3, but in particular symmetrically with respect to the plane P and with a distance d between them of between 0.5 and 10 mm, preferably of the order of 1.5 to 6 mm.
To show the importance of calculating the difference of the signals of the two pressure sensors or microphones in order to extract the oscillation frequency,
If we examine separately the pressure signal picked up by the probes 1 and 2 (i.e. the measurement orifices OM1 and OM2), it is more difficult to extract the oscillation frequency, whereas the latter is clearly more visible from the difference of the signals. Hence the need to calculate the difference of the pressure signals and especially at a high flowrate, i.e. above 1 l/min. Moreover, this makes it possible to eliminate, where they exist, electronic noise on the two sensors and the ambient acoustic noise, and also the pressure variations induced by the respiratory frequency of the patient. All of these noises (electronic, acoustic, patient's breathing) in fact disturb the pressure signals of the two sensors in the same way. It is therefore preferable to eliminate them by effecting a difference between the pressure signals.
The fluidic oscillation flowmeter according to the invention is particularly well adapted for use in a device for monitoring oxygen therapy of a patient at home, said monitoring device being connected, on the one hand, to a source of respiratory gas and, on the other hand, to a gas distribution interface, such as a breathing mask, a nasal cannula or similar, serving to supply respiratory gas, typically gaseous oxygen, to the patient.
It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1658167 | Sep 2016 | FR | national |
