TECHNICAL FIELD OF THE INVENTION

This invention relates to a breathing simulator comprising, amongst others, a piston pump. This invention also relates to a system and a method for calibrating a gas flowmeter thanks to a breathing simulator.

BACKGROUND OF THE INVENTION

In the field of indirect calorimetry, it is known to analyze the gases inhaled and exhaled by a patient, in particular in order to determine their 0 ₂ and C0 ₂ content. It is also known to measure the flow rate of the inhaled air and exhaled gases. In order to fulfil this function, one generally uses a gas flowmeter which can be of the rotating blades type or include one or several Pitot probes. The accuracy of such a flowmeter depends on the atmospheric conditions.

It is thus known to calibrate a gas flowmeter which belongs to an indirect calorimetry installation prior to using this flowmeter in such an installation. In order to fulfil this calibrating step, one can use a syringe which has a predetermined volume and which is used to inject air into the flowmeter. The operator is supposed to move the piston of the syringe at a constant given speed. Actually, this is not easy to do and some errors are generated. Alternatively, one can use a piston pump driven by a crank mechanism in order to simulate regular breathing of a patient. The input/output flow of such a pump is set by the mechanical definition of the crank mechanism and by the rotation speed of the driving means of this mechanism. The flow rate at the input/output port of the pump has a sinusoidal shape. Thus, such a pump is useful to calibrate a gas flow rate for a working session where a sinusoidal breathing of a patient will be analyzed, with a flow rate and a frequency substantially equal to the one of the crank mechanism.

Actually, many kinds of patients have to be studied, from a top level athlete to somebody suffering from mucoviscidosis or an equivalent disease, which strongly limits the lung capacity of a patient. Moreover, patients are often tested in different situations. They can be at rest, that is make no effort, or perform a physical exercise. In these different situations, the breathing scheme of each patient can be different, in terms of inhaled/exhaled air quantity, in terms of breathing frequency and in terms of breathing profile which is not always sinusoidal. In particular, in case of an intense effort, the breathing profile of a patient tends to be triangular or almost triangular. Moreover, differences exist in the respiratory schemes of the patients, depending on their age, sex and physical condition.

Thus, the known systems which allow calibrating a gas flowmeter in a single given configuration cannot be relevant for further use of the gas flowmeter in variable conditions, depending on the patients to be studied and on the exercises he or she is supposed to perform.

In another field of technology, that is in the field of check devices for breathing apparatuses, it is known from FR-A-2 663 233 to move a plate with respect to a fixed structure in order to contract or expand a variable volume chamber delimited by a bellows. Due to the shape of the bellows, the quantity of air pushed by the movable plate is not precisely known. Moreover, because of the bellows, the variable volume chamber has a significant dead volume. The movable plate is driven by a direct current motor, which is relatively slow and difficult to run with a high accuracy.

On the other hand, US-A-2007/259322 discloses a breathing simulator for the evaluation test of a respirator. No piston pump is disclosed, nor control means for the reciprocating movement of the piston of such a pump. The quantity of air provided to the respirator is not precisely controlled.

SUMMARY OF THE INVENTION

This invention aims at solving this problem with a new breathing simulator which provides a great flexibility in the simulated breathing, thus enabling to calibrate a gas flowmeter in conditions which are close to the intended conditions of use of this flowmeter.

To this end, the invention concerns a breathing simulator comprising a piston pump and driving means for driving a piston of the piston pump within a casing of the piston pump, with a reciprocating movement, said casing comprising a cylindrical sleeve and two end plates. According to the invention, the driving means include:

- an electric synchronous motor,

- a screw-nut connection between a shaft rotatively driven by the electric motor and a nut fixedly mounted on the piston,

- electronic control means piloting the electric synchronous motor on the basis of a target value for at least one parameter defining the reciprocating movement of the piston and

- input means for setting the target value.

Thanks to the invention, it is possible for an operator to set the target value of one or several parameters in accordance with a desired breathing scheme, in particular a breathing scheme globally representative of the one of the patient who will next breathe in a gas flowmeter calibrated with the breathing simulator of the invention. Thus, the invention allows to take into account the age, the sex, the physical condition of a patient, the fact that he/she is going to perform a physical exercise or not, and what kind of physical exercise he/she is going to perform when the flowmeter will be used in the framework of an indirect calorimetry installation. Moreover, because of its versatility, the breathing simulator of the invention can be used to simulate many pulmonar volumes such as the inspiratory or expiratory reserve volume, the residual lung volume etc... Thus, the breathing simulator of the invention can also be useful as a simulator of respiration for educational and training purposes. Since the piston has a reciprocating movement between the end plates of the casing and within the cylindrical sleeve, the quantity of air moved by the pump is accurately controlled. The acceleration of the piston, which is obtained through the synchronous motor, can be high, in particular higher than with a direct current motor, and its position precisely controlled. This allows accurately simulating many kinds of respiratory patterns. Because of the structure of the breathing simulator of the invention, it is possible to precisely simulate breathing on a large range, with unitary respiratory volumes between 0,4 liters and 4 liters and frequencies between 8 and 64 breathings in/out per minute. This allows using this simulator for calibrating a gas flowmeter for a large number of configurations of use.

According to further aspects of the invention, which are advantageous but not compulsory, the breathing simulator of the invention might incorporate one or several of the following features, taken in any technically admissible combination:

- The control means include a controller which feeds the synchronous motor with electric current.

- The input means include a function generator capable of delivering different kinds of periodic electric signals, including a sinusoidal signal, a triangular signal and at least a signal resulting from the combination of the sinusoidal signal and the triangular signal.

- The function generator is equipped with control means for selecting a mixing ratio between the sinusoidal signal and the triangular signal.

- The breathing simulator includes a sensor for detecting when the piston is in a given position.

- The sensor is a switch which is activated by the piston or a part secured in translation with the piston.

- The piston is equipped with at least one anti-rotation rod guided by a portion of the casing of the piston pump and the anti-rotation rod actuates the switch when the piston is in the given position. Moreover, the invention concerns a system for calibrating a gas flowmeter, this system including a breathing simulator as mentioned here-above and at least one duct to connect a port of its pump to a port of the gas flowmeter.

Finally, the invention concerns a method for calibrating a gas flowmeter, in particular an indirect calorimeter, this method being characterized in that it includes at least the following steps:

a) connecting a port of the pump of the breathing simulator as mentioned here- above to a port of the gas flowmeter,

b) selecting a target value for at least one parameter defining the reciprocating movement of the piston of the pump,

c) transmitting, to the electronic control means, a data representative of the selected target value.

According to further aspects of the invention, which are advantageous but not compulsory, this method might incorporate one or several of the following features, taken in any technically admissible combination:

- The at least one parameter is selected amongst:

- a first parameter representative of the maximum capacity of a variable volume chamber connected to the outlet port and defined by the piston and a fixed body of the pump,

- a second parameter representative of the frequency of the reciprocating movement of the piston,

- a third parameter representative of the shape of a curve representing the position of the piston during its reciprocating movement, as a function of time.

- The first parameter is converted by the electronic control unit as a target value for the piston stroke.

- The second parameter is converted by the electronic control unit as a target value for the translation speed of the piston.

- The third parameter is a mixing coefficient, at least between a sinusoidal profile and a triangular profile.

- At step b), a target value is chosen for each one of the three parameters.

- The method further includes the following step d), implemented before moving the piston with the reciprocating movement and consisting in moving the piston, in a given direction, until it reaches a predetermined position.

- When the gas flowmeter is to be used to measure gas flow during breathing in and out of a patient, the at least one parameter is chosen at step b) as a function of some physiological data of the patient and/or the type of physical exercise to be performed by the patient.

- At step b), the target value is chosen

- for the first and second parameters, depending on the sex, age and physical condition of the patient,

- for the first, second and third parameters, depending on the type of physical exercise to be preformed by the patient.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood on the basis of the following description which is given in correspondence with the annexed figures and as an illustrative example, without restricting the object of the invention. In the annexed figures:

- figure 1 is a schematic axial cut view of a breathing simulator according to the invention,

- figure 2 is a wiring scheme of the breathing simulator of figure 1 , and

- figure 3 is a block diagram of a method implemented with the simulator of figures 1 and 2.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The breathing simulator 2 represented on figure 1 includes a closed casing 4 made of a cylindrical sleeve 6 and two end plates 8 and 10.

End plate 8 is provided with a through hole 12 which is equipped with a connector

14.

End plate 10 supports an electric motor 20 which is located outside casing 4 and whose output shaft 22 is rotatably connected, via a connecting yoke 24, to a threaded rod 26. A first end 262 of threaded rod 26 is immobilized within yoke 24, whereas a second end 264 of threaded rod 26, opposite to first end 262, is rotatably supported within a correspondly shaped recess 28 of end plate 8.

End plates 8 and 10 are mounted on sleeve 6 via several screws 16 represented by their respective axes on figure 1 .

X2 denotes a longitudinal axis of simulator 2. Output shaft 22 and threaded rod 26 are aligned along axis X2. In other words, the respective longitudinal axes A22 and A26 of shaft 22 and rod 26 are superimposed with axis X2.

A piston 30 is slidably mounted within casing 4 and bears three O-rings 32 adapted to slide against the inner radial surface 34 of sleeve 6. Piston 30 has a reciprocal movement within sleeve 6 of casing 4, between end plates 8 and 10. A nut 36 is fixedly mounted on piston 30 via screws 38 represented by their respective axis. Nut 36 is provided with an inner thread which is complementary to the outer thread of rod 26, so that a screw-nut connection is realized between items 26 and 36. In other words, rotation of threaded rod 26 around axis X2, as shown by rotation arrows R1 and R2, induces a translation movement of piston 30 within casing 4, as shown by translation arrows T1 and T2.

The internal volume of casing 4 is divided by piston 30 into two variable volume chambers C1 and C2. Chamber C1 is defined between end plate 8 and piston 30, whereas chamber C2 is defined between end plate 10 and piston 30.

Casing 4 and piston 30 together form a piston pump 48 which is driven by motor 20.

Thus, by driving threaded rod 26 alternatively in rotation around axis X2, in the directions of arrow R1 and arrow R2, it is possible to move piston 30 within casing 4 with a reciprocating movement in the directions of arrows T1 and T2, in order to induce an intake airflow F1 or an exhaust airflow F2 which can be used to simulate breathing of a patient.

Chamber C1 is isolated from the surrounding atmosphere because end plate 8 is tightly mounted on sleeve 6 and because of the tightening function of O-rings 32. The only communication between chamber C1 and the outside of casing 4 occurs through connector 14.

Piston 30 is equipped with two anti-rotation rods 40 and 42 which are fixedly mounted on piston 30 and extend through two holes 44 and 46 provided on end plate 10. Since rods 40 and 42 are blocked by holes 44 and 46 in rotation around axis X2 with respect to end plate 10, they prevent piston 30 from rotating around axis X2. Thus, the screw-nut connection between items 26 and 36 is precise enough to adjust the position of piston 30 along axis X2 thanks to the rotation of output shaft 22 and threaded rod 26 which are rigidly connected in rotation.

Alternatively, simulator 2 may include only one anti-rotation rod or more than two such rods, e.g. four.

According to a non represented embodiment of the invention, an anti-rotation rod 40 or 42 can be guided by any portion of casing 4.

Motor 20 is a three-phase synchronous motor, which is controlled by a control unit

50 programmed via a personal computer 52.

A plate 54 is fixedly mounted on motor 20 and it is equipped with an electric switch 56 against which an end 402 of anti-rotation rod 40, which is opposite to piston 30, comes into abutment when piston 30 is in its rear most position or rear dead end position with respect to end plate 8, that is when chamber C1 has its largest volume. With this respect, one considers that the front of casing 4 is on the side of end plate 8, whereas the back of this casing is on the side of end plate 10. Thus, end plate 8 is the front end plate of casing 4, whereas end plate 10 is the rear or back end plate of this casing. Thanks to switch 56, which is connected to control unit 50, it is possible to know when piston 30 is in its rear dead end position along axis X2.

As shown on figure 2, control unit 50 includes an electronic controller 501 adapted to deliver three tensions, corresponding respectively to three phases U, V and W, to electric motor 20. Electronic controller 501 is fed by mains through a noise filter 502 and a breaker switch 503. In parallel to electric controller 501 , a 24 Volt generator 504 is connected behind breaker switch 503. Generator 504 feeds a power-on indicator light 505, a fan 506 and a touch screen 507. A bus line 508 connects electronic controller 501 to touch screen 507. Switch 56 is also connected to controller 501 .

In parallel to generator 504, a signal generator or "function generator" 509 is connected behind breaker switch 503 and delivers to an analog input port 510 of controller 501 a periodic signal S509 which can have a sinusoidal shape, a triangular shape, a square or rectangular shape or a combination of such shapes.

For example, signal generator 509 can be of the type marketed by company AGILENT under reference P2761 A, or any equivalent equipment.

Signal generator 509 is connected to a slot 51 1 which allows the user to select the type, the frequency and the amplitude of a reciprocating movement defined by output signal S509, via computer 52. Alternatively, slot 51 1 is used to connect a USB stick with some control data for signal generator 509.

According to an optional aspect of the invention, signal generator 509 is provided with a control knob 513.

Electronic controller 501 is adapted to feed three-phase synchronous electric motor 20 with a signal S501 elaborated within electronic controller 501 on the basis of signal S509 and which is delivered through an output analogic port 512.

Thus, control unit 50 allows to control electric motor 20 by providing it with a three- phase current, including phases U, V and W, and a control signal S501 which is going to govern the shape of the reciprocating movement of piston 30 along axis X2 with respect to time. Actually, signal S501 is included in the tensions delivered on phases U, V and W since these three tensions allow to directly actuate motor 20. Thus, the line showing signal S501 on figure 2 is logical and physical.

Because of the purely "electrical" control mode of piston 30 via motor 20 and screw- nut connection 26/36, one is not limited to a sinusoidal movement of piston 30 within casing 4, so that the type of reciprocating movement used for piston 30 can be adapted to the actual respiratory scheme or profile to be simulated. When a gas flowmeter F is to be calibrated with simulator 2, one connects an inlet port F1 of flowmeter F to connector 14, preferably via a flexible hose H.

Then, one considers the patient for which flowmeter F is going to be used and defines a predicted respiratory profile for this patient. For instance, if the patient is a top level athlete, then it is likely that its lung capacity will be high, so that the stroke S of piston 30 within casing 4 can be set to a relatively large value. On the contrary, in case of a patient with mucoviscidosis or a similar disease, the stroke S of piston 30 is set to a relatively low value. The value of the stroke S of piston 30 can also be set while taking into account the sex and/or the age of the patient. Stroke S is representative of the maximum capacity of chamber C1 ..Moreover, the frequency f of the reciprocating movement of piston 30 within casing 4, which corresponds to the velocity of piston 30 between its dead end positions, can also be set while taking into account the predicted respiratory profile of the patient.

According to another aspect, one can take into account the fact that the patient is going to be at rest, with an approximately sinusoidal respiratory scheme, or to perform a physical exercise, with an approximately triangular respiratory scheme. A respiratory scheme is a curve showing the position of piston 30 along axis X2 as a function of time. In such a case, one can select the type of reciprocating movement T1 and T2 of piston 30 within casing 4, between a sinusoidal type or a triangular type. For some specific studies, one can also consider using a square or rectangular type.

Actually, it is rare that the respiratory scheme of a patient is purely sinusoidal, purely triangular or purely square, so that it is also possible to mix different types of schemes and to generate signal S509 as a combined signal. This combination of signals can be obtained by proper programming of signal generator 509 via computer 52, via a USB stick connected to slot 51 1 or by a proper action on knob 513.

In case one considers only two types of respiratory schemes, namely a sinusoidal scheme or a triangular scheme, one defines a mixing ratio R as the percentage of triangular shape in signal S509. Thus, mixing ratio R equals zero when signal S509 is purely sinusoidal and equals one when signal S509 is purely triangular. A similar mixing ratio can also be used with three types of respiratory schemes or more. In any case, the mixing ratio is representative of the shape of a curve which embodies the motion of piston 30 along axis X2, as a function of time, during its reciprocating movement in the direction of arrows T1 and T2.

In any case, signal S509 is provided to input port 510 of controller 501 as representative of a target movement scheme for piston 30 within casing 4 and this signal is used by controller 501 to generate signal S501 provided to electric motor 20. More precisely, signal S509 includes information with respect to the stroke S, the frequency f and the mixing ratio R to be used for driving piston 30 in its reciprocating movement within pump 48. This information is treated by controller unit 501 to generate command signal S501 which is directly usable by motor 20.

Figure 3 represents a method for calibrating gas flowmeter F with simulator 2.

In a first step 1001 , connector 14 is connected to inlet part F1 via hose H, as explained here-above.

Then, a target value is selected in a second step 1002 for the stroke S, the frequency f and the mixing ratio R of the signal representative of the movement of piston 30 within casing 4. The target values are communicated to signal generator 509 via computer 52, via touch screen 507, via a USB stick connected to port 51 1 or via knob 513.

Then, the selected target values, say S _s , f _s and R _s , are transmitted to electronic controller 501 by signal generator 509, in a third step 1003. These values S _s , f _s and R _s are included in signal S509.

Step 1001 can occur before or after steps 1002 and 1003, or in parallel thereto. On the basis of values S _s , f _s and R _s , electronic controller can compute, in a further step 1004, some physical parameters of intake and exhaust air flows F1 and F2, including their flowrates Q1 and Q2. These flowrates Q1 and Q2 are provided as input data to flowmeter F, in a subsequent step 1005.

Thereafter or in parallel to steps 1004 and 1005, in a step 1006, piston 30 is moved backwards, that is towards end plate 10, until it reaches its back dead end position where end 402 of anti-rotation rod 40 closes switch 56. This is detected by electronic controller 501 via switch 56. With this step, one knows exactly the position of piston 30, even if control unit 50 has been switched off since its last use.

Thereafter, in a further step 1007, one drives motor 20 with signal S501 which corresponds to a given breathing capacity and flowrate within hose H. This step is performed for a pre-determined period of time, e.g. 30 seconds, in order for intake and exhaust air flows F1 and F2 to be stabilized. These air flows are detected by flowmeter F which displays the detected flowrates Q1 ' and Q2' of air flows F1 and F2. Flowrates Q1 and Q1 ', on the one hand, Q2 and Q2', on the other hand, are compared by flowmeter F in a further step 1008 where a first corrective coefficient k1 is computed as the ratio Q1 to Q1 ' and a second corrective coefficient k2 is computed as the ratio of Q2 to Q2'. k1 , respectively k2, equals 1 when Q1 ', respectively Q2', equals the nominal flowrate Q1 , respectively Q2, delivered by breathing simulator 2. The method ends with a step 1009 where touch screen 507 displays a message stating that flowmeter F is calibrated. Steps 1001 to 1009 together define a calibration sequence of the method of the invention.

Once flowmeter F has been calibrated via the computation of coefficients k1 and k2, these coefficients are applied on the flowrates detected by flowmeter F, until the next calibration sequence is implemented, in order to provide an accurate estimate of the actual flowrates of air going through the flowmeter.

According to a non represented alternative embodiment of the invention, switch 56 can be located within casing 4 in order to be directly actuated by piston 30 in its rear dead end position.

It is not compulsory to use three parameters such as S, f and R to implement the method of the invention. Actually, the method can be based on the use of only one or two parameters, or more than three parameters.

The respective technical features of the embodiments and alternative embodiments mentioned here-above can be combined to generate new embodiments.