AIR IN LINE DETECTOR FOR MEDICAL INFUSION PUMPS

Abstract

Disclosed is an air in infusion line detecting device, comprising an acoustic emitter adapted to be provided at one side of an infusion line and to vibrate at its resonance frequency so as to transmit an acoustic sound wave with a frequency corresponding to said resonance frequency, and an acoustic receiver adapted to be provided at another side of the infusion line and to be set into vibrations caused by the sound wave transmitted by said emitter through the infusion line and to generate an output signal indicating the characteristics of said vibrations. The device is characterized in that the resonance characteristics of said emitter and/or the distance between said emitter and said receiver is adapted so that the sound wave is generated as a standing wave between said emitter and said receiver.

Claims

1. An air in infusion line detecting device, comprising an acoustic emitter adapted to be provided at one side of an infusion line and to vibrate at its resonance frequency so as to transmit an acoustic sound wave with a frequency corresponding to said resonance frequency, and an acoustic receiver adapted to be provided at another side of the infusion line and to be set into vibrations caused by the sound wave transmitted by said emitter through the infusion line and to generate an output signal indicating the characteristics of said vibrations, wherein at least one of the resonance characteristics of said emitter or the distance between said emitter and said receiver is adapted so that the sound wave is generated as a standing wave between said emitter and said receiver.

2. The device according to claim 1, wherein the resonance frequencies of both the emitter and the receiver are essentially identical.

3. The device according to claim 1, further comprising a processing unit adapted to control said emitter and to at least one of evaluate or process the output signal from said receiver.

4. The device according to claim 3, wherein said processing unit comprises a frequency control adapted to control said emitter with respect to the frequency of the sound wave to be generated by said emitter.

5. The device according to claim 4, wherein said frequency control is adapted to control said emitter so as to carry out a frequency sweep or scan within a frequency range including inter alia the resonance frequency for detection of air in order to achieve an essentially optimal transmission of the sound wave in dependence on the distance between said emitter and said receiver and/or the characteristics of said emitter and/or said receiver due to an evaluation of the output signal carried out by said processing unit.

6. The device according to claim 5, wherein said frequency control is adapted to control said emitter so as to carry out the frequency sweep or scan around the resonance frequency within a range which at the start of the frequency sweep or scan is higher than a predetermined value and is reduced to said predetermined value during the continued frequency sweep or scan in order to decrease the power for the emitter and is extended beyond said predetermined value again in case said processing unit determines the absence of the output signal from the receiver in order to make sure that there is no error which might cause the absence of the output signal.

7. The device according to claim 5, wherein said frequency control is adapted to control said emitter so as to stop the frequency sweep or scan once said processing unit evaluates the output signal that said receiver receives an essentially clear sound wave.

8. The device according to claim 5, wherein said processing unit is adapted to determine from the output signal of said receiver during the frequency sweep or scan at least some frequencies of sound waves received by said receiver, and said frequency control is further adapted to further control said emitter so as to continue the frequency sweep or scan around these determined frequencies and, in case said processing unit determines the absence of the output signal, to repeat the frequency sweep or scan in essentially the same way in order to verify that it is air and no error which causes the absence of the output signal.

9. The device according to claim 5, wherein the frequency control is adapted to control the emitter so that a repetition rate of the frequency sweeps or scans is higher than a predetermined value in case said processing unit determines the absence of the output signal, and is reduced to said predetermined value so that said processing unit is able to determine the volume of air passed, wherein preferably said frequency control is adapted in such case to adjust the repetition rate so as to enable said receiver to be set into vibrations for detecting at least essentially all the air bubbles at the highest infusion rate used or to adjust it, preferably in a proportional manner, to the infusion rate in order to reduce power.

10. The device according to claim 5, wherein said processing unit is further adapted in case of the presence of the output signal from said receiver to time stamp it, to calculate the air volume from the infusion rate by multiplying the infusion rate with the sweep or scan repetition period and to add in a shifting time window to other volumes already calculated as well as to signal an alarm in case a predetermined volume of air per time is exceeded.

11. The device according to claim 10, said processing unit is adapted to signal an alarm which is a locally visual and/or acoustical and/or vibrating signal, and preferably to transmit said alarm to a hospital or a cloud based server and then preferably to a hospital alarm system.

12. The device according to claim 3, wherein said processing unit further comprises at least one noise cancelling filter adapted to filter the output signal from said receiver.

13. The device according to claim 12, wherein said at least one noise cancelling filter is a low pass filter or a band pass filter.

14. The device according to claim 12, wherein said processing unit further comprises a digitizer adapted to digitize the output signal from said receiver after having been filtered by said noise cancelling filter and to further filter the then digitized output signal wherein preferably said processing unit is further adapted to digitize the output signal only in case it is noiseless and to determine a precise band or even only one sweep or scan frequency period.

15. The device according to claim 5, wherein said processing unit is further adapted to determine whether or not the filtered output signal occurs concurrently with a frequency sweep or scan resulting in no detection of air, and said frequency control is further adapted to control said emitter in the absence of the output signal from said receiver to extend the frequency sweep or scan to all available frequencies and, if even then said processing unit determines the absence of the output signal from said receiver indicating that air is in the infusion line, to reduce the sweep or scan repetition period.

16. The device according to claim 1, comprising a single acoustic element which includes a combination of said emitter and said receiver and is adapted to be provided at one side of an infusion line, and further comprising a solid state wall element, preferably comprising hard plastic, adapted to be provided at the opposite side so as to reflect the sound wave transmitted by said emitter back to said receiver.

17. The device according to claim 1, wherein the emitter and/or the receiver comprises an ultrasound piezoelectric element.

18. The device according to claim 1, further comprising a support including a cavity which is provided to accommodate the infusion line and a lid adapted to close said cavity and to engage the infusion line so as to be held it inside the cavity in a predetermined correct down position, wherein said emitter and said receiver are provided at said support.

19. An infusion pump comprising: an acoustic emitter adapted to be provided at one side of an infusion line and to vibrate at its resonance frequency so as to transmit an acoustic sound wave with a frequency corresponding to said resonance frequency, and an acoustic receiver adapted to be provided at another side of the infusion line and to be set into vibrations caused by the sound wave transmitted by said emitter through the infusion line and to generate an output signal indicating the characteristics of said vibrations, wherein at least one of the resonance characteristics of said emitter or the distance between said emitter and said receiver is adapted so that the sound wave is generated as a standing wave between said emitter and said receiver.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 is a schematic cross-sectional view of an air in infusion line detecting device according to a first preferred embodiment of the present invention showing a housing, a piezoelectric emitter arranged at the one side of the housing parts, a piezoelectric receiver arranged at the other side of the housing and an infusion tubing arranged between the emitter and the receiver as well as a processing unit connected to the emitter and the receiver;

[0039] FIG. 2a schematically shows the embodiment of FIG. 1 (showing only parts of the housing and without showing the processing unit) in a vibrating moment wherein the inner surface of both the emitter and the receiver is in a maximum deflected position towards the tubing by the effect of a standing wave at a specific resonance frequency which is only indicated by arrows pointed to each other;

[0040] FIG. 2b schematically shows the embodiment of FIG. 1 (showing only parts of the housing and without showing the processing unit) in a vibrating moment wherein the inner surface of both the emitter and the receiver is in a maximum deflected position away from the tubing by the effect of the standing wave which is only indicated by arrows pointed away from each other; and

[0041] FIG. 3 is a schematic cross-sectional view of an in infusion line detecting device according to a second preferred embodiment of the present invention showing only parts of the housing, a single acoustic element including a combination of the emitter and receiver and an infusion tubing arranged between the single acoustic element and the opposite part of the housing, without showing the processing unit.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0042] FIG. 1 shows an air in infusion line detecting device according to a first preferred embodiment comprising a housing of which a first plate 1 and a second plate 2 are visible and form two sidewalls of the housing spaced from each other wherein preferably said plates 1 and 2 can be made of hard plastic. An emitter 3 which preferably can comprise a piezoelectric plate is fixed with its outer surface to the first plate 1, in particular by bonding, and a receiver 4 which preferably can comprise a piezoelectric plate is fixed with its outer surface to the second plate 2, in particular by bonding. Further shown is an infusion line or tubing 5 which is provided in a sandwich arrangement between the emitter 3 and the receiver 4 so that the emitter 3 and the receiver 4 are arranged opposite to each other with respect to the infusion line or tubing 5 within which an infusion liquid 6 is flowing. In the shown embodiment the inner surface of both the emitter 3 and the receiver 4 is in contact with the outer surface of the infusion tubing 5 whereby the infusion tubing 5 is slightly compressed so to ensure a permanent contact with the emitter 3 and the receiver 4.

[0043] FIG. 2a schematically shows by representation of two arrows pointed to each other that, by the effect of a standing wave at a specific resonance frequency resulting in vibrations or oscillations of the emitter 3 and the receiver 4, the inner surfaces of both the emitter 3 and the receiver 4 move simultaneously towards the infusion tubing 5 in a first half of each oscillation cycle. And FIG. 2b schematically shows by representation of two arrows pointed away from each other that, by the effect of the standing wave, the inner surfaces of both the emitter 3 and the receiver 4 move simultaneously away from the infusion tubing 5 in a second half of each oscillation cycle. With respect thereto it is noted that the amplitude of the vibrations or oscillations is rather small and not visible.

[0044] Piezoelectric elements, when they vibrate, become alternatively thinner or thicker by the effect of electric power supplied to the piezoelectric emitting element or by the effect of acoustic sounds exciting the piezoelectric receiving element. In order to utilize this effect, according to a preferred embodiment both the emitter 3 and the receiver 4 comprise a piezoelectric plate or are provided as a piezoelectric plate.

[0045] As the back or outer surface of both the emitter 3 and the receiver 4 is fixed to the housing, their free side or inner surface acts like a reciprocally moving piston to generate acoustic waves or to react to the acoustic waves. In the shown embodiment the free side or inner surface of both the emitter 3 and the receiver 4 is in contact with infusion tubing 5 carrying the infusion liquid 6 that behaves acoustically like water. The emitter 3 resonates with a specific frequency so as to generate and emit acoustic or sound waves, and the receiver 4 also resonates as reaction to said acoustic waves and accordingly generates an output signal, wherein the receiver 4 has essentially the same frequency characteristics as the emitter 3. But it is the size of the gap which defines a path of the acoustic waves through the infusion fluid 6 and makes standing waves possible at that specific resonance frequency. These standing waves increase the power at the receiver 4 and hence its voltage. There are differences in resonance frequency even in piezoelectric plates of the same dimensions, so that for both the emitter 3 and the receiver 4 preferably plates may be selected as the same resonance pairs.

[0046] Small differences between resonance frequencies of several pairs is compensated by carrying out a frequency sweep or scan that passes through all these frequencies. But since it is not possible to also ‘sweep’ the gap size, the standing waves cannot be exact but in a vicinity or an adjacent range with somehow lower than the maximum voltage in the receiver. As further shown in the figures, the tubing 5 is slightly compressed between the emitter 3 and the receiver 4 resulting in a smaller fluid width for two reasons, first to make a good contact with the emitter 3 and the receiver 4 at each side and second to reduce the fluid gap so to detect smaller air bubbles.

[0047] In presence of air in the tubing 5, the transmission is disturbed or interrupted so that the receiver 4 generates a small output signal, e.g. with a low or very low intensity, only or no output signal at all.

[0048] As further shown in FIG. 1, a processing unit 10 is provided which is schematically depicted as a block diagram. The processing unit 10 is adapted to control the emitter 3 through a connection line 3a and to evaluate and process the output signal from the receiver 4 through the connection line 4a. As also schematically shown in FIG. 1, the processing unit 10 comprises a frequency control 12, a noise cancelling filter unit 14, a digitizer 16 and an evaluation unit 18. The frequency control 12 is adapted to control the emitter 3 with respect to the frequency of the sound wave to be generated by the emitter 3. In particular, the frequency control 12 is adapted to control the emitter 3 so as to carry out a frequency sweep or scan within a frequency range which is assumed to also include the resonance frequency for detection of air in the infusion line 5 in order to achieve an essentially optimal transmission of the sound wave in dependence on the distance between the emitter 3 and the receiver 4 and/or the characteristics of the emitter 3 and/or the receiver 4 due to an evaluation of the output signal from the receiver 4 wherein such evaluation is carried out by the evaluation unit 18 of the processing unit 10. The range of the frequency sweep or scan around the resonance frequency may be larger at the start of the frequency sweep or scan and narrower during the continued frequency sweep or scan in order to decrease the power for the emitter 3 and is extended again in case the evaluation unit 18 determines the absence of the output signal from the receiver 4 in order to make sure that there is no error or variation which might cause the absence of the output signal. Further, the frequency control 12 controls the emitter 3 so as to stop the frequency sweep or scan once the evaluation unit 18 evaluates the output signal that the receiver 4 receives an essentially clear sound wave.

[0049] The evaluation unit 18 determines from the output signal of the receiver 4 during the frequency sweep or scan at least some frequencies of sound waves received by the receiver 4, wherein the frequency control 12 controls the emitter 3 so as to continue the frequency sweep or scan around these determined frequencies and, in case the evaluation unit 18 determines the absence of the output signal from the receiver 4, to repeat the frequency sweep or scan in essentially the same way, i.e. at the same repetition cycle, in order to verify that it is air and no error or variation, like e.g. a variation of the temperature, which causes the absence of the output signal from the receiver 4.

[0050] Further, the frequency control 12 controls the emitter 3 so that a repetition rate of the frequency sweeps or scans may vary and be higher than a predetermined value in case the evaluation unit 18 determines the absence of the output signal from the receiver 4, whereas the repetition rate is reduced to said predetermined value so that the evaluation unit 18 more precisely determines the length and, hence, the volume of air passed through the infusion line 5 between the emitter 3 and the receiver 4. In such case the frequency control 12 adjusts the repetition rate so as to enable the receiver 4 to be set into such vibrations which enable the detection of essentially all the air bubbles at the highest infusion rate in order to avoid any loss of air bubbles, or adjusts it in a proportional manner to the infusion rate in order to reduce power needed for the emitter 3. In case the evaluation unit 18 determines the presence of the output signal from the receiver 4, in the processing unit 10 the output signal is time stamped, the air volume is calculated from the infusion rate by multiplying the infusion rate with the sweep or scan repetition period and added in a shifting time window to other volumes which has already been calculated, wherein the processing unit 10 gives an alarm in case a predetermined or programmed volume of air per time is exceeded. Said alarm is a locally visual and/or acoustical and/or vibrating alarm and is preferably transmitted to a hospital or cloud based server and then preferably to a hospital alarm system.

[0051] As further schematically shown in FIG. 1, the noise cancelling filter unit 14 filters the output signal from the receiver 4. The noise cancelling filter unit 14 comprises one filter or a plurality of filters which may be a low-pass filter or a band-pass filter.

[0052] As also schematically shown in FIG. 1, the digitizer 16 is connected to the noise cancelling filter unit 14 and digitizes the output signal from the receiver 4 after having been filtered by the noise cancelling filter unit 14. The digitizer 16 may additionally filter the then digitized output signal in the digital domain but accepts only noiseless signals wherein a more precise band or even only one sweep or scan frequency period can be determined. Moreover, the evaluation unit 18 determines whether or not the filtered output signal occurs concurrently with a frequency sweep or scan which indicates a no air detection status, and the frequency control 12 controls the emitter 3 in the absence of the output signal from the receiver 4 as determined by the evaluation unit 18 so as to extend the frequency sweep or scan to all available frequencies and, if even then the evaluation unit 18 of the processing unit 10 determines the absence of the output signal from the receiver 4 indicating that air is in the infusion line 5, to reduce the sweep or scan repetition period.

[0053] As it is further retrievable from the FIG. 1, as parts of the housing shown are not only the plates 1 and 2, but also a bottom 20 and a lid 22, so that both the plates 1 and 2, the bottom 20 and the lid 22 encloses a cavity 24 which accommodates the infusion tubing 5. In the shown embodiment, the lid 22 closes the cavity 24 from the above and in its closed position engages the infusion tubing 5 so that it is held inside the cavity 24 in a predetermined correct down position against the bottom 20. So, the housing is provided as a support so as to hold the infusion tubing 5 inside the cavity 24 in the predetermined correct position.

[0054] FIG. 3 shows an alternative embodiment of the air in infusion line detecting device which comprises a single acoustic element 30 including a combination of the emitter 3 and receiver or at least an emitting and receiving function. This single acoustic element 30 is arranged at one side of the infusion tubing 5. At the opposite side of the infusion tubing 5 it is provided the second plate 2 as a solid state wall element, preferably comprising hard plastic, wherein this solid state wall reflects the sound wave transmitted by the emitter or emitting function back to the receiver or receiving function of the single acoustic element 30.