Ultrasound-based gas bubble and / or solid-state detector, dialysis device and method for such a detector

Abstract

Blood-side gas bubble and / or solid-state detector (1) based on ultrasound, comprising an ultrasound (US) transmitter (4) for transmitting an ultrasound (6) through a medium to be monitored to an ultrasound (US) receiver (8) of the gas bubble and / or solid-state detector (1), characterized in that a monitoring and / or limiting means or device is provided which is / are adapted to monitor and / or limit an energy input into the medium due to the ultrasound (6), wherein the US transmitter (4) is controlled by a control signal (18) via a control unit (32), wherein the control signal (18) is tapped for monitoring the energy input.

Description

[0001] The invention is based on an ultrasound-based gas bubble and / or solid-state detector for monitoring a medium. Furthermore, the invention relates to a dialysis machine with such a detector and a method using such a detector.

[0002] Ultrasound-based detectors (hereinafter referred to as detectors) are commonly used in dialysis machines to protect patients from dangerous air embolisms. For this purpose, a part of an extracorporeal blood circuit to be monitored, in the form of a blood tube, can be guided through an ultrasound path of the detectors. One detector has a piezo element that, when electrically excited at its resonant frequency, sends an ultrasound (US) pulse or US waves through the blood tube. The other detector, in the form of a piezo element, can convert this US pulse into an electrical signal. This signal can be compared with a reference voltage and evaluated by a comparator. A signal is then available at the output of the comparator, which provides information about whether there is "air" or "no air" (i.e. only fluid or blood) in the ultrasound path.

[0003] According to the publication "Imaging Techniques in Medicine. From Technology to Medical Application" by Prof. Dr. Olaf Dössel, University of Karlsruhe, ISBN 3-540-66014-3, ultrasound pulses can damage the patient's blood flowing through the bloodline. This damage can occur primarily through heat exposure and cavitation. Heat is generated locally in proportion to the sound intensity absorbed by the blood. Cavitation is an effect in which gas bubbles form in the tissue during a negative pressure phase of a ultrasound pulse, which then collapse during a pressure phase.

[0004] Document DE 197 38 146 B4 discloses an ultrasonic transducer that operates at or near a resonant frequency to generate a strong output signal from the ultrasonic transducer. The damage to the blood described above can occur during use of this ultrasonic transducer.

[0005] US 2012 / 0 285 870 A1 discloses a delivery device for liquid medications that limits the ultrasonic (US) energy input.

[0006] US 5 191 795 A discloses an ultrasonic detector for detecting air in a fluid passage.

[0007] In contrast, the invention is based on the object of creating an ultrasound-based gas bubble and / or solid-state detector that can be used reliably with minimal device complexity. Furthermore, the invention is based on the object of creating a dialysis machine with an ultrasound-based gas bubble and / or solid-state detector that is simply designed and can be used safely. Furthermore, the invention is based on the object of creating a method for a detector with which a medium to be monitored can be monitored reliably in a device-wise simple manner.

[0008] The problem with regard to the gas bubble and / or solid-state detector based on ultrasound is solved according to the features of claim 1, with regard to the dialysis machine according to the features of claim 11 and with regard to the method according to the features of claim 14.

[0009] According to the invention, an ultrasound-based gas bubble and / or solid-state detector (hereinafter referred to as detector), in particular an ultrasonic air bubble detection system or device, is provided for detecting air in a medium, in particular in blood. The detector has an ultrasonic (US) transmitter for transmitting ultrasound over or through the medium to an ultrasonic (US) receiver of the detector. Advantageously, an energy input into the medium due to the ultrasound is monitored and / or limited, for which purpose an adapted monitoring and / or limiting means or device is provided.

[0010] This solution has the advantage that excessive energy input into the medium can be detected and prevented. If the detector is used for dialysis, for example, the detector according to the invention can prevent damage to the blood caused by excessive energy input and, for example, resulting hemolysis. This means that the medium to be monitored and / or tested can be protected from excessive energies or from excessive energy input. The energy input to the medium to be monitored is thus limited to a tolerable level. A further advantage of monitoring the energy input is that, with knowledge of the energy input and with the help of the ultrasound received by the US receiver (amplitude and temporal signal curve), conclusions can be drawn about the nature of an object or a foreign medium in the medium to be monitored.For example, if the medium to be monitored is a known medium (air), the received ultrasound can even be used to determine the geometry (dimensions, volume).

[0011] Monitoring the energy input is achieved by simply monitoring the ultrasound generator. Ultrasound generation, in turn, is driven by a control signal. The ultrasound transmitter can be controlled by a control unit (microprocessor, microcontroller, µC) using the control signal. To monitor the energy input, the control unit's control signal can then simply be tapped. By monitoring the ultrasound generation, the energy input can be checked in a simple way, eliminating the need for additional sensors.

[0012] The tapped control signal can preferably be monitored by a second control unit (microprocessor, microcontroller, µC), which in this case represents the monitoring and / or limiting means. This advantageously means that monitoring is not left to the first control unit, but rather performed by a second, additional control unit, thereby increasing the safety of the system, particularly if the first control unit is faulty. The second control unit can, for example, compare the control signal with a target control signal and thus perform a pattern comparison. It is conceivable that the second control unit limits the energy input by suitable measures if necessary.

[0013] Advantageously, the ultrasonic transmitter (transducer) and the ultrasonic receiver (transducer) are each formed by at least one piezo element. The ultrasonic transmitter can then be supplied with a voltage from a voltage device or energy from an energy storage device to transmit the ultrasound. The voltage device can be, for example, an inductor arranged electrically in parallel with the ultrasonic transmitter. Alternatively or additionally, it is conceivable for the voltage device to be a voltage doubler circuit (cascade circuit). The voltage device can also have circuits that follow the principle of switching regulators.

[0014] Preferably, a burst interval of the control signal is monitored. This represents a time span between the start times of two consecutive charging processes of the voltage device. A reduction in the burst interval can be inferred from an increase in the energy input into the medium. The burst interval is compared, for example, with a target burst interval for monitoring purposes.

[0015] Alternatively or in addition to the burst interval, a charging time of the voltage device specified by the control signal or the energy in the energy storage device can be monitored. If the charging time of the voltage device increases, a higher energy input can be assumed. A change can be detected, in particular, by using a target charging time.

[0016] Alternatively or additionally, it is conceivable to monitor a number of stimuli (square-wave signals, pulses) emitted by the ultrasound transmitter per burst interval, which are particularly specified by the control signal. These can then be compared with a target number. If the number of stimuli increases, a higher energy input must be assumed.

[0017] Furthermore, it may be provided, alternatively or additionally, to monitor an ultrasonic (US) excitation frequency of the US transmitter, which may be specified by the control signal. This frequency is then compared, for example, with a target US excitation frequency. For example, a higher energy input may be caused by a change in the US excitation frequency.

[0018] Alternatively or additionally, a period of the control signal can be monitored.

[0019] If a change in the burst interval and / or the charging time and / or the number of stimuli and / or the US excitation frequency and / or the period duration is detected, an error signal can be output, particularly by the second control unit. The aforementioned changes in the respective parameters can arise, for example, from a temporary or permanent malfunction of the first control unit (software and / or hardware error).

[0020] In a further embodiment of the invention, in the event of a faulty energy input, one or more measures are initiated that limit or terminate the energy input. These measures can preferably be initiated by the second control unit, such as stopping the energy supply to the ultrasonic transmitter, stopping pumps, and / or closing valves.

[0021] For example, the measures as a whole also include hardware measures, in which the faulty energy input is limited, for example, by one or more components (electronic components, hardware components). Furthermore, it is conceivable to provide the design (dimensioning or selection) of the inductor with an appropriate saturation current as a hardware measure. Alternatively or additionally, Zener diodes can be provided for voltage limitation. Furthermore, it is alternatively or additionally conceivable to provide for an adaptation or misadaptation of impedances during operation of the piezo elements.

[0022] In a further embodiment of the invention, the ultrasound received by the ultrasound receiver can be converted into an electrical reception signal and compared with a reference value (reference voltage, reference signal, alarm threshold) using a comparator. Depending on the result of this comparison, the comparator outputs an output signal that indicates "air" or "no air," for example, when the detector is used in a dialysis machine.

[0023] The voltage device can be connected to a voltage source and to a ground to form an electrical circuit. The electrical circuit can be controlled by a switch, which is controlled depending on the control signal.

[0024] Preferably, in addition to the first reference value (alarm threshold), a second reference value (test threshold) is provided. The second reference value can then be used, in particular cyclically and for a predetermined, comparatively short period of time, instead of the first reference value. The first and second reference values are thus provided at the input of the comparison unit. The short-term comparison of the second reference value can be used to provide information about the functionality of the detector circuit and, secondly, to provide information about the coupling of the medium, which is carried as a liquid in a hose, for example, with the detector. If the detector were functioning correctly, the second reference value on the output side of the comparator would preferably signal "air", for example.If this is not the case, there may either be a circuit defect, or the coupling between the medium (e.g. the liquid in the hose) and the ultrasound transmitter and / or receiver may be in an unacceptable range. For example, an unacceptably good coupling or even an acoustic short circuit is possible, both of which lead to a distortion of the ultrasound between the ultrasound transmitter and receiver. This is caused, for example, by liquid entering between the ultrasound sensor, the hose, and the ultrasound receiver. However, there are also known cases in practice in which a user of the detector introduces a so-called ultrasound gel into the path between the ultrasound sensor, hose, and ultrasound receiver in order to eliminate supposed false alarms. In these cases, too, the sensitivity of the ultrasound sensor and receiver is reduced, which can then be detected using the method described.The safety system with the reference values in combination with the monitoring of the energy input thus results in an extremely safe detector.

[0025] By evaluating the received signal (time, amplitude), statements can be made about the properties (geometry) of the medium to be monitored. By comparing the received signal (time, amplitude) with the various reference values, statements can be made about the correct functioning of the sensor and the proper coupling between the sensor and the medium to be monitored (hose and liquid), as already explained above. A prerequisite for reliably deriving the received signal is reliable knowledge of the ultrasound (transmitted signal). This can be achieved by implementing the ultrasound monitoring described above.

[0026] According to the invention, a dialysis machine or an infusion device is provided that has a detector according to one of the preceding aspects. A flow path (tube) through which the medium (blood or infusion fluid) can flow can be arranged between the US transmitter and the US receiver. The use of the detector leads to a high level of safety for a patient connected to the dialysis machine, since damage to the blood due to a high energy input into the blood is avoided.

[0027] The first control unit of the dialysis machine can be designed to regulate and control components of the dialysis machine and the detector. The second control unit (supervisor) can then initiate protective measures for the patient and additionally monitor and / or limit the energy input into the medium. This allows the second control unit to reliably detect a defect or malfunction in the first control unit, and appropriate protective measures can then be initiated.

[0028] If the energy input is incorrect, one or more pumps in the dialysis machine may be stopped and / or one or more hose shut-off clamps may be closed.

[0029] A method according to the invention for an inventive gas bubble and / or solid-state detector based on ultrasound according to one of the preceding aspects comprises the following steps: - transmitting an ultrasound with an ultrasonic (US) transmitter via a medium to be monitored to an ultrasonic (US) receiver of the gas bubble and / or solid-state detector and - Monitor and / or limit the energy input into the medium due to ultrasound. This prevents, for example, damage to blood caused by ultrasound exposure.

[0030] Other advantageous developments of the invention are the subject of further subclaims.

[0031] Preferred embodiments of the invention are explained in more detail below with reference to the drawings. They show: Fig. 1 shows a schematic representation of a detector according to the invention, Fig. 2 in a schematic representation of a control signal for an ultrasonic transmitter of the ultrasonic detector, Fig. 3 shows a schematic representation of a dialysis machine with a detector, Fig. 4 in a schematic representation of a comparison unit of the detector for comparing a received signal with a target value, Fig. 5 in several curves input variables for the comparison unit from Fig. 4 and Fig. 6 shows in a diagram the effects of an energy input due to ultrasound in the blood of a patient.

[0032] According to Fig. 1 shows an ultrasound-based gas bubble or air bubble detector 1 (hereinafter referred to as detector) for detecting air in a medium in the form of blood from a dialysis patient, wherein the blood flows through a tube 2. For this purpose, the detector 1 has an ultrasound (US) transmitter 4 in the form of a piezo element for transmitting an ultrasound 6 through the tube 2. The ultrasound 6 can be received by an ultrasound (US) receiver 8. The US transmitter 4 and the US receiver 8 thus form an ultrasound path. To transmit an ultrasound, the US transmitter 4 is supplied with a voltage via an inductance 10 arranged electrically parallel to the US transmitter 4. The US transmitter 4 and the inductance 10 can be connected to a ground 14 via a switch 12. Furthermore, they are connected to a voltage source 16.A self-induction voltage of the inductance 10, which arises when the switch 12 opens, serves to provide the voltage required for the US transmitter 4. The US transmitter 4 is then controlled via a control signal 18. The control signal 18 is generated by a . Fig. 1 control unit (not shown). The ultrasound 6 is received by the ultrasound receiver 8 and converted into an electrical reception signal 20. This is then compared with a reference voltage 24 by a comparison unit 22 (comparator) and evaluated. An output signal 28 is available at an output 26 of the comparison unit 22, which provides information about whether there is "air" or "no air" (i.e., only liquid) in the ultrasound path.

[0033] In Fig. 2 shows the control signal 18 which, in the detector 1 according to the invention, consists of Fig. 1 is monitored in order to monitor and / or limit an energy input into the blood guided in the tube 2 due to the ultrasound 6. According to Fig. 2, the control signal 18 has a burst interval A, which is, for example, 50 to 900 µs. A frequency of the burst interval A is, for example, 1 to 15 kHz. A charging time B of the inductance 10 from Fig. 1 is, for example, 5 to 20 µs. The burst interval A is then the distance between two starting times of consecutive charging times B.

[0034] After a charging time B has elapsed, a number C of stimuli with a US excitation frequency D of the US transmitter 4 of, for example, 1 to 5 MHz are delivered with the control signal 18. For example, eight stimuli (C=8) are provided. The interval between two stimuli is 500 ns, for example, in the case of a US excitation frequency of 2 MHz. After the number C of ultrasound stimuli, a pause E is provided until the charging time B starts again. This pause is, for example, 300 to 500 µs (for example, 481 µs).

[0035] To monitor the energy input, the burst interval A and / or the charging time B and / or the US excitation frequency D and / or the number C of stimuli are monitored. If the burst interval A is reduced in the event of a fault, it must be assumed that a higher energy input into the tube 2 occurs with the blood. Likewise, a higher energy input must be expected if the charging time B of the inductance 10 increases. Furthermore, a higher energy input into the blood must be assumed if the previously defined number C of stimuli increases in a conceivable fault situation. A higher energy input into the blood can also be caused by a change in the US excitation frequency D.The changes in the respective parameters mentioned can, for example, be caused by a temporary or permanent error behavior of the microprocessors used for the control unit, either on the software or hardware side, which generate the control signal.

[0036] The control signal 18 from Fig. 2 is available at switch 12 and can be transmitted from there to a monitoring control unit. Knowledge of the energy input also allows the received signal 20 (amplitude and temporal signal profile) to be used to determine the properties of an object or foreign medium in the medium to be monitored, in this case blood. If the medium is a known medium, such as the air to be monitored in this case, the received signal 20 can then be used to determine its geometry (dimensions, volume).

[0037] According to Fig. 3 schematically shows, in addition to the detector 1, a dialysis machine 30 having the detector 1. The dialysis machine 30 has a first control unit 32 and a second control unit 34 (supervisor). The first control unit 32 serves to regulate and control components of the dialysis machine 30 and thus also of the detector 1. The second control unit 34 serves in particular to monitor the dialysis machine 30 in order to protect a patient using the dialysis machine 30.

[0038] The first control unit 32, together with a microprocessor 36, controls the ultrasound transmitter 4, which transmits the ultrasound via the tube 2 to the ultrasound receiver 8. The received signal 20 is processed according to Fig. 3 is passed on to the microprocessor 36 and to a microprocessor 40, which is connected to the second control unit 34. To monitor the control signal 18, which is used to control the US transmitter 4 via the signal path 38, the control signal 18 is tapped from the US transmitter 4 via a signal path 42 and fed to a channel of the second control unit 34 of the dialysis machine 30. The parameters A to D to be monitored are then transmitted via this channel, see Fig. 2. If a deviation from the target parameters is detected by the second control unit 34 in the monitored channel, it can initiate measures to prevent, stop, or limit damage to the blood in the tube 2. These measures include, for example, stopping one or more pumps and / or closing one or more tube clamps.

[0039] According to Fig. 4 can be used to monitor the sequence of the control signal 28 from Fig. 1 a method for evaluating the received signal 20 can be combined. This serves to detect errors in the US transmitter 4 or the US receiver 8 and to detect changes in coupling in the sensor path. According to Fig. 4, the received signal 20 is compared by the comparison unit 22 or another comparison unit with a reference value 44, which can be referred to as the alarm threshold (AS). The comparison unit 22 then indicates "air" or "no air" at its output 26 depending on the received signal 20, as already explained above. If there is now a cyclical change for a short time from the first reference value 44 to a second reference value 46, which serves as the test threshold (TS) at the input of the comparison unit 22, the received signal 20 is compared with the second reference value 46. This then allows a statement to be made about the functionality of the Fig. 1 and, on the other hand, statements can be made about the coupling between the hose 2 and the US transmitter 4 or the US receiver 8. If "air" is not signaled as expected at the output 26 when the second reference value 46 is used, either a circuit defect may be present, or the coupling between the hose 2 and the US transmitter 4 and / or the US receiver 8 may be in inadmissible ranges.

[0040] According to Fig. 5 shows a comparison with the first reference value 44 and the second reference value 46 using several curves. Fig. The diagram shown in Figure 5 has an ordinate indicating a voltage in V and an abscissa indicating a time in µs. The voltage ranges from 0 to 2.5 V and the time from -100 to 700 µs. The first reference value 44 has a voltage lying between 0.5 and 1 V and the second reference value 46 has a voltage lying between 2 and 2.5 V, with each reference value 44, 46 being approximately constant. A curve 48, which according to Fig. 5 is below the first reference value 44, the received signal 20 is Fig. 1, which results in fault-free operation when there is "air" in the hose 2. In this case, a comparison between the first reference value 44 and the second reference value 46 would result in "air" being displayed at the output 26 of the comparison unit 22. A curve 50 in Fig. 5, which intersects the first reference value 44, shows the received signal 20 when there is “no air” in the hose 2 during error-free operation. In this case, “no air” is output at output 26. A comparison with the second reference value 46 would indicate “air”. Another curve 52, which intersects the second reference value 46, shows the received signal 20 during a faulty coupling. If curve 52 is compared with the first reference value 44, it would be determined that “no air” is present, since curve 52 also intersects the first reference value 44. However, if the second reference value 46 is used, “air” should be displayed during error-free operation, since curves 48, 50 for the error-free received signal 20 lie below the second reference value 46.However, since in the event of a fault the curve 52 intersects the straight line of the second reference value 46, “no air” is reported, which indicates faulty operation.

[0041] According to Fig. 6 shows a diagram showing on the ordinate an intensity I in W / cm 2 the energy of ultrasound 6 from Fig. 1 and on the abscissa shows an exposure time t in s of the ultrasound 6. The intensity I is shown logarithmically between 0.01 and 100 and the exposure time is shown logarithmically between 0 and 10,000. Here, a safe area 54 and a possible damage area 56 are shown, which are separated by a curve 58. If the product of intensity and exposure time (I*t) lies in the safe area 54, that is, the product ≤ 50 Ws / cm 2 there is no damage to the blood in tube 2 Fig.1. However, if the product is larger and lies within the damage zone 56, damage to the blood may occur, for example, through the occurrence of hemolysis.

[0042] Disclosed is a detector with an ultrasonic transmitter for transmitting ultrasound through a medium to be tested, wherein the ultrasound can be received by an ultrasonic receiver. The energy input of the ultrasound into the medium to be monitored can be limited, monitored, and / or adjusted. List of reference symbols 1 detector 2 hoses 4 US channels 6 Ultrasound 8 US recipients 10 Inductance 12 switches 14 Mass 16 Voltage source 18 Control signal 20 Reception signal 22 Comparison unit 24 Reference voltage 26 Exit 28 Output signal 30 dialysis machine 32 first control unit 34 second control unit 36 microprocessor 38 Signal path 40 microprocessor 42 Signal path 44 first reference value 46 second reference value 48 Curve (air in fault-free operation) 50 curve (no air in fault-free operation) 52 Curve (faulty operation) 54 safe area 56 Damage area A burst interval B Loading time D Ultrasound excitation frequency C Number of stimuli E Break

Claims

[1] Blood-side gas bubble and / or solid-state detector (1) based on ultrasound, comprising an ultrasound (US) transmitter (4) for transmitting an ultrasound (6) through a medium to be monitored to an ultrasound (US) receiver (8) of the gas bubble and / or solid-state detector (1), characterized by that a monitoring and / or limiting means or device is provided which is / are adapted to monitor and / or limit an energy input into the medium due to the ultrasound (6), wherein the US transmitter (4) is controlled via a control unit (32) by a control signal (18), wherein the control signal (18) is tapped for monitoring the energy input. [2] Blood-side gas bubble and / or solid-state detector (1) based on ultrasound according to claim 1, wherein the monitoring and / or limiting means is adapted to effect the monitoring of the energy input by monitoring an ultrasound generation. [3] Blood-side gas bubble and / or solid-state detector (1) based on ultrasound according to claim 1, wherein the control signal (18) is monitored by a second control unit (34). [4] Blood-side gas bubble and / or solid-state detector (1) based on ultrasound according to one of the preceding claims, wherein the US transmitter (4) and the US receiver (8) are each formed by a piezo element, and wherein the US transmitter (4) is supplied with a voltage from a voltage device (16) for emitting the ultrasound (6). [5] Blood-side gas bubble and / or solid-state detector (1) based on ultrasound according to one of claims 1 to 4, wherein a burst interval (A) of the control signal (18) is monitored, which represents a time span between start times of two successive charging processes of the voltage device (16), and / or wherein a charging time (B) of the voltage device (16) is monitored, and / or wherein a number (C) of stimuli emitted by the US transmitter (4) per burst interval (A) is monitored, and / or wherein an ultrasonic excitation frequency (D) of the US transmitter (4) is monitored, and / or wherein a period duration of the control signal (18) is monitored. [6] Blood-side gas bubble and / or solid-state detector based on ultrasound (1) according to claim 5, wherein an error signal can be output when the charging time (B) is increased, and / or wherein an error signal can be output when the burst interval (A) is reduced, and / or wherein an error signal can be output when the number of stimuli (C) is increased, and / or wherein an error signal can be output when the ultrasound excitation frequency (D) is changed, and / or wherein an error signal can be output when the period duration is changed. [7] Blood-side gas bubble and / or solid-state detector (1) based on ultrasound according to one of the preceding claims, wherein, in the event of a faulty energy input, measures are initiated to limit or terminate the energy input. [8] Blood-side gas bubble and / or solid-state detector (1) based on ultrasound according to claim 7, wherein the erroneous energy input is limited by hardware measures. [9] Blood-side gas bubble and / or solid-state detector (1) based on ultrasound according to one of the preceding claims, wherein the ultrasound (6) received by the US receiver (8) can be converted into an electrical reception signal (20) and can be compared with a reference value (44) via a comparison unit (22), wherein an output signal (28) indicating a detection result is output in the comparison unit (22) as a function of the comparison. [10] Blood-side gas bubble and / or solid-state detector (1) based on ultrasound according to claim 9, wherein in addition to the first reference value (44) a second reference value (46) is provided, wherein the second reference value (46) is used cyclically and for a predetermined period of time. [11] Blood treatment device (30), in particular dialysis device (30), with an ultrasound-based gas bubble and / or solid-state detector (1) according to one of the preceding claims, wherein a flow path (2) through which the medium can flow is arranged between the US transmitter (4) and the US receiver (8). [12] Blood treatment device (30) according to claim 11, wherein the first control unit (32) is provided for regulating and controlling the blood treatment device (30), and wherein the monitoring and / or limiting means, in particular the second control unit (34), is provided for initiating protective measures for a patient, wherein the monitoring and / or limiting means, in particular the second control unit (34), monitors and / or limits the energy input into the medium. [13] Blood treatment device (30) according to claim 11 or 12, wherein in the event of a faulty energy input to the blood treatment device (30), one or more pumps are stopped and / or one or more hose shut-off clamps are closed. [14] Method for a gas bubble and / or solid state detector (1) based on ultrasound according to one of claims 1 to 10, comprising the steps: - transmitting an ultrasound (6) with an ultrasound (US) transmitter (4) through a medium to be monitored to an ultrasound (US) receiver (8) of the gas bubble and / or solid-state detector (1) and - Monitoring and / or limiting energy input into the medium due to ultrasound (6).

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