System and method for detecting venous needle dislodgement

Abstract

In one aspect, a method and system for detecting a change in fluid dynamics of a fluid flowing through an extracorporeal circuit is disclosed, the method and system comprising: establishing acoustic wave resonance in a lateral dimension of at least a portion of a tubing line associated with the extracorporeal circuit through which the fluid flows; monitoring a phase signal of the resonant acoustic wave; and identifying an occurrence of a change in fluid dynamics of the flowing fluid when the observed phase signal of the resonant acoustic wave indicates a deviation from an expected fluid flow characteristic. The change in fluid dynamics can be used to indicate a venous needle dislodgement event.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 047,727, filed July 2, 2020, which is incorporated herein by reference in its entirety. Technical Field

[0003] This disclosure generally relates to systems and methods for detecting fluid dynamic changes in a fluid flowing in an extracorporeal circuit, and more specifically to systems and methods that can be used to detect venous needle dislocation (VND) in a dialysis system. Background Technology

[0004] Venous needle dislocation (VND) during dialysis is a rare event. However, if a VND is not detected promptly, it can lead to fatal blood loss within minutes. For example, a patient with a normal blood volume of 3-5 L receiving a normal extracorporeal blood flow rate of 200-500 ml / min during dialysis may experience fatal blood loss within 2-5 minutes after a VND. The reported number of VNDs per treatment ranges widely, from 0.0008% to 0.1%, and it is estimated that 10-33% of VNDs result in death.

[0005] Several different methods have been implemented for detecting venous nodules (VNDs). However, these conventional methods have many drawbacks. In some of these conventional methods, venous line pressure is measured in various ways in an attempt to detect VNDs based on a sudden drop in venous line pressure. However, this pressure monitoring method is not robust because VNDs only cause small pressure changes in the venous return line. Conventional pressure monitoring systems with sufficient sensitivity to detect such small pressure changes have been used, but such systems require adequate damping or averaging to reduce noise in the measurement, which would otherwise adversely affect the system's response time. Furthermore, such systems require sensor contact with blood. In addition, these systems often produce many false positives, increasing the burden of monitoring and handling false alarms.

[0006] Another approach is to place a humidity detector at or near the patient's access point, which will send an alarm after blood leaks and is collected at the detector. Humidity detectors are not optimal either, as misplaced detectors can malfunction the system and the path of a leak cannot always be reliably predicted. Mechanical tube constriction devices are also not ideal, as there is a possibility of improper implementation.

[0007] Therefore, a reliable, robust, and cost-effective solution is needed to detect VND. Summary of the Invention

[0008] In one aspect, a method for detecting fluid dynamic changes in a fluid flowing through an external circuit is disclosed, the method comprising: establishing an acoustic resonance over at least a portion of a conduit associated with the fluid flowing through the external circuit; monitoring a phase signal of the resonant acoustic wave; and identifying the occurrence of a fluid dynamic change in the flowing fluid when the observed phase signal of the resonant acoustic wave indicates a deviation from a expected phase characteristic associated with the fluid flow.

[0009] As used herein, the term "phase characteristic" refers to the temporal variation of a phase signal that represents the normal (desired) fluid dynamics associated with fluid flow. For example, such a "phase characteristic" may refer to periodic variations in the phase signal (e.g., periodic variations in the phase signal due to a patient's heartbeat) and / or the average phase signal value.

[0010] In the embodiments discussed below, acoustic standing waves are established transversely across the pipeline (e.g., across the diameter). More generally, sound waves can be established along the dimensions of the pipeline that form a non-zero angle relative to the axial dimension, where the axial dimension is substantially parallel to the direction of fluid flow.

[0011] The steps of establishing a resonant sound wave may include emitting a sound wave into a portion of a pipeline, for example, along its lateral dimension (e.g., along the diameter of the pipeline), and detecting at least a portion of the sound wave after it has passed through a flowing fluid. The phase signal may correspond to the difference between the phase of the emitted sound wave and the phase of the detected sound wave.

[0012] In some embodiments, the extracorporeal circuit includes an extracorporeal dialysis circuit (e.g., a hemodialysis circuit), and the line is a venous return line of the extracorporeal dialysis circuit.

[0013] In some embodiments, the anticipated phase characteristics include phase characteristics associated with the patient’s heartbeat coupled to an extracorporeal circuit, such as a venous return line of a hemodialysis circuit.

[0014] In some embodiments, the hydrodynamic changes are caused by at least partial dislocation of the venous return line. For example, the deviation of the monitored phase from the expected phase characteristics may include a fundamental change in the phase characteristics (e.g., disappearance) indicating substantially complete dislocation of the venous return line.

[0015] In some embodiments, the sound wave is single-frequency. As an example, in such an embodiment, the sound wave may have a frequency in the range of about 1 to about 20 MHz, for example, in the range of about 1 MHz to about 5 MHz. The sound wave may be excited with any periodic waveform (e.g., sine wave, square wave, etc.) having a frequency selected within the said frequency range.

[0016] In some embodiments, the deviation of the monitored phase signal from the expected phase characteristics can be caused by one or more bubbles passing through a portion of the conduit that establishes acoustic resonance. In some cases, the passage of one or more bubbles through the conduit can be detected by detecting a significant drop in the amplitude of the acoustic signal and / or a large phase shift. In some embodiments, a change in the phase signal occurring within a time period of less than about 0.1 seconds can indicate the passage of one or more bubbles through the sensing portion of the device.

[0017] In some embodiments, the flow rate of fluid through an extracorporeal tubing can be adjusted in response to the detection of air bubbles within the fluid flow. Typically, the flow rate of the blood pump needs to be slowed or stopped entirely depending on the amount of air bubbles detected. For example, in some such embodiments, the fluid may be blood, such as blood flowing in the extracorporeal tubing of a dialysis system. In such embodiments, the blood flow rate can be reduced in response to air bubble detection while a phase signal is monitored until no air bubbles are detected. In some embodiments, a feedback control signal based on the phase output signal can be generated and applied to the blood pump to adjust the operation of the blood pump in response to the detection of one or more air bubbles flowing through a sensing portion of the device.

[0018] In some embodiments, the deviation of the monitored phase signal from the expected phase characteristic can be caused by changes in the hydrodynamic pressure of the fluid flowing through the external circuit. In some such embodiments, changes in the hydrodynamic pressure of the fluid can cause changes in the lateral dimension of at least a portion of the pipeline, thereby causing a shift in the monitored phase relative to the expected phase characteristic.

[0019] In some embodiments, the deviation between the monitored phase and the expected phase characteristics can indicate an inconsistent flow rate of fluid through the external circuit.

[0020] In some embodiments where the fluid is blood, deviations in the monitored phase from the expected phase characteristics can be caused by at least one blood clot.

[0021] In some embodiments, the extracorporeal circuit line may be in the form of a tube. As an example, such a tube may provide a venous return line for the extracorporeal circuit of a hemodialysis system, and the variation in the deviation of the monitored phase from the expected phase characteristics may be caused at least in part by the periodic expansion and contraction of the tube as fluid passes through it.

[0022] For example, by comparing the measured phase with previously obtained phase characteristics corresponding to expected hydrodynamics of normal fluid flow, a deviation between the measured phase and the expected phase characteristics can be observed. In some embodiments, an event, such as venous needle dislocation (VND), can cause a substantial disappearance of the phase signal characteristics, thereby indicating the occurrence of the event.

[0023] In one related aspect, a method is disclosed for detecting hydrodynamic changes in a fluid (e.g., blood) flowing in a tubing in fluid communication with a patient's blood vessels, the method comprising: establishing a resonant standing sound wave in a portion of the tubing; monitoring the phase signal of the resonant standing sound wave; and identifying the occurrence of a hydrodynamic change in the flowing fluid when the observed phase of the resonant sound wave (i.e., the difference between the phase of the emitted acoustic signal and the phase of the received acoustic signal) indicates a deviation from a expected phase characteristic associated with normal hydrodynamics of the flowing fluid. In some embodiments, such deviation may correspond to a substantial (or complete) disappearance of the phase signal.

[0024] In some embodiments, phase deviation may be caused by one or more bubbles passing through the pipeline.

[0025] In some embodiments, the tubing is a venous return tubing of a dialysis system, and the deviation of the phase signal relative to the expected phase characteristics associated with the blood flowing through the tubing can be caused by at least partial dislocation of the venous return tubing. For example, the substantial disappearance of a distinctive characteristic of the phase signal (phase signal feature) can indicate substantial complete dislocation of the venous return tubing.

[0026] In some embodiments, a tube having an inner lumen through which blood can flow forms a venous return line. In some cases, such a tube may have an inner diameter (ID) ranging from about 3 mm to about 5 mm (e.g., 3.5 mm (pediatric) or 4.3 mm (standard)) and an outer diameter (OD) ranging from about 5 mm to about 7 mm (e.g., 5.5 mm (pediatric) or 6.8 mm (standard)). Furthermore, in some cases, the tube may undergo periodic expansion and contraction, for example, due to the pulsation of blood circulating through the line, and this periodic expansion and contraction can cause the generation of phase characteristics. As described above and discussed in more detail below, changes in phase characteristics can indicate the occurrence of an event, such as partial or complete dislocation of the venous return line of the dialysis system.

[0027] Pipes can be formed from a variety of different materials, such as polyurethane, glass, polyvinyl chloride, silicone, and the like.

[0028] The establishment of an acoustic standing wave across a conduit (e.g., across the diameter of the conduit) can be achieved by coupling two acoustic transducers to opposite sides of the conduit, one of which (e.g., a piezoelectric device) generates and emits a sound wave into the conduit along its transverse dimension, and the other acoustic transducer detects at least a portion of the sound wave transmitted through the conduit wall and the flowing fluid (e.g., flowing blood). In some embodiments, the acoustic emitter and / or detector can be releasably coupled to the conduit.

[0029] In one related aspect, a system for detecting hydrodynamic changes in fluid circulating in a pipeline associated with an external circuit is disclosed. The system includes a sound wave emitter for emitting sound waves into an interior cavity of the pipeline, for example, emitting across the lateral dimension of the pipeline such that the sound waves travel through a portion of the fluid passing through the interior cavity. The system may further include: a detector for detecting at least a portion of the sound waves after they have passed through the fluid; and a phase detector for measuring a phase signal indicating a phase difference between the emitted and detected sound waves. Comparator circuitry may be employed to compare the measured phase signal with expected phase characteristics associated with the fluid flow, wherein a deviation between the measured phase signal and the expected phase characteristics, identified by the comparator, can indicate the occurrence of a hydrodynamic change in the flowing fluid. In some embodiments, the system may include an analyzer for correlating observed phase deviations with events associated with the hydrodynamics that cause a phase shift.

[0030] As an example, the analyzer may be configured to analyze phase deviations in order to identify events associated with phase deviations as any of the following events: (1) the passage of one or more air bubbles, (2) the passage of one or more blood clots, and (3) at least a portion of the tubing being displaced from at least a portion of its intended location.

[0031] In some embodiments, the acoustic transmitter can generate sound waves with frequencies ranging from about 1 to about 20 MHz, for example, from about 5 MHz to about 10 MHz. In some such embodiments, the sound waves are single-frequency.

[0032] In some embodiments, the extracorporeal circuit may be the extracorporeal circuit of a dialysis system (e.g., a hemodialysis system), and the analyzer may be configured to identify deviations in the phase signal relative to expected phase characteristics, said deviations indicating at least partial dislocation of the venous return tubing. For example, the analyzer may be configured to associate significant changes in the phase signal (e.g., the substantial disappearance of a distinctive characteristic of the phase signal associated with normal hydrodynamics) with substantially complete dislocation of the venous return tubing.

[0033] In some embodiments, the acoustic transducer may be accessible and / or releasably coupled to the line, such as a venous return line in a dialysis system. As an example, a coupling element (e.g., a clamp) may be used to releasably couple the acoustic transducer to the line.

[0034] In some embodiments, such a clamp may include two arms that are spring-biased relative to each other to allow a portion of an external tubing to be releasably held between their tips. In some embodiments, the tips of the clamp arms may include recesses, each of which may receive an element (e.g., a plastic element) that may be configured to receive one of an acoustic transducer, as discussed in more detail below.

[0035] For example, each plastic element may include a recess in which a housing containing one of the acoustic transducers can be positioned. Furthermore, each plastic element may include a pair of protrusions that can contact a corresponding pair of protrusions on another plastic element when a portion of the venous return tubing is held between the clamp arms. This facilitates holding the tubing between the two arms of the clamp.

[0036] In some embodiments, the housing for each acoustic transducer may include a body having an inner cavity extending from a proximal end of the body to its distal end. In some embodiments, the distal end of the housing may exhibit an expanding taper terminating at the distal surface of the body. Each housing may house a piezoelectric transducer for transmitting or receiving acoustic signals. A plurality of conductive elements extend through the inner cavity of the housing and are electrically coupled to the transducer to supply electrical power to the transmitting transducer and to transmit one or more detection signals generated by the receiving transducer to a signal processing / analysis module, as discussed in more detail below. In some embodiments, the inner cavities of both transducer housings may be at least partially filled with epoxy resin, such as tungsten epoxy resin.

[0037] In some embodiments, a dialysis system is disclosed, comprising a dialyzer, an arterial line providing a path for blood to flow from a patient's circulatory system to an inlet port of the dialyzer, a venous blood line providing a path for blood to flow from the dialyzer back to the patient's circulatory system, and an acoustic sensor removably coupled to the venous blood line. The acoustic sensor may be configured to establish an acoustic standing wave along a lateral dimension of a portion of the venous blood line and monitor a phase signal associated with the acoustic standing wave. Deviation of the monitored phase signal from expected phase characteristics may be used to identify at least partial dislocation of the venous return line. In some such embodiments, dislocation of the venous return line may result in the substantial loss of distinctive characteristics of the phase signal (e.g., characteristics corresponding to the patient's heartbeat).

[0038] In some embodiments, the acoustic sensor may include a transmitter for generating sound waves and a detector for detecting at least a portion of the sound waves after they have passed through a portion of the venous tubing. The transmitter and the detector may be positioned on opposite sides of the venous return tubing. The system may also include a phase comparator for determining the phase shift between the emitted and detected sound waves, thereby generating a phase signal (also referred to herein as a phase difference signal) that can be used to detect venous tubing dislocation in a manner disclosed herein.

[0039] In some embodiments, the acoustic sensor as described herein can be configured to locate an arterial or venous drip chamber found on an available hemodialysis (HD) machine. The diameter of these chambers can range, for example, from about 18 mm to about 30 mm.

[0040] A further understanding of the various aspects of this teaching can be obtained by referring to the detailed description below in conjunction with the relevant accompanying figures briefly described below. Attached Figure Description

[0041] Figure 1 This is a schematic representation of a dialysis system according to one embodiment of the present teaching;

[0042] Figure 2A A clamp is shown in two arms that house transmitting and receiving acoustic transducers, wherein the clamp is used to releasably couple a venous return line to the acoustic transducers;

[0043] Figure 2B An acoustic sensor according to one embodiment of this teaching is schematically depicted;

[0044] Figure 3A An acoustic sensor according to one embodiment is schematically depicted, wherein a piezoelectric film is used to generate and detect sound waves;

[0045] Figure 3B A schematic view of another embodiment of the venous line dislocation system according to this teaching, incorporated into a dialysis system, is shown, wherein a software method is used to determine the phase difference and perform data analysis;

[0046] Figure 3C The detected acoustic signal is presented using an analog circuit, which is described in the Examples section below;

[0047] Figure 3D It shows the relationship with Figure 3C The phase difference signal associated with the acoustic signal in the image is determined using an analog method;

[0048] Figure 3E It shows the relationship with Figure 3CThe phase difference signal associated with the acoustic signal in the image is determined using a software method;

[0049] Figure 4 The hardware platform of the control and signal processing unit according to this teaching is schematically depicted;

[0050] Figure 5A A simulation circuit is schematically depicted for simulating the function of a system for detecting VND in the extracorporeal circuit of a dialysis system according to an embodiment of this teaching.

[0051] Figure 5B A schematic depiction of in Figure 5A The hardware components used in the analog circuit depicted in the diagram;

[0052] Figure 6A and 6B Depicting Figure 6A Various schematic views of a fixture used in an analog circuit for coupling an acoustic sensor according to this teaching to a portion of the external piping of the analog circuit;

[0053] Figure 7 , 8 Figures 9 and 9 show oscilloscope traces of phase signals indicating the various stages of a test used to simulate the detection of VND events in an extracorporeal dialysis system.

[0054] Figure 10A The simulated phase signal corresponding to normal operation of an extracorporeal dialysis system is shown;

[0055] Figure 10B It shows the basis Figure 10A The probability of VND events derived from the phase signal depicted in the diagram;

[0056] Figure 10C The simulated phase signal indicating a VND event is shown;

[0057] Figure 10D It shows the basis Figure 10C The probability of the VND event derived from the phase signal shown;

[0058] Figure 11 An example of a feature associated with the opening and closing of an arterial pump, detected by a VND detection system in accordance with this teaching, is depicted.

[0059] Figure 12 The detection of heart rate signals based on the VND detection system according to this teaching is described;

[0060] Figure 13 The heart rate signal measured by the VND detection system according to this teaching will be compared with the heart rate signal measured by the infrared heart rate monitor;

[0061] Figure 14 The characteristics of a typical heart rate signal cycle are shown;

[0062] Figure 15A The heart rate signal detected during the operation of the arterial pump is compared with the heart rate measured by the pulse oximeter sensor worn by the patient;

[0063] Figure 15B It displays the corresponding time-frequency data of heart rate and arterial pump signals;

[0064] Figure 16A This shows a portion of a daily log of dialysis treatment in which an injection of a drug (e.g., Mircera) is introduced before the intravenous infusion chamber is reached;

[0065] Figure 16B The signal response to drug injection is shown;

[0066] Figure 17 Features from the automated pressure holding test are shown;

[0067] Figure 18A This shows a portion of a daily log of dialysis treatment with an ultrafiltration (UF) pump turned on and off;

[0068] Figure 18B An ultrafiltration (UF) pump signal is shown that interacts with arterial pump characteristics to generate a characteristic beat frequency;

[0069] Figure 19 The signals associated with automatic access traffic boosting are shown;

[0070] Figure 20 The frequency content of the phase signal in response to changes in pumping rate is shown;

[0071] Figure 21A This shows a portion of the daily log of dialysis treatment involving the introduction of heparin injections;

[0072] Figure 21B The signal response to heparin injection is shown;

[0073] Figure 22A This shows a portion of a daily log of dialysis treatment in which an injection of a drug (e.g., Hectorol) is introduced after the pump is turned off;

[0074] Figure 22B The signal response to drug injection and pump shutdown is shown;

[0075] Figure 23 A schematic diagram of the 2008T dialysis machine with an optical detector is depicted.

[0076] Figure 24 and 25 An example of a VND detection sensor integrated with an optical detector in the same housing is shown; and

[0077] Figure 26 An example of a sensor module is shown, including a VND detection sensor and an optical detector assembled in a 2008T dialysis machine. Detailed Implementation

[0078] In one aspect, the present invention relates to a VND detection system and method that can continuously sense venous pulses by employing a highly sensitive phase detector circuit. In some embodiments, the absence (or substantial absence) of phase characteristics can be used to detect VND events. As an example, the sensor can be incorporated as part of a dialysis system and can be configured to (e.g., releasably) couple to a disposable venous blood line. The sensor may include a transmitter configured to generate an ultrasonic standing wave that travels through the venous blood line to a receiver element on the opposite side of the venous blood line and is reflected back from the tube boundary. A receiving transducer is used to detect the standing wave established within the diameter of the fluid-filled tube, thereby allowing monitoring of the phase shift between the transmitted and received signals.

[0079] Hydrodynamic changes in blood flow can be monitored by measuring the phase shift between the transmitted and received signals of a standing wave (resonance condition) caused by venous blood flow, relative to a desired phase characteristic, such as that generated by a patient's heartbeat. The measured phase shift varies with blood flow and is sensitive enough to detect minute changes in flow conditions originating from a heartbeat or the operation of a pump. Although the various features of this teaching are described in conjunction with the detection of VND in the following discussion, it should be understood that this teaching can generally be applied to detecting changes in the velocity of sound or hydrodynamics of fluids (e.g., liquids) flowing through other extracorporeal circuits such as a cardiopulmonary bypass machine.

[0080] Figure 1 Figure 2 schematically depicts a dialysis system 100, incorporating a VND detection system 102 for detecting venous needle displacement (VND) according to one embodiment of this teaching.

[0081] The depicted hemodialysis system 100 includes a dialyzer 103 that receives arterial blood via an arterial line 109, which in turn receives blood via an arterial access point 110 (e.g., an arteriovenous (AV) fistula). A blood pump 108a facilitates the circulation of blood through the dialysis system. A blood thinner, such as heparin, may be introduced into the bloodstream via a heparin pump 108 before it is introduced into the dialyzer 103. The dialyzer 103 filters the blood, and the filtered blood is returned to the patient via a venous return line 105, which is coupled to the patient's vein via a venous access point 107 (e.g., an arteriovenous (AV) fistula) including a venous needle 107a inserted into the patient's circulatory system. An air detector / air trap 111 may be coupled to the venous return line to prevent air bubbles (if any) in the flowing blood from being introduced into the patient.

[0082] As an example, dialyzer 103 may include thousands of tiny porous tubes in which blood flows inside and dialysate flows outside. The pores in the tubes allow waste and excess fluid to transfer from the blood to the dialysate. Used dialysate is discarded via the dialyzer's output port, and fresh dialysate is introduced into the dialyzer from a reservoir via the dialyzer's input port.

[0083] Continue to refer to Figure 1 as well as Figure 2A and 2B In this embodiment, the VND detection system 102 includes an acoustic sensor 114 having an acoustic transmitting unit 114a and an acoustic receiving unit 114b (e.g., such as...). Figure 2B As shown, the acoustic sensor 114 can be coupled to a portion of the venous return line 105 via a clamp 115 (e.g., releasably). Various acoustic transmitting and receiving units can be employed. For example, in a non-limiting example, an ultrasonic transducer of model PT 25-4-X sold by Ultran can be used. The clamp 115 of the acoustic unit 114 may include two arms 117a and 117b, which are spring-biased relative to each other to allow releasably holding a portion of the venous blood line 105 between the tips of the two arms.

[0084] The tips of the two arms 117a / 117b of the clamp 115 may include recesses 118a and 118b for receiving two mounting elements 120a / 120b, each of which is further configured to receive one of the acoustic transducer units 114a and 114b of the acoustic sensor 114, as discussed in more detail below. Furthermore, each mounting element 120a / 120b includes a pair of protrusions (e.g., protrusions 121a / 121b) that can contact a corresponding pair of protrusions of another plastic element when a portion of a venous return line is secured between the two arms of the clamp.

[0085] refer to Figure 2A and 2B Each acoustic transducer unit 114a / 114b includes a housing 112a / 112b configured to be positioned within a central opening of a mounting element 120a / 120b (e.g., as shown in the image). Figure 2A (As shown). In this embodiment, the housings 112a / 112b may be made of a suitable plastic material (e.g., polydimethylsiloxane (PDMS)) and may include cavities 116a / 116b extending from the proximal end to the distal end of the housing, and the cavities 116a / 116b exhibiting an extended tapered shape terminating at the distal surface of the housing. Each of the housings 112a / 112b houses a piezoelectric transducer 119a / 119b for transmitting or receiving acoustic signals.

[0086] Multiple conductive elements 122a / 122b extend through the inner cavity of the housing and are electrically coupled to transducers 118a / 118b to supply electrical power to the transmitting transducer unit 114a and receive one or more detection signals generated by the receiving transducer unit 114b, and transmit the detection signals to a signal processing / analysis module, as discussed in more detail below. In this embodiment, to broaden the frequency response of the transducers, the inner cavities of the two transducer housings are at least partially filled with tungsten epoxy resin 122.

[0087] Each acoustic transducer unit 114a / 114b can be removably positioned in a corresponding recess of a mounting element 120a / 120b. The acoustic transducer units can be spring-loaded to allow for flexible partial contact between them and the tip of the venous conduit held between the clamp 115 and the venous conduit. For example, the pulsation of blood flowing through the venous conduit can cause some degree of expansion and contraction of the venous conduit. The flexible contact between the transmitting and receiving transducer units 114a / 114b and the venous conduit (i.e., a less rigid contact that allows for radial expansion and contraction of the venous conduit) allows this radial oscillation of the venous conduit to contribute to the phase shift between the transmitted and received acoustic signals, as discussed in more detail below.

[0088] In some embodiments, a piezoelectric film may be used to generate and / or receive acoustic signals. As an example, Figure 3A An embodiment is schematically depicted in which two piezoelectric membranes 400a / 400b are disposed on opposite sides of a portion of a venous return line 105. A clamp 401 is used to hold the piezoelectric membranes 400a / 400b in proper position relative to the venous return line 105. In this embodiment, the piezoelectric membrane 400a is used to generate an acoustic signal transmitted through the venous line in a direction substantially perpendicular to the direction of fluid flow, and the piezoelectric membrane 400b is used to receive at least a portion of the transmitted signal and generate a detection signal. For example, an oscillating voltage applied to the piezoelectric membrane 400a can cause the membrane to vibrate to generate an acoustic signal for transmission into the lumen of the line. Sound waves passing through the medium flowing through the line can cause the piezoelectric membrane 400b to vibrate, which in turn leads to the generation of an electrical signal.

[0089] Refer again Figure 1 The transmitting / receiving unit 200 operates under the control of the control and signal processing unit 201 to control the acoustic transmitting and receiving transducers 114a / 114b. Specifically, the control and signal processing unit 201 can operate the acoustic transmitting unit to transmit a continuous wave (CW) acoustic signal across the diameter of the vein conduit 105, and operate the acoustic receiving unit to detect at least a portion of the transmitted acoustic signal after it has passed through the vein conduit wall and flowing blood. In this way, a standing wave acoustic resonance can be established within the inner diameter of the vein conduit between the acoustic transmitting unit and the acoustic receiving unit.

[0090] The frequency of the acoustic signal can be selected to establish a standing wave acoustic resonance within the lateral dimension of the venous conduit. A standing wave is established in the fluid when an integer multiple of half the wavelength of the sound wave lies within the fluid path. As an example, the frequency of the sound wave can be in the range of approximately 1 to approximately 20 MHz, for example, in the range of approximately 5 MHz to approximately 10 MHz, although other frequencies may also be used. The choice of frequency is generally based on the acoustic transmission characteristics of the tube material, rather than being a limitation of this teaching. For example, in this embodiment, the frequency of the sound wave is approximately 3 MHz, but other frequencies may also be used. This frequency is selected based on the maximum amplitude of the received signal that indicates the resonance condition, and it depends on the tube diameter and the fluid velocity. As discussed in more detail, in some embodiments, the frequency of the applied acoustic signal can be scanned and the detected phase signal can be monitored to identify the optimal frequency to be applied to the acoustic sensor (i.e., the frequency at which the resonant sound wave is established).

[0091] As discussed in more detail below, the phase difference between the transmitted and received signals changes in response to other changes in the hydrodynamics of venous pulsation and / or flow.

[0092] like Figure 1 As shown, the detection signal generated by the acoustic transducer receiver unit 114b is received by the signal processing module 202. The signal processing module 202 includes a low-noise amplifier (LNA) 204 that amplifies the received signal. A phase detector 205 receives a portion of the transmitted signal and the amplified received signal, and compares the phases of the two signals to generate a phase difference signal. In this embodiment, the phase difference signal is filtered by a low-pass frequency filter 207 having a cutoff frequency of approximately 100 Hz, and amplified by an amplifier 209 before being transmitted to the transmit / receive unit 200, which communicates with the control and signal processing unit 201.

[0093] Continue to refer to Figure 1 The transmit / receive unit 200 includes an ADC (Analog-to-Digital Converter) module that receives and digitizes the amplified phase signal. The ADC communicates with an FPGA (Field Programmable Gate Array) that receives a reference signal from a crystal oscillator, provides a sampling clock for sampling the digitized phase signal, and transmits the sampled digitized phase signal to the communication interface of the control and signal processing unit 201 via a USB control module. The control and signal processing unit 201 can be configured to operate on the received acoustic signal, for example, in a manner discussed herein, to detect hydrodynamic changes in the flowing fluid, such as partial or complete VND events.

[0094] In addition to the communication interface, the control and signal processing unit 201 includes a processor, a memory module, and a display and keyboard. As an example, the processor may be a general-purpose and / or special-purpose microprocessor, such as a special-purpose instruction set processor, graphics processing unit, physical processing unit, digital signal processor, image processor, coprocessor, floating-point processor, network processor, and / or any other suitable processor that can be used in digital computing circuitry. Alternatively or additionally, the processor may include at least one multi-core processor and a front-end processor. As an example, in some embodiments, the memory module may include one or more permanent memory cells and one or more random access memory (RAM) cells. As an example, the permanent memory cell may be a magnetic disk (e.g., an internal or removable disk), a magneto-optical disk, one or more semiconductor memory devices (e.g., EPROM or EEPROM), flash memory, a CD-ROM, and / or a DVD-ROM.

[0095] Instructions and data for various components of the operating system, such as acoustic transducers and blood pumps, as well as the analysis of detected acoustic signals in accordance with this teaching, can be stored in permanent memory and can be transferred to RAM during execution.

[0096] A communication bus allows communication between various components of the control and signal processing unit 201. In some embodiments, instructions for analyzing the received phase signal may be stored in a memory module. The processor may execute these instructions to analyze the received phase signal, i.e., phase difference data. As discussed in more detail below, analysis of the phase difference data can enable the detection of deviations from expected characteristics. In some embodiments, the control and signal processing unit 201 may be configured to generate an alarm in response to the detection of such a deviation in the phase signal. In some embodiments, the control and signal processing unit 201 may be configured to communicate with the blood pump 108a to adjust the pump speed in response to the detection of a deviation in the phase signal from expected phase characteristics.

[0097] More specifically, in this embodiment, the control and signal processing unit 201 can be configured to operate on the phase difference signal to determine whether a VND event has occurred. Specifically, the control and signal processing unit 201 can be configured to compare the measured phase difference signal, such as the temporal variation of the phase difference signal, with an expected phase signal associated with expected blood flow characteristics to identify, for example, disturbances and / or abnormal flow associated with blood flowing through the venous line, if any. More specifically, in this embodiment, the expected phase characteristic is a characteristic associated with the heartbeat of a patient undergoing dialysis. In other words, when the venous needle is securely positioned within the patient's vein, the patient's heartbeat can generate characteristic pulsations in the venous line, which can be detected as a heartbeat phase difference characteristic. This heartbeat phase characteristic can be monitored to identify venous needle dislocation (e.g., partial or substantially complete dislocation). For example, venous needle dislocation can cause the distinctive heartbeat phase characteristic to substantially disappear.

[0098] Continue to refer to Figure 1 The control and processing unit 201 is also configured to control the operation of the transmitting / receiving unit, for example, to instruct the transmitting / receiving unit to apply a desired audio frequency to the VND acoustic sensor 114. For example, in this embodiment, the control and processing unit 201 may be configured to send control signals to a waveform generator (AWG) incorporated in the FPGA to generate a digital frequency signal applied to the acoustic sensor 114 at a desired frequency.

[0099] A digital-to-analog converter (DAC) converts a digital frequency signal into an analog signal, which can be stored in a buffer for application to the acoustic sensor 114. A portion of this signal can provide a reference signal to a phase detector to determine the phase difference between the transmitted and received signals.

[0100] In some embodiments, the control and processing unit 201 scans the acoustic frequencies applied to the acoustic sensor 114 across a frequency range to determine the optimal acoustic frequency, such as the resonant acoustic frequency, for the acoustic sensor.

[0101] As described above, the control and processing unit 201 receives and monitors the phase difference signal to indicate the deviation of the phase signal from the expected phase characteristics. In some embodiments, the control and processing unit 201 may be configured to apply a moving FFT window to the phase signal to analyze the signal for detecting the phase deviation from the expected phase signal. As an example, Figure 10A The analog phase signal corresponding to normal operation is shown. Figure 10B The probability of the VND event derived from the phase signal is shown. Figure 10C An analog phase signal indicating a VND event is shown. Figure 10D It shows from Figure 10C The probability of a VND event derived from the phase signal is shown. In this example, multiple independent features characterizing the phase are used in the probabilistic classifier algorithm to determine the likelihood that a VND event has occurred. This method has been shown to provide a fast step change response, for example, as... Figure 10D As shown, this also minimizes the occurrence of error alerts.

[0102] In some embodiments, changes in the monitored phase signal relative to expected phase characteristics can be used to detect one or more blood clots in fluid flow. For example, one or more blood clots can be detected by detecting changes in the phase shift and / or amplitude of the received signal.

[0103] In some embodiments, the methods and systems disclosed in U.S. Patent No. 7,228,740 (referred to herein as the “740 Patent”), incorporated herein by reference, can be employed as instructed by this teaching to measure the phase difference between transmitted and received acoustic signals and analyze the measured phase signal to obtain information about changes in blood composition. Furthermore, the methods and systems disclosed in the 740 Patent can be used to provide a scan of acoustic frequencies, measure the phase difference signal as a function of frequency, and analyze the frequency dependence of the measured phase difference signal to obtain composition information.

[0104] The above embodiments are hardware-based. As discussed in more detail below, phase detection can be performed via software operations on the digitized transmitted and received signals, as discussed in more detail below.

[0105] More specifically, Figure 3B A dialysis system 300 incorporating a VND detection system 302 according to another embodiment of this teaching is schematically depicted. Similar to the dialysis system 100 discussed above, an acoustic sensor 114 may be coupled (e.g., releasably) to the venous return line of the dialysis system. In this embodiment, a transmitting / receiving unit 320, operating under the control of a control and signal processing unit 310, actuates an acoustic transmitting unit 114a to emit sound waves across the diameter of the venous return line, and receives a detection signal generated by an acoustic receiving unit 114b after the detection signal is amplified by a low-noise amplifier 204.

[0106] In this embodiment, the detection of the phase difference between the transmitted and received acoustic signals is performed by a software module present on the control and signal processing unit 310. For example, an amplified high-frequency acoustic signal output by a low-noise amplifier 204 is received by a transmit / receive unit 320, which in turn sends a digital version of the acoustic signal to the control and processing unit 310. The phase difference between the transmitted and received acoustic signals can then be determined using instructions stored on the control and processing unit 310, such as those discussed below.

[0107] As an example, the following procedure can be used to determine and analyze phase signals.

[0108] The phase of the signal is given by the following equation:

[0109]

[0110] Where I is the in-phase component of the signal, often referred to as the real component, and Q is often referred to as the quadrature component or imaginary component. According to the equation above, to calculate the phase angle, I and Q need to be calculated. The following section outlines the steps required to calculate I and Q.

[0111] I and Q are generated:

[0112] The procedure for calculating I and Q is shown in the steps below. In the following discussion, Rx is the signal measured from the receiving transducer, and Tx is the transmitted signal measured directly.

[0113] 1. The first step in generating I and Q is to create in-phase and quadrature versions of the transmitted signal. This can be done by applying a Hilbert transform to the measured transmitted signal. This creates a complex signal in which the real components of the transformed signal are in-phase components (which are simply copies of the original transmitted signal), and the imaginary components are 90-degree phase-shifted versions of the original transmitted signal (also known as quadrature components).

[0114] 2. The next step is to mix the in-phase and quadrature components with the received signal (Rx). As an example, this can be done by applying pointwise multiplication of the two signals.

[0115] 3. After the signals are mixed, a low-pass filter (LPF) can be applied to the mixed signals.

[0116] 4. Subsequently, in some embodiments, the data can be cropped, for example, keeping the middle 80% of the low-pass filtered signal. This can reduce the impact of end-effects generated by the low-pass filtering step.

[0117] 5. Finally, the average value of the cropped data can be determined, which generates I and Q respectively.

[0118] As an explanation, Figure 3C An acoustic received signal obtained by using the analog loop discussed below is presented. The presented acoustic received signal has a frequency of 3 MHz and a duration of 0.7 seconds. Figure 3D It shows the relationship with Figure 3C The phase difference signal associated with the acoustic signal (i.e., the phase difference between the transmitted and received signals) is presented in the image, which is obtained by using an analog circuit (AD8302 chip). Figure 3E Presented with Figure 3C The phase difference signal associated with the acoustic signal is presented in the image, which is generated using software.

[0119] As discussed further below, certain measures can be taken when partial or complete VND is detected. For example, refer to... Figure 1 The control and signal processing unit 201 can be configured to shut down the pump 108a to slow blood loss.

[0120] In some embodiments, when a VND is detected, the control and signal processing unit 201 is configured to delay taking any action for a predefined period of time, for example, within the range of approximately 5 to approximately 10 seconds, and continue monitoring the phase difference signal to ensure that a VND event has actually occurred. This approach can reduce the occurrence of false alarms.

[0121] In some embodiments, in response to the detection of a phase change indicating a fluid dynamics change in the flow, the control and signal processing unit 201 can be configured to adjust the speed of the blood pump 108a. For example, the speed of the blood pump 108a can be reduced, and the phase signal can be monitored until no air bubbles are detected in the flow.

[0122] The control and signal processing unit 201 can be implemented using hardware, software, and / or firmware in manner known in the art, as disclosed in this teaching. As an example, Figure 4 A hardware platform 600 is schematically depicted, including components such as a processor 602, permanent memory 604, random access memory (RAM) 606, and a communication module (WIFI or Bluetooth) 608, as well as a communication bus 610 for connecting the processor 602 to these components.

[0123] As described above, in some embodiments, the acoustic sensor as described herein can be configured to locate an arterial or venous infusion chamber found on an available HD machine. The diameter of these chambers can range, for example, from about 18 mm to about 30 mm.

[0124] The following examples are provided to further illustrate various aspects of this teaching. These examples are provided for illustrative purposes and are not necessarily intended to indicate the best way to practice this teaching and / or the best results that can be obtained.

[0125] Example 1

[0126] A simulated venous pulse (fistula) connected via a hemodialysis needle to the output of a blood pump (the pump of a Fresenius dialysis machine, model: 2008T, referred to herein as the "Fresenius blood pump") was used to detect the simulated venous pulse above the "noise" generated by the blood pump.

[0127] Figure 5A An analog circuit for detecting venous pulses using a phase detection system and method according to one embodiment of this teaching is shown. The figure illustrates the hydraulic circuit and the positions of the VND sensor and dialysis needle insertion point relative to the cardiac pulse simulation pump and Fresenius blood pump.

[0128] Fresenius medical tubing from the 2008T dialysis machine kit, including the specified dialyzer part number 16LU04016, was used. The VND system was evaluated with the blood pump set to 100-275 ml / min and the VND sensor placed 0.5 m in front of the intravenous needle.

[0129] A small peristaltic pump, through which a venous needle is inserted, is used to simulate the beating of a vein or heart (fistula).

[0130] Figure 5BHardware for transmitting signals to and receiving signals from a VND sensor, and for processing signals for accurate phase detection, is shown.

[0131] A dual-channel Analog Discovery 2 device is used to transmit a continuous wave signal (Tx1) to one piezoelectric element of the VND sensor, while simultaneously receiving a signal from a second piezoelectric element via Rx1.

[0132] To ensure accurate phase difference measurement, the same Tx1 transmitted signal was also measured using the second input channel (Rx2) on the Analog Discovery 2 device.

[0133] Used on a tablet Application software written in a programming language is used to control the AnalogDiscovery 2 device, process the received signals in the manner discussed above, and record the raw processed data.

[0134] Use the following procedure to obtain the test results:

[0135] 1. Equipment settings:

[0136] 1.1 Install the 6.5mm medical tubing and dialyzer into the Fresenius 2008T dialysis machine. Using similar medical tubing and the specified peristaltic pump, form a... Figure 5A The heart simulator circuit shown.

[0137] 1.2 such as Figure 5A As shown, the VND sensor is installed on the intravenous line approximately 0.5 m prior to the intravenous needle. The sensor is acoustically coupled to the tube using Vaseline.

[0138] 1.3 Connect the BNC connector to the VND sensor.

[0139] 1.4 Fill the blood reservoir with red-dyed water.

[0140] 1.5 Turn on the Fresenius dialysis machine, enter "Service" mode, and then select "Maintenance" and "Arterial Pump". This allows manual control of the blood pump flow rate. Set the pump rate to 100-275 ml / min, and then turn off the pump.

[0141] 1.6 Fill the intravenous simulation tubing and dialysis tubing by running two pumps simultaneously.

[0142] 1.7 Launch the VND application and begin measurement.

[0143] 1.8 Set up two USB webcams to record the tablet screen and the area where the dialysis needle is inserted. Begin recording before performing the following test steps.

[0144] 2. Test Procedure

[0145] 2.1 Turn the heart simulator pump to the lowest setting (3.5V) and verify that pump pulsation is observed by looking at the phase output signal on the VND application.

[0146] 2.2 Carefully remove the dialysis needle from the pulse simulation line above a suitable collection basin. Verify that the phase output signal is now flat (i.e., without pulsation).

[0147] 2.3 Reinsert the dialysis needle and verify that pump pulsation is observed again by checking the phase output signal on the VND application.

[0148] 2.4 With the venous pulse simulator pump still running, turn on the Fresenius blood pump.

[0149] 2.5 Carefully remove the dialysis needle from the pulse simulation line. Verify that the amplitude of the phase output signal is significantly reduced, showing only small pulsations from the blood pump.

[0150] 2.6 The dialysis needle was reinserted very slowly to demonstrate that venous pulsation was only observed after the needle was fully inserted and there was no leakage.

[0151] 2.7 Set the blood pump rate to 500 ml / min, then remove the dialysis needle from the pulse simulation tubing. Verify that the phase output signal shows no significant change in frequency content or has undergone a significant phase shift.

[0152] 2.8 The dialysis needle was reinserted to demonstrate that venous pulsation was only observed again after the needle was fully inserted without leakage, and the mean phase value returned to its previous state.

[0153] Figure 7 , 8 Figures 9 and 1 show the oscilloscope traces of the phase detection signal associated with the test steps described above.

[0154] refer to Figure 7 Screen A shows the phase signal observed when the intravenous pump is turned on. Screen B shows the phase signal when the dialysis needle is removed while the intravenous pump is running, showing a substantial disappearance of the typical characteristics of the phase signal observed in Screen A. Screen C shows the phase signal when the dialysis needle is reinserted, showing a reproduction of the typical characteristics of the phase signal.

[0155] refer to Figure 8Screen A shows the phase signal observed when the Fresenius blood pump is turned on. Screen B shows the phase signal when the dialysis needle is removed with both pumps running, showing the substantial disappearance of the typical characteristics of the phase signal observed in Screen A. Screen C shows the phase signal after the dialysis needle is slowly reinserted, showing the gradual reproduction of the typical phase characteristics observed in Screen A.

[0156] refer to Figure 9 Screen A shows the phase signal when the blood pump rate is set to 500 ml / min, followed by removal of the dialysis needle while the intravenous pump is still running, demonstrating a significant change in the phase signal due to needle removal. Screen B shows the phase signal when the dialysis needle is slowly reinserted, showing the phase signal gradually returning to the typical phase signal observed in Screen A.

[0157] The above results demonstrate that the tests were successfully performed even when the blood pump was operating at a flow rate of 500 ml / min, and they illustrate the feasibility and high sensitivity of embodiments of the system and method for VND detection according to this teaching.

[0158] Those skilled in the art will understand that various changes can be made to the above embodiments based on this teaching without departing from the scope of the claimed subject matter.

[0159] Example 2

[0160] Clinical studies were conducted using the prototype VND sensor system based on this teaching. A clinical study was performed on 10 patients, with data collected twice per patient, resulting in a total of 20 datasets. Of the 10 patients, fistula access was established in 9 and catheter access was used in 1.

[0161] Throughout the clinical study, the system demonstrated consistent measurements among patients, and the signals attributed to the dialysis machine were consistent and reproducible. Many characteristics of the measurements correlated with events recorded in the treatment log during each data collection. Furthermore, test results indicated that patient movement did not have a significant impact.

[0162] Examination of the characteristics of data collected during clinical studies has shown that the VND sensor system according to this teaching can detect a variety of signals generated by the normal operation of the dialysis machine. Based on the measured characteristics, the measurement techniques according to this teaching have been shown to be able to distinguish VND events from a variety of other characteristics generated during the operation of the dialysis procedure.

[0163] For clinical research, a VND detection sensor was adapted into the CLIC device housing of a 2008T dialysis machine. The CLIC device housing is a component of the 2008T dialysis machine, enabling real-time, non-invasive measurement of hematocrit, percentage change in blood volume, and blood oxygen saturation. As described above, the VND detection sensor system includes a PZT ultrasound transmitter and receiver. The system transmits a frequency scan around the crystal's resonant frequency (3MHz) to identify the frequency that causes the maximum amplitude response. The system then transmits a signal at this frequency and measures the phase change between the transmitted and received signals caused by changes in pressure or sound velocity within the blood tubing. As described above, by measuring the phase change, VND events can be detected, and in some cases, various other characteristics caused by the operation of the dialysis machine, such as those caused by the patient's movements / motions, can also be detected.

[0164] In the following text, reference will be made to Figure 11-20 Examples describing characteristics of VND data measurements during a dialysis procedure.

[0165] Figure 11 Examples of features associated with the on / off state of the arterial pump detected by the VND system discussed above are depicted. For example... Figure 11 As shown, during data collection, in response to shutting down the arterial pump, the phase signal exhibited an initial decrease of approximately 10° / sec, followed by a slower decrease of approximately 0.25° / sec. Conversely, the phase signal showed a sharp increase in response to the arterial pump switching from an off state to an on state. Therefore, the phase signal exhibits unique characteristics indicative of the pump's operating status.

[0166] In addition to features associated with the operation of the dialysis machine, in some embodiments, the VND sensor according to this teaching can provide features associated with the patient's heart rate. As an example, such as... Figure 12 As shown, the heart rate signal can be easily observed when the arterial pump is turned off.

[0167] Figure 13 The heart rate signal measured by the VND detection system was compared with the heart rate signal measured by the infrared heart rate monitor. Figure 14 More detailed characteristics associated with the cycle of a typical heart rate signal are shown. (Reference) Figure 13 and 14 As can be seen, the VND detection system used in this embodiment is able to accurately monitor heart rate when the arterial pump is turned off.

[0168] Figure 15A and 15B This indicates that it is feasible to detect the heart rate signal of the subject while the arterial pump is running. Figure 15AThe heart rate signal detected during the operation of the arterial pump was compared with the heart rate measured by a pulse oximeter sensor worn by the patient. Figure 15B This figure shows the corresponding time-frequency data for the heart rate signal and the arterial pump signal. In this figure, brighter colors represent high amplitude levels, while darker colors represent weaker signals. In this paper, the STFFT (Short Time Fast Fourier Transform) method is used to extract the heart rate signal. However, this teaching is not limited to the STFFT method, and various other data processing methods can be used to extract the heart rate signal over several cycles (e.g., approximately 2 to 3 seconds).

[0169] Figure 16A and 16B The daily log of dialysis treatment and the signal response to the injection of a drug (e.g., Mircera) prior to the intravenous infusion chamber are shown separately. Figure 16B As shown, drug injection produces a smooth, positive phase shift, which is identifiable above a typical pump signal.

[0170] Figure 17 Features from an automated pressure holding test are shown. Figure 17 In the test, small increases in the phase angle at intervals of approximately 12 minutes can be observed, providing a characteristic indicative of the automated pressure maintenance test performed by the dialysis machine.

[0171] refer to Figure 18A and 18B The measured signal can reveal the ultrafiltration (UF) pump signal that interacts with the characteristics of the arterial pump to produce a characteristic beat frequency. Figure 18B The first part indicates that the UF pump is on, where the characteristic beat frequency is visible. At approximately 13:14, the UF pump shuts off (see [link]). Figure 18A Furthermore, the beat frequency disappears. In some embodiments, this feature can be used to identify the operating status of the UF pump.

[0172] Figure 19 Signals associated with automated access flow bolus injection (e.g., due to the injection of saline bolus, used for automated conductivity testing performed by a dialysis machine) are shown. Figure 19 During this process, due to automated pathway flow injection, a drop in phase data of a few degrees (e.g., about 2°) can be observed, occurring approximately every 41.5 minutes and lasting for 6 minutes.

[0173] Figure 20 The signal response to changes in pumping rate is shown. This signal was generated using the same STFFT method as described above for heart rate detection during pump operation. Figure 20As can be seen, the pump rate increased from 52 CPM to 72 CPM at approximately 17:10 (i.e., 300 to 400 mL / min).

[0174] Figure 21A and 21B A portion of the daily log of dialysis treatment and the signal response to heparin injection are shown. Figure 21B As shown, drug injection produces a smooth, positive phase shift, which is identifiable above a typical pump signal.

[0175] Figure 22A and 22B A portion of the daily log of dialysis treatment and the signal response to drug (e.g., Hectoral) injection are shown, followed by an arterial pressure alarm that triggers the arterial pump shutdown. Figure 22B As shown, drug injection produces a smooth, positive phase shift, which is identifiable above a typical pump. The phase signal responds to pump shutdown by exhibiting a phase shift similar to... Figure 11 The phase signal shown exhibits a similar initial descent characteristic. (See above reference.) Figure 11-20 The VND detection technology described herein provides sufficient sensitivity, reliability, and repeatability to distinguish not only VND events but also various other events (e.g., the operating status of one or more pumps, drug injection, and patient arm movement), thereby allowing VND events to be differentiated from other events. This, in turn, helps reduce the probability of false alarms.

[0176] In some embodiments, data communication (e.g., inputs and outputs) between the dialysis system and the VND detection system can be bidirectional. For example, the VND detection system can transmit one or more outputs to the dialysis system (e.g., VND alarms, raw VND data (e.g., phase angle)), and the VND detection system can receive one or more inputs from the dialysis system (e.g., dialysate temperature, dialysate conductivity, TMP, arterial pressure, venous pressure, UF rate, dialysate flow bypass, BTM arterial and venous temperature, Hct, blood pressure, voltage, and dialysis machine alarms (e.g., blood leak, arterial pressure, venous pressure, TMP, dialysate temperature, dialysate conductivity, blood pump stoppage, heparin stoppage, and air detection)). In addition to the data identified above, the dialysis system and the VND detection system can be configured to receive and transmit other data (e.g., clinician inputs, medication administration, etc.) between the two systems. In such embodiments, this data, available to both systems (VND detection system and dialysis system), can be used to improve the sensitivity and / or specificity of VND detection, and in particular, to reduce the probability of false alarms. As an example, VND identification algorithms can use inputs (e.g., UF pump shutdown or drug administration) to predict and / or verify changes in the phase signal of non-VND events.

[0177] Example 3 - Retrofitting a VND sensor into a dialysis machine and combining the VND sensor with a blood sensing sensor.

[0178] In some embodiments, the VND detection sensor according to this teaching can be retrofitted into existing dialysis machines, such as the Fresenius Healthcare 2008T or 5008S dialysis machines.

[0179] As an example, Figure 23 The front panel of a 2008T dialysis machine is depicted, which is equipped with an optical detector 2100 that optically distinguishes between the flow of opaque fluid (e.g., blood) and the flow of transparent fluid (e.g., saline).

[0180] In some embodiments, the VND detection sensor according to this teaching can be integrated with an optical detector. As an illustration, Figure 24 and 25 An example of a VND detection sensor 2300 and an optical detector 2100 integrated into the same housing 2110 is shown.

[0181] refer to Figure 24 and 25 The VND sensor 2300 has a pair of acoustic transmitting / receiving units 2314a and 2314b disposed in two opposing cavities in opposing walls of a recess 2120 configured to receive blood from the blood line. The transmitting / receiving units 2314a / 2314b can be used to establish standing resonant acoustic waves in a portion of the blood flowing through the blood line in the manner discussed above as the blood passes between the transmitting / receiving units.

[0182] As discussed above, the pair of acoustic transducer units 2314a and 2314b can be used to monitor the phase signal of the resonant acoustic wave to detect hydrodynamic changes in the flow within the blood tubing. In this embodiment, the structure and function of the optical detector 2100 can remain unchanged. Furthermore, the cover 2130 can be hingedly coupled to the housing 2110 and secured by a spring-biased latch 2140, such that the cover 2130 can hold the blood tubing within the recess 2120.

[0183] Figure 26An example of a sensor module 2500 is shown, comprising a VND detection sensor 2300 and an optical detector 2100 retrofitted to a 2008T dialysis machine. A printed circuit board (PCB) 2510 may be added, for example, adjacent to the level detector PCB, to support the operation of the VND retrofitted sensor. To allow communication between the VND sensor and the main processor of the 2008T machine, a socket 2520 may be provided on the PCB 2510 to accommodate a communication cable (e.g., an RS-232 connector). In some embodiments, to make the sensor module more compact, the electronic components associated with the VND detection sensor 2300 may be included within the housing 2110 of the sensor module 2500, thereby eliminating any need for an additional PCB 2510. In some embodiments, the sensor module 2500 may further include other sensors, such as a blood sensing sensor, a bubble detector, an electrolyte sensor, a venous pressure transducer, a temperature sensor, or the like, so that additional data can be employed to improve the sensitivity and / or specificity of VND detection, and in particular to reduce the probability of false alarms.

Claims

1. A system for detecting a change in fluid dynamics of a fluid flowing in at least one line associated with an extracorporeal circuit, comprising: a sound wave emitter for establishing a resonant standing acoustic wave perpendicular to a fluid flowing through an internal lumen of the at least one line such that the resonant standing acoustic wave propagates through a portion of the fluid traveling through the internal lumen; a detector for detecting at least a portion of the resonant standing acoustic wave after the resonant standing acoustic wave has passed through the fluid; a phase detector for measuring a phase signal indicative of a phase difference between the emitted sound wave and the detected sound wave; and a comparator for comparing the measured phase signal to an expected phase signature associated with the fluid dynamics of the fluid flowing through the at least one line, wherein a deviation between the measured phase signal and the expected phase signature identified by the comparator is indicative of an occurrence of a disturbance in the fluid flow.

2. The system of claim 1, wherein, The system further comprises an analyzer for correlating the deviation to an event causing the change in fluid dynamics.

3. The system of claim 2, wherein, The analyzer is configured to analyze the phase deviation in order to identify the event as any one of the following events: (1) a passage of one or more air bubbles; (2) a blood clot; and (3) at least partial dislodgement of at least a portion of the at least one line from an expected location.

4. The system of any of the preceding claims, wherein, The sound wave emitter generates sound waves having a frequency in a range of 1 MHz to 20 MHz.

5. The system according to any of the preceding claims 1-3, wherein, The sound wave emitter is configured to generate a single frequency sound wave.

6. The system of claim 2 or 3, wherein, The at least one line comprises a venous return line of a dialysis system.

7. The system of claim 6, wherein, The analyzer is configured to identify a deviation in the phase signal corresponding to at least partial dislodgement of the venous return line.

8. The system of claim 7, wherein, The analyzer is configured to correlate a substantial disappearance of the phase signal to a substantially complete dislodgement of the venous return line.

9. The system of claim 6, wherein, Any one of the sound wave emitter and the detector is releasably couplable to the venous return line.

10. The system of claim 9, wherein, The system further comprises a coupling element for releasably coupling any one of the sound wave emitter and detector to the venous return line.

11. The system of claim 10, wherein, The coupling element comprises a clamp.

12. The system of claim 11, wherein, The clamp comprises a spring-loaded clamp.

13. The system of claim 6, wherein, A dialysis system comprises a dialyzer that receives blood flowing from a patient's circulatory system via an input port thereof, and the venous return line transports blood exiting the dialyzer to the patient's circulatory system.

14. The system of claim 13, wherein, The detector is disposed proximate to the venous return line and is configured to establish an acoustic standing wave in a portion of the venous return line, and wherein the analyzer is configured to monitor a phase signal associated with the acoustic standing wave and identify at least partial dislodgement of the venous return line based on a deviation of the phase signal relative to an expected phase signature.

15. The system of any one of claims 10-14, wherein, The system further comprises a sensor comprising the sound wave emitter and the detector, and wherein the sensor comprises a phase comparator for determining a phase shift between a phase of the emitted sound wave and the detected sound wave.

16. The system of claim 13 or 14, wherein, The sound wave emitter and the detector are positioned on opposite sides of the venous return line.

17. The system of claim 13 or 14, wherein, The sound wave emitter and the detector are positioned on the same side of the venous return line.

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