Systems and methods for detecting intravenous needle dislodgement

Abstract

In one aspect, a method and system for detecting changes in fluid dynamics of a fluid flowing through an extracorporeal circuit is disclosed, the method including establishing an acoustic wave resonance across a transverse dimension of at least a portion of a line associated with the extracorporeal circuit through which the fluid flows, monitoring a phase signal of the resonating acoustic wave, and identifying the occurrence of a change in fluid dynamics of the flowing fluid when the observed phase signal of the resonating acoustic wave exhibits a deviation from an expected fluid flow signature. The change in fluid dynamics can be used to indicate a venous needle dislodgement event.

Description

Cross - reference to related applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 047,727, filed on July 2, 2020, which is hereby incorporated by reference in its entirety.

Background Art

[0002] The present disclosure generally relates to systems and methods for detecting changes in fluid dynamics of a fluid flowing within an extracorporeal circuit, and more specifically, to such systems and methods that can be used to detect venous needle dislodgement (VND) in a dialysis system.

[0003] Venous needle dislodgement (VND) during dialysis is a rare event. However, if VND is not detected promptly, it can lead to fatal blood loss within a few minutes. For example, a patient with a normal blood volume of 3 - 5 L with a normal extracorporeal blood flow of 200 - 500 ml / min during dialysis will typically reach fatal blood loss within 2 - 5 minutes after VND. The reported number of VNDs per treatment is in the wide range of 0.0008% - 0.1%, and it is estimated that 10 - 33% of VNDs result in death.

[0004] Several different approaches have been implemented to detect VND. However, these conventional approaches have several drawbacks. In some such conventional approaches, venous line pressure is measured in various ways in an attempt to detect VND based on a rapid decrease in venous line pressure. However, since VND causes only small pressure changes in the venous return line, such pressure monitoring approaches are not robust. Conventional pressure monitoring systems that have sufficient sensitivity to detect such small pressure changes have been utilized, but such systems require sufficient attenuation or averaging to reduce noise in the measurement, or else it will adversely affect the system's response time. Furthermore, such systems require sensor contact with the blood. Additionally, these systems typically cause many false detections, thus increasing the burden of monitoring and dealing with false alarms.

[0005] Another approach is to place a wetness detector at or near the patient's access point, but this will issue a warning after blood has leaked and been collected at the detector. Also, the wetness detector can render such a system worthless if it is placed incorrectly, and since the leakage path cannot always be reliably predicted, it is not optimal. Mechanical tube compression devices are also not optimal as they can be implemented inappropriately.

[0006] Therefore, a reliable, robust, and cost-effective solution for detecting VND is needed. SUMMARY OF THE INVENTION

[0007] In one aspect, a method for detecting a change in the fluid dynamics of a fluid flowing through an extracorporeal circuit is disclosed. The method includes establishing acoustic wave resonance across at least a portion of a line associated with the extracorporeal circuit through which the fluid flows, monitoring a phase signal of the resonant acoustic wave, and identifying the occurrence of a change in the fluid dynamics of the flowing fluid when the observed phase signal of the resonant acoustic wave indicates a deviation from a predicted phase signature associated with the fluid flow.

[0008] As used herein, the term "phase signature" refers to the temporal variation of a phase signal indicative of normal (desired) fluid dynamics associated with fluid flow. For example, such a "phase signature" can refer to periodic variations of the phase signal (e.g., periodic variations of the phase signal due to a patient's heartbeat) and / or an average phase signal value.

[0009] In the embodiments described below, an acoustic standing wave is established across the transverse direction of the line (e.g., across the diameter). More generally, the acoustic wave can be established along a dimension of the line that forms a non-zero angle with the axial dimension of the line, where the axial dimension is substantially parallel to the direction of fluid flow.

[0010] The step of establishing the resonant acoustic wave can include transmitting an acoustic wave into a portion of the line, e.g., along its transverse dimension (e.g., along the diameter of the line), and detecting at least a portion of the acoustic wave after it has passed through the flowing fluid. The phase signal can correspond to the difference between the phase of the transmitted acoustic wave and the phase of the detected acoustic wave.

[0011] In some embodiments, the extracorporeal circuit includes an extracorporeal dialysis circuit (such as a hemodialysis circuit), and the line is the venous return line of the extracorporeal dialysis circuit.

[0012] In some embodiments, the predicted phase signature includes a phase signature associated with the heartbeat of a patient coupled to the extracorporeal circuit, e.g., the venous return line of a hemodialysis circuit.

[0013]

[0013] In some embodiments, the change in fluid dynamics is caused by at least a partial dislodgment of the venous return line. For example, the monitored phase shift relative to the expected phase signature can include a substantial change (e.g., disappearance) of the phase signature indicating a substantially complete dislodgment of the venous return line.

[0014] In some embodiments, the acoustic wave is monochromatic. By way of example, in such embodiments, the acoustic wave can have a frequency in the range of about 1 to about 20 MHz, such as, for example, in the range of about 1 MHz to about 5 MHz. The acoustic wave can be excited by any periodic waveform (e.g., sine wave, rectangular wave, etc.) having a selected frequency within the frequency range.

[0015] In some embodiments, the monitored phase signal shift relative to the expected phase signature can be caused by one or more bubbles passing through a portion of the line across which acoustic wave resonance is established. In some cases, the passage of one or more bubbles through the line can be detected by a significant decrease in the amplitude of the acoustic signal and / or the detection of a large phase shift. In some embodiments, a change in the phase signal occurring over a time period of less than about 0.1 seconds can indicate that one or more bubbles have passed through the sensing portion of the device.

[0016] In some embodiments, the flow rate of fluid passing through the extracorporeal line can be adjusted in response to the detection of bubbles in the fluid flow. Typically, depending on the amount of detected bubbles, it may be necessary to slow down or completely stop the flow rate of the blood pump. For example, in some such embodiments, the fluid can be blood, such as blood flowing within the extracorporeal line of a dialysis system. In such embodiments, in response to the detection of bubbles, the blood flow rate can be reduced until no bubbles are detected while the phase signal is being monitored. 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 bubbles flowing through the sensing portion of the device.

[0017] In some embodiments, the shift of the monitored phase signal relative to the expected phase signature can be caused by a change in the hydrodynamic pressure of the fluid flowing through the extracorporeal circuit. In some such embodiments, the change in the hydrodynamic pressure of the fluid causes a change in the cross-sectional dimension of at least a portion of the line and can thus contribute to the shift of the monitored phase relative to the expected phase signature.

[0018] In some embodiments, the shift of the monitored phase from the expected phase signature can indicate an inconsistent flow rate of the fluid passing through the extracorporeal circuit.

[0019] In some embodiments where the fluid is blood, the shift of the monitored phase relative to the expected phase signature can be caused by at least one blood clot.

[0020] In some embodiments, the lines of the extracorporeal circuit can be in the form of tubes. By way of example, such tubes can provide the venous return line of the extracorporeal circuit of a hemodialysis system, and the change in the shift of the monitored phase relative to the expected phase signature can be caused at least in part by the periodic expansion and contraction of the tube as the fluid passes through the tube.

[0021] The measured phase shift from the expected phase signature can be observed, for example, by comparing the measured phase with a previously obtained phase signature corresponding to the expected fluid dynamics of normal fluid flow. In some embodiments, an event, such as a venous needle dislodgment (VND), can result in a substantial disappearance of the phase signal signature, thereby indicating the occurrence of the event.

[0022] In related aspects, a method of detecting a change in the fluid dynamics of a fluid (e.g., blood) flowing within a line in fluid communication with a patient's blood vessel is disclosed. The method includes establishing a resonant standing acoustic wave in a portion of the line, monitoring the phase signal of the resonant standing acoustic wave, and identifying the occurrence of a change in the fluid dynamics of the flowing fluid when the observed phase of the resonant acoustic wave (i.e., the difference between the phase of the transmitted acoustic signal and the phase of the received acoustic signal) indicates a deviation from an expected phase signature associated with the normal fluid dynamics of the flowing fluid. In some embodiments, such a deviation can correspond to a substantial (or complete) disappearance of the phase signal.

[0023] In some embodiments, the phase shift can be caused by one or more bubbles passing through the line.

[0024] In some embodiments, the line is the venous return line of a dialysis system, and the phase shift of the phase signal relative to the expected phase signature associated with the blood flow through the line can be caused by at least a partial dislodgment of the venous return line. For example, a substantial disappearance of a characteristic feature (phase signal signature) of the phase signal can indicate a substantially complete dislodgment of the venous return line.

[0025] In some embodiments, a tube having a lumen through which blood can flow forms a venous return line. In some cases, such a tube can have an inner diameter (ID) in the range of about 3 mm to about 5 mm (e.g., 3.5 mm (pediatric) or 4.3 mm (standard)) and an outer diameter (OD) in the range of about 5 mm to about 7 mm (e.g., 5.5 mm (pediatric) or 6.8 mm (standard)). Further, in some cases, the tube can undergo periodic expansion and contraction, for example, due to the pulsation of the blood circulating through the line, and such periodic expansion and contraction can result in the generation of a phase signature. As described above and in more detail below, changes in the phase signature can indicate the occurrence of an event, such as a partial or complete dislodgment of the venous return line of a dialysis system.

[0026] The tube can be formed of a variety of different materials, such as, for example, polyurethane, glass, polyvinyl chloride, and silicone.

[0027] The establishment of acoustic standing waves across the line (e.g., across the diameter of the tube) can be achieved by coupling two acoustic transducers to opposite sides of the line, where one acoustic transducer (e.g., a piezoelectric device) can generate an acoustic wave and transmit the wave along the transverse dimension within the line, and the other acoustic transducer can detect at least a portion of the acoustic wave transmitted through the tube wall and the flowing fluid (e.g., flowing blood). In some embodiments, the acoustic transmitter and / or detector can be removably coupled to the line.

[0028] In related aspects, a system for detecting changes in the fluid dynamics of a fluid circulating within a line associated with an extracorporeal circuit is disclosed. The system includes an acoustic wave transmitter for transmitting an acoustic wave into the lumen of the line, for example across its transverse dimension, such that the acoustic wave travels through a portion of the fluid traversing the lumen. The system may further include a detector for detecting at least a portion of the acoustic wave after it has passed through the fluid, and a phase detector for measuring a phase signal indicative of the phase difference between the transmitted acoustic wave and the detected acoustic wave. A comparator circuit may be used to compare the measured phase signal with a predicted phase signature associated with the fluid flow, and the offset identified by the comparator between the measured phase signal and the predicted phase signature can indicate the occurrence of a change in the fluid dynamics of the flowing fluid. In some embodiments, the system can include an analyzer for correlating the observed phase offset with an event associated with the fluid dynamics that causes the phase shift.

[0029] As an example, the analyzer may be configured to analyze the phase offset to identify an event associated with the phase offset as any one of (1) the passage of one or more bubbles, (2) the passage of one or more blood clots, and (3) at least partial dislodgment from the predicted position of at least a portion of the line.

[0030] In some embodiments, the acoustic transmitter can generate acoustic waves having a frequency in the range of about 1 to about 20 MHz, such as in the range of about 5 MHz to about 10 MHz. In some such embodiments, the acoustic wave is monochromatic.

[0031] In some embodiments, the extracorporeal circuit can be the extracorporeal circuit of a dialysis system (e.g., a hemodialysis system), and the analyzer can be configured to identify a phase shift of a phase signal relative to a predicted phase signature indicative of at least a partial dislodgment of the venous return line. For example, the analyzer can be configured to correlate a substantial change in the phase signal (e.g., a substantial disappearance of the characteristic features of the phase signal associated with normal fluid dynamics) with a substantially complete dislodgment of the venous return line.

[0032] In some embodiments, the acoustic wave transducer can be proximate to and / or removably coupled to a line, such as the venous return line of a dialysis system. By way of example, a coupling element (e.g., a clamp) can be used to removably couple the acoustic transducer to the line.

[0033] In some embodiments, such a clamp can include two arms that are spring-biased relative to each other and can be capable of removably holding a portion of the extracorporeal line between their tips. In some embodiments, the tips of the clamp arms can include recesses, each of which can be configured to receive an element (e.g., a plastic element) that can be configured to receive one of the acoustic transducers, as detailed below.

[0034] For example, each plastic element can include a recess in which a housing containing one of the acoustic transducers can be positioned. Further, each plastic element can include a pair of protrusions that can contact respective pairs of protrusions of the other plastic element when a portion of the venous return line is held between the clamp arms. This can facilitate holding the line between the arms of the clamp.

[0035] In some embodiments, the housing for each acoustic transducer can include a body having a lumen extending from a proximal end of the body to its distal end. In some embodiments, the distal end of the housing can exhibit a widening taper that terminates at the distal surface of the body. Each housing can accommodate a piezoelectric transducer for transmitting or receiving an acoustic signal. A plurality of conductive elements extend through the lumen of the housing and are electrically coupled to the transducer to supply 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 detailed below. In some embodiments, the lumens of two transducer housings can be at least partially filled with an epoxy, such as tungsten epoxy.

[0036] In some embodiments, a dialysis system is disclosed, the dialysis system including a dialyzer, an arterial line for providing a path for blood flow from a patient's circulatory system to an inlet port of the dialyzer, a venous blood line for providing a path for blood flow out of the dialyzer and into the patient's circulatory system, and an acoustic sensor detachably coupled to the venous blood line. The acoustic sensor can be configured to establish an acoustic standing wave along a transverse dimension of a portion of the venous blood line and to monitor a phase signal associated with the acoustic standing wave. A shift of the monitored phase signal relative to an expected phase signature can be used to identify at least a partial dislodgement of the venous return line. In some such embodiments, a dislodgement of the venous return line can result in a substantial disappearance of a characteristic signature of the phase signal (e.g., a signature corresponding to the patient's pulsation).

[0037] In some embodiments, the acoustic sensor can include a transmitter for generating an acoustic wave and a detector for detecting at least a portion of the acoustic wave after passing through a portion of the venous line. The transmitter and the detector can be positioned on both sides of the venous return line. The system can further include a phase comparator for determining a phase shift between the transmitted acoustic wave and the detected acoustic wave, thereby generating a phase signal (also referred to herein as a phase difference signal) that can be used to detect a dislodgment of the venous line in the manner disclosed herein.

[0038] In some embodiments, the acoustic sensors described herein can be configured to be positioned in an arterial or venous drip chamber found on an available hemodialysis (HD) device. The diameters of these chambers can be in the range of, for example, about 18 mm to about 30 mm.

[0039] A further understanding of the various aspects of the present teachings can be obtained by reference to the following detailed description in conjunction with the related drawings briefly described below.

Brief Description of the Drawings

[0040]

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DETAILED DESCRIPTION OF THE INVENTION

[0041] In one aspect, the present disclosure is directed to a VND detection system and method that can continuously sense venous pulsations by using a high-sensitivity phase detector circuit. In some embodiments, the absence (or substantial absence) of a phase signature can be used to detect a VND event. By way of example, the sensor can be incorporated as part of a dialysis system and configured to (e.g., removably) couple to a disposable venous blood line. The sensor can include a transmitter configured to generate an ultrasonic standing wave that travels across the venous blood line to a receiver element on the opposite side of the venous blood line and reflects back from the tube boundary. The receiver transducer is used to detect the standing wave established within the diameter of the fluid-filled tube, thus enabling monitoring of the phase shift between the transmitted signal and the received signal.

[0042] Changes in the fluid dynamics of blood flow can be monitored by measuring the phase shift between the transmitted signal and the received signal of the standing wave (resonant state) caused by venous blood flow relative to an expected phase signature, such as that generated due to the patient's agitation. The measured phase shift varies with blood flow and has sufficient sensitivity to detect minute variations in the flow state resulting from agitation or an operating pump. In the following description, various features of the present teachings will be described in relation to the detection of VND, but it should be understood that the present teachings are generally applicable to detecting changes in the speed of sound or fluid dynamics of a fluid (e.g., liquid) flowing through other extracorporeal circuits such as cardiopulmonary devices.

[0043] Figures 1 and 2 schematically show a dialysis system 100 incorporating a VND detection system 102 according to one embodiment of the present teachings for the detection of venous needle dislodgement (VND).

[0044] The illustrated hemodialysis system 100 includes a dialyzer 103 that receives arterial blood via an arterial line 109 that receives blood through an arterial access point 110 (e.g., an autologous subcutaneous arteriovenous (AV) fistula). A blood pump 108a facilitates the circulation of blood through the dialysis system. Before the blood flow is introduced into the dialyzer 103, a blood diluent, such as heparin, can be introduced into the blood flow via a heparin pump 108. The dialyzer 103 filters the blood, and the filtered blood is returned to the patient via a venous return line 105 that is coupled to the patient's vein via a venous access point 107 (e.g., an autologous subcutaneous arteriovenous (AV) fistula) that includes a venous needle 107a inserted into the patient's circulatory system. An air detector / air trap 111 can be coupled to the venous return line to prevent air, if present in the blood flow, from being introduced into the patient.

[0045] As an example, the dialyzer 103 can include thousands of microporous tubes through which the blood flows and through which a dialysate solution flows outside the tubes. The pores in the tubes allow waste products and excess body fluids to move from the blood to the dialysate. The used dialysate is discarded via an outlet port of the dialyzer, and fresh dialysate is introduced into the dialyzer from a reservoir via an inlet port of the dialyzer.

[0046] Continuing to refer to FIGS. 1 and 2A and 2B, in this embodiment, the VND detection system 102 includes an acoustic sensor 114 (e.g., illustrated in FIG. 2B) having an acoustic transmission unit 114a and an acoustic receiver unit 114b that can be (e.g., removably) coupled to a portion of the venous return line 105 via a clamp 115. Various acoustic transmission and reception units can be used. For example, non-limiting examples that can be used include ultrasonic transducers sold by Ultran under model number PT25-4-X. The clamp 115 of the acoustic unit 114 includes two arms 117a and 117b that are spring-biased against each other and can removably hold a portion of the venous blood line 105 between the tips of the two arms.

[0047] The tips of the two arms 117a / 117b of the clamp 115 may include recesses 118a and 118b for receiving two attachment elements 120a / 120b, and as will be detailed below, each of the attachment elements 120a / 120b is configured to receive one of the acoustic transducer units 114a and 114b of the acoustic sensor 114. Further, each attachment element 120a / 120b includes a pair of protrusions (such as protrusions 121a / 121b), and the pair of protrusions can contact the respective pair of protrusions of the other plastic element when a portion of the venous return line is fixed between the two arms of the clamp.

[0048] Referring to FIGS. 2A and 2B, each acoustic transducer unit 114a / 114b includes a housing 112a / 112b configured to be positioned within the central opening of the attachment element 120a / 120b (as shown, for example, in FIG. 2A). The housing 112a / 112b may be formed of a suitable plastic material (such as polydimethylsiloxane (PDMS)) in this embodiment, and may include a lumen 116a / 116b that may extend from the proximal end of the housing to its distal end and exhibits a widening taper that terminates at the distal surface of the housing. Each of the housings 112a / 112b houses a piezoelectric transducer 119a / 119b for transmitting or receiving an acoustic signal.

[0049] A plurality of conductive elements 122a / 122b extend through the lumen of the housing and are electrically coupled to the transducers 119a / 119b to supply power to the transmitting transducer unit 114a, receive one or more detection signals generated by the receiving transducer unit 114b, and transmit the detection signal(s) to a signal processing / analysis module, as will be detailed below. In this embodiment, the lumens of the two transducer housings are at least partially filled with tungsten epoxy 122 for the purpose of broadening the frequency response of the transducers.

[0050] Each acoustic transducer unit 114a / 114b can be removably positioned in a respective recess of the attachment elements 120a / 120b. The acoustic transducer unit can be spring-loaded to provide flexibility in contact with a portion of the venous line held between the tips of the clamp 115. For example, the pulsation of blood flowing through the venous line can cause a certain degree of expansion and contraction of the venous line. As will be described in detail below, the flexible contact between the transmission transducer unit and the reception transducer unit 114a / 114b and the venous line (i.e., a contact that is not overly rigid and thus allows for the occurrence of radial expansion and contraction of the venous line) enables such radial vibrations of the venous line to contribute to a phase shift between the transmitted acoustic signal and the received acoustic signal.

[0051] In some embodiments, a piezoelectric film can be used to generate and / or receive an acoustic signal. As an example, FIG. 3A schematically shows an embodiment in which two piezoelectric films 400a / 400b are disposed on both sides of a portion of the venous return line 105. A clamp 401 is used to maintain the piezoelectric films 400a / 400b in place relative to the venous return line 105. In this embodiment, the piezoelectric film 400a is used to generate an acoustic signal for transmission through the venous line in a direction substantially perpendicular to the direction of fluid flow, and the piezoelectric film 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 film 400a can cause vibration of the film to generate an acoustic signal for transmission into the lumen of the line. Acoustic waves passing through the medium flowing through the line can cause oscillatory motion of the piezoelectric film 400b, which in turn results in the generation of an electrical signal.

[0052] Referring again to FIG. 1, the transmit / receive unit 200 operates under the control of the control and signal processing unit 201 to control the acoustic transmit transducer and the acoustic receive transducers 114a / 114b. In particular, the control and signal processing unit 201 operates the acoustic transmit unit to transmit a continuous wave (CW) acoustic signal across the diameter of the vein line 105, and can operate the acoustic receive unit to detect at least a portion of the transmitted acoustic signal after passing through the vein wall and the blood flow. In this way, a standing wave acoustic resonance can be established within the inner diameter of the vein line between the acoustic transmit unit and the acoustic receive unit.

[0053] The frequency of the acoustic signal can be selected to facilitate establishing a standing wave acoustic resonance within the cross-sectional dimension of the vein line. A standing wave is established in the fluid when an integer number of half-wavelength acoustic waves fit within the flow path. By way of example, the frequency of the acoustic wave can be in the range of about 1 to about 20 MHz, such as, for example, in the range of about 5 MHz to about 10 MHz, although other frequencies can be used. The selection of the frequency is generally based on the acoustic transmission characteristics of the tube material and is not intended to limit the present teachings. For example, in this embodiment, the frequency of the acoustic wave is about 3 MHz, although other frequencies can be used. This frequency is selected based on the maximum amplitude of the received signal indicating a resonance state, which depends on the diameter of the tube and the speed of sound in the fluid. As will be described in detail, in some embodiments, the frequency of the applied acoustic signal can be swept and the detected phase signal can be monitored to identify the optimal frequency for application to the acoustic sensor (i.e., the frequency that leads to the establishment of a resonant acoustic wave).

[0054] As will be described in detail below, the phase difference between the transmitted signal and the received signal changes in response to venous pulsations and / or other variations in the fluid dynamics of the flow.

[0055] As shown in FIG. 1, 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. The phase difference signal is filtered by a low-pass frequency filter 207 having a cutoff frequency of about 100 Hz in this embodiment, amplified by an amplifier 209, and then transmitted to the transceiver unit 200 that communicates with the control and signal processing unit 201.

[0056] Continuing to refer to FIG. 1, the transceiver unit 200 includes an ADC (analog-to-digital converter) module that receives the amplified phase signal and digitizes the signal. The ADC communicates with an FPGA (field programmable gate array), and the FPGA receives a reference signal from a crystal oscillator, supplies 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 may be configured to act on the received acoustic signal to detect changes in the fluid dynamics of the flowing fluid, such as a partial or complete VND event, for example, in the manner described herein.

[0057] In addition to the communication interface, the control and signal processing unit 201 includes a processor, a memory module, as well as a display and a keypad. By way of example, the processor can be a general-purpose and / or dedicated microprocessor such as an application-specific instruction set processor, a graphics processing unit, a physics processing unit, a digital signal processor, an image processor, a coprocessor, a floating-point processor, a network processor, and / or any other suitable processor that can be used in digital computing circuits. Alternatively or additionally, the processor can comprise at least one multi-core processor and a front-end processor. By way of example, in some embodiments, the memory module can include one or more permanent memory units and one or more random access memory (RAM) units. By way of example, the permanent memory unit can be one or more of a magnetic disk (e.g., an internal or removable disk), a magneto-optical disk, a semiconductor memory device (e.g., an EPROM or EEPROM (registered trademark)), a flash memory, a CD-ROM, and / or a DVD-ROM disk. Instructions and data for operating various components of the system such as acoustic transducers, blood pumps, etc., as well as for the analysis of the detected acoustic signals according to the present teachings, can be stored in the permanent memory and transferred to the RAM during execution.

[0058] Instructions and data for operating various components of the system such as acoustic transducers, blood pumps, etc., as well as for the analysis of the detected acoustic signals according to the present teachings, can be stored in the permanent memory and transferred to the RAM during execution.

[0059] The communication bus enables communication between various components of the control and signal processing unit 201. In some embodiments, instructions for the analysis of the received phase signal may be stored in a memory module. The processor can execute these instructions to analyze the received phase signal, i.e., the phase difference data. As detailed below, the analysis of the phase difference data can result in the detection of an offset from the expected signature. In some embodiments, the control and signal processing unit 201 may be configured to generate an alarm in response to the detection of such an offset of 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 speed of the pump in response to the detection of an offset of the phase signal from the expected phase signature.

[0060] More specifically, in this embodiment, the control and signal processing unit 201 may be configured to act on the phase difference signal to determine whether a VND event has occurred. In particular, the control and signal processing unit 201 may compare the measured phase difference signal, e.g., the temporal variation of the phase difference signal, to an expected phase signal related to the expected blood flow signature to identify, for example, an interruption and / or abnormal flow associated with the blood flowing in the venous line. More specifically, in this embodiment, the expected phase signature is a signature related to the heartbeat of the patient undergoing dialysis. In other words, when the venous needle is properly positioned within the patient's vein, the patient's heartbeat can generate characteristic pulsations in the venous line, which can be detected as the phase difference signature of the heartbeat. Such a heartbeat phase signature can be monitored to identify venous needle dislodgment (e.g., partial or substantially complete dislodgment). For example, venous needle dislodgment can result in a substantial disappearance of the characteristic heartbeat phase signature.

[0061] Continuing to refer to FIG. 1, the control and processing unit 201 is also configured to control the operation of the transmission / reception unit and command the transmission / reception unit to apply a desired acoustic frequency to, for example, the VND acoustic sensor 114. For example, in this embodiment, the control and processing unit 201 may be configured to send a control signal to a waveform generator (AWG) incorporated in the FPGA to generate a digital frequency signal of a desired frequency for application to the acoustic sensor 114.

[0062] A digital-to-analog converter (DAC) converts the digital frequency signal into an analog signal, and the analog signal may be stored in a buffer for application to the acoustic sensor 114. A portion of the signal can be supplied to a phase detector as a reference signal to determine the phase difference between the transmitted signal and the received signal.

[0063] In some embodiments, the control and processing unit 201 sweeps the acoustic frequency applied to the acoustic sensor 114 over a frequency range to determine an optimal acoustic frequency for application to the acoustic sensor, such as a resonant acoustic frequency.

[0064] As described above, the control and processing unit 201 receives the phase difference signal and monitors the signal to indicate the deviation of the phase signal from the expected phase signature. 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 to detect a phase deviation from the expected phase signal. As an example, FIG. 10A shows a simulated phase signal corresponding to normal operation. FIG. 10B shows the probability of a VND event derived from the phase signal. FIG. 10C shows a simulated phase signal indicating a VND event, and FIG. 10D shows the probability of a VND event derived from the phase signal shown in FIG. 10C. In this example, a plurality of independent features characterizing the phase signature were used in a probabilistic classifier algorithm to determine the likelihood that a VND event occurred. This approach has been shown to provide a fast step change response, for example as shown in FIG. 10D, while minimizing the occurrence of false alarms.

[0065] In some embodiments, to detect one or more blood clots in a fluid flow, changes in the monitored phase signal relative to the expected phase signature can be used. For example, one or more blood clots can be detected by detecting changes in the phase shift and / or amplitude of the received signal.

[0066] In some embodiments, the methods and systems disclosed in U.S. Patent No. 7,228,740, incorporated herein by reference (referred to herein as the “‘740 patent”), which measure the phase difference between a transmitted acoustic signal and a received acoustic signal and analyze the measured phase signal to obtain information about changes in the composition of blood, can be used as is known by the present teachings. Further, the methods and systems disclosed in the ‘740 patent can provide a sweep 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 compositional information.

[0067] The above embodiments are hardware-based. As detailed below, phase detection can be performed via software operations performed on digitized transmitted and received signals, as detailed below.

[0068] More specifically, FIG. 3B schematically shows a dialysis system 300 incorporating a VND detection system 302 according to another embodiment of the present teachings. Similar to the dialysis system 100 described above, the acoustic sensor 114 can be (e.g., removably) coupled to the venous return line of the dialysis system. In this embodiment, a transmit / receive unit 320 operating under the control of a control and signal processing unit 310 activates an acoustic transmit unit 114a to emit acoustic waves across the diameter of the venous return line and receives the detection signal generated by the receive acoustic unit 114b after amplification of the detection signal by a low-noise amplifier 204.

[0069] In this embodiment, the detection of the phase difference between the transmitted acoustic signal and the received acoustic signal is performed by a software module residing on the control and signal processing unit 310. For example, the amplified high-frequency acoustic signal output by the low-noise amplifier 204 is received by the transmit / receive unit 320, which then sends a digitized version of the acoustic signal to the control and processing unit 310. Then, instructions stored on the control and processing unit 310, such as those described below, can be used to determine the phase difference between the transmitted acoustic signal and the received acoustic signal.

[0070] As an example, the following procedure can be used to determine and analyze the phase signal.

[0071] The phase of a signal is given by the following equation. φ = atan(Q / I) Equation (1) Here, I is the in-phase component of the signal, typically referred to as the real component, and Q is typically referred to as the quadrature or imaginary component of the signal. According to the above equation, it is necessary to calculate I and Q in order to calculate the phase angle. The following section outlines the steps required to calculate I and Q.

[0072] [I and Q Generation] The procedure for calculating I and Q is shown in the following steps. In the following description, Rx is the signal measured from the receive transducer and Tx is the directly measured transmit signal. 1. The first step in generating I and Q is to generate the in-phase and quadrature versions of the transmit signal. This can be done by applying a Hilbert transform to the measured transmit signal. This results in the generation of a complex signal where the real component of the transformed signal is the in-phase component (simply a replica of the original transmit signal) and the imaginary component is a 90-degree phase-shifted version of the original transmit signal (also known as the quadrature component). 2. The next step is to mix the in-phase and quadrature components with the received signal (Rx). As an example, the mixing can be done by applying a point-by-point multiplication of the two signals. 3. After the signals are mixed, a low-pass filter (lpf) can be applied to the mixed signals. 4. Subsequently, in some embodiments, the data can be cropped, for example, by maintaining the middle 80% of the low-pass filtered signal. This can reduce the impact of the end effect generated by the low-pass filtering step. 5. Finally, the average of the cropped data can be determined, whereby I and Q are each obtained.

[0073] As an illustration, FIG. 3C presents an acoustic received signal obtained by using the simulation circuit described in the following example section. The presented acoustic received signal has a frequency of 3 MHz and a duration of 0.7 seconds. FIG. 3D shows the phase difference signal associated with the acoustic signal presented in FIG. 3C (i.e., the phase difference between the transmitted signal and the received signal), where the phase difference signal is obtained by using an analog circuit (AD8302 chip). FIG. 3E presents the phase difference signal associated with the acoustic signal presented in FIG. 3C, where the phase difference signal is generated using software.

[0074] As will be further described below, after the detection of a partial or complete VND, some countermeasures can be taken. For example, referring to FIG. 1, the control and signal processing unit 201 can be configured to turn off the pump 108a to delay blood loss.

[0075] In some embodiments, upon detecting a VND, the control and signal processing unit 201 is configured to delay taking any action for a predetermined time period, e.g., a time period ranging from about 5 to about 10 seconds, and continue to monitor the phase difference signal to ensure that a VND event has actually occurred. Such an approach can improve the occurrence of false detections.

[0076] In some embodiments, in response to detecting a phase fluctuation indicating a change in the fluid dynamics of the flow, the control and signal processing unit 201 may be configured to adjust the speed of the blood pump 108a. For example, the speed of the blood pump 108a may be reduced, and the phase signal may be monitored until no bubbles are detected in the flow.

[0077] The control and signal processing unit 201 may be implemented using hardware, software, and / or firmware in a manner known in the art, as taught by the present disclosure. By way of example, FIG. 4 schematically shows a hardware platform 600 that includes, among other components, a processor 602, a permanent memory 604, a 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.

[0078] As described above, in some embodiments, the acoustic sensors described herein may be configured to be positioned in an arterial or venous drip chamber found in an available HD device. The diameter of these chambers may be in the range of, for example, about 18 mm to about 30 mm.

[0079] The following examples are provided to further clarify various aspects of the present disclosure. The examples are provided for illustrative purposes and are not necessarily intended to show the optimal way to implement the present disclosure and / or the optimal results that can be obtained.

[0080] [Example 1] A simulated venous pulsation (fistula) connected to the output of a blood pump (the pump of the Fresenius dialysis machine, model: 2008T, referred to herein as the "Fresenius blood pump") via a hemodialysis needle was used to detect a simulated venous pulsation that exceeds the "noise" generated by the blood pump.

[0081] Figure 5A shows a simulation circuit used to detect venous pulsation using a phase detection system and method according to an embodiment of the present teachings. The figure shows a hydraulic circuit, a heart beat simulation pump, and the locations of the VND sensor and the dialysis needle insertion point for the Fresenius blood pump.

[0082] Fresenius medical tubing for the model 2008T dialysis machine set including a specific dialyzer part number 16LU04016 was used. The VND system was evaluated using a blood pump set at 100 - 275 ml / min and a VND sensor located 0.5 m before the venous needle.

[0083] A small peristaltic pump into which the venous needle was inserted was used to simulate venous or heart pulsation (fistula).

[0084] Figure 5B shows the hardware used to transmit and receive signals with the VND sensor and process the signals for accurate phase detection.

[0085] A dual - channel analog discovery 2 device was used to transmit a continuous wave signal (Tx1) to one of the piezoelectric elements in the VND sensor, while the signal from the second piezoelectric element was received via Rx1.

[0086] To ensure precise phase difference measurement, the same Tx1 transmission signal was also measured using the second input channel (Rx2) on the analog discovery 2 device.

[0087] An application software written in the Python (registered trademark) programming language operating on a tablet computer was used to control the Analog Discovery 2 device, process the received signal in the manner described above, and log the raw processed data.

[0088] The following procedure was used to obtain the test results. 1. Equipment Setup: 1.1 Install a 6.5 mm medical tube and a dialyzer inside the Fresenius 2008T dialysis device. Use a similar medical tube and a specific peristaltic pump to form the heart simulator circuit shown in Figure 5A. 1.2 As shown in Figure 5A, install a VND sensor in the venous line approximately 0.5 m in front of the venous needle. Use vaseline to acoustically couple the sensor to the tube. 1.3 Connect a BNC connector to the VND sensor. 1.4 Fill the blood reservoir with red dyed water. 1.5 Turn on the Fresenius dialysis device, enter the "Service" mode, and then select "Maintenance" and "Art Pump". This enables manual control of the blood pump flow rate. Set the pump speed to 100 - 275 ml / min and then turn off the pump. 1.6 Fill the venous simulation line and the dialysis line by operating both pumps simultaneously. 1.7 Start the VND application and begin the measurement. 1.8 Set up two USB webcameras to record the tablet PC screen and the dialysis needle insertion area. Start the recording before performing the following test steps. 2. Test Steps 2.1 Turn on the heart simulation pump and set it to the lowest setting (3.5 V), and confirm that pump pulsation is observed by looking at the phase output signal on the VND application. 2.2 Carefully remove the dialysis needle from the pulsation simulation line and place it on a suitable catch basin. Confirm that the phase output signal is currently flat (i.e., there is no pulsation). 2.3 Reinsert the dialysis needle and confirm that the pump pulsation is observed again by viewing the phase output signal on the VND app. 2.4 With the venous pulsation simulation pump still operating, turn on the Fresenius blood pump. 2.5 Carefully remove the dialysis needle from the pulsation simulation line. Confirm that the amplitude of the phase output signal decreases significantly, showing only the smaller pulsations from the blood pump. 2.6 Reinsert the dialysis needle very slowly and demonstrate that venous pulsation is observed only when the needle is fully inserted and there is no leakage. 2.7 Set the blood pump speed to 500 ml / min and then remove the dialysis needle from the pulsation simulation line. Confirm that the phase output signal shows a significant change in frequency components or undergoes a significant phase shift. 2.8 Reinsert the dialysis needle and demonstrate that venous pulsation is observed again only when the needle is fully inserted and there is no leakage, and the average phase value returns to the previous state.

[0089] Figures 7, 8, and 9 present oscilloscope traces of the phase detection signals related to the above-described test steps.

[0090] Referring to Figure 7, Panel A shows the observed phase signal when the venous pump is turned on. Panel B shows the phase signal after removing the dialysis needle with the venous pump operating, indicating a substantial disappearance of the characteristic signature of the phase signal observed in Panel A. And Panel C shows the phase signal after reinserting the dialysis needle, indicating the reappearance of the characteristic signature of the phase signal.

[0091] Referring to FIG. 8, Panel A shows the observed phase signal when the Fresenius blood pump is turned on. Panel B shows the phase signal after the dialysis needle is removed with both pumps operating, indicating a substantial disappearance of the characteristic signature of the phase signal observed in Panel A. And Panel C shows the phase signal after the dialysis needle is slowly reinserted, indicating that the characteristic phase signature observed in Panel A gradually reappears.

[0092] Referring to FIG. 9, Panel A shows the phase signal when the blood pump speed is set to 500 milliliters per minute and then the dialysis needle is removed with the venous pump still operating, indicating a significant change in the phase signal due to the removal of the dialysis needle. Panel B shows the phase signal when the dialysis needle is slowly reinserted, indicating that the phase signal gradually returns to the characteristic phase signal observed in Panel A.

[0093] The above results demonstrate that the test was successfully conducted, and also show the feasibility and high sensitivity of the embodiments of the system and method according to the present teachings for VND detection even when the blood pump is operating at a flow rate of 500 ml / min.

[0094] Those skilled in the art will understand that various changes can be made to the above embodiments in view of the present teachings without departing from the scope of the subject matter claimed.

[0095] [Example 2] A clinical study was conducted using the prototype VND sensor system according to the present teachings. The clinical study was performed on 10 patients, and for each patient, two data collections were made, i.e., a total of 20 data sets were collected. Among the 10 patients, 9 patients had fistula access and 1 patient used catheter access.

[0096] Through clinical studies, the system demonstrated consistent measurements among patients, and the signals resulting from the dialysis device were consistent and reproducible. Many of the measured signatures correlated with events recorded in the treatment logs documented in each data collection. Additionally, the test results showed no significant effect due to patient movement.

[0097] Examination of the data signatures collected during the clinical study indicates that the VND sensor system according to the present teachings can detect various signals generated by the normal operation of the dialysis device. Based on the measured signatures, it has been demonstrated that the measurement technique according to the present teachings can distinguish VND events from various other signatures resulting from the operation of the dialysis procedure.

[0098] For the clinical study, a VND detection sensor was retrofitted to a Model 2008T dialysis device within the CLiC device housing, which is a component of the 2008T dialysis device that non-invasively measures hematocrit value, percent change in blood volume, and oxygen saturation in real time. The VND detection sensor system includes a PZT ultrasonic transmitter and receiver, as described above. The system transmits a frequency sweep around the resonance frequency of the crystal (3 MHz) to determine the frequency that derives the maximum amplitude response. The system then transmits at this frequency and measures the phase change between the transmitted and received signals caused by changes in pressure or the speed of sound inside the blood line. As described above, by measuring the phase change, VND events can be detected, and in some cases, various other signatures resulting from the operation of the dialysis device, such as those caused by patient behavior / movement, can also be detected.

[0099] Examples of signatures in the VND data measurements during the dialysis procedure will be described below with reference to FIGS. 11 to 20.

[0100] Figure 11 shows an example of a signature related to the on and off of an arterial pump detected by the above VND system. As shown in Figure 11, during data collection, in response to turning off the arterial pump, the phase signal showed an initial drop of about 10° / second, followed by a more gradual decrease of about 0.25° / second. In contrast, in response to switching the arterial pump from the off state to the on state, the phase signal showed a sharp increase. Therefore, the phase signal shows a clear signature indicating the operating state of the pump.

[0101] In addition to the signature related to the operation of the dialysis device, in some embodiments, the VND sensor according to the present teachings can provide a signature related to the patient's heart rate. As an example, as shown in Figure 12, when the arterial pump is turned off, the heart rate signal can be easily observed.

[0102] Figure 13 compares the heart rate signal measured by the VND detection system with that measured by an infrared heart rate monitor, and Figure 14 shows more detailed features related to the cycle of a typical heart rate signal. Referring to Figures 13 and 14, it can be seen that the VND detection system used in this example was able to precisely monitor the heart rate when the arterial pump was off.

[0103] Figures 15A and 15B illustrate that it was also possible to detect the subject's heart rate signal while the arterial pump was operating. Figure 15A compares the heart rate signal detected while the arterial pump was operating with the heart rate measured by a pulse oximeter sensor worn by the patient. Figure 15B is the corresponding time-frequency data showing the heart rate signal and the arterial pump signal. In this plot, brighter colors indicate higher amplitude levels and darker colors indicate weaker signals. Here, the STFFT (Short-Time Fast Fourier Transform) method was used to extract the heart rate signal. However, the present teachings are not limited to the STFFT method, and various other data processing methods can be used to extract the heart rate signal within several cycles of the heart rate (e.g., about 2 - 3 seconds).

[0104] Figures 16A and 16B respectively show the daily log of the dialysis treatment and the signal response to the injection of a drug (e.g., Mircera) introduced in front of the venous drip chamber. As shown in Figure 16B, the injection of the drug produces a smoothly varying positive phase shift, which is distinguishable and exceeds the typical pump signal.

[0105] Figure 17 shows the signature from the automatic pressure hold test. In Figure 17, a slight increase in the phase angle can be seen, which occurs at approximately 12-minute intervals and provides a signature indicating the automatic pressure hold test performed by the dialysis device.

[0106] Referring to Figures 18A and 18B, the measured signal can show an ultrafiltration (UF) pump signal that interacts with the arterial pump signature to produce a characteristic beat frequency. The first half of Figure 18B represents the signal when the UF pump is on, where the characteristic beat frequency can be seen. At approximately 13:14, the UF pump is turned off (see Figure 18A), and the beat frequency disappears. In some embodiments, such a signature can be used to identify the operating state of the UF pump.

[0107] Figure 19 shows the signal associated with the automatic access flow bolus (resulting from the injection of a saline bolus for an automatic conductivity test performed, for example, by a dialysis device). In Figure 19, it can be seen that due to the automatic access flow bolus, a decrease in the phase data by several degrees (e.g., approximately 2°) occurs every approximately 41.5 minutes and lasts for 6 minutes.

[0108] Figure 20 shows the signal response to a change in the pumping speed. The signal was generated using the same STFFT method as described above for heart rate detection while the pump was operating. In Figure 20, it can be seen that the pump speed increased from 52 CPM to 72 CPM (i.e., 300 - 400 mL / min) at approximately 17:10.

[0109] Figures 21A and 21B show, respectively, a portion of the daily log of the dialysis treatment and the signal response to the injection of heparin. As shown in Figure 21B, the injection of the drug produces a smoothly varying positive phase shift, which is distinguishable above the typical pump signal.

[0110] Figures 22A and 22B show, respectively, a portion of the daily log of the dialysis treatment and the signal response to the injection of a drug (e.g., Hectoral) and an arterial pressure alarm that triggers to stop the arterial pump following the injection. As shown in Figure 22B, the injection of the drug produces a smoothly varying positive phase shift, which is distinguishable above the typical pump. The phase signal showed an initial drop in response to the pump stop, similar to the phase signal signature shown in Figure 11. As described above with reference to Figures 11-20, the VND detection technique according to the present teachings can provide sufficient sensitivity, reliability, and reproducibility to identify not only VND events but also various other events (e.g., the operating state of one or more pumps, drug injection, and patient arm movement), thereby enabling discrimination between VND events and other events. This can then help reduce the probability of false alarms.

[0111] In some embodiments, the communication of data (e.g., inputs and outputs) between the dialysis system and the VND detection system can be bidirectional. For example, the VND detection system can send one or more outputs (e.g., VND alarms, VND raw data (e.g., phase angle)) to the dialysis system, and the VND detection system can receive one or more inputs (e.g., dialysate temperature, dialysate conductivity, TMP, arterial pressure, venous pressure, UF rate, dialysate flow bypass, BTM arterial and venous temperatures, Hct, blood pressure, voltage, and dialysis machine alarms (e.g., blood leak, arterial pressure, venous pressure, TMP, dialysate temperature, dialysate conductivity, blood pump stop, heparin stop, and air detection)) from the dialysis system. In addition to the data identified above, the dialysis system and the VND detection system can be configured to receive and send other data (e.g., clinician inputs, drug administrations, etc.) between the two systems. In such embodiments, the data available to the two systems (the VND detection system and the dialysis system) can be used to increase the sensitivity and / or specificity of VND detection, and in particular, to reduce the probability of false alarms. As an example, the VND identification algorithm can use an input (e.g., UF pump stop or drug administration) to anticipate and / or confirm a change in the phase signal that is not a VND event.

[0112] [Example 3 - Retrofitting a VND sensor to a dialysis machine and combining the VND sensor with a blood sensing sensor] In some embodiments, the VND detection sensor according to the present teachings can be retrofitted to an existing dialysis machine, such as a model 2008T or 5008S dialysis machine sold by Fresenius Medical Care.

[0113] As an example, FIG. 23 shows the front panel of a 2008T dialysis machine equipped with a photodetector 2100 that optically distinguishes between an opaque fluid flow (e.g., blood) and a transparent fluid flow (e.g., saline).

[0114] In some embodiments, the VND detection sensor according to the present disclosure can be integrated with a photodetector. By way of example, FIGS. 24 and 25 show an example of a VND detection sensor 2300 and a photodetector 2100 integrated within the same housing 2110.

[0115] Referring to FIGS. 24 and 25, the pair of acoustic transmit / receive units 2314a and 2314b of the VND sensor 2300 are disposed within two opposing cavities provided in opposing walls of a groove 2120 configured to receive a blood line. The transmit / receive units 2314a / 2314b can be used to establish a standing resonance acoustic wave in a portion of the blood flowing through the blood line in the manner described above when blood is passing between the transmit / receive units.

[0116] As described above, the pair of acoustic transducer units 2314a and 2314b can be used to monitor the phase signal of the resonance acoustic wave to detect changes in the fluid dynamics of the flow within the blood line. In this embodiment, the structure and function of the photodetector 2100 can be maintained without modification. Further, a lid 2130 can be hingedly coupled to the housing 2110 and secured by a spring-biased latch 2140 such that the lid 2130 can hold the blood line within the groove 2120.

[0117] FIG. 26 shows an example of a sensor module 2500 that includes a VND detection sensor 2300 and a photodetector 2100 retrofitted to a 2008T dialysis machine. To support the operation of the VND retrofit sensor, a printed circuit board (PCB) 2510 can be added, for example, adjacent to the level detector PCB. To enable communication between the VND sensor and the main processor of the 2008T device, a socket 2520 can 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 smaller, the electronic components associated with the VND detection sensor 2300 can be included within the housing 2110 of the sensor module 2500, eliminating the need for an additional PCB 2510. In some embodiments, the sensor module 2500 can further include other sensors, such as, for example, a blood sensing sensor, a bubble detector, an electrolyte sensor, a venous pressure transducer, or a temperature sensor, whereby additional data can be used to increase the sensitivity and / or specificity of VND detection, and in particular, reduce the probability of false alarms. The invention described in the claims of the present application at the time of filing is appended below. [C1] A method for detecting a change in fluid dynamics of a fluid flowing through an extracorporeal circuit, comprising: establishing acoustic wave resonance across at least a portion of the cross-sectional dimension of a line associated with the extracorporeal circuit through which the fluid flows; monitoring the phase signal of the resonant acoustic wave; and identifying the occurrence of a change in the fluid dynamics of the flowing fluid when the observed phase signal of the resonant acoustic wave indicates a deviation from a predicted phase signature associated with the fluid flow. A method comprising the steps of: [C2] The method according to C1, wherein the step of establishing the resonant acoustic wave comprises transmitting an acoustic wave along the cross-sectional dimension within the portion of the line and detecting at least a portion of the acoustic wave after passing through the flowing fluid. [C3] The method according to C2, wherein the phase signal corresponds to the difference between the phase of the transmitted acoustic wave and the phase of the detected acoustic wave. [C4] The method according to C1, wherein the extracorporeal circuit comprises an extracorporeal dialysis circuit. [C5] The method according to C1, wherein the line is the venous return line of the extracorporeal dialysis circuit. [C6] The method according to C1, wherein the predicted phase signature comprises a phase signature associated with the pulsation of a patient coupled to the extracorporeal circuit. [C7] The method according to C1, wherein the extracorporeal circuit comprises the venous return line of a hemodialysis circuit. [C8] The method according to C7, wherein the change in the fluid dynamics is caused by at least a partial dislodgment of the venous return line. [C9] The method according to C8, wherein the deviation of the monitored phase signal comprises a substantial disappearance of the signature of the phase signal indicating a substantially complete dislodgment of the venous return line. [C10] The method according to C1, wherein the acoustic wave is monochromatic. [C11] The acoustic wave has a frequency in the range of about 1 MHz to about 20 MHz, as described in C10. [C12] The method according to C1, further comprising changing the frequency of the acoustic wave and monitoring the shift of the phase signal as a function of frequency to identify an optimal frequency for the acoustic wave. [C13] The method according to C12, wherein the step of changing the frequency of the acoustic wave comprises applying frequency modulation to the acoustic wave. [C14] The method according to C1, wherein the deviation from the expected phase signature is caused by one or more bubbles passing through the portion of the line associated with the extracorporeal circuit. [C15] The method according to C14, further comprising adjusting the flow rate of the fluid in response to detection of the one or more bubbles. [C16] The method according to C15, wherein the fluid is blood. [C17] The method according to C1, wherein the deviation from the expected phase signature is caused by a change in the hydrodynamic pressure of the flowing fluid. [C18] The method according to C17, wherein the change in the fluid pressure causes a deviation in the cross-sectional dimension of the line and thus contributes to the phase deviation. [C19] The method according to C1, wherein the deviation from the expected phase signature is caused by an inconsistent flow rate of the fluid. [C20] The method according to C1, wherein the fluid is blood, and further comprising adjusting the blood flow rate in response to detection of the change in the fluid dynamics of the flowing fluid. [C21] The method according to C1, wherein the fluid is blood, and the deviation of the phase signal is caused by at least one blood clot. [C22] The method according to C1, wherein the line comprises a tube. [C23] The method according to C22, wherein the tube comprises the venous return line of the extracorporeal circuit of a dialysis system, and the phase deviation from the expected phase signature is partially caused by expansion and contraction of the tube as the fluid flows through the tube. [C24] The method according to C1, wherein the deviation of the expected fluid flow signature is identified by observing a shift in the average value of the phase signal that is greater than a predetermined threshold. [C25] A method for detecting a change in the fluid dynamics of a fluid flowing in a line in fluid communication with a patient's blood vessel, comprising: establishing a resonant standing acoustic wave in a portion of the line; monitoring a phase signal of the resonant acoustic wave; Identifying the occurrence of a change in the fluid dynamics of the flowing fluid when the observed phase of the resonant acoustic wave indicates a deviation from a predicted phase signature associated with the flowing fluid; A method comprising. [C26] The method according to C25, wherein the deviation corresponds to a shift in the observed phase signal that is greater than a predetermined threshold. [C27] The method according to C26, wherein the predicted phase signature is associated with the patient's heartbeat. [C28] The method according to C27, wherein the deviation of the phase signal from the predicted phase signature is caused by one or more bubbles passing through the line. [C29] The method according to C27, wherein the line is the venous return line of a dialysis system, and the deviation of the phase signal from the predicted phase signature is caused by at least a partial dislodgment of the venous return line. [C30] The method according to C27, wherein the deviation of the phase signal from the predicted phase signature comprises a substantial disappearance of the phase signal indicating a substantially complete dislodgment of the venous return line. [C31] The method according to C27, wherein the line comprises a tube having a lumen through which blood flows. [C32] The method according to C31, wherein the deviation from the predicted phase signature is caused by a change in the hydrodynamic pressure of the fluid flowing through the tube. [C33] The method according to C27, wherein the step of establishing the resonant standing acoustic wave comprises coupling an acoustic transmitter and an acoustic detector to the line. [C34] The method according to C33, wherein either the acoustic transmitter or the acoustic detector is removably coupled to the line. [C35] The method according to C34, wherein the acoustic transmitter is positioned on one side of the line and the acoustic detector is positioned on the opposite side of the line. [C36] A system for detecting a change in the fluid dynamics of a fluid flowing within a line associated with an extracorporeal circuit, comprising: An acoustic wave transmitter for transmitting an acoustic wave into the lumen of the line such that the acoustic wave travels through a portion of the fluid traversing the lumen; A detector for detecting at least a portion of the acoustic wave after it has passed through the fluid; A phase detector for measuring a phase signal indicative of a phase difference between the transmitted acoustic wave and the detected acoustic wave; A comparator for comparing the measured phase signal with a predicted phase signature related to the fluid dynamics of the fluid flowing through the line, comprising a system, wherein an offset identified by the comparator between the measured phase signal and the predicted phase signature indicates the occurrence of an interruption in the fluid flow. [C37] The system according to C36, further comprising an analyzer for correlating the offset with an event that causes the change in the fluid dynamics. [C38] The system according to C37, wherein the analyzer is configured to analyze the phase shift to identify the event as any one of (1) the passage of one or more bubbles, (2) a blood clot, and (3) at least partial displacement of at least a portion of the line from a predicted position. [C39] The system according to C36, wherein the acoustic wave transmitter generates acoustic waves having a frequency in the range of about 1 MHz to about 20 MHz. [C40] The system according to C36, wherein the acoustic wave transmitter is configured to generate a single-color acoustic wave. [C41] The system according to C36, wherein the line comprises a venous return line of a dialysis system. [C42] The system according to C37, wherein the analyzer is configured to identify an offset of the phase signal corresponding to at least partial displacement of the venous return line. [C43] The system according to C37, wherein the analyzer is configured to correlate a substantial disappearance of the phase signal with a substantially complete displacement of the venous return line. [C44] The system according to C36, wherein either the acoustic wave transmitter or the detector is removably coupled to the line. [C45] The system according to C44, further comprising a coupling element for removably coupling either the acoustic wave transmitter or the detector to the line. [C46] The system according to C45, wherein the coupling element comprises a clamp. [C47] The system according to C46, wherein the clamp comprises a spring-loaded clamp. [C48] a dialyzer, an arterial line for providing a path for blood flow from the patient's circulatory system to an inlet port of the dialyzer, a venous blood line for providing a path for blood flow exiting the dialyzer and entering the patient's circulatory system, an acoustic sensor disposed proximate to the venous blood line, comprising the acoustic sensor is configured to establish an acoustic standing wave in a portion of the venous blood line and monitor a phase signal related to the acoustic standing wave. A dialysis system in which an offset of the monitored phase signal relative to the expected phase signature indicates at least a partial dislodgment of at least a portion of the venous return line. [C49] The dialysis system according to C48, wherein the acoustic sensor comprises a transmitter for generating the acoustic wave. [C50] The dialysis system according to C49, wherein the acoustic sensor further comprises a detector for detecting at least a portion of the acoustic wave after passing through the portion of the venous line. [C51] The dialysis system according to C50, wherein the transmitter and the detector are positioned on both sides of the venous line. [C52] The dialysis system according to C50, wherein the transmitter and the detector are positioned on the same side of the venous line. [C53] The dialysis system according to C50, wherein the acoustic sensor further comprises a phase comparator for determining a phase shift between the phase of the transmitted acoustic wave and the phase of the detected acoustic wave. [C54] The dialysis system according to C48, wherein the acoustic sensor is disposed within a housing coupled to a panel of the dialysis system. [C55] The dialysis system according to C54, wherein the housing houses both the acoustic sensor and a photodetector that optically discriminates fluid flow based on opacity. [C56] The dialysis system according to C55, wherein the housing includes a groove configured to receive the venous blood line. [C57] The acoustic sensor is a transmitter provided on a first wall of the groove for generating the acoustic wave, and a detector provided on a second wall of the groove for detecting at least a portion of the acoustic wave after passing through the portion of the venous line, wherein the second wall is on the opposite side of the first wall, The dialysis system according to C56. [C58] The acoustic sensor is a lid hingedly coupled to the housing, and a latch configured to lock the lid to hold the venous blood line within the groove, The dialysis system according to C57, further comprising.

Claims

1. A system for detecting changes in the fluid dynamics of a fluid flowing within at least one line associated with an extracorporeal circuit, comprising: An acoustic wave transmitter for transmitting an acoustic wave into the lumen of the at least one line such that the acoustic wave travels through a portion of the fluid traversing the lumen; A detector for detecting at least a portion of the acoustic wave after it has passed through the fluid; A phase detector for measuring a phase signal indicative of a phase difference between the transmitted acoustic wave and the detected acoustic wave; A comparator for comparing the measured phase signal with a predicted phase signature associated with the fluid dynamics of the fluid flowing through the at least one line; comprising wherein an offset identified by the comparator between the measured phase signal and the predicted phase signature indicates the occurrence of an interruption in the fluid.

2. The system of claim 1, further comprising an analyzer for correlating the offset with an event that causes the change in the fluid dynamics.

3. The system of claim 2, wherein the analyzer is configured to analyze the offset to identify the event as any one of (1) the passage of one or more bubbles, (2) a blood clot, and (3) at least a partial dislodgment of at least a portion of the at least one line from a predicted position.

4. The system according to any one of claims 2 to 3, wherein the acoustic wave transmitter generates an acoustic wave having a frequency in the range of about 1 MHz to about 20 MHz.

5. The system according to any one of claims 2 to 3, wherein the acoustic wave transmitter is configured to generate a monochromatic acoustic wave.

6. The system according to any one of claims 2 to 5, wherein the at least one line comprises a venous return line of a dialysis system.

7. The system according to claim 6, wherein the analyzer is configured to identify an offset of the phase signal corresponding to at least a partial dislodgment of the venous return line.

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

9. The system according to any one of claims 6 to 8, wherein either the acoustic wave transmitter or the detector is removably coupled to the venous return line.

10. The system according to claim 9, further comprising a coupling element for removably coupling either the acoustic wave transmitter or the detector to the venous return line, the coupling element comprising a clamp, and optionally the clamp comprising a spring-loaded clamp.

11. The dialysis system according to claim 6, comprising a dialyzer for receiving blood flow from a patient's circulatory system through an inlet port of the dialyzer, and the venous return line delivers blood exiting the dialyzer and entering the patient's circulatory system.

12. 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 the analyzer monitors a phase signal associated with the acoustic standing wave and is configured to identify at least a partial dislodgment of the venous return line based on an offset of the phase signal relative to an expected phase signature.

13. The system according to any one of claims 10 to 12, further comprising a sensor including the acoustic wave transmitter and the detector, the sensor comprising a phase comparator for determining a phase shift between the phase of the transmitted acoustic wave and the phase of the detected acoustic wave.

14. The system according to claim 11 or 12, wherein the acoustic wave transmitter and the detector are positioned on both sides of the venous return line.

15. The system according to claim 11 or 12, wherein the acoustic wave transmitter and the detector are positioned on the same side of the venous return line.

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