Monitoring blood distribution in subjects

Abstract

A system for monitoring blood distribution in a subject, the system comprising a processor (38) responsive to Doppler ultrasound data representing arterial blood flow in at least two different locations of the subject, such as the neck and arm, to obtain velocity (C, B1, B2, B3) or volume flow at each location, to monitor changes in a predetermined function of blood flow, and to provide an output indicative of monitored changes that may be due to blood volume centralization. This may indicate the onset of hypovolemia or hypervolemia.

Description

Technical Field

[0001] The present invention relates to systems and methods for monitoring blood distribution in a subject, detecting hypovolemia, and to methods of processing data to detect hypovolemia in a patient.

[0002] The invention also relates to a computer program product for implementing such a method. Background Art

[0003] Hypovolemia, a state of decreased blood volume (especially plasma), which may result from hemorrhage, is a common complication in critical care. The important physiological response to this is hemodynamic centralization; that is, a redistribution of blood volume from the extremities to the chest and head. The body does this through peripheral vasoconstriction, thereby limiting blood flow to the extremities, which initially enables the heart to maintain adequate blood pressure for central, vital organs. As hypovolemia develops, the body cannot compensate and it will become unstable. Blood pressure will fall, resulting in inadequate perfusion of vital organs.

[0004] At the organ level, the body is able to maintain perfusion over a range of blood pressures (i.e., through autoregulation). For some organs, such as the brain, adequate perfusion can be maintained from lower to higher blood pressures. For other organs or body parts (such as the limbs and kidneys), perfusion is only well maintained over a narrow range of blood pressures—outside this range, perfusion is directly dependent on blood pressure. This is known as autoregulation. Figure 1 , which shows the volumetric blood flow through the organs according to the blood pressure and indicates the volume state. Each figure takes into account the diameter of the blood vessels. Line 10 represents the flow towards the brain through the carotid artery, while line 12 represents the flow through the brachial artery. The state p1 is hypovolemia, p2 is normovolemia, and p3 is hypervolemia. When the blood pressure drops from p2 to p1, centralization occurs and the brachial blood flow 12 is severely affected, as shown by the slope of this area. The carotid blood flow 10 is essentially unaffected until the volume drops further (as shown by the slope of this area). Therefore, in the case of centralization caused by hypovolemia, the flow to low priority organs or limbs will be significantly reduced and depend on the blood pressure, while the flow to high priority organs (such as the brain) will remain unchanged and be largely independent of the blood pressure.

[0005] Because blood pressure is initially maintained by centralization, conventional measurements (e.g., arterial blood pressure and heart rate) are unable to identify the onset and early stages of hypovolemia leading to insufficiency of blood volume. Therefore, it is desirable to detect centralization early to allow timely intervention, i.e., to find the cause and provide supportive fluid management.

[0006] Therefore, there is a need for a method for early detection of the onset of hypovolemia in a subject. Summary of the invention

[0007] The invention is defined in the claims.

[0008] The present invention provides a system for monitoring blood distribution in a subject, the system comprising:

[0009] an input for receiving Doppler ultrasound data representing arterial blood flow in at least two different locations of a subject;

[0010] A processor adapted to:

[0011] determining a predetermined function of arterial blood flow at the location; and

[0012] monitoring changes in the predetermined function; and

[0013] An output for providing blood distribution information based on monitored changes, said two locations of said subject being at significantly different distances from the heart, preferably at the carotid artery and at the brachial, femoral or radial artery.

[0014] Since blood flow in the vascular system varies differently with centralization depending on the distance from the heart, the present invention can detect hemodynamic centralization and thus hypovolemia, and can detect hypervolemia in a similar manner based on these differences.

[0015] Many different blood flow measures can be used to monitor differential changes occurring at two different locations. An average can be taken over a selected time period, flow rate or volume flow rate. This can reduce the effects of noise and small fluctuations and can provide a common basis for comparing flows. A measure of blood flow can include flow velocity integrated over the subject's heartbeat. Flow velocity varies periodically and its integration over the heartbeat can provide a suitable flow velocity average.

[0016] The processor preferably responds to the measurement of the diameter of the artery at each location where Doppler ultrasound data representing the velocity of arterial blood flow is obtained, and the measurement of blood flow then preferably includes volume flow and flow velocity based on the diameter. The diameter can be measured, for example, by pulse ultrasound Doppler technology. In the case of using an ultrasound probe (patch) to collect blood flow data on the object, one or other of these probes can be driven to provide an image of the arterial wall that can be used to derive the diameter, using known techniques. However, the arterial diameter can be obtained by other means, such as based on the patient's height, weight, age, gender, etc. in the medical record.

[0017] Arterial blood flow preferably comprises the volumetric flow rate integrated during a heartbeat of the subject.

[0018] The predetermined function of arterial blood flow is preferably a ratio of its values. For example, this can be the ratio of blood flow velocities collected from probes at different positions, or their time-integrated values, or the ratio of volumetric blood flow or time-integrated blood flow. However, other mathematical functions can be used instead of numerical division. For example, a constant can be added to or subtracted from each flow value before the division process, or a quadratic or more complex function can be applied to determine when the state deviates from normal blood volume. A lookup table can be used in the calculation instead of a mathematical function.

[0019] The processor is preferably configured to compare the predetermined function to a predetermined range of values ​​for the function and to provide an output indicative of the comparison as an indication of potential or incipient hypovolemia or hypervolemia in the subject. For example, the ratio of the values ​​may be compared to upper and lower values ​​of a range or to a specific standard value. A high value for the ratio of carotid flow to brachial flow indicates hypovolemia, while a low value indicates hypervolemia.

[0020] The system may include a fluid management system linked to the processor, e.g., wirelessly or by a cable within a hospital network, the fluid management system being configured to provide fluid to the subject and to control the provision of fluid in response to an output from the processor indicating potential hypovolemia or hypervolemia in the subject. In this manner, knowledge that the subject may be suffering from hypovolemia may be used to provide fluid, e.g., via an intravenous drip, to treat the condition.

[0021] The processor may also conveniently be configured to provide an output indicative of the subject's cardiac output based also on blood perfusion at at least one location obtained by integrating the blood velocity at that location multiplied by the diameter of the artery at that location over time, the diameter being obtained from an input to the processor. This may provide a display of a number of haemodynamic indices and / or vital signs such as blood pressure and pulse.

[0022] The system may include at least two Doppler ultrasound probes configured to measure arterial blood flow velocity in at least two different locations of a subject and provide Doppler ultrasound data to a processor. These may be provided, for example, as a kit, and they may preferably be connected to the processor via a cable. The drive of the probe in the transmit and receive cycles may be controlled locally in the probe or in the processor or another part of the overall system.

[0023] The system may include at least one Doppler ultrasound probe configured to image an artery at one of the subject's locations to provide a measure of the artery's diameter to the processor. This may operate using pulsed Doppler techniques. This may also have its own local driver arrangement, or may be driven by the processor or another part of the overall system.

[0024] The system may include a subject monitor configured to display hemodynamic data of the subject, the hemodynamic data including an output indicative of monitored changes.

[0025] The present invention also provides a method for monitoring blood distribution in a subject, comprising:

[0026] receiving Doppler ultrasound data representing arterial blood flow in at least two different locations of a subject;

[0027] determining a predetermined function of arterial blood flow at the location;

[0028] monitoring changes in the predetermined function; and

[0029] Providing blood distribution information based on monitored changes,

[0030] Therein, the two locations of the subject are at significantly different distances from the heart, preferably at the carotid artery and at the brachial artery, femoral artery or radial artery.

[0031] Preferably, this comprises comparing the predetermined function to a predetermined range of values ​​for the function and providing an output indicative of the result of the comparison as an indication of potential hypovolemia or hypervolemia in the subject.

[0032] The two locations of the subject are preferably at substantially different distances from the heart, preferably at the carotid artery and at the brachial, femoral or radial artery. This provides information about blood flow which can detect centralised features of hypovolemia, as blood flow is initially affected more in peripheral areas of the body than closer to the heart.

[0033] The present invention also provides a computer program product comprising a computer readable storage medium having computer readable program instructions embodied thereon for causing the system to implement the above method when run on a data processor of a processor of the above system. Such a computer program product can be used to configure an existing patient monitoring system to implement an embodiment of the present invention, thereby avoiding the need to replace such an existing patient monitoring system. Thus, the availability of such a computer program product is a cost-effective way to implement embodiments of the present invention. The present invention can use a conventional ultrasound probe or a low-profile ultrasound probe (patch) suitable for coupling to the body for a long period of time. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Embodiments of the invention are described in more detail by way of non-limiting examples with reference to the accompanying drawings, in which:

[0035] Figure 1 It is a graph of blood pressure and blood flow in two different parts of the body;

[0036] Figure 2 schematically depicts a patient monitoring system that may incorporate the present invention;

[0037] Figure 3 is a flow chart of a method for configuring a 2D or 3D ultrasound patch;

[0038] Figure 4 An ultrasonic diagnostic imaging system having an array transducer probe is shown in block diagram form, which may incorporate the present invention;

[0039] Figure 5 is a graph of flow velocity versus time measured at the carotid and brachial arteries;

[0040] Figure 6 is a block diagram illustrating a method of detecting changes in blood volume distribution embodying the present invention;

[0041] Figure 7 is shown in more detail in Figure 6 A block diagram of the three probes used in the method; and

[0042] Figure 8 It is a graph of blood pressure and blood flow to various parts of the body. DETAILED DESCRIPTION

[0043] It should be understood that the drawings are schematic and not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to indicate the same or similar parts.

[0044] The present invention uses Doppler data from two different ultrasound probes placed at different locations on the subject's body, preferably superficially and fixed using patches, to detect episodes of hypovolemia or hypervolemia based on changes in the data, preferably as a ratio of measures of arterial blood flow at these locations. Since both blood velocity and volumetric blood flow rate change differently when centralization occurs depending on its proximity to the heart (see Figure 1 ), so this difference can be used to warn that centralization is occurring and therefore the subject may be suffering from hypovolemia.

[0045] This can then lead to immediate treatment, for example, appropriate fluid management, which can be provided manually or automatically. For hypovolemia, fluid replacement will be required to compensate for plasma loss, for example, for hypervolemia, diuretics can be used.

[0046] First, the entire system used in a hospital will be described. This includes an ultrasound probe and a controller connected to a monitor that displays the subject's hemodynamic information, including the status of the blood flow rate.

[0047] The ever-decreasing size of ultrasound devices means that it is now possible to deploy these devices as wearable sensors, such as patches, for example for (semi-)continuous patient monitoring in a clinical setting, such as a hospital or other medical facility. It is well known that ultrasound devices can be used to collect hemodynamic data, such as blood flow, including peak flow, flow velocity and vessel diameter, by using Doppler ultrasound, from which patient parameters such as arterial perfusion, circulating volume status, fluid responsiveness, hemodynamic stability, etc. can be derived. For example, monitoring such hemodynamic parameters in hemodynamically unstable patients, such as patients recovering from surgery, may be useful.

[0048] Typically, such monitoring results are displayed on a patient monitor, i.e., a display device that displays one or more such parameters on its display screen, wherein the parameters may be displayed as traces that progress over time on a dedicated display area, so that a caregiver can assess the patient's hemodynamic stability by evaluating the displayed traces. In addition, the patient monitor typically includes a controller that evaluates the hemodynamic data so as to generate an alarm when an abnormality in the hemodynamic data is detected, so that a caregiver can be alerted and provided with any medical care that the patient may require.

[0049] This is known, for example, from US 2010 / 0312115 A1, which discloses a method for continuously non-invasively monitoring the hemodynamic state of an object by acquiring continuous ultrasound data via an ultrasound transducer attached to the object. A continuous arterial waveform is estimated based on the acquired ultrasound data, and hemodynamic parameters for each cardiac cycle are derived from the arterial waveform. The current hemodynamic state of the object is defined by setting limits on one or more hemodynamic parameters based on changes in these parameters over an initial time period, and these limits are used to continuously monitor the hemodynamic state of the object by comparing the current state of one or more hemodynamic parameters for the object with previously determined limits for the one or more hemodynamic parameters. In the event of a change in the current state of one or more hemodynamic parameters being detected, a trigger signal or an alarm is output to the hemodynamic state monitor, or in the event that no change event is detected, the arterial parameters are converted into a continuous estimate of the blood pressure.

[0050] When a wearable ultrasound device is deployed on a patient for such monitoring, the ultrasound device is typically configurable so as to locate the patient's artery to monitor and / or optimize the signal-to-noise ratio of the ultrasound echo signals collected by the ultrasound device. For example, the ultrasound device may include a plurality of ultrasound transducers that may be individually addressed in a configurable manner so as to electronically manipulate, i.e., change the angle of the ultrasound beam generated by the ultrasound device so as to locate the patient's artery in the field of view of the ultrasound device. This may involve manually positioning the ultrasound device on the patient and then electronically configuring the ultrasound device to obtain the optimal configuration of the ultrasound device with respect to the above-mentioned signal-to-noise ratio of the echo signals collected by the ultrasound device.

[0051] Figure 2 A patient monitoring system 14 is schematically depicted, although only one probe is shown, two or more probes may be used to implement the present invention. The patient monitoring system 14 comprises a patient monitor 20 under the control of a patient monitor controller 30. The patient monitor controller 30 is adapted to receive an ultrasound signal, such as an ultrasound Doppler signal, at an input 31, which is connected to a wearable ultrasound sensor probe 32 located on a body part 34 of the patient (e.g., an arm or leg or neck) to monitor an artery 36 within the body part 34. More specifically, the wearable ultrasound sensor probe 32 is typically arranged to obtain a series of ultrasound measurements from which the patient monitor controller 30 can derive hemodynamic (hemodynamic) data relating to blood flow through the patient's artery 36, and control the patient monitor 20 to display the derived hemodynamic data on a display screen of the patient monitor 20.

[0052] The patient monitor controller 30 typically includes a processor arrangement comprising one or more processors, depicted here by way of non-limiting example by a processor 38, which receives ultrasound measurement data from the wearable ultrasound sensor probe 32 and processes the received ultrasound measurement data to obtain hemodynamic data to be displayed on the patient monitor 20, and optionally performs an evaluation of the obtained hemodynamic data in order to determine trends in the hemodynamic data over time, such as changes in the hemodynamic data across a series of ultrasound measurements received from the wearable ultrasound sensor probe 32. In the context of the present application, when referring to a series of ultrasound measurements, it should be understood that this refers to a plurality of measurements performed during one or more cardiac cycles of a patient, from which hemodynamic data relating to these cardiac cycles can be derived. Preferably, the ultrasound measurements include ultrasound Doppler measurements, from which such hemodynamic data can be derived. As Figure 2The processor arrangement shown also includes a synchronization unit 40, which performs synchronization between the processor 38 and the patient monitor 20, for example to avoid that a reconfiguration of the wearable ultrasound sensor probe 32 causes a disruption in the continuity of the hemodynamic data displayed on the patient monitor 20. Although the processor 38 and the synchronization unit 40 are shown as separate entities, it will be immediately apparent to a person skilled in the art that such units may be implemented by a single processor or a plurality of processors working in coordination (e.g., separate processors or discrete processor cores of a multi-core processor).

[0053] The patient monitor controller 30 may be responsive to a user interface 42 which may take any suitable form. For example, the user interface 42 may be a touch screen of the patient monitor 20 or a touch screen of a separate device communicatively coupled to the patient monitor controller 30 in a wired or wireless manner. Alternatively, the user interface 42 may take the form of a touch pad, keyboard, mouse, trackball, or the like, or a combination thereof, as will be apparent to one skilled in the art. The user interface 42 may be used by a user of the patient monitoring system 14 to configure which hemodynamic data is to be displayed on a display screen of the patient monitor 20. For example, a user may select one or more hemodynamic waveforms, such as (beat-to-beat fluctuations) flow or peak flow, velocity, and vessel diameter (PFV, PVV, and VDV), and derived parameters such as arterial perfusion, circulating volume status fluid responsiveness, and hemodynamic status, to be displayed on the patient monitor 20, possibly together with an ultrasound image of the patient's artery captured by the wearable ultrasound sensor probe 32.

[0054] The patient monitor controller 30 may be responsive to additional patient monitoring devices 43, such as a ventilator, ECG monitoring device, etc., from which the patient monitor controller 30 receives other vital sign information of the patient being monitored by the wearable ultrasound sensor probe 32. As will be readily appreciated by those skilled in the art, a user of the patient monitoring system 14 may configure the system to display such other vital sign information on the patient monitor 20, for example, via the user interface 42.

[0055] The patient monitor controller 30 may also include an alarm generating unit 44 for generating an alarm when the processor 38 detects an abnormality in the hemodynamic data derived from the series of ultrasound measurements received from the wearable ultrasound sensor 32. Such an alarm generating unit 44 receives an output from the computing unit 45, and it may take any suitable form, such as a speaker for generating an audible alarm, etc., for sending the alarm in sequence to a communication module of a remote device 50 such as a pager, smart phone, etc., thereby alerting the caregiver to the fact that such an abnormality has been found. Such a communication module may be a wireless communication module implementing any suitable wireless communication standard (e.g., Wi-Fi (registered trademark), Bluetooth (registered trademark)), a mobile communication standard (e.g., GSM or UMTS), etc. Alternatively, the communication module may be a wired communication module that relays the alarm signal to the remote device 50 via a wired network using any suitable communication protocol. In yet another embodiment, the alarm generating unit 44 is adapted to generate an audible alarm as well as an alarm signal for the remote device 50.

[0056] The controller 30 can compare the inputs from the different monitoring sources 32, 43 to determine whether there are actual physiological changes in the patient, so that the alarm generation unit 44 of the patient monitor controller 30 can generate the aforementioned alarm to attract the attention of the caregiver so that the patient can receive the necessary medical care.

[0057] In this example, the controller 30 provides an output signal to a fluid management system 46, such as a bedside IV drip control, to set the fluid dispensing rate based on the monitored patient status.

[0058] The wearable ultrasound sensor probe 32 may include a plurality of ultrasound transducers, such as piezoelectric transducers or preferably capacitive micromachined ultrasound transducers (CMUTs), which may be individually addressed in order to configure the operation of the wearable ultrasound sensor probe 32. For example, the individual addressing of the ultrasound transducers may be controlled to configure the beam angle of the ultrasound beam generated by the wearable ultrasound sensor probe 32, such as Figure 234 , the wearable ultrasound sensor probe 32 may be configured to provide an artery 36 of the patient in the field of view of the wearable ultrasound sensor probe 32. The wearable ultrasound sensor probe 32 may be configured to provide an artery 36 of the patient in the field of view of the wearable ultrasound sensor probe 32 after the wearable ultrasound sensor probe 32 is placed on the patient's body region 34. The wearable ultrasound sensor probe 32 may be in any suitable form, such as an adhesive patch, a sensor strapped to the body part 34, or a combination thereof. Other suitable embodiments of the wearable ultrasound sensor probe 32 for securing it to the patient's body region 34 will be apparent to those skilled in the art. The wearable ultrasound sensor probe 32 may include a configuration unit (not shown) responsive to the synchronization unit 40 of the patient monitor controller 30, which may be adapted to configure the wearable ultrasound sensor. Alternatively, a processor arrangement of the patient monitor controller 30, such as the computing unit 38 and / or the synchronization unit 40, may be adapted to configure the wearable ultrasound sensor 32, as will be explained in more detail below.

[0059] Will be aided by Figure 3 Further details on positioning and calibration of the wearable ultrasound sensor probe 32 are provided. Figure 4 A flow chart of a method for positioning and calibrating a wearable ultrasound sensor probe 32, here a 2D ultrasound sensor, is illustrated. The method begins at operation 61 with providing a wearable ultrasound sensor probe 32, after which the method proceeds to operation 63, after which the wearable ultrasound sensor probe 32 is manually positioned by a caregiver on a body region of a patient, and the wearable ultrasound sensor probe 32 is electronically calibrated, for example by a systematic variation of the beam angle generated by the wearable ultrasound sensor probe 32, in order to detect an artery 36 of the patient in the Doppler ultrasound data generated by (acquired by) the wearable ultrasound sensor probe 32. In operation 65, it is checked whether such an artery 36 can be detected. If such an artery 36 cannot be detected, the method returns to operation 63, in which the caregiver manually repositions the wearable ultrasound sensor probe 32, after which its electronic calibration is repeated until the artery 36 is found, and the method then proceeds to operation 67.

[0060] In operation 67, a region of interest near the artery 36 is selected, and a dual-plane view of the artery is generated in operation 69 to check the alignment of the wearable ultrasound sensor probe 32 with the artery 36. In operation 71, during manual repositioning of the wearable ultrasound sensor probe 32 by the caregiver in operation 73 (optionally assisted by the acoustic guidance signal generated by the alarm generation unit 44), various diameters of the artery 36 are systematically evaluated. This iterative process in operations 71 and 73 is repeated until the maximum diameter of the artery 36 in both view planes is obtained, which indicates optimal alignment of the wearable ultrasound sensor probe 32 with the artery 36. After such optimal alignment is achieved, which is a positive result of the evaluation operation 71, the method terminates in operation 75.

[0061] Positioning and calibration method of 3D wearable ultrasound sensor probe 32 Figure 3 The method for a 2D wearable ultrasound sensor 32 shown in FIG. 7 differs in that the manual repositioning in operation 73 to optimize the alignment of the wearable ultrasound sensor probe 32 with the patient's artery 36 is replaced by an operation in which this repositioning is performed by electronic beam steering of the wearable 3D ultrasound sensor probe 32 .

[0062] The above-described method 100 performed by the processor of the patient monitor controller 30 may be implemented by computer-readable program instructions embodied on a computer-readable storage medium, which, when executed on a processor device, causes the processor device to implement any embodiment of the method 100. Any suitable computer-readable storage medium may be used for this purpose, for example, an optically readable medium such as a CD, DVD or Blu-ray disc, a magnetically readable medium such as a hard disk, an electronic data storage device such as a memory stick, etc. The computer-readable storage medium may be a medium accessible via a network such as the Internet, such that the computer-readable program instructions may be accessed via the network. For example, the computer-readable storage medium may be a network-attached storage device, a storage area network, a cloud storage, etc. The computer-readable storage medium may be an Internet-accessible service from which the computer-readable program instructions may be obtained. In one embodiment, the patient monitor controller 30 is adapted to retrieve the computer-readable program instructions from such a computer-readable storage medium, and to create a new computer-readable storage medium by storing the retrieved computer-readable program instructions in a data storage device of the patient monitor control unit 30, for example in a memory device or the like constituting a part of the patient monitor control unit 30.

[0063] For the sake of completeness, Figure 4An example of components that can form a known ultrasound imaging system is shown, which can be used in the system of the present invention. The transducer array 106 of the CMUT unit 108 as described above is used to transmit ultrasound and receive echo information. The transducer array 102 of the system 110 can generally be a one-dimensional or two-dimensional array of transducer elements, which can be scanned in a 2D plane or in three dimensions for 3D imaging. One such array can be used as each of the two or more probes of the present invention.

[0064] The transducer array 106 is coupled to a microbeamformer 112, which controls the transmission and reception of signals by the CMUT array elements. The microbeamformer can at least partially beamform the signals received by groups or "patches" of transducer elements, for example, as described in U.S. Pat. Nos. 5,997,479 (Savord et al.), 6,013,032 (Savord), and 6,623,432 (Powers et al.).

[0065] The microbeamformer 112 is coupled to a transmit / receive (T / R) switch 116 via a probe cable (e.g., a coaxial line), which switches between transmit and receive modes and protects the main beamformer 120 from high energy transmit signals when the microbeamformer is not present or not in use, and the transducer array 106 is operated directly by the main system beamformer 120. The transmission of ultrasound beams from the transducer array 106 under the control of the microbeamformer 112 is directed by a transducer controller 118 coupled to the microbeamformer and the main beamformer 120 via the T / R switch 116, which receives input from a user operating a user interface or control panel 138. One of the functions controlled by the transducer controller 118 is the direction in which the beam is steered and focused. The beam can be steered straight forward from the transducer array 106 (perpendicular to the transducer array 26), or at a different angle for a wider field of view.

[0066] The transducer controller 118 may be coupled to control a voltage source 145 of the transducer array. For example, the voltage source 145 sets DC and AC bias voltages applied to the CMUT cells of the CMUT array 106, for example to generate ultrasound RF pulses in a transmit mode.

[0067] The partially beamformed signals generated by the microbeamformer 112 are forwarded to the main beamformer 120, where the partially beamformed signals from individual patches of transducer elements are combined into a fully beamformed signal and digitized. For example, the main beamformer 120 may have 128 channels, each of which receives partially beamformed signals from tens or hundreds of patches of the CMUT transducer unit 108. In this way, the signals received by thousands of transducer elements of the transducer array 106 can effectively contribute to a single beamformed signal.

[0068] The beamformed signals are coupled to a signal processor 122. The signal processor 122 may process the received echo signals in various ways, such as bandpass filtering, decimation, I and Q component separation, and harmonic signal separation for separating linear and nonlinear signals, so as to be able to identify nonlinear (higher harmonics of the fundamental frequency) echo signals returned from tissue and microbubbles.

[0069] The signal processor 122 may optionally perform additional signal enhancements such as speckle reduction, signal synthesis, and noise removal. The bandpass filter in the signal processor 122 may be a tracking filter, wherein its passband slides from a higher frequency band to a lower frequency band as echo signals are received from increasing depths, thereby rejecting noise at higher frequencies from larger echoes where there is no anatomical information in these frequencies.

[0070] The processed signal is coupled to a B-mode processor 126 and to a Doppler processor 128. The B-mode processor 126 detects the amplitude of the received ultrasound signal for imaging structures in the body (e.g., tissues and blood vessels of organs in the body). The B-mode image of the structure of the body can be formed in a harmonic image mode or a fundamental image mode, or a combination of the two, for example, as described in U.S. Pat. No. 6,283,919 (Roundhill et al.) and U.S. Pat. No. 6,458,083 (Jago et al.).

[0071] The Doppler processor 128 can process temporally separate signals from tissue motion and blood flow for detecting motion of matter, such as flow of blood cells in the image field. The Doppler processor 40 typically includes a wall filter having parameters that can be set to and / or reject echoes returned from selected types of material in the body. For example, the wall filter can be set to a passband characteristic that passes signals with relatively low amplitude from other higher velocity materials while rejecting relatively strong signals from lower or zero velocity materials.

[0072] This passband characteristic will pass signals from flowing blood while rejecting signals from nearby fixed or slowly moving targets (such as the walls of the heart). The opposite characteristic will pass signals from the moving tissue of the heart while rejecting blood flow signals, which is called tissue Doppler imaging, detecting and depicting the movement of tissue. The Doppler processor receives and processes a sequence of temporally discrete echo signals from different points in the image field, and the sequence of echoes from a particular point is called a ensemble. A series of echoes received in rapid succession in relatively short intervals can be used to estimate the Doppler shift of flowing blood, which has a Doppler frequency-to-velocity correlation, indicating the blood flow velocity. A series of echoes received over a longer period of time is used to estimate the velocity of slower flowing blood or slower moving tissue.

[0073] The structure and motion signals generated by the B-mode (and Doppler) processor(s) are coupled to a scan converter 132 and a multi-planar reformatter 144. The scan converter 132 arranges the echo signals in a desired image format according to the spatial relationship in which the echo signals are received. For example, the scan converter may arrange the echo signals into a two-dimensional sector-shaped format, or a pyramidal three-dimensional (3D) image.

[0074] The scan converter may overlay a B-mode structural image with colors corresponding to the motion of points in the image field with their Doppler estimated velocities to generate a color Doppler image that depicts the motion of tissue and blood flow in the image field. A multiplanar reformatter 144 converts echoes received from points in a common plane in a volumetric region of the body into an ultrasound image of that plane, for example, as described in U.S. Pat. No. 6,443,896 (Detmer). A volume renderer 142 converts echo signals of a 3D data set into a 3D image of a projection as seen from a given reference point, as described in U.S. Pat. No. 6,530,885 (Entrekin et al.).

[0075] The 2D or 3D images are coupled from the scan converter 132, the multiplanar reformatter 144, and the volume renderer 146 to the image processor 130 for further enhancement, buffering, and temporary storage for display on the image display 140. In addition to being used for imaging, the blood flow values ​​generated by the Doppler processor 128 and the tissue structure information generated by the B-mode processor 126 are coupled to the quantification processor 134. The quantification processor generates measurements of different flow conditions (e.g., volume rate of blood flow) and structural measurements (e.g., size and gestational age of an organ). The quantification processor 46 can receive output from the user control panel 138, such as points in the anatomical structure of the image to be measured.

[0076] The output data from the quantification processor is coupled to the image processor 136 to generate measurement images and values, wherein the images are on the display 140. The graphics processor 136 may also generate graphic overlays for display with the ultrasound image. These graphic overlays may include standard identifying information, such as the patient name, date and time of the image, imaging parameters, etc. For these purposes, the graphics processor receives input from the user interface 138, such as the patient name.

[0077] The user interface is also coupled to the transmit controller 118 to control the generation of ultrasound signals from the transducer array 106, and therefore the images generated by the transducer array and the ultrasound system. The user interface may also be coupled to a multi-planar reformatter 144 to select and control the planes of a plurality of multi-planar reformatted (MPR) images, which may be used to perform quantitative metrics in the image field of the MPR image.

[0078] As will be appreciated by those skilled in the art, the above-described embodiments of the ultrasound diagnostic imaging system are intended to give non-limiting examples of such ultrasound diagnostic imaging systems. The skilled person will immediately appreciate that several variations in the architecture of the ultrasound diagnostic imaging system are possible without departing from the teachings of the present invention. For example, as also indicated in the above-described embodiments, the microbeamformer 12 may also be omitted, the ultrasound probe 104 may not have 3D imaging capabilities, etc.

[0079] Now refer to Figures 1 to 7 Describes the preferred embodiment of the present invention. It will be understood that this may be incorporated into the above reference Figure 2 and 3 or Figure 4 In systems of the type described, two or more ultrasound probes are used and placed at separate locations on the patient's body to detect arterial blood flow and preferably also arterial diameter.

[0080] Place two or more low-cost ultrasound patches (such as Figure 2 The probes 32 are respectively placed on the skin over the large arteries (e.g., the carotid and brachial arteries) to detect the onset of centralization by monitoring the immediate phase of blood flow redistribution. Typically, at rest, brachial blood flow is four times lower than carotid blood flow. The blood flow in the radial and femoral arteries has its own typical ratio to the carotid blood flow. This ratio forms a measure of blood volume distribution that is independent of the patient and cardiac output. Changes in the ratio of the (highest, lowest, or average) brachial artery volume flow (or flow velocity) to the (highest, lowest, or average) carotid artery volume flow (or flow velocity) between the sensor sites indicate volume redistribution and centralization in critical illness, such as limb ischemia in vascular surgery. This low-cost, easy-to-implement solution allows timely intervention in hemodynamic insufficiency and supports optimal fluid management of perioperative patients.

[0081] Figure 5 A simple example of how the signal can be analyzed to detect volume (re)distribution is given. The carotid flow velocity C displayed over three heartbeats is compared to the brachial artery flow velocity, and trace B1, with a ratio of values ​​less than 2 (here about 1.2), indicates excessive blood volume (centralization), trace B2, with a ratio of 4, indicates normal blood volume (no centralization), and trace B3, with a ratio greater than 8, indicates insufficient blood volume (centralization). In this example, the ratio of peak velocities is used as a proxy for the ratio of "stroke volume" (i.e. the amount of blood flowing through the artery in each heartbeat). Another option is to integrate the Doppler velocity during the heartbeat and obtain the corresponding "distance" ratio. Alternatively, the volume flow rate can be obtained by integrating the Doppler velocity measurements (over the relevant period) and multiplying by the arterial diameter to obtain the beats per minute and the actual volume flowing through the artery per minute; multiplying this rate by the duration of the heartbeat gives the "stroke volume". The arterial diameter may be found in a calibration table that takes into account sex, age, height and weight, measured by a priori point verification and input into the monitor controller 30, or, as described above, may be measured by an ultrasound sensor probe, for example by imaging 32. Pulsed Doppler imaging may be used for this purpose. The same probe as for Doppler velocity measurements may be used.

[0082] Figure 6 Schematically depicts how the flow signals are input into an algorithm run by a program in the processor 38 of the controller 30, which derives blood volume (re)distribution. In steps 201 and 202, blood flow signals are obtained from the carotid and brachial (or other) arteries, e.g. Figure 5 The Doppler flow velocity signal shown. As described above, by integrating the Doppler velocity over each cycle (e.g., one heartbeat) and multiplying by an estimate of the arterial diameter, a volume estimate for each location can be calculated. The ratio of these volume estimates (e.g., Vbrachial / Vnectal) is then determined. In step 204, the program determines whether the ratio is obtained for the first time in the current operation of the monitoring system since initialization. The first ratio in the estimated time series is generally considered to be a reference ratio. If the first ratio is considered to be within the expected range (e.g., Vbrachial / Vnectal is 3-5), the ratio is set or reset to a reference value in step 208. Successive ratios are compared to the reference value and stored as updated ratios in step 206. When the new ratio is significantly different from the reference (e.g., a difference of 10% or more), a notification can be provided in step 210 because this indicates that a change in blood volume distribution has occurred (an increase indicates centralization, while a decrease indicates recovery or fluid overload). In addition, if the first ratio is far outside the expected range (e.g., Vbrachial / Vnectal>6), a notification can be provided in step 210 because this can indicate centralization.

[0083] Reference Figure 5 and the range indicating hypovolemia, etc., the reference value of the ratio of the flow rate is set to 4. If it becomes more than 8, it indicates hypovolemia, and if it is less than 2, it indicates hypervolemia. This simple algorithm can be adjusted by setting a ratio reference value in step 208 and using predetermined percentages above and below the reference value as upper and lower thresholds.

[0084] The output from step 210 is Figure 2 The additional input 43 of the controller 30 is processed to generate a hemodynamic display in the monitor 20 and optionally an alarm from the unit 44. This indicates to the caregiver the onset of hypovolemia or hypervolemia, resulting in a centralization of blood volume. As described above, this indication can be compared with other monitored signs. This can enable a distinction between hypovolemia and hypervolemia.

[0085] One result may be that the controller 30 automatically signals a fluid management unit 46, such as a bedside controller, to increase or decrease the rate of intravenous saline or plasma flow to the patient.

[0086] In more detail, the program walks through Figure 7 The steps shown in the figure, wherein the probe configuration is determined at initialization to set the number of probes and their positions. Successively, each probe is configured according to these positions. Specifically, the size of the scanning area (or volume) is set, and the pulse characteristics of the probe, such as frequency, power, and number of pulses, are set.

[0087] To quantify velocity in a specific artery, a PW (Pulsed Wave) Doppler is used to set the ROI and measure the area. Using CW (Continuous Wave) Doppler will give an average of all flow in the US beam (not limited to a fixed depth). Both modes can therefore be used to advantage.

[0088] In this example, three probes (patches) A, B and C similar to probe 32 are provided and attached to the carotid, brachial and femoral arteries of the body, respectively. Probes A, B and C are set in steps 302, 304 and 306, and then in steps 308, 310 and 312, each probe performs Doppler velocity measurements in a configured measurement region over a time period that typically spans the cardiac cycle. From these measurements, a ROI of a region of interest and a quality estimate of the detected flow can be derived. The ROI represents the estimated location of the artery through which the flow is measured. The quality estimate is used to indicate whether a reliable flow measurement can be performed.

[0089] In step 314, the probe configurations are all updated. For each probe, possible probe configurations are determined to measure flow continuously. With these settings, in steps 316 and 318, probes A and B are reconfigured (i.e., the steering angles and drive schemes of the probes are set for focus and frequency) to achieve optimal continuous flow measurement. This requires measuring the velocity of a specific area, updating the ROI to track possible motion of the artery (or probe), and updating the phase estimate in the cardiac cycle. If the scan quality is insufficient during initialization, after step 314, the probe (in this example, probe C) can be temporarily disabled in step 320 for continuous flow measurement. For each enabled probe, the measurement parameters are updated simultaneously, and then the scan is performed simultaneously in boxes 322 and 324, respectively. In box 322, the regional ROI is updated in step 326, and the scanning period is updated in step 328. In box 324, the regional ROI is updated in step 332, and the scanning period is updated in step 334. Doppler scanning is performed in steps 330 and 336. The flow data from these scans is processed in step 340 to determine the cardiac cycle period, and the (average) ratio from each scan is determined in step 350. In this example, only the data from probes A and B are processed to derive the ratio.

[0090] Figure 7 The program shown may be repeated regularly, for example at 15 minute intervals.

[0091] When two ultrasound patches are used for flow monitoring in two major arteries (e.g. the carotid and brachial arteries or the brachial and radial arteries), the flow signals obtained can also be used to provide an estimate of cardiac output. This can be provided by the controller as an additional output for display on the monitor 20. In principle, this is also feasible using only one ultrasound patch. When only one patch is used, it should be placed on an artery through which perfusion is highly dependent on cardiac output. The brachial artery or an artery located downstream thereof (e.g. the radial artery) is a good choice. However, using two patches not only doubles the accuracy, but also extends the dynamic range for cardiac output when the second (more peripheral) patch is placed on an artery with more stable perfusion over a larger dynamic output range. The dynamic range of the system (i.e. the range of cardiac output that it can reliably measure) will then increase accordingly because two patches or the measurements of two patches can be used. As an example, and with further reference to Figure 1, as cardiac output is gradually reduced, radial perfusion will decrease first, followed by brachial perfusion. In this way, radial perfusion will quickly reach a minimum value when cardiac output decreases (i.e., there is no longer any correlation between radial perfusion and cardiac output), while brachial perfusion still exhibits a dependence on cardiac output. Adding another patch, for example to the carotid artery, could increase the dynamic range of the system to very high and very low cardiac outputs (i.e., the range of the brain's autoregulatory range).

[0092] Although the above method only describes the use of probes at two locations, the use of multiple probes in multiple arteries is a way to increase range or resolution. Figure 8 As shown in FIG. 1 , in addition to the carotid artery, line 10, and the brachial artery, line 12, the blood flow of the heart, line 401, and the kidney (renal artery), line 402, is also measured, which is consistent with the Figure 1 Lines 10 and 12 are identical. From a Figure 8 Starting with an arterial probe that has flow properties similar to those of lines 401 and 12, a wide range of varying pressures can be measured, but the resolution / accuracy is low. Adding probes to an artery that exhibits flow properties similar to those of lines 10 and 402 between the extremes will increase the accuracy of the measurement. Vice versa, when starting with a probe with properties similar to those of lines 401 and 10, adding a probe with properties such as line 12 will increase the range. Actual blood pressure values ​​can be derived from the flow measurements, and multiple flow measurements can be made simultaneously at specific locations where the relative width of the constant pressure range is known, such as Figure 8 The figure shows that when the flow is measured at multiple locations, multiple pressure values ​​BP1 from BP2 and BP3 can be distinguished according to the ratio between the flow rates using lines 401, 10 and 402 according to a simple algorithm. On the other hand, for other pressures (such as BP4 from BP5), these pressure differences are indistinguishable. The change in flow provides the input for centralization.

[0093] Changes in the diameter of the inferior vena cava (IVC), for example, may provide additional information about the fluid status of a patient and may be used in conjunction with monitoring of changes as described in accordance with the present invention.

[0094] One aspect of the present disclosure is a diagnostic method of making and using blood flow measurements at two different locations on the body. This method of detecting episodes of hypovolemia (and / or hypervolemia) comprises making Doppler ultrasound measurements of arterial blood flow velocity at at least two different locations on a subject, preferably simultaneously or in rapid succession, to obtain a measurement of blood flow at each location, monitoring changes in a predetermined function of the measurements of blood flow, and providing an output indicative of the monitored changes. Preferably, the output includes information as to whether the monitored changes indicate hypovolemia or hypervolemia.

[0095] As described above, embodiments utilize a controller. A controller can be implemented in a variety of ways using software and / or hardware to perform the various functions required. A processor is an example of a controller that employs one or more microprocessors that can be programmed using software (e.g., microcode) to perform the required functions. However, a controller can be implemented with or without a processor, and can also be implemented as a combination of dedicated hardware for performing some functions and a processor (e.g., one or more programmed microprocessors and associated circuits) for performing other functions.

[0096] Although in the described embodiments the controller is separate from the probes, its functionality may alternatively be integrated into one or more of the probes.

[0097] The communication between the probe and the controller is described as wireless in the embodiments, but they can be wired by having a cable between the probes or between the probe and the controller or between the two. In this case, the probe can be powered by an external power source (such as the controller), so no internal power source is required. However, the wired connection may make the use of the probe more difficult and painful.

[0098] The probe is conveniently mounted on the surface of the skin in the form of a patch. However, the present invention may use more invasive techniques, such as a probe within the tissue of the subject.

[0099] Examples of controller components that may be used in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field programmable gate arrays (FPGAs).

[0100] In various implementations, a processor or controller may be associated with one or more storage media, such as volatile and non-volatile computer memory, such as RAM, PROM, EPROM, and EEPROM. The storage media may be encoded with one or more programs that perform the desired functions when run on one or more processors and / or controllers. The various storage media may be fixed within a processor or controller, or may be transferable so that one or more programs stored thereon may be loaded into a processor or controller.

[0101] Those skilled in the art will be able to understand and implement other variations of the disclosed embodiments in practicing the claimed invention by studying the drawings, the disclosure and the claims. In the claims, the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. Although specific measures are recited in mutually different dependent claims, this does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be interpreted as limiting the scope.

Claims

1. A system for monitoring blood distribution in a subject, the system comprising: An input unit (31) for receiving Doppler ultrasound data representing a first arterial blood flow value at a first location of the subject and a second arterial blood flow value at a second location of the subject; A processor (38) adapted to: performing a first comparison of the first arterial blood flow value and the second arterial blood flow value, wherein the first comparison comprises calculating a ratio between the first arterial blood flow value and the second arterial blood flow value, wherein the ratio is related to the blood distribution in the subject; and performing a second comparison of the ratio between the first arterial blood flow value at the first location of the subject and the second arterial blood flow value at the second location of the subject with a first threshold associated with hypovolemia and a second threshold associated with hypervolemia; When the ratio is greater than the first threshold, hypovolemia is detected; and When the ratio is less than the second threshold, detecting the hypervolemia; and An output unit (45) is configured to generate an output indicating the hypovolemia when the ratio is greater than the first threshold, and to generate an output indicating the hypervolemia when the ratio is less than the second threshold.

2. The system according to claim 1, wherein: The first arterial blood flow value comprises an arterial blood flow velocity integrated over a period of a heartbeat of the subject.

3. The system according to claim 1, wherein: The processor (38) is responsive to a measurement of a diameter of the artery at the first location, and wherein the volumetric flow rate of the blood is based on the diameter and flow velocity.

4. The system according to claim 3, wherein: The first arterial blood flow value comprises the volumetric flow rate integrated over a period of a heartbeat of the subject.

5. The system according to any one of claims 1 to 4, wherein: The processor (38) is configured to generate an output indicative of the subject's cardiac output based on blood perfusion in at least the first location, the blood perfusion being obtained by integrating over time a blood flow velocity at the first location multiplied by a diameter of an artery at the first location.

6. The system according to any one of claims 1 to 4, comprising at least two Doppler ultrasound probes (32), the at least two Doppler ultrasound probes being configured to measure arterial blood flow velocity of the object in at least the first position and the second position, and to provide the Doppler ultrasound data to the processor (38).

7. The system of any one of claims 1-4, comprising at least one Doppler ultrasound probe (32) configured to image an artery at one of the first position or the second position of the subject to provide a diameter of the artery to the processor (38).

8. The system of any one of claims 1-4, comprising a subject monitor (20) configured to display the output indicative of the hypovolemia or the hypervolemia.

9. The system according to claim 1, wherein: The first location comprises a carotid artery, and wherein the second location comprises a brachial artery, a femoral artery, or a radial artery.

10. A method performed by a system for monitoring blood distribution in a subject, comprising: receiving Doppler ultrasound data representing a first arterial blood flow value at a first location on the subject and a second arterial blood flow value at a second location on the subject; performing a first comparison of the first arterial blood flow value and the second arterial blood flow value, wherein the first comparison comprises calculating a ratio between the first arterial blood flow value and the second arterial blood flow value; performing a second comparison of the ratio between the first arterial blood flow value at the first location of the subject and the second arterial blood flow value at the second location of the subject with a first threshold associated with hypovolemia and a second threshold associated with hypervolemia; when the ratio is greater than the first threshold, hypovolemia is detected; When the ratio is less than the second threshold, detecting the hypervolemia; and An output indicative of the hypovolemia is generated when the ratio is greater than the first threshold, and an output indicative of the hypervolemia is generated when the ratio is less than the second threshold.

11. The method according to claim 10, wherein: The first location comprises a carotid artery, and wherein the second location comprises a brachial artery, a femoral artery, or a radial artery.

12. A computer program product comprising a computer readable storage medium having computer readable program instructions embodied thereon, which when executed on a data processor of the processor (38) of the system according to any one of claims 1 to 9, cause the system to implement the method according to any one of claims 10 or 11.

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