MEASUREMENT OF BLOOD FLOW IN A BLOOD VESSEL

Description

[0001] This document describes an ultrasound device for measuring fluid flows, in particular for measuring blood flow in a blood vessel. The ultrasound device comprises measuring electronics, at least three piezoceramics, and a housing. According to the invention, each piezoceramic is arranged within the housing at a different angle to the sound emission surface of the housing. Furthermore, the housing includes at least one means for attaching it to a patient or an aid.

[0002] Arterial blood flow through the carotid artery (Latin: Arteria Carotis Communis) can serve as a representative measure for assessing the effectiveness of resuscitation measures. The current state of the art in evaluating chest compressions still relies on compression rate and compression depth. However, the actual blood flow generated and the associated cerebral oxygenation are unknown to both the rescuer and the medical personnel. Animal studies have already demonstrated that survival after cardiac arrest is directly dependent on cerebral blood flow during resuscitation [1]. Thus, patients often survive the resuscitation event but may not recover due to a poor neurological prognosis.Even if spontaneous circulation is achieved, the neurological outcome of the patients is directly dependent on the quality of resuscitation and the minimization of "no-flow" periods, during which no oxygen-rich blood is transported to the brain.

[0003] The neural structures of the brain are sensitive to oxygen deprivation and can suffer severe, irreversible damage at an early stage [2]. The consequences of ineffective resuscitation may not become apparent until later in the course of therapy. Under these circumstances, the patient's seemingly stable condition can lead to premature discharge, with a relapse into cardiac arrest occurring only after leaving the hospital. Monitoring carotid blood flow during resuscitation can significantly support the rescuer's performance by triggering a signal in the event of insufficient blood supply. Therefore, measuring this informative surrogate parameter is essential, as it can provide information about the quality of chest compressions in both in-hospital and pre-hospital settings and allows for indirect inferences about cerebral blood supply.

[0004] Two methods are most commonly used in hospitals to determine the time-resolved blood flow in arteries and veins. In patients with invasive arterial lines, blood flow during resuscitation can be recorded using pressure curves. However, invasive lines for blood pressure measurement are less common outside of intensive care units and are usually only inserted in outpatient settings after successful resuscitation.

[0005] Modern ultrasound devices with Doppler sonography combined with B-mode imaging offer a fast and generally non-invasive alternative. Doppler sonography utilizes the measured frequency differences between emitted and received ultrasound signals, created by the Doppler effect, to detect moving matter. The ultrasound waves reflected by red blood cells can thus be used to measure the velocity of blood flow during resuscitation.

[0006] Doppler ultrasound measurement of arterial blood flow in the common carotid artery is theoretically possible during resuscitation, but devices designed for stationary use are not practical for this application. The ultrasound transducers and computers used for measurement / analysis are too large and require mains power. Furthermore, the transducers require manual operation; long-term, fixed attachment to the patient, where no one needs to hold the device, is practically impossible.

[0007] However, the device also lacks additional mounting options and a compact design that would allow for quick, easy, and robust attachment of the ultrasound transducer over an artery without compromising it. Furthermore, interpreting the results of B-mode and Doppler sonography requires a certain level of expertise that is not universally available in emergency medical services. Therefore, automated evaluation of hemodynamic parameters would be necessary. This, in turn, requires additional signal processing steps to compensate for artifacts caused by body and transducer movements.

[0008] Portable ultrasound devices are already commercially available and offer features such as Doppler sonography. The L7 Linear Handheld Ultrasound Scanner from Clarius (Vancouver, CA) is one such device, which uses multiple integrated ultrasound transducers to detect tissue structures and movements.

[0009] Another solution was developed by the research group led by Joseph Eibl et al. (EP 3823536). This involves an ultrasound module that is attached to a patient's neck and then performs Doppler sonographic measurements. The frequency differences are recorded and analyzed within the module, and wireless communication allows the measurements to be visualized on external devices such as tablets or similar computers. The ultrasound patch is intended for long-term monitoring and analysis of blood flow in human vessels. The measurement is performed using continuous Doppler ultrasound, which is achieved via two piezoelectric ceramic elements within the device. One element continuously emits ultrasound signals, and the other ceramic element continuously receives the reflections of these signals.

[0010] However, handling, attachment, and measurement procedures reveal room for improvement. The device's LEDs only indicate the Bluetooth connection status; therefore, the system lacks an independent way to inform the user about the quality of the generated blood flow. Measured values ​​must be displayed via an additional device, a fact that makes its use less appealing for emergency situations. This negates the advantage of attaching the device to the patient, as a tablet or PC now has to be handled briefly to set up a display.While the adhesive strip allows for continuous measurement without additional device handling, it effectively prevents rapid adjustment of the position. Inaccurate patch placement above the carotid artery or vessel displacement would significantly impact measurement effectiveness. The continuous-wave Doppler method, using a transmitter and receiver, offers the advantage of broad coverage of the scanned area. However, this also results in the capture of a large proportion of interfering signals (e.g., tissue movement), the filtering of which can affect the quality of the blood flow signal. This disadvantage is exacerbated by the motion artifacts generated during resuscitation, as demonstrated in the color Doppler images from a resuscitation by Koch et al. [3].Furthermore, quantitative position and orientation of the carotid artery using only one receiver probe is impractical, making accurate determination of quantitative blood flow difficult. If the area above the carotid artery needs to be exposed during resuscitation, rapid removal and reattachment of the system is also impossible. Due to the use of only one receiver element, determining the angle between the vessel axis and the ultrasound beam is also not possible. Individual positions of the carotid artery relative to the skin surface cannot be taken into account in the calculation, thus distorting the blood flow calculation.

[0011] The solutions described either do not allow for longer-term measurements without a user having to hold the ultrasound probes in position, or do not allow any change to the measurement site after the ultrasound module has been attached to the neck.

[0012] The limited flexibility in positioning the desired system is a major drawback, as no adjustments to the measurement position can be made during resuscitation. Furthermore, the area on the neck occupied by the measuring device cannot be quickly removed to allow for easy reattachment after patient repositioning, the insertion of invasive access devices, or other procedures. In addition, the devices rely on external systems and do not provide direct information to the user.

[0013] WO 2017 / 096487 discloses a portable monitoring device that operates exclusively with transducer pairs.

[0014] EP 3 505 071 A1 discloses an ultrasound head for a continuous-wave ultrasound device for measuring blood flow in the patient.

[0015] US 2006 / 241460 A1 discloses a device for measuring the rheology of blood and an associated method using ultrasound.

[0016] US 2017 / 332995 A1 discloses a system and a method for the automated assessment of a patient's hemodynamic properties.

[0017] Based on the prior art, the object of the present invention is therefore to overcome the disadvantages of the prior art and to provide a method for measuring blood flow in a blood vessel which reliably and directly provides quantitative information about the blood flow in a blood vessel, wherein the ultrasound device used can be quickly attached and removed.

[0018] For this purpose, the invention provides a method according to claims 1 to 3. Detailed description

[0019] The ultrasound device is used to measure blood flow in a blood vessel. The ultrasound device comprises measuring electronics, at least three piezoelectric ceramic elements, and a housing. The at least three piezoelectric ceramic elements are arranged within the housing.

[0020] In one version, the housing has exactly three piezoceramics.

[0021] Each piezoceramic element within the housing is positioned at a different angle to the housing's sound emission surface. This angle is determined by the angle between the normal of the piezoceramic element and the normal of the sound emission surface. The housing wall through which the sound waves generated by the piezoceramics exit towards body tissue, and through which the reflected ultrasound waves enter the housing, is referred to as the sound emission surface.

[0022] In one embodiment, the piezoceramics can be arranged at an angle between 90° and 0°, preferably between 75° and 0°, to the sound emission surface of the housing. The angles of the piezoceramics differ between ±5° and ±30°, preferably between ±10° and ±25°.

[0023] The piezoceramics are mounted on a coupling path within the housing. This coupling path is preferably made of biocompatible materials with low damping and good impedance matching to the piezoceramics and the skin. The housing design ensures that the positions, and therefore the angles, of the piezoceramics within the housing are known.

[0024] Any conventional ceramic suitable for use in ultrasound applications can be used as the piezoceramic. A composite ceramic is preferred. Particularly preferred is the use of a filled piezoceramic, such as a lead zirconate titanate ceramic (PZT ceramic) with a polymer filling. The geometry of the piezoceramic is selected to generate a substantially homogeneous sound field. The piezoceramic preferably has a rectangular or elliptical cross-section. The size of the piezoceramic is chosen to fit within the housing, allowing the sound emission surface of the housing to be positioned over the entire area of ​​the patient's neck.

[0025] All piezoceramics are designed to emit continuous wave Doppler ultrasound signals (cw) and / or pulsed Doppler ultrasound signals (burst).

[0026] The device is designed to operate in at least three modes, where each mode refers to a specific measurement sequence. For example, different piezoceramics are used in different modes for emitting and / or receiving ultrasound signals.

[0027] The first mode, hereinafter referred to as Mode 0, served to assess the correct position and coupling of the ultrasound device according to the invention to a patient. In Mode 0, one piezoceramic element acts as a transmitter, while all available piezoceramics act as receivers. When pulse Doppler signals are transmitted, all piezoceramics, including the transmitting element, act as receivers.

[0028] A second mode, referred to below as Mode 1, is used to determine the vessel depth, vessel diameter, and Doppler angles of the piezoceramics. In Mode 1, all piezoceramics are used sequentially as transmitters, while all available piezoceramics simultaneously receive the reflected ultrasound signal. When pulse Doppler signals are transmitted, all piezoceramics, including the transmitting ceramic, function as receivers.

[0029] A third mode, hereinafter referred to as Mode 2, is used for quantified blood flow measurement. In Mode 2, one piezoceramic acts as the transmitter, while all available piezoceramics simultaneously act as receivers. When pulse Doppler signals are used, all piezoceramics, including the transmitting ceramic, function as receivers. In a preferred embodiment, the ultrasound device is configured to measure in at least three modes, wherein in all modes one piezoceramic acts as the transmitter and all available piezoceramics act as receivers, and wherein in at least two modes all available piezoceramics that function as receivers act as receivers simultaneously.

[0030] In the context of the present invention, "at the same time" means that the respective piezoceramics measure the ultrasound signal received by the piezoceramics at exactly the same time.

[0031] Simultaneously measuring the ultrasound signal at at least two different angles enables a very precise determination of the Doppler angle. The Doppler angle is the angle between the sound path and the direction of blood flow in the blood vessel. The angles of the piezoceramics to the sound exit surface are known from the design of the ultrasound device.

[0032] The ultrasound device also includes integrated measuring electronics for controlling the piezoceramics. These electronics are responsible for energy control, data acquisition, demodulation, audio processing, and evaluation of the Doppler signals. Among other things, the electronics supply electrical energy to the piezoceramics for ultrasound generation. The housing also contains a circuit board with a multi-pole cable connection to the measuring electronics. This circuit board is connected to the piezoceramics and is responsible for amplifying and demodulating the transmitted and measured signals.

[0033] In one version, the measuring electronics and the circuit board are set up to activate separate but also synchronized transmit and receive periods for each piezoceramic element.

[0034] In one version, the measuring electronics also include a data storage device. The measurement signals from the ultrasound device can be stored on this data storage device. This makes it possible to evaluate the measurement data after an animation process and, for example, to store it in an electronic patient record.

[0035] In one version, the measuring electronics therefore still have an output for a connection to a network, for example via WLAN, Bluetooth or cable, and / or an output for an external storage medium, such as a USB port. Stored data can be read out via this output(s).

[0036] In one embodiment of the present invention, the measuring electronics are arranged in the same housing as the at least three piezoceramics. In another embodiment, the measuring electronics are arranged in a separate housing spaced apart from the housing containing the at least three piezoceramics. In this embodiment, the ultrasonic device accordingly comprises two housings. The housings are connected to each other by suitable cables.

[0037] The ultrasound device is preferably powered by a suitable portable energy storage device and / or by a connection to the mains power supply via an adapter.

[0038] The ultrasound emitted by the ultrasound device falls within the range of non-invasive diagnostic ultrasound. Non-invasive diagnostic ultrasound is defined in DIN EN 60601-2-37 (Medical electrical equipment, Part 2-37). By definition, non-invasive ultrasound does not constitute an intervention on the body being examined.

[0039] In one embodiment, the housing further comprises at least one means for attaching the housing to a patient or to an assistive device. Preferably, the ultrasound device is attached to the patient's neck by means of the at least one means of attaching the housing. The ultrasound device is thus attached to the body in a detachable and non-invasive manner. If the ultrasound device is attached to an assistive device by means of the at least one means of attachment, the assistive device is preferably suitable for being attached to the patient's neck. In one embodiment, the assistive device to which the housing can be attached by means of the at least one means of attachment is a Laerdal Stiffneck collar.

[0040] In a preferred embodiment, the housing has exactly one means for attaching the housing to a patient or to an assistive device.

[0041] The at least one fastening device is selected from the group comprising plastic brackets, neck collars and cuffs, in particular neck collars and cuffs made of elastic textile. The at least one fastening device allows the ultrasound device to be fixed to the body, especially to a person's neck.

[0042] Devices that are attached to the neck using self-adhesive materials are known in the prior art. A disadvantage of these devices is that body hair can make application and skin contact difficult or even impossible. Furthermore, the adhesive material, such as a plaster, blocks access to the neck. After removing the self-adhesive material, skin irritation can occur, or existing skin conditions can be exacerbated. Attachment with a self-adhesive material is also less robust against neck rotation or tissue movement, as the neck is not fixed in place. This can cause the measurement area to shift, potentially resulting in insufficient coverage of a blood vessel.

[0043] The device does not require self-adhesive materials for attaching the ultrasound probe to the body. This is particularly advantageous when measuring blood flow in a blood vessel in a patient's neck. A key aspect of measuring blood flow in a blood vessel is the correct positioning of the measuring piezoceramics over the vessel in question. Here, the ultrasound probe offers the advantage that its position can be quickly changed and adjusted as needed. Skin irritation is avoided, and even if the patient has hair on their neck, application is straightforward.

[0044] In one embodiment, the housing containing at least three piezoceramics can be attached to a Laerdal-Stiffneck collar using a plastic bracket. The housing is positioned so that the sound emission surface rests against the patient's neck. In another embodiment, the measuring electronics are not located within the housing containing the at least three piezoceramics, but rather in a separate housing. This separate housing can be attached to the side of the Laerdal-Stiffneck collar facing away from the patient.

[0045] In another version, the position and pressure on the neck can be adjusted to the patient using manually inflatable air cushions. Activating a non-return valve on a pump and releasing a locking mechanism on the neck brace ensure easy removal of the ultrasound device. In this version, the ultrasound device housing therefore still features at least one inflatable air cushion.

[0046] In one embodiment, the position of the ultrasound device is changed by moving the holder on the neck brace, whereby, due to the contact pressure, the position of the ultrasound device cannot be changed when the neck brace is closed.

[0047] In one embodiment, the housing containing at least three piezoceramics is fixed to the patient's neck using a stretchable textile, a rubber band, or a specially designed neck collar. The rubber band can, for example, pass through the housing and run between the measuring electronics, the at least three piezoceramics, and the coupling path. The ultrasound device is then positioned on the neck so that the sound emission surface is in contact with the patient's neck.

[0048] In one embodiment, the measured signals are transmitted to an external screen. For this purpose, the ultrasound device has appropriate connections for data transmission (Wi-Fi, Bluetooth, cable, etc.).

[0049] In another embodiment, the ultrasound device further comprises at least one signal transmitter in the form of a display and / or an acoustic signal output. This eliminates the need for connections to third-party devices, monitors, or similar equipment. Instead of data transmission via Bluetooth or wireless LAN, measured values ​​are immediately evaluated by the measuring electronics and used for display. The display and / or the acoustic signal thus provide immediate information about the blood flow in the monitored blood vessel. For this purpose, one embodiment uses LEDs that display the approximate, instantaneous blood flow value and / or the signal strength of the measurement signal and / or an assessment of the approximate blood flow during the past minute(s).

[0050] In one embodiment, the signal transmitter is located on the housing of the ultrasound device and is arranged in such a way that the signal transmitter is clearly visible.

[0051] If the measuring electronics are arranged in a further housing which is spaced apart from the housing with the at least three piezoceramics, then in one embodiment the signal transmitter can also be arranged on the housing which includes the measuring electronics.

[0052] In a preferred embodiment, the blood flow in a blood vessel can thus be measured and displayed, for example, during the resuscitation of a patient.

[0053] If the ultrasound device has at least one signal transmitter, the signal transmitter is controlled by the measuring electronics in the housing.

[0054] Furthermore, the invention comprises a non-invasive method for measuring blood flow in a blood vessel using an ultrasound device, comprising the steps a) Performing a measurement in Mode 0, in which one piezoceramic acts as a transmitter while all available piezoceramics act as receivers; b) Assessing whether a blood-filled blood vessel is detected during the measurement in Mode 0 based on the measured values ​​and outputting information on whether a blood-filled blood vessel is detected during the measurement; c) Performing a measurement in Mode 1, in which each piezoceramic acts as a transmitter in succession while all available piezoceramics act as receivers, with the reflected ultrasound signals being simultaneously recorded by the receivers and with the measurement gate depth (transit time window) being varied for each piezoceramic; d) Calculating the vessel depth, vessel diameter, and Doppler angles of the individual piezoceramics from the measurement data of the measurement in Mode 1;e) Performing a measurement using Mode 2, with one piezoceramic acting as a transmitter while all available piezoceramics act as receivers, with the reflected ultrasound signals being simultaneously recorded by the receivers; f) Calculating the blood flow velocity from the measurement signals of the Mode 2 measurement and the calculated vessel depth, vessel diameter, and Doppler angles of the piezoceramics.

[0055] All features described for the ultrasound device apply equally to the method according to the invention and vice versa.

[0056] In one embodiment of the present invention, the ultrasound device is attached to the skin on the neck of a patient via a holder.

[0057] In principle, the method according to the invention can obtain a reflection signal through the vessel wall and a reflection signal from scattering at the erythrocytes. This allows for the detection of wall movements and erythrocyte movements, respectively. Both the erythrocyte movement and the wall movement are caused by blood flow.

[0058] After the ultrasound signal has been generated, the energy supply is interrupted when using pulsed Doppler ultrasound signals in order to receive the reflections of the emitted ultrasound waves. Depending on the speed of the red blood cells and the angle of the emitted ultrasound waves to the vessel axis, the reflected mechanical waves undergo a frequency shift due to the Doppler effect.

[0059] In one process step, a measurement is first performed in mode 0, in which one piezoceramic acts as the transmitter, while all available piezoceramics act as receivers. "All available piezoceramics act as receivers" means that in continuous wave (CW) mode, one piezoceramic transmits while all others receive, and in pulse-Doppler mode, all piezoceramics, including the one acting as the transmitter, receive. Measurement synchronization is achieved via internal system triggers.

[0060] This mode is used to assess the correct position and coupling of the transducer to the system being measured (e.g., neck).

[0061] In a preferred embodiment, in mode 0, the piezoceramic element whose angle to the sound emission surface deviates least from 90° is used as the transmitter. If a piezoceramic element is arranged in the ultrasound device at exactly a 90° angle to the sound emission surface, the piezoceramic element whose angle to the sound emission surface deviates least from that of the piezoceramic element with a perpendicular angle to the ultrasound emission surface is used. This results in a good compromise between the scatter signal of the blood cells (largest possible Doppler angle) and the reflection signal of the wall motion (smallest possible Doppler angle). The gate depth for the pulse Doppler measurement is preferably chosen to be small, and the gate size large. The selection of suitable parameters is familiar to those skilled in the art. The gate depth is synonymous with the measurement gate depth, which is also referred to as the transit-time window.

[0062] In one embodiment, parameter profiles for various patient neck proportions are provided for rapid gate adjustment, allowing the user to select one that corresponds to the patient's neck proportions. For example, when measuring an averagely proportioned neck with low body fat, a measurement range of 12 mm to 30 mm depth in the patient's body tissue should be covered. At a sound speed of 1.5 mm / µs, this results in a gate depth / receive time (the return path doubles the time) of 12 mm 1 , 5 mm / μ s ∗ 2 = 8 μ s ∗ 2 = 16 μ s and a gate size / reception duration (subtract half the gate depth) of 30 mm 1 , 5 mm / μ s ∗ 2 − 8 μ s = 24 μ s

[0063] The reflections measured by the respective piezoceramics are used to calculate spectrograms. These can be adjusted with power / intensity limits and value ranges. Based on the low-frequency power levels in the spectrogram, a visual-manual or automatic confirmation can be made as to whether the set Doppler gate covers a blood-filled vessel. If coverage is successful, the spectrograms contain periodically high signal power levels / intensities / power levels in the low frequencies, which are generated by vessel wall movements. For automatic evaluation, stored reference values ​​are used to compare the measurement signals. According to the invention, a comparison of the measured values ​​with reference values ​​and an assessment of whether a blood-filled vessel is detected during the measurement takes place. Subsequently, information is output indicating whether a blood-filled vessel is detected during the measurement.The information can be displayed on a connected screen and / or via LEDs and / or by emitting an acoustic signal.

[0064] In one embodiment of the present invention, the position of the ultrasound device on the patient can be changed if no blood-filled blood vessel is detected in the measurement.

[0065] As per the procedure, a measurement is then performed using Mode 1. In Mode 1, each piezoceramic acts as a transmitter in succession, while all available piezoceramics act as receivers. Measurements with different gate depths are performed with each piezoceramic. The reflected ultrasound signals are simultaneously recorded by the receivers.

[0066] The mode is used to determine the vessel depth, vessel diameter and Doppler angle of each piezoceramic in the ultrasound device according to the invention.

[0067] In mode 1, according to the invention, all piezoceramics are used sequentially as transmitters. While one piezoceramic transmits, all available piezoceramics receive the reflections and scattered signals. The fact that all available piezoceramics operate as receivers means that in continuous wave (CW) operation, one piezoceramic transmits while all the others receive, and in pulse-Doppler operation, all piezoceramics, including the one acting as a transmitter, receive. Measurement synchronization is achieved via internal system triggers.

[0068] The measurement is performed in multiple measurement loops. The measurement gate depth is iteratively increased for all receiving piezoceramics. A measurement is taken for a defined time at each gate displacement step. In one embodiment, the gate size is the same for each gate depth. In this embodiment, a measurement loop comprises one iteration loop over the gate depth.

[0069] In a further embodiment, the gate size can also be iteratively changed for each gate depth. In this embodiment, a measuring loop comprises two iteration loops, one for the gate size and one for the gate depth.

[0070] A measurement using mode 1 means that measurement loops are traversed for all piezoceramics of the ultrasonic device.

[0071] Once all measurements for the transmitting piezoceramic element are complete, its transmitting function is deactivated, and another piezoceramic element can take over the transmitter function. The measurement loop can then be repeated.

[0072] Each measurement within a measurement loop consists of acquiring Doppler data for each piezoceramic and calculating the spectrogram, which represents the power distribution across the frequency range. The received signal waveforms are demodulated from their carrier frequency and their spectral properties are analyzed using a short-time Fourier transform. The result of this transformation, the ratio of signal power to the corresponding frequencies, is plotted over time to form the spectrogram. By applying limit values ​​within the spectrogram, the maximum frequencies with sufficient power received by the piezoceramics can be determined using an envelope function.

[0073] For each measurement, it can be checked whether detection of a blood vessel is likely with the respective piezoceramic's gate setting, as long as blood is flowing through it. In one embodiment, the Doppler data are measured and stored for each gate setting for each transducer. Preferably, a distinction is made between low- and high-frequency regions of the calculated spectrograms, and thus a separation between vessel wall movements and blood scattering signals, via predefined threshold values. These threshold values ​​are stored in the measurement electronics.

[0074] A piezoceramic element oriented at a perpendicular angle to the vessel axis exhibits no output in the higher-frequency ranges that reflect blood flow, but does produce output in the lower Doppler frequencies that reflect wall movements. By comparing the spectrograms of different transducers, the piezoceramic element with the smallest angle deviation from 90° to the sound exit surface can be identified if several transducers along the gate displacement exhibit different signal intensities above the frequency threshold. A comparison of the low-frequency signal outputs of these piezoceramics along the different gate depths is used to determine the vessel depth and approximate the vessel diameter.

[0075] If vessel wall movements occur in the spectrograms of a piezoceramic, the power of which increases or decreases proportionally with the gate depth, the distance to the vessel can be determined for this piezoceramic.

[0076] In one embodiment, an envelope function of the maximum intensity is calculated along the time axis of the spectrogram. If the envelope function exhibits signs of periodic behavior in the desired frequency range of a human pulse or the resuscitation rate (54 BPM - 120 BPM), this can be taken as an indication that the associated piezoceramic is highly likely to detect blood flow in the vessel.

[0077] If several transducers cover the blood-filled vessel with their sound field, the vessel's position, and thus the exact Doppler angle, can be calculated based on the fixed angular relationships between the transducers. Spectrogram data are then converted from frequency values ​​to quantified velocity values ​​by substituting the Doppler angles.

[0078] According to the invention, the best parameterization with respect to transmitter-receiver settings and gate characteristics is determined by comparing the signal power of the enveloping functions in the blood flow frequency range (of all spectrograms from all Doppler configurations). This means that the optimal piezoceramic transmitter is determined, along with the corresponding optimal gate depth and, if necessary, gate length.

[0079] The parameter set and all recorded Doppler data, as well as the parameters derived from them, are preferably stored in the measuring electronics.

[0080] According to the invention, the vessel depth, vessel diameter, and Doppler angle of the individual piezoceramics are calculated from the measurement data of the measurement in mode 1. The vessel depth and vessel diameter result from the gate variation, taking into account the speed of sound and the angle of incidence to the normal. The Doppler angle is obtained from the mean frequency shifts for two piezoceramics as follows: parameter Sign Volume flow V̇ Average velocity in the vessel v Vessel diameter d Ultrasound transmission frequency f 0 speed of sound c Doppler transmission angle α SE Doppler reception angle α EM Average frequency shift D f Angle of a piezoceramic to the sound emission surface β

[0081] Volume flow in pipes: V ˙ = v ¯ π 4 d 2

[0082] Doppler law Δf ¯ = f 0 v ¯ c cos α SE + cos α EM

[0083] For two receivers when measuring with the same transmitter at the same time, the following applies: Δf 1 ¯ = f 0 v ¯ c cos α SE + cos α EM 1 Δf 2 ¯ = f 0 v ¯ c cos α SE + cos α EM 2

[0084] About the known angles ( β 1 , β2) From the construction and consideration of the law of refraction, all angles can be determined as a function of α EM 1. Show: α SE = α EM 1 + β ′ 1 α EM 2 = α EM 1 + β ′ 2

[0085] Dividing (3) and (4) and substituting (5) yields an equation from which the Doppler angle can be determined. α EM 1 can determine: Δf 1 ¯ Δf 2 ¯ = cos α EM 1 + β 1 + cos α EM 1 cos α EM 1 + β 1 + cos α EM 1 + β 2

[0086] According to the invention, a measurement is performed using mode 2. In mode 2, one piezoceramic acts as a transmitter, while all available piezoceramics act as receivers. The reflected ultrasound signals are simultaneously received by the receivers. The fact that all available piezoceramics act as receivers means that in continuous wave (CW) operation, one piezoceramic transmits while all other piezoceramics receive, and in pulse-Doppler operation, all piezoceramics, including the one acting as a transmitter, receive. Measurement synchronization is achieved via internal system triggers.

[0087] According to the invention, a parameter set determined from mode 1 and stored in the measuring electronics is retrieved and used for the configuration of all piezoceramics.

[0088] Here, a parameter set can be selected by a user, or the parameter set that exhibited the best signal-to-noise ratio (SNR) during measurement in Mode 1 can be selected automatically. Preferably, the parameter set is selected automatically. The configuration determines which piezoceramic emits ultrasound signals and the depth and size of the receiving port of each piezoceramic. According to the invention, continuous pulse-Doppler measurement with constant settings takes place in Mode 2. Spectrograms are calculated based on the received data. During the calculation, stored information on the Doppler angle of each piezoceramic can be used to determine flow velocities from the frequency values ​​of the spectrograms. Envelope functions or flow curves are calculated from the calculated data.Several flow-related information can then be determined from the flow curves, such as mean blood flow velocity, peak systolic velocity, peak end-diastolic velocity, pulse / resuscitation rate.

[0089] According to the invention, the speed of the blood flow and / or the volume flow is calculated from the measurement signals of the measurement with mode 2 and the calculated vessel depth, vessel diameter and Doppler angle of the piezoceramics.

[0090] In one embodiment, the calculated blood flow is displayed via a display on the ultrasound device.

[0091] In one embodiment, the measured blood flow values ​​can be evaluated over time to determine whether the ultrasound device is correctly positioned over the blood vessel and whether a blood flow is generated that corresponds to previously programmed target values. For this purpose, at least one target value for the blood flow is stored in the measuring electronics. LEDs, located either on the ultrasound device, indicate to the user the magnitude of the generated blood flow and / or the quality of the measured signal and / or the blood flow profile of the last minute(s). In one embodiment, the displays can be implemented via an LED strip for the current velocity, a status LED for the flow profile (e.g., red-yellow-green for 1 minute, 10 minutes, 30 minutes), and status LEDs (e.g., red-yellow-green) for the signal / position quality.

[0092] In another embodiment, an acoustic signal is emitted when the calculated blood flow deviates from a target value stored in the measuring electronics.

[0093] The ultrasound device and the method according to the invention offer numerous advantages over the prior art. A Doppler measuring device is provided that can be flexibly and quickly attached to the patient without requiring the user to hold the device or restricting its position after attachment. This is not possible with devices known from the prior art. Furthermore, the invention establishes pulsed Doppler sonographic measurements in resuscitation scenarios and the associated advantages of controlled transmission and reception of ultrasound waves from different angles. This approach allows for a more targeted examination of the hemodynamic properties of the blood vessel beneath the ultrasound device and its movements. Internal evaluation and calculation of blood flow parameters also enables the immediate display of relevant measurement parameters via integrated LEDs, thus providing real-time feedback.The invention eliminates the need for self-adhesive materials to attach the ultrasound device to the patient's neck. Instead, it utilizes plastic brackets that can be attached to a Laerdal-Stiffneck collar or secured to the neck via an elastic textile or a specially designed collar. Manually inflatable air cushions allow for adjustment of the position and pressure on the neck, depending on the patient. Activating a non-return valve on the pump and unlocking a locking mechanism on the collar ensure easy removal of the measuring module. The position of the ultrasound device is changed by sliding the bracket on the collar; however, due to the pressure exerted, the position of the ultrasound device remains fixed when the collar is closed.The probe used for ultrasound measurement consists of at least three piezoceramics, each with a different angle of incidence for Doppler sonographic measurement. With a coordinated pulse-Doppler measurement, one piezoceramic can act as both transmitter and receiver. The position of the blood vessel can be determined from the measured values ​​based on the pulse reflections and the relative magnitude of the Doppler signals. Since the Doppler angle is directly incorporated into the calculation of flow velocities, these can be determined precisely. The angular positions of the piezoceramics are fixed, and the Doppler angle of each piezoceramic is precisely known from the measurements. With conventional devices, the Doppler angle must be manually plotted by the user, leading to inaccuracies. Therefore, the automated determination of the Doppler angle offers an advantage over the conventional method for determining flow velocities.Determining the vessel diameter along with the flow velocities allows for the quantification of erythrocyte volumetric flow. During chest compressions, it is possible to analyze the frequency profiles over time for vessel movement and thus determine which piezoceramic is best suited for calculating blood flow and which patient-specific receiver port should be used. Information regarding vessel movement is contained in the low-frequency range of the spectrum and is more powerful than frequency variations caused by blood flow. By comparing the power values ​​in the frequency ranges from previously conducted examinations, it can be determined whether the ultrasound device adequately captures the blood vessel or whether a repositioning of the ultrasound device or an adjustment of the Doppler receiver port is advisable.The measuring electronics allow for iterative shifting of the receiving gate. An evaluation of the achieved signal strengths can provide information about the depth of the vessel and whether the center of the vessel is being targeted. The invention also eliminates the need for connections to third-party devices such as monitors for display purposes. Instead of data transmission via Bluetooth or wireless LAN, measured values ​​are evaluated immediately and used to display the resuscitation progress. The clear display provides the user with simple and rapid feedback, including the detection of the blood vessel and / or the current flow and / or recently recorded blood flow values. For this purpose, LEDs can be used to display the approximate current blood flow value and / or the signal strength of the measurement signal and / or the evaluation of the approximate flow over the past minute(s).

[0094] Furthermore, the metrological setup of the device according to the invention offers the following advantages: A comparison of pulse Doppler data from differently angled piezoceramics with large sample volumes provides information about the basic coverage of a blood-filled vessel by the sound fields of the piezoceramics; a comparison of pulse Doppler data from differently angled piezoceramics with small sample volumes and different gate depths allows the calculation of vessel depth, vessel diameter, and the piezoceramic-specific Doppler angle to the vessel without prior knowledge; automatic intensity evaluation of the spectrograms and flow curve calculation enables optimal measurement configurations of the piezoceramics without manual input; adjusting the gate depth to the patient-specific gate depth significantly improves the signal-to-noise ratio;Substituting the piezoceramic-specific Doppler angles in the calculation of the Doppler spectrograms enables an automatically quantified velocity calculation within the acquired sample volume; substituting the piezoceramic-specific Doppler angles bypasses the common use of the angle between the piezoceramic and the vessel axis for flow calculation, thus enabling a more robust calculation of flow velocities; approximating the vessel diameter and quantifying the actual blood flow velocities allows for the quantification of volumetric flow; comparing the spectrogram intensities, the determined flow information, and the frequency response of the calculated flow curves with stored reference values ​​allows for an assessment of sensor positioning and blood flow;Without prior knowledge, the system can be used in a simple technical design with multicolored LEDs to display the currently detectable blood flow, the quality of the flow signals, and the quality of the blood flow over a past period.

[0095] In addition to measuring blood flow during resuscitation, the ultrasound device and method according to the invention can also be used for: Non-invasive cardiac time-volume approximation or cardiac pulse analysis in the intensive care unit; non-invasive examination for signs of peripheral occlusive disease.

[0096] The present invention will now be explained in more detail with reference to 7 figures and 3 exemplary embodiments. Figure 1 depicts an ultrasound device; Figure 2 depicts an ultrasound device on a blood vessel in body tissue; Figure 3 depicts a Laerdal-Stiffneck collar with an ultrasound device; Figure 4 depicts a section of a Laerdal-Stiffneck collar with an ultrasound device; Figure 5 depicts a section of a Laerdal-Stiffneck collar with an ultrasound device; Figure 6 symbolically represents the envelope of the intensities of a spectrogram and the signals caused by vascular motion; Figures 7(A) to (E) depict envelopes of the intensities of spectrograms.

[0097] Figure 1 Figure 500 represents, in simplified form, an ultrasonic device 500. The ultrasonic device 500 has three piezoceramics 10, 11, 12. Piezoceramic 10 is oriented at an angle. β 1 and the piezoceramic 12 at an angle β2 arranged in housing 100. The angle is determined as the angle between the normal of the piezoceramic and the normal of the sound emission surface 101 of the housing, through which the ultrasound is emitted. For clarity, the angle for the piezoceramic 11 is not shown.

[0098] Figure 2 Figure 1 represents an ultrasound device 500 positioned at a blood vessel 51 in body tissue 50. The three piezoceramics 10, 11, 12 are each arranged at different angles in the housing 100 and therefore emit the ultrasound at correspondingly different angles into the blood vessel 51, which lies in the body tissue 50.

[0099] Figure 3Figure 1 represents a Laerdal-Stiffneck cervical collar 70. An ultrasound device 500 is attached to this collar. The ultrasound device 500 has a housing 100 in which three piezoceramics 10, 11, 12 are arranged. The housing 100 also has a holder 1010 with which the housing is attached to the Laerdal-Stiffneck cervical collar 70. Furthermore, the ultrasound device 500 expands an air cushion 80a, the air pressure of which can be regulated via the access 80b. This can be done, for example, using a syringe. In this embodiment, the measuring electronics are housed in a further housing, which is attached to the side of the Laerdal-Stiffneck cervical collar 70 facing away from the patient. The housing 100 with the piezoceramics 10, 11, 12 is connected by a cable to the further housing containing the measuring electronics.

[0100] Figure 4This shows a section of a Laerdal-Stiffneck cervical collar 70 with an ultrasound device 500. The one for Figure 3 The described features are even more clearly recognizable. The description of the Figure 3 meets in the same way the Figure 4 to.

[0101] Figure 5 Figure 1 shows a section of a Laerdal-Stiffneck collar 70 with an ultrasound device 500. The back of the ultrasound device 500 is visible. In this embodiment, the mounting of the ultrasound device 500 is designed such that the position of the housing 100, and thus of the piezoceramics 10, 11, 12, on the Laerdal-Stiffneck collar 70 can be changed. This allows the position of the housing 100 on a patient's neck to be adjusted. The position of the housing 100 is changed using the adjusting screw 121 and the positioning strip 120. By turning the adjusting screw, the housing can be moved along the positioning strip.

[0102] Figure 6 The envelope symbolically represents the intensities of a spectrogram. This envelope reflects the signal component caused by blood flow in the vessel. The points on the time axis symbolize the signals caused by vessel movement. The first point always reflects the signal caused by vessel movement during dilation, and the immediately following point reflects the signal caused by vessel movement during constriction.

[0103] Figure 7 (A) to (E) These figures represent the envelopes of the intensities of spectrograms recorded with a piezoceramic at various gate depths. The figures are described in more detail in embodiment 2. Example 1

[0104] The ultrasound device was integrated into a Laerdal cervical collar. In this configuration, it can be attached to the patient after they have been safely positioned without spontaneous circulation. The measurement module was located on the collar at a point that proved optimal for measuring carotid blood flow using Doppler sonography in several test subjects. After application, the coverage of the ultrasound sensor was checked, and the contact pressure was optimized by inflating the air cushion. Example 2

[0105] The ultrasound device was integrated into a Laerdal cervical collar and attached to a phantom with simulated blood flow. The phantom was made of agar-agar gel with added aluminum oxide. This phantom transmitted ultrasound in accordance with the requirements for tissue phantoms used to test ultrasound devices as specified in DIN IEC 60601-2-37.

[0106] A pump to generate simulated blood flow was connected to the phantom in a closed circuit via elastic silicone tubing and nozzles. One silicone tube thus simulated a blood vessel.

[0107] The measurement was performed using an ultrasound device. In the Figures 7 (A) to (C) The graphs show measurement curves for measurements using a piezoceramic as transmitter and receiver for various gate depths. The gate length was 2 µs in each case.

[0108] In the Figure 7 (A)A gate depth of 14 µs was used. No measurement signal could be recorded in this range, which was caused by the simulated blood flow in the vessel. The gate depth was not large enough for the blood vessel to be detected by the ultrasound signal.

[0109] In the Figure 7 (B) A gate depth of 18 µs was used. Initial information about blood flow could be obtained from the spectrogram.

[0110] The gate depth was then changed to 22 µs. With these parameters, the simulated blood flow in the vessel could be accurately represented ( Figure 7 (C) ).

[0111] With an even greater gate depth of 26 µs ( Figure 7 (D) Information about blood flow could also be obtained, however the signal intensity was lower compared to the measurement taken in Figure 7 (C)The center of the simulated blood flow had already been passed. With a further increase in gate depth to 30 µs ( Figure 7 (E) The intensity decreased further, and no information could be extracted from the spectrogram to obtain sufficient information about the simulated blood flow. At this gate depth, the blood vessel was no longer adequately covered.

[0112] The following information was obtained from the measurement data: Length of the path for piezoceramics to the beginning of the vessel (position of the vessel) 18 μ s ∗ 1 , 5 mm μ s ∗ 1 2 = 13 , 5 mm Length of the covered path for piezoceramics inside the vessel (without angle correction) (diameter of the vessel) 32 μ s − 18 μ s ∗ 1 , 5 mm μ s ∗ 1 2 = 10 , 5 mm

[0113] By measuring with at least one additional piezoceramic, the Doppler angle can be calculated according to formulas (3) to (6). Example 3

[0114] An ultrasound device with three piezoceramics was constructed. The piezoceramics were arranged at angles of 0°, 10°, and 25°. The device's housing also featured an LED display and a flexible textile holder for securing the device to a patient's neck. literature

[0115] [1] SH Friess et al. Hemodynamic directed cardiopulmonary resuscitation improves short-term survival from ventricular fibrillation cardiac arrest. Crit Care Med 2013; 41:2698-704. [2] A. Schneider et al. 'Cerebral Resuscitation After Cardiocirculatory Arrest', Anesthesia & Analgesia, vol. 108, no. 3, pp. 971-979, Mar. 2009. [3] M. Koch et al. Carotid Artery Ultrasound in the (peri-)Arrest Setting-A Prospective Pilot Study. J Clin Med 2022;11(2):469. Published 2022 Jan 17. doi:10.3390 / jcm11020469 Reference symbol list

[0116] 10, 11, 12 Piezoceramic 50 Body tissue 51 Blood vessel 70 Laerdal Stiffneck collar 80a Air cushion 80b Access 100 Housing 101 Sound emission surface 120 Positioning strip 121 Adjusting screw 500 Ultrasound device

Claims

1. Non-invasive method for measuring blood flow in a blood vessel by means of an ultrasound device (500) comprising measuring electronics, at least three piezoceramic elements (10, 11, 12) and a housing (100), each piezoceramic element (10, 11, 12) being arranged in the housing (100) at a different angle to the sound emission surface of the housing (101); the housing (100) further having at least one means for attaching the housing to a patient or to an auxiliary means; characterized in that the method comprises the steps of a) performing a measurement using a mode 0 in which one piezoceramic element (10, 11, 12) acts as a transmitter, while all available piezoceramic elements (10, 11, 12) act as receivers; b) assessing whether a blood-filled blood vessel is detected during the measurement on the basis of the measured values using the mode 0, and outputting information as to whether a blood-filled blood vessel is detected during the measurement; c) performing a measurement using a mode 1, in which each piezoceramic element (10, 11, 12) acts as a transmitter in succession, while all available piezoceramic elements (10, 11, 12) act as receivers, the reflected ultrasound signals being received simultaneously by the receivers and the measurement gate depth being varied for each piezoceramic element; d) calculating the vessel depth, vessel diameter and Doppler angles of the individual piezoceramic elements (10, 11, 12) from the measurement data from the measurement using the mode 1; e) performing a measurement using a mode 2, in which one piezoceramic element (10, 11, 12) acts as a transmitter, while all available piezoceramic elements (10, 11, 12) act as receivers, the reflected ultrasound signals being received simultaneously by the receivers; f) calculating the speed of blood flow from the measurement signals from the measurement using the mode 2 and the calculated vessel depth, vessel diameter and Doppler angles of the piezoceramic elements (10, 11, 12).

2. Method according to claim 1, characterized in that the method further comprises the step of displaying the calculated blood flow by means of a display on the housing (100).

3. Method according to claim 1 or claim 2, characterized in that the method further comprises the step of emitting an acoustic signal if the calculated blood flow deviates from a setpoint value stored in the measuring electronics.