Estimate central blood pressure

Abstract

An apparatus for estimating the central blood pressure of a subject. The apparatus includes a sensor patch comprising an array of sensors configured to measure an indication of blood pressure in peripheral blood vessels and to perform ultrasound imaging of the peripheral blood vessels. The apparatus further includes a processor configured to obtain a peripheral pressure signal, including a pressure waveform, based on the blood pressure indication from the sensor patch, and to derive an image of the peripheral blood vessels based on the signal received from the sensor patch. A blood vessel diameter is determined based on the time-varying image of the peripheral blood vessels, including a vessel diameter waveform, and an estimate of the central blood pressure of the subject is derived based on the pressure waveform and / or the vessel diameter waveform.

Description

Technical Field

[0001] This invention relates to estimating the central blood pressure of a subject. Background Technology

[0002] In clinical practice, blood pressure measurement is routinely used to assess and classify patients' overall health status. Long-term elevated blood pressure (hypertension) is associated with a variety of complications, such as heart failure, stroke, and chronic kidney disease.

[0003] The measurement of maximum (systolic) pressure varies depending on the location within the arterial tree because pressure wave reflections from vascular bifurcation and changes in vessel diameter cause amplification effects. Therefore, systolic pressure at peripheral locations (e.g., the brachial artery) is not equal to systolic pressure at central locations (e.g., the aorta).

[0004] Central aortic pressure provides important diagnostic information, such as risk factors for adverse outcomes like mortality, and the effectiveness of treatments (e.g., antihypertensive management) has different effects on central and peripheral (brachial) pressure. Therefore, non-invasive estimation of the central pressure waveform will be a key indicator.

[0005] The most popular central pressure estimation techniques rely on the measurement of peripheral pressure. These techniques can be divided into two approaches: force-based vascular displacement measurement (e.g., planar pressure measurement) or ultrasound-based vascular diameter imaging.

[0006] In force-based methods, changes in vessel diameter caused by the blood pressure waveform are measured by external force at a peripheral location (e.g., the arm or neck). This measurement is then calibrated to generate a substitute peripheral blood pressure waveform. This waveform is then transformed into a central waveform using a transfer function in the frequency domain. The Sphymocor (trademark) device uses this method. Other devices also use the same force-based approach but do not perform mathematical transformations on the pressure signal.

[0007] Force-based measurements (plane pressure measurement) have been applied to the carotid artery to derive central pressure waveforms. However, the depth of the carotid artery requires skilled operators to obtain reliable signals using this force-based technique.

[0008] In ultrasound-based methods, changes in blood vessel diameter caused by blood pressure waveforms are measured using ultrasound images. The waveforms are then calibrated to generate alternative blood pressure waveforms.

[0009] Because it avoids the aforementioned problems, the use of ultrasound is advantageous. Academic research reports the use of ultrasound imaging to determine alternative pressure signals.

[0010] Different methods produce varying quality measurements under different conditions. An improved method for estimating central blood pressure is desired, one that can produce high-quality results in a wide range of applications. Summary of the Invention

[0011] This invention is defined by the claims.

[0012] According to an example of one aspect of the present invention, an apparatus for estimating the central blood pressure of a subject is provided, the apparatus comprising:

[0013] A sensor patch comprising an array of sensors, the array of sensors being configured as follows:

[0014] Measurements indicate blood pressure in peripheral blood vessels; and

[0015] Ultrasound imaging is performed on the peripheral blood vessels, wherein the same sensor is used for both blood pressure measurement and ultrasound imaging; and

[0016] The processor is configured as follows:

[0017] A peripheral pressure signal, including a pressure waveform, is obtained based on the indication of blood pressure from the sensor patch;

[0018] The image of the peripheral blood vessels is derived based on the signal received from the sensor patch;

[0019] The vessel diameter is determined as a waveform based on peripheral vascular images over time; and

[0020] An estimate of the central blood pressure waveform of the object is derived from the pressure waveform and / or the blood vessel diameter waveform.

[0021] The sensor patch can measure an indication of blood pressure at the peripheral location and perform ultrasound imaging at the same location. The indication of blood pressure can be, for example, the force on the skin caused by changes in blood pressure at the peripheral location. Changes in vessel diameter can be measured by using ultrasound imaging capabilities to image the vessels. Both the peripheral pressure signal and the vessel diameter can be used to estimate central blood pressure from peripheral vessels in a non-invasive manner. By combining these two capabilities into a single sensor patch, a more robust and reliable estimation of central blood pressure can be achieved.

[0022] The processor can be configured to determine the diameter of peripheral blood vessels by applying an automatic tracking algorithm to images of peripheral blood vessels in color Doppler mode.

[0023] Applying automatic tracking algorithms to peripheral vascular images (in color Doppler mode) can reliably and consistently measure the change in peripheral vascular diameter over time.

[0024] The sensor array may include:

[0025] Capacitive micromechanical ultrasonic transducer (cMUT);

[0026] piezoelectric sensor; or

[0027] Piezoresistive sensor.

[0028] Therefore, various sensors can be configured to function as both ultrasonic imaging sensors and pressure sensors.

[0029] The processor may also be adapted to:

[0030] Determine the quality factor for each of multiple peripheral pressure waveform cycles and vessel diameter waveform cycles;

[0031] The overall pressure waveform is created based on the pressure waveform period and its corresponding quality factor; and

[0032] The overall diameter waveform is created based on the period of the blood vessel diameter waveform and its corresponding quality factor.

[0033] The central blood pressure is estimated based on the overall pressure waveform and / or the overall diameter waveform.

[0034] The overall waveform can be determined by applying different weights to the peripheral pressure waveform period and the vessel diameter waveform period, for example, based on quality, regularity, and / or by comparing the signal with the expected signal (e.g., using lower weights for low-quality / unexpected signals).

[0035] For example, the vessel diameter may not be determined perpendicular to the vessel. In this case, the quality factor of the vessel diameter is low because it cannot accurately represent the true vessel diameter. Therefore, peripheral pressure waveforms can be used alone to estimate central blood pressure.

[0036] The processor can be adapted to derive estimates of central blood pressure in the following ways:

[0037] Apply a frequency-based transfer function to the overall pressure waveform and / or the overall diameter waveform; or

[0038] The overall pressure waveform and / or overall diameter waveform are transformed into an estimate of central blood pressure using a physics-based model.

[0039] The processor may also be adapted to:

[0040] The estimated mean and diastolic blood pressure values ​​were calibrated to the mean and diastolic blood pressure values ​​obtained from the pressure cuff measurements.

[0041] The average blood pressure and diastolic pressure values ​​at different parts of the body can generally be assumed to be constant. However, the maximum value of the waveform varies based on anatomical location. Therefore, once the waveform is obtained, its shape can be calibrated to the accurate blood pressure value using the actual average value and diastolic pressure value from the pressure cuff measurements.

[0042] The device may further include:

[0043] A housing unit for accommodating a sensor patch and a processor, wherein the housing unit includes an opening, and wherein the opening is for sensing an area of ​​the sensor patch.

[0044] The straps are attached to the housing unit; and

[0045] Skin interface at the opening of the housing unit.

[0046] The present invention also provides a method for estimating central blood pressure, the method comprising:

[0047] The blood pressure readings of peripheral blood vessels are measured to derive the pressure waveform from the sensor on the sensor patch;

[0048] Ultrasound imaging of peripheral blood vessels is performed using the same sensor as the blood pressure measurement indicator;

[0049] The vessel diameter is determined as a waveform based on peripheral vascular images over time; and

[0050] Estimate the center blood pressure waveform of the object from the pressure waveform and / or blood vessel diameter waveform.

[0051] The diameter of the blood vessel can be determined by applying an automatic tracking algorithm to an image in color Doppler mode.

[0052] The method may also include:

[0053] The method may also include:

[0054] Determine the quality factors for multiple peripheral pressure waveform cycles and multiple vessel diameter waveform cycles;

[0055] The overall pressure waveform is created based on the pressure waveform period and its corresponding quality factor; and

[0056] The overall diameter waveform is created based on the period of the blood vessel diameter waveform and its corresponding quality factor.

[0057] The central blood pressure is estimated based on the overall pressure waveform and / or the overall diameter waveform.

[0058] The central blood pressure can be estimated based on:

[0059] Apply a frequency-based transfer function to the overall pressure waveform and / or the overall diameter waveform; or

[0060] The overall pressure waveform and / or overall diameter waveform are transformed into an estimate of central blood pressure using a physics-based model.

[0061] The method may also include calibrating the estimated mean and diastolic blood pressure values ​​to the cuff mean and cuff diastolic blood pressure values ​​obtained from the pressure cuff measurements.

[0062] The present invention also provides a computer program including computer program code, which, when executed by a processor, causes the processor to perform the method described above.

[0063] These and other aspects of the invention will become apparent and will be explained with reference to the embodiments described below. Attached Figure Description

[0064] To better understand the invention and to more clearly illustrate how it can be practiced, reference will now be made to the accompanying drawings by way of example only, wherein,

[0065] Figure 1 A representation of a sensor patch used to measure peripheral blood vessel diameter and blood pressure is shown;

[0066] Figure 2 The pressure waveform measured at the object's skin is shown;

[0067] Figure 3 The diagram shows the diameters between the relative inner surfaces and relative outer surfaces of the blood vessels, measured based on image analysis.

[0068] Figure 4 The velocity waveform (three cycles) and the corresponding vessel diameter waveform are shown.

[0069] Figure 5 Example pressure waveforms at different anatomical locations are shown;

[0070] Figure 6 An example of a capacitive cMUT sensor is shown;

[0071] Figure 7 A known design of a cMUT element (so-called cell) for sensor patch 102 is shown;

[0072] Figure 8 and 9 The operating principle of such a cMUT component is described;

[0073] Figure 10This illustrates a method for measuring pressure and imaging the same sensor on a sensing patch; and

[0074] Figure 11 A wearable device with sensing patches is shown. Detailed Implementation

[0075] The invention will be described with reference to the accompanying drawings.

[0076] It should be understood that while the detailed description and specific examples indicate exemplary embodiments of the devices, systems, and methods, they are intended for illustrative purposes only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the devices, systems, and methods of the present invention will be better understood from the following description, the appended claims, and the accompanying drawings. It should be understood that the drawings are schematic only and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to denote the same or similar parts.

[0077] This invention provides an apparatus for estimating the central blood pressure of a subject. The apparatus includes a sensor patch comprising an array of sensors configured to measure an indication of blood pressure in peripheral blood vessels and perform ultrasound imaging of the peripheral blood vessels. The apparatus also includes a processor configured to obtain a peripheral pressure signal, including a pressure waveform, based on the blood pressure indication from the sensor patch, and to derive an image of the peripheral blood vessels based on the signal received from the sensor patch. A blood vessel diameter is determined based on the time-varying image of the peripheral blood vessels, including a blood vessel diameter waveform, and an estimate of the central blood pressure of the subject is derived based on the pressure waveform and / or the blood vessel diameter waveform.

[0078] Figure 1 A representation of a sensor patch 102 for measuring peripheral vascular diameter and blood pressure is shown. The ultrasound patch has an array of sensors for ultrasound imaging, from which the diameter of peripheral vascular 104 can be obtained, and it is also used to measure the force at skin 106, which represents blood pressure. The sensor patch 102 measures both at the same anatomical location, thus obtaining two different measurements related to blood pressure at one location. These measurements are temporally close enough that they can be considered simultaneous. For example, the measurements can be interleaved in the time intervals of the measurement cycle.

[0079] The sensors include ultrasonic sensors, which can be configured to receive reflected echo signals as part of the ultrasonic imaging process, or they can receive pressure signals related to the dominant pressure or force applied to the sensor.

[0080] As blood flow 110 through peripheral blood vessels 104 increases, in response to changes in blood pressure, the diameter of blood vessels 104 increases and then decreases. This change in diameter forces the skin 106 to bulge. Therefore, changes in blood pressure can be monitored from the pressure at the sensor patch 102 on the surface of the skin 106.

[0081] Figure 2 The pressure waveform 202 measured at the skin 106 of the subject is shown. Time is shown on the x-axis, and the pressure from the sensor patch on the skin 106 is shown on the y-axis. The pressure waveform 202 is based on the measurement of the force from the skin 106 of the subject and provides an indication of blood pressure in the peripheral blood vessels 104.

[0082] The waveform consists of a repeating signal shape with a period equal to the heartbeat cycle (i.e., a repetition period of 204).

[0083] When used for ultrasound imaging, an array of sensors from sensor patch 102 can be used to capture images of blood vessels beneath the skin surface. Image analysis can then be used to measure the diameter of the peripheral blood vessel 104 by measuring the difference between the two distal endpoints of the vessel 104 passing through a plane 108 extending from sensor patch 102. Plane 108 can be perpendicular to the skin 106, or it can be at other angles to accommodate the peripheral blood vessel 104 that is not parallel to the skin 106. Ideally, plane 108 is perpendicular to the peripheral blood vessel 104.

[0084] Figure 3 The diagram shows the diameters between the relative inner and outer surfaces of blood vessels, measured based on image analysis. The top vessel diameter waveform 304 shows the variation in vessel diameter based on outer wall tracking, while the bottom vessel diameter waveform 302 shows the variation in vessel diameter based on inner wall tracking. The inner wall refers to the inner wall of the blood vessel, and the outer wall refers to the outer wall of peripheral blood vessels. Figure 3 The vessel diameter waveforms 302 and 304 can be obtained from M-mode or B-mode ultrasound imaging. A cycle 306 is shown in the box.

[0085] When blood pressure rises within a blood vessel, the vessel diameter increases because the vessel wall is flexible. The vessel diameter waveforms 302 and 304 for the outer and inner surfaces may differ because the thickness of the vessel wall changes when the internal pressure changes. Typically, the vessel diameter waveform 302 for the inner wall will be used to derive an estimate of the central blood pressure waveform.

[0086] Ultrasonic imaging can also monitor flow conditions. Figure 4A graph showing velocity waveform 402 (three cycles) and corresponding vessel diameter waveform 302 is presented. The x-axis represents time, the right y-axis represents blood flow velocity, and the left y-axis represents vessel diameter. Blood flow velocity is represented by dashed lines, and vessel diameter by continuous black lines. Blood velocity (in the vessel) can be obtained using Doppler spectral imaging with sensor patch 102.

[0087] Therefore, the volumetric flow rate of blood can be extracted by multiplying the average velocity by the area of ​​blood vessel 104. This area can be obtained by assuming that blood vessel 104 is circular and using the average diameter from blood vessel diameter waveform 302.

[0088] The quality factor can be determined for each cycle of the pressure waveform 202 and each cycle of the vessel diameter waveform 302. Irregular cycles and cycles with a lot of noise will have a low quality factor. Cycles with a low quality factor may be discarded. The quality factor can be a numerical value (i.e., any number between 0 and 1) or a binary factor (i.e., 0 represents low quality, and 1 represents adequate quality). For example, the quality factor can be determined by comparing the minimum, maximum, and / or average variation of the cycle with a predetermined threshold range.

[0089] In one example, an overall waveform is created from period 204 of the pressure waveform 202 and period 306 of the blood vessel diameter waveform 302. Using the same time scale (e.g., the minimum period / foot, as it represents the start of each heartbeat), multiple periods are then combined (with sufficient quality factors) to create an average waveform. The periods used can be weighted based on the quality factor.

[0090] For example, an overall pressure waveform can be created from five different cycles to filter out minute differences between each cycle of the pressure waveform 202. In another example, the pressure waveform 202 of an object can be measured for up to ten seconds, providing, for example, nine pressure waveform cycles. However, the object may have moved within these 10 seconds, so one of the pressure waveform cycles may have a different shape than the others. Therefore, that different pressure waveform cycle will have a low quality factor and will be discarded before the overall pressure waveform is created.

[0091] Central blood pressure can be estimated using either the overall pressure waveform or the overall vessel diameter waveform.

[0092] Figure 5Example pressure waveform cycles at different anatomical locations are shown. The first waveform cycle 502 is for the ascending aorta, the second waveform cycle 504 is for the thoracic aorta, and the third waveform cycle 506 is for the middle of the abdominal aorta, the fourth waveform cycle 508 is for the distal abdominal aorta, the fifth waveform cycle 510 is for the femoral location, and the sixth waveform cycle 512 is for the saphenous vein location. Central blood pressure can be, for example, for the ascending aorta or the thoracic aorta.

[0093] The overall pressure waveform at one location can be transformed to the center location using a transfer function. A frequency-based transfer function can correct for pressure wave distortion caused by bifurcation, changes in vessel diameter, and other factors. Alternatively, a physics-based model (simulating the viscoelastic tube of a blood vessel) can be used to determine the transfer function. Thus, the transfer function transforms the overall pressure waveform into a central pressure waveform.

[0094] For example, frequency-based methods are described in the following article: "Validation of the transferfunction technique for generating central from peripheral upper limb pressure waveform", David Gallagher et al., American Journal of Hypertension, Vol. 17, No. 11, November 2004, pp. 1059-1067.

[0095] Physics-based approaches are described, for example, in the following article: “Derivation of the ascendingaortic-carotid pressure transfer function with an arterial model,” M, Karamanoglu et al., American Journal of Physiology, Heart and Circulatory Physiology, vol. 271, no. 6, December 1, 1996.

[0096] The overall vessel diameter waveform can be transformed into a second pressure waveform for the peripheral location, and then the second pressure waveform can be further transformed into a pressure waveform for the central location (i.e., the central pressure waveform).

[0097] The morphology of the diameter waveform is very similar to that of the pressure waveform, as can be seen in the following article: “Relationship between the pressure and diameter of the carotid artery in humans.”, Sugawara, M., Niki, K., Furuhata, H. et al., Heart Vessels 15, 49–51 (2000).

[0098] The diameter waveform is transformed into a second pressure waveform by calibration via cuff pressure measurement results. Once calibrated via cuff pressure measurement, the second pressure waveform can be transformed from peripheral blood pressure to central blood pressure using either a frequency-based transfer function or a physics-based method.

[0099] The central pressure waveform can be obtained from either or both of the overall pressure waveform and the overall vessel diameter waveform. If obtained from both, a combination of central pressure waveforms obtained from each method (e.g., a weighted average) can be used.

[0100] The overall pressure waveform and the overall vessel diameter waveform may have different artifacts. Therefore, a combination of the two may be less useful than either one alone. In these cases, only one of them can be used to determine the central pressure waveform.

[0101] For example, the weight of each method may depend on the quality factor of the waveform used. The central pressure waveform can also be obtained solely from the pressure waveform 202 and / or solely from the vessel diameter waveform 302. However, a set of waveform periods is not required, and a single period for each waveform can be used.

[0102] The central blood pressure waveforms obtained from these two methods are typically not calibrated to the actual blood pressure value. Instead, these methods only provide the accurate waveform shape.

[0103] from Figure 5 As can be seen, the farther the pressure measurement is from the center of blood pressure, the higher the peak value of the waveform. However, regardless of the anatomical location, the average and minimum (diastolic) values ​​of the pressure waveform remain relatively constant.

[0104] Therefore, the average and diastolic blood pressure values ​​from a pressure cuff (or other device that can accurately measure mean and diastolic blood pressure at any anatomical location) can be used to calibrate the central pressure waveform. This is done by ensuring that the pressure cuff value is equal to both the diastolic and average values ​​of the central pressure waveform. The central blood pressure can then be determined based on the central pressure waveform (i.e., the systolic, diastolic, and mean blood pressure values, and the general shape of the waveform). The calibrated central pressure waveform is typically displayed on a monitor.

[0105] In a preferred implementation, MEMS devices are used for pressure sensing and ultrasonic imaging. Such devices implement on-chip pressure sensing functionality and are therefore system components in a variety of applications. MEMS pressure sensors can be classified based on the sensing method used.

[0106] Piezoelectric sensors detect applied pressure by changing their electrical potential as the sensor's output. When pressure is applied, the diaphragm of a piezoelectric pressure sensor deforms. This deformation generates a voltage. Piezoelectric pressure sensors use metallized quartz or ceramic materials as the sensing element. Typically, this type of pressure sensor is designed with an amplifier to enhance the electrical interface. Arrays of piezoelectric sensors can also be used for ultrasonic imaging. However, piezoelectric pressure sensors are highly susceptible to shock and vibration.

[0107] Alternatively, piezoresistive pressure sensors provide a change in resistance. When pressure is applied, both the diaphragm and the piezoresistive material bend. This means that the applied pressure causes the piezoresistive material to become slightly longer and thinner. This deformation causes a change in the resistance of the piezoresistive material. Therefore, by measuring the output voltage of a monitoring circuit, such as a Wheatstone bridge circuit, the change in pressure can be determined, and thus the pressure applied to the sensor can be determined. Arrays of piezoresistive sensors can also be used for ultrasonic imaging.

[0108] Figure 6 An example of a capacitive cMUT sensor 602 is shown. This is the preferred sensor implementation. The sensor 602 experiences a capacitance change proportional to the applied pressure. The sensor 602 has two conductive plates: a measuring plate 604 and a reference plate 606. The measuring plate 604 bends under pressure, while the reference plate 606, serving as a reference to the measuring plate 604, has a fixed position. Once the measuring plate 604 bends, the distance between the two plates changes. The pressure applied to the measuring plate changes the capacitance; therefore, the capacitive sensor 602 can be used as a pressure sensor.

[0109] The capacitive sensor 602 has several advantages over piezoresistive and piezoelectric pressure sensors. It exhibits very stable operation and the measured output is highly linear.

[0110] Figure 7 A known design for a cMUT element (so-called cell) for sensor patch 102 is shown. The cMUT element includes a flexible membrane or diaphragm 714 suspended above a silicon substrate 712, with gaps or cavities 718 between them. In this example, a first electrode 722 is located on the base plate of the cell on the upper surface of the substrate 712. A second electrode 720 is positioned on the diaphragm 714 and moves with the diaphragm. In the example shown, both electrodes are circular.

[0111] A dielectric (not shown) is provided on the substrate 712 and below the top (second) electrode 720. A separator may alternatively be used as a dielectric layer.

[0112] Preferably, the composition and thickness of the two dielectrics can be equal, but they can also be asymmetrical (different materials and thicknesses).

[0113] The membrane 714 is fixed relative to the top surface of the substrate 712 and is configured and sized to define a spherical or cylindrical cavity 718 between the membrane 714 and the substrate 712.

[0114] Other implementations of the electrode 720 design can be considered, such as embedding the electrode 720 in the film 714, or depositing it as an additional layer on the film 714.

[0115] The first electrode may be directly exposed to the gap 718 or separated from the gap 718 by an electrical insulating layer or film to prevent short circuit between the second electrode 720 and the first electrode 722.

[0116] exist Figure 7 In this example, the first electrode 722 is grounded. Other arrangements, such as a grounded second electrode 720 or two floating second electrodes 720 and the first electrode 722, are of course equally feasible.

[0117] The electrodes of the cMUT element provide the capacitor plates of the device, and the gap 718 is the dielectric between the capacitor plates. When in imaging mode, the changing size of the dielectric gap between the plates provides a changing capacitance when the diaphragm vibrates, which is sensed as the response of the cMUT element to the received acoustic echo.

[0118] The spacing between electrodes is controlled by applying a static voltage (e.g., DC bias) to the electrodes using a voltage source 701. The voltage source 701 may also optionally include separate stages 702 and 704 for providing DC and AC or excitation components of the drive voltage for the cMUT element, respectively, for example, in transmit mode. The first stage 702 may be adapted to generate the static (DC) voltage component, and the second stage 704 may be adapted to generate an alternating variable drive or excitation voltage component with a set alternating frequency, typically the difference between the total drive voltage and the aforementioned static component.

[0119] The static or bias component of the applied drive voltage preferably satisfies or exceeds a threshold voltage to force the cMUT element into its collapsed state. This has the advantage that the first stage 702 can include a relatively large capacitor, such as a smoothing capacitor, to generate a particularly low-noise static component of the overall voltage, which typically dominates the overall voltage, such that the noise characteristics of the overall voltage signal are dominated by the noise characteristics of this static component.

[0120] It is known that by applying a static voltage above a certain threshold, the cMUT element is forced into a collapsed state, in which the film 714 collapses onto the substrate 712. This threshold can depend on the exact design of the cMUT element and is defined as a DC bias voltage, called the collapse voltage, at which the film 714 adheres (contacts) to the bottom of the cell by the force generated by the electric field between the electrodes. The amount (area) of contact between the film 714 and the substrate 712 depends on the applied bias voltage.

[0121] Increasing the contact area between the film 714 and the substrate 712 increases the resonant frequency of the film 714.

[0122] The frequency response of the collapsed-mode cMUT element can be altered by adjusting the DC bias applied to the cMUT electrodes after collapse. As a result, the resonant frequency of the cMUT element increases with a higher DC bias applied to the electrodes.

[0123] The principle behind this phenomenon is Figure 8 and Figure 9 As shown in the image. Figure 8 and Figure 9 The cross-sectional view in each illustration is shown one-dimensionally by the distances D1 and D2 between the external support of the membrane 714 and the point where the diaphragm begins to contact the bottom plate of the cavity 718. It can be seen that when a relatively low bias voltage is applied... Figure 8 The distance D1 in the distance is a relatively long distance. Figure 9 The distance D2 in the middle is much shorter due to the application of a higher bias voltage. These distances can be compared to long and short strings fixed at the ends and then pulled out. A long, relaxed string and a shorter, tighter string will vibrate at a lower frequency when pulled out. Similarly, Figure 8 The resonant frequency of the cMUT element will be lower than that affected by the higher pull-down bias voltage. Figure 9 The resonant frequency of the cMUT element in the middle.

[0124] Therefore, a typical cMUT design includes flexible membranes or diaphragms, for example, formed of silicon nitride, suspended above a silicon substrate, with gaps or cavities between them. These gaps are created by removing the sacrificial layer during manufacturing. A first electrode is positioned on the base plate of a cell on the upper surface of the substrate, and a second electrode is positioned on the diaphragm and moves with it. This same architecture can be used as a pressure sensor or an ultrasonic transmitter and receiver (involving the measurement of pressure from ultrasonic echoes).

[0125] The operation of cMUT components is well known to those skilled in the art.

[0126] Currently, assessing pressure and vascular imaging require two separate devices. The sensor patch of this invention allows these two functions to be combined in a single device, resulting in benefits in terms of workflow, manufacturing, and cost. Therefore, the sensor patch can use a single transducer array to send and receive ultrasound signals and measure pressure at the same location.

[0127] Figure 10 This demonstrates how an array of the same sensors can be used for both ultrasound imaging and pressure sensing. The device includes a controller 800 provided on an ASIC 802. An array of cMUT devices 804 is provided, for example, monolithically integrated with the ASIC 802. Each cMUT device may include several actual cMUT elements (i.e., cells).

[0128] For imaging mode, controller 800 includes an ultrasonic transmitting circuit 806 and an ultrasonic receiving circuit 808 for each cMUT device 804. A switching device 810 for each cMUT device couples the transmitting and receiving circuitry to cMUT device 804. System controller 816 controls the timing of when to transmit and when to begin receiving, and thus controls the switching devices 810 of the different cMUT devices. The cMUT devices may be connected to the transmitting and receiving circuitry for imaging mode, or all cMUT devices may be isolated from the transmitting and receiving circuitry for a separate pressure sensing mode, also controlled by system controller 816. Therefore, the devices can switch between imaging mode and pressure sensing mode.

[0129] The controller also includes measurement circuitry 812 for measuring the capacitance (or more generally, any pressure-related electrical characteristic) of the cMUT device. Measurement circuitry 812 is connected to the cMUT device via a second switch 814. A second switch 814 is then present for each cMUT device 804. However, a single measurement circuitry 812 can be provided. Therefore, for pressure sensing mode, all cMUT devices 804 can be electrically connected in parallel. If there are multiple ASIC dies, each with a corresponding cMUT device subarray, then each semiconductor die may have measurement circuitry.

[0130] To measure capacitance, the measurement circuit 812 includes an oscillator circuit that, in combination with the cMUT device, defines oscillation characteristics, and an output circuit that provides an output signal FC that depends on the oscillator frequency.

[0131] The measurement circuit 812 in this example includes an oscillator 813 to measure the cMUT capacitance, which depends on the sensed pressure. Therefore, the oscillator is an example of a capacitor frequency converter circuit.

[0132] The ASIC 802 is connected to the system controller 816, which provides control commands for transmission, processes received reflected echo signals, and receives pressure measurement signals (output signal FC in this example). The system controller 816 also provides a bias voltage to the cMUT devices. The bias voltage is, for example, the same for all cMUT devices in the array.

[0133] During ultrasound imaging, system controller 816 sends a request for a transmission event to the ASIC, which then delivers a high-voltage pulse to the cMUT device. The ASIC receives the echo signal and sends it to the system controller. Switch 810 closes and switch 814 opens.

[0134] During pressure sensor mode, switch 810 is open and switch 814 is closed. The ASIC's measurement circuit 812 converts the capacitance value of the cMUT into an output signal FC. The frequency of signal FC is related to the capacitance of the cMUT.

[0135] When the pressure changes, the capacitance of the cMUT changes, and therefore the resonant frequency represented by the output signal FC also changes.

[0136] Figure 10 The example is based on converting the capacitance of a cMUT device (or more precisely, a parallel combination of cMUT devices from an ASIC) to a frequency. Capacitance can alternatively be converted to a signal having a duty cycle, voltage, or current representing the capacitance. cMUT capacitance can alternatively be converted to a digital signal.

[0137] Ultrasound images are composed of frames, each consisting of multiple transmit and receive events. Pressure sensing can occur after each frame or after a sequence of multiple frames. Thus, image generation and pressure sensing are performed in real time. Each imaging frame includes, for example, a transmit cycle and a receive cycle. Typically, the frame duration is approximately 20 μs, and the minimum duration of the pressure sensing function is approximately 10 μs.

[0138] This provides sequential pressure sensing and imaging modes. Pressure can be sensed while reconstructing ultrasound images. Pressure sensing and imaging are determined so efficiently within the same time frame.

[0139] Pressure sensing does not need to be updated at such a high rate (every 30 microseconds in this case), so the temporal impact of pressure sensing on the frame rate can be reduced by decreasing the rate of pressure measurement. Therefore, a pressure sensing cycle can be performed every N imaging frames. Each imaging frame also includes a transmission cycle and a reception cycle.

[0140] The value of N can be on the order of 1000. The resulting combined frame duration is 20 milliseconds, which is negligible compared to the pressure reading duration, but the pressure is updated at a sufficiently high rate (50 Hz in this case). Lower frequency pressure measurements are, of course, possible.

[0141] Other methods exist for using a cMUT unit as a pressure sensor. For example, a closed-loop feedback path can be used to keep the capacitance of the cMUT device constant by adjusting the bias voltage Vbias. An oscillator circuit can then be used to convert the capacitance into a frequency. The output frequency can then be compared to a fixed reference frequency, and an error signal can be used in a phase-locked loop (PLL) control system that tunes the bias voltage Vbias of the cMUT device so that the output frequency is constant and equal to the reference frequency.

[0142] In another example, the resonant frequency of the cMUT device (rather than the oscillation frequency of the oscillator circuit that includes the cMUT device capacitance) can be measured. Methods suitable for measuring the resonant frequency of a cMUT are well known in the art.

[0143] The sensor's flexible diaphragm (whether piezoelectric, piezoresistive, or capacitive) is mounted along the periphery of blood vessel 104. This type of MEMS device is highly sensitive to blood pressure. Pressure applied anywhere in a closed, incompressible fluid is transmitted equally in all directions throughout the fluid, ensuring that pressure changes remain constant. Therefore, equal forces are transmitted along the surface of the sensor's diaphragm. The pressure corresponding to no deflection or a reference deflection is known and can be used to calibrate the measurement.

[0144] The same sensor (whether piezoelectric, piezoresistive, or capacitive) is used for both pressure sensing and ultrasound imaging. An integrated ultrasound transducer is used to determine vessel diameter. Measurements can be taken using either M-mode or B-mode imaging. An automated algorithm can be used to find the diameter, allowing for vessel tracking and real-time diameter extraction using color Doppler mode. Stroke volumetric flow rate can be extracted from the velocity waveform 402 using spectral Doppler and the measured vessel diameter.

[0145] Both pressure waveform 202 and vessel diameter waveform 302 can be used to estimate the central aortic waveform. By combining these two methods (based on force and vessel diameter), more consistent and robust central pressure estimation can be achieved.

[0146] Figure 11A wearable device with a sensing patch is illustrated. The use of capacitive sensors also opens up options for wearable concepts. Since ultrasonic imaging and pressure sensing capabilities can be integrated into a single package, the sensor patch 102 can be applied to the body as a wearable concept using an acoustic skin interface 1004. In this example, the sensor patch 102 is attached to a band 1002 and has an acoustic skin interface 1004 between the sensor patch 102 and the intended contact area with the skin 106.

[0147] The wearable device may also have a housing unit that houses the sensor patch 102 and the required processor. The housing unit then has an opening for the sensor patch 102, through which the sensing area of ​​the sensor patch (the portion that performs pressure sensing and ultrasound imaging) passes. An acoustic skin interface 1004 is placed at the opening. The strap 1002 is designed to be worn around the subject's wrist, allowing the sensor patch 102 to measure blood pressure from the radial artery 104a.

[0148] Alternatively, the sensor patch 102 can be used on the carotid artery, because this vessel 104 is closer to the heart than other vessels in the body's periphery (i.e., the arm / leg).

[0149] In general, one example of the present invention involves the following workflow:

[0150] (i) Acquire force signals and determine the surface displacement waveform from them;

[0151] (ii) Acquire M-mode images and determine the waveform of the blood vessel diameter;

[0152] (iii) Determine the quality of the waveform (e.g., periodicity, heart rate, etc.), since frequency-based transfer functions should only be applied to periodic waveforms, and therefore irregular waveforms should be discarded;

[0153] (iv) Use landmarks (e.g., from ECG traces) to create an overall (averaged) signal of the external pressure waveform period;

[0154] (v) Use a transfer function to transform the waveform to the central aortic pressure waveform; and

[0155] (vi) Use the cuff pressure value to calibrate the transformed waveform.

[0156] Technicians will be able to easily develop computers for performing any of the methods described herein. Therefore, each step of the flowchart can represent a different action performed by a processor and can be executed by the corresponding module of the processor.

[0157] As described above, the system utilizes a processor to perform data processing. A processor can be implemented in various ways, using software and / or hardware, to perform a variety of required functions. A processor typically employs one or more microprocessors, which can be programmed using software (e.g., microcode) to perform the desired functions. A processor can be implemented as a combination of dedicated hardware for performing some functions and one or more programmed microprocessors and associated circuitry for performing other functions.

[0158] Examples of circuits that may be used in various embodiments of this disclosure include, but are not limited to, conventional microprocessors, application-specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

[0159] In various implementations, the processor may be associated with one or more storage media, such as volatile and non-volatile computer memories, such as RAM, PROM, EPROM, and EEPROM. The storage media may be encoded with one or more programs that, when run on one or more processors and / or controllers, perform the required functions. The various storage media may be fixed within the processor or controller, or they may be portable, allowing one or more programs stored thereon to be loaded into the processor.

[0160] Those skilled in the art, through studying the accompanying drawings, the disclosure, and the claims, will be able to understand and implement variations of the disclosed embodiments when practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the words "a" or "an" do not exclude a plurality.

[0161] A single processor or other unit can perform the functions of several items described in the claims.

[0162] Although specific measures are described in different dependent claims, this does not imply that combinations of these measures cannot be used advantageously.

[0163] Computer programs can be stored / distributed on suitable media such as optical storage media or solid-state media that are provided together with or as part of other hardware, but they can also be distributed in other forms such as via the Internet or other wired or wireless telecommunications systems.

[0164] If the term “suitable” is used in the claims or description, it should be noted that the term “suitable” is intended to be equivalent to the term “configured as”.

[0165] Any reference numerals in the claims should not be construed as limiting the scope.

Claims

1. A device for estimating the central blood pressure of a subject, the device comprising: A sensor patch (102) comprising an array of sensors configured as follows: In the first mode, force is measured at the skin (106) of the object, wherein the force provides an indication of blood pressure in the peripheral blood vessels (104); and In the second mode, ultrasound imaging is performed on the peripheral blood vessels (104), wherein the same sensor is used for both the blood pressure measurement in the first mode and the ultrasound imaging in the second mode; and The processor is configured as follows: A peripheral pressure signal, including a pressure waveform (202), is obtained based on the indication of blood pressure from the sensor patch (102); The image of the peripheral blood vessels is derived from the ultrasound imaging from the sensor patch (102); The vessel diameter is determined as a vessel diameter waveform based on the image of the peripheral vessels over time (302). An estimate of the central blood pressure waveform of the object is derived from the pressure waveform (202) and the blood vessel diameter waveform (302).

2. The device according to claim 1, wherein, The processor is configured to: The diameter of the peripheral blood vessel is determined by applying an automatic tracking algorithm to the image in color Doppler mode.

3. The device according to any one of claims 1 or 2, wherein, The sensor array includes: Capacitive micromechanical ultrasonic transducer (cMUT); piezoelectric sensor; or Piezoresistive sensor.

4. The device according to claim 1 or 2, wherein, The processor is also adapted to: Determine the quality factor for each of the plurality of peripheral pressure waveform periods (204) for the pressure waveform and the vessel diameter waveform period (306) for the vessel diameter waveform; The overall pressure waveform is created based on the pressure waveform period (204) and its corresponding quality factor; and The overall diameter waveform is created based on the vessel diameter waveform period (306) and its corresponding quality factor. The central blood pressure is estimated based on the overall pressure waveform and / or the overall diameter waveform.

5. The device according to claim 4, wherein, The processor is adapted to derive an estimate of the central blood pressure in the following manner: Apply a frequency-based transfer function to the overall pressure waveform and / or the overall diameter waveform; or The overall pressure waveform and / or the overall diameter waveform are transformed into an estimate of the central blood pressure using a physics-based model.

6. The device according to claim 1 or 2, wherein, The processor is also adapted to: The estimated mean and diastolic blood pressure values ​​were calibrated to the mean and diastolic blood pressure values ​​obtained from the pressure cuff measurements.

7. The device according to claim 1 or 2, wherein, The processor is further configured to transform the vessel diameter waveform (302) into a second pressure waveform for the peripheral vessels, and wherein the processor is configured to derive the estimate of the central blood pressure waveform of the object from the pressure waveform (202) and / or the second pressure waveform.

8. The device according to claim 1 or 2, further comprising: A housing unit for accommodating the sensor patch (102) and the processor, wherein the housing unit includes an opening, and wherein the opening is for the sensing area of ​​the sensor patch (102); Binding straps (1002), which are attached to the housing unit; and Skin interface (1004) at the opening of the housing unit.

9. A method for estimating the central blood pressure of a subject, the method comprising: In a first mode, a force is measured at the skin (106) of the object using a sensor patch (102), wherein the force provides an indication of blood pressure in peripheral blood vessels (104) to derive a pressure waveform (202) from the sensor of the sensor patch (102). In a second mode, ultrasound imaging of the peripheral blood vessel (104) is performed using the sensor patch to derive an image of the peripheral blood vessel from the sensor of the sensor patch (102), wherein the same sensor is used for the blood pressure measurement in the first mode and the ultrasound imaging in the second mode. The processor uses the indication of blood pressure from the sensor patch (102) to obtain a peripheral pressure signal including a pressure waveform (202); The processor is used to derive an image of the peripheral blood vessels based on the ultrasound imaging from the sensor patch (102); The processor uses the image of the peripheral blood vessel (104) over time to determine the blood vessel diameter as a blood vessel diameter waveform (302); and The processor is used to derive an estimate of the central blood pressure waveform of the object based on the pressure waveform (202) and the blood vessel diameter waveform (302).

10. The method according to claim 9, wherein, The diameter of the blood vessel was determined by applying an automatic tracking algorithm to the image in color Doppler mode.

11. The method according to any one of claims 9 or 10, further comprising: Determine the quality factors for multiple peripheral pressure waveform periods (204) of the pressure waveform and multiple vessel diameter waveform periods (306) of the vessel diameter waveform; The overall pressure waveform is created based on the pressure waveform period (204) and its corresponding quality factor; and The overall diameter waveform is created based on the vessel diameter waveform period (306) and its corresponding quality factor. The central blood pressure is estimated based on the overall pressure waveform and / or the overall diameter waveform.

12. The method according to claim 11, wherein, The central blood pressure is estimated based on: Apply a frequency-based transfer function to the overall pressure waveform and / or the overall diameter waveform; or The overall pressure waveform and / or the overall diameter waveform are transformed into an estimate of the central blood pressure using a physics-based model.

13. The method of claim 9 or 10, further comprising calibrating the estimated mean and diastolic blood pressure values ​​of the central blood pressure to the mean and diastolic blood pressure values ​​of the cuff obtained from the pressure cuff measurements.

14. The method according to claim 9 or 10, further comprising transforming the vessel diameter waveform (302) into a second pressure waveform for the peripheral vessels, and deriving the estimate of the central blood pressure waveform of the object based on the pressure waveform (202) and / or the second pressure waveform.

15. A computer program product comprising computer-readable code configured to cause, when executed by a processor, the processor to operate the device according to any one of claims 9 to 14 using the method described in any one of claims 1 to 8.

Images