System and method for measuring blood pressure

Abstract

Systems and methods for measuring blood pressure. In some embodiments, the system includes a speckle plethysmography sensor and processing circuitry. The system may be configured to: perform blood flow measurements and measurements of cuff pressure of a subject using a speckle plethysmography sensor when the cuff pressure of a cuff worn by the subject changes; and calculating a first blood pressure from the blood flow measurement and the cuff pressure measurement.

Description

[0001] Cross-reference to (one or more) related applications This application claims priority and benefits to U.S. Provisional Application No. 63 / 514994 (filed July 21, 2023, entitled "CUFF-BASED BLOOD PRESSURE MEASUREMENT USING BLOOD FLOW"), the entire contents of which are incorporated herein by reference. Technical Field

[0002] One or more aspects of embodiments of this disclosure relate to health monitoring, and more specifically, to systems and methods for measuring blood pressure. Background Technology

[0003] For subjects, blood pressure can be a useful biomarker, for example, as a general indicator of some aspects of the subject's health, or as a diagnostic tool when investigating diseases.

[0004] The aspects of this disclosure pertain to this general technical environment. Summary of the Invention

[0005] According to one embodiment of the present disclosure, a system is provided, including: a speckle plethysmography sensor; and processing circuitry, the system being configured to: perform blood flow measurement and cuff pressure measurement of the subject using the speckle plethysmography sensor when the cuff pressure of a cuff worn by the subject changes; and calculate a first blood pressure from the blood flow measurement and the cuff pressure measurement.

[0006] In some embodiments: the first blood pressure is systolic blood pressure, and the calculation of the first blood pressure includes using speckle plethysmography pulse detection to calculate the first blood pressure.

[0007] In some embodiments: the first blood pressure is systolic blood pressure, and the calculation of the first blood pressure includes using a low-frequency speckle volumetric plethysmography method to calculate the first blood pressure.

[0008] In some embodiments: the first blood pressure is systolic blood pressure, and the calculation of the first blood pressure includes: calculating a first value of the first blood pressure using speckle plethysmography pulse detection; and calculating a second value of the first blood pressure using a low-frequency speckle plethysmography method.

[0009] In some embodiments, the calculation of the first blood pressure also includes calculating a weighted sum of a first value of the first blood pressure and a second value of the first blood pressure.

[0010] In some embodiments, the first blood pressure is systolic blood pressure, and the system is also configured to calculate diastolic blood pressure from blood flow measurements and cuff pressure measurements.

[0011] In some embodiments, diastolic blood pressure calculation includes using pulse template matching to calculate diastolic blood pressure.

[0012] In some embodiments, diastolic blood pressure calculation includes using maximal amplitude detection to calculate diastolic blood pressure.

[0013] In some embodiments, the calculation of diastolic blood pressure includes: calculating a first value of diastolic blood pressure using pulse template matching; and calculating a second value of diastolic blood pressure using maximal amplitude detection.

[0014] In some embodiments, the calculation of diastolic blood pressure also includes calculating a weighted sum of a first value of diastolic blood pressure and a second value of diastolic blood pressure.

[0015] According to one embodiment of the present disclosure, a method is provided, comprising: measuring a first blood pressure, the measurement of the first blood pressure comprising: causing a change in cuff pressure on a cuff on a subject's appendage; generating a speckle volumetric signal from a speckle volumetric sensor on the appendage; and determining the first blood pressure based on the speckle volumetric signal and based on the cuff pressure.

[0016] In some embodiments: the first blood pressure is systolic blood pressure, and determining the first blood pressure includes: reducing cuff pressure; and determining the cuff pressure at a time point where a measurement of blood flow based on a speckle plethysmography signal indicates an increase in blood flow.

[0017] In some embodiments, blood flow is measured based on a pulse detection method.

[0018] In some embodiments, the pulse detection method includes: calculating a measurement of the quality of a candidate pulse; and evaluating whether the candidate pulse is part of a pulse sequence.

[0019] In some embodiments, the evaluation of whether a candidate pulse is part of a pulse sequence includes: determining whether the amplitude of the candidate pulse is consistent with the amplitude trend within the pulse sequence, and determining whether the time position of the candidate pulse is consistent with the time position of the pulse sequence.

[0020] In some embodiments, blood flow is measured based on a low-frequency speckle volumetric plethysmography method.

[0021] In some embodiments, blood flow measurement is also based on a pulse detection method.

[0022] In some embodiments: the first blood pressure is diastolic blood pressure, and determining the first blood pressure includes: reducing cuff pressure; and determining the cuff pressure at the time point at which the speckle volumetric signal has the maximum amplitude.

[0023] In some embodiments: the first blood pressure is diastolic blood pressure, and determining the first blood pressure includes: reducing cuff pressure; and determining the cuff pressure at a time point where the inconsistency between the speckle volumetric recording signal and the template waveform is less than a threshold.

[0024] In some embodiments: the first blood pressure is diastolic blood pressure, and determining the first blood pressure includes: reducing cuff pressure; and determining the cuff pressure at a time point at which the low-frequency speckle volumetric signal stops increasing. Attached Figure Description

[0025] These and other features and advantages of this disclosure will be appreciated and understood by referring to the specification, claims and accompanying drawings, wherein: Figure 1 This is a schematic diagram of a subject's arm and a system for measuring blood pressure according to an embodiment of the present disclosure; Figure 2A is a graph of cuff pressure according to an embodiment of the present disclosure; Figure 2B is a graph of blood flow velocity according to an embodiment of the present disclosure; Figure 2C This is a graph of Korotkoff sounds according to an embodiment of the present disclosure; Figure 3 These are curves of cuff pressure and blood flow velocity according to an embodiment of the present disclosure. Figure 4 It is a graph of cuff pressure and low-frequency blood flow velocity according to an embodiment of the present disclosure; Figure 5 It is a graph of blood flow velocity according to an embodiment of the present disclosure; and Figure 6 These are graphs of blood flow velocity and templates according to an embodiment of the present disclosure. Detailed Implementation

[0026] The detailed description set forth below in conjunction with the accompanying drawings is intended as a description of exemplary embodiments of the systems and methods for measuring blood pressure provided in this disclosure, and is not intended to represent the only forms in which the disclosure may be constituted or utilized. The description is illustrated to illustrate features of the disclosure. However, it is to be understood that the same or equivalent functions and structures may be implemented through different embodiments, which are also intended to be covered within the scope of this disclosure. As indicated elsewhere herein, similar element designations are intended to indicate similar elements or features.

[0027] Various methods can be used to measure a subject's blood pressure. For example, a blood pressure cuff (e.g., an inflatable cuff (containing an inflatable pneumatic bladder) that can be fixed around the upper arm to apply pressure to the upper arm, the pressure corresponding to the (pneumatic) pressure in the cuff) can be attached to the subject's upper arm, the cuff can be inflated until arterial blood flow stops, and then the cuff can be gradually deflated while monitoring the pressure in the cuff; then the systolic (blood) pressure can be read from the pressure sensor as the pressure during the first (K1) phase of the Korotkoff sound, and the diastolic (blood) pressure can be read from the pressure sensor as the pressure during the fifth (K5) phase of the Korotkoff sound.

[0028] In another method, the blood pressure cuff can be inflated or deflated, and the pressure in the cuff can be gradually increased or decreased simultaneously. The cuff pressure (e.g., the pneumatic pressure in the cuff) can be measured with sufficient accuracy and bandwidth to detect pressure fluctuations in the cuff due to variations in arterial pressure (e.g., arterial pressure in the brachial artery) with the cardiac cycle. These cuff pressure fluctuations can be small or zero in amplitude when the cuff pressure is high enough to impede blood flow in the brachial artery, and when the cuff pressure is low enough that the pressure on the arm is small and (therefore) arterial pressure fluctuations have little effect on the cuff pressure. At some point between these two extremes of cuff pressure, the fluctuations in cuff pressure can have maximum amplitude; the average cuff pressure at the point of maximum amplitude (referred to herein as "pressure at maximum amplitude") can be used as an approximation of the mean arterial pressure, which is defined herein as equal to one-third of the systolic pressure plus two-thirds of the diastolic pressure. In this context, "mean cuff pressure" is the average of (fluctuating) cuff pressure, such as a time average over one or more cardiac cycles, or the average of the maximum and minimum cuff pressures during a cardiac cycle.

[0029] In some embodiments, the blood flow rate downstream of the cuff (in the direction of arterial blood flow) may be used in conjunction with adjustments to the cuff pressure (and measurements of the cuff pressure) to perform a blood pressure measurement (discussed in more detail below). Such blood pressure measurements can be used, for example, to improve the accuracy of blood pressure measurements made using a cuff alone (e.g., by obtaining cuff calibration) or to improve the accuracy of blood pressure measurements made using another blood pressure measurement system (which can be calibrated using the systems and methods disclosed herein). Such blood pressure measurement systems may be systems using sensors that are (i) one or more plethysmography sensors or (ii) one or more plethysmography sensors and one or more speckle plethysmography sensors. Compared to systems using only a cuff, for example, the systems and methods described herein can achieve blood pressure measurements with higher accuracy (e.g., measurements of systolic and diastolic blood pressure), and therefore, the systems and methods described herein provide improvements in the technology of blood pressure measurement.

[0030] Figure 1 A system for measuring blood pressure is shown in some embodiments. A cuff 105 is secured around the subject's upper arm. The cuff 105 is connected to an inflation control system 110, which may include a pump and one or more valves (e.g., metering valves) or flow meters for (i) pumping air into the cuff to increase cuff pressure or (ii) reducing cuff pressure by allowing the cuff to deflate (by allowing air to escape from the cuff to the atmosphere). The rate of inflation or deflation can be controlled, for example, by adjusting the pump speed or by opening or closing the metering valve in the inflation control system 110. A pressure sensor 115 (which may have sufficient accuracy and bandwidth to detect pressure fluctuations in the cuff due to variations in arterial pressure with the cardiac cycle) is pneumatically connected (e.g., integrated therein) to the pneumatic bladder of the cuff 105 and measures the pressure in the cuff 105 (e.g., in the pneumatic bladder of the cuff 105).

[0031] Controller 120 (which may be processing circuitry (discussed in more detail below)) is connected to inflation control system 110 and to pressure sensor 115. The processing circuitry can control the inflation and deflation of cuff 105, for example, it can cause the pressure to increase or decrease smoothly (at a substantially constant rate) and monotonically (except for pressure fluctuations in the cuff due to arterial pressure fluctuations with the cardiac cycle) during inflation and deflation. In some embodiments, controller 120 includes a feedback controller (e.g., a feedback controller implemented in software or firmware) that receives a pressure signal from pressure sensor 115 and performs closed-loop control of the cuff pressure such that the cuff pressure follows a pressure setpoint (e.g., a pressure setpoint that is increasing or decreasing at a constant rate).

[0032] A sensor for measuring blood flow velocity may be attached to the subject's arm at a point downstream of cuff 105 (for arterial flow). This sensor may be or may include a speckle volumetric sensor 125. The speckle volumetric sensor 125 may include (i) a coherent light source (e.g., a semiconductor laser) for illuminating the subject's tissue (including the artery downstream of cuff 105), and (ii) an image sensor for receiving light that has interacted with (e.g., scattered from) the tissue (including blood in the artery). The light that has interacted with the tissue and the blood in the artery may form a speckle pattern on the image sensor. The speckle pattern may change as blood moves through the artery; the rate at which the speckle pattern changes may depend on (e.g., be proportional to) the blood flow velocity. The measured image contrast (also referred to as speckle contrast (e.g., speckle contrast measured by the image sensor)) may decrease as the blood flow velocity (and the rate at which the speckle pattern changes) increases, because changes in the speckle pattern due to moving scatterers occur faster than the integration time for each exposure. Therefore, the measured speckle contrast can depend on the blood flow velocity and can be used to measure the blood flow velocity. The measured speckle contrast can also be affected by the spatial integration over the region of each pixel of the image sensor (e.g., by the speckle-pixel size ratio), the temporal integration over the exposure time of each exposure, and the effects of laser coherence and polarization. The measured blood flow velocity can be a discrete-time (sampled) signal with a sampling rate equal to the frame rate of the image sensor (e.g., a sampling rate between 10 Hz and 1000 Hz).

[0033] Figures 2A-2C show cuff pressure (Figure 2A), arterial blood flow velocity (Figure 2B) measured by speckle plethysmography (SPG), and Korotkoff sounds in an example of cuff inflation and deflation of cuff 105. Figure 2C As can be seen from Figures 2A-2C, when the cuff pressure is high enough (e.g., high enough to stop arterial blood flow), the fluctuations in blood flow velocity with the cardiac cycle cease, and when the cuff pressure is reduced (e.g., by deflation), the first Korotkoff sound 205 occurs approximately simultaneously with a local peak 210 (representing a heartbeat) in the blood flow velocity as measured by speckle plethysmography. Instantaneous blood flow velocity can vary over time and can differ from the mean blood flow velocity (which may also be referred to as low-frequency blood flow velocity) at any point in the cardiac cycle.

[0034] Systolic blood pressure can be transmitted through Figure 1The system is measured using several methods. Such methods may include increasing the cuff pressure sufficiently to stop arterial flow, then decreasing the cuff pressure, and determining the cuff pressure at a time point where a measurement of blood flow based on a speckle plethysmography signal indicates a temporary, localized increase in blood flow during at least a portion of the cardiac cycle. In a first method for measuring systolic blood pressure, an increase in blood flow is detected using speckle plethysmography pulse detection (by detecting the first pulse during cuff deflation), and the cuff pressure at that time (e.g., the average cuff pressure at the time of the first detected pulse, or the instantaneous cuff pressure at the time of the first detected pulse) can be used as the measured systolic blood pressure.

[0035] As used herein, “pulse detection” refers to the detection of a blood flow velocity signal caused by the cardiac cycle (e.g., not by other mechanisms, such as noise). Therefore, pulse detection may involve detecting (e.g., distinguishing it from noise) a blood flow velocity peak corresponding to ventricular contraction, or it may involve detecting (e.g., distinguishing it from noise) a waveform corresponding to the entire cardiac cycle. Similarly, the “pulse” being detected can be a portion of the cardiac cycle (e.g., a peak corresponding to ventricular contraction) or the entire cardiac cycle.

[0036] Pulse detection can be performed using any of several methods or any combination thereof. In a first method, a time interval (e.g., an interval having a length approximately equal to the length of the cardiac cycle) can be selected as a candidate pulse. This selection may involve, for example, selecting a time interval that includes local peaks in the blood flow velocity signal. One or more methods can then be used to evaluate the candidate pulse, and a determination can be made based on this evaluation, such as whether the candidate pulse is a pulse. For example, one or more of various measurements of the quality (or “quality metric”) of the candidate pulse can be applied to the candidate pulse. Examples of quality metrics include (i) whether the time between a candidate pulse and an adjacent detected pulse is less than a threshold interval (e.g., less than 1.75 seconds), (ii) whether the amplitude of the candidate pulse (e.g., peak-to-peak amplitude) is at least a small fraction (e.g., at least 15%) of the pre-inflated pulse amplitude, (iii) whether the rise time of the blood flow velocity peak (e.g., 25%–75% rise time) is less than a small fraction (e.g., less than 50%) of the interval between pulses, (iv) whether the number of zero crossings in the candidate pulse (e.g., in the blood flow velocity corresponding to the candidate pulse) is less than a threshold (e.g., whether there are fewer than 5 zero crossings), and (v) whether the Euclidean distance between a candidate pulse and an adjacent detected pulse is less than a threshold distance (e.g., less than 0.2 times the peak-to-peak amplitude of the candidate pulse or less than 0.2 times the peak-to-peak amplitude of the adjacent detected pulse). As used herein, “Euclidean distance” is the square root of the sum of the squares of the sample-to-sample differences.

[0037] In the second method, pulse detection may include assessing whether a candidate pulse is part of a sequence of detected pulses. This may involve, for example, assessing whether the temporal location of the candidate pulse coincides with the temporal location of the sequence of detected pulses. For example, features in the blood flow velocity signal (e.g., the onset or peak of a contraction peak) may be identified for the candidate pulse, and its temporal location may be compared to where it would be if it were part of a regularly spaced sequence of pulses, which is a set of hypothetical regular pulses fitted (by adjusting the frequency and phase of this set of hypothetical pulses) to the sequence of detected pulses. Using this method, the closer the temporal location is to its hypothetical location within that set of hypothetical regular pulses, the higher the quality measurement of the candidate pulse can be. For example, if the offset between the temporal location of the candidate pulse and the hypothetical location is less than a threshold (where the threshold may be, for example, between 0.05 and 0.35 times the interval between the pulses in the set of hypothetical regular pulses), then (and only then) the candidate pulse can be determined to be a pulse. In some embodiments, a candidate pulse is identified as a pulse only if its temporal position is near the first detected pulse in the sequence of detected pulses (e.g., if it precedes the first detected pulse by an interval of one pulse). In some embodiments, a combination of the methods disclosed herein can be used to determine whether a candidate pulse is a pulse. For example, each of the methods disclosed herein can be used to generate a score for the candidate pulse (based on a corresponding measurement of quality), and the candidate pulse can then be identified as a pulse only if the weighted average of the scores exceeds a threshold.

[0038] As another example, the assessment of whether a candidate pulse is part of a pulse sequence may include determining whether the amplitude of the candidate pulse is consistent with the amplitude trend within the sequence of detected pulses. For example, in some embodiments, a pulse is first detected after the cuff pressure has dropped below the systolic pressure (e.g., because the pulse amplitude may increase after the cuff pressure drops below the systolic pressure, making such subsequent pulses more detectable). The system may then reanalyze the blood flow velocity signal acquired before the first detected pulse and attempt to detect one or more additional pulses (using the timing of the already detected pulses to aid in the detection of such earlier pulses). The earlier pulses may then be detected, for example, based on their temporal location (as discussed above) or also (or alternatively) based on their amplitude. For example, because the pulse amplitude is initially expected to increase after the cuff pressure drops below the systolic pressure, a candidate pulse with a larger (peak-to-peak) amplitude compared to the next detected pulse may be determined not to be a pulse (and, for example, determined to be caused by noise).

[0039] Figure 3 Two graphs are shown: one showing the cuff pressure. Figure 3 The upper curve) and the curve of blood flow velocity signal ( Figure 3 The upper graph shows the systolic blood pressure 305 and diastolic blood pressure 310 determined using the methods disclosed herein. The lower graph shows the initiation 315 of multiple pulses in the blood flow velocity signal before cuff inflation and after cuff deflation, the initiation 320 and peak 325 due to noise, the initiation 330 of the first pulse detected during deflation (which can be detected using one or more of the methods disclosed herein), the initiation 335 of each of the multiple additional pulses during deflation from systolic to diastolic blood pressure, and the peak 340 of each of the multiple pulses.

[0040] In some embodiments, low-frequency speckle plethysmography is used as a measurement of blood flow to determine systolic blood pressure (e.g., Figure 4 (As shown in the illustration). Figure 4 This is a graph plotting the low-frequency (filtered) blood flow velocity (LSPG) signal for cuff pressure during inflation (upper part of the graph) and deflation (lower part of the graph). The low-frequency blood flow velocity signal can be obtained from the blood flow velocity (SPG) signal by low-pass filtering (e.g., with a cutoff frequency of 0.5 Hz), and the cuff pressure signal can also be processed by low-pass filtering (e.g., with a cutoff frequency of 0.15 Hz). Figure 4 In this method, a minimum value in the low-frequency blood flow velocity signal can be used as an estimate of the systolic blood pressure (e.g., to determine the systolic blood pressure) as shown (where the systolic blood pressure is located midway between a minimum value extending from 125 mmHg to 135 mmHg). The minimum value can be the point where the low-frequency blood flow velocity signal first indicates an increase in blood flow during deflation. Diastolic blood pressure can also be estimated as the cuff pressure during deflation where the increase in low-frequency blood flow velocity stops. In some embodiments, the systolic blood pressure is calculated as a weighted sum of: (i) a first value of systolic blood pressure determined using speckle plethysmography pulse detection; and (ii) a second value of systolic blood pressure determined using a low-frequency speckle plethysmography method.

[0041] Figure 5 The illustration shows a method for determining the onset of a pulse with a peak 505 in some embodiments. A first tangent 510 is a (horizontal) tangent to the blood flow velocity (SPG) signal at its minimum value immediately preceding the peak 505, and a second tangent 515 is a tangent at the point where the slope between the minimum value and the peak 505 is greatest. Figure 5 In this method, the time corresponding to the intersection of the tangents 510 and 515 is defined as the start of the pulse.

[0042] Available includes Figure 4 The method (discussed above) can be any of several different methods or any combination thereof to measure diastolic blood pressure. In one method (which may be called “pulse template matching”), a template waveform of blood flow velocity during the cardiac cycle is acquired and stored (or averaged and stored) before cuff inflation, and is then used during cuff deflation to determine diastolic blood pressure. During cuff deflation, after the cuff pressure begins to drop below the systolic pressure, the blood flow velocity waveform may become distorted (relative to the pre-inflation waveform) because the compression of the arteries by the cuff during some or all of the cardiac cycle impedes or stops blood flow. As the cuff pressure continues to decrease, the waveform becomes more similar to the pre-inflation waveform. Thus, each detected pulse (e.g., detected using the pulse detection method discussed above) can be compared with one or more stored templates (e.g., templates formed by averaging multiple pre-inflated waveforms), and the template matching error (e.g., inconsistency between the speckle volumetric recording signal and the template waveform) can be calculated (e.g., by calculating the Euclidean distance between the candidate pulse and the template). Figure 6 The waveform 605 of a detected pulse and the waveform 610 of a template are shown in one example. If the pulse is the first pulse with a template matching error less than a threshold (e.g., a threshold between 0.05 and 0.3 times the peak-to-peak amplitude of the detected pulse or the template) (and, in some embodiments, if the pulse also meets certain diastolic pulse requirements), the diastolic pressure can be determined as the cuff pressure at the time the pulse was received. The diastolic pulse requirements may include the requirement that the cuff pressure at the time of the diastolic pulse is less than the mean arterial pressure.

[0043] In another method for determining diastolic blood pressure (referred to as "maximum amplitude detection"), the cuff pressure at the time of the detected pulse with the maximum amplitude (e.g., peak-to-peak amplitude) in the blood flow velocity signal during cuff deflation is used as the diastolic blood pressure (provided that the cuff pressure at the time of said pulse is less than the mean arterial pressure). In some embodiments, diastolic blood pressure is calculated as a weighted sum of values ​​determined using different methods disclosed above, for example, as a weighted sum of: (i) a first value of diastolic blood pressure determined using pulse template matching; and (ii) a second value of diastolic blood pressure determined using maximum amplitude detection.

[0044] While some examples of a pressure cuff and speckle plethysmography sensor 125 comprising a pressure cuff on the subject's arm are disclosed herein, the invention is not limited to such embodiments, and these components may be placed on the subject in other ways, such as on another limb (e.g., on a leg) or on another appendage (e.g., on a toe or finger, or on the tail of a tailed vertebrate). Use of the systems and methods disclosed herein is not limited to measurements on humans, and these systems and methods may be used, for example, on other mammals or other vertebrates. While some examples of methods comprising determining (e.g., estimating) blood pressure while the cuff is being deflated are disclosed herein, in other embodiments, cuff pressure may vary in different ways; for example, blood pressure may be estimated while the cuff is being inflated.

[0045] As used herein, “a portion” of something means “at least some” of that thing, and so may mean less than or all of that thing. Thus, as a special case, “a portion” of something includes the whole thing, that is, the whole thing is an example of a portion of something. As used herein, when a second quantity is “within Y” of a first quantity X, it means that the second quantity is at least XY and at most X+Y. As used herein, when a second number is “within Y%” of a first number, it means that the second number is at least (1-Y / 100) times the first number and at most (1+Y / 100) times the first number. As used herein, the word “or” is inclusive, such that, for example, “A or B” means (i) A, (ii) B, and (iii) either A or B.

[0046] The terms “processing circuitry” and “components for processing” are used herein to refer to any combination of hardware, firmware, and software used to process data or digital signals. Processing circuitry hardware may include, for example, application-specific integrated circuits (ASICs), general-purpose or special-purpose central processing units (CPUs), digital signal processors (DSPs), graphics processing units (GPUs), and programmable logic devices such as field-programmable gate arrays (FPGAs). In processing circuitry as used herein, each function is performed by hardware configured (i.e., hardwired) to perform that function or by more general-purpose hardware (such as a CPU) configured to execute instructions stored in a non-transitory storage medium. Processing circuitry may be fabricated on a single printed circuit board (PCB) or distributed across several interconnected PCBs. Processing circuitry may include other processing circuitry; for example, processing circuitry may include two processing circuits (FPGA and CPU) interconnected on a PCB.

[0047] As used herein, when a method (e.g., adjustment) or a first quantity (e.g., a first variable) is referred to as “based on” a second quantity (e.g., a second variable), it means that the second quantity is an input to the method or affects the first quantity. For example, the second quantity may be an input to a function that computes the first quantity (e.g., only input, or one of several inputs), or the first quantity may be equal to the second quantity, or the first quantity may be the same as the second quantity (e.g., at the same location or multiple locations in memory where it is stored).

[0048] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the inventive concept. As used herein, the terms “substantially,” “approximately,” and similar terms are used as approximate terms rather than terms of degree and are intended to take into account the inherent deviations in measurements or calculations that would be recognized by one of ordinary skill in the art.

[0049] Any numerical range described herein is intended to include all subranges of the same numerical precision falling within the described range. For example, a range “1.0 to 10.0” or “between 1.0 and 10.0” is intended to include all subranges between (and inclusive of) the described minimum value of 1.0 and the described maximum value of 10.0, that is, such as a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, for example, 2.4 to 7.6. Similarly, a range described as “within 35% of 10” is intended to include all subranges between (and inclusive of) the described minimum value of 6.5 (i.e., (1–35 / 100) multiplied by 10) and the described maximum value of 13.5 (i.e., (1+35 / 100) multiplied by 10), that is, such as a minimum value equal to or greater than 6.5 and a maximum value equal to or less than 13.5, for example, 7.4 to 10.6. Any maximum numerical limit described herein is intended to include all lower numerical limits thereunder, and any minimum numerical limit described herein is intended to include all higher numerical limits thereunder.

[0050] Although exemplary embodiments of systems and methods for measuring blood pressure have been specifically described and illustrated herein, many modifications and variations will be apparent to those skilled in the art. Therefore, it should be understood that systems and methods for measuring blood pressure constructed according to the principles of this disclosure may be implemented differently than those specifically described herein. The invention is also defined in the following claims and their equivalents.

Claims

1. A system comprising: Speckle volumetric sensor; as well as Processing circuit, The system is configured as follows: When the cuff pressure of the cuff worn by the subject changes, the speckle plethysmography sensor is used to perform blood flow measurements on the subject and measurements of the cuff pressure. as well as The first blood pressure is calculated from the blood flow measurement and the cuff pressure measurement.

2. The system as claimed in claim 1, wherein: The first blood pressure is the systolic pressure, and The calculation of the first blood pressure includes using speckle volume plethysmography pulse detection to calculate the first blood pressure.

3. The system as claimed in claim 1 or claim 2, wherein: The first blood pressure is the systolic pressure, and The calculation of the first blood pressure includes using a low-frequency speckle volumetric plethysmography method.

4. The system as described in any of the preceding claims, wherein: The first blood pressure is the systolic pressure, and The calculation of the first blood pressure includes: A first value of the first blood pressure was calculated using speckle plethysmography pulse detection; and The second value of the first blood pressure was calculated using a low-frequency speckle volume plethysmography method.

5. The system as described in claim 4, wherein, The calculation of the first blood pressure further includes: calculating a weighted sum of the first value of the first blood pressure and the second value of the first blood pressure.

6. The system as described in any of the preceding claims, wherein: The first blood pressure is the systolic pressure, and The system is also configured to calculate diastolic blood pressure from the blood flow measurement and the cuff pressure measurement.

7. The system of claim 6, wherein, The calculation of the diastolic blood pressure includes using pulse template matching to calculate the diastolic blood pressure.

8. The system as claimed in claim 6 or claim 7, wherein, The calculation of the diastolic blood pressure includes using maximum amplitude detection to calculate the diastolic blood pressure.

9. The system according to any one of claims 6 to 8, wherein, The calculation of the diastolic blood pressure includes: The first value of the diastolic blood pressure was calculated using pulse template matching; and The second value of the diastolic blood pressure was calculated using the maximum amplitude detection.

10. The system of claim 9, wherein, The calculation of diastolic blood pressure further includes calculating a weighted sum of the first value of diastolic blood pressure and the second value of diastolic blood pressure.

11. A method comprising: Measure your first blood pressure. The measurement of the first blood pressure includes: This causes a change in the cuff pressure on the subject's appendage; A speckle volumetric signal is generated from a speckle volumetric sensor on the appendage; and The first blood pressure is determined based on the speckle volume plethysmography signal and the cuff pressure.

12. The method of claim 11, wherein: The first blood pressure is systolic blood pressure, and The determination of the first blood pressure includes: Reduce the pressure on the cuff; and The cuff pressure is determined at the time point indicated by the increase in blood flow based on the measurement of blood flow from the speckle volumetric signal.

13. The method of claim 12, wherein, The blood flow measurement is based on a pulse detection method.

14. The method of claim 13, wherein, The method for pulse detection includes: Calculating the quality of candidate pulses; and Evaluate whether the candidate pulse is part of a pulse sequence.

15. The method of claim 14, wherein, The evaluation of whether the candidate pulse is part of a pulse sequence includes: Determine whether the amplitude of the candidate pulse is consistent with the amplitude trend within the pulse sequence, and Determine whether the time position of the candidate pulse is consistent with the time position of the pulse sequence.

16. The method of claim 12, wherein, The blood flow measurement is based on a low-frequency speckle volumetric plethysmography method.

17. The method of claim 16, wherein, The blood flow measurement is also based on pulse detection methods.

18. The method of claim 11, wherein: The first blood pressure is diastolic blood pressure, and The determination of the first blood pressure includes: Reduce the pressure on the cuff; and The cuff pressure is determined at the time point when the speckle volumetric signal has the maximum amplitude.

19. The method of claim 11 or claim 18, wherein: The first blood pressure is diastolic blood pressure, and The determination of the first blood pressure includes: Reduce the pressure on the cuff; and The cuff pressure is determined at the time point when the inconsistency between the speckle volume plethysmography signal and the template waveform is less than a threshold.

20. The method of any one of claims 11, 18, and 19, wherein: The first blood pressure is diastolic blood pressure, and The determination of the first blood pressure includes: Reduce the pressure on the cuff; and The cuff pressure was determined at the time point at which the low-frequency speckle volumetric plethysmography signal ceased to increase.

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