Extrapolation methods for blood pressure measurement

Abstract

A method for shortening a measurement period for a user's blood pressure begins with the step of measuring pressure data and optical data over the measurement period using a biometric monitoring device, where the pressure data reflects pressures applied by a finger of the user to the biometric monitoring device, and where the optical data reflects a flow of blood through the finger that is detected by the biometric monitoring device. The method continues with the steps of terminating the measurement period at a measurement endpoint, obtaining extrapolated pressure values and extrapolated optical values that reflect an extrapolated period after the measurement endpoint, generating an extrapolated curve using the pressure data, the optical data, the extrapolated pressure values, and the extrapolated optical values and estimating of the user's blood pressure using the extrapolated curve.

Description

EXTRAPOLATION METHODS FOR BLOOD PRESSURE MEASUREMENTRELATED APPLICATIONS

[0001] This application claims the benefit of United States Provisional Patent Application Serial No. 63 / 521,840 filed June 19, 2023 and entitled, “Extrapolation Methods for Blood Pressure Measurement,” the disclosure of which is herein incorporated by reference.FIELD OF THE INVENTION

[0002] This invention generally relates to measuring blood pressure and, more particularly, but not by way of limitation, to methods for shortening the measurement time for a user's blood pressure through data extrapolation.BACKGROUND OF THE INVENTION

[0003] There is a growing recognition of the importance of enabling people to take greater control of their health. Notwithstanding this growth of emphasis on personal health management, there is a shortage of biometric measurement devices that are accurate, affordable, easy to use, and readily available to the public. Integrating the functionality7for biometric measurement and monitoring into a portable and widely available product, such as a key fob or cellphone, would greatly enhance the ability7of people to manage their health.

[0004] Blood pressure, for example, is a fundamental diagnostic parameter that is used throughout the world to assess health. The basic measurements for this vital sign are diastolic blood pressure, the lowest pressure observed during the pulse cycle, and systolic blood pressure, the highest pressure observed during the pulse cycle. At least three methods have been established for measuring absolute arterial blood pressure without inserting a measurement device into the artery: auscultatory, oscillometric and volume clamp methods. There are also relative measurement methods that detect changes or trends in blood pressure, but these methods require calibration for each user.

[0005] With reference to traditional oscillometric methods for blood pressure measurement, automatic sphygmomanometers such as an inflatable cuff are often used toocclude blood flow in an artery, usually the brachial or radial (wrist) artery. The cuff is then more slowly deflated to allow blood to begin to flow again. During deflation, the flow is detected by observing small pressure fluctuations introduced into the cuff by the pulse.

[0006] To enhance user functionality , alternatives to the traditional cuff have been developed to determine blood pressure by measuring photoplethysmography (PPG) signals from a body part (e.g., a finger) until arterial occlusion is achieved. The pressure at which the target artery is occluded is representative of the blood pressure and the pulsatile arterial blood volume waveforms can be used to calculate blood pressure, among other biometrics. These alternative devices differ from automatic blood pressure cuffs, which rely on Korotkoff sounds rather than PPG signals to estimate blood pressure.

[0007] In most PPG-based measuring systems, one or more light emitting diodes (LEDs) or other photoemitters emit light into a vascular structure while one or more photoreceptors (e.g., photodiodes) measure the reflective or transmissive light produced by' the photoemitter. To successfully estimate blood pressure using a PPG approach, it is crucial to obtain a high-quality PPG signal from the user. The user’s pulse can be evaluated by measuring the alternating current (AC) signal attributable to the cyclical pulse, while limiting the impact of the less-cyclical direct current (DC) signal attributable to baseline blood flow and tissues within the target vascular structure.

[0008] To successfully estimate blood pressure using a PPG approach, an external pressure that is greater than systolic blood pressure must be applied by (or to) the body part with the PPG sensor. Applying such high external pressures by the body part to the sensor may be uncomfortable. Further, it may take an extended period for the pressure applied by the body part to increase enough to exceed systolic blood pressure. For devices that rely on a user to apply the external pressures, user compliance may diminish with an extended measurement time. For example, a user may become tired and lose concentration towards the end of themeasurement, and the user may therefore interfere with the measurement quality by failing to apply pressure in a consistent manner, moving around, talking, or shifting the placement of the body part on the measuring device, as a non-exhaustive list of examples. Aside from usabilityissues, the PPG signals obtained at higher pressures may be unreliable due to distortions from, for example, harmonic interference. Each of these limitations may negatively affect the quality of the PPG signals obtained and thereby reduce the accuracy of the blood pressure measurement.

[0009] A need exists, therefore, for systems and methods to obtain accurate blood pressure measurements from biosignals, such as a PPG signal, while avoiding the signal distortions that occur when applying higher external pressures to a body part and / or when taking a blood pressure measurement over an extended period of time.SUMMARY OF THE INVENTION

[0010] In some embodiments, a method for shortening a measurement period for a user’s blood pressure is disclosed. The method may include the steps of measuring pressure data and optical data over the measurement period using a biometric monitoring device; terminating the measurement period at a measurement endpoint; and obtaining extrapolated pressure values and extrapolated optical values that reflect an extrapolated period after the measurement endpoint. The pressure data may reflect pressures that are applied by a finger of the user to the biometric monitoring device, and the optical data may reflect a flow of blood through the finger that is detected by the biometric monitoring device. The method may further include the steps of generating an extrapolated curve using the pressure data, the optical data, the extrapolated pressure values, and the extrapolated optical values; and estimating the user’s blood pressure using the extrapolated curve.

[0011] In other embodiments, a method for measuring a user’s blood pressure is disclosed. The method may include the step of measuring pressure data and optical data overthe measurement period using a biometric monitoring device, where the pressure data reflects pressures applied by a finger of the user to the biometric monitoring device, and where the optical data reflects a flow of blood through the finger that is detected by the biometric monitoring device. The method may further include the steps of terminating the measurement period at a measurement endpoint and generating an initial curve using the optical data and the pressure data. Other steps of the method may include obtaining extrapolated pressure values and extrapolated optical values that reflect an extrapolated period after the measurement endpoint; modifying the initial curve to include the extrapolated pressure values and the extrapolated optical values; and estimating the user’s blood pressure using the resulting extrapolated curve.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 depicts a PPG-based biometric monitoring device suitable for taking blood pressure measurements, in accordance with an exemplary embodiment.

[0013] FIG. 2 is a graph depicting the application of the extrapolated processing method disclosed herein in accordance with an exemplary embodiment.

[0014] FIG. 3 is a diagram depicting a method for shortening a measurement period for a user’s blood pressure in accordance with an exemplary embodiment.

[0015] FIG. 4 is a diagram depicting a method for shortening a measurement period for a user’s blood pressure in accordance with another exemplary embodiment.DETAILED DESCRIPTION

[0016] It has been discovered that an accurate blood pressure measurement may be obtained from data collected before the point of arterial occlusion using extrapolation methods. Such extrapolation methods use measured pressure data and optical data to predict additional pressure values and optical values that may be used alongside the measured data to estimate blood pressure using predictive techniques or analytical models. Advantages of theseextrapolation methods over previous systems include reduction in measurement time and improved usability. For example, in certain embodiments, these extrapolation methods may reduce measurement time by half or more compared to the time required to perform the same blood pressure measurement without extrapolation.

[0017] Turning to FIG. 1, shown therein is a biometric monitoring device 100, which is well-suited for measuring blood pressure, pulse, blood oxygenation, or other biometrics. The biometric monitoring device 100 includes a body 102 and a finger trough 104 configured to locate the user’s fingertip onto the biometric monitoring device 100. The biometric monitoring device 100 further includes one or more photoemitters 106, one or more photoreceptors 108 and one or more control circuits 110 which is electrically connected to the photoemitters 106 and photoreceptors 108. The photoemitters 106, photoreceptors 108 and control circuits 110 together present a PPG module 112. The biometric monitoring device 100 may also include a pressure sensor 114 configured to measure the force applied by the fingertip to the biometric monitoring device 100. The pressure sensor 114 is also connected to the control circuits 110. Although the biometric monitoring device 100 in FIG. 1 is designed for use with the user’s fingertip, it will be appreciated that the biometric monitoring device 100 can also be configured for use with other vascular body parts, including toes, wrists, ears, arm, and neck.

[0018] In exemplary embodiments, the photoemitters 106 are light emitting diodes (LEDs) configured to output light (e.g., green, red, infrared) at a selected and controllable intensity (amplitude) based on a command signal from the control circuits 110. In the same exemplary embodiments, the photoreceptors 108 are photodiodes configured to output a voltage signal to the control circuits 1 10 in response to the detection of light. The strength of the signal produced by the photoreceptors 108 can be tuned or adjusted to increase or decrease the sensitivity and output of the photoreceptors 108. Although the control circuits 110, photoemitters 106 and photoreceptors 108 are depicted as separate, interconnected componentsin FIG. 1, it will be appreciated that these components can also be presented on a common circuit board with integrated connectivity.

[0019] The biometric monitoring device 100 is configured for connection with a mobile computing device 116, which can be a smart phone, tablet, watch or personal computer. The biometric monitoring device 100 can be connected to the mobile computing device 116 through a wired or wireless (e.g., Bluetooth) connection. In some cases, the biometric monitoring device 100 and mobile computing device 116 are integrated together as a unitary mobile monitoring device.

[0020] The mobile computing device 116 provides instructions to the user through an application program 118. The application program 118 guides the user through the process of obtaining a blood pressure measurement with the biometric monitoring device 100. The application program 118 can include visual references 120 that serve as guides or limits for the application of pressure. In FIG. 1, the visual references 120 are displayed on either side of a line 122 depicting the actual force applied by the user’s finger on the pressure sensor 114. The application program 118 can move the visual references 120 up or down to instruct the user to increase or decrease the amount of pressure applied by the user’s finger on the pressure sensor 114. It will be appreciated that the mobile computing device 116 and the biometric monitoring device 100 are not drawn to scale in FIG. 1.

[0021] In one embodiment, a method 200 is disclosed for shortening a measurement period 124 for a user’s blood pressure using the biometric monitoring device 100. In this embodiment, the method includes step 202 of measuring pressure data and optical (PPG) data over a measurement period 124 using the biometric monitoring device 100. The pressure data, which may be measured using the pressure sensor 114. reflects the pressures applied by a finger of the user to the biometric monitoring device 100. The optical data reflects the flow of blood through the finger, where the flow of blood is detected by the PPG module 112 of the biometricmonitoring device 100. More particularly, the optical data reflects the flow of blood through an artery in the finger, preferably a transverse palmar arch artery7.

[0022] The method 200 further includes step 204 of terminating the measurement period 124. As illustrated in the graph of FIG. 2, the measurement period 124 for measuring pressure data and optical data may terminate at a measurement endpoint 126. Ending measurements at the measurement endpoint 126 may involve detecting a point where the pressure data indicates that pressures applied by the user's finger to the biometric monitoring device 100 are above a mean arterial pressure 128. Any pressure measurements obtained prior to the measurement endpoint 126 need not be substantially above the mean arterial pressure 128. In exemplary7embodiments, the measurement endpoint 126 occurs when the pressures applied by7the user’s finger are slightly above the mean arterial pressure 128. It will be appreciated that the term “slightly” may reference a difference in pressure from between about 1% and about 5% above the mean arterial pressure 128. The termination of the measurement period 124 may be based, in whole or in part, on the detection of pressures that are above the mean arterial pressure 128.

[0023] In some embodiments, the measurement period 124 is terminated by providing an indicator on the mobile computing device 116 to the user to remove the finger from the biometric monitoring device 100. The indicator may include visual, audible, or tactile indicators, or combinations of the same.

[0024] As shown in FIG. 3, the method 200 includes the further step 206 of obtaining extrapolated pressure values and extrapolated optical values that reflect an extrapolated period 130 after the measurement endpoint 126. In certain exemplary embodiments, these extrapolated pressure values and extrapolated optical values are obtained by applying algorithms, machine learning, artificial intelligence, or physiology -informed theoretical models to the pressure data and to the optical data that has been collected from the user. These algorithms and models maybe applied to all the pressure and optical data that has been measured or to only portions of each.

[0025] Similarly, the algorithms and models can be used to extrapolate pressure and PPG values from the collected pressure data and optical data by identifying a correlation or other relationship between the pressures applied by the user and a corresponding reduction or increase in the flow of blood as measured by the PPG signal, and thereby estimating a point 132 at which the applied pressures would have occluded the artery within the user’s finger had the measurement period 124 continued until arterial occlusion. As noted in FIG. 2, the point of arterial occlusion 132 occurs later than the measurement endpoint 126 at a pressure that is higher than the mean arterial pressure 128. The estimated applied pressures up to and at the point of arterial occlusion 132 sen e as the extrapolated pressure values. By applying the same correlation or other relationship that was identified between the pressure data and the optical data, the extrapolated pressure values can be used to determine the extrapolated optical values. This step of extrapolating the PPG signal for expected pressure readings can be performed by the mobile computing device 11 .

[0026] Using a combination of the pressure data and the optical data that were obtained until the measurement endpoint 126 and the extrapolated pressure values and extrapolated PPG values that were obtained after the measurement endpoint 126, an extrapolated curve may be generated (step 208) and used for estimating the user’s blood pressure (step 210). In some nonlimiting exemplary embodiments, the process of generating the extrapolated curve may include steps of relating the optical data to corresponding pressure data; relating the extrapolated optical values to corresponding extrapolated pressure values; and plotting the optical data and the extrapolated optical values over the corresponding pressure data and the corresponding extrapolated pressure values to produce the extrapolated curve.

[0027] In another aspect a method 300 for measuring a user’s blood pressure involves obtaining pressure data and optical data during the measurement period 124 using the biometric monitoring device 100 (step 302), terminating the measurement period 124 (step 304), and generating an initial curve using the pressure data and the optical data that was obtained until the measurement endpoint 126 (step 306). Extrapolated pressure values and extrapolated optical values are obtained for the extrapolated period 130 following the measurement endpoint 126 (step 308). Although step 308 is depicted in FIG. 4 as occurring after step 306, it will be appreciated that the extrapolated pressure values and extrapolated optical values may be obtained before or after generating the initial curve. In some embodiments in which extrapolation is performed after step 306, the initial curve of the pressure data and the optical data is used to estimate the extrapolated optical values and the extrapolated pressure values. After the initial curve has been generated and the extrapolated values are obtained, the initial curve is modified (step 310) to include the extrapolated pressure and optical values and to thereby generate the extrapolated curve that is used to estimate the user’s blood pressure at step 312.

[0028] In some instances, all portions of the pressure data and the optical data that were measured are used to generate the initial curve, the extrapolated curve, or both. In other instances, only a subset of the pressure data and the optical data is used for this purpose. In the latter cases, the method may further include the step of identifying the subset of the pressure data and the optical data that will be used for generating the initial curve and / or extrapolated curve.

[0029] It will be appreciated that various processes and / or algorithms may be employed to estimate the user’s blood pressure using the extrapolated curve. In exemplary embodiments, the extrapolated curve may be used to estimate the user’s systolic blood pressure, diastolic blood pressure, or both.

[0030] In the foregoing specification, the invention has been described with reference to specific embodiments thereof. However, it will be evident that various modifications and changes can be made thereto without departing from the broader scope of the invention as set forth in the appended claims. Accordingly, the specification is to be regarded in an illustrative rather than a restrictive sense. For example, different measurement periods, biometric monitoring devices, body parts, arteries, curves, theoretical models, and algorithms not specifically identified or described in this disclosure or not evaluated in a particular embodiment are still expected to be within the scope of this invention.

[0031] The present invention may suitably comprise, consist of, or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term “about” in reference to a given parameter is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the given parameter). As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

Claims

It is claimed:

1. A method for shortening a measurement period for a user’s blood pressure comprising: measuring pressure data and optical data over the measurement period using a biometric monitoring device, wherein the pressure data reflects pressures applied by a finger of the user to the biometric monitoring device, and wherein the optical data reflects a flow7of blood through the finger that is detected by the biometric monitoring device; terminating the measurement period at a measurement endpoint; obtaining extrapolated pressure values and extrapolated optical values that reflect an extrapolated period after the measurement endpoint; generating an extrapolated curve using the pressure data, the optical data, the extrapolated pressure values, and the extrapolated optical values; and estimating of the user’s blood pressure using the extrapolated curve.

2. The method of claim 1, wherein the step of measuring the pressure data and the optical data over the measurement period further comprises: using a pressure sensor on the biometric monitoring device to measure the pressure data, and using a photoplethysmography sensor on the biometric monitoring device to measure the optical data.

3. The method of claim 1 , wherein the step of terminating the measurement period at the measurement endpoint further comprises: detecting when the pressure data indicates pressures are above a mean arterial pressure; andinitiating termination of the measurement period based on detection that pressures are above a mean arterial pressure.

4. The method of claim 1 , wherein the step of terminating the measurement period further comprises providing an indicator to the user to remove the finger from the biometric monitoring device.

5. The method of claim 4. wherein the step of providing the indicator to the user to remove the finger from the biometric monitoring device further comprises providing visual indicators, audible indicators, tactile indicators, or combinations of the same to the user.

6. The method of claim 1, wherein the step of obtaining the extrapolated pressure values and the extrapolated optical values further comprises applying physiology-informed models to the pressure data and the optical data.

7. The method of claim 6, wherein the step of obtaining the extrapolated pressure values and the extrapolated optical values further comprises the steps of: identifying a correlation between the pressure data and the optical data; estimating applied pressures from the measurement endpoint to a point at which arterial occlusion would have occurred in the user’s finger had the measurement period continued, wherein the applied pressures serve as the extrapolated pressure values; and determining the extrapolated optical values by applying the correlation between the pressure data and the optical data to the extrapolated pressure values.

8. The method of claim 1, further comprising the step of generating an initial curve using the pressure data and the optical data, wherein the step of generating the extrapolated curve further comprises the step of modifying the initial curve to include the extrapolated pressure values and the extrapolated optical values.

9. The method of claim 8, wherein the step of generating the initial curve using the pressure data and the optical data further comprises: identifying a subset of the pressure data and the optical data; and using the subset of the pressure data and the optical data to generate the initial curve.

10. The method of claim 8, wherein the step of obtaining the extrapolated pressure values and the extrapolated optical values further comprises using the initial curve of the pressure data and the optical data to estimate the extrapolated pressure values and the extrapolated optical values.

11. The method of claim 1, wherein the step of generating the extrapolated curve further comprises: relating the optical data to corresponding pressure data; relating the extrapolated optical values to corresponding extrapolated pressure values; and plotting the optical data and the extrapolated optical values over the corresponding pressure data and the corresponding extrapolated pressure values to produce the extrapolated curve.

12. The method of claim 1, wherein the step of generating the extrapolated curve using the pressure data and the optical data further comprises:identifying a subset of the pressure data and the optical data; and using the subset of the pressure data and the optical data to generate the extrapolated curve.

13. The method of claim 1, wherein the step of estimating the user’s blood pressure using the extrapolated curve further comprises: using the extrapolated curve to estimate the user’s systolic blood pressure; and using the extrapolated curve to estimate the user’s diastolic blood pressure.

Images