Devices, systems and methods for blood pressure measurement

Abstract

Devices, methods, and systems for sleeveless blood pressure (BP) measurement are provided. Devices, methods, and systems include determining blood pressure using an oscillographic finger press approach using a smartphone or other readily available device. Further devices, methods, and systems are provided to improve BP calculations via modeling and / or additional measurements using ECG and DC PPG.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 388,021 filed on July 11, 2022 and U.S. Provisional Patent Application Serial No. 63 / 482,868 filed on February 2, 2023, the contents of all of which are incorporated herein by reference in their entirety.

[0003] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0004] This invention was made with government support under Grant No. HL146470 awarded by the National Institutes of Health. The government has certain rights in this invention. Technical Field

[0005] The disclosed subject matter relates to devices, systems, and methods for measuring blood pressure. The disclosed devices and systems can perform cuffless blood pressure measurements by using an oscillometric finger press or hand raise technique to determine a blood pressure cuff. Background Art

[0006] About one-third of adults worldwide have high blood pressure (BP). Although prevalence increases with age, many people develop hypertension in early adulthood (e.g., more than one-fifth of US adults under 40 years of age have hypertension). The condition is often asymptomatic, but for a given age, the risk of stroke and heart disease increases monotonically with increasing BP. Lifestyle changes and a number of inexpensive, once-daily medications can reduce BP and cardiovascular risk. However, only about three in seven people with hypertension are aware of their condition, and only one in seven has their BP under control. Epidemiological data on hypertension in resource-poor settings are even more alarming. As a result, hypertension has become a leading cause of disability-adjusted life years lost.

[0007] Auscultatory and oscillometric blood pressure measurement devices play an important role in the management of hypertension. At the same time, because these devices rely on an inflatable cuff, they may be responsible for poor hypertension awareness and control rates. Cuff-based devices are not readily available, especially in resource-poor settings. As a result, most people do not check their blood pressure regularly. Regular measurements in daily life are needed to circumvent the white coat and masking effects of patients presenting with higher or lower BP than usual in the clinic, and to average out the large changes in BP that occur over time due to stress, physical activity, and other factors. If BP could be measured more conveniently, many people would be aware of their condition or motivated to take medication.

[0008] As a result, cuffless BP monitoring devices are becoming widely adopted. However, the devices being investigated often have the severe limitation of requiring calibration with a cuff device in order to output measurements in mmHg. Summary of the invention

[0009] The objects and advantages of the disclosed subject matter will be set forth in and will be apparent from the following description, and will be learned by the practice of the disclosed subject matter. Additional advantages of the disclosed subject matter will be realized and obtained by the devices particularly pointed out in the written description and claims thereof, as well as by the attached drawings.

[0010] To achieve these and other advantages and in accordance with the purposes of the disclosed subject matter, as embodied and broadly described, the disclosed subject matter includes apparatus, methods, and systems for blood pressure monitoring.

[0011] The disclosed subject matter provides a method for determining a user's diastolic blood pressure using a device having a photoplethysmography (PPG) force sensor unit. The method may include providing visual or audio instructions with the device, measuring PPG oscillations and finger pressure of a finger with the PPG force sensor unit, calculating the width of each of the PPG oscillations as a function of finger pressure, calculating the diastolic blood pressure using the PPG oscillation width relative to the finger pressure function, and outputting the diastolic blood pressure on a graphical user interface of the device or sending the diastolic blood pressure to a database repository. In a non-limiting embodiment, the instructions may instruct the user to position a finger on the PPG force sensor unit and press the finger on the PPG force sensor unit with varying finger pressure.

[0012] In some embodiments, the method for determining diastolic blood pressure may further include detecting a curvature of the PPG oscillation width relative to the finger pressure function. In a non-limiting embodiment, the curvature of the PPG oscillation width relative to the finger pressure function may be detected by fitting at least two curves to the function and using the intersection of the curves.

[0013] In some embodiments, the width of each PPG oscillation may be calculated as the ratio of the area to the height of the oscillation.

[0014] In certain embodiments, the method for determining diastolic blood pressure may further include measuring an electrocardiogram (ECG) with additional electrodes incorporated into the device and calculating the width of each PPG oscillation as the pulse arrival time of each of the oscillations, the pulse arrival time being detected as the time delay between the R wave of the ECG and the PPG trough (foot).

[0015] In certain embodiments, the method for determining diastolic blood pressure may further include determining systolic blood pressure by using the value of the pulse arrival time relative to the pulse arrival time at the bend of the finger pressure function.

[0016] In some embodiments, additional features extracted from the PPG oscillations and finger pressure may be used to calculate diastolic blood pressure. In a non-limiting embodiment, the additional features may include the finger pressure at the maximum slope of the PPG oscillation amplitude versus finger pressure function.

[0017] The disclosed subject matter provides a method for determining a user's systolic blood pressure using a device having a photoplethysmography (PPG) force sensor unit and electrocardiogram (ECG) electrodes. The method may include providing visual or audio instructions with the device, measuring a total PPG including a direct current (DC) component, PPG oscillations, and applied finger pressure with the PPG force sensor unit, measuring the ECG simultaneously with the electrodes, calculating an average of each PPG beat over an R-wave to R-wave interval of the ECG as a function of applied finger pressure, and calculating the systolic blood pressure using the PPG average relative to the finger pressure function. In a non-limiting embodiment, the instructions may instruct the user to position a finger on the PPG force sensor unit and press the finger on the PPG force sensor unit with varying finger pressure.

[0018] In certain embodiments, the method for determining systolic blood pressure may further include calculating systolic blood pressure, including detecting a curvature of the PPG mean relative to a finger pressure function. In a non-limiting embodiment, the curvature of the PPG mean relative to the finger pressure function may be detected by fitting at least two curves to the function and using the intersection of the curves. In a non-limiting embodiment, systolic blood pressure may be calculated using additional features extracted from the total PPG, finger pressure, and ECG. In a non-limiting embodiment, the additional features may include the finger pressure at the minimum slope of the PPG oscillation amplitude relative to the finger pressure function. In a non-limiting embodiment, the additional features may include the value of the pulse arrival time at the curvature of the pulse arrival time relative to the finger pressure function.

[0019] The disclosed subject matter provides a method for determining a user's pulse pressure using a device. The method may include providing visual or audio instructions to the user with the device to position a finger on a camera and an adjacent screen of the device, thereby measuring a total PPG from the finger via the camera of the device, and measuring a finger contact parameter via a touch screen sensor of the screen, providing visual or audio instructions to the user to apply finger pressure on the camera and screen based on the measurements, providing visual or audio instructions to the user with the device to lower or raise the hand relative to the user's heart level while maintaining finger pressure, measuring hydrostatic blood pressure changes (ρgh) in the finger by using the device's accelerometer measurements and arm length, and calculating pulse pressure from the PPG and ρgh measurements.

[0020] In some embodiments, the method for determining pulse pressure may further include providing instructions to the device for a one-time initialization to determine optimal placement guidelines for a finger on the camera and screen.

[0021] In some embodiments, the finger contact parameters may include the touch centroid. In a non-limiting embodiment, the PPG oscillations may be used as a guide to determine the amount of finger pressure on the screen and camera when the hand is raised or lowered. In a non-limiting embodiment, the PPG oscillations and finger contact parameters may be used as a guide to determine the amount of finger pressure to maintain on the screen and camera during the hand being raised or lowered. In a non-limiting embodiment, the finger contact parameters may be used as a guide to maintain finger pressure on the screen and camera during the hand being raised or lowered. In a non-limiting embodiment, a timer may be used as a further guide to indicate the amount of time required for the hand to be raised or lowered.

[0022] In some embodiments, pulse pressure may be calculated using at least one of ρgh at the minimum slope and maximum slope of the PPG oscillation amplitude relative to the ρgh function or the width of the PPG oscillation amplitude as a function of ρgh.

[0023] In certain embodiments, the method for determining pulse pressure may further include measuring diastolic blood pressure by measuring a maximum finger contact parameter via a firm finger press by the user, and comparing the finger contact parameter to the maximum area to determine whether the diastolic blood pressure is low.

[0024] The disclosed subject matter provides a method of determining blood pressure using a device having a photoplethysmography (PPG) force sensor unit and ECG electrodes. The method may include receiving a pressure measurement from a touch of a finger on the PPG force sensor unit, receiving an ECG from the electrodes, calculating diastolic blood pressure using the width of each alternating current (AC) blood volume oscillation as a function of finger pressure with a processor of the device, calculating systolic blood pressure using the average of each direct current (DC) blood volume beat over the RR interval of the ECG as a function of finger pressure with the processor, and outputting the blood pressure on a graphical user interface of the device or sending the blood pressure to a database repository.

[0025] The disclosed subject matter provides a system for determining a subject's blood pressure. The system may include a sensor configured to measure finger pressure, finger photoplethysmography (PPG) oscillations, a finger PPG DC component and an ECG, a display configured to provide visual or audio instructions to guide the subject to position a finger at a predetermined position, and a processor. In a non-limiting embodiment, the processor may be configured to calculate diastolic and systolic blood pressures, and display the calculated diastolic and systolic blood pressures on the display. In a non-limiting embodiment, the diastolic blood pressure may be calculated using a PPG oscillation width relative to a finger pressure function. In a non-limiting embodiment, the systolic blood pressure may be calculated using a PPG average.

[0026] It is to be understood that both the foregoing general description and the following detailed description and the accompanying drawings are examples and are provided for the purpose of illustration and are not intended in any way to limit the scope of the disclosed subject matter.

[0027] The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to illustrate and provide a further understanding of the device of the present disclosure. The drawings together with the description serve to explain the principles of the disclosed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The subject matter of the present application will be more readily understood from the following detailed description when read in conjunction with the accompanying drawings, in which:

[0029] Figure 1 is a diagram illustrating an oscillometric finger pressure method for cuff-free and calibration-free monitoring of blood pressure (BP) via a readily available device such as a smartphone.

[0030] Figure 2A is a diagram showing a smartphone-based device with a customized PPG force sensor unit to implement the oscillometric finger pressure method. Figure 2B is a graph showing a comparison of a cuffless device and a cuff device.

[0031] FIG. 3 is a diagram showing an iPhone X application implementing an oscillometric finger press method via PPG and force sensors already available in high-end mobile phones.

[0032] Figure 4 is a diagram showing a model of the oscillometric method and a specific oscillogram. The oscillogram is nominally a function relating the amplitude of blood volume oscillations to the external pressure of the artery.

[0033] Figure 5A-5D is a diagram showing the difference in model parameters of fingers and conventional arm parts.

[0034] Figure 6is a diagram showing the well-known maximum amplitude and derivative algorithms for calculating BP values ​​from oscillograms and model predictions about how these algorithms perform.

[0035] Figure 7 is a graph showing the model predicted oscillations as DP increases.

[0036] Figure 8 is a graph showing how the model can be modified to predict DC PPG and AC PPG oscillations as external pressure increases.

[0037] Fig. 9 is a diagram showing a prototype device for making additional measurements of ECG and DC PPG (as opposed to conventional PPG oscillations alone).

[0038] Fig.10 is a diagram showing a method of measuring finger DP and SP from PPG oscillations, finger pressure, and ECG during actuation such as finger press.

[0039] Fig.11 It shows that P PAT , P AHR and P maxslope (exist Fig.10 DP (defined in ).

[0040] Fig.12 It shows that P PAT and P AHR is a diagram of the indicator of DP in the finger.

[0041] Fig.13 is a graph showing the P PAT P AHR More robust graph, since ECG is a robust sensing method.

[0042] Fig.14 It shows that P PAT , P AHR and P maxslope Figures that can be combined via simple averaging to further improve the accuracy of the DP calculation (N=34).

[0043] Fig.15 is a graph showing the finger pressure at a fixed value (e.g., at P PAT ) minslope The combination with PAT is better than P alone. minslope (N=34) Plot with better correlation with arm cuff SP. The results in each graph of this figure were obtained via leave-one-out cross-validation.

[0044] Fig.16 is a diagram showing a method of measuring finger SP from total PPG and finger pressure during actuation such as finger pressing.

[0045] Fig.17 It shows that P DCpeak Figures that correlated well with arm cuff SP (N=14).

[0046] Fig.18 is a graph showing total PPG versus finger pressure during actuations, such as finger compressions with hand raised, at heart level, and hand lowered (N=2).

[0047] Fig.19 : is a diagram showing a method of converting finger BP into arm BP.

[0048] Fig. 20 is a diagram showing an innovative application of measuring pulse pressure (PP=SP-DP) using only a standard smartphone (without 3D touch capabilities).

[0049] Fig.21 is a diagram showing the Samsung Galaxy S21 app that measures PPG (R, G, and B AC+DC channels), accelerometer (X-axis, Y-axis, and Z-axis), and finger contact area (large and small radius, x-center and y-center positions).

[0050] Fig. 22 It shows the use of Fig. 20 Figure 2. Graph of exemplary measurements of PP for the guidance system described in (N=3).

[0051] Fig.23 is a diagram showing that the base of the nail located on top of the front camera is a suitable default position for obtaining large amplitude PPG oscillations.

[0052] Fig.24 is a diagram showing an ideal sensor for testing the oscillometric hand-raising method of measuring pulse pressure (PP).

[0053] Fig.25 is a diagram showing the three-step process of calculating PP.

[0054] Fig.26 is a graph showing the cuffless PP (width) versus the arm cuff PP (N=22). The correlation coefficient (r) is 0.75. The mean and standard deviation of the PP error are -2.9 and 7.4 mmHg.

[0055] Fig. 27 is a graph illustrating an example model for improving oscillometric BP calculations.

[0056] Fig.28is a graph showing PPG oscillations during pressure increase.

[0057] Fig.29 is a graph showing example model predictions for a collapsible finger artery.

[0058] Fig.30 is a graph showing the extension of the disclosed model to AC+DC PPG and prediction.

[0059] Fig.31 is a graph showing a model-based DP and SP calculation algorithm.

[0060] Fig.32 An image of an example benchtop system for evaluating the disclosed devices and models is shown.

[0061] Fig.33 is a graph showing the accuracy of the disclosed model and algorithm.

[0062] Fig.34 is a graph showing the correlation between DC PPG results, and systolic and diastolic references.

[0063] Fig.35 is a graph showing the DC PPG results using leave-one-out (LOO) regression.

[0064] Fig.36 is a graph showing the correlation between minimum slope prediction and vologram curvature measurement.

[0065] Fig.37 is a graph illustrating example volume map tortuosity measurements. DETAILED DESCRIPTION

[0066] Reference will now be made in detail to embodiments of the disclosed subject matter, examples of which are illustrated in the accompanying drawings. The disclosed subject matter will be described in conjunction with a detailed description of the system.

[0067] The terms used in this specification generally have their ordinary meanings in the art, in the context of the disclosed subject matter, and in the specific context in which each term is used. Certain terms are discussed below or elsewhere in the specification to provide additional guidance to practitioners when describing the compositions and methods of the disclosed subject matter.

[0068] As used herein, the use of the word "a" or "an" can mean "one" when used in conjunction with the term "comprising" in the claims and / or the specification, but it is also consistent with the meaning of "one or more", "at least one", and "one or more than one". In addition, the terms "having", "including", "containing", and "comprising" are interchangeable, and those skilled in the art recognize that these terms are open-ended terms.

[0069] The term "about" or "approximately" means within an acceptable error range for a particular value as determined by one of ordinary skill in the art, which error range will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, according to the practice in the art, "about" can mean within 3 or more standard deviations. Alternatively, "about" can mean a range of up to 20% (preferably, up to 10%; more preferably, up to 5%; and still more preferably, up to 1%) of a given value. Alternatively, particularly for biological systems or processes, the term can mean within an order of magnitude of a value, preferably, within 5-fold; and more preferably, within 2-fold.

[0070] A "user" or "subject" herein is a vertebrate, such as a human or a non-human animal, such as a mammal. Mammals include, but are not limited to, humans, primates, farm animals, sports animals, rodents, and pets.

[0071] The disclosed subject matter provides systems and techniques for determining a subject's blood pressure. For example, the disclosed subject matter provides techniques for determining a user's diastolic blood pressure, systolic blood pressure, and / or a user's pulse pressure using a device having a photoplethysmography (PPG) force sensor unit.

[0072] In certain embodiments, a method for determining a user's diastolic blood pressure may include providing visual or audio instructions that may instruct the user to position a finger on a PPG force sensor unit and press the finger on the PPG force sensor unit with varying finger pressure. The PPG force sensor unit may be configured to measure the user's PPG and the applied finger pressure. The PPG force sensor unit may include a camera PPG sensor, a finger PPG sensor, and a force sensor, or a combination thereof. The PPG force sensor unit may be configured to detect PPG oscillations and finger pressure applied from the subject's finger on the PPG sensor unit. In a non-limiting embodiment, the PPG sensor may obtain the PPG oscillations without using a force sensor.

[0073] In certain embodiments, a method for determining diastolic blood pressure may include measuring PPG oscillations of a finger and an applied finger pressure with a PPG force sensor unit. In a non-limiting embodiment, the PPG oscillations may be variable amplitude PPG oscillations. For example, since the PPG oscillations may be proportional to the blood volume oscillations in the artery, and the arterial volume-pressure relationship is nonlinear (S-shaped), the PPG oscillation amplitude may increase to a maximum value when the applied finger pressure is swept, and then decrease to zero when the artery is blocked. In a non-limiting embodiment, a method for determining diastolic blood pressure may include calculating the width of each of the PPG oscillations as a function of the applied finger pressure, calculating the diastolic blood pressure using the PPG oscillation width relative to the finger pressure function, and outputting the diastolic blood pressure on a graphical user interface of the device or sending the diastolic blood pressure to a database repository. For example, when a user presses their finger on the sensor to change the external pressure of the underlying artery, a variable amplitude PPG oscillation may be obtained from the PPG waveform. In a non-limiting embodiment, during the increase of the external finger pressure, the finger PPG waveform may include an alternating current (AC) component and a direct current (DC) component. In a non-limiting embodiment, the AC component may reflect the pulsation of the blood, and the DC component may reflect the non-pulsating component of the PPG signal. In a non-limiting embodiment, the DC component and / or the AC component of the PPG waveform may be used to determine how much finger pressure the user needs to apply on the PPG sensor (e.g., a camera or finger PPG sensor). For example, the user may first press hard on the PPG sensor to determine the highest DC value based on the user input. The device may show a graph recording the relationship between the DC values ​​and time, where the y-axis range may be set by the highest DC level identified. The processor may determine the DC level at which the AC oscillation amplitude is maximum, which may correspond to the average BP, and display a constant target line to guide the user to obtain this level of basic transmural pressure (external pressure of the underlying artery minus internal pressure) by pressing their fingers or raising their hands.

[0074] In some embodiments, the method for determining diastolic blood pressure may further include detecting a bend in the PPG oscillation width relative to the finger pressure function (i.e., a sudden change in the slope of the function). For example, the bend in the PPG oscillation width relative to the finger pressure function may be detected by fitting at least two curves to the function and using the intersection of the curves.

[0075] In certain embodiments, the width of each PPG oscillation may be calculated as the area to height ratio of the oscillation. For example, the area may be defined as the area between the trough to trough of the PPG waveform beat and the line between the two troughs. The height may be defined as the trough to peak amplitude of the PPG waveform beat. The area to height ratio may be the ratio between the two. In a non-limiting embodiment, a method for determining diastolic blood pressure may include measuring an electrocardiogram (ECG) with additional electrodes incorporated into the device, and calculating the width of each PPG oscillation as the pulse arrival time of each of the oscillations, i.e., as the time delay between the R wave of the ECG and the trough of the PPG. For example, the pulse arrival time (PAT) and the area to height ratio (AHR) are both indicators of the width of the oscillation, and the pulse arrival time (PAT) is the time delay between the ECG R wave and the trough of the PPG. When the PAT and AHR are plotted against finger pressure to produce a "PAT and AHR oscillogram", a reference marker may be identified to represent the finger diastolic pressure (DP). For example, two lines / curves may be fitted to each of these oscillograms, and the intersection point (P PAT or P AHR ) gives the DP. In a non-limiting embodiment, the method may further include determining the systolic blood pressure using the value of the pulse arrival time relative to the pulse arrival time at the bend of the finger pressure function. The systolic blood pressure may be calculated using an inverse relationship with the pulse arrival time and directly proportional to the subject's height. These coefficients are derived from population data.

[0076] In some embodiments, diastolic blood pressure can be calculated using at least one of the width algorithms and each of the additional features extracted from the PPG oscillations and the finger pressure. The additional features can include the finger pressure at the maximum slope of the PPG oscillation amplitude versus finger pressure function. For example, diastolic blood pressure can be calculated using at least the pressure at the bend of the width versus pressure relationship. For example, the maximum slope (P) of a standard oscillogram ("altitude oscillogram") can be calculated using the maximum slope (P) of the PPG oscillation amplitude versus finger pressure function. maxslope ) and minimum slope (P minslope ) can indicate the pressure at fingers DP and SP respectively.

[0077] The disclosed subject matter provides a method of determining a user's systolic blood pressure using a device having a photoplethysmography (PPG) force sensor unit and ECG electrodes. The method may include providing visual or audio instructions with the device, wherein the instructions instruct the user to position a finger on the PPG force sensor unit and press the finger on the PPG force sensor unit with varying finger pressure, and measuring a total PPG including a direct current (DC) component, PPG oscillations, finger pressure applied to the PPG force sensor unit, and measuring an ECG simultaneously with the electrodes.

[0078] In some embodiments, a method for determining a user's systolic blood pressure may include calculating an average value of each PPG beat over an R-wave to R-wave interval of an ECG as a function of applied finger pressure, and calculating systolic blood pressure using the PPG average value relative to the finger pressure function. In a non-limiting embodiment, the PPG beat may reflect the pulsation of the PPG at each heartbeat, and the average value of the PPG beat may reflect the average value within the beat. For example, three lines may be fitted to the upper envelope of a graph of the total (DC+AC) PPG relative to finger pressure, and the latter two lines (P DCpeak ) represents the finger SP( Fig.16 ).

[0079] In some embodiments, the method for determining systolic blood pressure may further include detecting a bend in the PPG mean value relative to the finger pressure function (i.e., a sudden change in the slope of the function). For example, the bend in the PPG mean value relative to the finger pressure function may be detected by fitting at least two curves to the function and using the intersection of the curves.

[0080] In some embodiments, additional features extracted from the total PPG, finger pressure, and ECG may be used to calculate systolic blood pressure. In a non-limiting embodiment, the additional features may include the finger pressure at the minimum slope of the PPG oscillation amplitude relative to the finger pressure function. In a non-limiting embodiment, the additional features may include the value of the pulse arrival time relative to the bend of the finger pressure function. The pulse arrival time is defined as the time delay between the ECG R wave to the PPG trough.

[0081] The disclosed subject matter provides a method for determining a user's pulse pressure using a device. The method may include providing visual or audio instructions that may instruct the user to position a finger on a camera and an adjacent screen of the device to measure photoplethysmography (PPG) from the finger via the camera of the device, and measuring finger contact parameters via a touch screen sensor of the device, providing visual or audio instructions to the user to apply finger pressure on the camera and screen based on the measurements, providing visual or audio instructions to the user with the device to lower or raise the hand relative to the user's heart level while maintaining the finger pressure guided by the finger contact parameters, and measuring hydrostatic blood pressure changes (ρgh) in the finger by using the device's accelerometer measurements and arm length. In a non-limiting embodiment, the finger contact parameters may include touch centroid. The finger contact parameters are any parameters derived from the screen capacitive sensor array in the mobile phone (e.g., touch centroid and touch area).

[0082] In certain embodiments, a method for determining pulse pressure may include calculating pulse pressure from PPG and ρgh measurements. For example, when a user lowers their hand with their arm extended, the internal blood pressure in the finger may increase by an amount equal to ρgh, where ρ is the blood density, g is the gravity constant, and h is the vertical distance between the hand position and the heart, due to the weight of the blood column in the arm (the "hydrostatic effect"), and thus the arterial transmural pressure may change. In a non-limiting embodiment, the hydrostatic BP change (ρgh) may be measured using an accelerometer and the length of the arm, because the angle of the arm according to the gravity vector can be calculated from the accelerometer, and h can be calculated using trigonometry with the arm length. Alternatively, the hydrostatic BP change may be estimated without the use of an accelerometer / gyroscope or any other sensor. While maintaining constant finger pressure, the user lowers the phone to the floor and raises it upward in intuitive and fixed increments (e.g., approximately 45 degrees at a time for 3-5 seconds, guided by audio / visual cues). The hydrostatic BP change may then be estimated based on the known increments.

[0083] In certain embodiments, the PPG oscillations may be used as a guide to determine the amount of finger pressure on the screen and camera when the hand is raised or lowered. In non-limiting embodiments, the PPG oscillations and the finger contact parameters may be used as a guide to determine the amount of finger pressure on the screen and camera to maintain during the hand being raised or lowered. In non-limiting embodiments, the finger contact parameters may be used as a guide to maintain finger pressure on the screen and camera during the hand being raised or lowered. In non-limiting embodiments, a timer may be used as a further guide to indicate the amount of time required for the hand to be raised or lowered.

[0084] In some embodiments, pulse pressure may be calculated using at least one of ρgh at the minimum slope and maximum slope of the PPG oscillation amplitude relative to ρgh function or using the width of the PPG oscillation amplitude as a function of ρgh.

[0085] In some embodiments, a method for determining pulse pressure may include measuring diastolic blood pressure by measuring a maximum finger contact parameter via firm finger pressure by a user, and comparing the finger contact parameter to the maximum finger contact parameter to determine whether the diastolic blood pressure is lower. For example, if the ratio between the maximum contact area and the contact area at the diastolic reference mark (any algorithm that detects diastolic pressure) is low, the diastolic pressure may be lower. If the ratio between the maximum contact area and the contact area at the diastolic reference mark (any algorithm that detects diastolic pressure) is high, the diastolic pressure may be higher. These ratios can be developed using population data. In a non-limiting embodiment, systolic pressure can be estimated using any of the proposed algorithms to calculate pulse pressure by adding it to the diastolic pressure.

[0086] In certain embodiments, the method for determining pulse pressure may include providing instructions for a one-time initialization to determine optimal placement guidance for a finger on a camera and screen. For example, the disclosed device may perform a one-time initialization phase to measure PPG oscillations at different thumb positions to identify optimal thumb placement. During initialization, the user may be guided to gradually place more of the finger on the screen. The device may identify finger positioning that provides a suitable screen contact area without approaching force saturation. For example, but not limited to, the disclosed device may provide a visual indicator that may guide the user to place the finger to produce the largest area of ​​screen contact without force saturation. The initialization may also create an outline of the thumb and its box size for guiding thumb placement thereafter.

[0087] In some embodiments, blood pressure changes in the finger can be measured when the device is in different vertical positions relative to the user's heart level. In a non-limiting embodiment, the touch sensor adjacent to the camera can be the screen of the device. In a non-limiting embodiment, the distance from the device to the user's heart can be an arm's length.

[0088] The disclosed subject matter provides a method of determining blood pressure using a device having a photoplethysmography (PPG) force sensor and ECG electrodes. The method may include receiving a measurement from a touch of a finger on a PPG force sensor unit, receiving an ECG from the electrodes, calculating diastolic blood pressure (BP) using the width of each alternating current (AC) blood volume oscillation as a function of finger pressure with a processor of the device, calculating systolic BP using the average of each direct current (DC) blood volume beat over the RR interval of the ECG as a function of finger pressure by the processor, and outputting the BP on a graphical user interface of the device or sending the BP to a database repository.

[0089] The disclosed subject matter provides a system for determining a subject's blood pressure. The system can perform the disclosed method for measuring blood pressure, DP, SP, pulse pressure, or a combination thereof. An example system may include a sensor configured to measure finger pressure, finger photoplethysmography (PPG) oscillations, finger PPG DC component, and ECG, a display configured to provide visual or audio instructions to instruct a user / subject to position a finger, thumb, hand, or a combination thereof in a predetermined position, and a processor configured to perform the disclosed method for measuring blood pressure, DP, SP, pulse pressure, or a combination thereof.

[0090] In some embodiments, the processor can be configured to calculate diastolic blood pressure and systolic blood pressure, and display the calculated diastolic blood pressure and systolic blood pressure on the display. In a non-limiting embodiment, the diastolic blood pressure can be calculated using the relationship between the PPG oscillation width and the finger pressure function, and the systolic blood pressure can be calculated using the PPG average value.

[0091] Example

[0092] Example 1

[0093] like Figure 1 As shown in , the disclosed subject matter is based on the oscillometric principle for cuff-free and calibration-free BP monitoring via readily available handheld devices (such as smart wearable devices, tablets or smartphones). Such devices may include not only a processor that can calculate and evaluate, but also a photoplethysmography (PPG) and a force transducer useful for BP monitoring. The user can act as an actuator (instead of a cuff) by pressing the tip of their index finger on the device or mobile phone (kept at heart level) to steadily increase the external pressure of the underlying artery. The mobile phone embedded with photoplethysmography (PPG) and a force transducer acts as a sensor (instead of a cuff device) to measure the resulting variable amplitude blood volume oscillations and the applied finger pressure. The mobile phone also provides visual feedback on a graphical user interface (GUI) or audio feedback via a mobile phone speaker to guide finger actuation, and an algorithm is applied to calculate BP based on a measurement method comparable to that of an oscillometric cuff device.

[0094] Figure 2A A device consisting of a custom-made PPG force sensor unit fixed to the back of a readily available device to implement the "oscillometric finger press method" is shown. Figure 2B As shown, the device produces BP measurements within the normal blood pressure range with an accuracy level comparable to that of FDA-approved finger cuff volume clamping devices. In a non-limiting embodiment, as shown in FIG3 , the oscillometric finger press method can be implemented as a smartphone (e.g., iPhone) application (“app”) by utilizing a front-facing camera as a PPG sensor and utilizing an array of sensitive strain gauges under the screen (“3D Touch”) as a force sensor.

[0095] The disclosed subject matter provides devices, methods, and systems for improving the accuracy of BP calculations based on physiological modeling. In certain embodiments, the method includes a related oscillometric hand raise / lower method for cuffless and calibration-free monitoring of BP using standard devices (such as smartphones), where sensitive force sensing is generally not possible. The disclosed method can overcome the deficiencies in certain devices that are not capable of sensitive force sensing. In other embodiments, the method includes guiding a user to correctly perform hand actuation.

[0096] Oscilloscope Modeling

[0097] As shown in Figure 4, the oscillometric model explains the S-shaped blood volume-transmural pressure relationship of the artery, where the transmural pressure includes the internal BP of the artery minus the external pressure. Model assumptions include a purely elastic arterial wall and a linear relationship between the blood volume oscillations and the oscillations measured via the PPG (or cuff). In some embodiments, the model can predict the oscillogram of a typical BP calculation (i.e., the oscillation amplitude as a function of the external pressure), or the model can predict the oscillations.

[0098] As shown in FIG. 5 , when the external pressure is slightly higher than the internal BP, the digital artery collapses (ie, nearly a “collapsible digital artery”). Figure 5A It was shown that the digital arteries are collapsible, that is, when the external pressure is slightly higher than the internal BP, the digital arteries are completely flattened. Figure 5B-Figure 5C means Figure 4 PP is the pulse pressure and DP is the diastolic BP. Mathematically, this corresponds to Figure 4 The smaller b value of the finger in the model. However, for the occurrence of large arm artery collapse, the external pressure can be significantly higher than the internal BP. This difference is used to derive an accurate finger index wave BP calculation algorithm.

[0099] like Figure 6 As shown in , the derivative algorithm is more accurate for the finger than for the arm due to differences in model parameters. In particular, the external pressure at the maximum and minimum slopes of the oscillogram needs to correspond closely to the diastolic and systolic BP (DP and SP) of the finger. However, the derivative operation may amplify measurement noise.

[0100] like Figure 7 As shown, due to the collapsibility of the finger, as the external pressure increases, the model predicts that the width of each oscillation will narrow. However, as DP increases, narrowing occurs at higher external pressures. In some embodiments, narrowing begins at DP (or slightly above DP because the finger artery is not completely collapsible). Similarly, when the external pressure is slightly above SP, it is necessary to eliminate the oscillation.

[0101] like Figure 8 As shown in , the tissue surrounding the artery can be taken into account when predicting the change in DC PPG plus AC PPG with increasing external pressure. In particular, as external pressure increases, this tissue compresses to a certain extent. Therefore, the DC PPG due to this tissue decreases and then saturates (top right corner of the figure). The original artery model (top left corner of the figure) can be added to this tissue model to predict the total PPG as external pressure increases (bottom).

[0102] Improved blood pressure calculation

[0103] The disclosed subject matter provides an improved method for calculating BP via modeling and / or use of additional measurements of ECG and DC PPG (as opposed to conventional PPG oscillations alone). For purposes of example and not limitation, Fig. 9 As shown in , the device can perform additional measurements. In addition, ECG can be useful for monitoring BP and arrhythmias simultaneously.

[0104] like Fig.10 As shown in Figure 1, both the pulse arrival time (PAT) and the area height ratio (AHR) are indicators of oscillation width. The pulse arrival time (PAT) is the time delay between the ECG R wave and the PPG trough. When PAT and AHR are plotted against finger pressure to produce a "PAT and AHR oscillogram", a clear fiducial marker clearly indicates the finger DP. For example, two lines / curves can be fitted to each of these oscillograms, and the intersection point (P PAT or P AHR ) gives the DP. The P of the standard oscillogram (“height oscillogram”) maxslope or P minslope Represent fingers DP and SP respectively.

[0105] like Fig.11 As shown in PAT , P AHR and P maxslope There was a good correlation with the arm cuff DP (N=34). The arm cuff DP was systematically higher than the finger DP, as shown in Figure 5. P PAT and P AHR The finger DP is overestimated and its data points are close to the identity line.

[0106] like Fig.12 As shown in PAT and P AHR is an indicator of DP in the finger, but not in the arm (N=5), because the larger arm arteries are non-collapsible.

[0107] In one example, if Fig.13 As shown in Figure , during the subjects' exercise (N=4), P PAT Depicted as being larger than P AHR More robust, as ECG is a particularly robust sensing method.

[0108] In certain embodiments, P PAT , P AHR and P maxslope can be combined to further improve the accuracy of DP calculation (N=34), such as Fig.14For example, the three indices can be averaged (as shown as "DP Estimate") or used as independent variables in a linear regression to predict DP. Alternatively, the two closest indices can be averaged.

[0109] like Fig.15 As shown in , at a fixed finger pressure (e.g., at P PAT ) minslope The combination with PAT is better than P alone. minslope (N=34) has a better correlation with the arm cuff SP. It is known that PAT under the contact pressure of the fixed PPG sensor has a certain correlation with SP. In some embodiments, P PAT P minslope and PAT can be combined in various ways, including as independent variables in linear regression (“SP estimation”, e.g. Fig.15 As shown in FIG. 5 , the arm cuff SP is not as good as the arm cuff DP as a reference for the finger SP.

[0110] In one example, if Fig.16 As shown in FIG, three lines are fitted to the upper envelope of the total (DC+AC) PPG versus finger pressure graph, and the last two lines (P DCpeak ) represents the finger SP, so as to measure the finger SP according to the total PPG and the finger pressure. The three lines are fitted to the upper envelope of the relationship curve of the total PPG relative to the finger pressure, and the intersection point of the latter two lines (P DCpeak ) represents the finger SP. This method assumes that the fiducial marker occurs after the tissue is fully compressed (i.e., Figure 8 saturation in ).

[0111] like Fig.17 As shown, P DCpeak There was good correlation with arm cuff SP (N=14).

[0112] like Fig.18 As shown in , a graph of total PPG versus finger pressure changes as the hand is raised, at heart level, and lowered. A typical graph at heart level would look similar to Figure 8 The graph is shifted to the right due to the increase in finger BP via the hydrostatic effect. Tissue can be fully compressed at a certain pressure (e.g. 80 mmHg) regardless of the vertical position of the hand. Therefore, by artificially increasing BP by lowering the hand, the total PPG can be caused entirely by the artery. The lower graph in the figure looks like Figure 8 (Top left) Model predictions due to only the arterial component. For purposes of example and not limitation, the method for estimating SP is to perform oscillometric finger presses with the hand fully lowered, applying Fig.17The method detects the finger SP and corrects the measurement to heart level by subtracting ρgh, where ρ is the known blood density, g is gravity, and h is the length of the arm. In another embodiment, the method of estimating BP is to detect pulse pressure via a strong cross-correlation between the upper envelope and the lower envelope (PP=SP–DP). The front camera of the phone can be used to capture an image of the face during finger compression. This image can be used to verify that the phone is correctly positioned during finger compression (i.e., the hand is fully lowered) by comparing it to a reference image.

[0113] like Fig.19 As shown in , arm BP can be calculated from finger BP. The maximum oscillation can be where the sigmoid blood volume-transmural pressure relationship is most linear, thus best representing the finger BP oscillation shape (step 1). Any of the above BP calculations can be used instead of P minslope and P maxslope to calibrate the maximum oscillation (step 2). The resistive voltage drop from the arm to the finger is first offset by adding a constant (e.g., 10 mmHg) to the finger BP (step 3). The transfer function based on a physical tube-load model of arterial wave reflections is then applied to derive the arm BP (step 4). Γ and T d is a fixed value, such as 0.3 milliseconds and 72 milliseconds, for example. Alternatively, T d is a function of the BP value, or the transfer function is based on a black box model (e.g., an autoregressive exogenous input model).

[0114] BP applications for readily available devices without force sensing

[0115] Given that every adult is at real risk for developing hypertension, and that smartphones are accessible to billions of people, including those in low-resource settings, it is desirable to convert a standalone smartphone into a blood pressure monitor. However, many readily available devices, such as smartphones, do not include 3D Touch or similar sensitive force sensors.

[0116] The idea of ​​converting a standard smartphone into an absolute BP sensor is based on previous methods that use arm rather than finger actuation. In the traditional oscillometric method, a cuff compresses the artery to change its external pressure. In the process, the device also measures the cuff pressure, which indicates both the blood volume oscillation in the artery (AC cuff pressure) and the external pressure (DC cuff pressure). BP can be calculated from the resulting oscillogram, which is a function that relates variable amplitude blood volume oscillations to the applied pressure. The abscissa of the oscillogram can be more generally regarded as the change in arterial transmural pressure (in this case, internal BP minus external cuff pressure). Therefore, previous methods involve changing the internal pressure of the artery rather than the external pressure to change the transmural pressure. When the user of the finger-worn ring device puts down their hand with their arm straight, the internal BP in the finger increases by an amount equal to ρgh, where h is the vertical distance between the position of the hand and the heart, due to the weight of the blood column in the arm (the "hydrostatic effect"). In this way, the arterial transmural pressure can be changed without a cuff. The device includes a PPG sensor, a force sensor, and an accelerometer. The accelerometer and the length of the arm allow the measurement of hydrostatic BP changes, ρgh. The BP variation for a typical arm length is about 50 mmHg relative to heart level. For an average BP of 80 mmHg, the transmural pressure variation is about 30 to 130 mmHg. However, an oscillogram in both positive and negative transmural pressure regimes is required to accurately calculate BP. Therefore, the ring needs to be worn tight enough to generate a negative transmural pressure. A force sensor of known area measures the ring contact pressure on the finger, which is subtracted from the hydrostatic BP variation. BP can then be estimated from the PPG oscillations as a function of the transmural pressure variation.

[0117] One problem is that the ring needs to be applied with a pressure equal to about average BP, but BP is the target of the measurement. Another problem with introducing hand-raise actuation to smartphones is that it eliminates the need for a force sensor. However, most readily available devices, such as smartphones, have PPG sensors in the form of a camera and a three-axis accelerometer / gyroscope combination.

[0118] To address at least the noted issues, and as described in U.S. Provisional Application No. 63 / 135,430 (the contents of which are incorporated by reference in their entirety), measurements may be limited to PP. PP will aid in the detection of isolated systolic hypertension, a common form of hypertension that occurs with aging.

[0119] In one embodiment, Fig. 20As shown in , readily available devices known in the industry, such as but not limited to smartphones, tablets, laptops, watches, and wearable devices, can be used to measure absolute PP. These steps are parallel to the steps for performing traditional arm cuff BP measurements. Software that can be installed on any readily available device, such as through an operating system or through an app interface, can guide the user through the actuation phase of the body, fingers, and hands to perform measurements. The app or software builds an oscillogram and then uses it to calculate PP. The software can instruct the user to raise their arm and keep the device (such as a mobile phone) at an elevated height to start from the positive side of the transmural pressure interval where the finger blood pressure decreases. In step 1, the device guides the user to place the thumb on the front camera in a box that reflects the size of their thumb to measure the PPG at the transverse palmar arch artery ("artery"). In step 2, the device uses the screen contact area measurement to guide the user to gradually press with the thumb to reduce the transmural pressure until the artery is blocked (as measured via PPG oscillations). The contact area at this point is recorded and further used to guide the user to maintain their contact area during the hand lowering phase, and therefore keep the contact pressure constant. At this stage, ρgh is calculated based on the acceleration perpendicular to the screen and the arm length. In step 3, while maintaining the contact area, the device guides the user to lower their hand in increments (e.g., from +60 degrees to -60 degrees relative to the heart, at an angle of approximately 30 degrees or 20 degrees at a time, for 3-5 seconds) via audio / visual prompts from the phone. In step 4, PP is calculated from the PPG and ρgh data collected during the hand lowering process using an algorithm such as that mentioned above. Since the thumb contact pressure is unknown, SP and DP cannot be calculated. If the contact area exceeds certain predetermined limits too frequently, the user will be asked to try again.

[0120] In one example, if Fig.21 As shown in , an exemplary smartphone, the Samsung Galaxy S21, is provided for measuring PPG (R, G, and B AC+DC channels), acceleration (X-axis, Y-axis, and Z-axis), and finger contact area (large and small radius, X center position, and Y center position).

[0121] In one example, if Fig. 22 As shown in Fig. 20 The guidance system in (N=3) provides an exemplary measurement of PP. The device calculates an oscillogram from 9 different heights (average of 5 seconds per height).

[0122] In one example, if Fig.23 As shown in , the base of the nail can be positioned on top of the front camera to obtain large amplitude PPG oscillations. The optimal position can vary on the order of millimeters around the base of the nail.

[0123] For step 1, the app can include a one-time initialization phase to measure PPG oscillations at different thumb positions to identify the best thumb placement. This initialization can also create an outline of the thumb and its box size, which is used to guide thumb placement thereafter, such as Fig. 20 An example of creating a box size is discussed in the following article: "An iPhone Application for Blood Pressure Monitoring via the Oscillometric Finger Pressing Method" Chandrasekhar, A., Natarajan, K., Yavarimanesh, M. et al., Sci Rep (Scientific Reports) 8, 13136 (2018) https: / / doi.org / 10.1038 / s41598-018-31632-x (also available at https: / / www.nature.com / articles / s41598-018-31632-x ), the contents of which are incorporated herein by reference in their entirety.

[0124] For step 2, the thumb and hand actuation phases are used to measure BP via a standard smartphone, and guidance through these phases is key to the app's ease of use. This guidance can be done by placing the hand at heart level, lowering it, or raising it.

[0125] In some embodiments, the contact area (large and small radius, center of mass of the touch) can be used as a guide. The parameter of the contact area measured by the capacitive sensor array under the smartphone screen is used as a substitute for applying contact pressure to guide the user to slowly increase the thumb pressure. The app measures the PPG amplitude in the background to determine the required pressure. For example, when the hand is fully raised (i.e., artery occlusion), the PPG oscillation amplitude needs to be smaller, and when the hand is at heart level, the PPG oscillation amplitude needs to be larger. The center of mass of the touch can be used to correct for any subtle finger movement, where the large or small radius remains unchanged. For ease of application, a mathematical transformation can be applied to the contact area measurement to approximately linearize the nonlinear contact area-contact pressure relationship.

[0126] In other embodiments, DC PPG can be used for guidance. DC PPG is a function of the transmural pressure of the artery, has an S-shaped shape, and flattens under negative transmural pressure, such as Fig.16 The user can be guided to increase the pressure so that the DC PPG traces an S shape. The point where it flattens out can be used as the initial thumb pressure required with the hand fully raised.

[0127] In other embodiments, AC PPG can be used for guidance. As contact pressure increases, the amplitude of the PPG oscillation gradually increases, reaches a maximum, and then decreases. When the hand is fully raised, the user can be guided to block the artery by pressing until the PPG oscillation appears and then disappears.

[0128] In other embodiments, applied finger pressure can be used for guidance. For phones or devices with 3D touch, with the hand fully raised, thumb force measured by a strain gauge array below the screen can be used to guide artery occlusion. The app measures the PPG oscillation amplitude in the background to determine the required thumb pressure.

[0129] For step 3, the user needs to maintain their thumb pressure and lower / raise their hand continuously or in increments.

[0130] In one embodiment, the contact area parameters (large and small radius, centroid of touch) can be used in step 3 to guide the hand raising / lowering. A graph of contact area (via any possible combination of touch parameters) versus time is shown. The user is then guided to maintain the contact area throughout the hand lowering / raising process. The user is given audio / color cues to guide them to lower / raise their hand in increments.

[0131] In another embodiment, an accelerometer can be used for guidance. ρgh is measured by the user's arm length and the accelerometer via a single axis or applying principal component analysis to all axes. The latter can allow the user to hold the phone in an arbitrary orientation. A graph of ρgh versus time then guides the user to continuously lower / raise their hand over a period of 20-40 seconds. In particular, the guidance causes ρgh to vary linearly over a period of time. During the hand lowering / raising process, no guidance is provided to maintain thumb pressure. However, contact area changes and non-physiological oscillogram measurements in the background can be used to prompt the user to try again. In addition, the user can be taught to maintain thumb contact pressure during the initialization phase. In this phase, the user will practice maintaining AC or DC PPG over time while the hand is at different but fixed levels relative to the heart.

[0132] In other embodiments, applied finger pressure can be used for guidance. For phones with 3D touch, guide the user to maintain thumb contact pressure via screen force measurement. Guide the user to lower / raise the hand via audio / color cues.

[0133] In other embodiments, DC PPG can be used for guidance. A graph of DC PPG versus time is shown. By generating an S-shaped DC PPG over 20-40 seconds, the user is guided to lower / raise their hand while maintaining thumb contact pressure.

[0134] Multiple versions of the app are possible using different boot methods and can be customized to the user's preferences. The app can include video demonstrations to teach the user how to perform the procedure.

[0135] In one example, if Fig.24 As shown in , a standard wired sensor including a ρgh sensor can be used to test the hand-raising protocol. The ρgh sensor can be a tube that fluidically interfaces to a pressure transducer.

[0136] In one example, if Fig.25 As shown in , a three-step process can be used to calculate PP. First, the upper and lower envelopes of the PPG oscillations are detected. Second, an oscillogram is constructed by plotting the difference in the envelope as a function of ρgh. Then, two half-Gaussian functions are fit to the normalized oscillogram. Third, the width of the oscillogram is calculated as the change in ρgh between the maximum and minimum slopes of the fit. This width is used as an indicator of PP.

[0137] like Fig.26 As shown in , the width of the oscillogram represents PP. By converting finger PP to arm PP (e.g., using Fig.19 Further accuracy improvement can be obtained by using the method in , where the maximum oscillation is scaled by the width of the oscillogram after removing its mean. The mean and standard deviation of the PP error are -2.9 and 7.4 mmHg.

[0138] like Fig.26 As shown in , the oscillometric hand raise / lower method can use any type of sensor known in the art. In some embodiments, this includes ideal sensors such as Fig.24 In contrast, algorithm development using software such as readily available device apps can introduce random variability in the data but can be exploited if ideal sensors are not available.

[0139] In other embodiments, estimating DP includes measuring the maximum thumb contact area by firmly pressing the thumb. Fig. 20 If the contact area of ​​step 2) is relatively small compared to the maximum contact area, the DP can be on the lower side. Therefore, for people <65 years old, high PP is not a sign of risk.

[0140] In some embodiments, estimating thumb contact pressure may include capturing thumb contact pressure using available software, such as, but not limited to, software provided by the University of Michigan Force-feeling phone app, as described in the following document: "Force-feeling phone: Software lets mobile devices sense pressure" (available at https: / / news.umich.edu / force-feeling-phone-software- lets-mobile-devices-sense-pressure / In another embodiment, estimating the thumb contact pressure includes using a deep touch technology, such as Google deep touch, as described in the following article: “Sensing Force-Based Gestures on the Pixel 4” (available at

[0141] https: / / ai.googleblog.com / 2020 / 06 / sensing-force-based-gestures-on- pixel-4.html get).

[0142] Example 2:

[0143] A model for improved oscillometric BP calculation

[0144] The disclosed subject matter further provides reliable BP calculations that can be used in clinical BP ranges.For example, the disclosed subject matter provides a model for improving oscillometric BP calculations.

[0145] The disclosed model can find the BP signature in the finger wave measurement. For example, the disclosed model can be an s-shaped blood volume-pressure relationship of the artery. The input of the model can be the BP waveform under different external pressures, and the output can be the changing blood volume waveform.

[0146] Fig. 27 The response of the blood volume waveform predicted by the model to an external pressure ramp caused by finger compression is shown. High pass filtering and scaling of this waveform predicts the measured PPG oscillation waveform. Comparison of the envelopes of the two waveforms shows that the oscillogram, that is, the height of the oscillation as a function of external pressure, is proportional to the difference in the y-axis inverse sigmoidal relationship evaluated at SP and DP. The derivative of the sigmoidal relationship is the arterial compliance curve. This curve can be well represented by a three parameter exponential linear function, completing the model.

[0147] exist Fig.28 , PPG oscillations during pressure increase are shown. In some embodiments, the zero oscillation may include a noise floor or an oscillation that does not change. Causes of noise or unpredicted physiology may include proximal PPG oscillations, physiological responses to contraction, and tissue inhibition of arterial collapse.

[0148] When external pressure is only slightly above BP, the arteries in the fingers may become completely blocked or collapse. Fig.29 As shown in , this property indicates that the b model parameter representing the width of the left side of the arterial compliance curve is smaller for the finger artery than the traditional brachial artery. Additional data show that the c parameter representing the width of the right side of the curve is also smaller for the finger artery. Therefore, the disclosed model can predict that the external pressure at the maximum and minimum slopes of the oscillogram can better indicate the finger DP and SP than the brachial artery DP and SP. However, differentiation can amplify noise.

[0149] The model also shows that the width of the oscillations decreases as the external pressure increases. Due to the small value of the b parameter, the width begins to decrease once the external pressure exceeds the DP. Therefore, the model specifically predicts an unconventional "wide" oscillogram indicating the DP via a "bend" in the curve. Models with smaller b values ​​further show that the oscillations can be completely eliminated when the external pressure begins to exceed the SP. However, as mentioned above, detecting arterial blockage has proven difficult due to noise and other reasons.

[0150] like Fig.30 As shown in , based on the Beer-Lambert Law, assuming that the tissue compression due to arterial dilation is small compared to the tissue compression due to applied finger pressure, and the tissue is fully compressed between DP and SP, the disclosed model can be further extended to AC+DC PPG. Since the DC component of PPG can help to robustly detect arterial occlusion and thus help SP calculation, the model can be extended to AC+DC PPG and prediction. Due to the slow external pressure ramp caused by finger pressure, the tissue will compress to a certain pressure until it is fully compressed. Therefore, PPG decreases due to tissue and then saturates. Fig.30 The simulated AC+DC PPG caused by the artery of the original model is shown. Summing the two can provide the predicted AC+DC PPG. The extended model can predict the relationship of AC+DC PPG to finger pressure to represent SP via the bend in the curve (i.e., the sudden change in the slope of the function). By using the average PPG difference, the model prediction can provide accuracy and similarity to the actual measurement.

[0151] In certain embodiments, the disclosed subject matter provides a BP calculation algorithm based on the disclosed model predictions. Fig.31An example of the steps of a model-based DP and SP calculation algorithm is shown. During the first step, the oscillation width can be quantified using the area-to-height ratio and the pulse arrival time obtained via ECG, and the AC+DC PPG can be quantified via the average value over each ECG RR interval (e.g., average PPG beat). During the second step, these three features and the oscillation height are plotted relative to finger pressure. The model-predicted signatures can be detected to calculate three DP features and two SP features.

[0152] Fig.32 An image of an example desktop system for evaluating the disclosed devices and models is shown. The desktop system can be used to evaluate the disclosed algorithm for an arm cuff device in a patient. The user can also intervene to change their BP.

[0153] Fig.33 is a graph showing the accuracy of the disclosed model and algorithm. The average of the three DP features and the average of the two SP features produced a BP error of about 8.5 mmHg and a correlation of about 0.9 relative to the automatic cuff device. The width oscillation changes helped the DP calculation, while the DC PPG did not improve the SP calculation of the PPG oscillation. However, in contrast to the PPG oscillation, the DC PPG generally showed clear fiducial markers around the SP and may ultimately prove to be beneficial.

[0154] Fig.34 The correlation between systolic and diastolic references in DC PPG is shown. In 18 subjects, a total of 35 measurements were performed in various arm positions (i.e., raised, heart level, and lowered). Of the 35 measurements, 7 were performed in the raised level, 17 were performed at heart level, and 11 were performed in the lowered level. Fig.34 The high adjusted brachial artery cuff systolic and diastolic references are shown.

[0155] Fig.35 , DC PPG results using leave-one-out (LOO) regression are shown. A total of 35 measurements were taken in 18 subjects at various arm positions (i.e., raised, heart level, and lowered). Of the 35 measurements, 7 were taken at the raised level, 17 were taken at the heart level, and 11 were taken at the lowered level. Fig.36 Correlations between volumetric curvature measurements and minimum slope predictions are shown. Fig.37 An example method for volumetric tortuosity measurement is shown. Fig.37 As shown in , the method may include collecting data, averaging the PPG from the RR intervals, and finding the inflection point using a 2-line fit.

[0156] like Figure 33-36As shown, the regression minimum slope (Minslope) prediction of SP (correlation coefficient r, standard deviation of error σ e ) With the published measurement techniques (e.g., from AC research (r: 0.69.σ e :13.1) and DC study (r 0.91, σ e :8.8)). This may be due to improved measurement protocol (i.e., cuff placement, required compression linearity, and defined measurement-device orientation), accuracy of height offsets (i.e., height probe and robust heart level definition), or enhanced analysis (i.e., removed pulses recorded during non-increased compressions, required per-subject data consistency).

[0157] Plethysmogram curvature and minimum slope (Minslope) are derived from different PPG information (ie, shape and amplitude), predicting SP to be relatively average, and there may be little room for improvement due to the gill-shaped arm cuff reference.

[0158] The volumetric maps (AC and DC PPG versus finger pressure) show clear fiducial markers that indicate SP and are reproducible. Thus, analysis of high-noise data can distinguish DC PPG as a more noise-robust predictor of SP.

[0159] Although the disclosed subject matter is described herein according to certain preferred embodiments, it will be appreciated by those skilled in the art that various modifications and improvements may be made to the disclosed subject matter without departing from its scope. Similarly, additional features known in the art may be incorporated, such as disclosed in WO Publication WO201303787A2, U.S. Provisional Application No. 63 / 135430 and U.S. Provisional Application No. 63 / 388,021, the contents of each of which are incorporated by reference in their entirety. In addition, although the individual features of an embodiment of the disclosed subject matter may be discussed herein or shown in the drawings of an embodiment rather than in other embodiments, it should be clear that the individual features of an embodiment may be combined with one or more features of another embodiment or features from multiple embodiments.

[0160] In addition to the various embodiments described and claimed, the disclosed subject matter also relates to other embodiments with any other possible combination of features disclosed and claimed herein. Therefore, the specific features presented herein can be combined with each other in other ways within the scope of the disclosed subject matter, so that the disclosed subject matter includes any appropriate combination of features disclosed herein. Therefore, for the purpose of illustration and description, the foregoing description of the specific embodiments of the disclosed subject matter has been presented. It is not intended to be exhaustive or to limit the disclosed subject matter to those disclosed embodiments. It will be apparent to those skilled in the art that various modifications and changes can be made to the equipment, methods and systems of the disclosed subject matter without departing from the spirit or scope of the disclosed subject matter. Therefore, it is intended that the disclosed subject matter is included in the modifications and changes within the scope of the appended claims and their equivalents.

Claims

1. A method of determining a user's diastolic blood pressure using a device having a photoplethysmography (PPG) force sensor unit, the method comprising: providing visual or audio instructions to the user with the device, wherein the instructions instruct the user to position a finger on the PPG force sensor unit and press the finger on the PPG force sensor unit with varying finger pressure; measuring the PPG oscillation of the finger and the finger pressure with the PPG force sensor unit; calculating the width of each of the PPG oscillations as a function of finger pressure; Diastolic blood pressure was calculated using the PPG oscillation width versus finger pressure function; as well as The diastolic blood pressure is output on a graphical user interface of the device or sent to a database repository.

2. The method of claim 1 , further comprising detecting a curvature of the PPG oscillation width relative to a finger pressure function.

3. The method according to claim 2, characterized in that The bending of the PPG oscillation width with respect to the finger pressure function is detected by fitting at least two curves to the function and using the intersection points of the curves.

4. The method according to claim 1, characterized in that: The width of each PPG oscillation is calculated as the ratio of the area to the height of the oscillation.

5. The method according to claim 1, further comprising: Measuring an electrocardiogram (ECG) using additional electrodes incorporated into the device; as well as The width of each PPG oscillation is calculated as the pulse arrival time of each of the oscillations, which is detected as the time delay between the R-wave of the ECG and the PPG trough.

6. The method of claim 5, further comprising determining systolic blood pressure using the value of the pulse arrival time at a bend in the pulse arrival time relative to finger pressure function.

7. The method according to claim 1, characterized in that Diastolic blood pressure is calculated using additional features extracted from the PPG oscillations and finger pressure.

8. The method according to claim 7, characterized in that The additional feature includes the finger pressure at the maximum slope of the PPG oscillation amplitude versus finger pressure function.

9. A method of determining a user's systolic blood pressure using a device having a photoplethysmography (PPG) force sensor unit and electrocardiogram (ECG) electrodes, the method comprising: providing visual or audio instructions to the user with the device, wherein the instructions instruct the user to position a finger on the PPG force sensor unit and press the finger on the PPG force sensor unit with varying finger pressure; Measuring a total PPG including a DC component, a PPG oscillation, and an applied finger pressure with the PPG force sensor unit; measuring ECG using the electrodes; calculating the average of each PPG beat over the R-wave to R-wave interval of the ECG as a function of applied finger pressure; and The systolic blood pressure was calculated using the PPG mean versus finger pressure function.

10. The method of claim 9, further comprising detecting a curvature of the PPG average with respect to a finger pressure function.

11. The method according to claim 10, characterized in that The curvature of the PPG average with respect to the finger pressure function is detected by fitting at least two curves to the function and using the intersection of the curves.

12. The method according to claim 9, characterized in that Systolic blood pressure is calculated using additional features extracted from the total PPG, finger pressure, and ECG.

13. The method according to claim 12, characterized in that The additional feature includes the finger pressure at the minimum slope of the PPG oscillation amplitude versus finger pressure function.

14. The method according to claim 12, characterized in that The additional features include the value of the pulse arrival time at the bend in the pulse arrival time relative to finger pressure function.

15. A method of determining a user's pulse pressure using a device, comprising: providing visual or audio instructions to a user having the device, wherein the instructions instruct the user to position a finger over a camera and a screen of the device to measure a total photoplethysmography (PPG) from the finger via the camera of the device and a finger contact parameter via a touch screen sensor of the screen; providing visual or audio instructions to the user with the device to apply finger pressure on the camera and the screen based on the measurements; providing visual or audio instructions to the user with the device to lower or raise the fingered hand relative to the user's heart level while maintaining the finger contact parameter; measuring a hydrostatic blood pressure change ρgh in the finger by using an accelerometer measurement of the device and arm length; and Pulse pressure is calculated from the PPG and ρgh measurements.

16. The method of claim 15, further comprising providing instructions to the device for a one-time initialization to determine optimal placement guidance for the finger on the camera and the screen.

17. The method according to claim 15, characterized in that The finger contact parameters include a touch centroid.

18. The method according to claim 15, characterized in that The PPG oscillations are used as a guide to determine the amount of finger pressure to maintain on the screen and the camera during hand raising or lowering.

19. The method according to claim 15, characterized in that The PPG oscillations and finger contact parameters are used as guides to determine the amount of finger pressure to maintain on the screen and the camera during hand raising or lowering.

20. The method of claim 15, wherein finger contact parameters are used as a guide to maintain the finger pressure on the screen and the camera during hand raising or lowering.

21. The method according to claim 15, characterized in that A timer was used as a further guide to indicate the amount of time required for the hand to be raised or lowered.

22. The method according to claim 15, characterized in that The pulse pressure is calculated using at least one of ρgh at the minimum slope and the maximum slope of the PPG oscillation amplitude with respect to the ρgh function or the width of the PPG oscillation amplitude as a function of ρgh.

23. The method of claim 15, further comprising measuring diastolic blood pressure by measuring a maximum finger contact parameter via a firm finger press by the user, and comparing the finger contact parameter to the maximum finger contact parameter to determine if diastolic blood pressure is lower.

24. A method of determining blood pressure using a device having a photoplethysmography (PPG) force sensor unit and ECG electrodes, the method comprising: receiving measurements from a touch of a finger on the PPG force sensor unit; receiving an ECG from the electrodes; calculating, with a processor of the device, diastolic blood pressure using the width of each AC blood volume oscillation as a function of finger pressure; calculating, by the processor, systolic blood pressure using an average value of each DC blood volume beat over the RR interval of the ECG relative to a finger pressure function; as well as The blood pressure is output on a graphical user interface of the device or sent to a database repository.

25. A system for determining blood pressure of a subject, comprising: a sensor configured to measure finger pressure, finger photoplethysmography (PPG) oscillations, finger PPG DC component, and ECG; a display configured to provide visual or audio instructions to instruct the subject to position a finger at a predetermined location; as well as A processor, the processor being configured to: calculating diastolic blood pressure and systolic blood pressure, wherein the diastolic blood pressure is calculated using a PPG oscillation width versus finger pressure function, and wherein the systolic blood pressure is calculated using a PPG average; as well as The calculated diastolic blood pressure and systolic blood pressure are displayed on a display.

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