Apparatus, system, and method for blood pressure measurement

Abstract

Apparatuses, methods, and systems for cuffless blood pressure (BP) measurement are provided. The apparatuses, methods, and systems include the use of an oscillometric finger press method for determining blood pressure using a smartphone or other readily available computing device. Further apparatuses, methods, and systems are provided for improving BP calculations through the use of modeling and / or additional measurements of ECG and DC PPG.

Description

Technical Field

[0001] Cross - reference to related applications This application claims priority to U.S. Provisional Patent Application No. 63 / 388,021, filed on July 11, 2022, and U.S. Provisional Patent Application No. 63 / 482,868, filed on February 2, 2023, all of which are hereby incorporated by reference in their entirety.

[0002] Statement regarding federally - sponsored research or development This invention was made with government support under grant number HL146470 awarded by the National Institutes of Health. The U.S. government has certain rights in this invention.

[0003] The subject matter of the present disclosure relates to devices, systems, and methods for measuring blood pressure. The disclosed devices and systems can perform cuffless blood pressure measurement and determine blood pressure by using oscillometric finger pressing or hand-raising techniques.

Background Art

[0004] High blood pressure (BP) affects approximately one in three adults worldwide. The incidence increases with age, but many people develop hypertension early in adulthood (e.g., more than one in five U.S. adult Americans under 40 years old have hypertension). Symptoms are usually asymptomatic, but the risk of stroke and heart disease increases monotonically with blood pressure at a given age. Lifestyle changes and many inexpensive once-daily drug therapies can reduce blood pressure and cardiovascular risk. However, only three in seven hypertensive patients are aware of their condition, and only one in seven of these controls their blood pressure. Epidemiological data on hypertension in low-resource settings are more alarming. As a result, hypertension has emerged as a major cause of loss of disability-adjusted life years.

[0005] Auscultatory and oscillometric BP measurement devices are useful for the management of hypertension. At the same time, since these devices rely on an inflatable cuff, they can be held responsible for the recognition and control rates of severe hypertension. Cuff-based devices are not easily accessible, especially in low-resource settings. Therefore, most people do not check their blood pressure regularly. Regular measurements during daily life are necessary to avoid the white coat and mask effects in clinics where patients exhibit higher or lower blood pressure than normal, and to average out the large fluctuations in blood pressure caused by stress, physical activity, and other factors. If blood pressure could be measured more simply, many people would become aware of their condition and be motivated to take their medications.

[0006] Therefore, cuffless BP monitoring devices are widely demanded. However, the devices under development are generally troubled by the consumable limitation that they require calibration using a cuff device to output the measured values in mmHg units. SUMMARY OF THE INVENTION

[0007] The objects and advantages of the disclosed subject matter are set forth in the description which follows, are apparent from the description, and are learned by practice of the disclosed subject matter. Further advantages of the disclosed subject matter are realized and attained by the devices particularly pointed out in this specification and the claims thereof, as well as from the accompanying drawings.

[0008] To achieve these and other advantages, and in accordance with the purpose of the disclosed subject matter, as embodied and broadly described, the disclosed subject matter includes devices, methods, and systems for blood pressure monitoring.

[0009] 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 can include providing visual or auditory instructions to the device, measuring PPG oscillations of the finger and finger pressure with the PPG force sensor unit, calculating each width of the PPG oscillations as a function of the finger pressure, calculating the diastolic blood pressure using a PPG oscillation width versus finger pressure function, and outputting the diastolic blood pressure to a graphical user interface of the device or transmitting the diastolic blood pressure to a database repository. In non-limiting embodiments, the instructions can instruct the user to place a finger on the PPG force sensor unit and press the finger on the PPG force sensor unit at various finger pressures.

[0010] In certain embodiments, the method for determining diastolic blood pressure can further include detecting a flexion of the PPG oscillation width relative to the finger pressure function. In non-limiting embodiments, the flexion of the PPG oscillation width relative to the finger pressure function can be detected by fitting at least two curves to the function and using the intersection of the curves.

[0011] In certain embodiments, each width of the PPG oscillations can be calculated as the ratio of the area to the height of the oscillation.

[0012] In certain embodiments, the method for determining diastolic blood pressure can further include measuring an electrocardiogram (ECG) using additional electrodes incorporated into the device and calculating each width of the PPG oscillations as the pulse arrival time of each oscillation detected as the time delay between the R wave of the ECG and the PPG foot.

[0013] In certain embodiments, the method for determining diastolic blood pressure can further include determining the systolic blood pressure by using the value of the pulse arrival time at the flexion of the pulse arrival time relative to the finger pressure function.

[0014] In certain embodiments, the systolic blood pressure can be calculated using additional features extracted from the PPG oscillations and the applied finger pressure. In non-limiting embodiments, the additional features can include the finger pressure at the maximum gradient of the PPG oscillation amplitude with respect to the finger pressure function.

[0015] The disclosed subject matter provides a method for determining a user's systolic blood pressure using a device having a photoplethysmograph (PPG) force sensor unit and an electrocardiogram (ECG) electrode. The method can include providing visual or auditory instructions to the device, measuring the total PPG including the DC component, the PPG oscillation, and the applied finger pressure using the PPG force sensor unit, simultaneously measuring the ECG with the electrode, calculating an average of each PPG beat over the interval from R-wave to R-wave of the ECG as a function of the applied finger pressure, and calculating the systolic blood pressure using the PPG average with respect to the finger pressure function. In non-limiting embodiments, the instructions can instruct the user to place a finger on the PPG force sensor unit and press the finger on the PPG force sensor unit with various finger pressures.

[0016] In certain embodiments, a method for determining systolic blood pressure can include detecting a flexion of the PPG average with respect to the finger pressure function. In non-limiting embodiments, the flexion of the PPG average with respect to the finger pressure function can be detected by fitting at least two curves to the function and using the intersection of the curves. In non-limiting embodiments, the systolic blood pressure can be calculated using additional features extracted from the total PPG, the finger pressure, and the ECG. In non-limiting embodiments, the additional features can include the finger pressure at the minimum gradient of the PPG oscillation amplitude with respect to the finger pressure function. In non-limiting embodiments, the additional features can include the value of the pulse arrival time at the flexion of the pulse arrival time to the finger pressure function.

[0017] The disclosed subject matter provides a method for determining a user's pulse pressure using a device. The method includes providing visual or audio instructions to the user by the device to position a finger on the device's camera and an adjacent screen of the device, measuring a total PPG from the finger via the device's camera, measuring finger contact parameters via the device's touch screen sensor, providing visual or audio instructions to the user to apply finger pressure on the camera and the screen based on the measurements, providing visual or audio instructions to the user by the device to lower or raise the hand relative to the user's heart level while maintaining the finger pressure, measuring a hydrostatic blood pressure change (ρgh) within the finger by using the device's accelerometer measurements and the length of the arm, and calculating a pulse pressure from the PPG and ρgh measurements.

[0018] In certain embodiments, the method for determining pulse pressure can further include providing an initialization command to the device to determine an optimal placement guide for the finger on the camera and the screen.

[0019] In certain embodiments, the finger contact parameters can include a contact center of gravity. In non-limiting embodiments, the PPG vibration can be used as a guide for determining the amount of finger pressure on the screen and the camera to be maintained during hand raising or lowering. In non-limiting embodiments, the PPG vibration and the finger contact parameters can be used as a guide for determining the amount of finger pressure on the screen and the camera to be maintained during hand raising or lowering. In non-limiting embodiments, the finger contact parameters can be used as a guide for maintaining the finger pressure on the screen and the camera during hand raising or lowering. In non-limiting embodiments, a timer can be used as an additional guide for indicating the time taken for hand raising or lowering.

[0020] In certain embodiments, the pulse pressure can be calculated using at least one of ρgh at the minimum and maximum gradients of the PPG oscillation amplitude with respect to the ρgh function, or the width of the PPG oscillation amplitude as a function of ρgh.

[0021] In certain embodiments, a method for determining pulse pressure can further include measuring the systolic blood pressure by measuring the maximum finger contact parameter via a firm finger pressure by the user, and comparing the finger contact parameter with the maximum area to determine whether the systolic blood pressure is low.

[0022] The disclosed subject matter provides a method for determining blood pressure using a device having a photoplethysmograph (PPG) force sensor unit and an ECG electrode. The method can include receiving a pressure measurement from a finger touch on the PPG force sensor unit, receiving an ECG from the electrode, calculating the diastolic blood pressure by the device's processor using the width of each alternating current (AC) blood volume oscillation versus finger pressure function, calculating the systolic blood pressure by the processor using the average of each direct current (DC) blood volume pulsation over the RR interval of the ECG versus finger pressure function, and outputting the blood pressure on the device's graphical user interface or sending the blood pressure to a database repository.

[0023] The disclosed subject matter provides a system for determining a subject's blood pressure. The system can include a sensor configured to measure finger pressure, finger photoplethysmograph (PPG) vibration, finger PPG DC component, ECG, and a display configured to provide visual or auditory instructions for guiding the subject to place a finger in a predetermined position, and a processor. In non-limiting embodiments, the processor can be configured to calculate the diastolic and systolic blood pressures and display the calculated diastolic and systolic blood pressures on the display. In non-limiting embodiments, the diastolic blood pressure can be calculated using the PPG vibration amplitude versus finger pressure function. In non-limiting embodiments, the systolic blood pressure can be calculated using the PPG average.

[0024] It should be understood that both the foregoing general description and the following detailed description and the drawings are examples and are provided for the purpose of illustration and are not intended to limit the scope of the disclosed subject matter in any way.

[0025] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate devices of the disclosed subject matter and are included to provide a further understanding thereof. Together with the description, the drawings serve to explain the principles of the disclosed subject matter.

Brief Description of the Drawings

[0026] The subject matter of this application will be more readily understood from the following detailed description when read in conjunction with the accompanying drawings:

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Embodiments for Carrying Out the Invention

[0027] Here, embodiments of the disclosed subject matter are referred to in detail, and an example thereof is shown in the accompanying drawings. The disclosed subject matter is described in conjunction with a detailed description of the system.

[0028] The terms used in this specification generally have their ordinary meanings in the context of the disclosed subject matter and in the specific context in which each term is used. Specific terms are discussed below or elsewhere in this specification to provide further guidance to the practitioner when describing the compositions and methods of the disclosed subject matter.

[0029] As used in this specification, the use of the term "a" or "an" can mean "one" when used in connection with the term "comprising" in the claims and / or the specification, but is also consistent with the meanings of "one or more", "at least one", and "more than one". Further, the terms "having", "including", "containing", and "comprising" are interchangeable, and those skilled in the art will recognize that these terms are open terms.

[0030] The terms "about" or "approximately" mean within an acceptable error range for a particular value as determined by one of ordinary skill in the art, which depends in part on how the value is measured or determined, i.e., on the limitations of the measurement system. For example, "about" can mean within three or more standard deviations in accordance with the practice in the art. Alternatively, "about" can mean within up to 20%, preferably up to 10%, more preferably up to 5%, and even more preferably up to 1% of a given value. Alternatively, especially with respect to biological systems or processes, the term can mean within an order of magnitude, preferably within a factor of five, more preferably within a factor of two of a value.

[0031] As used herein, "user" or "subject" is a vertebrate, such as a human or non-human animal, such as a mammal. Mammals include, but are not limited to, humans, primates, livestock, sport animals, rodents, and pets.

[0032] 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 photoplethysmograph (PPG) force sensor unit.

[0033] In certain embodiments, a method for determining a user's diastolic blood pressure can include providing visual or auditory instructions that can direct a user to place a finger on a PPG force sensor unit and press the finger on the PPG force sensor unit at various finger pressures. The PPG force sensor unit can be configured to measure a user's PPG and the applied finger pressure. The PPG force sensor unit can include a camera PPG sensor, a finger PPG sensor, a force sensor, or combinations thereof. The PPG force sensor unit can be configured to detect PPG oscillations and the applied finger pressure from a subject's finger on the PPG sensor unit. In non-limiting embodiments, the PPG sensor can obtain PPG oscillations without using a force sensor.

[0034] In certain embodiments, a method for determining diastolic blood pressure can include measuring finger PPG oscillations and an applied finger pressure with a PPG force sensor unit. In non-limiting embodiments, the PPG oscillations can be variable amplitude PPG oscillations. For example, the PPG oscillations can be proportional to blood volume oscillations in an artery, and since the arterial volume-pressure relationship is non-linear (S-shaped), when sweeping the applied finger pressure, the PPG oscillation amplitude increases to a maximum and then decreases to zero when the artery is occluded. In non-limiting embodiments, a method for determining diastolic blood pressure can include calculating each width of the PPG oscillations as a function of the applied finger pressure, calculating the diastolic blood pressure using a PPG oscillation width versus 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, variable amplitude PPG oscillations can be obtained from a PPG waveform when a user presses a finger on the sensor, thereby changing the external pressure on the underlying artery. In non-limiting embodiments, a finger PPG waveform can include an alternating current (AC) component and a direct current (DC) component during an increase in external finger pressure. In non-limiting embodiments, the AC component can reflect the pulsation of blood, and the DC component can reflect the non-pulsatile component of the PPG signal. In non-limiting embodiments, the DC and / or AC components of the PPG waveform can be used to determine how much finger pressure a user needs to apply to a PPG sensor (e.g., a camera or a finger PPG sensor). For example, a user can first press the PPG sensor hard to determine the highest DC value based on user input. The device can show a graph for recording the DC value versus time, and the y-axis range can be set by the identified highest DC amount. A processor can determine the DC amount at which the AC oscillation amplitude is maximum, which can correspond to the mean BP, and show a constant target line for guiding the user to achieve this amount of substantial transmural pressure (external-internal pressure of the underlying artery) by pressing the finger or raising the hand.

[0035] In certain embodiments, the method for determining diastolic blood pressure can further include detecting a flexion of the PPG oscillation amplitude with respect to the sphygmomanometer function (i.e., a sharp change in the gradient of the function). For example, the flexion of the PPG oscillation amplitude with respect to the sphygmomanometer function can be detected by fitting at least two curves to the function and using the intersection of the curves.

[0036] In certain embodiments, the width of each PPG oscillation can be calculated as the ratio of the area to the height of the oscillation. For example, the area can be defined as the region between the PPG waveform beats from trough to trough and the line between the two troughs. The height can be defined as the amplitude from the trough to the peak of the PPG wave beat from the pulsation. The ratio of the area to the height can be the ratio between the two. In a non - limiting embodiment, the method for determining diastolic blood pressure can include measuring an electrocardiogram (ECG) using additional electrodes incorporated in the device, and calculating the width of each PPG oscillation as the pulse arrival time of each oscillation as the time delay between the R wave of the ECG and the PPG foot. For example, the pulse arrival time (PAT) which is the time delay between the ECG R wave and the PPG foot and the area - to - height ratio (AHR) are both indicators of the oscillation width. When plotting the PAT and AHR against the sphygmomanometer readings to obtain a "PAT and AHR oscillogram", a reference marker can be identified to indicate the diastolic pressure (DP) of the finger. 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. In a non - limiting embodiment, the method can further include determining the systolic blood pressure using the value of the pulse arrival time at the flexion of the pulse arrival time with respect to the sphygmomanometer function. Systolic pressure can be calculated in a relationship that is inversely proportional to the pulse arrival time and proportional to the height of the subject. The coefficient is found from the population data.

[0037] In certain 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 oscillation and the finger pressure. The additional features can include the finger pressure at the maximum gradient of the PPG oscillation amplitude with respect to the finger pressure function. For example, diastolic blood pressure can be calculated using at least the pressure at the inflection of width versus pressure. For example, the pressures at the highest (P maxslope ) and lowest gradients (P minslope ) of the reference oscillogram (“height oscillogram”) can indicate the finger DP and SP, respectively.

[0038] The disclosed subject matter provides a method for determining a user's systolic blood pressure using a device having a photoplethysmograph (PPG) force sensor unit and ECG electrodes. The method can include providing visual or auditory instructions to the device, the instructions instructing the user to position a finger on the PPG force sensor unit, press the finger on the PPG force sensor unit with various finger pressures, measure the total PPG including the DC component, the PPG oscillation, and the applied finger pressure using the PPG force sensor unit, and simultaneously measure the ECG with the electrodes.

[0039] In certain embodiments, a method for determining a user's systolic blood pressure can include calculating an average of each PPG pulse over the interval from R-wave to R-wave of the ECG as a function of the applied finger pressure, and calculating the systolic blood pressure using the PPG average with respect to the finger pressure function. In non-limiting embodiments, the PPG pulse can reflect the pulse of the PPG for each heartbeat, and the average of the PPG pulses can reflect the average value within that pulse. For example, three lines can be fitted to the upper envelope of a graph showing the overall (DC + AC) PPG versus finger pressure, and the intersection (P DCpeak ) of the second of the second two lines indicates the finger SP (Figure 16).

[0040] In certain embodiments, a method for determining systolic blood pressure can further include detecting a flexion of the PPG average with respect to the sphygmomanometric function (i.e., a sharp change in the slope of the function). For example, the flexion of the PPG average with respect to the sphygmomanometric function can be detected by fitting at least two curves to the function and using the intersection of the curves.

[0041] In certain embodiments, systolic blood pressure can be calculated using additional features extracted from total PPG, sphygmomanometry, and ECG. In non-limiting embodiments, the additional features can include the sphygmomanometry at the minimum slope of the PPG oscillation amplitude with respect to the sphygmomanometric function. In non-limiting embodiments, the additional features can include the value of the pulse arrival time at the flexion of the pulse arrival time to the sphygmomanometric function. The pulse arrival time is defined as the time delay between the ECG R wave and the PPG foot.

[0042] The disclosed subject matter provides a method for determining a user's pulse pressure using a device. The method can include providing a visual or audible instruction to the user to place a finger on the device's camera and an adjacent screen to measure photoplethysmography (PPG) from the finger via the device's camera and to measure finger contact parameters via the device's touch screen sensor, providing a visual or audible instruction to the user to apply a sphygmomanometry on the camera and the screen based on the measurement, providing a visual or audible instruction to the user using the device to lower or raise the hand with respect to the user's heart level while maintaining the sphygmomanometry guided by the finger contact parameters, and measuring the hydrostatic blood pressure change (ρgh) within the finger by using the device's accelerometer measurement and the length of the arm. In non-limiting embodiments, the finger contact parameters can include the center of contact. The finger contact parameter is any parameter derived from a screen capacitance sensor array (e.g., touch center of gravity and touch area) within the telephone.

[0043] In certain embodiments, a method for determining pulse pressure can include calculating the pulse pressure from PPG and ρgh measurements. For example, as the user straightens their arm and lowers their hand, the internal blood pressure in the finger may increase by an amount equal to ρgh due to the weight of the arm blood column (“hydrostatic effect”), where ρ is the density of blood, g is the gravitational constant, and h is the vertical distance between the position of the hand and the heart, thus being able to vary the arterial wall pressure. In non-limiting embodiments, the hydrostatic BP change (ρgh) can be measured using an accelerometer and the length of the arm. This is because the angle of the arm due to the gravitational vector can be calculated from the accelerometer, and h can be calculated using trigonometry for the length of the arm. Alternatively, the hydrostatic BP change can be estimated without using an accelerometer / gyroscope or any other sensor. While maintaining a constant finger pressure, the user lowers the phone to the floor and raises it back up in intuitive and fixed increments (e.g., about 45 degrees for 3 - 5 seconds as induced by an audio / visual cue). Then, the hydrostatic BP change can be estimated based on the known increments.

[0044] In certain embodiments, the PPG vibration can be used as a guide for determining the amount of finger pressure on the screen and camera to be maintained during hand raising or lowering. In non-limiting embodiments, the PPG vibration and finger contact parameters can be used as a guide for determining the amount of finger pressure on the screen and camera to be maintained during hand raising or lowering. In non-limiting embodiments, the finger contact parameters can be used as a guide for maintaining the finger pressure on the screen and camera during hand raising or lowering. In non-limiting embodiments, a timer can be used as an additional guide for indicating the time taken for hand raising or lowering.

[0045] In certain embodiments, the pulse pressure can be calculated using ρgh at at least one of the minimum gradient and the maximum gradient of the PPG vibration amplitude with respect to the ρgh function, or using the width of the PPG vibration amplitude as a function of ρgh.

[0046] In certain embodiments, a method for determining pulse pressure can include measuring systolic blood pressure by measuring a maximum finger contact parameter via a firm finger pressure by a user, and comparing the finger contact parameter to the maximum finger contact parameter to determine whether the systolic blood pressure is low. For example, if the ratio of the maximum contact area to the contact area at a systolic reference marker (any algorithm for detecting systole) is low, the systole can be low. If the ratio of the maximum contact area to the contact area at a systolic reference marker (any algorithm for detecting systole) is high, the systole can be high. These ratios can be created using population data. In non-limiting embodiments, the diastolic pressure can be estimated using any of the proposed algorithms that calculate the pulse pressure by adding it to the systolic pressure.

[0047] In certain embodiments, a method for determining pulse pressure can include providing instructions for a one-time initialization to determine an optimal placement guide for the finger on the camera and screen. For example, the disclosed device can perform a one-time initialization phase to measure PPG vibrations across different thumb positions, thereby identifying the best thumb placement. During initialization, the user can be guided to incrementally place more fingers on the screen. The device can identify a finger positioning that provides an appropriate area of screen contact without approaching force saturation. For example, without limitation, the disclosed device can provide a visual indicator that can guide the user to place a finger that can result in the maximum area of screen contact without force saturation. This initialization can also create a profile of the thumb and its box dimensions for guiding the subsequent placement of the thumb.

[0048] In certain embodiments, the blood pressure changes in the finger can be measured when the device is at different vertical positions relative to the user's heart level. In non - limiting embodiments, the touch sensor adjacent to the camera can be the screen of the device. In non - limiting embodiments, the distance of the device from the user's heart can be the length of the arm.

[0049] The disclosed subject matter provides a method for determining blood pressure using a device having a photoplethysmograph (PPG) force sensor and an ECG electrode. The method includes receiving measurements from a finger touch on the PPG force sensor unit, receiving an ECG from the electrode, calculating diastolic blood pressure (BP) using the processor of the device with the width of each alternating current (AC) blood volume oscillation versus finger pressure function, calculating systolic BP using the mean of each direct current (DC) blood volume pulsation over the RR interval of the ECG versus finger pressure function by the processor, and outputting the BP on the graphical user interface of the device or transmitting the BP to a database repository.

[0050] The disclosed subject matter provides a system for determining a subject's blood pressure. The system can execute the disclosed method for measuring blood pressure, DP, SP, pulse pressure, or combinations thereof. An exemplary system can include a sensor configured to measure finger pressure, finger photoplethysmograph (PPG) vibration, finger PPG DC component, and ECG, a display configured to provide visual or audio instructions to direct the user / subject to position a finger, thumb, hand, or combinations thereof at a predetermined location, and a processor configured to execute the disclosed method for measuring blood pressure, DP, SP, pulse pressure, or combinations thereof.

[0051] In certain embodiments, the processor may be configured to calculate diastolic and systolic blood pressures and display the calculated diastolic and systolic blood pressures on a display. In non-limiting embodiments, the diastolic blood pressure can be calculated using a PPG amplitude vs. finger pressure function, and the systolic blood pressure can be calculated using a PPG average.

[0052] Examples Example 1 As shown in FIG. 1, the disclosed subject matter is based on an oscillometric principle for cuffless and calibration-free BP monitoring via an accessible handheld device such as a smart wearable device, a tablet, or a smartphone. Such a device can include not only a processor capable of calculating and evaluating, 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 index fingertip against the device or phone (held at heart level) to steadily increase the external pressure on the underlying artery. A phone embedded with a photoplethysmography (PPG) and a force transducer functions as a sensor (instead of a cuff device) for measuring the resulting variable amplitude blood volume oscillations and the applied finger pressure. The phone also provides visual feedback on a graphical user interface (GUI) or audio feedback via the phone speaker to guide finger actuation and applies an algorithm for calculating BP from measurements equivalent to those of an oscillometric cuff device.

[0053] Figure 2A shows a device consisting of a custom PPG force sensor unit fixed to the back of a device that is readily available for performing the "oscillometric finger press method". As shown in Figure 2B, this device obtains BP measurements with a level of accuracy comparable to that of a finger cuff volume clamp device that has cleared FDA standards over a normal blood pressure range. In a non-limiting embodiment, the oscillometric finger press method, as shown in Figure 3, can be implemented as a smartphone (iPhone (registered trademark)) application ("app") by using the front camera as a PPG sensor and the sensitivity distortion gauge array ("3D touch") under the screen as a force sensor.

[0054] The disclosed subject matter provides devices, methods, and systems for improving BP calculation accuracy based on physiological modeling. In certain embodiments, the method includes a related oscillometric hand raising / lowering method for cuffless and calibration-free BP monitoring using a standard device such as a smartphone, where highly sensitive force sensing is not normally available. The disclosed method can overcome the drawbacks in certain devices where sensitive force sensing is not available. In other embodiments, the method includes guiding the user to perform the hand movement appropriately.

[0055] Osmometric modeling As shown in Figure 4, the oscillometric model explains the S-shaped blood volume - transmural pressure relationship in the artery, where the transmural pressure includes the internal BP of the artery minus the external pressure. The model assumptions include a purely elastic arterial wall and a linear relationship between the blood volume oscillations via PPG (or cuff) and the measured oscillations. In certain embodiments, the model can predict an oscillogram (i.e., the oscillation amplitude versus external pressure function) for typical BP calculations, or the model can predict the oscillations.

[0056] As shown in Fig. 5, the digital artery folds when the external pressure is slightly higher than the internal BP (i.e., the "digital artery that can be folded"). Fig. 5A shows that the digital artery can be folded in the sense that it is completely folded when the external pressure is slightly higher than the internal BP. Figs. 5B - 5C refer to the model parameters of Fig. 4. PP is the pulse pressure and DP is the diastolic blood pressure. Mathematically, this corresponds to a small b value of the finger in the model of Fig. 4. However, due to a greater occurrence of brachial artery collapse, the external pressure can become significantly higher than the internal pressure. This difference is utilized to arrive at an accurate digital oscillometric BP calculation algorithm.

[0057] As shown in Fig. 6, the differential algorithm is more accurate for the finger than for the arm due to differences in model parameters. In particular, the external pressures at which the slope of the oscillogram is maximum and minimum need to correspond exactly to the diastolic and systolic blood pressures (DP and SP) of the finger. However, the differential operation may amplify measurement noise.

[0058] As shown in Fig. 7, this model predicts that due to the foldability of the finger, the width of each vibration narrows as the external pressure increases. However, as DP increases, stenosis occurs at a higher external pressure. In certain embodiments, the stenosis begins at DP (or slightly higher than DP since the digital artery is not completely foldable). Similarly, the vibration needs to be extinguished when the external pressure slightly exceeds SP.

[0059] As shown in Fig. 8, in predicting the DC PPG + AC PPG vibration with the increase of external pressure, the tissue around the artery can be considered. In particular, as the external pressure increases, the tissue compresses to a certain point. As a result, the DC PPG decreases and then saturates due to the tissue (upper right in the figure). By adding the original artery model (upper left in the figure) to this tissue model, the total PPG can be predicted as the external pressure increases (bottom).

[0060] Improvement of blood pressure calculation The disclosed subject matter provides an improved method for calculating BP through modeling and / or use of additional measurements of ECG and DC PPG (as opposed to only conventional PPG oscillations). By way of example and not limitation, an apparatus as shown in FIG. 9 can perform additional measurements. Further, the ECG is useful for simultaneous monitoring of blood pressure and arrhythmias.

[0061] As shown in FIG. 10, both the Pulse Arrival Time (PAT), which is the time delay between the ECG R wave and the PPG foot, and the Area Height Ratio (AHR) are indicators of the oscillation amplitude. When PAT and AHR are plotted against finger pressure to obtain a "PAT and AHR oscillogram", it is clear that distinct reference markers indicate 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 ) indicates the DP. The P maxslope or P minslope of the reference oscillogram ("height oscillogram") indicates the finger DP and SP, respectively.

[0062] As shown in FIG. 11, P PAT , P AHR , and P maxslope correlate well with the arm cuff DP (N = 34). As shown in FIG. 5, the arm cuff DP is systematically higher than the finger DP. P PAT and P AHR overestimate the finger DP, and their data points are close to the discrimination line.

[0063] As shown in FIG. 12, P PAT and P AHR are indicators of the finger DP but not of the brachial artery (N = 5) because the upper arm artery is not foldable.

[0064] In one embodiment, as shown in FIG. 13, since the electrocardiogram is a particularly robust sensing method, P PAT is shown to be more robust than P AHR during subject movement (N = 4).

[0065] In certain embodiments, as shown in FIG. 14, P PAT , P AHR , and P maxslope can be combined to further improve the accuracy of the DP calculation (N = 34). For example, the three metrics can be averaged (the "estimated DP") or used as independent variables in a linear regression to predict the DP. Alternatively, the two closest indices can be averaged.

[0066] As shown in FIG. 15, when P PAT or P AHR is used in combination with P minslope at a fixed finger pressure (e.g., P minslope ), the arm cuff SP correlates better with the finger SP than P minslope alone (N = 34). It is known that PAT at a fixed PPG sensor contact pressure shows some correlation with the SP. In certain embodiments, P PAT and PAT at P minslope can be combined in various ways including as independent variables in a linear regression (the "estimated SP" shown in FIG. 15). Since the arm cuff DP is for the finger DP, the arm cuff SP is not as good a reference as the finger SP as shown in FIG. 5.

[0067] In one embodiment, as shown in FIG. 16, three lines are fitted to the upper envelope of the plot of total (DC + AC) PPG versus finger pressure, and the intersection of the second two lines (P DCpeak ) indicates the finger SP for measuring the finger SP from the total PPG and finger pressure. The three lines are fitted to the upper envelope of the plot of total PPG versus finger pressure, and the intersection of the second two lines (P DCpeak ) indicates the finger SP. This method assumes that this reference marker occurs after the tissue is fully compressed (i.e., saturation in FIG. 8).

[0068] As shown in FIG. 17, P DCpeak correlates well with the arm cuff SP (N = 14).

[0069] As shown in Fig. 18, the total PPG vs. finger pressure plot changes with the hand raised, at heart level, and lowered. The conventional plot at heart level appears similar to the model prediction in Fig. 8. The plot shifts to the right due to the increase in finger BP via the hydrostatic effect. The tissue can be completely compressed at some pressure (e.g., 80 mmHg) regardless of the vertical position of the hand. As a result, by artificially increasing the BP via the lowered hand, the total PPG can be entirely artery - originated. The lower plot in the figure appears similar to the model prediction by only the arterial component in Fig. 8 (upper left). By way of example and not limitation, a method for estimating the SP is to perform oscillometric finger compression with the hand completely lowered, apply the method of Fig. 17 to detect the finger SP, and correct the measured value to heart level by subtracting ρgh. ρ is the known blood density, g is the gravity, and h is the arm length. In another embodiment, a method for estimating the BP is to detect the pulse pressure (PP = SP - DP) via a strong cross - correlation between the upper envelope and the lower envelope. The front camera of the phone can be used to capture an image of the face while the finger is being pressed. This image can be used to verify whether the phone is correctly positioned (i.e., the hand is completely lowered) while the finger is being pressed by comparing it with a reference image.

[0070] As shown in Fig. 19, the arm BP can be calculated from the finger BP. The maximum vibration is the case where the S - shaped blood volume - transmural pressure relationship is most linear and thus best shows the finger BP vibration shape (step 1). P minslope and P maxslope Instead, any of the above blood pressure calculations can be used to calibrate the maximum vibration (step 2). The resistive pressure drop from the arm to the finger is first countered by adding a constant (e.g., 10 mmHg) to the finger BP (step 3). Then, a transfer function based on the physical tube - loading model of arterial wave reflection is applied to derive the arm BP (step 4). Γ and T d are fixed values, e.g., 0.3 and 72 milliseconds. Alternatively, T dIs it a function of blood pressure values, or is the transfer function based on a black box model (e.g., an autoregressive exogenous input model).

[0071] BP app for devices readily available without force detection Given that all adults have a true risk of developing hypertension and that billions of people, including those in low-resource settings, have access to smartphones, it is desirable to convert a stand-alone smartphone into a BP monitor. However, many readily available devices, such as smartphones, do not have 3D touch or similarly sensitive force sensors.

[0072] The idea of converting a standard smartphone into an absolute BP sensor is based on a conventional method that uses arm movement instead of finger movement. In conventional oscillometry, the cuff compresses the artery and changes its external pressure. During this process, the device 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 oscillogram resulting from a function that relates the variable amplitude blood volume oscillation to the applied pressure. The abscissa of the oscillogram can more generally be considered as the change in the transmural pressure of the artery (in this case, the internal blood pressure - external cuff pressure). Thus, the method described above involves changing the internal pressure of the artery rather than the external pressure to change the transmural pressure. As the user of the finger-worn ring device straightens the arm and lowers the hand, the internal BP of the finger increases by an amount equal to ρgh due to the weight of the blood column in the arm ("hydrostatic effect"). h is the vertical distance between the position of the hand and the heart. In this way, the transmural pressure of the artery changes without a cuff. The device includes a PPG sensor, a force sensor, and an accelerometer. The accelerometer and the length of the arm enable the measurement of the hydrostatic BP change, ρgh. The typical blood pressure change for an arm length is about ±50 mmHg relative to the heart level. When the average blood pressure is 80 mmHg, the transmural pressure variation is about 30 - 130 mmHg. However, the oscillograms in both the positive and negative transmural pressure regimes are required to accurately calculate the BP. Therefore, the ring needs to be firmly attached enough to generate a negative transmural pressure. The force sensor in the known area measures the ring contact pressure on the finger, which is subtracted from the hydrostatic BP change. Then, the BP can be estimated from the PPG oscillation as a function of the transmural pressure change.

[0073] One problem is that the ring needs to be applied with a pressure equal near the average blood pressure, which is what is sought for the measurement. Another problem regarding bringing about the action of raising the hand to the smartphone is eliminating the need for a force sensor. However, most readily available devices such as smartphones have a PPG sensor in the form of a combination of a camera and a 3-axis accelerometer / gyroscope.

[0074] To at least solve the above problems and, as described in U.S. Provisional Application No. 63 / 135,430, the entire contents of which are incorporated by reference, the measurement can be limited to PP. PP is useful for detecting isolated systolic hypertension, which is a common form of hypertension that occurs with aging.

[0075] In one embodiment, as shown in FIG. 20, an absolute PP can be measured using readily available devices known in the industry, such as, but not limited to, smartphones, tablets, laptops, watches, and wearable devices. The process is parallel to the process used for conventional wrist cuff blood pressure measurement. Software that can be installed on any readily available device, either via an operating system or via an app interface, can guide the user through the movement phases of the body, finger, and hand for measurement. The app or software constructs an oscillogram and uses it to calculate the PP. The software can instruct the user to raise their arm and hold a device such as a phone at an elevated height so that the finger blood pressure starts on the positive side of the trans-wall pressure regime where it is reduced. In step 1, the user is guided to place their thumb on the front camera within a box that reflects the size of the user's thumb so that the device can measure the PPG in the palmar arch artery (the "artery"). In step 2, the device guides the user in the screen contact area measurement to gradually press with the thumb to lower the trans-wall pressure until the artery is occluded (as measured via PPG vibration). The contact area at this point is recorded and further used to guide the user to keep the contact area, and thus the contact pressure, constant while lowering the hand. In this phase, ρgh is calculated from the acceleration perpendicular to the screen and the length of the arm. In step 3, while maintaining the contact area, the device guides the user to lower their hand incrementally (e.g., for 3 - 5 seconds at a time, from +60 degrees to -60 degrees relative to the heart, about 30 degrees or 20 degrees) via audio / visual cues from the phone. In step 4, the PP is calculated based on the PPG and the ρgh data collected while lowering the hand, using an algorithm as described above. Since the contact pressure of the thumb is unknown, the SP and DP cannot be calculated. If the contact area deviates from a predetermined boundary too frequently, the user is asked to retry.

[0076] In one example, as shown in FIG. 21, a Samsung Galaxy S21, an exemplary smartphone, is provided, and measures PPG (R, G, and B AC+DC channels), accelerometer (X, Y, and Z axes), and finger contact area (major radius and minor radius, xy center position).

[0077] In one example, as shown in FIG. 22, exemplary measurements of PP are provided using the induction system of FIG. 20 (N = 3). The device calculates an oscillogram based on nine different heights (each held for an average of 5 seconds).

[0078] In one example, as shown in FIG. 23, in order to obtain a large-amplitude PPG oscillation, the base of the fingernail can be placed above the front camera. The optimal position can vary on the order of millimeters around the base of the nail.

[0079] In step 1, the app can include one initialization phase to measure PPG oscillations across different thumb positions, thereby identifying the best thumb placement. This initialization can then, as shown in the upper right of FIG. 20, also create a profile of the thumb and its box dimensions to guide the placement of the thumb. An example of creating the box dimensions is described in the following reference: “An iPhone Application for Blood Pressure Monitoring via the Oscillometric Finger Pressing Method” by Chandrasekhar, A., Natarajan, K., Yavarimanesh, M. et al. Sci Rep 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 content of this reference is hereby incorporated by reference in its entirety.

[0080] In step 2, the thumb and hand movement phases are used to measure BP with a standard smartphone, and guidance through those phases is key to the usability of the app. This guidance can be implemented using a hand positioned at heart level, a lowered hand, or a raised hand.

[0081] In certain embodiments, the contact area (major and minor radii, contact centroid) can be used for guidance. The parameters of the contact area measured by the capacitive sensor array under the smartphone screen are used as a surrogate for the applied contact pressure to guide the user to slowly increase the thumb pressure. The app measures the PPG oscillation amplitude in the background and determines the required pressure. For example, the PPG oscillation amplitude should be small when the hand is fully lifted (i.e., the artery is occluded) and large when the hand is at heart level. The centroid of the touch can be used to correct any non-trivial finger movement where the major or minor radius does not change. To facilitate application, a mathematical transformation can be applied to the contact area measurement to approximately linearize the non-linear contact area-contact pressure relationship.

[0082] In other embodiments, DC PPG can be used for guidance. As shown in FIG. 16, the DC PPG as a function of the transmural pressure of the artery has an S-shaped profile and flattens at negative transmural pressure. The user is guided to increase the pressure, whereby the DC PPG traces the sigmoid. The point at which this flattens can be used as the required initial thumb pressure when the hand is fully lifted.

[0083] In other embodiments, AC PPG can be used for guidance. As the contact pressure increases, the PPG oscillation gradually increases in amplitude to a maximum and then decreases. When the hand is fully lifted, the user occludes the artery by pressing until the PPG oscillation appears and is then guided to disappear.

[0084] In other embodiments, the applied acupressure can be used for guidance. In the case of a phone or device with 3D touch, the thumb force measured by the strain gauge array under the screen can be used to guide arterial occlusion when the hand is fully lifted. The app measures the PPG oscillation amplitude in the background and determines the required thumb pressure.

[0085] In step 3, the user needs to maintain the pressure of their thumb and lower / raise their hand continuously or incrementally.

[0086] In one embodiment, the contact area parameters (major radius and minor radius, contact centroid) can be used to guide the raising / lowering of the hand in step 3. A plot of contact area (by any possible combination of touch parameters) versus time is displayed. The user is then guided to maintain the contact area throughout the hand lowering / lifting procedure. An audio / color cue is given to the user to guide the user to lower / raise their hand incrementally.

[0087] In another embodiment, an accelerometer can be used for guidance. ρgh is measured using the length of the user's arm and the accelerometer, either through a single axis or through the application of principal component analysis for all axes. The latter can enable the user to hold the phone in any orientation. A plot 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 is such that ρgh changes linearly over the period. No guidance is given to maintain the thumb pressure while lowering / raising the hand. However, the variation in contact area on the back and non - physiological oscillogram measurements can be used to prompt the user to retry. Additionally, the user can be instructed to maintain the thumb contact pressure during the initialization phase. In this phase, the user maintains AC or DC PPG while the hand is at different fixed levels relative to the heart.

[0088] In other embodiments, the applied acupressure can be used for guidance. In the case of a phone with 3D Touch, the user is guided to maintain the thumb contact pressure via screen force measurement. The user is guided to lower / raise the hand via voice / color cues.

[0089] In other embodiments, DC PPG can be used for guidance. A plot of DC PPG versus time is displayed. The user is induced to lower / raise the hand while maintaining the thumb contact pressure by generating an S-shaped DC PPG over 20 - 40 seconds.

[0090] Using guidance by various means, multiple versions of the app can be considered and adjusted to the user's preference. The app can include a video demonstration teaching the user how to perform the procedure.

[0091] In one example, as shown in FIG. 24, a standard wired sensor including a ρgh sensor can be used to test the hand-raising protocol. The ρgh sensor can be a tube having a liquid interface to a pressure transducer.

[0092] In one example, as shown in FIG. 25, PP can be calculated using a 3-step procedure. First, the upper and lower envelopes of the PPG oscillation are detected. Second, the oscillogram is constructed by plotting the difference of the envelopes as a function of ρgh. Next, two half-Gaussian functions are fitted to the normalized oscillogram. Third, the width of the oscillogram is calculated as the change in ρgh between the maximum and minimum gradients of the fit. This width is used as an indicator of PP.

[0093] As shown in FIG. 26, the width of the oscillogram represents PP. Further improvement in accuracy can be obtained by converting the finger PP to the arm PP (for example, using the method of FIG. 19, the maximum vibration is scaled by the width of the oscillogram after removing its average value). The average and standard deviation of the PP error were -2.9 and 7.4 mmHg, respectively.

[0094] As shown in FIG. 26, the oscillometric hand-lifting method can operate using any type of sensor known in the art. In certain embodiments, this includes an ideal sensor such as that of FIG. 24 for developing a PP calculation algorithm. In contrast, using software such as a device app readily available for algorithm development can introduce random variability into the data, but can be used when an ideal sensor is not available.

[0095] In other embodiments, estimating DP involves measuring the maximum thumb contact area by firmly pressing the thumb. If the contact area from the first press (step 2 of FIG. 20) is relatively small compared to the maximum contact area, the DP may be on the lower side. Thus, in people under 65 years old, a high PP is not a sign of risk.

[0096] In certain embodiments, estimating the thumb contact pressure can include capturing the thumb contact pressure using available software. This can be software provided with the University of Michigan ForcePhone app, for example, as described in the following publication: “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 can include using a deep touch technology such as Google Deep Touch. This is described in the following publication: “Sensing Force-Based Gestures on the Pixel 4” (available at https: / / ai.googleblog.com / 2020 / 06 / sensing-force-based-gestures-on-pixel-4.html).

[0097] Example 2: Model for improving oscillometric BP calculation The disclosed subject matter further provides reliable BP calculations that can be used for clinical BP ranges. For example, the disclosed subject matter provides a model for improving oscillometric BP calculations.

[0098] The disclosed model can find a BP signature in finger oscillometric measurements. For example, the disclosed model can be the S-shaped blood volume-pressure relationship of an artery. The input to the model can be the BP waveform at different external pressures, and the output can be the changing blood volume waveform.

[0099] Figure 27 shows the model-predicted blood volume waveform in response to an external pressure gradient by finger pressing. The high-pass filtering and scaling of this waveform predict the measured PPG oscillation waveform. Comparing the envelopes of the two waveforms, it is shown that the oscillogram (which is also a function of oscillation height versus external pressure) is proportional to the difference in the y-axis inverse sigmoid relationship evaluated at SP and DP. The derivative of the S-shaped relationship is the arterial compliance curve. This curve can be well represented by a three-parameter exponential-linear function that completes the model.

[0100] Figure 28 shows the PPG oscillation during pressure increase. In certain embodiments, zero oscillation can include noise floor or invariant oscillation. The cause of the noise or unforeseen physiological characteristics can include proximal PPG oscillation, physiological response to contraction, and tissue inhibition of arterial folding.

[0101] When the external pressure slightly exceeds the blood pressure, the finger artery may be completely occluded or folded. As shown in Figure 29, this characteristic indicates that the b model parameter, which represents the left width of the arterial compliance curve, is smaller for the finger artery than for the conventional brachial artery. Additional data suggests that the c parameter, which represents the right width 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 gradients of the oscillogram better indicates the finger DP and SP than the brachial DP and SP. However, discrimination may amplify noise in some cases.

[0102] This model also shows that the oscillation amplitude decreases with an increase in external pressure. Since the b parameter value is small, the decrease in width begins when the external pressure exceeds the DP. Therefore, the model specifically predicts that the non-conventional "width" oscillogram indicates the DP through the "bend" of the curve. A model with a smaller b further shows that it can completely eliminate the oscillation when the external pressure begins to exceed the SP. However, it turns out that detecting arterial occlusion is difficult due to noise and other reasons as described above.

[0103] As shown in Figure 30, the disclosed model is smaller compared to the tissue compression by finger pressure with tissue compression due to arterial dilation applied, and based on the Beer-Lambert law, assuming that the tissue is completely compressed between DP and SP, it can be further extended to AC+DC PPG. Since the DC component of PPG can robustly detect arterial occlusion and thus assist in SP calculation, the model can be extended to AC+DC PPG and prediction. When the finger is pressed and the external pressure slowly rises, the tissue is compressed to a certain pressure until it is completely compressed. Therefore, PPG decreases and saturates due to the tissue. Figure 30 shows the simulated AC+DC PPG due to the artery from the original model. By summing the two, the predicted AC+DC PPG can be obtained. The extended model can predict that the AC+DC PPG for finger pressure shows the SP through the flexion in the curve (i.e., the sharp change in the gradient of the function). The model prediction can provide accuracy and similarity to the actual measurement by using the average PPG beat.

[0104] In one embodiment, the disclosed subject matter provides a BP calculation algorithm based on the disclosed model prediction. Figure 31 shows an example of the steps for a model-based DP and SP calculation algorithm. During the first step, the amplitude can be quantified using the area-to-height ratio and through the pulse arrival time obtained from the ECG, and the AC+DC PPG can be quantified through the average over each ECG RR interval (e.g., the mean PPG beat). During the second step, these three features and the vibration height are plotted against the finger pressure. The model prediction signature can be detected to calculate the three DP features and the two SP features.

[0105] Figure 32 shows an image of an exemplary bench-top system for evaluating the disclosed device and model. The bench-top system can be used to evaluate the disclosed algorithm against a patient's wrist cuff device. The user can also make an intervention to change their blood pressure.

[0106] Figure 33 is a graph showing the accuracy of the disclosed models and algorithms. The average of the three DP features and the average of the two SP features resulted in a BP error of approximately 8.5 mmHg and a correlation of approximately 0.9 for the automatic cuff device. The wide oscillation variation helped with the DP calculation, but the DC PPG did not improve the SP calculation more than the PPG oscillation. However, in contrast to the PPG oscillation, the DC PPG typically shows a clear reference marker around the SP and can ultimately be proven beneficial.

[0107] Figure 34 shows the correlation between the systolic and diastolic references in DC PPG. A total of 35 measurements were performed at various arm positions (i.e., arm raised, heart level, and arm lowered) across 18 subjects. Of the 35 measurements, 7 were performed at the upper level, 17 at the heart level, and 11 at the lower level. Figure 34 shows the references for the systolic and diastolic oscillometric upper arm cuffs.

[0108] Figure 35 shows the DC PPG results using leave-one-out (LOO) regression. A total of 35 measurements were performed at various arm positions (i.e., arm raised, heart level, and arm lowered) across 18 subjects. Of the 35 measurements, 7 were performed at the upper level, 17 at the heart level, and 11 at the lower level. Figure 36 shows the correlation between the plethysmogram bend measurement and the minimum gradient prediction. Figure 37 shows an exemplary method for the plethysmogram bend measurement. As shown in Figure 37, the method can include collecting data, averaging the PPG from the RR intervals, and using a two-line fit to find the inflection point.

[0109] As shown in FIGS. 33 to 36, the regression minimum gradient prediction of SP (correlation coefficient r, standard deviation of error σe) was improved by the disclosed measurement techniques (e.g., from the AC case (r: 0.69, σe: 13.1) to the DC case (r: 0.91, σe: 8.8)). This may be due to the improved measurement protocol (i.e., cuff placement, required press linearity, and defined orientation of the measurement device), height offset accuracy (i.e., height probe and robust definition of the heart level), or enhanced analysis (i.e., removed pulses recorded during non-increasing press, required data consistency for each subject).

[0110] The plethysmogram flexion and minimum gradient are obtained from different PPG information (i.e., shape and amplitude), predict SP equally on average, and may have little margin for improvement based on the arm cuff standard.

[0111] The plethysmogram (AC and DC PPG vs. finger pressure) can indicate SP and shows a reproducible distinct reference marker. Thus, the analysis of high-noise data can distinguish DC PPG as a more noise-robust predictor of SP.

[0112] The disclosed subject matter is described herein with respect to specific preferred embodiments, but those skilled in the art will recognize that various modifications and improvements can be made to the disclosed subject matter without departing from its scope. Additional features known in the art, such as those disclosed in WO2013003787A2, US Provisional Application 63 / 135430, and US Provisional Application 63 / 388,021, can be incorporated as well, and the contents of each of these are hereby incorporated by reference in their entirety. Further, the individual features of one embodiment of the disclosed subject matter, which may be discussed herein or shown in the drawings of one embodiment and not shown in other embodiments, are clearly combinable with one or more features of another embodiment, or features from multiple embodiments.

[0113] Illustrated and in addition to the various embodiments claimed, the disclosed subject matter also contemplates other embodiments having any other possible combination of the features disclosed and claimed herein. Accordingly, the specific features presented herein can be combined with one another within the scope of the disclosed subject matter so that the disclosed subject matter includes any suitable combination of the features disclosed herein. Accordingly, the foregoing description of specific embodiments of the disclosed subject matter has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosed subject matter to the embodiments disclosed. It will be apparent to those skilled in the art that various modifications and variations can be made in the apparatus, method, and system of the disclosed subject matter without departing from the spirit or scope of the disclosed subject matter. Accordingly, the disclosed subject matter is intended to include modifications and variations that come within the scope of the appended claims and their equivalents.

Claims

1. A method for determining a user's diastolic blood pressure using a device having a photoplethysmography (PPG) force sensor unit, comprising: providing visual or auditory instructions to the user using the device, the instructions instructing the user to position a finger on the PPG force sensor unit and press the finger with various finger pressures on the PPG force sensor unit; measuring the PPG vibration and finger pressure of the finger by the PPG force sensor unit; calculating the width of each of the PPG vibrations as a function of the finger pressure; calculating the diastolic blood pressure using a function of finger pressure with respect to the PPG vibration width; outputting the diastolic blood pressure on a graphical user interface of the device or transmitting the diastolic blood pressure to a database repository; A method having the above steps.

2. The method according to claim 1, further comprising detecting a flexion of the PPG vibration width with respect to the function.

3. The method according to claim 2, wherein the flexion of the PPG vibration width with respect to the function is detected by fitting at least two curves to the function and using the intersection of the curves.

4. The method according to claim 1, wherein the width of each of the PPG vibrations is calculated as the ratio of the area to the height of the vibration.

5. The method further comprises: measuring an electrocardiogram (ECG) by additional electrodes incorporated in the device; calculating the width of each of the PPG vibrations as a pulse arrival time for each of the vibrations detected as a time delay between the R wave of the ECG and the PPG foot; The method according to claim 1, having the above steps.

6. The method according to claim 5, further comprising determining the systolic blood pressure using the value of the pulse arrival time at the flexion of the pulse arrival time with respect to the function.

7. The method according to claim 1, wherein the diastolic blood pressure is calculated using additional features extracted from the PPG vibration and finger pressure.

8. The method according to claim 7, wherein the additional features include the finger pressure at the maximum gradient of the finger pressure function with respect to the PPG vibration amplitude.

9. A method for determining a user's systolic blood pressure using a device having a photoplethysmography (PPG) force sensor unit and an electrocardiogram (ECG) electrode, comprising: Providing a visual or auditory instruction to the user using the device, the instruction instructing the user to position a finger on the PPG force sensor unit and press the finger with various finger pressures on the PPG force sensor unit; Measuring a total PPG including a DC component, PPG oscillation, and applied finger pressure using the PPG force sensor unit; Measuring an electrocardiogram by the electrodes; Calculating an average of each PPG beat over an interval from R wave to R wave of the ECG as a function of the applied finger pressure; Calculating a systolic blood pressure using the PPG average for the function; A method having the above.

10. The method according to claim 9, further comprising detecting a flexion of the PPG average with respect to the function.

11. The method according to claim 10, wherein the flexion 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, wherein the systolic blood pressure is calculated using additional features extracted from the total PPG, finger pressure, and ECG.

13. The method according to claim 12, wherein the additional feature includes a finger pressure at a minimum gradient of the finger pressure function with respect to the PPG oscillation amplitude.

14. The method according to claim 12, wherein the additional feature includes a value of the pulse arrival time at the flexion of the pulse arrival time with respect to the finger pressure function.

15. A method for determining a user's pulse pressure using a device, comprising: Providing a visual or voice command to the user using the device, the command instructing the user to position a finger on the camera and screen of the device and measure total photoplethysmography (PPG) from the finger via the camera of the device and measure finger contact parameters via the touch screen sensor of the screen; Providing a visual or auditory instruction to the user using the device to apply finger pressure to the camera and the screen based on the measured values; Providing a visual or auditory command to the user using the device to lower or raise the finger of the hand with respect to the user's heart level while maintaining the finger contact parameter; Measuring the hydrostatic blood pressure change (ρgh) of the finger using the accelerometer of the device and the length of the arm; Calculating the pulse pressure from the PPG and ρgh measurement values; A method having the above steps.

16. The method according to claim 15, further comprising providing an initialization command to the device once to determine an optimal placement guide for the finger on the camera and the screen.

17. The method according to claim 15, wherein the finger contact parameter includes the touch center of gravity.

18. The method according to claim 15, wherein the PPG vibration is used as a guide for determining the amount of finger pressure on the screen and the camera to be maintained during hand raising or lowering.

19. The method according to claim 15, wherein the PPG vibration and the finger contact parameter are used as guides for determining the amount of finger pressure on the screen and the camera to be maintained during hand raising or lowering.

20. The method according to claim 15, wherein the finger contact parameter is used as a guide for maintaining the amount of finger pressure on the screen and the camera during hand raising or lowering.

21. The method according to claim 15, wherein a timer is used as an additional guide for indicating the time taken for hand raising or lowering.

22. The method according to claim 15, wherein the pulse pressure is calculated using ρgh at at least one of the minimum gradient and the maximum gradient of the PPG vibration amplitude with respect to the ρgh function, or using the PPG vibration amplitude as a function of ρgh.

23. Measuring the diastolic blood pressure by measuring the maximum finger contact parameter through strong finger pressure by the user, Comparing the finger contact parameter with the maximum finger contact parameter to determine whether the diastolic blood pressure is low, The method according to claim 15, further comprising the above steps.

24. A method for determining blood pressure using a device having a photoplethysmography (PPG) force sensor unit and an ECG electrode, Receiving a measurement value from the touch of a finger on the PPG force sensor unit; Receiving an ECG from the electrode; Calculating the diastolic blood pressure by using the width of each alternating current (AC) blood volume vibration versus finger pressure function by a processor of the device; a step of calculating systolic blood pressure by using, by the processor, an average of each DC blood volume pulsation over an RR interval of the ECG-to-arterial pressure function; a step of outputting the blood pressure on a graphical user interface of the device or transmitting the blood pressure to a database repository; A method having the above. [

25. ] A system for determining a subject's blood pressure, comprising: a sensor configured to measure arterial pressure, finger photoplethysmogram (PPG) vibration, finger PPG DC component, and electrocardiogram (ECG); a display configured to provide visual or auditory instructions for instructing the subject to place a finger at a predetermined position; a processor, a step of calculating diastolic blood pressure and systolic blood pressure, wherein the diastolic blood pressure is calculated using a PPG vibration amplitude-to-arterial pressure function and the systolic blood pressure is calculated using a PPG average; a step of displaying the calculated diastolic blood pressure and systolic blood pressure on the display; a processor configured to perform the above; A system comprising the above.

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