Wearable devices with plethysmographic sensors

Abstract

Central blood pressure parameters are monitored using a smartwatch or smartband. The PPG sensor on the smartwatch or smartband is suitable for sensing blood perfusion in the finger (or lower wrist / radial artery) of the person wearing the smartwatch or smartband. The PPG signal captures cardiovascular characteristics that can be detected after appropriate filtering and processing. Signal processing using a transfer function method generates an uncalibrated central pressure waveform that can be used to calculate various cardiovascular parameters or parameter indices displayed on the smartwatch or smartband. Digital signal processing can be implemented in the smartwatch or smartband, smartphone, laptop, or cloud.

Description

Background Art

[0001] Due to its proximity to the heart, the aortic blood pressure waveform has waveform characteristics that reflect the state of the cardiovascular system. These characteristics are clinically important indicators of arterial and cardiac load, and are also early independent predictors of cardiovascular events and disease. However, in the past, accurately recording a high-fidelity aortic blood pressure waveform required invasive treatment to insert a catheter with a pressure sensor into the artery. Therefore, non-invasive methods were created to estimate the aortic pressure waveform and its cardiovascular-related characteristics from peripheral (e.g., radial artery, brachial artery) arterial pressure pulse recordings.

[0002] One of the most commonly used and effective methods is to use a transfer function to convert a high-fidelity, non-invasively recorded peripheral pressure waveform into a central aortic pressure waveform with cardiovascular-related characteristics (Michael O'Rourke, "Method for determining the pressure pulse and related parameters in the ascending aorta from the contour of the pressure pulse in the peripheral artery," U.S. Patent No. 5,265,011, November 23, 1993). The transfer function is expressed as the harmonic ratio between the input peripheral pressure waveform and the output central aortic pressure waveform. Instead of using a pressure-to-pressure transfer function, another method applies a different transfer function to convert the brachial artery volume displacement waveform acquired by the cuff into a central pressure waveform with characteristics (Ahmad Qasem, "Brachial Cuff," U.S. Patent No. 9,314,170, April 19, 2016). The brachial cuff must be inflated to a set pressure value to record a consistent brachial artery volume displacement signal.

[0003] The central pressure waveform and its characteristics estimated by these methods have been validated and have been shown to provide clinically valuable predictors of arterial stiffness, cardiac load stress, arterial age, cardiac exercise capacity, and cardiovascular risk. Monitoring, managing, and controlling these measured characteristics is important even in the absence of symptoms. Providing data or information about these characteristics to the general population would be useful or beneficial for monitoring cardiac health. However, these clinically meaningful characteristics currently require measurement in a clinical setting using medical devices that require meticulous tonometry recording of the radial artery pulse signal or recording of the brachial artery volume displacement pulse by inflating a cuff to a set pressure.

[0004] The present invention addresses the accessibility of these features to the general population by converting signals from common wearable PPG (plethysmography) sensors on mobile smartphones, fitness bands, or smartwatches into a central aortic pressure waveform with cardiovascular-related features similar to the output of the method patented by O'Rourke and Qasem. This new method applies a transfer function to convert the PPG signal from the finger into a central pressure waveform signal. Features are then calculated from the central pressure waveform and displayed as cardiac health indicators to guide users in frequently monitoring their health.

[0005] The purpose of this invention is to process and convert ordinary wearable smart watch or mobile PPG sensor signals into central aortic pressure pulses with cardiovascular related characteristics in order to display these health indicators and thus guide ordinary users to maintain and manage their heart health. Summary of the Invention

[0006] The present invention relates to a method for monitoring central blood pressure parameters using a PPG sensor, which is ideally on a smartwatch or smartband, but aspects of the invention can also be used in embodiments using a laptop or mouse. The smartwatch or smartband is configured with a microcontroller unit (MCU) and a PPG sensor, which is suitable for sensing blood perfusion in a finger (e.g., the index finger) of a person wearing the smartwatch or smartband. It has been found that sensing blood perfusion in the finger produces a signal in which, after appropriate filtering and processing, cardiovascular characteristics can be detected. On the other hand, cardiovascular characteristics cannot be detected, at least not reliably, by placing the back of the wrist against the PPG sensor. Figure 8 An example of an inverted finger PPG pulse and an inverted wrist PPG pulse is shown. The inverted finger PPG pulse has a feature as shown by the arrow, while the inverted wrist PPG pulse has no feature.

[0007] When a user places their finger on the exposed optical portion of the PPG sensor, the PPG sensor outputs a raw analog PPG signal. In some embodiments, the PPG sensor is embedded in the housing of a smartwatch or smart band, with the optical portion of the PPG sensor exposed through the sidewalls and / or bezels of the smartwatch or smart band. The optical portion of the PPG sensor can be flush with the surface of the housing, but ideally, the optical portion is recessed or raised relative to the housing surface. The raised or recessed optical portion provides tactile feedback to the user, making it easier for them to ensure their finger fully covers the optical portion of the PPG sensor. In other embodiments, the PPG sensor can be attached to a wristband connected to the smartwatch or smart band, with the optical portion of the PPG sensor exposed externally from the wristband. In other embodiments, the PPG sensor can be located on the watch's surface or on the smart band's electronic module. The user places their finger on the PPG sensor for a period exceeding approximately 5 seconds to capture multiple cycles. The PPG sensor outputs the raw analog PPG signal to the MCU on the smartwatch or smart band. The MCU or other electronic circuitry on the smartwatch or smart band converts the raw analog PPG signal into a digital signal. While the present invention can be implemented using the cloud, ideally, the digital signal is processed on a smartwatch or smartband using its MCU. If the cloud is used, the digital signal is transmitted from the smartwatch or smartband to the cloud for further computation. The MCU on the smartwatch or smartband can process the data before transmitting it to the cloud. Additionally, some digital processing can be performed on a smartphone associated with the smartwatch or smartband, or a combination of the smartphone and the cloud.

[0008] The digital signal is processed through a low-pass filter and a high-pass filter. The purpose of the high-pass filter is to remove drift from the signal. The purpose of the low-pass filter is to remove noise, but it is important that the low-pass filter does not filter out relevant physiological data. After processing through the low-pass and high-pass filters, the digital signal must be inverted. The filtered finger PPG signal is inversely proportional to the blood volume in the finger. It is important to find the portion of the waveform corresponding to the bottom of the central aortic pressure waveform. The reason for inversion is that the filtered finger PPG has a negative slope at the beginning of the pulse, while the pressure signal has a positive slope (rising branch). By inverting the PPG signal, the finger PPG and pressure pulses will have similar characteristics, which is important when estimating the transfer function. If the input and output signals have common, aligned characteristics, the transfer function tends to be more stable. The next step is to detect individual pulses in the filtered and inverted digital PPG signal. Several individual pulses are then averaged to produce an averaged, uncalibrated PPG pulse.

[0009] A transfer function or a combination of transfer functions is applied to the averaged uncalibrated PPG pulses to generate an uncalibrated aortic pressure waveform that retains cardiovascular waveform features. The retained cardiovascular waveform features of the uncalibrated aortic pressure waveform include a first shoulder, a second shoulder, and a notch, see e.g. Figure 7 One or more generalized transfer functions represent harmonic ratios of amplitude and phase to convert the averaged uncalibrated PPG pulses into an uncalibrated aortic pressure waveform that preserves cardiovascular-related characteristics. In one embodiment, there are two transfer functions: one that converts the averaged PPG pulses into an uncalibrated radial pressure pulse, and a second transfer function that converts the uncalibrated radial pressure pulses into an uncalibrated central aortic pulse. In another embodiment, one transfer function converts the averaged PPG pulses into an uncalibrated central aortic pulse.

[0010] The next step is to detect waveform features in the uncalibrated aortic pressure waveform and calculate parameters related to the uncalibrated aortic pressure waveform. Useful parameters may include, for example, the ratio of the area under the systolic curve divided by the area under the diastolic curve, or the ratio of the systolic pressure at the first and second shoulders relative to the total height, or the ratio of the peripheral pressure waveform height to the central pressure waveform height, or other parameters or calculated values, such as a total score. One or more of the calculated parameters, or an indication of the calculated parameters, are displayed on the smartwatch or smartband for easy viewing by the user.

[0011] Depending on the placement of the PPG sensor, blood perfusion can also be sensed by placing the palmar side of the wrist against the sensor. More specifically, using a PPG sensor to measure perfusion in the radial artery from the lower wrist can, if measured correctly, produce a waveform that exhibits cardiovascular characteristics. For example, a wristband with a PPG sensor can be used, placed against the lower wrist or palmar wrist at an appropriate location. It has been found that sensing blood perfusion by placing a PPG sensor against the lower wrist to measure blood perfusion through the radial artery produces a signal that, after appropriate filtering and processing, can detect cardiovascular characteristics. Of course, the transfer function used to convert the PPG signal from the lower wrist or palmar wrist must be determined separately from the transfer function used to convert the PPG signal from the finger.

[0012] Additional embodiments of the present invention include placing a PPG sensor on a laptop or mouse. In a laptop embodiment, the PPG sensor can be located on the keyboard or in a location separate from the keyboard and trackpad. The user can place their finger (index finger) on the PPG sensor to take a measurement. In a mouse embodiment, the PPG sensor can be located on one of the mouse buttons, where a finger (index finger) naturally rests. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a flow chart showing the steps involved in sensing blood perfusion in a finger using a PPG sensor, and processing the signal using, in part, a transfer function method to produce an uncalibrated central pressure pulse, detecting cardiovascular characteristics from the uncalibrated central pressure pulse, and displaying the parameters, for example, on a smartwatch.

[0014] Figure 2 is a schematic diagram of one embodiment of a smartwatch having an embedded PPG sensor with optical elements exposed through the bezel or crown of the watch.

[0015] Figure 3 is a schematic diagram of another embodiment of a smartwatch having a PPG sensor mounted on a watch band with optical elements exposed upward from the watch band.

[0016] Figure 4 is a schematic diagram of another embodiment of a smartwatch having an embedded PPG sensor with optical elements exposed through a side wall of the watch case opposite the bezel. Figure 4A A PPG sensor with a recessed optical portion is shown. Figure 4B A PPG sensor with a raised optical portion is shown.

[0017] Figure 5 is a flow chart showing the steps involved in sensing a PPG signal and processing the signal to produce an averaged PPG pulse, which in turn is converted to a central pressure pulse using a transfer function method.

[0018] Figure 6 is a schematic diagram showing how to detect the start of a rising branch in an inverted PPG signal.

[0019] Figure 7 is a schematic diagram showing waveform features detected in an uncalibrated central aortic pressure waveform.

[0020] Figure 8 is a graph comparing the filtered and inverted PPG signal from the finger with the filtered and inverted signal from the back of the wrist.

[0021] Figure 9 A display for a smartwatch is provided wherein the software displays an indication of waveform parameters calculated from an uncalibrated central pressure pulse and / or an uncalibrated peripheral pressure pulse.

[0022] Figure 10 is a schematic diagram of an embodiment of a smart bracelet having an embedded PPG sensor with optical elements exposed along the side of the housing of the electronic module.

[0023] Figure 11 is shown with Schematic diagram of the setup used to test the accuracy of the present invention compared to the accuracy of the system.

[0024] Figure 12A and 12B The present invention and Calculation and comparison of enhancement indices for data collected by the system.

[0025] Figure 13A and 13B The present invention and Calculation and comparison of pressure amplification of data collected by the system.

[0026] Figure 14A and 14B The present invention and Calculation and comparison of exercise capacity of data collected by the system.

[0027] Figure 15A The central aortic waveform of a healthy person generated using the present invention is shown. Comparison of central aortic waveforms generated by the systems. Figure 15B The central aortic waveform of an unhealthy person generated using the present invention is shown in FIG. Comparison of central aortic waveforms generated by the systems. DETAILED DESCRIPTION

[0028] Figure 1 The general steps for implementing the present invention are shown. In general, the first step, Box 1, is to sense the raw signal with a PPG sensor that is designed to measure the PPG signal from a finger or wrist. Preferably, the PPG sensor is configured to measure the PPG signal from the user's index finger. The PPG sensor is ideally located on a smartwatch or smartband, but can also be located on a laptop, a mouse, or connected to an electronic device such as a smart phone. The second step, Box 2, is to process the raw signal to generate a signal such as Figure 1 The third step, Box 3, is to apply one or more transfer functions to generate an aortic pressure waveform, which is Figure 1 The central pressure pulse is shown in FIG. The fourth step, Block 4, is detecting waveform features in the central aortic pressure waveform and calculating one or more clinically meaningful parameters, including a summary score. The fifth step, Block 5, is displaying the calculated parameters and summary score, for example, on a display of a smartwatch or smart band, or on another display.

[0029] The PPG sensor unit consists of one or more LED light sources (e.g., green, red, or infrared), a photodetector, and the necessary circuitry to drive the LEDs and photodetector. The PPG sensor unit has two sections: optical and electrical. The optical section is made of a transparent material that allows light to pass through the PPG sensor unit to the person, and vice versa. The optical section of the PPG sensor unit can be extended using a light pipe.

[0030] The PPG sensor unit can be embedded in wearable devices such as smart watches or smart bracelets. The PPG signal can be sent to an MCU (microcontroller unit) or the cloud or smartphone for further processing and calculation. The PPG sensor component can be designed to operate in reflection or transmission mode.

[0031] Figure 2 One embodiment of a smartwatch 14 implementing the present invention is shown. Figure 2 In FIG, a PPG sensor unit 10 is embedded in a watch 14 with its optical portion 12 facing the crown or bezel 16. The user places a finger (eg, index finger) on the crown 16 to record raw finger PPG pulses.

[0032] Figure 3 Another embodiment of a smartwatch 114 implementing the present invention is shown. The PPG sensor unit 110 is on a wristband 118, with the optical portion 112 facing upward and exposed near the body of the smartwatch 114. The user places a finger (e.g., index finger) on the optical portion 112 to record raw finger PPG pulses.

[0033] Figure 4 Another embodiment of a smartwatch 214 implementing the present invention is shown. A PPG sensor unit 210 is embedded in the watch housing 214, with its optical portion 212 facing away from the bezel 216 of the watch 214. The user places a finger (e.g., index finger) on the optical portion 212 to record raw finger PPG pulses.

[0034] Figure 4A A PPG sensor 210A is shown having a recessed optical portion 212A. Figure 4B A PPG sensor 210B is shown with a raised optical portion 212B. The recessed portion 212A and raised portion 212B provide tactile feedback to the user for positioning their finger over the optical portion of the PPG sensor. The tactile feedback helps the user fully cover the exposed optical portion of the PPG sensor 212, which maximizes the amount of reflected light from the measurement finger and improves the reliability and accuracy of the system.

[0035] Figure 5The digital processing steps for processing the raw PPG signal (6) are shown. The raw PPG recording signal (6) is an analog signal that may have a duration of 5 seconds or more and is transmitted from the PPG sensor to the smartwatch or smartband for digital signal processing preferably on an MCU on the smartwatch or smartband or on an associated smartphone, and some processing may also be performed in the cloud. Figure 5 The signal processing steps shown include: converting the analog signal to a digital signal through an A / D converter (7), filtering the digital signal through high-pass and low-pass filters (8), inverting the filtered digital PPG signal (10), detecting pulses in the inverted PPG signal (12), and averaging the PPG pulses (13). All of these steps and calculations can be implemented in the MCU or in the cloud.

[0036] Still refer to Figure 5 , an A / D converter (7) digitizes the raw analog PPG signal (6) and samples the signal at a sampling frequency (fs) of not less than 100 Hz. Then, a high-pass filter is applied to the digital signal to reduce the signal baseline drift, and a low-pass filter is applied to remove high-frequency artifact noise, see step (8). For the high-pass filter, the cutoff frequency can be between 0.003-0.05 Hz and the pass frequency can be between 0.95-1.05 Hz. An example of a high-pass filter is a Butterworth high-pass filter, which has a -50 dB cutoff frequency of 0.01 Hz and a -3 dB pass frequency of 1 Hz. The -3 dB frequency of the low-pass filter is between 30 and 50 Hz. Both filters should have low phase delay. Both filters are applied to the digital signal to produce the filtered PPG signal (9).

[0037] Then, referring to step (10), the filtered PPG signal is inverted by implementing the following formula.

[0038] InvPPGSig=-PPGSig Formula 1

[0039] Where PPGSig is the filtered PPG signal (9) and InvPPGSig is the inverted PPG signal (11). Because the central pressure pulse begins with an ascending branch (high positive slope line) indicating cardiac ejection, while the recorded filtered finger PPG pulse begins with a negative slope line, the filtered PPG signal needs to be inverted. Because the goal is to generate a central pressure pulse, it is important to have similar start-up characteristics on both pulses. Therefore, the finger PPG pulse is inverted to have a similar ascending branch characteristic to the central pressure pulse at the beginning of the pulse.

[0040] The next step (12) is to detect the start and end of each pulse in the inverted PPG signal (11). Figure 6 The start of the pulse is determined by calculating the first derivative and identifying the peak of the pulse rising branch corresponding to the start of the pulse. After the pulse (12) is detected, a plurality of signal pulses are generated, for example, 10 pulses are generated. Figure 5 In step (14) of , these pulses are averaged to produce an averaged PPG pulse.

[0041] See also Figure 1 In step 3 of the present invention, the averaged PPG pulses (14) are input into one or more transfer functions to produce an averaged central pressure waveform that preserves cardiovascular characteristics. The transfer function represents the harmonic ratio of amplitude and phase between the input and output signals. The formula of the transfer function can be expressed in frequency domain or time domain format. The PPG waveform to aortic pressure transfer function is predetermined from simultaneous recordings of the PPG waveform and an invasive (e.g., catheter) or equivalent non-invasive (e.g., SphygmoCor) aortic pressure waveform. The estimation involves frequency harmonic analysis or estimating the coefficients of the impulse response. The transfer function can be expressed and written in the frequency domain format below.

[0042] a) Amplitude

[0043]

[0044] Among them, |H a→b (f)|is Sig b To Sig a The transfer function frequency-amplitude ratio,

[0045] Sig a is the input signal in the frequency domain,

[0046] Sig b is the output signal in the frequency domain, and

[0047] f is the frequency in Hz, ranging from 0 to fs / 2.

[0048] b) Phase

[0049] Phase(H a→b (f))=Phase(Sig b (f))-Phase(Sig a (f)) Formula 3

[0050] Among them, the phase (H a→b (f)) is H at frequency f a→b (f) Angle.

[0051] Phase (Sig a(f)) is Sig at frequency f a angle, and

[0052] Phase (Sig b (f)) is Sig at frequency f a angle.

[0053] In the time domain, the transfer function can be expressed as an impulse response or a set of coefficients, which, when converted to the frequency domain, is equivalent to H a→b (f).

[0054] Imp a→b (t) = IFFT[H a→b (f)] Equation 4

[0055] Where Imp(t) is the impulse response in the time domain,

[0056] IFFT is the Inverse Fast Fourier Transform, and

[0057] t is the time from 0 to the pulse length time in milliseconds.

[0058] Assume that Sig b is the central aortic pressure waveform in the frequency domain, Sig a is the average PPG signal in the frequency domain (14).

[0059] AoPW(t)=FFT(Sig b (f)) Formula 5

[0060] PPG(t)=FFT(Sig a (f)) Formula 6

[0061] Where AoPW(t) is the central aortic pressure waveform in the time domain,

[0062] PPG(t) is the averaged PPG pulse (14), and

[0063] FFT is Fast Fourier Transform.

[0064] The aortic pressure waveform can be calculated from the PPG pulses (14) using a transfer function in the frequency domain or the time domain. First, in the frequency domain, the frequency of the aortic pressure can be calculated as

[0065] Sig b (f) = H a→b (f)×Sig a (f) Formula 7

[0066] Among them, the Inverse Fast Fourier Transform (IFFT) can be used to transform Sig b (f) Aortic pressure waveform AoPW(t) converted into time domain

[0067] AoPW(t)=IFFT[Sig b (f)] Formula 8

[0068] To calculate AoPW(t) in the time domain, use the following formula:

[0069] AoPW(t)=Imp a→b (t)*PPG(t) Formula 8 Wherein, * is the convolution operation.

[0070] Alternatively, an intermediate transfer function that converts the PPG waveform into a radial pressure waveform can be predetermined using a tensiometer from simultaneous recordings of the PPG waveform and the radial pressure waveform. Similar techniques as described above can be used to determine the intermediate transfer function. Data representing the radial pressure waveform can then be input into the transfer function, which converts the radial pressure waveform into a central aortic pressure waveform, as is known in the art.

[0071] Figure 7 A central aortic pressure waveform is shown having characteristics resulting from the application of one or more transfer functions. Figure 1 As shown in Box 4, the software is configured to detect Figure 7 The software uses the first derivative method to detect the notch after the peak. The notch will be the first zero crossing of the first derivative after the aortic pulse peak. The notch represents the end of the systolic phase (heart ejection) and the beginning of the diastolic phase (heart filling). Because the second peak is the result of reflected pressure that increases the heart load, detecting the first and second systolic peaks provides an estimate of the additional load on the heart. Figure 7 As shown, the software can also be configured to calculate the area under the contraction curve (AUC1), which represents the work of the heart during pumping and also reflects the body's demand for oxygenated blood. Figure 7 As shown, the software can be configured to calculate the area under the diastolic curve (AUC2), which represents the work of the heart during ventricular filling and also reflects the heart's oxygenated blood supply. The ratio of AUC2 to AUC1, which is the ratio of oxygenated blood supply to body demand, has been shown to be related to physical fitness and endurance. Figure 7 These parameters are displayed, for example, on a display screen of a smart watch or smart bracelet as health indicators to help users monitor their health status.

[0072] Figure 9 A display for a smartwatch (or other display, such as a display on a smart bracelet) is shown, wherein software displays an indication of a cardiac parameter calculated from an uncalibrated mean central pressure pulse. The label "cardiac stress" is calculated based on the difference between the first and second systolic peaks relative to the pulse height. Figure 9The arrows in the graph point to the green area, indicating that the calculated parameters are good. By calculating the amplification ratio, which is the ratio of peripheral pulse height to central pulse height, and comparing the amplification ratio with published studies of healthy individuals, the displayed "heart age" is correlated with healthy cardiovascular age. The label "exercise capacity" is the ratio of the diastolic area under the curve to the systolic area under the curve. The total score (ARTY) is based on a combination of detected cardiac features.

[0073] Figure 10 3 is a schematic diagram of an embodiment of a smart wristband 314 having an embedded PPG sensor 310 with optical elements 312 exposed along the side of the housing of the electronic module. Although not shown, the smart wristband 314 may have visual indicators such as LEDs, but does not necessarily have a UI (user interface) screen. If it has a display screen, it may display something like Figure 9 If not, the visual indicator needs to be adjusted or the information / data can be transferred to another device for display and possible further processing.

[0074] A method for generating a central aortic pressure pulse based on non-invasive peripheral blood pressure waveform measurement The accuracy of the present invention was systematically tested. The TRANSPORT® system is a commercial embodiment of the system described in the above-referenced US Patent No. 5,265,011 to O'Rourke, is FDA cleared, and is considered the gold standard for non-invasive measurement of central aortic pressure waveforms. Figure 11 is shown with Schematic diagram of the setup used to test the accuracy of the present invention compared to the system. Several recordings (3 to 9) of 10 seconds duration were obtained from 13 subjects (4 females, 9 males) aged 20-65 years. The subjects provided a wide range of central aortic pressure waveforms (young, old, healthy, unhealthy). Reference Figure 11 According to known technology, the tensiometer 402 is used to measure the radial pressure pulse of the subject 400. At the same time, the PPG sensor 404 is used to measure the index finger of the subject. The signal from the tensiometer 402 is transmitted to System 406 is connected to the pulse system 406, and the central pressure waveform data output from the pulse system 406 is recorded in the data acquisition system 408. At the same time, the signal from the PPG sensor 404 is transmitted to the system 410 constructed according to the present invention, and the central pressure waveform data output from the system 410 is also recorded in the data acquisition system 408.

[0075] Figure 12A Shown are the central aortic pressure waveform and the parameters identified and used to calculate the augmentation index (AIx). Figure 12BThe augmentation index (AIx) calculated from the central aortic pressure waveform derived from data collected using the PPG sensor of the present invention is compared with the augmentation index (AIx) calculated from the central aortic pressure waveform derived from data collected using the PPG sensor of the present invention. A graph showing the augmentation index (AIx) calculated from the central aortic pressure waveform derived from data collected by the system. The overall correlation was 0.91, with higher AIx values ​​indicating greater correlation.

[0076] Figure 13A The pressure amplification between the central pressure waveform (heart) and the peripheral pressure waveform (wrist or finger) is shown. Figure 13B The pressure amplification values ​​calculated from the central aortic pressure waveform derived from the data collected using the present invention are compared with the pressure amplification values ​​calculated from the central aortic pressure waveform derived from the data collected using the present invention. Figure 2. Graph of pressure amplification values ​​calculated from the central aortic pressure waveform derived from data collected by the system and the tonometry. The overall correlation was 0.96.

[0077] Figure 14A Shown are the central aortic pressure waveform and the parameters identified and used to calculate exercise capacity (EC). Figure 14B The exercise capacity (EC) calculated from the central aortic pressure waveform derived from data collected using the present invention is compared with the exercise capacity (EC) calculated from the central aortic pressure waveform derived from data collected using the present invention. Figure 2. Exercise capacity (EC) calculated from the central aortic pressure waveform derived from data collected by the system and the tonometry. The overall correlation was 0.94.

[0078] Figure 15A The central aortic waveform of a healthy person generated using the present invention is shown. Comparison of central aortic waveforms generated by the systems. Figure 15B The central aortic waveform of an unhealthy person generated using the present invention is shown in FIG. Comparison of central aortic waveforms generated by the systems.

[0079] As described above, the present invention can also be implemented by placing the lower wrist or palm side against the PPG sensor to measure blood perfusion. Although one or more transfer functions must be applied to the different locations where input data is obtained, other aspects of digital signal processing (filtering, inversion, detection of waveform bottoms, conversion to an uncalibrated central pressure waveform, detection of waveform features, calculation of parameters, and display on the smartwatch) should be similar to those described above for the finger.

Claims

1. A method for monitoring a central blood pressure parameter using only a finger PPG signal from a PPG sensor, the method comprising the following steps: Provided is a wearable smart watch or smart bracelet having a microcontroller unit (MCU) and a PPG sensor, wherein the PPG sensor is adapted to sense blood perfusion in a finger of a person wearing the smart watch or smart bracelet, and when the user places their finger on an exposed optical portion of the PPG sensor, the PPG sensor outputs a raw analog PPG signal; placing the user's finger on the exposed optical portion of the PPG sensor for a period of more than 5 seconds and outputting a raw analog PPG signal to an MCU; Converting the original analog PPG signal into a digital signal; Processing the digital signal through a low-pass filter and a high-pass filter; After the digital signal is processed by the low-pass filter and the high-pass filter, inverting the digital signal; detecting individual pulses in the digital PPG signal after the digital PPG signal has been filtered and inverted; Averaging several individual pulses to produce an averaged, inverted, uncalibrated PPG pulse; applying a generalized perfusion-pressure transfer function to the averaged, inverted, uncalibrated PPG pulse to generate an uncalibrated peripheral pressure waveform, and applying a generalized peripheral pressure-central pressure transfer function to the uncalibrated peripheral pressure waveform to generate an uncalibrated aortic pressure waveform having preserved cardiovascular waveform characteristics, wherein the preserved cardiovascular waveform characteristics of the uncalibrated aortic pressure waveform include a first shoulder, a second shoulder, and a notch, the generalized perfusion-pressure transfer function representing a harmonic ratio of amplitude and phase to transform the averaged, inverted, uncalibrated PPG pulse into the uncalibrated peripheral pressure waveform, and the generalized peripheral pressure-central pressure transfer function representing a harmonic ratio of amplitude and phase to transform the uncalibrated peripheral pressure waveform into the uncalibrated aortic pressure waveform having preserved cardiovascular waveform characteristics; detecting waveform features in the uncalibrated aortic pressure waveform and calculating parameters related to the uncalibrated aortic pressure waveform; as well as One or more calculated parameters or indications of calculated parameters are displayed.

2. The method according to claim 1, wherein The PPG sensor is embedded in the housing of the smart watch or smart bracelet, and the optical part of the PPG sensor is exposed through the side wall of the housing or the frame on the side wall of the housing.

3. The method according to claim 1, wherein The PPG sensor is attached to a wristband connected to the smart watch or smart bracelet, and an optical part of the PPG sensor is exposed outward from the wristband.

4. The method according to claim 1, wherein The optical portion of the PPG sensor is exposed through the surface of the smart watch.

5. The method according to claim 1, wherein One or more steps after the original analog PPG signal is converted into the digital signal are implemented in the cloud.

6. The method according to claim 1, wherein One or more steps after the original analog PPG signal is converted into the digital signal are implemented on the smartphone.

7. The method according to claim 1, wherein The exposed optical portion of the PPG sensor is recessed relative to a surrounding surface of the PPG sensor, or is raised relative to a surrounding surface of the PPG sensor, so that the user's finger receives tactile feedback of whether the entire optical portion is covered by the user's finger.

8. A method for monitoring a central blood pressure parameter using only a lower wrist PPG signal from a PPG sensor, the method comprising the following steps: A smart watch or smart bracelet having a microcontroller unit (MCU) and a PPG sensor is provided. The PPG sensor has an optical portion adapted to sense blood perfusion in the lower wrist of a person wearing the smart watch or smart bracelet. When the user places their lower wrist against the exposed optical portion of the PPG sensor, the PPG sensor is configured to output a raw analog PPG signal in response to the sensed blood perfusion in the lower wrist of the person wearing the smart watch or smart bracelet. sensing blood perfusion in the user's lower wrist for a period of more than 5 seconds using an optical portion of the PPG sensor against the user's lower wrist, and outputting a raw analog PPG signal to an MCU; Converting the original analog PPG signal into a digital signal; Processing the digital signal through a low-pass filter and a high-pass filter; After the digital signal is processed by the low-pass filter and the high-pass filter, inverting the digital signal; detecting individual pulses in the digital PPG signal after the digital PPG signal has been filtered and inverted; Averaging several individual pulses to produce an averaged, inverted, uncalibrated PPG pulse; applying a generalized perfusion-pressure transfer function to the averaged, inverted, uncalibrated PPG pulse to generate an uncalibrated peripheral pressure waveform, and applying a generalized peripheral pressure-central pressure transfer function to the uncalibrated peripheral pressure waveform to generate an uncalibrated aortic pressure waveform having preserved cardiovascular waveform characteristics, wherein the preserved cardiovascular waveform characteristics of the uncalibrated aortic pressure waveform include a first shoulder, a second shoulder, and a notch, the generalized perfusion-pressure transfer function representing a harmonic ratio of amplitude and phase to transform the averaged, inverted, uncalibrated PPG pulse into the uncalibrated peripheral pressure waveform, and the generalized peripheral pressure-central pressure transfer function representing a harmonic ratio of amplitude and phase to transform the uncalibrated peripheral pressure waveform into the uncalibrated aortic pressure waveform having preserved cardiovascular waveform characteristics; detecting waveform features in the uncalibrated aortic pressure waveform and calculating parameters related to the uncalibrated aortic pressure waveform; as well as One or more calculated parameters or indications of calculated parameters are displayed.

9. The method according to claim 8, wherein One or more steps after the original analog PPG signal is converted into the digital signal are implemented in the cloud.

10. The method according to claim 8, wherein One or more steps after the original analog PPG signal is converted into the digital signal are implemented on the smartphone.

11. A method for monitoring a central blood pressure parameter using only a finger PPG signal from a PPG sensor, the method comprising the following steps: providing a PPG sensor adapted to sense blood perfusion in a person's finger, the PPG sensor outputting a raw analog PPG signal when the person places their finger on an optical portion of the PPG sensor; placing the person's finger on the optical portion of the PPG sensor for a period of more than 5 seconds and outputting a raw analog PPG signal to a microcontroller; Converting the original analog PPG signal into a digital signal; Processing the digital signal through a low-pass filter and a high-pass filter; After the digital signal is processed by the low-pass filter and the high-pass filter, inverting the digital signal; detecting individual pulses in the digital PPG signal after the digital PPG signal has been filtered and inverted; Averaging several individual pulses to produce an averaged, inverted, uncalibrated PPG pulse; applying a generalized perfusion-pressure transfer function to the averaged, inverted, uncalibrated PPG pulse to generate an uncalibrated peripheral pressure waveform, and applying a generalized peripheral pressure-central pressure transfer function to the uncalibrated peripheral pressure waveform to generate an uncalibrated aortic pressure waveform having preserved cardiovascular waveform characteristics, wherein the preserved cardiovascular waveform characteristics of the uncalibrated aortic pressure waveform include a first shoulder, a second shoulder, and a notch, the generalized perfusion-pressure transfer function representing a harmonic ratio of amplitude and phase to transform the averaged, inverted, uncalibrated PPG pulse into the uncalibrated peripheral pressure waveform, and the generalized peripheral pressure-central pressure transfer function representing a harmonic ratio of amplitude and phase to transform the uncalibrated peripheral pressure waveform into the uncalibrated aortic pressure waveform having preserved cardiovascular waveform characteristics; detecting waveform features in the uncalibrated aortic pressure waveform and calculating parameters related to the uncalibrated aortic pressure waveform; as well as One or more calculated parameters or indications of calculated parameters are displayed.

12. The method according to claim 11, wherein The PPG sensor is located on a laptop computer, and the optical portion is exposed so that the person can place their index finger on the optical portion of the PPG sensor to measure blood perfusion in the person's finger.

13. The method according to claim 11, wherein The PPG sensor is located on a button of a computer mouse, and the optical portion is exposed so that the person can place their index finger on the optical portion of the PPG sensor to measure blood perfusion in the person's finger.

14. The method according to claim 11, wherein One or more steps after the original analog PPG signal is converted into the digital signal are implemented in the cloud.

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