Wearable device having a plethysmogram sensor

Abstract

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

Description

Technical Field

[0001] The present invention relates to a method for monitoring central blood pressure parameters.

Background Art

[0002] Since the aortic blood pressure waveform is close to the heart, it has waveform characteristics that reflect the state of the cardiovascular system. These characteristics are clinically important indicators of arterial and cardiac load and independent early prediction markers for cardiovascular events and diseases. However, in the past, an invasive procedure of inserting a catheter with a pressure sensor inside the artery was required to accurately record a high-fidelity aortic blood pressure waveform. As a result, a non-invasive method was created to estimate the aortic blood pressure waveform with cardiovascular-related characteristics from peripheral (e.g., radial, brachial) arterial pressure pulse recordings.

[0003] One of the most used and verified methods is a method of using a transfer function to convert a high-fidelity non-invasively recorded peripheral pressure waveform into a central aortic blood pressure waveform with cardiovascular-related characteristics (Patent Document 1). The transfer function is expressed as the harmonic ratio between the input peripheral pressure waveform and the output central aortic blood pressure waveform. Instead of using the pressure-to-pressure transfer function, in another method, a different transfer function that converts the brachial artery volume displacement waveform obtained by a cuff into a central pressure waveform with characteristics was applied (Patent Document 2). In order to record a consistent brachial volume displacement signal, it was necessary to inflate the brachial cuff to a set pressure value.

[0004] The central pressure waveforms estimated from these methods and their characteristics have been verified and have been shown to provide clinically valuable indicators of predictors of arteriosclerosis, cardiac load stress, arterial age, cardiac exercise capacity, and cardiovascular risk. Even in the absence of symptoms, it is important to monitor, manage, and control these measured characteristics. Providing data or information regarding these characteristics to a population would be useful and beneficial in monitoring heart health. However, currently, these clinically important characteristics need to be measured in a clinical setting using medical devices that require fine tonometer recordings of the radial artery pulse signal or using medical devices that require inflating a cuff to a pressure set to record upper arm volume displacement pulses.

[0005] The present invention addresses the convenience of these characteristics for a population by converting signals from common wearable PPG (photoplethysmograph) sensors on a mobile smartphone, fitness band, or smartwatch into a central aortic pressure waveform having cardiovascular-related characteristics similar to the output of the methods according to Patent Documents 1 and 2. This new method applies a transfer function that converts the PPG signal from the finger into a central pressure waveform signal, then calculates characteristics from the central pressure waveform, and displays them as heart health indicators to guide the user to frequently monitor their health status.

[0006] An object of the present invention is to process signals from a common wearable smartwatch or mobile PPG sensor, convert them into a central aortic pressure pulse having cardiovascular-related characteristics, display these health indicators, and guide the general user to maintain and manage their heart health status.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

[0008] The present invention is directed to a method of monitoring central blood pressure parameters, desirably using a PPG sensor on a smartwatch or smartband. However, aspects of the present invention may also be useful in embodiments that utilize a laptop or a mouse. A smartwatch or smartband is constructed to have a microcontroller unit (MCU) and a PPG sensor adapted to sense blood perfusion in a finger (e.g., index finger, etc.) of a person wearing the smartwatch or smartband. It has been discovered that sensing blood perfusion in the finger results in a signal that can detect cardiovascular features after appropriate filtering and processing. On the other hand, even if the back side of the wrist is pressed against the PPG sensor, at least reliable detection of cardiovascular features cannot be achieved. FIG. 8 shows an example of an inverted finger PPG pulse and an inverted upper wrist PPG pulse. The inverted finger PPG pulse has features as indicated by the arrows, while the inverted upper wrist PPG pulse has no features.

[0009] When a user presses a finger against 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 smartband, and the optical portion of the PPG sensor is exposed through the sidewall of the smartwatch or smartband and / or the bezel on the sidewall. The optical portion of the PPG sensor may be flush with the surface of the housing, but it is desirable for the optical portion to be recessed or raised relative to the housing surface. The raised or recessed portion of the optical portion can provide tactile feedback to the user and can easily ensure that the finger completely covers the optical portion of the PPG sensor. In other embodiments, the PPG sensor can be attached to a list band connected to a smartwatch or smartband with the optical portion of the PPG sensor exposed outward from the list band. In other embodiments, the PPG sensor can be located on one side of the electronic module of a watch or smartband. The user presses a finger against the PPG sensor for a period exceeding about 5 seconds to capture several cycles. The PPG sensor outputs a raw analog PPG signal to the MCU on the smartwatch or smartband. The MCU or other electronic circuit on the smartwatch or smartband converts the raw analog PPG signal into a digitized signal. Although this digitized signal can be used to implement the present invention using the cloud, preferably, it is processed on the smartwatch or smartband using that MCU. If the cloud is used, the digitized signal is transmitted from the smartwatch or smartband to the cloud for further computing. The MCU on the smartwatch or smartband can process the data before transmitting the data to the cloud. In addition, it is possible to perform part of the digital processing on a smartphone associated with the smartwatch or smartband, or in combination with the smartphone and the cloud.

[0010] The digitized 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 exclude relevant physiological data. The digitized signal must be inverted after being processed through the low-pass filter and the high-pass filter. The filtered finger PPG signal is inversely proportional to the volume of blood in the finger. It is important to find a part of the wave corresponding to the foot of the central aortic pressure waveform. The reason for inversion is that the filtered finger PPG has a negative slope at the start of the pulse, while the pressure signal has a positive slope (upstroke). By inverting the PPG signal, the finger PPG and the pressure pulse will have important similar characteristics when estimating the transfer function. The transfer function tends to be more stable when the input and output signals have common aligned characteristics. The next step is to detect individual pulses in the digitized PPG signal after filtering and inverting. Next, several individual pulses are averaged to generate an average uncalibrated PPG pulse.

[0011] A transfer function or combination of transfer functions is applied to the average uncalibrated PPG pulse to generate an uncalibrated aortic pressure waveform with preserved cardiovascular waveform characteristics. The preserved cardiovascular waveform characteristics of the uncalibrated aortic pressure waveform, including the first shoulder, the second shoulder, and the incisura, can be seen, for example, in Figure 7. One or more generalized transfer functions represent the harmonic ratios in amplitude and phase for converting the average uncalibrated PPG pulse into an uncalibrated aortic pressure waveform with preserved cardiovascular-related characteristics. In one embodiment, there are two transfer functions: one that converts the average PPG pulse into an uncalibrated radial pressure pulse, and a second transfer function that converts the uncalibrated radial pressure pulse into an uncalibrated central aortic pulse. In another embodiment, one transfer function converts the average PPG pulse into an uncalibrated central aortic pulse.

[0012] 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 ratios such as the ratio of the systolic curve area under the curve divided by the diastolic curve area under the curve, or the ratio of systolic pressure at the first and second shoulders with respect to the overall height, or the ratio of the height of the peripheral pressure waveform to the height of the central pressure waveform, or other parameters or calculated values such as a composite score. One or more of the calculated parameters or indices of these calculated parameters are displayed on a smartwatch or smartband so that the user can conveniently view them.

[0013] Depending on the position of the PPG sensor, blood perfusion can also be sensed by pressing the palm side of the wrist against the sensor. More specifically, by using a PPG sensor to measure perfusion within the major radial artery from the lower wrist, a waveform indicative of cardiovascular characteristics can result when appropriately measured. For example, it is possible to use a wristband in which the PPG sensor is placed on the lower or palm side of the wrist at an appropriate position. It has been found that sensing blood perfusion by pressing a PPG sensor against the lower wrist to measure blood perfusion through the major radial artery results in a signal from which cardiovascular characteristics can be detected after appropriate filtering and processing. Of course, the transfer function for converting the PPG signal from the lower or palm side of the wrist must be determined separately from the transfer function for converting the PPG signal from the finger.

[0014] Further embodiments of the present invention include placing a PPG sensor on a laptop computer or a 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 index finger on the PPG sensor for measurement. In a mouse embodiment, the PPG sensor can be located on one of the mouse buttons where the index finger naturally rests.

Brief Description of the Drawings

[0015]

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DETAILED DESCRIPTION OF THE INVENTION

[0016] FIG. 1 shows the general steps for implementing the present invention. Generally, in block 1 which is the first step, a raw signal is sensed using a PPG sensor designed to measure a PPG signal from a finger or wrist. Preferably, the PPG sensor is configured to measure a PPG signal from the user's index finger. The PPG sensor is desirably located on a smartwatch or smartband, but can be located on a laptop, on a mouse, or can also be tethered to an electronic device such as a smartphone. In block 2 which is the second step, the raw signal is processed, whereby a PPG pulse results as shown in FIG. 1. In block 3 which is the third step, one or more transfer functions are applied to generate an aortic pressure waveform, and the aortic pressure waveform is shown in FIG. 1 as a central pressure pulse. In block 4 which is the fourth step, waveform features in the central aortic pressure waveform are detected and one or more clinically important parameters including a summary score are calculated. In block 5 which is the fifth step, the calculated parameters and summary score are displayed, for example, on the display of a smartwatch or smartband, or on another display.

[0017] The PPG sensor unit includes one or more LED light sources such as green, red, or infrared, a photodetector, and the circuitry necessary to drive the LED and photodetector. The PPG sensor unit has two parts, an optical part and an electrical part. The optical part is composed of one or more transparent materials, enabling light to pass from the PPG sensor unit to a human and from the human to the PPG sensor unit. The optical part of the PPG sensor unit can be extended using one or more light pipes.

[0018] The PPG sensor unit can be embedded inside a wearable device such as a smartwatch or a smart band. The PPG signal can be sent to an MCU (Microcontroller Unit) or the cloud, or to a smartphone for further processing and calculation. The PPG sensor package can be designed to operate in a reflection mode or a transmission mode.

[0019] FIG. 2 illustrates an embodiment of a smartwatch 14 implementing the present invention. In FIG. 2, the PPG sensor unit 10 is embedded in the watch 14, and the optical portion 12 faces the crown or bezel 16. The user places a finger such as the index finger on the crown 16 to record the PPG pulse of the live finger.

[0020] FIG. 3 illustrates another embodiment of a smartwatch 114 implementing the present invention. The PPG sensor unit 110 is on the wristband 118, and the optical portion 112 faces upward and is exposed next to the body of the smartwatch 114. The user places a finger such as the index finger on the optical portion 112 to record the PPG pulse of the live finger.

[0021] FIG. 4 illustrates another embodiment of a smartwatch 214 implementing the present invention. The PPG sensor unit 210 is embedded in the housing 214 of the watch, and the optical portion 212 faces outward as viewed from the bezel 216 of the watch 214. The user presses a finger such as the index finger against the optical portion 212 to record the PPG pulse of the live finger.

[0022] FIG. 4A shows a PPG sensor 210A having a recessed optical portion 212A. FIG. 4B shows a PPG sensor 210B having a raised optical portion 212B. The recessed portion 212A and the raised portion 212B provide the user with tactile feedback for placing a finger on the optical portion of the PPG sensor. The tactile feedback contributes to the user completely covering the exposed optical portion 212 of the PPG sensor, thereby maximizing the amount of reflected light from the measurement finger and improving the reliability and accuracy of the system.

[0023] Figure 5 shows the digital processing steps for processing the raw PPG signal (6). The raw PPG recording signal (6) is an analog signal that can have a duration of 5 seconds or more, and is preferably sent from a PPG sensor to a smartwatch or smartband for digital signal processing on the MCU of the smartwatch or smartband, or of the associated smartphone. Further, some processing may also occur in the cloud. The signal processing steps shown in Figure 5 include converting the analog signal to a digital signal via an A / D converter (7), filtering the digital signal via a high-pass filter and a low-pass filter (8), inverting the filtered digital PPG signal (10), detecting the pulses in the inverted PPG signal (12), and averaging the PPG pulses (13). All of these steps and calculations can be performed either in the MCU or on the cloud.

[0024] Referring further to Figure 5, the A / D converter (7) digitizes the raw analog PPG signal (6) and samples the signal at a sampling frequency (fs) of 100 Hz or more. Next, a high-pass filter is applied to the digitized signal to reduce 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 stop frequency may be 0.003 - 0.05 Hz, and the pass frequency may be 0.95 - 1.05 Hz. An example of a high-pass filter is a Butterworth high-pass filter with a -50 dB stop frequency of 0.01 Hz and a -3 dB pass frequency of 1 Hz. The low-pass filter will have a -3 dB frequency of 30 to 50 Hz. Both filters should have a small phase delay. Both filters are applied to the digitized signal to generate the filtered PPG signal (9).

[0025] Next, the following equation

[0026]

Number

[0027] The next step (12) is to detect the start and end of each pulse in the inverted PPG signal (11). The start of the pulse is determined by calculating the first derivative and identifying the peak (see Figure 6), which corresponds to the ascending stroke of the pulse at the start of the pulse. After a pulse is detected (12), a number of signal pulses, for example 10 pulses, are generated. By averaging these pulses, one average PPG pulse is generated (see step (14) in Figure 5).

[0028] The average PPG pulse (14) is input into one or more transfer functions (see step 3 in Figure 1), and an average central pressure waveform with preserved cardiovascular characteristics is generated. The transfer function represents the harmonic ratio in amplitude and phase between the input signal and the output signal. The equation of the transfer function can be described in the form of frequency or time domain. The transfer function from the PPG waveform to the aortic pressure is determined in advance from the simultaneous recording of the PPG waveform and the invasive (e.g., catheter, etc.) or equivalent non-invasive (e.g., SphygmoCor, etc.) aortic pressure waveform. The estimation includes frequency harmonic analysis or estimation of the coefficients for the impulse response. The transfer function can be represented and described in the following frequency domain form. (a) Amplitude

[0029] [Number] Here, |H a→b (f)| is the transfer function frequency amplitude ratio of Sig a with respect to Sig b , and Sig a is the input signal in the frequency domain, Sig b is the output signal in the frequency domain, and furthermore, f is the frequency ranging from 0 to fs / 2 in Hz. (b) Phase

[0030] [Number] Here, Phase(H a→b (f)) is the angle of H a→b (f) at frequency f, Phase(Sig a (f)) is the angle of Sig a at frequency f, and furthermore, Phase(Sig b (f)) is the angle of Sig b at frequency f.

[0031] In the time domain, the transfer function can be represented as a set of coefficients that can be equal to H a→b (f) when converted to the impulse response or the frequency domain.

[0032] [Number] Here, Imp(t) is the impulse response in the time domain, IFFT is the inverse fast Fourier transform, and furthermore, t is the time (in milliseconds) from 0 to the pulse length time.

[0033] Sig bas the central aortic pressure waveform, Sig, in the frequency domain a is assumed to be the average PPG signal (14) in the frequency domain.

[0034]

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[0035]

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[0036] The calculation of the aortic pressure waveform from the PPG pulse (14) using the transfer function can be performed in the frequency or time domain. First, in the frequency domain, the aortic pressure at a frequency is

[0037]

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[0038]

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[0039]

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[0040] Alternatively, an intermediate transfer function for converting a PPG waveform into a radial pressure waveform can be determined in advance from the simultaneous recording of the PPG waveform and the radial pressure waveform using a tonometer. The intermediate transfer function can be determined using a technique similar to the above. Next, data representing the radial pressure waveform can be input into a transfer function that converts the radial pressure waveform into a central aortic pressure waveform, as is known in the art.

[0041] Figure 7 shows a central aortic pressure waveform having features resulting from the application of one or more transfer functions. As shown in box 4 of FIG. 1, the software is configured to detect the features shown in FIG. 7. The software applies a first derivative method to detect a notch after the peak. The notch is the first zero crossing of the first derivative after the aortic pulse peak. The notch represents the end of the systolic phase (cardiac ejection) and the start of the diastolic phase (cardiac filling). Since the second peak is the result of the reflected pressure applied to the load on the heart, an excessive load on the heart is estimated by detecting the first and second systolic peaks. Also, as shown in FIG. 7, the software can be configured to calculate the area under the systolic curve (AUC1), which represents the work done by the heart during the pumping action, which also reflects the body's demand for oxygen-rich blood. As shown in FIG. 7, the software can also be configured to calculate the area under the diastolic curve (AUC2), which represents the work done by the heart during ventricular filling, which also reflects the supply of oxygen-rich blood by the heart. The ratio of AUC2 to AUC1 is also the ratio of the supply of oxygen-rich blood to the body's demand and has been shown to be related to physical fitness and endurance. These parameters shown in FIG. 7 are displayed on the display of a smartwatch or smartband, for example, as health indicators that contribute to a user monitoring their health status.

[0042] Figure 9 shows a display for a smartwatch (or other display such as a display on a smartband), with software displaying an indicator of cardiac parameters calculated from the uncalibrated mean central pressure pulse. The label "Cardiac Stress" is calculated as the difference between a first systolic peak and a second systolic peak with respect to the height of the pulse. The arrow in Figure 9 is directed towards the green region, which means that the calculated parameters are good. The displayed "Cardiac Age" correlates with a healthy cardiovascular age by calculating the amplification ratio, i.e., the ratio of the height of the peripheral pulse to the height of the central pulse, and further comparing that amplification ratio to studies of published healthy populations. The label "Exercise Capacity" is the ratio of the diastolic curve area under the curve to the systolic curve area under the curve. The overall score (ARTY) is based on a combination of detected cardiac features.

[0043] Figure 10 is a schematic view of an embodiment of a smartband 314 having an embedded PPG sensor 310 with an optical element 312 exposed along the side of the housing of the electronic module. Although not shown, the smartband 314 may have a visual indicator such as an LED, but does not necessarily have a UI (user interface) screen. If it has a display screen, it can display information similar to that shown in Figure 9. If it does not, it may be necessary to adapt a visual indicator or send the information / data to another device for display and possibly further processing.

[0044] The accuracy of the present invention was tested against the SphygmoCor system for generating central aortic pressure pulses based on non-invasive peripheral blood pressure waveform measurements. The SphygmoCor system is a commercial embodiment of the system described in Patent Document 1 above, is approved by the FDA, and is considered the gold standard for non-invasive measurement of central aortic pressure waveforms. FIG. 11 is a schematic diagram illustrating the setup for testing the accuracy of the present invention compared to the SphygmoCor system. Several recordings (from 3 to 9) were taken from 13 subjects (4 females and 9 males) aged 20 to 65 years over a 10-second duration. The subjects provided a wide range of central aortic pressure waveform shapes (young, old, healthy, non-healthy). Referring to FIG. 11, a tonometer 402 was used to measure the radial pressure pulse of subject 400 according to known techniques. At the same time, a PPG sensor 404 was used to measure the subject's index finger. The signal from the tonometer 402 was sent to the SphygmoCor system 406, and the central pressure waveform data output from the SphygmoCor system 406 was recorded in the data acquisition system 408. At the same time, the signal from the PPG sensor 404 was sent to a system 410 constructed according to the present invention, and the central pressure waveform data output from the system 410 was also recorded in the data acquisition system 408.

[0045] FIG. 12A illustrates the central aortic pressure waveform and parameters identified and used to calculate the augmentation index (AIx). FIG. 12B is a plot comparing the augmentation index (AIx) for the calculated central aortic pressure waveform obtained on data collected using the present invention with a PPG sensor and the augmentation index (AIx) for the central aortic pressure waveform obtained on data collected using the SphygmoCor system. The correlation is 0.91 overall, and the higher the value of AIx, the closer it seems to be.

[0046] Figure 13A illustrates the pressure amplification between the central pressure waveform (heart) and the peripheral pressure waveform (wrist or finger). Figure 13B is a plot comparing the calculated pressure amplification for the central aortic pressure waveform obtained on data collected using the present invention that uses a PPG sensor to detect pressure in the finger, with the pressure amplification for the central aortic pressure waveform obtained on data collected using a tonometer and SphygmoCor system to measure the radial pressure waveform. The correlation is 0.96 overall.

[0047] Figure 14A illustrates the central aortic pressure waveform and parameters identified and used to calculate exercise capacity (EC). Figure 14B is a plot comparing the calculated exercise capacity (EC) for the central aortic pressure waveform obtained on data collected using the present invention that uses a PPG sensor to detect pressure in the finger, with the exercise capacity (EC) for the central aortic pressure waveform obtained on data collected using a tonometer and SphygmoCor system to measure the radial pressure waveform. The correlation is 0.94 overall.

[0048] Figure 15A shows a comparison of the central aortic waveform of a healthy subject generated using the present invention and the central aortic waveform generated using the SphygmoCor system. Figure 15B shows a comparison of the central aortic waveform of a non - healthy subject generated using the present invention and the central aortic waveform generated using the SphygmoCor system.

[0049] As described above, the present invention can also be implemented by pressing the lower wrist or the palm side against a PPG sensor to measure blood perfusion. Although one or more transfer functions must adapt to different positions to obtain input data, other aspects of digital signal processing (filtering, inversion, detection of the feet of the waveform, conversion to an uncalibrated central pressure waveform, detection of waveform features, calculation of parameters, and display on a smartwatch) should be similar to those described above with respect to the finger.

Claims

1. Providing a wearable smartwatch or smartband, wherein the wearable smartwatch or smartband has a microcontroller unit (MCU) and a PPG sensor adapted to sense blood perfusion in a finger of a person wearing the smartwatch or smartband, and the PPG sensor outputs a raw analog PPG signal when the user presses a finger against the exposed optical portion of the PPG sensor; Pressing the user's finger against the exposed optical portion of the PPG sensor for a period exceeding about 5 seconds and outputting the raw analog PPG signal to the MCU; Converting the raw analog PPG signal into a digital signal; Processing the digital signal through a low-pass filter and a high-pass filter; Inverting the digital signal after processing through the low-pass filter and the high-pass filter; Detecting individual pulses in the filtered and inverted digital PPG signal; Averaging several individual pulses to generate an average PPG pulse; Applying one or more transfer functions to the average PPG pulse to generate an aortic pressure waveform with preserved cardiovascular waveform characteristics, wherein the preserved cardiovascular waveform characteristics of the aortic pressure waveform include a first shoulder, a second shoulder, and a notch, and the generalized one or more transfer functions are transfer functions implemented in the frequency domain or the time domain using the frequency amplitude ratio of the output signal in the frequency domain to the input signal in the frequency domain for converting the average PPG pulse into an aortic pressure waveform with preserved cardiovascular waveform characteristics; Detecting waveform characteristics in the aortic pressure waveform and calculating parameters related to the aortic pressure waveform; Displaying one or more of the calculated parameters or indicators of the calculated parameters; A method for monitoring central blood pressure parameters, comprising:

2. The method according to claim 1, wherein the PPG sensor is embedded in the housing of the smartwatch or smartband, and the optical portion of the PPG sensor is exposed through a sidewall of the housing or a bezel on the sidewall of the housing.

3. The method according to claim 1, wherein the PPG sensor is attached to a wristband connected to the smartwatch or smartband, and an optical portion 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 one side of the smartwatch.

5. The method according to claim 1, wherein the one or more transfer functions include a first transfer function that converts the inverted PPG signal of the average into a peripheral pressure waveform, and a second transfer function that converts the peripheral pressure waveform into the aortic pressure waveform.

6. The method according to claim 1, wherein one or more steps after the raw analog PPG signal is converted into a digitized signal are performed in the cloud.

7. The method according to claim 1, wherein one or more steps after the raw analog PPG signal is converted into a digitized signal are performed on a smartphone.

8. The exposed optical portion of the PPG sensor is recessed or raised with respect to the surface of the surrounding PPG sensor so that the user's finger receives tactile feedback as to whether the entire optical portion is covered by the user's finger. The method according to claim 1.

9. A step of providing a smartwatch or smartband, the smartwatch or smartband having a microcontroller unit (MCU) and a PPG sensor adapted to sense blood perfusion at the wrist of a person wearing the smartwatch or smartband, the PPG sensor Outputting a raw analog PPG signal when the user presses the lower wrist against the exposed optical portion of the PPG sensor; Pressing the user's lower wrist against the exposed optical portion of the PPG sensor for a period exceeding about 5 seconds and outputting a raw analog PPG signal to the MCU; Converting the raw analog PPG signal into a digitized signal; Processing the digitized signal through a low-pass filter and a high-pass filter; Inverting the digitized signal after processing through the low-pass filter and the high-pass filter; Detecting individual pulses in the digitized PPG signal after filtering and inverting; Averaging a plurality of individual pulses to generate an average PPG pulse; Applying one or more transfer functions to the average PPG pulse to generate an aortic pressure waveform in which cardiovascular waveform features are preserved, wherein the preserved cardiovascular waveform features of the aortic pressure waveform include a first shoulder, a second shoulder, and a notch, and the generalized one or more transfer functions are transfer functions implemented in the frequency domain or the time domain using the frequency amplitude ratio of the output signal in the frequency domain to the input signal in the frequency domain for converting the average PPG pulse into an aortic pressure waveform in which the cardiovascular waveform features are preserved; Detecting waveform features in the aortic pressure waveform and calculating parameters related to the aortic pressure waveform; Displaying one or more of the calculated parameters or indicators of the calculated parameters; A method for monitoring central blood pressure parameters, comprising:

10. The method according to claim 9, wherein the one or more transfer functions include a first transfer function for converting the average inverted PPG signal into a peripheral pressure waveform and a second transfer function for converting the peripheral pressure waveform into the aortic pressure waveform.

11. The method according to claim 9, wherein one or more steps after the raw analog PPG signal is converted into a digital signal are performed in the cloud.

12. The method according to claim 9, wherein one or more steps after the raw analog PPG signal is converted into a digital signal are performed on a smartphone.

13. Providing a PPG sensor adapted to sense blood perfusion in a human finger, the PPG sensor outputting a raw analog PPG signal when the human presses a finger against the exposed optical portion of the PPG sensor; Pressing the human finger against the exposed optical portion of the PPG sensor for a period exceeding about 5 seconds and outputting a raw analog PPG signal to a microcontroller; Converting the raw analog PPG signal into a digital signal; Processing the digital signal through a low-pass filter and a high-pass filter; Inverting the digital signal after processing through the low-pass filter and the high-pass filter; Detecting individual pulses in the digitized PPG signal after applying a filter and inverting; Averaging several individual pulses to generate an average PPG pulse; Applying one or more transfer functions to the average PPG pulse to generate an aortic pressure waveform with preserved cardiovascular waveform features, wherein the preserved cardiovascular waveform features of the aortic pressure waveform include a first shoulder, a second shoulder, and a notch, and the generalized one or more transfer functions are transfer functions implemented in the frequency domain or the time domain using the frequency amplitude ratio of the output signal in the frequency domain to the input signal in the frequency domain for converting the average PPG pulse into an aortic pressure waveform with preserved cardiovascular waveform features; Detecting waveform features in the aortic pressure waveform and calculating parameters related to the aortic pressure waveform; Displaying one or more of the calculated parameters or indicators of the calculated parameters; A method for monitoring central blood pressure parameters, including.

14. The method according to claim 13, wherein the PPG sensor is embedded in the housing of a smartwatch or a smart band, and the optical portion of the PPG sensor is exposed through the side wall of the housing or through a bezel on the side wall of the housing.

15. The method according to claim 13, wherein the PPG sensor is attached to a wristband configured to be worn by the person, and the optical portion of the PPG sensor is exposed outward from the wristband.

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

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

18. The method according to claim 13, wherein the one or more transfer functions include a first transfer function that converts the inverted average PPG signal into a peripheral pressure waveform, and a second transfer function that converts the peripheral pressure waveform into the aortic pressure waveform.

19. The method according to claim 13, wherein one or more steps after the raw analog PPG signal is converted into a digitized signal are performed in the cloud.

20. The exposed optical portion of the PPG sensor is recessed or raised relative to the surrounding surface of the PPG sensor so that the human finger receives tactile feedback as to whether the entire optical portion is covered by the human finger. The method according to claim 13.

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