Method for monitoring a user's blood pressure using a cuffless monitoring device

Abstract

A method for monitoring a user's blood pressure (BP) using a cuffless monitoring system, the cuffless monitoring system comprising a pulsatility waveform measurement device configured to measure a pulsatility waveform signal of the user, the method comprising an initialization routine (10), the initialization routine comprising: performing an appropriateness routine (20) for adjusting measurement parameters (103) of the pulsatility waveform measurement device; and performing a reliability test for determining the reliability of the measurement. The method provides incremental feedback of the appropriateness of the acquired signal, the reliability of the pulsatility waveform, and the repeatability of the absolute BP value.

Description

Technical Field

[0001] The present disclosure relates to a method for monitoring a user's blood pressure (BP) using a cuffless monitoring system. Background Art

[0002] Cuffless BP monitors determine BP, avoiding the need to apply physical force to the body. The main advantage of this approach is that they allow for a more comfortable measurement experience, being "stress-free", and are easier to implement in ambulatory setups, such as at home and during sleep. However, because the physical quantity measured is not BP (it is simply a reading of a physiological quantity related to BP), these monitors typically require a step of transforming the measured physical quantity into a BP estimate (in mmHg).

[0003] For cuffless BP monitors, a distinction can be made between 1) an initialization phase (or determination of the user's calibration parameters that allow transformation of the measured physical quantity towards a BP estimate) and 2) a monitoring BP phase (or application of these calibration parameters to determine the BP reading). Note that for some devices and / or users, the determination of the initialization parameters may be performed at the start and repeated after a given period of time.

[0004] Typically, cuffless BP monitors require a three-step process to determine a BP value (see Reference 1: "The Handbook of Cuffless Blood Pressure Monitoring" by Sola et al., ISBN 978-3-030-24701-0).

[0005] First, the pulsatility waveform is detected. Cuffless BP monitors rely on information related to arterial pulsatility, i.e., the diameter changes of the artery or arterial bed that occur during the cardiac cycle. At a given body location and for each cardiac cycle, the arrival of the arterial pressure wave generates a diameter change of the arterial bed, which causes a gross displacement of the surrounding anatomical structures. Pulsatility energy can be captured from the skin surface by various sensors. The common feature of these sensors is the generation of an electrical signal that encodes a pulsatility waveform whose contour describes the diameter change of the underlying arterial bed.

[0006] Secondly, an uncalibrated BP estimate is generated. The pulsatility waveform is then analyzed to generate uncalibrated BP values ​​for systolic and diastolic pressures. This step typically relies on a technique known as pulse wave analysis (PWA). PWA is the study of the morphology of the pulse pressure waveform. Because the pulsatility waveform is generated by the diameter changes of the arterial bed, and because the diameter changes are generated by the arrival of pressure waves at the arterial bed, it is known that the pulsatility signal contains relevant information about the pressure waveform in the time, amplitude, and frequency domains.

[0007] And again, transforming the uncalibrated BP value into a calibrated BP value. This final step of the cuffless BP monitor is intended to transform the uncalibrated BP value (expressed in arbitrary units) into systolic and diastolic BP values ​​(expressed in mmHg units) that can be interpreted according to established clinical practice (see reference 2: Williams et al., "2018 ESC / ESH Guidelines for the management of arterial hypertension: The Task Force for the management of arterial hypertension of the European Society of Cardiology (ESC) and the European Society of Hypertension (ESH)", https: / / doi.org / 10.1093 / eurheartj / ehy339). This calibration step utilizes as input the uncalibrated BP value and a set of calibration parameters that characterize the transformation for a given subject. Examples of calibration parameters include a) population-by-population parameters, and b) user-dependent parameters.

[0008] The per-population calibration parameters characterize the transformation towards calibrated BP values ​​by taking into account the morphological information of the users (age, size, weight, gender, ethnicity, ...) and applying a pre-computed initialization model (see Ref. 1).

[0009] The user-dependent calibration parameters characterize the transformation towards a calibrated BP value by performing at least one absolute BP measurement on the user by means of an external method or device.

[0010] A combined initialization process including population-wise and user-dependent calibration parameters is also possible. Other initialization processes are also possible based on evolutionary learning on user data (see Reference 1). The initialization phase can be implemented by performing simultaneous reading of at least 1) the pulsatility waveform obtained by means of a pulsatility waveform measurement device, and 2) the absolute BP value of the user obtained by means of an absolute BP measurement device.

[0011] US7544168B2 discloses simultaneously measuring a user's pulsatility waveform signal by using a pulsatility waveform device, measuring the user's absolute BP value by using an absolute BP measurement device, and further obtaining a calibration parameter of the user.

[0012] US 2019 / 0274553 A1 discloses a BP monitoring system that allows simultaneous use of a pulsatility waveform measurement device and an absolute BP measurement device (an integrated system), as well as non-simultaneous use of a pulsatility waveform measurement device and an absolute BP measurement device (a retrofit system that allows a manual calibration process in which a user enters a reference BP value into a user interface).

[0013] US 2019 / 0274553 A1 also discloses an initialization phase that detects whether there is an incorrect position and / or position change and / or excessive movement during measurement, and further instructs the user via a user interface to restart the measurement steps.

[0014] US 7,455,643 B1 discloses a method for automatically deciding when to perform an initialization step and how and when to update user calibration parameters.

[0015] US 2019 / 0274553 A1 discloses an initialization phase that instructs the user to start initialization when a predetermined condition has been met. For example, after a predetermined time has passed, or by monitoring other parameters, such as the user's heart rate.

[0016] However, known devices and methods cannot provide a good user experience for the entire initialization step. For example, the user should measure the pulsatile waveform signal and obtain a reference cuff value with good quality at the same time. However, in real life, the pulsatile waveform signal is not always adequate or reliable for processing (noise signal, signal corrupted by motion, signal corrupted by ambient light interference, device incorrectly set on the user), and the cuff-based measurement results are not always reliable (because of poor placement of the cuff, or successive cuff measurements provide non-repeatable readings). In addition, before obtaining feedback on whether the initialization is successful, the user must wait until the entire process is executed. This may result in a very poor user experience. This is particularly important for devices and methods that will be used outside of a clinical environment (e.g., at home). Summary of the invention

[0017] In the present disclosure, a method for monitoring a user's BP using a cuffless monitoring system, the cuffless monitoring system including a pulsatility waveform measurement device configured to measure a pulsatility waveform signal of the user, the method including: an initialization routine including providing an absolute BP measurement device configured to measure an absolute BP value of the user and measuring the absolute BP value, and calculating calibration parameters using the measured absolute BP value; and a monitoring routine including placing the pulsatility waveform measurement device on the user, measuring the pulsatility waveform signal, generating an uncalibrated blood pressure value from the measured pulsatility waveform, and calculating a calibrated blood pressure value from the uncalibrated blood pressure value and the calibration parameters. The initialization routine further includes: generating guidance information, the guidance information indicating how to set the pulsatility waveform measurement device on the user; setting the pulsatility waveform measurement device on the user according to the first guidance information; executing an adequacy routine, wherein the adequacy routine includes the following steps: adjusting measurement parameters of the pulsatility waveform measurement device, measuring a first segment of a pulsatility waveform signal for a first time period, determining an adequacy value of the measured first segment of the pulsatility waveform by determining an amplitude of a baseline value or by determining a pulsation amplitude of the first segment of the pulsatility waveform signal; and repeating the adequacy routine if the adequacy value is less than an adequacy threshold. The suitability routine; if the suitability value is equal to or greater than the suitability threshold, performing a reliability test, wherein the reliability test includes the following steps: measuring a second segment of the pulsating waveform signal for a second time period, wherein the second time period occurs at a time after the first time period; and determining a first reliability value of the measured second segment of the pulsating waveform from time or amplitude-related characteristics of the second segment of the pulsating waveform; if the first reliability value is less than the reliability threshold, repeating the initialization routine; if the first reliability value is equal to or greater than the reliability threshold, performing the steps of measuring the absolute BP value and using the measured absolute BP value to calculate the calibration parameters.

[0018] The method disclosed herein provides "real-time" and incremental feedback of the adequacy of acquired signals, the reliability of pulsatility waveforms, and the repeatability of absolute BP values ​​while initialization is ongoing, so as to save the user time and wasted effort. The method allows interactive correction of any deviations.

[0019] The methods disclosed herein can be used when the initialization phase is performed by using an absolute BP measurement device in the form of an automated BP monitor reference device based on an upper arm or wrist cuff. The methods can also be used by using manual measurements performed by a technician. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Exemplary embodiments of the present invention are disclosed in this description and illustrated by the accompanying drawings, in which:

[0021] Figure 1 relates to a method for monitoring a user's BP including an initialization routine according to an embodiment;

[0022] Figure 2 schematically illustrates a cuffless monitoring system according to another embodiment;

[0023] Figure 3 An initialization routine according to an embodiment is shown;

[0024] Figure 4 shows an initialization routine according to another embodiment;

[0025] Figure 5 illustrates a schematic representation of a method according to yet another embodiment;

[0026] Figure 6 shows an initialization routine according to yet another embodiment; and

[0027] Figure 7 An initialization routine according to yet another embodiment is shown. DETAILED DESCRIPTION

[0028] Figure 1 A method for monitoring a user's blood pressure (BP) using a cuffless monitoring system is disclosed. According to one embodiment, Figure 2 The cuffless monitoring system schematically shown in comprises a pulsatility waveform measurement device 1 configured to measure a pulsatility waveform signal of a user. The method comprises an initialization routine 10, which comprises the following steps: providing an absolute BP measurement device 2 configured to measure an absolute BP value of a user and measuring the absolute BP value, and calculating calibration parameters using the measured absolute BP value.

[0029] The method comprises a monitoring routine including the steps of placing a pulsatility waveform measurement device on a user 11, measuring a pulsatility waveform signal 12, generating an uncalibrated blood pressure value 13 from the measured pulsatility waveform, and calculating a calibrated blood pressure value 14 from the uncalibrated blood pressure value and calibration parameters.

[0030] The initialization routine 10 may be initiated (triggered) 100 by a user or may be triggered automatically. In the latter case, the initialization routine 10 may be triggered at regular time intervals, for example once every hour, once a week, or once a month.

[0031] exist Figure 3In the embodiment shown in , the initialization routine 10 includes: generating guidance information 101 indicating how to set the pulsatility waveform measurement device on the user; and setting the pulsatility waveform measurement device on the user 102 .

[0032] The guidance information may further indicate how to connect the pulsatility waveform measurement device and / or the absolute BP measurement device, how to charge or turn on the device, how to set the device on the user, how to adopt an appropriate body posture, how to position a limb, how to position the body part where the measurement device is located, how to relax before and / or during measurement, how to perform maneuvers or exercises before and / or during measurement, how to breathe before and / or during measurement (including interactive guidance on breathing rate and depth), a countdown from 5 seconds to 1 second before a new measurement for the measurement device will begin, a countdown from 5 seconds to 1 second before a new measurement for the absolute BP device will begin, the status and / or results of any routines of the initialization phase, the number of performed iterations of the initialization routine, the number of remaining measurements, and reasons for unsuccessful initialization routines, including but not limited to low appropriateness of the pulsatility waveform signal, low reliability of the pulsatility waveform signal, or low repeatability of the measured absolute BP values.

[0033] The initialization routine 10 further includes executing a suitability routine 20, which includes the steps of adjusting measurement parameters of the pulsatile waveform measurement device 103, measuring a first segment of the pulsatile waveform signal for a first time period 104, and determining a suitability value for the measured first segment of the pulsatile waveform 105. If the suitability value is less than a suitability threshold, the suitability routine is iterated 106.

[0034] The initialization routine 10 further includes performing a reliability test, which includes the following steps: measuring a second segment of the pulsating waveform signal for a second time period 107; and determining a first reliability value 108 for the measured second segment of the pulsating waveform; wherein if the reliability value is less than a reliability threshold, the initialization routine is iterated 109.

[0035] If the reliability value is less than the reliability threshold, the initialization routine is iterated 109. In other words, steps 101 to 108 are repeated until the reliability value is equal to or greater than the reliability threshold. When the reliability value is equal to or greater than the reliability threshold, the initialization routine 10 is completed and the monitoring routine can be started in an automated manner.

[0036] In another aspect, the suitability and reliability thresholds may include predefined values ​​that have been determined in a training set of data.

[0037] In one aspect, the second reliability value may be variable at each iteration of the initialization routine 10 .

[0038] In yet another aspect, the suitability and reliability thresholds may be adjusted based on the number of iterations of the initialization routine 10. The suitability and reliability thresholds may decrease as the number of iterations of the initialization routine increases. The advantage of decreasing the reliability threshold as the number of iterations increases is that it allows the initialization routine iterations to be made less selective than subsequent initialization routines, thereby avoiding the user from becoming blocked during the initialization process. For example, during the first iteration of the initialization routine, a selective reliability threshold allows ensuring that the pulsatility waveform measurement device is properly worn before allowing the user to continue with the routine. At later iterations, the initialization routine does not need to be re-iterated for small movements of the pulsatility waveform measurement device.

[0039] In yet another aspect, the duration of the second time period can be adjusted according to the user's heart rate so that the second time period includes at least three heartbeats. Here, for users with a fast heart rate, the duration of the second time period is shorter.

[0040] In a further aspect, the method may comprise the step of inputting subject-dependent information. The reliability threshold may then be adjusted based on the subject-dependent information. This step provides a user-dependent reliability threshold.

[0041] refer to Figure 3 , the reliability tests 107-109 may be performed once (and only once) after executing the suitability routine 20. If the reliability value is less than the reliability threshold, the initialization routine 10 is repeated.

[0042] Figure 4A method according to another embodiment is shown, wherein the performing reliability test can be repeated one or more times. For example, once the reliability tests 107-109 have been performed and the reliability value is equal to or greater than the reliability threshold, instead of starting the monitoring routine, another reliability test is performed. In other words, the reliability tests 107-109 can be performed multiple times within a single iteration of the initialization routine 10. Therefore, another second segment 107 of the pulsating waveform signal is measured, which can be added to the previously measured second segment 107 of the pulsating waveform signal, thereby allowing an improved determination of the reliability value 108. When performing a supplementary reliability test, the reliability threshold used in the second reliability test can vary. For example, the second reliability threshold can be increased between two subsequent reliability tests so as to increase the selectivity of the test at each supplementary reliability test. When performing a supplementary reliability test, the second time period can vary. For example, the second time period can be increased between two subsequent reliability tests so as to increase the accuracy of the determined reliability value 108 at each supplementary reliability test. The second time period can be between 1 second and 30 seconds. For example, the second time period may have a duration of 2, 5, 8, 10, 15 or 30 seconds.

[0043] In the case where the pulsatility waveform measurement device is designated to be in contact with the user, such as a photoplethysmography (PPG) sensor that is designated to be in contact with the user's tissue (such as the skin), the reliability value of the measured second segment of the pulsatility waveform may depend on the contact. The contact, in turn, may depend on the correct positioning and / or attachment of the pulsatility waveform measurement device on the user. For example, in the case where the pulsatility waveform measurement device includes a PPG sensor arranged on a wristband or chest strap, the contact is affected by the tension in the strap. In the case where the pulsatility waveform measurement device is contactless, such as a camera-based sensor, the reliability value may depend on the focus and / or direction of the radiation signal emitted by the contactless sensor. The reliability value will further reflect whether the pulsatility waveform measurement device is correctly worn by the user and / or attached to the appropriate part of the user.

[0044] The reliability value may be determined by analyzing the measured second segment of the pulsatility waveform. For example, determining the reliability value may include the amplitude of the second segment of the pulsatility waveform. The amplitude of the second segment of the pulsatility waveform may correspond to the amount of optical radiation (DC component) that reaches the sensor after having penetrated the tissue, and to an indication of whether the pulsatility waveform measurement device is worn. In particular, the reliability value may indicate wearing / not wearing. The reliability value may correspond to the absence of measurement of the pulsatility waveform signal by the pulsatility waveform measurement device.

[0045] In one aspect, the reliability value can be determined from the morphology (shape or waveform) of the measured second segment of the pulsatile waveform.For example, the reliability value can be determined based on how well the second segment of the pulsatile waveform represents a cardiovascular signal (a good quality signal).

[0046] On the other hand, the reliability value can be determined from time or amplitude related features, which are obtained, for example, by pulse wave analysis of the second segment of the pulsatility waveform. These features can be calculated in the time or frequency domain or any other transformed domain. Such features can include the amplitude of the signal, the repeatability of the signal, and features representing the cardiovascular signal. These features can be identified for each pulse of the measured pulsatility waveform signal or in the average pulse. Statistics on the repeatability of pulses across the measured pulsatility waveform signal can also be determined.

[0047] In yet another aspect, the reliability value can be determined by determining whether the measured pulsatility waveform signal contains detectable information about the blood pressure. For example, the determination of the reliability value can include quantifying the presence and / or reliability of information included in the measured second segment of the pulsatility waveform for BP determination. For example, for the arrival time method, the determination of the reliability value can include determining the reliability of the detection of the bottom (foot) of the waveform. For the pulse wave analysis method, the determination of the reliability value can include whether the analysis can be successfully performed (e.g., whether relevant pulse wave analysis features can be detected).

[0048] In one embodiment, the pulsatility waveform measurement device may include a local processing module 3. In this configuration, the determination of the reliability value may be performed in the local processing module 3. There is no need to transmit the measured second segment of the pulsatility waveform signal to the remote device. However, the computing power and / or memory size of the local processing module 3 may be limited. The code and / or calculations executed in the local processing module may also become available to a third party (by acquiring the wearable pulsatility waveform measurement device).

[0049] In another embodiment, the cuffless monitoring system includes a remote processing module 4 that is remote from the pulsatility waveform measurement device. The remote processing module 4 can be used to perform the determination of the reliability value. Here, the pulsatility waveform signal device may include a transmission module 5, which is configured to transmit the measured second segment of the pulsatility waveform signal to the remote processing module 4. The remote processing module can be a remote server, or any other device with processing capabilities, such as a smart phone or PC. The remote processing module allows complex calculations to be performed, and the risk of the code and / or calculations executed in the remote processing module becoming available to third parties is limited.

[0050] In yet another embodiment, the determination of the suitability value is performed in the local processing module 3. In the case where the reliability tests 107-109 are performed multiple times within a single iteration of the initialization routine 10 (see Figure 4 ), the determination of the reliability value can be performed in the local processing module 3 for at least the initial reliability test 107-109, and the determination of the reliability value for the subsequent reliability tests 107-109 is completed in the remote processing module 4. The advantage of this process is that the calculations performed in the local processing module can provide quick feedback to the user, and more complex and critical calculations can be performed on the remote processing module. The determination of the reliability value for one or more initial reliability tests 107-109 can use very little data and therefore requires less computing power. The determination of the reliability value for the subsequent reliability tests 107-109 uses more data (longer measurement time period) and requires more computing power. The latter determination is more accurate.

[0051] The appropriateness and reliability thresholds can be further adjusted for the user. For example, the reliability threshold can be adjusted depending on the user's age, skin color, skin perfusion, fat mass, and cardiovascular status. The reliability threshold can be further adjusted, for example, in a timely manner, in the context of using the cuffless monitoring system.

[0052] In one embodiment, the cuffless monitoring system includes an additional measuring device configured to measure an additional signal. The method may further include a step of measuring the additional signal. The reliability value may then be determined by using the measured additional signal. The additional signal may include any one of the following: a motion signal, a signal representing the pressure between the pulsatility waveform measuring device and the user's tissue, a bioimpedance or biopotential signal, an optical signal characterizing the interface between the pulsatility waveform measuring device and the user's tissue. The additional signal may further include a tension signal, such as for measuring the tension of the band when the waveform measuring device includes an optical sensor in a wristband or chest strap. The additional signal may further include an optical signal, such as for characterizing the interface between the sensor and the tissue (skin).

[0053] In one embodiment, the pulsatility waveform measurement device includes a PPG device, which includes at least a light source and a light detector and an analog-to-digital converter (ADC). The adjusting of the measurement parameters includes: adjusting the emission power of the light source and / or the sensitivity of the light detector and / or the ambient light rejection characteristics and / or the gain and bandwidth of the ADC. The measurement parameters can be further adjusted by adjusting the analog filtering and / or the ambient light rejection characteristics.

[0054] The pulsatility waveform measurement device may include a plurality of light source channels, and the measurement parameters may be adjusted by selecting the light source channels. Similarly, the pulsatility waveform measurement device may include a plurality of light detectors, and the measurement parameters may be adjusted by selecting the light detector channels.

[0055] The first segment of the pulsatile waveform signal may be measured for a first time period of 10 ms, 100 ms, or 1000 ms.

[0056] In one aspect, the adequacy value of the measured first segment may be determined by determining the amplitude of a baseline value of the signal (DC value) and / or by determining the amplitude of a pulsation of the signal (AC value).

[0057] In one aspect, the suitability threshold may be a predefined value that has been determined in a training set of data. The suitability threshold may be adjusted during an initialization process.

[0058] In one embodiment, the suitability value may be determined by determining the amplitude of a baseline value, or determining the pulsatile amplitude of a first segment of a pulsatile waveform signal.

[0059] The suitability threshold may be a predefined value that has been determined in a training set of data. The suitability threshold may be adjusted as a function of the number of repetitions of the suitability routine (i.e., the steps of adjusting the measurement parameters 103, measuring the first segment 104, and determining the suitability value 105). In one aspect, the suitability threshold decreases with the number of repetitions of steps 103, 104, 105.

[0060] Figure 5 1 shows a schematic representation of an initialization routine 10 according to yet another embodiment. Here, the initialization routine 10 further includes an absolute BP routine, which includes performing a plurality of absolute BP measurements 110 to obtain a plurality of measured absolute BP values, and determining a repeatability 112 of the measured absolute BP values. Figure 5 , first and second measurements of absolute BP values ​​are shown. If the repeatability is less than a repeatability threshold 112, the initialization routine may be iterated.

[0061] exist Figure 5 In the example of , the absolute BP routines 110-112 may be performed after performing the reliability tests 107-109. Figure 6 In another embodiment shown in FIG. 1 , the absolute BP routines 110 - 112 may be performed in parallel with the reliability tests 107 - 109 .

[0062] exist Figure 7 In yet another embodiment shown in , the absolute BP routines 110-112 may be executed in parallel with the reliability tests 107-109 only after the reliability tests have been executed at least once. Figure 7 As shown in the example of , reliability tests 107-109 are first performed after executing the suitability routine 20. When the reliability value is equal to or greater than the reliability threshold, at least additional reliability tests 107-109 are performed in parallel with the absolute BP routines 110-112.

[0063] The repeatability of the measured absolute BP values ​​can be determined by any one or a combination of the following steps: calculating the difference between the measured absolute BP values, calculating the spread across the measured absolute BP values, or calculating the difference between the measured absolute BP value and a previously measured BP value for the same user. Typically, the repeatability value is calculated as the inverse of the illustrated calculation, so that very different absolute BP values ​​will generate very low repeatability values.

[0064] When the reliability value is equal to or greater than the reliability threshold, and when the repeatability of the measured absolute BP value is equal to or greater than the repeatability threshold 112, the initialization routine 10 is complete and the monitoring routine may begin.

[0065] Alternatively, the initialization routine 10 may be completed based on a combination of repeatability and reliability values ​​113 of the measured absolute BP values ​​(see Figure 5 and Figure 6 ). Examples of such combinations may include: determining whether two calculated reliability values ​​remain stable during two measurements of absolute BP values, determining whether an uncalibrated blood pressure value remains stable during two measurements of absolute BP values, determining whether two obtained calibration parameters remain stable during two measurements of absolute BP values, determining whether calibration parameters and absolute BP values ​​change in the same or different directions, and determining whether obtained calibration parameters are comparable to calibration parameters previously obtained for the same user.

[0066] The repeatability threshold may be between 4 mmHg and 10 mmHg, or between 8 mmHg and 10 mmHg, or be 8 mmHg.

[0067] In one aspect, calculating the calibration parameters may include measuring a pulsatile waveform signal, generating an uncalibrated blood pressure value from the measured pulsatile waveform, calculating a function that transforms the uncalibrated blood pressure value to the measured absolute BP, and defining the calibration parameters as a representation of the calculated function.

[0068] In other aspects, the pulsatility waveform measurement device may include an optical sensor that is intended to be worn on the wrist, upper arm, earlobe, inside the ear canal, chest, forehead, under the skin, fingertip, finger phalanx, inside the body, such as in a natural orifice, or implanted (e.g., under the skin).

[0069] Pulsatility waveform measurement devices may include optical sensors, distance sensors, RF sensors, acoustic sensors, temperature sensors, pressure sensors, ultrasonic sensors, bioimpedance sensors, electrical sensors, tonometer sensors, cuff-based sensors, strain sensors.

[0070] Absolute BP measurement devices may include an upper arm cuff, a wrist cuff, a finger cuff, or any other automated cuff.

[0071] The absolute BP measurement device may be any of a manual measurement performed by a technician via the so-called auscultatory method, an automated measurement performed by an upper arm or wrist cuff via the so-called oscillometric method, an automated measurement performed by a finger cuff via the so-called volume clamp method, an automated measurement performed by an invasive arterial line catheter, or any other means for obtaining an absolute reading of the user's BP. The absolute BP measurement results may be used to calculate a user-dependent calibration model to be stored in a database and further used each time a method for monitoring BP is used to obtain a calibrated BP reading for that particular user. An example of a user-dependent calibration model is given in Reference 1.

[0072] Performing multiple absolute BP measurements 110 may include limiting the maximum allowed inflation of the cuff. This is important for safety and comfort reasons. For example, during the initialization routine, a maximum of 3, 4, or 5 uses of the absolute BP measurement device may be allowed.

[0073] A minimum allowed time between two consecutive iterations of the initialization routine may also be introduced. For example, the time elapsed between two initialization iterations may be longer than 10 minutes, 30 minutes or 60 minutes.

[0074] The cuffless monitoring system may include a user interface (see Figure 2 ). The user interface may include a smartphone (smartphone application), a computer program, a website, etc.

[0075] The user interface may be used to manually or automatically input the measured absolute BP value. The measured absolute BP value may be automatically input by establishing a connection (wireless, such as Bluetooth or WiFi, or wired, via a serial or parallel communication bus) between the absolute BP measurement device and the local processing module. The measured absolute BP value may be manually input from an external measurement device or by a skilled operator.

[0076] The user interface may be used to display (possibly visually and / or audibly) the guidance information 101 , for example by means of a video, an image, an interactive learning, a user manual, a telephone call or a video conference.

[0077] The user interface may further be used to remind the user to restart (trigger) the initialization routine 10 after a certain period of time and / or when a change in signal quality or other information is detected (e.g., if a change in the pulsatile waveform is detected, or a change in any cardiovascular parameter (heart rate) is detected). A new initialization routine 10 may be executed for the reasons described above.

[0078] The cuffless monitoring system may be configured to begin a monitoring routine when the initialization routine 10 is completed.

Claims

1. A method for monitoring a user's blood pressure (BP) using a cuffless monitoring system, the cuffless monitoring system comprising a pulsatility waveform measurement device configured to measure a pulsatility waveform signal of the user, the method comprising: an initialization routine (10), comprising providing an absolute BP measurement device configured to measure an absolute BP value of a user and measuring the absolute BP value, and calculating calibration parameters using the measured absolute BP value; as well as A monitoring routine comprising placing the pulsatility waveform measurement device on a user (11), measuring a pulsatility waveform signal (12), generating an uncalibrated blood pressure value (13) from the measured pulsatility waveform, and calculating a calibrated blood pressure value (14) from the uncalibrated blood pressure value and the calibration parameters; Characterized in that the initialization routine (10) further comprises: generating guidance information (101), the guidance information indicating how to set the pulsatility waveform measurement device on a user; Setting the pulsatility waveform measurement device on the user according to first guidance information (102); Executing a suitability routine (20), wherein the suitability routine includes the following steps: adjusting measurement parameters of the pulsatility waveform measurement device (103), measuring a first segment of the pulsatility waveform signal for a first time period (104), determining a suitability value (105) of the measured first segment of the pulsatility waveform by determining an amplitude of a baseline value or by determining a pulsation amplitude of the first segment of the pulsatility waveform signal; wherein if the suitability value is less than a suitability threshold, repeating the suitability routine (20); If the suitability value is equal to or greater than the suitability threshold, a reliability test is performed, wherein the reliability test includes the steps of: measuring a second segment of the pulsatile waveform signal for a second time period (107), wherein the second time period occurs at a time after the first time period; and determining a first reliability value (108) for the measured second segment of the pulsatile waveform from a time or amplitude-related feature of the second segment of the pulsatile waveform; If the first reliability value is less than the reliability threshold, repeating the initialization routine (10); If the first reliability value is equal to or greater than the reliability threshold, the steps of measuring the absolute BP value and calculating the calibration parameter using the measured absolute BP value are performed.

2. The method according to claim 1, Wherein the reliability threshold is varied at each iteration of the initialization routine (10).

3. The method according to claim 1, Wherein the execution reliability test (107-109) is only performed once after executing the suitability routine (20).

4. The method according to claim 1, Wherein the performing of the reliability test (107-109) includes performing the reliability test (107-109) multiple times.

5. The method according to claim 4, Wherein the second time period and / or the reliability threshold value are varied when performing at least repeated reliability tests (107-109).

6. The method according to claim 1, Wherein the pulsatility waveform measurement device comprises a local processing module; and The determination of the first reliability value is performed in the local processing module.

7. The method according to claim 1, wherein the cuffless monitoring system comprises a remote processing module remote from the pulsatility waveform measurement device; and The determination of the first reliability value and / or the suitability value is performed in the remote processing module.

8. The method according to claim 1, wherein the pulsatility waveform measurement device includes a local processing module, and the cuffless monitoring system includes a remote processing module remote from the pulsatility waveform measurement device; The determination of the first reliability value is performed in the local processing module (3) for at least a first one of the reliability tests (107-109) and in the remote processing module (4) for subsequent reliability tests (107-109).

9. The method according to claim 8, The determination of the suitability value is performed in the local processing module.

10. The method according to claim 1, Wherein the predefined duration of the second time period is adjusted according to the heart rate of the user such that the second time period includes at least three heart beats.

11. The method according to claim 1, The suitability and reliability thresholds are predefined values ​​that have been determined in a training set of data.

12. The method according to claim 11, Wherein the suitability and reliability thresholds are adjusted as a function of the number of iterations of the initialization routine (10).

13. The method according to claim 12, Wherein the suitability and reliability thresholds decrease with increasing number of iterations of the initialization routine (10).

14. The method according to claim 1, including the step of inputting subject-dependent information; and The appropriateness and reliability thresholds are adjusted based on the subject-dependent information.

15. The method according to claim 1, wherein the cuffless monitoring system includes an additional measurement device configured to measure an additional signal; and The method further comprises the step of measuring the additional signal.

16. The method according to claim 15, Wherein the first reliability value is determined by using the measured additional signal.

17. The method according to claim 15 or 16, The additional signal comprises any one of: a motion signal, a signal representing the pressure between the pulsatility waveform measurement device and the user's tissue, a bioimpedance or biopotential signal, a tension signal, an optical signal characterizing the interface between the pulsatility waveform measurement device and the user's tissue.

18. The method according to claim 1, wherein the pulsatility waveform measurement device comprises a PPG device, wherein the PPG device comprises at least a light source channel, a light detector and an analog-to-digital converter ADC; and The adjusting of the measurement parameters of the pulsating waveform measurement device comprises: The emission power of the light source and / or the sensitivity and / or the ambient light rejection characteristics of the light detector and / or the gain and bandwidth of the ADC are adjusted.

19. The method according to claim 18, wherein the pulsatility waveform measurement device comprises a plurality of light source channels; and Wherein, adjusting the measurement parameters of the pulsatility waveform measurement device includes selecting a light source channel.

20. The method according to claim 18 or 19, wherein the pulsatility waveform measurement device comprises a plurality of light detectors; and Wherein said adjusting the measurement parameters of said pulsatility waveform measurement device comprises selecting a light detector channel.

21. The method according to claim 1, The first time period is 10ms, 100ms or 1000ms.

22. The method according to claim 1, The initialization routine (10) further includes a BP routine, and the BP routine includes: performing a plurality of absolute BP measurements (110) to obtain a plurality of measured absolute BP values, and determining a repeatability of the measured absolute BP values; Wherein if the repeatability value is less than a repeatability threshold value (112), the initialization routine (10) is iterated.

23. The method according to claim 22, Wherein the BP routine is executed after the reliability test (107-109) is performed.

24. The method according to claim 22, Wherein the BP routine is executed in parallel with the execution reliability test (107-109).

25. The method according to claim 24, Wherein said BP routine is executed in parallel with said executing reliability test only after said reliability test (107-109) has been executed at least once.

26. The method according to claim 22, Wherein determining the repeatability of the measured absolute BP value is performed by any one or a combination of the following steps: calculating the difference between the measured absolute BP values, calculating the spread across the measured BP values, or calculating the difference between the measured absolute BP value and a previously measured BP value for the same user.

27. The method according to claim 22, Wherein the repeatability threshold is between 4 mmHg and 10 mmHg.

28. The method according to claim 22, Wherein the repeatability threshold is between 8 mmHg and 10 mmHg.

29. The method according to claim 22, The repeatability threshold is 8 mmHg.

30. The method according to claim 1, The calculated calibration parameters include: A pulsatile waveform signal is measured, an uncalibrated blood pressure value is generated from the measured pulsatile waveform, a function is calculated that transforms the uncalibrated blood pressure value to the measured absolute BP, and the calibration parameter is defined as a representation of the calculated function.

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