WO2024109467A1 - Device and method for pulse wave measurement, medium, and program product - Google Patents

Abstract

Embodiments of the present disclosure provide a device and method for pulse wave measurement, a medium, and a program product, and relate to the field of medical treatment. The provided device comprises a plurality of receiving antennas configured to acquire a plurality of echo signals associated with a pulse wave of a user, wherein the plurality of echo signals are at the same time period. The device further comprises a processor configured to determine, on the basis of the plurality of echo signals, measurement results of pulse waves of a first part and a second part of the body of the user, wherein the first part and the second part are different parts in a group of body parts. By means of the single device of the embodiments of the present disclosure, the pulse wave measurement results of different body parts of the user in the same time period can be determined.

Description

Device, method, medium and program product for pulse wave measurement

This application claims priority to a Chinese patent application filed with the China Patent Office on November 25, 2022, with application number 202211493683.X and invention name “Device, method, medium and program product for pulse wave measurement”, the entire contents of which are incorporated by reference in this application.

Technical Field

Embodiments of the present disclosure generally relate to the medical field. More specifically, embodiments of the present disclosure relate to a device, method, computer-readable storage medium, and computer program product for pulse wave measurement.

Background technique

A pulse wave refers to a wave formed by the pulsation (vibration) of the heart that propagates along the arteries and blood flow to the periphery. Each beat of the heart generates a pulse wave that propagates along the aorta and the arterial tree. The propagation time difference of the pulse wave from the aortic valve to the measurement point of the peripheral blood vessels within one heartbeat cycle can be called the pulse wave transmission time, also known as the pulse transmission time (PTT). At present, a scheme has been proposed to analyze physiological health status using pulse wave measurement results. For example, pulse transmission time, especially the pulse transmission time of the aorta, can be used to evaluate cardiovascular health, such as heart function, arterial blood vessel condition, blood pressure, etc. Therefore, a scheme that can obtain accurate pulse wave measurement results is needed to better analyze physiological health status.

Summary of the invention

An embodiment of the present disclosure provides a solution for pulse wave measurement.

In a first aspect of the present disclosure, a device for pulse wave measurement is provided. The device includes multiple receiving antennas, which are configured to obtain multiple echo signals associated with a user's pulse wave, wherein the multiple echo signals are in the same time period. The device also includes a processor, which is configured to determine the measurement results of the pulse wave at a first part and a second part of the user's body based on the multiple echo signals, wherein the first part and the second part are different parts of a group of body parts. In this way, a single device according to an embodiment of the present disclosure can determine the pulse wave measurement results within the same time period at different parts of the user's body.

In some embodiments of the first aspect, the group of body parts includes at least two of the neck, abdomen, and chest. Thus, the pulse wave measurement results that can be determined using a single device of an embodiment of the present disclosure may include a pulse wave signal of the neck, a pulse transit time of the thoracic and abdominal aorta, and the like.

In some embodiments of the first aspect, determining the measurement results of the pulse wave at a first part and a second part of the user's body based on the multiple echo signals includes: determining multiple beams based on digital beamforming of the multiple echo signals, each beam having a corresponding direction; determining multiple pulse wave signals corresponding to the multiple beams; and determining a first pulse wave signal corresponding to the first part and a second pulse wave signal corresponding to the second part in the multiple pulse wave signals. In this way, pulse wave signals corresponding to two body parts can be determined using a single device, and the two pulse wave signals are in the same time period.

In some embodiments of the first aspect, determining the measurement results of the pulse wave at the first part and the second part of the user's body based on the multiple echo signals further includes: determining the pulse wave at the first part based on the first pulse wave signal and the second pulse wave signal. In this way, the transit time of the pulse wave between two body parts can be accurately determined based on two simultaneous pulse wave signals using a single device.

In some embodiments of the first aspect, based on digital beamforming of the plurality of echo signals, determining the plurality of beams comprises: performing weighted addition on the plurality of echo signals based on a set of weights, and determining a beam corresponding to the set of weights. In this way, a plurality of beams with different directions can be determined, thereby increasing the range in which pulse wave measurement can be performed.

In some embodiments of the first aspect, determining multiple pulse wave signals corresponding to multiple beams includes: determining, based on each of the multiple beams, a micro-motion trajectory of the user's skin in response to the pulse wave as the pulse wave signal corresponding to the beam. In this way, the user's pulse wave signal can be collected using electromagnetic waves.

In some embodiments of the first aspect, determining a first pulse wave signal corresponding to a first part and a second pulse wave signal corresponding to a second part from a plurality of pulse wave signals comprises: determining a first pulse wave signal that satisfies a first condition from a plurality of pulse wave signals, the first condition being associated with at least one of a respiratory feature and a heartbeat feature of the first part; and determining the second pulse wave signal from a plurality of pulse wave signals based on the first pulse wave signal. In this way, a pulse wave signal corresponding to a specific body part can be efficiently acquired.

In some embodiments of the first aspect, based on the first pulse wave signal, determining the second pulse wave signal from the plurality of pulse wave signals comprises: determining a range of the beam direction corresponding to the second part based on the direction of the first beam corresponding to the first pulse wave signal and the position of the first part, wherein the angle between the beam direction within the range and the direction of the first beam is greater than a predetermined angle value; and determining the second pulse wave signal that satisfies a second condition from a group of pulse wave signals corresponding to the beam within the range, wherein the second condition is associated with the pulse wave signal strength. In this way, the efficiency of determining the pulse wave signal corresponding to the specific second part can be improved.

In some embodiments of the first aspect, determining the conduction time of the pulse wave between the first site and the second site based on the first pulse wave signal and the second pulse wave signal includes: determining the conduction time of the pulse wave between the first site and the second site based on matched filtering between the first pulse wave signal and the second pulse wave signal. In this way, the pulse wave conduction time can be determined quickly and accurately.

In some embodiments of the first aspect, the device includes a millimeter wave radar sensor, and the plurality of receiving antennas are included in the millimeter wave radar sensor. Using the millimeter wave radar sensor, the accuracy of the pulse wave measurement result can be improved.

In some embodiments of the first aspect, acquiring multiple echo signals associated with the user's pulse wave includes acquiring the multiple echo signals at a measurement site on the user's body, the measurement site being different from the first site and the second site. In this way, pulse wave measurements at different sites of the body can be determined at a single measurement site.

In some embodiments of the first aspect, the device is a wearable device worn at the measurement site, or a handheld device operated near the measurement site. In this way, a user-friendly, non-intuitive pulse wave measurement solution can be provided.

In a second aspect of the present disclosure, a method for pulse wave measurement is provided. The method includes acquiring a plurality of echo signals associated with a user's pulse wave, wherein the plurality of echo signals are in the same time period. The method also includes determining the measurement results of the pulse wave at a first part and a second part of the user's body based on the plurality of echo signals, wherein the first part and the second part are different parts of a group of body parts. In this way, the method according to an embodiment of the present disclosure can efficiently determine the pulse wave measurement results at different parts of the user's body within the same time period.

In some embodiments of the second aspect, the group of body parts includes at least two of the neck, abdomen, and chest. Thus, the pulse wave measurement results that can be determined using the method of the embodiments of the present disclosure may include the pulse wave signal of the neck, the pulse transit time of the thoracic and abdominal aorta, etc.

In some embodiments of the second aspect, based on the plurality of echo signals, a first part and a second part of the user's body are determined. The measurement result of the pulse wave at the two body parts includes: determining a plurality of beams based on digital beamforming of a plurality of echo signals, each beam having a corresponding direction; determining a plurality of pulse wave signals corresponding to the plurality of beams; and determining a first pulse wave signal corresponding to the first part and a second pulse wave signal corresponding to the second part from the plurality of pulse wave signals. In this way, two pulse wave signals corresponding to two body parts respectively can be determined based on the echo signals within one time period, and the two pulse wave signals are in the same time period.

In some embodiments of the second aspect, determining the measurement results of the pulse wave at the first part and the second part of the user's body based on the multiple echo signals further includes: determining the conduction time of the pulse wave between the first part and the second part based on the first pulse wave signal and the second pulse wave signal. In this way, the conduction time of the pulse wave between the two body parts can be accurately determined based on the two simultaneous pulse wave signals.

In some embodiments of the second aspect, based on digital beamforming of multiple echo signals, determining multiple beams includes: performing weighted addition on the multiple echo signals based on a set of weights, and determining a beam corresponding to the set of weights. In this way, multiple beams with different directions can be determined, thereby increasing the range in which pulse wave measurement can be performed.

In some embodiments of the second aspect, determining multiple pulse wave signals corresponding to multiple beams includes: determining, based on each of the multiple beams, a micro-motion trajectory of the user's skin in response to the pulse wave as the pulse wave signal corresponding to the beam. In this way, the user's pulse wave signal can be collected using electromagnetic waves.

In some embodiments of the second aspect, determining a first pulse wave signal corresponding to a first part and a second pulse wave signal corresponding to a second part from a plurality of pulse wave signals comprises: determining a first pulse wave signal that satisfies a first condition from a plurality of pulse wave signals, the first condition being associated with at least one of a respiratory feature and a heartbeat feature of the first part; and determining the second pulse wave signal from a plurality of pulse wave signals based on the first pulse wave signal. In this way, a pulse wave signal corresponding to a specific body part can be efficiently acquired.

In some embodiments of the second aspect, based on the first pulse wave signal, determining the second pulse wave signal from the plurality of pulse wave signals comprises: determining a range of the beam direction corresponding to the second part based on the direction of the first beam corresponding to the first pulse wave signal and the position of the first part, wherein the angle between the beam direction within the range and the direction of the first beam is greater than a predetermined angle value; and determining the second pulse wave signal that satisfies a second condition from a group of pulse wave signals corresponding to the beam within the range, wherein the second condition is associated with the pulse wave signal strength. In this way, the efficiency of determining the pulse wave signal corresponding to the specific second part can be improved.

In some embodiments of the second aspect, determining the conduction time of the pulse wave between the first site and the second site based on the first pulse wave signal and the second pulse wave signal includes: determining the conduction time of the pulse wave between the first site and the second site based on matched filtering between the first pulse wave signal and the second pulse wave signal. In this way, the pulse wave conduction time can be determined quickly and accurately.

In some embodiments of the second aspect, the method can be performed by a device including a millimeter wave radar sensor, and the millimeter wave radar sensor includes multiple receiving antennas for acquiring multiple echo signals associated with the user's pulse wave. The millimeter wave radar sensor can improve the accuracy of the pulse wave measurement result.

In some embodiments of the second aspect, acquiring multiple echo signals associated with the user's pulse wave includes acquiring the multiple echo signals at a measurement site on the user's body, the measurement site being different from the first site and the second site. In this way, pulse wave measurements at different sites of the body can be determined at a single measurement site.

In some embodiments of the second aspect, the method can be performed by a wearable device worn at the measurement site, or by a handheld device operated near the measurement site. In this way, a user-friendly, non-intuitive pulse wave measurement solution can be provided.

In a third aspect of the present disclosure, a device for pulse wave measurement is provided. The device includes an acquisition unit configured to acquire A plurality of echo signals associated with the pulse wave of the user are obtained, wherein the plurality of echo signals are in the same time period. The apparatus further comprises a determination unit configured to determine the measurement results of the pulse wave at a first part and a second part of the user's body based on the plurality of echo signals, wherein the first part and the second part are different parts of a group of body parts.

In a fourth aspect of the present disclosure, a computer-readable storage medium is provided, on which a computer program is stored, wherein the computer program is executed by a processor to implement the method provided in the second aspect.

In a fifth aspect of the present disclosure, a computer program product is provided, comprising computer executable instructions, which implement part or all of the steps of the method of the second aspect when the instructions are executed by a processor.

It can be understood that the device of the third aspect, the computer storage medium of the fourth aspect, or the computer program product of the fifth aspect provided above is used to execute at least a portion of the method provided in the second aspect. Therefore, the explanation or description of the second aspect is also applicable to the third aspect, the fourth aspect, and the fifth aspect. In addition, the beneficial effects that can be achieved in the third aspect, the fourth aspect, and the fifth aspect can refer to the beneficial effects in the corresponding method, which will not be repeated here.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features, advantages and aspects of the embodiments of the present disclosure will become more apparent with reference to the following detailed description in conjunction with the accompanying drawings. In the accompanying drawings, the same or similar reference numerals represent the same or similar elements, wherein:

FIG1 is a schematic diagram showing an example environment in which various embodiments of the present disclosure can be implemented;

FIG2 shows a flow chart of a method for pulse wave measurement according to some embodiments of the present disclosure;

FIG3 is a schematic diagram showing a process of determining multiple beams according to some embodiments of the present disclosure;

FIG4 shows a schematic diagram of a determined pulse wave signal according to some embodiments of the present disclosure;

FIG5 is a schematic diagram showing a process of determining a pulse wave signal according to some embodiments of the present disclosure;

FIG6 shows a schematic block diagram of an apparatus for pulse wave measurement according to some embodiments of the present disclosure; and

FIG. 7 illustrates a block diagram of a computing device capable of implementing various embodiments of the present disclosure.

Detailed ways

Embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although certain embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be construed as being limited to the embodiments described herein, which are instead provided for a more thorough and complete understanding of the present disclosure. It should be understood that the drawings and embodiments of the present disclosure are only for exemplary purposes and are not intended to limit the scope of protection of the present disclosure.

In the description of the embodiments of the present disclosure, the term "including" and similar terms should be understood as open inclusion, that is, "including but not limited to". The term "based on" should be understood as "based at least in part on". The term "one embodiment" or "the embodiment" should be understood as "at least one embodiment". The terms "first", "second", etc. may refer to different or the same objects. Other explicit and implicit definitions may also be included below.

As briefly mentioned above, the pulse wave measurement results can be used to evaluate physiological health conditions. For example, pulse transit time, especially aortic pulse transit time, can be used to evaluate cardiovascular health. Currently, some schemes for pulse wave measurement have been proposed. For example, a pressure sensor can be used to collect the user's pulse wave signal through the skin micro-movement caused by cardiac ejection. For another example, an optical sensor can be used to collect the pulse wave signal through the change in light penetration depth caused by cardiac ejection. By analyzing the collected pulse wave signal, for example, by comparing it with a standard pulse wave signal, the user's physiological health condition can be evaluated.

In particular, two synchronous sensors placed at corresponding parts of the body can be used to simultaneously measure the pulse wave. Based on the two synchronous pulse wave signals measured, the pulse transit time can be determined and the pulse transit time can be used to evaluate the user's physiological health. For example, the pulse transit time between the carotid artery and the femoral artery can be measured using planar pressure wave measurement. However, this measurement requires advanced equipment and well-trained operators, and is difficult to implement even in ordinary clinics.

At present, some commercial consumer-grade pulse wave measurement devices have been proposed. These devices can be worn on the user's extremities (e.g., wrists, arms), for example, in the form of wristbands to conveniently measure pulse waves. The device can include multiple sensors or unidirectional sensor arrays arranged at different positions to measure pulse wave signals at different positions. The device can also determine the pulse transit time based on the pulse wave signals collected at different positions.

However, on the one hand, since the pulse transit time between different positions of the human body is usually in the order of milliseconds to subseconds, when multiple sensors are arranged far apart, complex cables or other equipment may be required to synchronize multiple sensors in time for accurately measuring the pulse transit time. This may increase the cost and power consumption of the device. In addition, deploying multiple sensors and cables may reduce the user experience.

On the other hand, common sensors worn on the extremities may have difficulty obtaining pulse wave measurement results in areas such as the chest and abdomen, and therefore it is difficult to determine the pulse transit time of the thoracic and abdominal aorta, which is more medically valuable.

In order to at least partially solve the above problems and other potential problems, various embodiments of the present disclosure provide a scheme for pulse wave measurement. According to various embodiments described herein, a device for pulse wave measurement is provided. The device includes multiple receiving antennas configured to obtain multiple echo signals associated with the user's pulse wave, wherein the multiple echo signals are in the same time period. The device also includes a processor configured to determine the measurement results of the pulse wave at a first part and a second part of the user's body based on the multiple echo signals, wherein the first part and the second part are different parts of a group of body parts. In this way, a single device according to an embodiment of the present disclosure is able to determine the pulse wave measurement results within the same time period at different body parts of the user. Various example embodiments of the present disclosure are described below with reference to the accompanying drawings.

FIG. 1 shows a schematic diagram of an example environment 100 in which multiple embodiments of the present disclosure can be implemented. FIG. 1 shows a device 110 for measuring a pulse wave of a user 101 according to an embodiment of the present disclosure. As shown in FIG. 1 , the device 110 may be configured to operate at a measurement site (e.g., a wrist) of the body of the user 101 to determine beam 1 and beam 2 corresponding to the carotid artery and abdominal artery of the user 101, respectively. The device 110 may also determine pulse wave measurement results at the carotid artery and abdominal artery, respectively, based on beam 1 and beam 2. In some embodiments, the pulse wave measurement result may include a pulse wave signal. Alternatively or additionally, the pulse wave measurement result may include information determined based on the pulse wave signal, such as pulse transit time, pulse wave velocity, etc.

It should be understood that the above environment 100 is only exemplary and does not constitute a limitation on the scope of the present disclosure. Depending on the actual application, the device 110 can be a contact or non-contact device. The device 110 can be a wristband device or an armband device worn at other measurement sites. The device 110 can be worn on the user's neck, waist, arm, wrist, leg, knee, wrist, etc. The device 110 can also be other forms of devices, such as a handheld device or a fixed device. The pulse wave measurement result can be obtained by placing the device 110 near the human body or close to the measurement site of the body. The device 110 can be used to determine the pulse wave measurement results at multiple sites such as the chest and legs of the user 101.

In some embodiments, the user 101 may manually wake up the device 110 to perform the pulse wave measurement function. Alternatively or additionally, the device 110 may be configured to periodically perform the pulse wave measurement function. Alternatively or additionally, the device 110 may be awakened to perform the pulse wave measurement function in response to determining that the user 101 is in a specific posture.

Fig. 2 shows a schematic diagram of a process 200 for measuring a pulse wave according to some embodiments of the present disclosure. The process 200 may be implemented by a suitable module in the device 110. The process 200 for measuring a pulse wave shown in Fig. 2 will be described below with reference to Fig. 1 .

As shown in FIG2 , in block 210, multiple echo signals associated with the pulse wave of the user are acquired, wherein the multiple echo signals are in the same time period. Referring to FIG1 , the multiple echo signals may be received by multiple receiving antennas in the device 110. It should be understood that the device 110 also includes one or more transmitting antennas for transmitting electromagnetic waves to the user 101. The emitted electromagnetic waves The wave is disturbed by the micro-movement of the skin of the user 101 caused by the pulse wave, and is reflected as an echo to multiple receiving antennas. Since the multiple receiving antennas have corresponding arrangement positions, each receiving antenna can obtain an echo signal in a corresponding direction, and the multiple echo signals are in the same time period, that is, the multiple echo signals are synchronous. In this way, the multiple echo signals obtained by the multiple receiving antennas can reflect the pulse wave information of different body parts of the user 101 in the same time period.

In some embodiments, the device 110 may acquire multiple echo signals at a measurement site of the body of the user 101. Examples of measurement sites may include a wrist, an arm, a leg, etc. The device 110 may be worn at the measurement site of the user 101 to perform a pulse wave measurement function. Alternatively or additionally, the device 110 may be operated near the measurement site to perform the pulse wave measurement function. When performing the pulse wave measurement function, the device 110 may activate (multiple) transmitting antennas and multiple receiving antennas to record echo signals for a time period. The time period lasts for at least one complete heartbeat cycle to be used to determine multiple measurement results of the pulse wave within the same heartbeat cycle based on the echo signals.

In some embodiments, the device 110 may include a millimeter wave radar sensor, and the multiple receiving antennas are included in the millimeter wave radar sensor. Since the wavelength of the millimeter wave radar sensor is shorter, a more accurate pulse wave measurement result can be determined. Alternatively, the device 110 may include other types of electromagnetic wave sensors to obtain multiple echo signals associated with the user's pulse wave.

In box 220, based on multiple echo signals, the measurement results of the pulse wave at the first and second parts of the user's body are determined, wherein the first and second parts are different parts in a group of body parts. The measurement results can be determined by the processor in the device 110 based on the multiple echo signals. In some embodiments, a group of body parts includes at least two of the neck, abdomen and chest. In some examples, the first and second parts can be the chest and abdomen, respectively, and the measurement results can include the pulse transit time of the thoracic and abdominal aorta. In other examples, the group of body parts can also include the legs, and the measurement results can include the pulse transit time of the femoral artery. In some embodiments, the group of body parts can also include other body parts of interest. In some embodiments, the measurement site can be different from the first and second parts. For example, the measurement site can be a wrist, and the first and second parts can be the chest and abdomen, respectively.

In some embodiments, the device 110 may determine multiple beams based on digital beamforming of multiple echo signals, and each beam has a corresponding direction. Digital beamforming (also known as digital beam forming, DBF) refers to a method of using digital signal processing technology in the digital domain to weight the antenna amplitude and phase to form a beam in a specified direction. Using digital beamforming, multiple beams with different directions can be formed based on multiple echo signals, and each beam is associated with a set of corresponding weights. In other words, by weighting multiple echo signals based on a set of weights, a beam with a specific direction can be determined.

FIG3 shows a schematic diagram of a process 300 for determining multiple beams according to some embodiments of the present disclosure. As shown in FIG3 , multiple receiving antennas in the device 110, such as receiving antenna 310-1, receiving antenna 310-2, and receiving antenna 310-M (collectively referred to as receiving antenna 310) can receive corresponding multiple echo signals (labeled as x ₁ , x ₂ , ..., x _M ). Based on digital beamforming of the multiple echo signals, the device 110 can determine multiple beams with different directions, such as beams 350-1, 350-2, and 350-3 (collectively referred to as beams 350). In some embodiments, performing digital beamforming on the multiple echo signals includes weighted addition of the multiple echo signals based on a set of weights, thereby determining a beam corresponding to the set of weights. In this way, multiple beams with different directions can be determined.

As shown in FIG3 , a plurality of echo signals (x ₁ , x ₂ , …, x _M ) may be weighted based on a first set of weights (w ₁₁ , w ₁₂ , …, w _1M ) to determine a beam 350-1 in a first direction. A plurality of echo signals (x ₁ , x _{2 , …, x M ) may be weighted based on a second set of weights (w 21 , w 22 , …, w 2M ) to determine a beam 350-2 in a second direction. A plurality of echo signals (x 1 , x 2 , … , x M )} may be weighted based on a third set of weights (w ₃₁ , w ₃₂ , …, w _3M ) to determine a beam 350-3 in a third direction. As shown in FIG3 , a bandpass filter (BPF), a low noise amplifier (LNA) or the _like may be used to generate a plurality of echo signals. The signal processors such as amplifier (LNA), local oscillator (LO), analog to digital converter (AD) are used to process multiple echo signals to better perform digital beamforming.

In this way, the multiple receiving antennas 310 can obtain multiple echo signals in the same time period, and the device 110 can form multiple beams 350 with different directions based on the echo signals in the same time period. By using digital beamforming, multiple beams can be efficiently formed, thereby obtaining a larger range in which pulse wave measurement can be performed. In addition, since the multiple echo signals are in the same time period, the multiple beams 350 formed are completely synchronous.

In some embodiments, the device 110 may include multiple transmit antennas, and the multiple transmit antennas and the multiple receive antennas may form a multi-input multi-output (MIMO) array. In this case, multiple beams that are completely synchronous and have different directions may be similarly determined, and the specific details are not repeated here.

Continuing to refer to FIG2 , based on the determined multiple beams, the processor in the device 110 also determines multiple pulse wave signals corresponding to the multiple beams. Since each of the multiple beams is formed by the spatial superposition of electromagnetic fields, each beam can provide pulse wave information in a specific direction without involving signal crosstalk when collecting pulse wave signals in different directions. Therefore, the corresponding pulse wave signal can be accurately determined based on the multiple beams.

As described above, the echo signal is disturbed by the micro-motion of the skin caused by the pulse wave, so the multiple beams obtained by digital beamforming the echo signal also reflect the pulse wave information of the user 101. In some embodiments, the micro-motion trajectory of the skin of the user 101 in response to the pulse wave can be determined based on each beam, and the micro-motion trajectory can be used as the pulse wave signal corresponding to the beam. In some embodiments, a micro-motion algorithm can be used to determine the micro-motion trajectory of the skin. It should be understood that other suitable algorithms can also be used to determine the pulse wave signal based on the beam. A non-limiting example of a micro-motion algorithm is given below.

The emitted electromagnetic wave T(t) is expressed as follows (1), where _fc represents the frequency of the electromagnetic wave, It represents the initial phase when transmitting. It should be understood that this phase is caused by the signal generation and RF part of the transmitter:

The echo R(t) generated by the emitted electromagnetic wave encountering a target with micro-motion x(t) is shown in the following equation (2):

in

Where Δf represents the Doppler frequency shift of the target, represents the phase change caused by the RF part of the receiver, _d0 represents the distance between the target and the radar antenna. It should be understood that this distance is much larger than x(t), _θ0 represents the phase change caused by the reflection characteristics of the target when it reflects, θ represents the phase change not related to micro-motion, and λ represents the wavelength of the electromagnetic wave.

As shown in the above formula, the phase part Φ(t) contains the micro-motion information of the target. When the target vibrates periodically with x(t), its echo phase is displayed as a signal with a certain periodicity in the time domain. For example, when the target is a body part of the human body, the echo signal can reflect the micro-motion of the skin at the body part caused by the pulse wave. Therefore, the micro-motion algorithm can be used to determine the corresponding pulse wave signal based on the formed beam (i.e., R(t) in Formula 2).

FIG4 shows a schematic diagram 400 of a pulse wave signal determined according to some embodiments of the present disclosure. FIG4 shows a waveform graph 441 of a pulse wave signal of the abdominal aorta and a waveform graph 442 of a pulse wave signal of the carotid artery and the radial artery. The horizontal axis of the graph 441 is time, and the vertical axis is the normalized amplitude of the pulse wave signal. The graph 442 shows the pulse wave signal of the carotid artery and the pulse wave signal of the radial artery. The horizontal axis of the graph 442 is the number of sampling points, and the vertical axis is the normalized intensity of the pulse wave signal. As shown in the graph 442, the amplitude of the pulse wave signal of the carotid artery is generally greater than the amplitude of the pulse wave signal of the radial artery.

Based on the determined multiple pulse wave signals, the device 110 can determine a first pulse wave signal corresponding to the first part and a second pulse wave signal corresponding to the second part from the multiple pulse wave signals. In this way, a pulse wave signal corresponding to a specific body part can be further determined from the determined multiple pulse wave signals to provide a more meaningful measurement result.

In some embodiments, the device 110 may determine a first pulse wave signal that satisfies a first condition among multiple pulse wave signals, the first pulse wave signal corresponding to a first part of the body of the user 101. The first condition is associated with at least one of a heartbeat feature and a breathing feature of the first part. In other words, a pulse wave signal that satisfies the first condition associated with the first part may be identified among the multiple pulse wave signals as the first pulse wave signal corresponding to the first part.

For example, when the first part is the chest, the first condition may be that the heartbeat intensity of the pulse wave signal is higher than a threshold value and the respiration intensity of the pulse wave signal is higher than a threshold value. For another example, when the first part is the abdomen, the first condition may be that the respiration intensity of the pulse wave signal is higher than a threshold value and the heartbeat intensity is lower than a threshold value. For another example, when the first part is the neck, the first condition may be that the respiration intensity of the pulse wave signal is lower than a threshold value and the heartbeat intensity is lower than a threshold value. It should be understood that the above thresholds may be the same or different. The respiration intensity and heartbeat intensity of the pulse wave signal may be analyzed by converting the pulse wave signal in the time domain into a pulse wave signal in the frequency domain.

Additionally, a candidate pulse wave signal may be first determined from the plurality of pulse wave signals based on the strength of the plurality of pulse wave signals, and the candidate pulse wave signal may be a group of pulse wave signals with higher strength. By analyzing whether the candidate pulse wave signal satisfies the first condition, a first pulse wave signal corresponding to the first part that satisfies the first condition may be determined from the candidate pulse wave signals.

In some embodiments, a second pulse wave signal corresponding to a second part may be determined from among a plurality of pulse wave signals based on the determined first pulse wave signal corresponding to the first part. A range of beam directions corresponding to the second part may be determined based on the direction of the first beam corresponding to the first pulse wave signal and the position of the first part, wherein the angle between the beam directions within the range and the direction of the first beam is greater than a predetermined angle value.

For example, in the case where the first part is the chest, the range of directions whose angle with the direction of the first beam is greater than a predetermined angle value can be determined as the range of beam directions corresponding to the second part. The predetermined angle value can be any suitable value, such as 20°, 25°, 30°, 35°, etc. Additionally, in the case where the second part is the neck, the range of directions whose angle with the direction of the first beam is greater than a predetermined angle value and is toward the human head can be determined as the range of beam directions corresponding to the second part. Similarly, in the case where the second part is the abdomen, the range of directions whose angle with the direction of the first beam is greater than a predetermined angle value and is toward the human feet can be determined as the range of beam directions corresponding to the second part.

Based on the determined range, a second pulse wave signal satisfying a second condition may be determined from a group of pulse wave signals corresponding to the beam within the range, the second condition being associated with the pulse wave signal intensity. In other words, a pulse wave signal satisfying the second condition may be selected from a group of pulse wave signals corresponding to the beam within the range as the second pulse wave signal corresponding to the second part. The second condition may be that the intensity of the pulse wave signal is higher than a threshold value. Alternatively or additionally, the second condition may be that the intensity of the pulse wave signal is the largest in the group of pulse wave signals. In this way, since the second pulse wave signal is identified only within a specific range, the efficiency of determining the second pulse wave signal corresponding to the second part may be improved.

FIG5 shows a schematic diagram of a process 500 for determining a pulse wave signal according to some embodiments of the present disclosure. The process 500 may be implemented by a processor in the device 110. As shown in FIG5, in box 501, the processor may receive multiple echo signals from multiple receiving antennas. In box 510, the processor may perform digital beamforming on the multiple echo signals to determine multiple beams with corresponding directions. In some embodiments, the processor may digitally scan the multiple beams to determine the pulse wave signal with the maximum intensity. Specifically, during the digital scanning process, a corresponding beam may be obtained for each set of weights. By performing micro-motion solution on the beam, the corresponding pulse wave signal may be obtained. By applying each set of weights to the multiple echo signals, the pulse wave signal with the maximum intensity may be determined. Then, the pulse wave signal may be judged whether it corresponds to the first part by comparing the first condition associated with the first part. If it is determined that the pulse wave signal does not meet the first condition, the above steps may be performed again (for example, digital beamforming to determine multiple beams, and/or to determine a pulse wave signal with greater intensity) to finally determine a pulse wave signal that meets the first condition and has greater intensity as the pulse wave corresponding to the first part. Signal.

For example, as shown in FIG. 5 , beam 1 may be determined at box 521 based on digital beamforming. A pulse wave signal 523 corresponding to beam 1 may be determined using micromotion resolution at box 522. In response to determining that the pulse wave signal 523 has an intensity higher than a threshold value and/or has the largest intensity among multiple pulse wave signals corresponding to multiple beams, the body part corresponding to beam 1 may be determined at box 524 using at least one of a heartbeat feature and a breathing feature of the pulse wave signal 523. Alternatively or additionally, a distance resolution may be performed on beam 1 to determine a distance 525 between the source of beam 1 and the measurement site, and the body part corresponding to beam 1 may be determined based on the distance 525. Alternatively or additionally, the body part corresponding to beam 1 may be determined based on a beam direction 526 of beam 1. In this way, a first pulse wave signal satisfying a first condition associated with a first site may be efficiently determined among multiple pulse wave signals.

Based on the determined first pulse wave signal corresponding to the first part, for example, pulse wave signal 523, a second pulse wave signal corresponding to the second part can be determined. The range of the beam direction corresponding to the second part can be determined based on the direction of the first beam corresponding to the first pulse wave signal and the position of the first part. The beam can be digitally scanned within the range to determine the pulse wave signal that satisfies the second condition. Specifically, a search space for weight parameters corresponding to the range can be determined. In some embodiments, the search space for weight parameters corresponding to the range can be determined based on a machine learning algorithm or any other suitable method. For each set of weights in the search space, a corresponding beam can be formed and the beam can be micro-solved to obtain the corresponding pulse wave signal.

For example, as shown in FIG. 5 , beam 2 may be determined at box 531, and a pulse wave signal 533 corresponding to beam 2 may be determined using a micro-motion solution at box 532. In response to determining that the pulse wave signal 533 satisfies a second condition, such as having an intensity higher than a threshold, a body part corresponding to beam 2 may be determined at box 534. For example, the body part corresponding to beam 2 may be determined based on at least one of a heartbeat feature and a breathing feature of the pulse wave signal 533. Alternatively or additionally, a distance solution may be performed on beam 2 to determine a distance 535 between a source of beam 2 and a measurement site, and the body part corresponding to beam 2 may be determined based on the distance 535. Alternatively or additionally, the body part corresponding to beam 2 may be determined based on a beam direction 536 of beam 2. In this way, a second pulse wave signal corresponding to a second site may be efficiently determined among a plurality of pulse wave signals.

Using process 500, a pulse wave signal having a maximum intensity may be searched and the corresponding body part may be output, so that a first pulse wave signal corresponding to a first part and a second pulse wave signal corresponding to a second part may be determined among a plurality of pulse wave signals.

Continuing to refer to FIG. 2, in some embodiments, the device 110 may output a first pulse wave signal and a second pulse wave signal as a pulse wave measurement result. Alternatively or additionally, the device 110 may determine the conduction time of the pulse wave between the first part and the second part based on the first pulse wave signal and the second pulse wave signal as a pulse wave measurement result. In some embodiments, the pulse transit time may be determined based on matched filtering between the first pulse wave signal and the second pulse wave signal. For example, the pulse transit time may be determined based on the time delay of a specific feature in the first pulse wave signal and the second pulse wave signal. Examples of specific features may include a peak with the largest amplitude or a trough with the smallest amplitude in the pulse wave waveform, etc.

The above description of the scheme for pulse wave measurement according to an embodiment of the present disclosure refers to Figures 1 to 5. It should be understood that the above processes 200 and 500 are merely exemplary and do not constitute a limitation on the scope of the present disclosure. According to an embodiment of the present disclosure, a single non-contact, medium-to-short distance pulse transit time measurement scheme can be provided. A user-friendly, non-sensing device that can collect thoracic and abdominal aortic pulse transit time in a wearable form can be provided. According to the scheme of the present disclosure, the multi-beamforming principle can be used to obtain multiple simultaneous beams to determine the pulse wave signals at different body parts within the same time period. In other words, a single device can be used to simultaneously collect pulse wave signals at two spatially separated body parts. Therefore, more accurate pulse wave measurement results can be obtained, such as pulse wave signals that do not interfere with each other, and/or accurate pulse wave signals between two body parts. The exact pulse transmission time.

Example devices and equipment

FIG6 shows a block diagram of an apparatus 600 for pulse wave measurement according to an embodiment of the present disclosure, and the apparatus 600 may include multiple modules for performing corresponding steps in processes 200 and 500 as discussed in FIG2 and FIG5. As shown in FIG6, the apparatus 600 includes: an acquisition unit 610, configured to acquire multiple echo signals associated with the user's pulse wave at a measurement site of the user's body, wherein the multiple echo signals are in the same time period; and a determination unit 620, configured to determine the measurement results of the pulse wave at a first site and a second site of the user's body based on the multiple echo signals, wherein the first site and the second site are different sites in a group of body sites, and the measurement site is different from the first site and the second site. With this device, the pulse wave measurement results at different body sites of the user can be determined at a single measurement site.

In some embodiments, the group of body parts may include at least two of the neck, abdomen, and chest. Thus, the pulse wave measurement results that can be determined using a single device of an embodiment of the present disclosure may include a pulse wave signal of the neck, a pulse transit time of the thoracic and abdominal aorta, and the like.

In some embodiments, the determination unit 620 is configured to: determine multiple beams based on digital beamforming of multiple echo signals, each beam having a corresponding direction; determine multiple pulse wave signals corresponding to the multiple beams; and determine a first pulse wave signal corresponding to the first part and a second pulse wave signal corresponding to the second part in the multiple pulse wave signals. In this way, pulse wave signals corresponding to two body parts can be determined using a single device, and the two pulse wave signals are in the same time period.

In some embodiments, the determination unit 620 is configured to determine the conduction time of the pulse wave between the first part and the second part based on the first pulse wave signal and the second pulse wave signal. In this way, the conduction time of the pulse wave between the two body parts can be accurately determined based on the two simultaneous pulse wave signals using a single device.

In some embodiments, the determination unit 620 is configured to: based on digital beamforming of multiple echo signals, determine multiple beams including: weighted addition of multiple echo signals based on a set of weights, and determine a beam corresponding to the set of weights. In this way, multiple beams with different directions can be determined, thereby increasing the range in which pulse wave measurement can be performed.

In some embodiments, the determination unit 620 is configured to determine the micro-movement trajectory of the user's skin in response to the pulse wave based on each of the multiple beams as a pulse wave signal corresponding to the beam. In this way, the user's pulse wave signal can be collected using electromagnetic waves.

In some embodiments, the determination unit 620 is configured to: determine a first pulse wave signal that satisfies a first condition among multiple pulse wave signals, the first condition being associated with at least one of a respiratory feature and a heartbeat feature of a first part; and determine a second pulse wave signal among multiple pulse wave signals based on the first pulse wave signal. In this way, a pulse wave signal corresponding to a specific body part can be efficiently acquired.

In some embodiments, the determination unit 620 is configured to: determine the range of the beam direction corresponding to the second part based on the direction of the first beam corresponding to the first pulse wave signal and the position of the first part, the angle between the beam direction within the range and the direction of the first beam is greater than a predetermined angle value; and determine the second pulse wave signal that meets the second condition in a group of pulse wave signals corresponding to the beam within the range, the second condition being associated with the pulse wave signal strength. In this way, the efficiency of determining the pulse wave signal corresponding to the specific second part can be improved.

In some embodiments, the determination unit 620 is configured to determine the pulse wave transit time between the first site and the second site based on matched filtering between the first pulse wave signal and the second pulse wave signal. In this way, the pulse wave transit time can be determined quickly and accurately.

In some embodiments, the acquisition unit 610 includes a sensor unit, which may include a plurality of receiving antennas. The invention provides a millimeter wave radar sensor with a plurality of receiving antennas configured to obtain a plurality of echo signals associated with the user's pulse wave. The millimeter wave radar sensor can improve the accuracy of the pulse wave measurement result.

In some embodiments, the acquisition unit 610 is configured to acquire multiple echo signals at a measurement site of the user's body, the measurement site being different from the first site and the second site. In this way, pulse wave measurements at different sites of the body can be determined at a single measurement site.

FIG7 shows a schematic block diagram of an example device 700 that can be used to implement an embodiment of the present disclosure. Device 700 can be used to implement the functions of device 110 shown in FIG1 . As shown, device 700 includes a computing unit 701, which can perform various appropriate actions and processes according to computer program instructions stored in a random access memory (RAM) 703 and/or a read-only memory (ROM) 702 or computer program instructions loaded from a storage unit 708 into RAM 703 and/or ROM 702. Various programs and data required for the operation of device 700 can also be stored in RAM 703 and/or ROM 702. Computing unit 701 and RAM 703 and/or ROM 702 are connected to each other via bus 704. Input/output (I/O) interface 705 is also connected to bus 704.

Multiple components in the device 700 are connected to the I/O interface 705, including: an input unit 706, such as a keyboard, a mouse, etc.; an output unit 707, such as various types of displays, speakers, etc.; a storage unit 708, such as a disk, an optical disk, etc.; and a communication unit 709, such as a network card, a modem, a wireless communication transceiver, etc. The communication unit 709 allows the device 700 to exchange information/data with other devices through a computer network such as the Internet and/or various telecommunication networks. The transceiver in the communication unit 709 can be used to implement the functions of the transmitting antenna and the receiving antenna in the device 110.

The computing unit 701 may be a variety of general and/or special processing components with processing and computing capabilities. Some examples of the computing unit 701 include, but are not limited to, a central processing unit (CPU), a graphics processing unit (GPU), various dedicated artificial intelligence (AI) computing chips, various computing units running machine learning model algorithms, digital signal processors (DSPs), and any appropriate processors, controllers, microcontrollers, etc. The computing unit 701 may be used to implement the functions of the processor in the device 110. The computing unit 701 performs the various methods and processes described above, such as process 500. For example, in some embodiments, the process 500 may be implemented as a computer software program, which is tangibly included in a machine-readable medium, such as a storage unit 708. In some embodiments, part or all of the computer program may be loaded and/or installed on the device 700 via RAM and/or ROM and/or communication unit 709. When the computer program is loaded into RAM and/or ROM and executed by the computing unit 701, one or more steps of the process 500 described above may be performed. Alternatively, in other embodiments, the computing unit 701 may be configured to perform the process 500 in any other appropriate manner (eg, by means of firmware).

In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented by software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a server or terminal, the process or function described in the embodiment of the present application is generated in whole or in part. The computer instructions can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from one website site, computer, server or data center to another website site, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that can be accessed by a server or terminal or a data storage device such as a server or data center that includes one or more available media integrated. The available medium can be a magnetic medium (such as a floppy disk, a hard disk, and a tape, etc.), or an optical medium (such as a digital video disk (digital video disk, DVD), etc.), or a semiconductor medium (such as a solid-state hard disk, etc.).

Furthermore, although operations are depicted in a particular order, this should be understood as requiring that such operations be performed in the particular order shown. In some embodiments, the present invention provides a method for implementing a plurality of embodiments of the present invention in a plurality of ways. The method of implementing a plurality of embodiments of the present invention in a plurality of ways may be performed in a plurality of ways, such as by performing the plurality of operations of the present invention in a predetermined order or in a sequential order, or requiring that all illustrated operations should be performed to obtain the desired result. Under certain circumstances, multitasking and parallel processing may be advantageous. Similarly, although some specific implementation details are included in the above discussion, these should not be interpreted as limiting the scope of the present disclosure. Certain features described in the context of a separate embodiment may also be implemented in a single implementation in combination. On the contrary, the various features described in the context of a single implementation may also be implemented in multiple implementations individually or in any suitable sub-combination.

Although the subject matter has been described in language specific to structural features and/or methodological logical actions, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or actions described above. On the contrary, the specific features and actions described above are merely example forms of implementing the claims.

Claims (23)

1. A device for pulse wave measurement, comprising:

   a plurality of receiving antennas configured to acquire a plurality of echo signals associated with a user's pulse wave, the plurality of echo signals being in the same time period; and

   A processor is configured to determine measurement results of the pulse wave at a first site and a second site of the user's body based on the plurality of echo signals, wherein the first site and the second site are different sites in a group of body sites.
2. The apparatus of claim 1, wherein the set of body parts includes at least two of the following: neck, abdomen, and chest.
3. The device according to claim 1 or 2, wherein determining the measurement results of the pulse wave at the first part and the second part of the user's body based on the multiple echo signals comprises:

   Based on digital beamforming of the plurality of echo signals, a plurality of beams are determined, each beam having a corresponding direction;

   determining a plurality of pulse wave signals corresponding to the plurality of beams; and

   A first pulse wave signal corresponding to the first site and a second pulse wave signal corresponding to the second site are determined from among the plurality of pulse wave signals.
4. The device of claim 3, wherein determining the measurement results of the pulse wave at the first and second parts of the user's body based on the plurality of echo signals further comprises:

   Based on the first pulse wave signal and the second pulse wave signal, a transmission time of the pulse wave between the first site and the second site is determined.
5. The apparatus according to claim 3 or 4, wherein determining the plurality of beams based on digital beamforming of the plurality of echo signals comprises:

   The plurality of echo signals are weightedly added based on a set of weights, and a beam corresponding to the set of weights is determined.
6. The apparatus according to any one of claims 3 to 5, wherein determining a plurality of pulse wave signals corresponding to the plurality of beams comprises:

   Based on each of the plurality of beams, a micro-motion trajectory of the user's skin in response to the pulse wave is determined as a pulse wave signal corresponding to the beam.
7. The device according to any one of claims 3 to 6, wherein determining a first pulse wave signal corresponding to the first part and a second pulse wave signal corresponding to the second part among the plurality of pulse wave signals comprises:

   determining the first pulse wave signal satisfying a first condition among the plurality of pulse wave signals, the first condition being associated with at least one of a respiratory feature and a heartbeat feature of the first part; and

   The second pulse wave signal is determined among the plurality of pulse wave signals based on the first pulse wave signal.
8. The apparatus according to claim 7, wherein determining the second pulse wave signal among the plurality of pulse wave signals based on the first pulse wave signal comprises:

   Determine, based on the direction of the first beam corresponding to the first pulse wave signal and the position of the first part, a range of the beam direction corresponding to the second part, wherein the angle between the beam direction within the range and the direction of the first beam is greater than a predetermined angle value; and

   The second pulse wave signal satisfying a second condition is determined from a group of pulse wave signals corresponding to the beams within the range, where the second condition is associated with pulse wave signal strength.
9. The apparatus according to claim 4, wherein based on the first pulse wave signal and the second pulse wave signal, Determining the transmission time of the pulse wave between the first site and the second site includes:

   The transit time of the pulse wave between the first site and the second site is determined based on matched filtering between the first pulse wave signal and the second pulse wave signal.
10. The device according to any one of claims 1 to 9, wherein the device comprises a millimeter wave radar sensor, and the plurality of receiving antennas are included in the millimeter wave radar sensor.
11. The device according to any one of claims 1 to 10, wherein acquiring a plurality of echo signals associated with the pulse wave of the user comprises: acquiring the plurality of echo signals at a measurement site of the user's body, the measurement site being different from the first site and the second site.
12. The device according to claim 11, wherein the device is a wearable device worn at the measurement site, or a handheld device operated near the measurement site.
13. A method for pulse wave measurement, comprising:

    Acquire a plurality of echo signals associated with the user's pulse wave, wherein the plurality of echo signals are in the same time period; and

    Based on the plurality of echo signals, measurement results of the pulse wave at a first site and a second site of the user's body are determined, wherein the first site and the second site are different sites in a group of body sites.
14. The method of claim 13, wherein the set of body parts includes at least two of the neck, abdomen, and chest.
15. The method according to claim 13 or 14, wherein determining the measurement results of the pulse wave at the first part and the second part of the user's body based on the multiple echo signals comprises:

    Based on digital beamforming of the plurality of echo signals, a plurality of beams are determined, each beam having a corresponding direction;

    determining a plurality of pulse wave signals corresponding to the plurality of beams; and

    A first pulse wave signal corresponding to the first site and a second pulse wave signal corresponding to the second site are determined from among the plurality of pulse wave signals.
16. The method of claim 15, wherein determining the measurement results of the pulse wave at the first and second parts of the user's body based on the plurality of echo signals further comprises:

    Based on the first pulse wave signal and the second pulse wave signal, a transmission time of the pulse wave between the first site and the second site is determined.
17. The method according to any one of claims 15 to 16, wherein determining a plurality of pulse wave signals corresponding to the plurality of beams comprises:

    Based on each of the plurality of beams, a micro-motion trajectory of the user's skin in response to the pulse wave is determined as a pulse wave signal corresponding to the beam.
18. The method according to any one of claims 15 to 17, wherein determining a first pulse wave signal corresponding to the first part and a second pulse wave signal corresponding to the second part from among the plurality of pulse wave signals comprises:

    determining the first pulse wave signal satisfying a first condition among the plurality of pulse wave signals, the first condition being associated with at least one of a respiratory feature and a heartbeat feature of the first part; and

    The second pulse wave signal is determined among the plurality of pulse wave signals based on the first pulse wave signal.
19. The method according to claim 18, wherein determining the second pulse wave signal from among the plurality of pulse wave signals based on the first pulse wave signal comprises:

    Based on the direction of the first beam corresponding to the first pulse wave signal and the position of the first part, a range of the beam direction corresponding to the second part and an angle between the beam direction within the range and the direction of the first beam are determined. greater than a predetermined angle value; and

    The second pulse wave signal satisfying a second condition is determined from a group of pulse wave signals corresponding to the beams within the range, where the second condition is associated with the pulse wave signal strength.
20. The method according to claim 16, wherein determining the transit time of the pulse wave between the first site and the second site based on the first pulse wave signal and the second pulse wave signal comprises:

    The transit time of the pulse wave between the first site and the second site is determined based on matched filtering between the first pulse wave signal and the second pulse wave signal.
21. The method according to any one of claims 13 to 20, wherein acquiring a plurality of echo signals associated with the pulse wave of the user comprises: acquiring the plurality of echo signals at a measurement site of the user's body, the measurement site being different from the first site and the second site.
22. A computer-readable storage medium having a computer program stored thereon, wherein the program, when executed by a processor, implements the method according to any one of claims 13 to 21.
23. A computer program product comprises computer executable instructions, wherein the computer executable instructions implement the method according to any one of claims 13 to 21 when executed by a processor.