NL2019604B1

NL2019604B1 - System for estimation of pulse transit time and blood pressure

Info

Publication number: NL2019604B1
Application number: NL2019604A
Authority: NL
Inventors: Buxi Dilpreet; Torfs TOM
Original assignee: Stichting Imec Nederland; Imec Vzw
Priority date: 2016-09-21
Filing date: 2017-09-21
Publication date: 2018-11-02
Also published as: DE202016105262U1; NL2019604A

Abstract

A system for estimation of pulse transmission time and blood pressure is provided. At least one capacitive sensor is included for providing a first signal that is indicative of at least part of an electrocardiographic waveform of the user. A radio frequency transmitter is included to output a radio frequency wave into a body of the user. A radio frequency receiver is included to receive at least part of the radio frequency wave reflected from an artery within the body of the user. A second signal is output that is indicative of an arrival of a pulse wave at a location within the artery. A processing unit is arranged to determine a pulse transit time based on the first signal and the second signal.

Description

Technical Field

The present disclosure relates to the field of estimation of pulse wave velocity (PWV) and pulse transit time (PTT) for blood flow and blood pressure monitoring in a living being. In particular, the present disclosure relates to the field of estimation of pulse wave velocity and pulse transit time using radio frequency waves.

Background

Blood pressure, the pressure exerted by circulating blood upon the walls of e.g. an artery, may be identified as a major vital sign together with e.g. body temperature, heart rate (pulse) and respiratory rate. A blood pressure deviating from its normal range may be indicative of one or many ongoing or imminent health related issues of a living being (such as a human), and may cause further issues if not properly detected and/or if left untreated. As tut example, low blood pressure (hypotension) may be indicative of internal bleeding or sepsis. High blood pressure (hypertension) may result from e.g. stress and contribute to an increased risk of for example heart disease, stroke and/or kidney failure. As acknowledged by the World Health Organization (WHO), a large percentage of adults worldwide may experience hypertension, resulting in both e.g. increased morbidity and increased costs.

To estimate blood pressure, invasive methods such as intra-arterial measurements through a cannula may be performed. Other, non-invasive, methods may include e.g auscultatory or oscillometric measurements using external cuffs (sphygmomanometers) and e.g. stethoscopes. In addition, non-invasive methods based on the pulse wave velocity (or corresponding pulse transit time) principle may also be performed, wherein the blood pressure within an artery (or arterial tree) may be related to the velocity of a pressure pulse wave travelling along the artery (or arterial tree).

Frequent estimating of blood pressure may be cumbersome and/or impractical for the individual. In light of the above, an improved, more flexible, non-invasive and more convenient way of estimating blood PWV (and e.g. blood pressure) is required.

Summary of the Invention

An object of the present disclosure is therefore to at least partially fulfill the above requirements. This and other objects are achieved by means of a system and a seating or lying arrangement as defined in the independent claims. Other embodiments are defined by the dependent claims.

According to a first aspect of the present disclosure, the system may include at least one capacitive sensor for providing a first signal indicative of at least part of an electrocardiographic waveform of a user.

The system may include a radio frequency transmitter for transmitting a radio frequency wave into a body of the user.

The system may include a radio frequency receiver for receiving at least part of the radio frequency wave reflected from an artery within the body of the user and for providing a second signal indicative of an arrival of a pulse wave at a location within the artery.

A pulse transit time of the user may be determined (or estimated) by the system according to the present disclosure. The at least one capacitive sensor may function without it being in physical contact with the skin of the user, and it may provide the first signal even if the user is wearing clothing items such as e.g. a t-shirt, a sweater, a jacket or similar. From the first signal, a lime of generation of a pulse wave by e.g. a ventricular muscle may be determined. From the second signal, a time of arrival of the pulse wave at a location within the artery may be determined. By comparing the time of generation and arrival of the pulse, the pulse transit time may be determined (or estimated) if the distance travelled by the pulse is known or approximately known.

In one or more embodiments of the present disclosure, the system may include a processing unit arranged for determining a pulse transit time (PTT) based on the first signal and the second signal. The processing unit may contain e.g. software, hardware or a combination of both that it may use for determining the PTT.

Owing to the present disclosure, the pulse transit time of the user may be determined without the user having to remove one or more clothing items and with little intrusion in the other activities performed by the user.

According to a second aspect of the present disclosure, the seating or lying arrangement may comprise a support for supporting a user when said user is sitting or lying in the seating or lying arrangement.

The seating or lying arrangement may further comprise at least one capacitive sensor, provided at the support, for providing a first signal indicative of at least part of an electrocardiographic waveform of the user.

The seating or lying arrangement may further comprise a radio frequency transmitter, provided at the support, for transmitting a radio frequency wave into a body of the user.

The seating or lying arrangement may further comprise a radio frequency receiver, provided at the support, for receiving at least part of the radio frequency wave reflected from an artery within the body of the user and for providing a second signal indicative of an arrival of a pulse wave at a location within the artery.

The seating or lying arrangement may thus Lie arranged to enable a first signal indicative of at least part of an electrocardiographic waveform of the user and a second signal indicative of an arrival of a pulse wave at a location within the artery to be acquired while a user is seated or lying in the seating or lying arrangement. Hence, the first and second signals which may be used for determining a pulse transit time of the user may be acquired while the user is using the seating or lying arrangement for other activities

In one or more embodiments of the present disclosure, the capacitive sensor may include at least a first capacitive electrode and a second capacitive electrode. The first signal may be output based on a differential measurement of signals from the first capacitive electrode and the second capacitive electrode. By using at least two capacitive electrodes and a differential measurement, the effect of noise common to both electrodes may be reduced and the signal-to-noise ratio in the first signal may be improved.

In one or more embodiments, the system may include a first support for supporting an upper part of a body of the user. The system may also include a second support for supporting a lower part of the body of the user. The pulse transit time of the user may be determined while the user is using the system for other activities.

In one or more embodiments, the first support may for example form part of a backrest of a seating arrangement, and the second support may for example form part of a seat of the seating arrangement. The seating arrangement may for example be an office chair, and the pulse transit time of the user may be determined while the user is busy doing office work. As another example, the seating arrangement may be a car seat, and the pulse transit time of the user may be determined while the user is busy driving.

In one or more embodiments, the first support and the second support may be integral and for example form part of a bed and may support a user when lying down. The pulse transit time of the user may then be determined while the user is lying in the bed, e.g. while resting or sleeping.

In one or more embodiments, the at least one capacitive sensor may be provided at the first support. By providing the at least one capacitive sensor at the first support, the first signal may be provided while the back of the user is supported against the first support (e.g., when the skin of the user is in proximity but not necessarily in physical contact with the at least one capacitive sensor). The at least one capacitive sensor may, for example, be located at the first support at a position of the shoulders or upper back of a user seated normally or lying down.

In one or more embodiments, the at least one capacitive sensor may be provided at the second support (e.g. the seat of a seating arrangement or part of a bed). This may be beneficial e.g. if the user is wearing a thicker jacket (e.g. a winter jacket), as sensing would only need to be performed through a thinner layer of pants or through a skirt.

In one or more embodiments, the at least one capacitive sensor may be provided at the first support, and at least one of the radio frequency transmitter and the radio frequency receiver may be provided at the first support at a position closer to the second support than the at least one capacitive sensor. For example, the at least one capacitive sensor may be provided at a location of the shoulders or upper back of a user seated normally or lying down, and at least one of the radio frequency transmitter and the radio frequency receiver may be provided at a location of the lower back and aorta of the same user.

In one or more embodiments, at least one of the radio frequency transmitter and the radio frequency receiver may be provided at the second support. As an example, providing at least one of the radio frequency transmitter and the radio frequency receiver at the second support may allow for detection of a blood pulse travelling through e.g. an upper leg in for example a femoral artery or a branch of said femoral artery.

In one or more embodiments, a central line of the first support may extend along a longitudinal direction of the first support, and at least one of the radio frequency transmitter and the radio frequency receiver may be provided at the first support at a position within a distance from the central line. The distance from the central line may e.g. be 10 cm. For example, the distance may be selected such that at least one of the transmitter and the receiver is provided sufficiently close to the aorta of a user seated normally or lying down. The distance may be larger than 10 cm if the transmitter and/or receiver are/is such that the second signal indicative of the arrival of the pulse wave at a location within the artery may still be output.

In one or more embodiments, the processing unit may be arranged to determine the pulse transit time as a difference between a time of arrival of the pulse wave at the location within the artery and a time corresponding to a peak in the electrocardiographic wave of the user. The peak in the electrocardiographic wave may e.g. be an R-peak (or QRS peak). It is also envisaged that other features of the electrocardiographic wave of the user may be used to determine the pulse transit time.

In one or more embodiments, the processing unit may further be arranged for estimating a blood pressure of the user based on the determined pulse transit time. By estimating the blood pressure, the present disclosure may allow for a vital sign of the user to be monitored in a more convenient and less intrusive way, while the user is e.g. performing other activities using the system (for example as a seating arrangement or as a bed). The estimated blood pressure may for example be presented to the user on a display, or presented to the user using other forms of interactive devices such as a speaker, a haptic feedback system, a mechanical signal, an electromagnetic signal or similar. The estimated blood pressure may be logged and stored such that it may be received (and analyzed) at a later time. The blood pressure may be estimated continuously, or at the command of the user, or similar. The blood pressure may be estimated from the pulse transit time (or pulse wave velocity, which may be inversely proportional lo the pulse transit time), by e.g. relating pulse wave velocity to compliance of a blood vessel.

hi one or more embodiments, the estimated blood pressure may be a relative blood pressure, e.g. it may indicate an increase or decrease from an earlier blood pressure measurement rather than an absolute measure of blood pressure. This may be beneficial if e.g. a trend of blood pressure is assumed more relevant than absolute values, or e.g. if absolute values would require additional calibration procedures.

In one or more embodiments, the processing unit may have access to a calibration log relating previously determined pulse transit times to simultaneously recorded corresponding blood pressures. By using the calibration log, the processing unit may determine (or estimate) e.g. blood pressure for the user based on the determined pulse transit times by performing a table look-up operation (and also e.g. one or more interpolation steps, if required).

In one or more embodiments, the calibration log may be based on determined pulse transit times and corresponding blood pressures for the user.

The present disclosure relates to all possible combinations of features mentioned herein, including the ones listed above as well as other features which will be described in what follows with reference to different embodiments. Any embodiment described herein may be combinable with other embodiments also described herein, and the present disclosure relates also to all such combinations.

Brief description of Drawings

The above, as well as additional objects, features, advantages and applications of the inventive seating arrangement, will be better understood through the following illustrative and nonlimiting detailed description of embodiments. Reference is made to the appended drawings, in which:

Figure 1 illustrates an embodiment of a system according to one or more embodiments of the present disclosure;

Figure 2 illustrates an embodiment of a system according to one or more embodiments of the present disclosure;

Figure 3 illustrates an embodiment of a system according to one or more embodiments of the present disclosure; and

Figure 4 illustrates representative exemplary signals for the determination/estimation of pulse transit time according to one or more embodiments of the present disclosure.

In the drawings, like reference numerals will be used for like elements unless stated otherwise. Unless explicitly staled to the contrary, the drawings show only such elements that are necessary to illustrate the example embodiments, while other elements, in the interest of clarity, may be omitted or merely suggested.

Detailed Description

Exemplifying embodiments will now be described more fully hereinafter with reference to the accompanying drawings. The drawings show currently preferred embodiments, but the invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

Some embodiments of a system according to the present disclosure will now be described with reference mainly to figures 1 and 2.

Figure 1 illustrates an embodiment of a system 100 in form of an office chair (a seating arrangement). The system 100 may have a first support 110 and a second support 112, which may be arranged to support the upper and lower body of a user seated normally in the office chair. Here, the first support 110 forms part of the backrest of the office chair, and the second support 112 forms part of the seat of the office chair. The office chair in this embodiment is equipped also with armrests, a headrest and wheels, but some or all of these are envisaged as being optional and not necessarily a part of the system 100.

The system 100 may include at least one capacitive sensor 120. In this embodiment, the at least one capacitive sensor 120 is provided at the first support 110, but it is envisaged that the at least one capacitive sensor 120 may be provided at other locations, such as for example the second support 112. The capacitive sensor 120 includes a first capacitive electrode 122 and a second capacitive electrode 124 which are provided in a symmetrical fashion on both sides of a central line L that extends along a longitudinal direction of the first support 110. The central line L preferably aligns with a longitudinal direction of the spine of a user normally seated in the seating arrangement. Herein, “normally seated” is assumed to mean that the user is using the seating arrangement 100 as intended, i.e. sits more or less upright with its back at least partially supported against the first support 110 and its behind at least partially supported by the second support 112.

The system 100 may include a radio frequency transmitter 132 and a radio frequency receiver 134. In this embodiment, the transmitter 132 and the receiver 134 are provided at the first support 110, close to each other and at a position al or in proximity the central line L. The transmitter 132 and the receiver 134 are illustrated as two separate parts, but it is envisaged that they may also be combined into a single part, a transceiver. If provided as separate parts, the transmitter 132 and the receiver 134 may not necessarily be located close together but may be positioned apart as long as the radio frequency wave output or transmitted by the transmitter 132 may be received by the receiver 134 after being reflected from an artery within the body of a user seated normally in the seating arrangement. It is also envisaged that at least one of the transmitter 132 and the receiver 134 may be provided at the first support and away from the central line L. For example, at least one of the transmitter 132 and the receiver 134 may be provided at a distance within 10 cm from the central line L.

Herein, a radio frequency receiver and transmitter may be part of for example a continuous wave (CW) radar, a modulated (FM, PM, etc.) or pulsed (UWB) radar.

The system 100 may include a processing unit 140. The processing unit 140 is in this embodiment provided at the lower part of the first support 110, but it is envisaged that the processing unit 140 may be provided at other locations, such as e.g. at the second support 112, at the base, in a headrest, armrest or similar or together with the capacitive sensor 120, the transmitter 132 or the receiver 134. The processing unit 140 may be hidden within e.g. the first support 110 such that it is not visible from an outside, or the processing unit 140 may be visible from the outside. It may also be envisaged that the processing unit 140 is provided separate from the office chair shown in Figure 1.

The at least one capacitive sensor 120 (including e.g. the capacitive electrodes 122 and 124) and/or the radio frequency transmitter 132 and receiver 134 (or transceiver) may be provided such that at least one of them are visible from an outside of the chair. It is also envisaged that at least one of them may be provided such that they are not visible from an outside of the chair, and be embedded within for example the first support 110 or the second support 112.

The at least one capacitive sensor 120, the radio frequency transmitter 132 and receiver 134, and the processing unit 140 may be connected together using e.g. one or more wires or wireless connections (based on e.g. Bluetooth, IEEE 802.11 or other suitable protocols or varieties thereof). The components may, if wired together, be connected in e.g. a star topology with the processing unit 140 in the middle. It is also envisaged that other topologies may be used, such as e.g. a bus or ring network. If necessary, components (such as the at least one capacitive sensor 120, the receiver 134 and the processing unit 140) may each or together include the components needed for either or both of wire or wireless communication.

After receiving a first signal (indicative of at least part of an electrocardiographic waveform of the user and thereby allowing a timing of emission of blood from the left ventricle into the aorta to be deduced) from the at least one capacitive sensor 120 and a second signal (indicative of an arrival of a pulse wave at a location within an artery of the user) from the radio frequency receiver 134, the processing unit 140 may determine a pulse transit time (PTT) based on the first signal and the second signal as a time difference of events deduced from the first signal and the second signal. The PTT may also be indicative or converted to a pulse wave velocity by relating the PTT to a known distance travelled by the blood flow from the aortic valve to the location in the artery where pulse wave arrival is measured. This distance may correspond to or be related to a distance along the central line L between the capacitive sensor 120 and the radio frequency receiver 134.

The determined PTT may be communicated further by for example the processing unit 140 outputting a third signal indicative of the PTT, using e.g. a wire or a wireless link (not shown). The third signal may be used to for example present the determined (or estimated) PTT to the user using a display, a speaker or some other mechanical, electrical or electromagnetic device (e.g. a haptic feedback device or similar). The third signal may also be conveyed to a storage unit or a further processing unit, with or without being presented to the user.

The processing unit 140 may be provided separate from the office chair in figure 1, and the processing unit 140 may then (or in other situations) be e.g. a smartphone, a PDA, a laptop/notebook or desktop computer, or similar.

Owing to the present disclosure, the system 100 may allow for the PTT of a user to be determined while the user is using the system 100 for other activities (i.e., the user may have his PTT estimated while sitting in the office chair of the seating arrangement in figure 1 to perform office work). By combination of the at least one capacitive sensor and the radio frequency transmitter and receiver, the user would not be required to remove any clothing items (such as a tshirt, sweater or jacket), and the PTT of the user may be determined without the user having to adjust or depart from his daily working routines (e.g., the user is not required to stand up and/or leave his room in order to determine his PTT). By relating the determined PTT to a blood pressure, the user’s blood pressure may be determined in the same way, and a vital sign of the user may be determined and monitored with little or no added discomfort or inconvenience for the user.

Although the system 100 in figure 1 is illustrated with an office chair, a system according to the present disclosure may also form part of and/or be used in/with other arrangements.

Figure 2 illustrates an embodiment of a system 200 in form of a bed (a lying arrangement). The system 200 may have a support, which may have a first and a second part forming a first support 210 and a second support 212. The first and second part may be integral in a common support, such as a mattress of the bed. However, the first and second part may also be separate parts of a bed construction, such as in an adjustable bed. If the first support and the second support forms part of a bed, the above described advantages may be achieved instead when the user is e.g. lying down in the bed to rest or e.g. to sleep. It is envisaged that such a bed may e.g. be a hospital bed.

The first support 210 may support an upper body of the user and the second support 212 may support a lower body of the user when the user is lying down.

In this embodiment, the at least one capacitive sensor 220 is provided at the first support 210, but it is envisaged that the at least one capacitive sensor 220 may be provided at other locations, while being able to acquire a first signal indicative of at least part of an electrocardiographic waveform of the user and thereby allowing a timing of emission of blood from the left ventricle into the aorta to be deduced.

hi this embodiment, the radio frequency transmitter 232 and the radio frequency receiver 234 are provided at the first support 210, close to each other and at a position at or in proximity of a central line L’ that extends along a longitudinal direction of the first support 210. The transmitter 232 and the receiver 234 may be arranged at a position of the first support 210 where a lower back of the user may be positioned when lying down. It should be envisaged that the transmitter 232 and the receiver 234 may be positioned in alternative manner as long as the radio frequency wave output or transmitted by the transmitter 232 may be received by the receiver 234 after being reflected from an artery within the body of a user lying in the lying arrangement. For instance, the transmitter 232 and the receiver 234 may be arranged in the first support 210. It is also envisaged that the transmitter 232 and the receiver 234 may be combined into a single part, a transceiver.

The processing unit 240 is in this embodiment provided at the lower part of the first support 210, but it is envisaged that the processing unit 240 may be provided at other locations, such as e.g. at the second support 212, at a bedstead or similar or together with the capacitive sensor 220, the transmitter 232 or the receiver 234. The processing unit 240 may be provided separate from the bed in figure 2, and the processing unit 240 may then (or in other situations) be e.g. a smartphone, a PDA, a laptop/notebook or desktop computer, or similar.

Figure 3 illustrates an embodiment of a system 300 in form of car seat (a seating arrangement). The system 300 may have a first support 310 (in form of a backrest) and a second support 312 (in form of a seat), which may be arranged to support the behind and back of a user seated normally in the car seat while e.g. driving a car or while riding a car as a passenger. Here, “car” is also envisaged to mean any vehicle in which a user may be seated during use (such as e.g. a boat, a train or an airplane).

The car seat in this embodiment is equipped with a headrest, but this is envisaged as being optional.

The system 300 may include at least one capacitive sensor 320. In this embodiment, the at least one capacitive sensor 320 is provided at the second support 312, but it is envisaged that the at least one capacitive sensor 320 may be provided at other locations, such as for example the first support 310. The capacitive sensor 320 includes a first capacitive electrode 322 and a second capacitive electrode 324 that may sense and measure at least part of an electrocardiographic waveform of the user seated normally in the car seat. Here, and in other embodiments of the present disclosure, the at least one capacitive sensor 320 may also include fewer or more than two capacitive electrodes.

The system 300 may include a radio frequency transceiver 330. In this embodiment, the transceiver 330 is provided at the first support 310 al a position approximately on a central line L” that extends along a longitudinal direction of the first support 310. The transceiver 330 includes a radio frequency transmitter and receiver (not shown), and a radio frequency wave output by the transceiver 330 and received by the transceiver 330 after being reflected from an artery within the body of a user seated normally in the car seat. As mentioned earlier herein, it is envisaged that the transceiver may be provided at a position not approximately on the central line L”, but for example at a distance within e.g. 10 cm from the central line L”. As also mentioned earlier herein, this distance may be larger if the functioning of the transceiver may still be maintained.

The system 300 may include a processing unit 340. In this embodiment, the processing unit 340 is provided at the side of the second support 312, although it may be envisaged that the processing unit 340 is provided at other locations, such as e.g. at the first support 310 or base of the car seat. The components (at least the at least one capacitive sensor 320, the transceiver 330 and the processing unit 340) may be connected together in a wired or wireless fashion (as described earlier herein).

The processing unit 340 may be a separate component (such as e.g. a microprocessor or similar), or a component already installed in a car in which the car seat of the system 300 may be installed. The processing unit 340 may for example be part of e.g. the car’s media and entertainment system, or a part of another onboard computer. Communication between components 320, 330 and 340, or between the processing unit 340 and other onboard computers in a car, may for example, in addition or as an alternative to separate wire or wireless communication, take place using the car’s built in bus (e.g. via CAN, LIN, GMLAN or similar). It is envisaged that the components 320, 330 and 340 may each or together include additional components needed for such communication.

By connecting the seating arrangement 300 to a bus in the car, it may be envisaged that for example the determined PTT may be provided on the bus, and presented to the user using e.g. the car’s media and entertainment system, or similar. By relating blood pressure to PTT, the same applies for the blood pressure of the user, which may also (or instead) be presented lo the user.

Although the systems 100 and 300 have here been illustrated as seating arrangements in form of an office chair and a car seat, and the system 200 has been illustrated as a lying arrangement, it is envisaged that such seating or lying arrangements are not necessarily part of a system according to the present disclosure. A system may, for example, only contain at least one capacitive electrode, a radio frequency transmitter and a radio frequency receiver, and be installed in an already existing seating arrangement or in e.g. a bed or other suitable lying arrangement.

With reference to Figure 4, more details about determination/estimation of PTT will now be described. Figure 4 illustrates exemplary signals 410 and 420 as output by one or more embodiments of the present disclosure.

A first signal 410 may be output by the at least one capacitive sensor 120, 220, 320, indicative of at least part of an electrocardiographic waveform of the user. In figure 3, the first signal 410 shows three peaks (R-peaks) of such a waveform. A second signal, 420, may be output by a radio frequency receiver 134, 234, 330, indicative of an arrival of a pulse wave at a location within an artery of the user. In figure 4, the second signal shows at least two peaks, each peak in the second signal 420 being located between peaks of the first signal 410. In figure 4, the horizontal axis corresponds to time, while the vertical axis corresponds to amplitudes of the respective signals 410 and 420.

The first signal 410 may be used to detect for example the generation of a blood pulse by a ventricular muscle in the heart of the user. The at least one capacitive sensor 120, 220, 320 may for example register the electrical signals resulting from a depolarization of the ventricular muscle, and the signal amplitude may be output in the first signal 410.

The second signal 420 may, for example, indicate the amplitude of a radio frequency wave that is received by the radio frequency receiver 134, 234, 330 after having reflected from the wall of an artery. When the blood pulse reaches the artery at a location of reflection of the radio frequency wave, the size of the artery (e.g. its diameter) may increase. As a result, the distance between the radio frequency receiver 134, 234, 330 and the wall of the artery is thus reduced, leading to an increase in received signal strength (of the reflected radio frequency wave) and an increase in signal amplitude. This may be illustrated by a peak in the second signal 420. After the blood pulse passes the artery at the location of reflection, the distance between the artery wall and the radio frequency receiver 134, 234, 330 may be reduced again, and the amplitude may decrease. From the second signal 420, the arrival of the blood pulse (e.g. a pulse arrival time, PAT) at the location of reflection may be deduced, e.g. by determining the position of a peak in the second signal 420.

By estimating a distance 430 in time between a peak in the first signal 410 and a peak in the second signal 420, the time taken for the blood pulse to travel from e.g. the heart of the user to above location of reflection may be determined. This distance in time 430 may correspond to or be indicative of the pulse transit time, PTT. A processing unit 140, 240, 340 may for example receive the first signal 410 and the second signal 420 and determine (or estimate) the PTT based on the first signal 410 and the second signal 420.

Based on the determined PTT, a blood pressure of the user may also be estimated by e.g. the processing unit 140, 240, 340. In one or more embodiments of the present disclosure, the blood pressure of the user may be estimated using a relationship between e.g. arterial stiffness/compliance and PTT (or PWV). The pulse wave velocity (PWV) may be estimated by dividing the pulse transit time with the travelling distance of the blood pulse from the hearth to the above location of reflection. This travelling distance may be known from e.g. the position of the radio frequency receiver 134, 234, 330. As an example, if PWV is estimated, systolic blood pressure (P) may be estimated from a linear model P = a X PWV + b where a and b are coefficients that may be derived using measured values of blood pressure and PWV for an individual user or one or more groups of users. In other embodiments, such models may not be linear and may contain fewer or more coefficients.

In one or many embodiments of the present disclosure, the processing unit 140, 240, 340 may have access to a calibration log in which data relating previously measured values of blood pressure to simultaneously measured values of PTT (or PWV) are stored. These measurement values may be collected using other devices for measuring blood pressure, such as cuffs.

From the calibration log, coefficients (parameters) for the model relating blood pressure and PTT (or PWV) may be extracted. As an example, data found in the calibration log may be collected from a population of different users, and averages or other representative quantities may be extracted. By so doing, estimates of blood pressure may be provided also for new users for whom data is not earlier recorded. In other embodiments, the calibration log may contain previous values of measurements of blood pressure and PTT (or PWV) for the user using the seating arrangement, and calibration of the model may then be achieved for the specific user.

It is also envisaged herein that calibration may be performed on regular basis, and that the calibration log may be updated with additional measurement values.

In some situations, estimating absolute blood pressure from PTT (or PWV) may be difficult, especially if calibration is not performed for the specific user. This may be due to e.g. variations in size, artery wall thickness, age, and other physiological aspects between different users, and also due to the specific location of the sensors involved in the determination of blood pressure. According to the present disclosure, the estimated blood pressure may instead be a relative blood pressure. For example, the estimated blood pressure may be given only relative to the value of a previously estimated blood pressure. Such relative values may still be useful, e.g. if the trend of the blood pressure is important and not its actual value. Phrased differently, it may be interesting to know if a blood pressure is increasing, decreasing or remaining unchanged instead of knowing its exact value. The non-contact implementation of pulse transit time determination in the seating arrangement according to the present disclosure may make such a use case attractive, as frequency, semi-continuous measurements are possible in an unobtrusive way without the user needing to take any special action in addition to be in proximity with the system (e.g. seated in a seating arrangement, lying in a bed, or similar).

Although features and elements are described above in particular combinations, each feature or element may be used alone without the other features and elements or in various combinations with or without other features and elements.

Additionally, variations to the disclosed embodiments may be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used to advantage.

Claims

Clauses

1. A system 100, including:

at least one capacitive sensor 120 for providing a first signal indicative or at least part of an electrocardiographic waveform or a user;

a radio frequency transmitter 132 for transmitting a radio frequency wave into a body of the user;

a radio frequency receiver 134 for receiving at least part of the radio frequency wave reflected from an artery within the body of the user and for providing a second signal indicative of an arrival of a pulse wave at a location within the artery; and a processing unit 140 arranged lor determining a pulse transit time based on the first signal and the second signal.

2. The system 100 or clause 1, where the capacitive sensor 120 comprises at least a first capacitive electrode 122 and a second capacitive electrode 124, and the first signal is based on a differential measurement of signals from the first capacitive electrode 122 and the second capacitive electrode 124.

3. The system 100 or any one of clauses 1-2, further including a first support 110 for supporting an upper body of the user and a second support 112 for supporting a lower body of the user.

4. The system 100 or clause 3, which is the least one capacitive sensor 120, is provided at the first support 110.

5. The system 100 or clause 3, which is the least one capacitive sensor 120, is provided at the second support 112.

6. The system 100 or any one of the clauses 3-5, at least one of the radio frequency transmitter 132 and the radio frequency receiver 134 is provided at the first support 110.

7. The system 100 or clause 3 or 4, the at least one capacitive sensor 120 is provided at the first support 110 and at least one of the radio frequency transmitter 132 and the radio frequency receiver 134 is provided at the first support 110 at a position closer to the second support 112 than the least one capacitive sensor 120.

8. The system 100 or any one of clauses 3-7, at least one of the radio frequency transmitter 132 and the radio frequency receiver 134 is provided at the second support 112.

9. The system of any one of clauses 3-8, in a central line L of the first support 110 extends along a longitudinal direction of the first support 110, and at least one of the radio frequency transmitter 132 and the radio frequency receiver 134 is provided at the first support 110 at a position within 10 centimeters from the central line L.

10. The system 100 or any one of clauses 3-9, the first support 110 forms part of a backrest or a seating arrangement and the second support 112 forms part of a seat or said sealing arrangement.

11. The system 100 or any one of clauses 3-9, the first support 110 and the second support 112 form part of a bed.

12. The system 100 or any one of the preceding clauses, the processing unit is arranged to determine the pulse transit time as a difference between a time or arrival of the pulse wave at the location within the artery and a time corresponding to an R -peak in the electrocardiographic wave of the user.

13. The system 100 or any one of the preceding clauses, the processing unit is further arranged for estimating a blood pressure or the user based on the determined pulse transit time.

14. The system 100 or clause 13, the estimated blood pressure is a relative blood pressure.

15. The system 100 or clause 13 or 14, the processing unit has access to a calibration log related previously determined pulse transit times to simultaneously recorded corresponding blood pressures.

16. The system 100 or clause 15, the calibration log is based on determined pulse transit times and corresponding blood pressures for the user.

17. A seating or lying arrangement, including:

a support for supporting a user when said user is sitting or lying in the seating or lying arrangement;

at least one capacitive sensor 120, provided at the support, for providing a first signal indicative or at least part of an electrocardiographic waveform of the user;

a radio frequency transmitter 132, provided at the support, for transmitting a radio frequency wave into a body of the user; and a radio frequency receiver 134, provided at the support, for receiving at least part of the radio frequency wave reflected from an artery within the body of the user and for providing a second signal indicative of an arrival of a pulse wave at a location within the artery.

18. A seating arrangement according to clause 17, the support comprises a first support 110 for supporting an upper body of the user and a second support 112 for supporting a lower body of the user.

19. The seating arrangement according to clause 18, the first support 110 forms part of a backrest or said seating arrangement and said the second support 112 forms part of a seat or said seating arrangement.

20. A lying arrangement according to clause 17, the support forms part of a bed and supports a user when lying down.

Conclusions

A system (100) comprising:

at least one capacitive sensor (120) for providing a first signal indicative of at least a portion of an electrocardiographic waveform of a user;

a radio frequency transmitter (132) for transmitting a radio frequency wave in a body of the user;

a radio frequency receiver (134) for receiving at least a portion of the radio frequency wave reflected from a blood vessel within the body of the user to provide a second signal indicative of an arrival of a pulse wave at a location within the blood vessel; and a processing unit (140) adapted to determine a pulse transition time based on the first signal and the second signal.

The system (100) of claim 1, wherein the capacitive sensor (120) comprises at least a first capacitive electrode (122) and a second capacitive electrode (124), the first signal being based on a differential measurement of signals from the first capacitive electrode (122) and the second capacitive electrode (124).

The system (100) of any one of claims 1-2, further comprising a first support (110) for supporting a user's upper body and a second support (112) for supporting a user's lower body.

The system (100) of claim 3, wherein at least one capacitive sensor (120) is mounted on a first support (110).

The system (100) of claim 3, wherein at least one capacitive sensor (120) is mounted on a second support (112).

The system (100) of any one of claims 3-5, wherein at least one of the radio frequency transmitter (132) and the radio frequency receiver (134) is arranged on the first support (110).

The system (100) according to claim 3 or 4, wherein at least one capacitive sensor (120) is provided on the first support (110) and at least one of the radio frequency transmitter (132) and the radio frequency receiver (134) is provided. on the first support (110) at a position closer to the second support (112) than the at least one capacitive sensor (120).

The system (100) of any one of claims 3-7, wherein at least one of the radio frequency transmitter (132) and the radio frequency receiver (134) is disposed on the second support (112).

The system (100) of any one of claims 3-8, wherein a center line L of the first support (110) extends along a longitudinal direction of the first support (110), and with at least one of the radio frequency transmitter (132) ) and the radio frequency receiver (134) is mounted on the first support (110) at a position within 10 centimeters of the center line L.

The system (100) of any one of claims 3-9, wherein the first support (110) forms a part of a backrest of a seating arrangement and wherein the second support (112) forms a portion of a seat of the seating arrangement.

The system (100) of any one of claims 3-9, wherein the first support (110) and the second support (112) form a portion of a bed.

The system (100) according to any of the preceding claims, wherein the processing unit is arranged to determine the pulse transition time as a difference between an arrival time of the pulse wave at the location within the blood vessel and a time corresponding to the R peak in the electrocardiographic wave of the user.

The system (100) according to any of the preceding claims, wherein the processing unit is further adapted to estimate the blood pressure of the user based on the determined pnl transition time.

The system (100) of claim 13, wherein the estimated blood pressure is a relative blood pressure.

The system (100) of claim 13 or 14, wherein the processing unit has access to a calibration log related to predetermined pulse transition times, to simultaneously record corresponding blood pressures.

The system (100) of claim 15, wherein the calibration log is based on predetermined pulse transition times and corresponding blood pressures from the user.

17. Sitting or lying arrangement, comprising:

a support for supporting the user when the user is seated or lying in the sitting or lying arrangement;

at least one capacitive sensor (120) mounted on a support for providing a first signal indicative of at least a portion of an electrocardiographic waveform of the user;

a radio frequency transmitter (132) provided on the support for transmitting a radio frequency wave in the user's body; and a radio frequency receiver (134) disposed on the support for receiving at least a portion of the radio frequency wave reflected from a blood vessel within the body of the user and for providing a second signal indicative of the arrival of a pulse wave at a location within the blood vessel.

The seating arrangement of claim 17, wherein the first support (110) comprises for supporting a user's upper body and a second support (112) for supporting a user's lower body.

The seating arrangement of claim 18, wherein the first support (110) forms a portion of a backrest of the seating arrangement and wherein the second support (112) forms a portion of the seat of the seating arrangement.

A lying arrangement according to claim 17, wherein the support forms a part of a bed and supports a user when it has flipped down.

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