WO2013011211A1

WO2013011211A1 - Acoustic device for obtaining heart rate

Info

Publication number: WO2013011211A1
Application number: PCT/FR2012/000295
Authority: WO
Inventors: Claude Desgorces; Dominique Henault
Original assignee: Aptim; Csp Conseil
Priority date: 2011-07-20
Filing date: 2012-07-16
Publication date: 2013-01-24
Also published as: FR2978027B1; FR2978027A1

Abstract

The invention relates to a cardiac monitoring device (1) comprising: a microphone (3), a bracelet (5) arranged to receive the microphone (3), and an electronic processing unit (7) connected to the microphone (3). The bracelet (5) can be fitted to the wrist (13) in such a way that the microphone (3) can be maintained substantially facing a blood vessel (11) and in contact with the skin (9).

Description

Acoustic device for acquiring the heart rhythm

The invention relates to a cardiac monitoring device.

The follow-up of people prone to cardiac disorders, for example the elderly, involves a regular monitoring of their heart rate, even a continuous follow-up. The cost and overcrowding of cardiac monitoring systems are often incompatible with an independent, home-based life of the person.

Cardiac monitoring devices of the electrocardiogram (ECG) type have been miniaturized, and allow such monitoring. However, these systems remain expensive to manufacture and maintain, and have reduced autonomy.

The invention improves the situation.

A cardiac monitoring device comprises a microphone, a bracelet arranged to receive the microphone, an electronic processing unit connected to the microphone, the bracelet being adapted to be fitted to a wrist so that the microphone can be held substantially facing a blood vessel and in contact with the skin.

This device is particularly advantageous, it makes it possible to monitor a heart rhythm and to detect an abnormality therein in an automated manner. The device has high availability, offers improved autonomy, and is composed of inexpensive elements.

Other features and advantages of the invention will appear on examining the detailed description below, and the attached drawings, in which:

FIG. 1 is a general sectional view of the device on the wrist of a person,

FIG. 2 is a diagrammatic sectional view of the device of FIG. 1 on the arm of a person,

FIG. 3 represents a block diagram of the device of FIG. 1,

FIG. 4 is a graphical representation of a signal at the output of the microphone,

FIG. 5 is a graphical representation of a signal at the output of the microphone, before thresholding, FIG. 6 is a graphical representation of a heart rhythm presenting extrasystoles,

FIG. 7 is a graphical representation of an ECG signal,

FIG. 8 is a graphical representation of an ECG signal,

- Figure 9 is a schematic representation of an electronic card.

The attached drawings are essentially of a certain character, and may not only serve to complete the invention, but also contribute to its definition, if any.

As shown in FIG. 1, the cardiac monitoring device 1 comprises a microphone 3, a bracelet 5 and an electronic processing system 7.

The device 1 comprises, here, a battery not shown in Figure 1 to power the various components. The battery is chosen according to the constraints of capacity, charging time, size and weight. The applicant uses, in the example described here, lithium batteries sold by the company "KoKam". The batteries can, depending on the needs, have a capacity between 500 mAh and 2 Ah for an approximate autonomy between 15 and 60 hours.

This battery is controlled by a load control circuit and a control circuit also not shown in FIG. 1. The load control circuit is, in the example described here, a "MAX1555" circuit sold by the company "Maxim Integrated Products, Inc. "which allows charging via a USB port. The charge control circuit may be provided with an end of charge indicator, for example an indicator light. Alternatively, other types of charge control circuit may be used. The control circuit is a linear regulator "MAX8881" sold by the company "Maxim Integrated Products, Inc.", which provides a direct current, of the order of 200 mA here. Alternatively, other types of charge control circuit may be used. The USB port can also be used to program the microcontroller 31 from a computer.

The bracelet 5, shown schematically in Figure 1, is adapted for the wearing of the device 1 wrist 9. The bracelet 5 comprises a strip of flexible material. This band is longer than the circumference of the wrist 9 and width of a few centimeters. This strip is here covered with a fastening system for example self-gripping type "Velcro ®". Alternatively, other types of fastening system may be used. The bracelet 5 can thus be fixed and detached by the user. The bracelet 5 thus allows sufficient clamping so that the microphone 3 does not slip on the skin 9 of the wrist 13, while preserving good blood circulation and therefore the quality of the measurement. Advantageously, the band of the bracelet 5 comprises anti-allergenic materials.

In the mounted state, the microphone 3 is pressed against the skin 9 substantially opposite a blood vessel 11, as shown in FIG. 2. In the example described here, the blood vessel 11 is a radial artery of the wrist 13, 'a person. The choice of the blood vessel 11 facing which the device 1 is mounted is made according to the perceptible pulse, which depends in general on the intensity of the pulse in the vessel 11, the distance between the vessel 11 and the surface of the skin 9, and the space available to place the device 1.

Other parameters may be taken into account. The choice may also take into account the practical use of the device 1 day-to-day, and in particular in relation to continuous use. For example, although the radial artery of the wrist 13 undergoes less intense heart pulsations than the femoral artery of the thigh, the choice of the wrist 13 is motivated by the not very constraining appearance of the wearing of a bracelet 5, the picture of a watch. On the contrary, a device 1 placed near the thigh could be binding for the wearing of clothes and for the practice of walking.

The microphone 3 comprises a support surface 17 which is arranged to come into contact with the skin 9 of the wrist 13. Said surface 17 has an opening 19 for acoustic acquisition. When the device 1 is in place, that is to say that the microphone 3 is pressed against the skin 9, an air pocket 21 is trapped between the skin 9 and a membrane 23 of the microphone 3 at the level of the 19. In the case of open microphones, the surface 17 may be continuous with the membrane 23. The microphone 3 is a low frequency microphone. The microphone 3 may be a micro-dish with a sensitivity of about 58 dB. The microphone 3 may for example be a microphone "KEEG1542TBL-A" sold by the company "Farnell". Alternatively, other types of microphone may be used. Alternatively, the device 1 may comprise a plurality of microphones 3 on a common support. This simplifies the implementation of the bracelet 5 preserving the quality of the measurement.

Alternatively, the device 1 may comprise a visual indicator, for example a diode, activated when receiving a signal from the microphone 3. This allows the person to verify the correct positioning of the microphone 3 during fixation of the bracelet 5.

The point of the inner face of the wrist 13, the radial artery 11 of which is closest, is referred to here as the outcropping point 15. The outcropping point 15 represents the preferred zone of application of the microphone 3. Indeed, when the blood flow passes through and deforms the blood vessel 11, it creates a pulsation or pulse. This pulsation displaces the skin 9 located at the outcropping 15 of the artery 11. The movement of the skin 9 causes a displacement of the air trapped in the air pocket 21. The movement of the air causes a movement of the air the membrane 23 of the microphone 3 is the movement of this membrane 23 which is measured by the device 1 to characterize the pulse.

The processing of the microphone output signal 3 is performed by an electronic processing system or unit 7. The electronic processing unit 7 is, in the example described here, an electrical circuit or an electronic card but it can also be several cards or a dedicated microprocessor system-like system ("SoC" for "System on Chip" or "NoC" for "Network on Chip"). As can be seen in FIG. 1, the electronic card 7 is here supported by the bracelet 5, opposite the microphone 3 with respect to the wrist 13. The electronic card 7 and the microphone 3 are then connected by a cable 4. The electronic card 7 may be located in a box that may itself contain other elements. FIG. 3 shows the schematic organization of a part of the device 1 comprising the electronic card 7.

The electronic card 7 comprises an amplifier 25, an analog / digital converter 27 (ADC), a low-pass filter 29, a microcontroller 31 and a useful signal output 33. The amplifier 25, controlled by the microcontroller 31, amplifies the signal output from the microphone 3. The term amplifier designates, here, an amplification chain, an example of which is shown in FIG. 9. The amplifier 25 comprises an operational amplifier "LM358D Sold by Texas Instruments. Alternatively, other types of amplifiers may be used. The amplifier 25 is adjustable, for example by means of a potentiometer. The output of the amplifier 25 is connected to the analog / digital converter 27.

The analog / digital converter 27 transforms the analog signal received from the amplifier 25. At the output, the analog / digital converter 27 transmits a digital signal that can be used by a digital device. At this point, the output signal of the analog / digital converter 27 comprises all the components of the sound picked up by the microphone 3.

The skeleton facilitates the transmission of many sound waves. Any shock transmitted to the skeleton can be found at the level of the signal picked up by the microphone 3. Thus, although the microphone 3 is pressed against the skin 9, parasitic acoustic waves can reach the microphone 3. On the other hand, despite the stable positioning of the microphone 3 thanks to the bracelet 5, slight movements and for example friction between the microphone 3 and the surface of the skin 9, can generate noise sound waves disturbing the signal transmitted by the microphone 3.

These parasitic sound waves can have an inconvenient amplitude for measuring the pulse. They can saturate the signal of the microphone 3 and at least partially scramble the sounds from the pulse passing through the vessel 11, and make the signal obtained unusable over certain periods. Such a signal is shown in Figure 4. The risk of seeing highly disturbed areas such as Area 37, increases with the movements of the person. On the other hand, the input signal of the microphone 3 is exploitable over a long period when the person is at rest, for example asleep.

The output of the analog / digital converter 27 is connected to the low-pass filter 29. The low-pass filter 29 passes only the low frequencies, for example less than ten hertz. As a variant, this filter 29 may select frequencies below a few tens or hundreds of hertz. This filtering operation is adapted to let only the signal characteristic of sound waves of the pulse and eliminate the vast majority of parasitic sound waves. In the example described here, the low-pass filter 29 is digital, and the output of the low-pass filter 29 is connected to the microcontroller 31. In a variant, the low-pass filter is analog and disposed at the output of the amplifier. 25 and input of the analog / digital converter 27. In another variant, the low-pass filter is a mechanical filter.

The microcontroller 31 may comprise for example a model "7PIC24F J32 GA002" sold by the company "DIGIKEY". The microcontroller 31 may also include a quartz oscillator at 7.3728 MHz referenced "547-6430" and sold by the company "RS". Alternatively, other types of microcontroller may be used.

The microcontroller 31 is connected to a pay and display machine shown in FIG. 9. This time stamp, for example the DSI component 3238 sold by the company "Maxim Integrated Products, Inc.", may enable the microcontroller 31 to associate a time reference with the measurements. Alternatively, other types of time stamp may be used. On the other hand, the microcontroller 31 may be connected to a switch (not shown in FIG. 3) which, when activated by the person, makes it possible to place a time mark in the recording of the measurement. This switch allows, for example, the person to place a time marker in the recording of measurements when he feels particular symptoms such as palpitations or pain. This additional information may be interpreted later by a health professional.

The microcontroller 31 includes an output 32 connected to the amplifier 25 to control it. Thus, if the signal received by the microcontroller 31 has an amplitude lower than a chosen level, the microcontroller 31 activates the amplifier 25. Conversely, if the signal received by the microcontroller 31 has an amplitude greater than another chosen level, that is to say, there is saturation, the microcontroller 31 deactivates the amplification by the amplifier 25. The activation and deactivation levels are set by calibration according to the components used.

As long as the microcontroller 31 receives a signal of amplitude that is too small (respectively too high), it sends an error message of the "signal weak" type (respectively "saturated signal") on an output 33 of the wanted signal. When the amplitude of the signal received by the microcontroller 31 is situated between the two levels described above, the microcontroller 31 verifies that the signal is exploitable and correctly filtered. If it is not the case, it sends an error message of the "disturbed signal" type on the output 33 of useful signal. If the signal is properly amplified and filtered, it can be considered exploitable. The microcontroller 31 then sends a message of the "correct signal" type to the output 33 of useful signal. In this case, the microcontroller 31 applies a signal processing algorithm. An example of a signal usable at the input of the microcontroller 31 is shown in FIG. 5. The maxima 39 and the minimum 41 are clearly identifiable. The division of the signal into periods comprising a maximum 39 and a minimum 41 is possible by selection by thresholding. The thresholds are represented by two horizontal lines 40 in FIG. 5. The values of the thresholds can be determined by prior calibration. The duration 45 of a period (on the abscissa in FIG. 5) is identifiable.

Here, signal processing includes thresholding. Thresholding consists of isolating the input signal, the peaks exceeding a threshold value. In other words, the goal is to keep only the positive extrema 39 of the signal. The temporal positions (represented on the abscissa in FIG. 5) of the positive extrema 39 correspond to the heart beats. The microcontroller 31 transmits on its output 33 of useful signal a signal indicating the time of each beat collected. In the example described here, signal processing consists of storing a sequential window of about 2 seconds of recorded measurements. Then, the recorded sequence is processed by the microcontroller 31 for about 2 milliseconds.

The output signal 33 of useful signal from the microcontroller 31 is transmitted to a computer 43. The computer 43 records the time differences between two successive beats. He deduces the average duration between two heartbeats, for example for a succession of beats over a period of thirty seconds and derives a number of beats per unit time, it provides output. As a variant, the computer 43 transmits at output the gross average, that is to say the average duration between two successive beats. At the output of the device 1, it is therefore possible to obtain either an error message resulting from a signal that is too weak or saturated, or an error message due to an intensity of signals perceived too high, or a message validating the obtaining of the signal and a value corresponding to an average heart rate and / or, for each beat, a time value (absolute or relative).

During its tests, the Applicant has made readings with a tensiometer, simultaneously with measurements with the device 1. The results show a correspondence of measured values when the signal of the device 1 is exploitable.

The device 1 makes it possible to identify abnormal cardiac conditions. Among these conditions, one counts in a nonlimiting way:

- a heart rate lower than 30 beats / minute

- a heart rate exceeding 130 beats / minute

- a cardiac pause of 3 seconds or more, - a salvo of 3 or more extrasystoles.

Quantitative parameters related to the detection of these conditions may vary. The values of these conditions can be preprogrammed in the device 1 and / or be adjusted by a health professional via a computer connected to the device 1. In the event of a cardiac anomaly, the signal obtained after treatment shows abnormalities of regularity in the rhythm of the pulse. The extrasystoles, represented in FIG. 6, are an example of abnormalities that can be identified by means of the device 1. Specific and various configurable alerts can thus be provided in case of obtaining values corresponding to the aforementioned cardiac abnormalities. In Figure 6, at least one of the durations 45 between two extrema 39 (right in the figure) is significantly different from another (left). This is characteristic of an abnormal heart rhythm. The device 1 allows to trigger a specific alert to the detection of such an anomaly.

In addition to the heart rate, the signal picked up by the microphone 3 reveals additional details, especially in the form of the peaks, which can be interpreted by specialists in the field of cardiology. A medical electrocardiograph captures electrical signals emitted by the heart through electrodes. This measurement is therefore not sensitive to the mechanical elasticity of air and human tissues, as opposed to an acoustic measurement. The particular forms obtained on the electrocardiogram (ECG) obtained as a result of the electrocardiograph measurement can be interpreted by a health professional. An example of a "normal" electrocardiogram (ECG) is given by way of example in FIG. 7. In addition to the heart rhythm, the device 1 can output a signal of the type of that of an electrocardiogram (ECG). The precise forms of the acoustic wave make it possible to detect indices that may, for example, be heralding a myocardial infarction. A dome-like aspect 42 of the cardiac pike, called the "Pardée wave", is one of these cues. Such an aspect is given by way of example on an ECG in FIG. 8. The detection of these indices can be automated so as to trigger specific alerts for conditions other than myocardial infarction.

The computer 43 comprises, in the example described here, a useful output 34 which can be connected to a data storage unit. The storage unit here is a micro-SD card. The micro-SD card is removably connected to a micro-SD connector. The micro-SD connector is itself connected to the useful output 34, for example by a serial link. The storage capacity of this type of card is important, for example 2 GB or more. This type of card is standard (for example used in digital cameras) and is easy to use with most current computers.

As a variant, the storage unit can be any type of flash memory, for example the M25P64, having a capacity of at least 8 MB. It is then fixed non-releasably in the device 1, for example soldered on the circuit board. This flash memory is then associated with a USB connector to allow data to be retrieved on a computer. This type of component has the advantage of being robust, having a fast write speed and having a reduced size.

The computer 43 comprises, here, a useful output 34 which can be connected to a communication module not shown. This communication module may be a GPRS type mobile telephone transceiver, which is capable of transmitting data in the form of packets, and establishing a GSM type communication with a rescue service. The communication module could be a 3G or other type of mobile radio transceiver, or any other type of radio transmitter for transferring data. Depending on the detected event, the device 1 can send data via the communication module to the rescue service. Alternatively, the device 1 may also include an emergency button whose activation triggers the sending of an emergency signal via the communication module independently of the pulse measurement. This further increases the security provided by the device 1 by allowing the person to voluntarily trigger an alert even if the electronic card 7 did not activate the communication module. The emergency button can also be coupled to the switch to place a time mark in the measurement record. This makes it possible to analyze a posteriori the possible link between the parameters measured via the microphone 3 at the moment of activation of the emergency button and the incident that led the person to trigger the emergency button.

Alternatively, the computer 43 is remote, that is to say located remote from the microcontroller 31. The useful signal output 33 of the microcontroller 31 can be connected to a short-range communication module. The signal can be transmitted to the computer 43. The computer 43 then comprises an input adapted to receive the signal at the output of the useful signal from the microcontroller 31. The useful output 34 of the computer 43 can be connected to a second communication module. This variant makes it possible to limit the bulk at the location of the pulse pickup, here the bulk of the bracelet 5 at the wrist 13. A separate set of the bracelet 5 comprising the computer 43 and / or a communication module can, for example, be placed in a pocket or belt of the person.

FIG. 9 represents an electronic processing card 7. The electronic processing card 7 here comprises a supply subassembly 52 including the battery, the regulation circuit and the load control circuit, a connector 53 for programming the microcontroller 31 and for recharging, the microcontroller 31, the amplification system 25, a time stamp 50, a connector 51 for a micro-SD card, a connector 54 for the connection via the cable 4 of the microphone 3, a switch 55 for time stamping, a switch on / off 56 of the device 1 and the control LEDs 57 to indicate the end of the load, the reception of a signal by the microphone 3 and the activation state of the device 1.

The cardiac monitoring device 1 may be integrated into a medical surveillance device having other characteristics, for example that described in the patent application FR 10/03211. The medical monitoring device makes it possible in particular to detect falls and to remotely locate the wearer of the device.

The applicant's research has shown that a reading of sixteen measurements per second is a minimum below which the curves that have been extrapolated are unclear. The number of readings per unit of time is adaptable according to the type of anomalies to be detected.

The increase in the number of points specifies the measurement but increases the size of the files and therefore the necessary storage capacity (a measurement representing one byte or eight bits), as well as the energy consumption. As an example, for 256 points per second for 24 hours of measurement, the file weighs about 21 MB. A micro-SD card of 2 GB can therefore contain the measurements of a hundred days.

As a variant, the device may comprise a conventional watch dial or adapted for direct reading of the information at the output 34 of the computer 43. This dial may be arranged in a box that is common to that of the electronic card 7, cf. figure 1.

The invention allows an acoustic acquisition of the heart rate which can be as efficient as an acquisition system of the electrocardiogram (ECG) type. The installation is very simple, inexpensive and not binding for the person. The invention is furthermore adaptable to an existing medical surveillance device, which may furthermore, and without limitation, include a fall sensor, a location device, a transmitter and a wireless receiver for data transmission. On the other hand, the data from the cardiac monitoring device can be stored in memory for a chosen duration, which may allow for example a doctor monitoring the person who wears the device to analyze the evolution of his pulse, or the medical emergency department to have additional data. The cardiac monitoring device of the invention therefore makes it possible to extend and improve medical monitoring and prevention services for many people, while reducing the costs borne by social systems and private health insurance. The health professional may, in addition, adapt itself the type and duration of the information to be memorized, the values of the alarm trigger limits, depending on his patient.

Claims

claims

1. Cardiac monitoring device (1), characterized in that it comprises:

a microphone (3),

a bracelet (5) arranged to receive the microphone (3),

an electronic processing unit (7) connected to the microphone (3),

the bracelet (5) being adapted to be fitted to a wrist (13) so that the microphone (3) can be held substantially facing a blood vessel (1 1) and in contact with the skin (9), and wherein the electronic processing unit (7) comprises an amplification chain (25) and a microcontroller (31) controlling the amplification chain (25).

2. Device according to claim 1, wherein the bracelet (5) is further arranged to receive a computer (43).

3. Device according to claim 2, wherein the computer (43) is connected to a communication module.

4. Device according to one of claims 1 to 3, comprising a plurality of microphones (3).

5. Device according to one of claims 1 to 4, further comprising a data storage unit connected to the output of the electronic processing unit (7).

6. Device according to claim 5, wherein a switch (55) is connected to the electronic processing unit (7) so as to trigger a time stamp in a record of the data storage unit.

7. Device according to one of claims 3 to 6, further comprising an emergency button connected to the communication module for sending an alert signal independently of the electronic processing unit (7).