WO1998047427A1

WO1998047427A1 - Device for sensing respiratory movements

Info

Publication number: WO1998047427A1
Application number: PCT/FR1998/000800
Authority: WO
Inventors: Michel Therin
Original assignee: Nextryte Limited
Priority date: 1997-04-21
Filing date: 1998-04-21
Publication date: 1998-10-29
Also published as: FR2762205A1; CA2287964A1; FR2762205B1; AU7534598A; EP0977511A1

Abstract

The invention concerns a device sensing an infant's respiratory movements which is placed in a child's bed and triggers a local and/or remote alarm signal on sensing that the infant has stopped breathing. The mattress (1) is divided in at least two parts (2, 3), with each of which are associated one or two piezoelectric sensors (4, 5; 6, 7), or any other type of force sensors. All the sensors are functionally connected to an electronic box (8), which comprises circuits combining the signals (S1, S2, S3, S4) coming from the different sensors (4 to 7). The functioning condition of the sensors (4 to 7) is thus detected and indicated by signalling means (10 to 13), thereby reducing any possibility of mistriggering.

Description

Device for detecting respiratory movements.

The present invention relates to a device for detecting respiratory movements, in particular but not exclusively to the respiratory movements of an infant placed in a crib, the device making it possible to detect the respiratory arrest of the infant and then to trigger a local alarm. and / or remotely. More particularly, this device belongs to the type comprising, for the detection of respiratory movements, at least one piezoelectric type sensor, or other force sensor, placed at the level of the mattress of the crib, and functionally connected to a electronic unit processing the signals from one or more sensors and provided with signaling means.

Devices of this kind are already described, for example in the documents GB-A-2192460, EP-A-0514744 and O-A-9603075. In the absence of an analog signal at the output of the or each sensor, these devices trigger an audible and / or light alarm, locally or remotely, the absence of signal at the sensor output being considered as representative of cessation of infant breathing. Such a device is reassuring in principle, in particular to prevent sudden death of the infant. However, it involves risks of untimely tripping if the number of sensors is insufficient, which is the case with the currently known embodiments.

Thus, in the document GB-A-2190460 cited above, a single sensor is placed at the level of the mattress. Inopportune triggers are possible if the infant is standing too far from the sensor, or if this single sensor is subject to technical failure. Document EP-A-0514744 provides a certain improvement, by having two detectors under the mattress, each detector being associated with half a mattress. Thus, the device is assumed to work properly, even if the infant is standing towards one end of the bed. However, this document does not specify how the signals from the detectors are processed.

The document WO-A-9603075 envisages one or more force sensors, such as piezoelectric gauges, but in case of plurality of sensors, this document also does not provide any precision on the mode of processing of the signals coming from these sensors.

The present invention aims to remedy these drawbacks or shortcomings, by providing a device of the type concerned, in which the probability of inadvertent trips is significantly reduced, so as to obtain a device of high reliability.

To this end, in the device for detecting respiratory movements which is the subject of the invention, the mattress is divided into at least two parts, as regards detection, and each part of the mattress is associated with at least one sensor, while that the electronic unit includes circuits which combine the signals from the various sensors so as to detect and report the overall operating state of the sensors.

A satisfactory result is obtained, for example, by dividing the mattress into two parts or "half-mattresses" with each of which are associated two piezoelectric sensors or other force sensors, therefore by providing a total of four sensors. By thus placing two sensors under each part of the mattress, the two sensors operating in principle simultaneously and identically, a particularly reliable "redundant" system is produced. The electronic unit, analyzing the signals from here of the four sensors by logically combining them, makes it possible to know at all times the overall operating state of the mattress, according to a principle which can be as follows: - if the four sensors, or at least three of these sensors are in good condition normal operating, the device is considered to be in the normal state, each half-mattress in this case comprising at least one sensor in operating state; - if only two out of four sensors are in working condition, the device considered as a whole is in degraded operating mode;

- if only one sensor is in working order, the electronic unit triggers an audible and / or light alarm, signaling a technical and not physiological failure, which should be remedied;

- finally, if none of the four sensors delivers a signal, the electronic unit also triggers the alarm, which in the latter case may indicate a detected respiratory arrest.

The device is therefore designed to detect and signal these different situations in a distinctive manner, necessarily triggering the alarm in the last two cases. To this end, according to a particular embodiment of the device which is the subject of the invention, it comprises in its electronic unit:

- separate amplification means for each of the analog signals from the different piezoelectric sensors, or other force sensors;

means for converting the amplified analog signals into logic signals, and for shaping these logic means;

- a first logic circuit with "OR" gate function, combining the logic signals representative of the state different sensors to indicate the normal state of the device or trigger the alarm and, - another logic circuit with door function "OR EXCLUSIVE", combining the logic signals representative of the state of the different sensors to indicate the operating mode degraded, corresponding to the operating state of two out of four sensors.

According to another aspect of the invention, the sensor or sensors associated with each half-mattress are piezoelectric sensors supported by a structure comprising an upper plate, a lower plate, and elastic spacers interposed between the upper plate and the plate lower, the piezoelectric sensor or sensors being mounted on the lower plate while the upper plate is designed to support the corresponding half-mattress. Preferably, each of the structures thus formed is surrounded by a protective envelope. Thanks to these very simple constructive arrangements, the device of the invention is made independent of the mattress, and it provides good protection for the sensors while preventing them from being crushed. An important advantage is thus obtained, compared with known devices, the sensors of which are generally incorporated into the mattresses, and comprise a special mounting between wedges.

In a variant of the invention, the sensor or sensors associated with each half-mattress are resistive force sensors, having a resistance whose ohmic value decreases when an increasing pressure is applied; these force sensors are supported by a structure comprising an upper plate, a lower plate, shims interposed between the upper plate and the lower plate, the force sensor or sensors being mounted on the lower plate while a transmission block d '' efforts, in semi-rigid material, is interposed between the upper plate of the above structure and the or each force sensor. This variant uses resistive sensors which are particularly well suited to the application concerned, said sensors being particularly suitable for detecting movements at slow frequencies, and having a low sensitivity to noise and parasitic vibrations.

In any case, the invention will be better understood with the aid of the following description, with reference to the appended schematic drawing representing, by way of example, embodiments of this device for detecting respiratory movements:

Figure 1 is a block diagram of the detection device according to the present invention, in a first embodiment.

FIG. 2 is a diagram of the electronic circuits of this detection device.

Figure 3 shows the practical mounting of the piezoelectric sensors. Figure 4 is a view similar to Figure 3, but relating to a second embodiment of the object of the invention detection device.

FIG. 5 is a block diagram of the electronic circuits, which can be incorporated into the device of FIG. 4.

In Figure 1, the reference 1 generally designates the mattress of a crib.

The mattress 1 is divided at mid-length, as regards the detection of respiratory movements, into two parts called half-mattresses 2 and 3. The first half-mattress 2 is associated with two piezoelectric sensors 4 and 5. The second half mattress 3 are associated with two other piezoelectric sensors 6 and 7. The four piezoelectric sensors 4 to 7, of a type known per se, are sensitive to the respiratory movements of the infant resting in the bed, each sensor converting the mechanical or acoustic signal, which requests it, into an analog frequency signal SI, S2, S3 and S4 respectively.

The four sensors 4 to 7 are connected to an electronic unit 8, by a set of electrical conductors 9 transmitting the signals SI to S4. The electronic unit 8 processes the signals SI to S4 coming from the various sensors 4 to 7, by combining them logically. This electronic unit 8 comprises various signaling means 10, 11, 12 and 13, of the sound and / or light type, comprising in particular:

- a first indicator light 10 for signaling normal operation;

- a second indicator light 11 for signaling a degraded operation;

- a local audible alarm 12 for signaling a technical failure or respiratory arrest;

- a last indicator light 13 for controlling the power supply. The electronic circuits of the device are shown in FIG. 2. These circuits comprise, at the output of each piezoelectric sensor 4, 5, 6 or 7, a first operational amplifier 14 with large gain followed by a second operational amplifier 15 with big gain. The analog frequency signal SI, S2, S3 or S4 from each sensor 4 to 7 is thus strongly amplified, the analog signal at the output of the second operational amplifier 15 being able to be approximately a thousand times higher than the input signal of the first operational amplifier 14.

The second operational amplifiers 15 have their respective outputs connected, two by two, to two monostable circuits 16 and 17. Each monostable circuit 16 or 17 converts the amplified analog signal, coming from the amplifiers 15, into a logic signal, which is set in formed by a "RC" circuit associated with this monostable circuit, and composed of a potentiometer 18 and a capacitor 19.

Between the first amplifiers 14 and the second amplifiers 15, as well as between the second amplifiers 15 and the two monostable circuits 16 and 17, there are provided respective link capacitors 20 and 21 eliminating the DC component of the signal.

Each monostable circuit 16 or 17 has two outputs, respectively 22, 23 and 24, 25 delivering a logic signal. All outputs 22 to 25 are connected to the same logic circuit 26, with an "OR" gate function, which performs a logic calculation for the display of normal operation as well as for the triggering of the alarm.

An output 27 of the logic circuit 26 is connected, via a switching transistor 28, to a first light-emitting diode 10 constituting here the indicator light for signaling normal operation. The output 27 of the logic circuit 26 is also connected, via another switching transistor 29, to a second light-emitting diode 30, connected in parallel with the local audible alarm 12, for signaling the technical failure or of the general alarm. In parallel with the light-emitting diode 30 and with the local audible alarm 12, a relay 31 is also connected, provided for triggering an additional alarm located at a distance, not shown. The outputs 22, 23, 24 and 25 of the monostable circuits 16 and 17 are also connected to another logic circuit 32, having a gate function "exclusive OR", for the detection of degraded operation, that is to say the situation in which two of the four sensors 4, 5, 6 and 7 are in working condition. The output of logic circuit 32 is connected to the first circuit logic 26. A second output 33 of this logic circuit 26 is connected, by a last switching transistor 34, to a third light-emitting diode 11 here constituting the indicator light for signaling degraded operation.

While FIG. 1 very schematically shows the association of the two pairs of piezoelectric sensors 4, 5 and 6, 7 with the two half-mattresses, respectively 2 and 3, FIG. 3 represents the practical mounting of these sensors 4 to 7.

For the entire bed, two support structures 35 and 36 are provided here, placed respectively under the two half-mattresses 2 and 3. Each support structure 35 or 36 consists of an upper plate 37 made of wood or plywood, d 'a lower plate 38 also made of wood or plywood, and spacers 39 of rubber or elastomer, placed between the two plates 37 and 38. The two piezoelectric sensors 4, 5 or 6, 7 are mounted on the face upper of the lower plate 38, and thus take place between the two plates 37 and 38. Each structure 35 or 36 is surrounded by a sealed plastic envelope or cover, not shown.

FIG. 4 shows, similarly to FIG. 3, another embodiment, further comprising two support structures 35 and 36, associated respectively with two half-mattresses 2 and 3, and each composed of an upper plate 37 and d a lower plate 38, between which shims 39 are interposed. On the upper face of the lower plate 38 of each structure 35 or 36 is mounted a single sensor, respectively 40, 41, which is here a resistance force sensor, whose ohmic value decreases when increasing pressure is applied. In known manner, such a sensor comprises two superposed sheets of polymer, one covered with an array of electrodes, and the other with a semiconductor material, the entire sensor having a thickness less than a millimeter. A force transmission block, respectively 42, 43, of semi-rigid material, is interposed between the upper plate 37 of each structure 35 or 36, and the corresponding force sensor 40 or 41. The two resistive force sensors 40 and 41 are connected, by electrical conductors 44, to an electronic assembly 8 shown very schematically in FIG. 5.

Referring to this FIG. 5, each resistive force sensor 40 or 41 is electrically inserted in a bridge comprising at least one other fixed resistance 45 or 46, the intermediate point of the bridge being connected, by a filtering capacitor respectively 47 or 48 , at the input of an amplification and filter assembly, respectively 49 or 50. The capacitor 47 or 48 transmits only the resistance variations of the associated force sensor 40 or 41 to the amplification and filter assembly corresponding 49 or 50; this assembly 49 or 50 makes it possible, among other things, to filter the parasitic frequencies, by transmitting, for example, only the frequencies between 10 and 60 strokes per minute, which can correspond to respiratory movements.

The respective outputs 51 and 52 of the two amplification and filtering assemblies 49 and 50 are connected to inputs of a microcontroller 53, which includes a clock and reset means. The microcontroller 53 analyzes the signals from the two amplification and filtering assemblies 49 and 50, and translates the movements detected by the two force sensors 40 and 41, considering that if at least one of these two sensors 40 and 41 detects at least one movement during a monitoring cycle (of duration to be defined beforehand), the situation is normal. Conversely, if no movement is detected by all the sensors 40 and 41 during the monitoring cycle, the situation is anyway to be considered as abnormal, that the cause in either an absence of respiratory movements of the infant, or a disconnection or a breakdown of all the sensors 40 and 41.

The microcontroller 53 has several outputs connected to a signaling assembly, here again comprising:

a first indicator light 10, such as a light-emitting diode, the illumination of which indicates a normal situation; a second indicator light 11, such as a light-emitting diode, the illumination of which indicates an abnormal situation (absence of respiratory movements, or simultaneous failure of the two sensors 40 and 41); a third indicator light 13, such as a light-emitting diode, the illumination of which indicates a faulty electrical supply (electric batteries or discharged battery);

a local audible alarm 12, of the buzzer or loudspeaker type, controlled by means of a switching transistor 54, which is triggered at the same time as the second indicator light 11 is lit, and for a predetermined duration, for audibly report any abnormal situation.

The microcontroller 53 is also connected to a safety block 55, which controls, via a switching transistor 56, another sound alarm 57 of the vibrator or speaker type. The security block 55 triggers the audible alarm 57, for a predetermined period, in the event of an electronic failure (in particular blocking of the microcontroller 53). This second audible alarm 57 is also triggered, in redundancy with the first audible alarm 12, when an absence of movement is observed. The audible alarms 12 and 57 can only be stopped by manually actuating the on / off button (not shown) of the device.

It goes without saying that the invention is not limited to the sole embodiments of this device for detecting respiratory movements which have been described above, by way of examples; on the contrary, it embraces all the variants respecting the same principle, the electronic circuits described being in particular replaceable by all equivalents, ensuring the same functions, and the signaling and alarm means also being possible in any suitable form. . Thus, in generalization of the example illustrated by FIG. 5, for any number of sensors, the microcontroller can analyze the signals coming from the amplification and filtering means, by considering as normal the situation according to which all the sensors, or all but one of the sensors detect movement, and as abnormal (therefore triggering an alarm) the situation where a lower number of sensors, or no sensor, detects movement. In the same vein, the field of application of the invention is not limited to the detection of the respiratory movements of an infant, but it extends, more generally, to medical, hospital and geriatric environments.

Claims

1. Device for detecting respiratory movements, in particular respiratory movements of an infant placed in a crib, the device comprising at least one piezoelectric type sensor (4 to 7), or other force sensor ( 40,41), placed at the level of the mattress (1) of the crib, and operatively connected ent to an electronic unit (8) processing the signals coming from or sensors and provided with signaling means (10 to 13), the device making it possible to detect the respiratory arrest of the infant and then to trigger a local and / or remote alarm, characterized in that the mattress (1) is divided into at least two parts (2, 3), as regards detection, and in that each part (2, 3) of the mattress (1) is associated with at least one sensor (4 to 7; 40,41), while the electronic unit (8) comprises circuits (26 , 32; 53) which combine the signals (SI, S2, S3, S4) from the different sensors (4 to 7; 40,41) in a way re to detect and report the overall operating state of the sensors (4 to 7; 40.41).

2. Device for detecting respiratory movements according to claim 1, characterized in that the mattress (1) is divided into two parts or "half-mattress" (2, 3) with each of which are associated two piezoelectric sensors ( 4, 5; 6, 7) or other force sensors.

3. Device for detecting respiratory movements according to claim 2, characterized in that it is designed to detect and signal, separately:

- the normal operating state of the four sensors (4, 5; 6, 7) or of at least three of these sensors, the device then being considered to be in the normal state; - the operating state of only two out of four sensors, the device then being considered to be in degraded operating mode;

- the operating state of a single sensor, or the fact that none of the four sensors (4 to 7) delivers a signal, the device then being considered as technically defective or having detected respiratory arrest, an alarm (12 ) being triggered in this case.

4. Device for detecting respiratory movements according to claim 3, characterized in that the electronic unit (8) comprises:

- separate amplification means (14, 15) of each of the analog signals (SI, S2, S3, S4) from the different piezoelectric sensors (4, 5; 6, 7), or other force sensors;

means for converting (16, 17) the amplified analog signals into logic signals, and for shaping (in 18, 19) these logic signals; - a first logic circuit (26) with an "OR" gate function, combining the logic signals representing the state of the various sensors (4, 5, 6, 7) to indicate the normal state of the device or trigger the alarm ( 12), and, - another logic circuit (32) with "EXCLUSIVE" gate function, combining the logic signals representative of the state of the various sensors (4, 5; 6, 7) to indicate the degraded operating mode , corresponding to the operating state of two out of four sensors.

5. Device for detecting respiratory movements according to claim 4, characterized in that the means for converting the logic signals are constituted by monostable circuits (16, 17), the associated shaping means being constituted by a circuit " RC "(18, 19).

6. Device for detecting respiratory movements according to claim 4 or 5, characterized in that the first logic circuit (26) has an output (27) connected, via a switching transistor (29), to a local audible alarm (12), and to a relay (31) connected in parallel with the local audible alarm (12) provided for triggering an additional remote alarm.

7. Device for detecting respiratory movements according to claim 1, characterized in that the electronic unit (8) comprises:

- amplification and filtering means

(49, 50) of each of the signals from the various sensors (40, 41), - a microcontroller (53) to the inputs of which the outputs (51, 52) of the amplification and filtering means (49, 50) are connected , the microcontroller (53) analyzing the signals from said means (49, 50), considering as normal the situation according to which all the sensors (40, 41), or all the sensors except one, detect a movement, and as abnormal the situation where a lower number of sensors, or no sensor, detects a movement, an alarm (11, 12) is then triggered.

8. Device for detecting respiratory movements according to claim 7, characterized in that the microcontroller (53) is connected to a safety block (55), which controls an alarm (57) in the event of an electronic failure, in particular blocking of the microcontroller

(53), the alarm (57) also being triggered, in redundancy with the aforementioned alarm (11, 12), when an absence of movement is observed.

9. Device for detecting respiratory movements according to any one of claims 1 to 8, characterized in that the piezoelectric sensor or sensors (4 to 7), or other force sensors (40, 41), associated with each half-mattress (2, 3), are supported by a structure (35 , 36) comprising an upper plate (37), a lower plate (38) and elastic spacers or shims (39) interposed between the upper plate (37) and the lower plate (38), the sensors (4 to 7; 40, 41) being mounted on the lower plate (38) while the upper plate (37) is provided to support the corresponding half-mattress (2, 3).

10. Device for detecting respiratory movements according to claim 9, characterized in that each aforementioned structure (35, 36) is surrounded by a protective envelope.

11. Device for detecting respiratory movements according to any one of claims 1 to 10, characterized in that the sensor or sensors associated with each half-mattress (2, 3) are resistive force sensors (40, 41) , having a resistance whose ohmic value decreases when an increasing pressure is applied.

12. Device for detecting respiratory movements according to all of claims 9 and 11, characterized in that a force transmission block (42, 43), made of semi-rigid material, is interposed between the upper plate ( 37) of the aforementioned structure (35, 36) and the or each force sensor (40, 41).