US20200085328A1 - Device for Monitoring of Patient's Vital Signs - Google Patents

Abstract

The subject of the invention is a device for monitoring patient's vital functions, in particular for measuring respiratory and heart rate. This is achieved by using a piezoelectric transducer which also forms with measuring electrode a measuring capacitor. In addition, a comparator capacitor is used to increase resistance to changes in the measuring conditions.

Description

TECHNICAL FIELD
• The invention relates to a device for monitoring patient's vital functions such as respiratory and heart rate and changes or arrhythmia thereof.
BACKGROUND OF THE INVENTION
• Various devices for monitoring various vital functions are known in the art. These monitoring devices are used especially in hospitals, mostly in intensive care units, but also in aftercare departments or in nursing homes. Devices are known where there is no need for a direct connection with the patient, which facilitates patient care, as there is no need for patient's cooperation. The direct contact with the patient means various types of for example adhesive sensors or sensors that are inserted into the patient's body.
• Majority of the known devices consist of a pad which incorporates one or more sensors of different types. These sensors can detect a change in force applied to the pad, for example by means of various force sensors with offset measurement, strain gauges or sensors employing piezoelectric effect. Furthermore, the sensors can also detect vibrations of the bed-deck caused by the patient, for example, by using various MEMS (micro-electromechanical sensor) sensors. The pad is placed under the area where the patient is located, usually under the mattress.
• Device employing appropriately configured strain gauges is described in U.S. Pat. No. 7,699,784. The disadvantage of this solution is that there is often an unwanted reaction to the surrounding forces, due to the configuration of the strain gauges so that the patient's breathing and heartbeat can be recorded.
• Devices employing the principle of direct piezoelectric effect are utilized because of their low price and simplicity in measuring high-frequency vital functions, such as heartbeat. An example of such device is disclosed in U.S. Pat. No. 6,984,207. However, these devices are not suitable for measuring low-frequency vital functions, such as breathing.
• For measuring low-frequency vital functions, sensors for measuring offset are used, for example, capacity sensors utilizing capacity changes due to change in the size of the air gap between the electrodes, as disclosed, for example, in patent application WO2006131855.
• The device can also be as disclosed in patent application WO2010080794 where the pad is filled with fluid, and the pressure sensor senses changes in the pressure caused by breathing and patient's pulse. The problem with this solution is in the production complexity of the special pad filled with liquid.
• The device can also employ the video signal evaluation principle as disclosed so in application WO2013027027, where it is possible to evaluate some vital functions on the basis of the light intensity ratio of two different wavelengths reflected from the patients skin. However, this principle is inaccurate and very difficult to perform in poor lighting conditions.
• The device can also be formed by mattresses into which the sensor is inserted, as disclosed in U.S. Pat. No. 7,652,581 However, this method is disadvantageous due to the high price of the mattress adapted for this purpose.
• Indirect measurement of the patient's vital functions raises sensor accuracy requirements so that they are able to respond also to minor changes caused by breathing or patient's heartbeat and at the same time so that they are not disturbed by undesirable external forces, Meeting these requirements can be achieved by using a combination of sensors, which increases the cost of this device. This problem is partially solved by patent application CZ2013-781, which utilizes a sensor consisting of three conductive electrodes, where one electrode is a piezoelectric sensor and a second electrode together with a third electrode forms a capacity sensor. However, this solution still has high production costs, mechanical complexity and insufficient precision. The disadvantage of this device is also that the piezoelectric sensor is made of a mixture of PolyVinilDene Fluoride and Polyethylene terephthalate material, such sensor has a number of drawbacks in the said application of measuring patient's vital functions. Above all, this material is insufficiently stiff, resulting in the need to regulate the forces applied on the sensor with a rigid, stiffer cover. Furthermore, this sensor needs to be supported from one side by a spring to avoid excessive vibration. The piezoelectric sensor also has a disadvantage in the electromechanical properties of used material, with an elongation of 1% there is a charge in the order of Coulomb units which does not allow sufficient accuracy of either measuring vital functions, such as heartbeat and breathing, or detecting weaker signals such as peristaltic body manifestations.
SUMMARY OF THE INVENTION
• The abovementioned drawbacks are removed by a device for monitoring patient's vital functions comprising a computing unit and a piezoelectric transducer. The advantage lies in the fact that it further comprises a measuring electrode coupled to a board forming a measuring capacitor together with a piezoelectric transducer. The piezoelectric transducer and the measuring capacitor are electrically connected to the computing unit. The piezoelectric transducer is deformable and is propped against the board on at least two places so that a flexible part of the piezoelectric transducer is located between these places. The place for the bent portion of the piezoelectric transducer is achieved, for example, by the saucer-type shape of the piezoelectric transducer or by placing the piezoelectric transducer on the elevated place of the board or through the hole in the board. This advantage is utilized for mechanical simplification of the design and simultaneously for reduction of the failure rate.
• Preferably it is utilized that the piezoelectric transducer comprises a first electrode and a second electrode and a piezoelectric element formed by piezoelectric material located therebetween. The first electrode and the second electrode are electrically connected with the computing unit. In a preferred embodiment, the piezoelectric element is formed by piezoceramics.
• Preferably it is utilized that the second electrode has a circular shape.
• Preferably it is utilized that the measuring electrode forms together with the first electrode or the second electrode the measuring capacitor.
• Preferably it is utilized that it further comprises a printed circuit board. The computing unit, the piezoelectric transducer and the measuring capacitor are located on the printed circuit board.
• Preferably it is utilized that the second electrode or the first electrode is on two places of the perimeter of the area adjoining the printed circuit board attached so that each attachment allows the deformation of the piezoelectric transducer.
• Preferably it is utilized that it further includes a comparator capacitor. The comparator capacitor is electrically connected with the computing unit.
• Preferably it is utilized that the comparator capacitor comprises a first comparator electrode and a second comparator electrode. The first comparator electrode and the second comparator electrode are electrically connected with the computing unit.
• Preferably it is utilized that it further includes a sampling capacitor. The sampling capacitor is electrically connected with the computing unit.
• Preferably it is utilized that it further includes a shielding electrode of the measuring capacitor. The shielding electrode of the measuring capacitor is electrically connected with the computing unit. The shielding electrode of the measuring capacitor has the same electrical potential as the measuring electrode. In a preferred embodiment, it also includes a shielding electrode of the comparator capacitor. The shielding electrode of the measuring capacitor is electrically connected to the computing unit. The shielding electrode of the comparator capacitor has the same electrical potential as the first comparator electrode or the second comparator electrode.
• Preferably it is utilized that it further comprises the printed circuit board. The shielding electrode of the measuring capacitor, the shielding electrode of the comparator capacitor, the comparator capacitor and the sampling capacitor are located on the printed circuit board.
• It is preferably utilized that the shielding electrode of the measuring capacitor is located opposite of the measuring electrode and the shielding electrode of the comparator capacitor is located opposite of the first comparator electrode or the second comparator electrode.
EXEMPLARY EMBODIMENT OF THE INVENTION
• An exemplary embodiment of the invention is adevice21 for monitoring patient's vital functions according toFIG. 1,FIG. 2 andFIG. 3 comprising apiezoelectric transducer8, a comparator capacitor9, a printedcircuit board7, a plating3 and acomputing unit10. The plating3 may be, for example, of copper. Thecomputing unit10, according to the preferred embodiment, consists of a single processor, but may also consist of other computing parts communicating with each other by wire or wirelessly.
• Thepiezoelectric transducer8 utilized here for the purpose of measuring vital functions is a component for generating sound, namely an electro-acoustic transducer used in watches, as a siren or as a buzzer. The piezoelectric transducer has suitable mechanical-deformative properties for measuring vital functions, which means that springs and additional members transferring their deformations caused by movements associated with patient's vital functions to the measuring element are not necessary in comparison with prior art devices, thus achieving low production costs, higher measuring accuracy, and simplicity of theentire device21. A semiconductor component and a circuit utilized for measuring capacity in touchscreen displays (charge transfer technology/method) are utilized in measuring capacity with this component and another measuring (static) electrode4. A specific exemplary embodiment is described below.
• In the exemplary embodiment, thedevice21 is on the side of thepiezoelectric transducer8 covered by, for example, a plastic diaphragm which protects thedevice21 against water and dust and at the same time also removes the mechanical resonance oscillation of thedevice21. Thedevice21 is on the side opposite of thepiezoelectric transducer8 covered by for example plastic foil which ensures the minimum height of theentire device21. The plastic film may be replaced by any flexible or movable cover which ensures the transfer of forces to thepiezoelectric transducer8 without its stiffness significantly affecting the resulting force being transmitted to thepiezoelectric transducer8. Thedevice21 for monitoring patient's vital functions may be adapted for insertion into the pad. The pad can be stored, for example, between the mattress and the bed frame, in the mattress or between the mattress and the patient's body. The device may also be adapted for a direct placement on the bed frame and for detachable locking, for example, with a snap fastener.
• Thepiezoelectric transducer8 consists of thepiezoelectric element1 from piezoceramics, thefirst electrode25 and thesecond electrode2. Piezoceramics are for example piezoceramic materials based on lead zirconate titanate [Pb[Zr_xTi_1-x]O₃with 0≤x≤1] or sodium bismuth titanate [NaBi(TiO₃)₂] or other piezoceramic material. By using such material, the required electromechanical properties are achieved, namely generation of charge in range of 130-930 pC/N. Thepiezoelectric element1 is located between thefirst electrode25, for example, from silver, optionally from alloys with similar electrical properties, and thesecond electrode2. Thepiezoelectric transducer8 may have different shapes, such as a circle, a triangle, square, or other shapes. A preferred shape is the circular shape, which ensures the most uniform decomposition of forces. The shape of thepiezoelectric transducer8 is usually a circle delimited in its height dimension by two parallel planes. Preferably, form modification of thepiezoelectric transducer8 can be utilized, when its center is pressed in the direction of axis perpendicular to one of the delimiting planes and a board-like shape emerges, where the center is located in one plane and in parallel plane lie the borders of thepiezoelectric transducer8. The board-like shape is best illustrated by the shape of the second electrode2 (or the entire piezoelectric transducer8) inFIG. 2. Thesecond electrode2 may be made of brass, aluminum, copper or another metallic material. The locations of the electrodes are interchangeable, it is essential that thepiezoelectric element8 is positioned in the middle between them. Thesecond electrode2 may have a circular or optionally board, like shape. Alternatively, the second electrode may have the shape of ellipse, polygon, most frequently of rectangle, square, or another shape. Shape of thesecond electrode2 is preferably derived from the shape of thepiezoelectric transducer8. Thesecond electrode2 is flat and its surface is in a rest position approximately parallel to thepiezoelectric element1. Thesecond electrode2 is located on the plating3 for electrical connection with the ground. This creates a firm connection with the printedcircuit board7. Thesecond electrode2 is connected at least in two places to cause the required deformation of thepiezoelectric transducer8. These two places may be located, for example, opposite of each other on the opposite sides of the length of thepiezoelectric transducer8. In an alternative embodiment, the attachment can be provided so that that thefirst electrode25 is located on the plating3 and thereby thepiezoelectric transducer8 is connected with the printedcircuit board7. In a preferred embodiment, thesecond electrode2 is connected in at least three places adjoining the printedcircuit board7 to provide greater stability and better course of deformation of thepiezoelectric transducer8. Preferably, these places are in the piezoelectric transducer with circular shape positioned so that they create a triangle when connected. Alternatively, thepiezoelectric transducer8 may be connected to any fixed board in this way, but by connecting to the printedcircuit board7, the dimensions of theentire device21 are minimized. The measuringcapacitor23 consists of thesecond electrode2 and the measuring electrode4. The measuring electrode4 is connected with the printedcircuit board7 and forms electrode with higher electrical potential. The dielectric of the measuringcapacitor23 is formed by an air gap. On the opposite side of the printedcircuit board7 opposite of the measuring electrode4 there is the shieldingelectrode6 of the measuringcapacitor23. The shieldingelectrode6 of the measuringcapacitor23 has the same electrical potential as the measuring electrode4 and together they can form a shieldingcapacitor24 which provides resistance to external influences for example by the approximation of metal material. In some cases, two or morepiezoelectric transducers8 may be located on onecircuit board7.
• The comparator capacitor9 consists of thefirst comparator electrode26, thefirst comparator electrode26 can be made, for example, of brass, aluminum, copper. Thefirst comparator electrode26 is located on the plating3 for electrical connection with the ground. The comparator capacitor9 further consists of a second comparator electrode5. The second comparator electrode5 is located on the printedcircuit board7 and forms an electrode with higher electrical potential: The dielectric of the comparator capacitor9 is formed by an air gap. On the opposite side of the printedcircuit board7 opposite of the second comparator electrode5 is located the shieldingelectrode27 of the comparator capacitor9. The shieldingelectrode27 of the comparator capacitor9 has the same electrical potential as the comparator electrode5 and together they can form a shieldingcapacitor24 which provides resistance to external influences for example by the approximation of metal material.
• Thecomputing unit10 combines piezoelectric voltage measurement and capacity measurement functions, for example, by means of charge transfer technology.Piezoelectric element1 is connected to thecomputing unit10 through a charge amplifier. Furthermore, the measuringcapacitor23, the comparator capacitor9, the shieldingcapacitor24 and thesampling capacitor11 are connected to thecomputing unit10. The use of the measuringcapacitor23 and the comparator capacitor9 causes resistance to changes in the measuring conditions such as temperature or humidity.
• Furthermore, a method for monitoring patient's vital functions according to the above-mentioned exemplary embodiment is described. Heartbeat, breath and other vital functions of the patient, for example peristalsis, generate forces transmitted to thedevice21 for monitoring patient's vital functions. With respect to the construction of thedevice21, it is ensured that the vital functions of the patient are measurable without the need for permanent connection of thedevice21 with the patient's body, for example by means of gluing or implanting. Thedevice21 is capable of measuring patent's vital functions in contact with the skin of the patient, but also in contact with patient's clothing, mediated through the mattress on which the patient is placed, or through the pad in which thedevice21 for monitoring vital functions may be located. The measuringcapacitor23 and the comparator capacitor9 are used to measure slowly changing forces generated by, for example, breathing. During breathing, due to the applied forces, deflection of the central portion of the second electrode2 (and therefore to the entire piezoelectric transducer8) occurs, and thus also change in the air gap between thesecond electrode2 and the measuring electrode4. Due to the construction where thepiezoelectric transducer8 is attached to the board by one of the electrodes, a non-mediated deflection of thepiezoelectric transducer8 without the need for additional force transmitting components is enabled. The size of the air gap between thefirst comparator electrode26 and the second comparator electrode5 is independent of the action of the forces. The change in the capacity of the measuringcapacitor23 is dependent both on the varying air gap size and on the change of permittivity of the air gap. The change in the capacity of the comparator capacitor9 is dependent only on change in permittivity of the air gap. The capacity of the measuringcapacitor23 and the capacity of the comparator capacitor9 ratio will remove the dependence of the capacitance change on dielectric permittivity and thereby the independence of changing the measuring conditions.
• Capacity changes are evaluated for example by charge transfer technology. The charge transfer technology operates on the principle of charging the capacitor and subsequent transfer of the accumulated charge into thesampling capacitor11, wherein the number of accumulated charge transfers into the sampling capacitor is counted, until the voltage at thesampling capacitor11 reaches the same value as the stable reference voltage. It is clear to a person skilled in the art that other methods of measuring capacity can be utilized, for example, the resonance method. In order to measure fast-changing forces caused for example by pulse, a direct piezoelectric effect of the piezoelectric material is used, where by deformation of the piezoelectric material due to external forces, a charge which is through the charge amplifier transferred to thecomputing unit10 is generated where the voltage is evaluated. The output data are then transmitted via thedata wire22 to thecontrol unit20. Thecomputing unit10 can be provided as a microprocessor, its location on the printedcircuit board7 ensures a protection of the signal because the distance of the transmitted non-digital signal is very small.
• Further, a method for communication of the measuring elements A₁to A_N13,14,15 which may be devices for monitoring vital functions of a patient21 or sensors of other type according toFIG. 4 is described. The pad contains a plurality of measuring elements A₁to A_N13,14,15 connected by at least onetrigger wire12 with thecontrol unit20. The measurement elements A₂through A_N-1are connected by thedata wires22 with the adjacent measuring elements and the measuring elements A₁and A_N13,15 are connected by thedata wire22 with the adjacent element. The measuringelement A₁13 is connected by the data wire also with thecontrol unit20. By connecting the measuring elements A₁to A_N13,14,15 by thedata wires22, a serial data connection of these measuring elements A₁to A_N13,14,15, is established, resulting in a reduction in the required amount of cableway. Thetrigger wire12 is connected to thetrigger19, task of which is to transmit the signal for initiation of the measurement and for transmission of the measured information, Upon receipt of the signal from thetrigger19, the data message from each measuring element A_Kis sent through thedata wire22 to the measuring element A_K-1which subsequently sends it through the data wire to the measuring element A_K-2, this way the data message is sent through thedata wires22 to the measuringelement A₁13 from where it is sent through thedata wire22 to thecontrol unit20, the transfer process is repeated until the data message from theA_N15 is received in thecontrol unit20. K takes values frominterval 1 to N. The data messages are sent from all measuring elements A₁to A_N13,14,15 simultaneously, so that the data message from the measuringelement A₁13 arrives first, then the data message from the measuringelement A₂14 arrives and finally the data message from the measuringelement A_N15 arrives. The method described above describes only one branch of the measuringelement A₁13, the measuringelement A₂14 to the measuringelement A_N15, there can be more of these branches connected to thecontrol unit20 as, for example, inFIG. 4, branch B, with measuringelement B₁16, measuringelement B₂17 to measuringelement B_N18.
LIST OF REFERENCE SIGNS
• 1—piezoelectric element
• 2—second electrode
• 3—plating
• 4—measuring electrode
• 5—second comparator electrode
• 6—shielding electrode of measuring capacitor
• 7—printed circuit board)
• 8—piezoelectric transducer
• 9—comparator capacitor
• 10—computing unit
• 11—sampling capacitor
• 12—trigger wire
• 13—measuring element A₁
• 14—measuring element A₂
• 15—measuring element A_N
• 16—measuring element B₁
• 17—measuring element B₂
• 18—measuring element B_N
• 19—trigger
• 20—control unit
• 21—device for monitoring patient's vital functions
• 22—data wire
• 23—measuring capacitor
• 24—shielding capacitor
• 25—first electrode
• 26—first comparator electrode
• 27—shielding electrode of comparator capacitor

Claims (12)

1. A device for monitoring patient's vital functions comprising a computing unit, a piezoelectric transducer, a measuring electrode, forming together with the piezoelectric transducer a measuring capacitor, wherein the piezoelectric transducer and the measuring capacitor are electrically connected with the computing unit, wherein the measuring electrode is connected to a board, wherein the piezoelectric transducer is propped against the board, on which the measuring electrode is connected, in least at two positions, wherein between the at least two locations is located a flexible portion of the piezoelectric transducer.

2. The device for monitoring patient's vital functions according toclaim 1, wherein the piezoelectric transducer comprises a first electrode and a second electrode and a piezoelectric element positioned between the first and second electrodes formed by piezoelectric material, wherein the first electrode and the second electrode are electrically connected with the computing unit.

3. The device for monitoring patient's vital functions according toclaim 2 wherein the piezoelectric element is formed by piezoceramics.

4. The device for monitoring patient's vital functions according toclaim 2, wherein the measuring electrode forms together with the first electrode or the second electrode the measuring capacitor.

5. The device for monitoring patient's vital functions according toclaim 1 wherein the board is a printed circuit board on which the computing unit, the piezoelectric transducer and the measuring capacitor are located.

6. The device for monitoring patient's vital functions according toclaim 4 wherein the second electrode or the first electrode is in three places of the perimeter of an area of the printed circuit board attached so that each attachment enables deformation of the piezoelectric transducer.

7. The device for monitoring patient's vital functions according toclaim 1 further comprising a comparator capacitor which is electrically connected with the computing unit.

8. The device for monitoring patient's vital functions according toclaim 7 wherein the comparator capacitor comprises a first comparator electrode and a second comparator electrode, wherein the first comparator electrode and the second comparator electrode are electrically connected with the computing unit.

9. The device for monitoring patient's vital functions according toclaim 1 further comprising a sampling capacitor which is electrically connected with the computing unit.

10. The device for monitoring patient's vital functions according toclaim 8 further comprising a shielding electrode of the measuring capacitor electrically connected with the computing unit and having the same electrical potential as the measuring electrode and/or a shielding electrode of the comparator capacitor electrically connected with the computing unit which has the same electrical potential as the first comparator electrode or the second comparator electrode.

11. The device for monitoring patient's vital functions according toclaim 10 wherein on the printed circuit board is further located any element chosen from the group of the shielding electrode of the measuring capacitor, shielding electrode of the comparator capacitor, the comparator capacitor and the sampling capacitor.

12. The device for monitoring patient's vital functions according toclaim 10 wherein the shielding electrode of the measuring capacitor is located opposite of the measuring electrode and the shielding electrode of the comparator capacitor is located opposite of the first comparator electrode or the second comparator electrode.

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