Device for contactless monitoring of patient's vital signs

Device for contactless monitoring of a patient's vital signs in the form of a measuring mat comprising at least one measuring element. The measuring element comprises a piezoelectric sensor with a first and a second conductive electrode and a piezoelectric element. Near the piezoelectric sensor is a third conductive electrode. The exertion of a mechanical force on the cover of the measuring element results in a change in the distance between at least one of the electrodes of the piezoelectric sensor and the third conductive electrode. This change in distance is expressed as a difference in the detected parameter corresponding to a change in the patient's vital signs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application, filed under 35 USC 371, is a United States National Stage Application of International Application No. PCT/CZ2014/000112, filed Oct. 8, 2014, which claims priority to CZ Application No. PV 2013-781, filed on Oct. 8, 2013, the disclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The invention is a device for monitoring a patient's vital signs. The patient's respiratory and pulse rate is measured using a measuring mat with one or more built-in measuring members. Each of these measuring members consists of a unique sensor which senses the mechanical action of forces on the mat resulting from the patient's breathing and pulse.

TECHNICAL BACKGROUND

Current art offers a great number of devices for monitoring a patient's vital signs. These monitors are regularly used in many hospitals, primarily in intensive care units. Thanks to modern technologies a patient doesn't have to be connected to a device by any cables and there is no longer a necessity of a patient and hospital personnel to cooperate for the successful monitoring of the patient's vital signs. These contactless monitoring systems can also be used in aftercare departments or nursing homes.

Most of these modern, but no longer overly unique, devices are based on a similar principle. The main component of the measuring device is a mat with one or more integrated sensors. These sensors may be of different types. One of the types is a sensor which senses changes in forces acting on the mat. Another method uses accelerometers measuring the vibrations of the mattress platform in order to measure vital signs. It is also possible to use, for example, piezoelectric sensors and also additional capacitive sensors. The mat is located under the location where the patient is recumbent generally under the mattress.

Many embodiments of mats are known, i.e. in patent application WO 2010080794 the mat is filled with a fluid and a pressure sensor senses changes in pressure caused by the patient's breath and pulse rate. The problem of the solution is the complexity of manufacturing a special mat filled with fluid.

One interesting solution is an evaluation of vital signs on the basis of an analysis of video signal. Some vital signs are calculated on the basis of the ratio of the intensity of light of two different wavelengths reflected from the patient's skin. Such a solution is described for example in patent application WO 2013027027. But this method is not very accurate and it is also difficult to make a measurement using this method under poor lighting conditions.

There are also known solutions where the measuring member is integrated in the mattress. We can see such a solution for example in U.S. Pat. No. 7,652,581. One disadvantage may be the price of the mattress adapted for this purpose.

Strain gauges, the main role of which is evaluation of a patient's weight, may also be used for the implementation of a measuring device. If they are correctly adapted they can also record the vibrations caused by breathing and heartbeat. But highly sensitive strain gauges are necessary for this method of measurement and they may be prone to interference and can often react to ambient forces which are not a subject of interest. We can see such a solution in U.S. Pat. No. 7,699,784.

As a result of the drop in the purchasing price of piezoelectric sensors they are used in many branches, from medical devices, uses in the army or for building security. Piezoelectric sensors are used in medical devices, for example in plethysmography, measuring of blood pressure, measuring tremors, the movement of a patient or measuring the pulse rate. Piezoelectric sensors work on the principle that they react to deformation by generating measurable electrical voltage. They can be used to measure force, flexion, extension and other values. The problem is that a piezoelectric sensor reacts very badly to low frequency changes such as respiratory frequency. We can find the use of these piezoelectric sensors for contactless monitoring of vital signs in U.S. Pat. No. 6,984,207, for example.

Capacitive sensors are often a part of medical equipment, and their advantage is that compared to piezoelectric sensors they are also sensitive to low frequency mechanical changes which are result of applied forces. For this reason they have a wide range of uses, from measuring the level of liquid, measuring position or measuring force, which can be used to measure a patient's respiration, for example. The use of these capacitive sensors is described for example in patent application WO 2006131855.

Contactless measurement of a patient's vital signs may be performed using inductive sensors that measure the bio-impedance of the patient, on the basis of which the patient's physiological expressions are evaluated. Such an embodiment is given, for example, in patent application WO 2006129212.

A modern trend in medicine is lower intervention in the patient's daily activities and so contactless measurement of the patient's vital signs is more attractive. Most often embodiment of the present measurement of vital signs is a mat consisting of one or more types of sensors. The sensors are for example piezoelectric, pressure or capacitive sensors. These sensors differ in terms of their ability to react to mechanical changes resulting from the patient's vital signs. For example a piezoelectric sensor is distinguished by the fact that it reacts well to dynamic changes which can be caused for example by the patient's pulse. Capacitive sensors react well to slow changes such as a patient's respiration. The problem given by making contactless equipment for the measurement of a patient's vital signs is that the sensors must be sensitive to even slight changes caused mainly by the breathing and pulse of the patient and they must not be disrupted by ambient forces. This can be achieved through a combination of different types of sensors but it leads to very expensive measuring devices.

SUMMARY OF INVENTION

Mentioned problems are resolved by a device for contactless monitoring of the patient's vital signs including a measuring mat including one or more measuring members. One part of the measuring member is a piezoelectric sensor including a first and a second conductive electrode and a piezoelectric element. This is a unique solution because it contains a third conductive electrode proximate to the piezoelectric sensor. If the mechanical force is applied on the cover of the measuring member the distance between at least one of the electrodes of the piezoelectric sensor and the third conductive electrode changes. This solution is advantageous because only one type of a measuring element modified in this way is used for the contactless monitoring of the patient's vital signs.

Application of a mechanical force on the cover caused by the patient's vital signs results the deflection of a metal strip. The arrangement of the metal strip, cover and supporting body is approximately symmetrical, which means that the same perpendicular force can exert anywhere on the entire surface of the cover, and it is expressed as the same deflection of the metal strip. In an advantageous embodiment the measuring member includes a flexible member which exerts a mechanical force on the piezoelectric sensor via in the direction to the metal strip. An alternative embodiment contains the piezoelectric sensor mechanically fixed to the metal strip.

In an advantageous embodiment the device for contactless monitoring of a patient's vital signs is able to measure the change in position or presence of a patient.

DETAILED DESCRIPTION OF DRAWINGS

FIG. 1andFIG. 2show two different embodiments of the measuring mat1for contactless measurement of a patient's vital signs. Using this measuring mat1it is possible to perform contactless measurement of a patient's vital signs. The mat1can be inserted between the patient support of a bed and the mattress, in an armchair, a chair or between any backrest and patient's body. The measuring mat1may be adapted in both ways by changing its dimensions and the layout of measuring members2. One part of the measuring mat1is a cable3for power supply or signal transmission. This cable3may also be adapted for data communication and the measuring mat1may also be expanded to include a module for wi-fi, Bluetooth® or other means of wireless communication for data communication. For easy handling and cleaning the measuring mat1cover is made of flexible waterproof material such as Gore-Tex® textile, plastic sheeting or other light, waterproof materials.

FIG. 3shows a measuring member2including a cover4, supporting body5and metal strip6against which a piezoelectric sensor7is pressed from below. The metal strip6flexes when a vertical force is applied on the cover4. The supporting body5is shaped so that the metal strip6fits precisely into part of the supporting body5and also so that there is protection for the main part of the measuring member2including the sensor for monitoring slow changes, for example a capacitive sensor8and sensor for monitoring rapid changes, for example a piezoelectric sensor7. The cover4presses in several places against the metal strip6and in this way it transfers to the metal strip6the force applied on it from the surroundings. One part of the measuring member2is a cable3serving for example for power supply and signal transfer.

FIG. 4shows a piezoelectric sensor7including a first conductive electrode9and a second conductive electrode10. An piezoelectric element (not in figure) is placed between these conductive electrodes9,10. The construction of such piezoelectric sensors7is generally known, one example may be the DT Series piezoelectric sensor7made by the company Measurement Specialties. The piezoelectric sensor7attached to a circuit board, for example a printed circuit board12. One part of the printed circuit board12is a third conductive electrode13near the piezoelectric sensor7. Along with one of the conductive electrodes9,10of the piezoelectric sensor7the third conductive electrode13forms a capacitor the parameters of which change depending on the distance between at least one of the conductive electrodes9,10of the piezoelectric sensor7and third conductive electrode13. First conductor14, second conductor15and third conductor16serve to connect the electrodes9,10,13with the processing unit17.

FIG. 5toFIG. 8show a detailed description of the principle according to the invention.FIG. 5shows a cross-section of the measuring member2in the first position, where no external force is applied on the cover4. It shows the cover4, supporting body5of the measuring element, metal strip6, first rail18and second rail19, which the metal strip6is put on. The piezoelectric sensor7presses against approximately the centre of the metal strip6and is connected at the other end to the circuit board12. One part of the measuring member2, as inFIG. 5, may be a flexible member20which interacts with the piezoelectric sensor7via a force in the direction to the metal strip6. This flexible member20may be a spring. In an alternative embodiment the piezoelectric sensor is fixed to the metal strip6and a spring doesn't have to be a part of the measuring member2.

FIG. 6shows a cross-section of the measuring member2subjected to a perpendicular force on the cover4. The transmission of this perpendicular force independent of the place of exerting occurs via two points of contact between the cover4and the metal strip6. So the applying of a perpendicular force on the cover4expressed by a deflection of the metal strip6at a place near the piezoelectric sensor7from its original position. The fact that the technical arrangement of the metal strip6, cover4and supporting body5is approximately symmetrical means that the same perpendicular force can act anywhere on the entire surface of the cover4it is expressed as the same deflection of the metal strip6.

FIG. 7andFIG. 8show how the action of a perpendicular force is expressed on a piezoelectric sensor7itself.FIG. 7shows a section of the central part of the measuring member2. InFIG. 6the measuring member2is shown with the circuit board12and with the piezoelectric sensor7in the first position where no external force exerts on the cover.FIG. 8shows this part of the measuring member2with applied perpendicular force on the cover4. If the perpendicular force acts on the cover4the metal strip deflects from its first position in the direction away from the supporting body5. Since the piezoelectric sensor7is pushed by the flexible member20against the metal strip6, during the deflection of the metal strip6the piezoelectric sensor7moves with it. The distance between at least one of the conductive electrodes9,10on the piezoelectric sensor7and the third conductive electrode13increases, which results in a drop in the measured capacity. An ordinary expert skilled in the art is capable of designing an alternative solution where the application of a perpendicular force on the cover4causes the metal strip6to deflect in the direction to the supporting body5of the measuring member2. Hence the distance between at least one of the conductive electrodes9,10on the piezoelectric sensor7and the third conductive electrode13will decrease and this increases the measured capacity.

The application of the perpendicular force on the cover4causes a deformation of the piezoelectric sensor7, which generates a voltage between the first conductor14and the second conductor15. This method of measuring reacts to rapidly caused changes, for example, by the patient's pulse. The deflection of the piezoelectric sensor7causes a change in distance between one of the conductive electrodes9,10of the piezoelectric sensor7and the third conductive electrode13from distance a to distance b. It results in a change of capacitance of the formed capacitor measured between one of the conductive electrodes9,10of the piezoelectric sensor and the third conductive electrode13. This second method of measuring senses with great accuracy small changes caused by mechanical expressions of the patient's body. Low frequency changes in capacity correspond, for example, to respiratory rate where a sudden and significant increase or decrease in capacity may be evaluated as a change of the patient's presence, i.e., whether or not the patient is in bed. The region of interest for the evaluation of the respiratory rate or increase in weight is the frequency spectrum of changes lower than 1 Hz. A signal with a frequency of 0.2 Hz may be evaluated as the respiratory rate. In contrast, the region of interest for evaluation of the pulse rate is the frequency spectrum of changes around 1 Hz and higher, the pulse rate may be detected up to 10 Hz.

Based on an appropriate layout of measuring members2in the mat1, the processing unit17can give information about the patient's position, and if there is a danger that the patient will fall out of bed, it can inform the personnel by signalling a risk of the patient exiting the bed or the patient falling from the bed. This signalling may be visual, audio or in some other form. The signalling can also have a local or system scope, where the risk information is sent by the processing unit17to a server, from where the information is distributed to remote devices such as a monitor in a nurse station or a mobile device with which a nurse is equipped. The stopping of measurement may be another reason why to evaluate the risk of exiting the bed.

On the basis of the measurement of slow changes in capacity, in an advantageous embodiment the processing unit17can be configured so that it measures the patient's weight and can give information about a reduction or increase in the patient's weight in the case of long-term monitoring.1mat2measuring member3cable4cover5supporting body6metal strip7piezoelectric sensor8capacitance sensor9first conductive electrode10second conductive electrode11circuit board12third conductive electrode13first conductor14second conductor15third conductor16processing unit17first rail18second rail19flexible member