WO2007106040A1

WO2007106040A1 - Monitoring device for diminishing the risk of acuiring pressure ulcers

Info

Publication number: WO2007106040A1
Application number: PCT/SE2007/050286
Authority: WO
Inventors: Disa Lidman; Bengt Ragnemalm; Johan Thorfinn
Original assignee: Sencere Medical Ab
Priority date: 2006-03-14
Filing date: 2007-04-27
Publication date: 2007-09-20
Also published as: EP2143090A1; EP2143090A4; WO2007106040A8; SE0600562L

Abstract

A sitting pressure and decubitus ulcer alarm, especially useful for para- or tetraplegic persons who do not feel how they sit. The alarm contains a number of pressure sensors distributed over the expected critical surface. The sitting pressure is continuously supervised for every measuring point as well as the duration of the pressure. If in any of the measuring points the pressure is high enough to cause decreased circulation the person seated will be alarmed before the lack of circulation has started to cause injuries. When the alarm occurs the person sitting thus must change the sitting posture or in any other way unload the temporarily overloaded area during enough long time in order to let new blood flow into the vessels of the area in danger. Therefore the alarm supervises that also this time interval is long enough. The alarm ideally points to where and when the pressure overload is nearly occurring and it is temporarily stopped when pressure unload occurs. Firstly the person seated is alarmed, but it is also possible that the care-givers will be alarmed e.g. if the person seated is not changing his or her position.

Description

Monitoring device for diminishing the risk of acuiring pressure ulcers.

TECHNICAL FIELD

The invention relates to a device for diminishing the risk of acquiring pressure ulcers in the sitting or lying position with the purpose to be placed underneath the person who is in danger of acquiring pressure ulcers.

BACKGROUND OF THE INVENTION

Pressure ulcer development is a major problem in many groups of patients, among others in patients with spinal cord injuries (SCI) who are for long periods sitting down in their wheel chairs. The prevalence of pressure ulcers among these groups has been reported to be as high as 20 - 30 %. Other exposed groups are old patients or persons that have a decreased sense of consciousness, due to injury or disease, for instance in intensive care or during surgery.

Risk factors for developing pressure ulcers are for instance damp environment or raised body temperature. However, there are no scientific doubts whatsoever that pressure in it self constitutes the largest risk. The bony prominences exerts a pressure on the overlying tissues during sitting that results in relative or absolute lack of oxygen (tissue ischemia). The sitting pressure needs to exceed a certain level to occlude feeding arterial vessels, musculocutaneous arteries and capillary tree to cause ischemia, and this level of pressure must last over a certain period of time to risk tissue damage. If the pressure and following ischemia is not relieved, permanent cell damage will occur and a pressure ulcer develops. In healthy individuals with intact sensory and motor function this is not a problem, since the ischemia results in an increase of afferent sensory pain stimuli before permanent cell damage occurs so that the body position can be changed and areas exerted to pressure relieved.

The pressure ulcer is in it self a medical hazard as it can become the forerunner of serious (potentially life threatening) infections. The ulcer also imposes social limitations and inconvenience for the patient. When treating it the ulcer has to be dressed daily and repeated cleansings of the wound is necessary. The alternative is plastic surgery. When using conventional dressings the healing period takes several months, during which the patient must relieve his or her area of sitting continuously. The rehabilitation after an operation usually takes about four to six weeks and both methods inflicts great suffering for the patient and high costs for the society.

Preventive care is today considered the best treatment. This is given by providing pressure relieving cushions both in wheel chairs and beds, for those patients that lie down. According to the recommendations the patient should not be sitting upright for more than 2 hours at a time before a period of unloading. Patients confined to bed are often using turning schemes, meaning that the nursing staff have to change their position of the body every two to three hours.

There is a need for a technical helping device that is cheap and easy to use, trustworthy and that in it self does not create any pressure towards the patient's tissues, for measuring pressure in the purpose of decreasing the risk of developing pressure ulcers among exposed groups of patients by altering the user when the pressure is too high or has lasted too long.

SUMMARY OF THE INVENTION

The purpose of the invention is to diminish the aforementioned risk to develop pressure sores. This is achieved, according to the investigation, through measurement of the amount of pressure at a number of spots on the loaded surface and the duration of the time the pressure occurs. Through this the person seated or lying or the nurses will be alerted if the pressure lasts long enough so that a continued pressure could lead to damage of the loaded skin.

The invention has been realised in a battery operated electronic device. The device can be made small (e.g. having a main body with the dimensions 62 x 54 x7 mm/60 g) and measures the pressure in eight spots simultaneously. The device is preferably built around a commercially available pressure sensor called Flexiforce (Tekscan Inc, USA) which has been shown to give reproducible results on repeated measurements. The electronic components attached to a number of the sensors, support sound-alarm, logging and storing of pressure data during long time periods (days) in a memory card (Secure Digital) and relaying of data via USB and/or Bluetooth wireless data transmission. Data can also be supervised and analysed by an external unit in real-time. The invention includes: Pressure sensors, a Communication unit and an Alarm unit. The exact placement and distribution of the functions of the units can be done in different ways depending on how the system is constructed. The placement of the different functions are now chosen for practical reasons so that both units have the same surface area.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a battery operated electronic device according a preferred embodiment of the invention,

Figure 2 shows a block diagram over a Communication unit circuit board including a battery according to the according the preferred embodiment of the invention, Figure 3 shows block diagram over an Alarm unit according to the according the preferred embodiment of the invention, and

Figure 4 shows a flow chart indicating in principle a control loop of battery operated electronic device according to a preferred embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 show a battery operated electronic device 1 according a preferred embodiment of the invention which comprises a main body 2 which is connected to pressure sensors 5 via a data cable 4. The main body 2 comprises a Communication unit circuit board 20, a battery 3, and an Alarm unit 30.

Figure 2 shows a block diagram over the Communication unit circuit board 20 including the battery 3 and Figure 3 shows block diagram over the Alarm unit 30.

The Communication unit board 20 comprises a Microcontroller 21, an Analogue to digital converter 22, a Bluetooth module 23, Voltage converters 26, an USB connector 24, a Battery charger 25 and a Connector to the Alarm unit 27. Power is supplied to Communication unit circuit board 20 via the Battery 3 which is connected to the battery charger 25 and the Voltage converters 26.

The Alarm unit 30 comprises Pressure sensor amplifiers 31, an Audible alarm device 32, an USB controller 33, a Digital memory card reader 34, a Connector to the Communication unit 35, and a Connector to sensors 36.

The battery 3 supplies power to the Communication unit board 20 and the Alarm unit 30 and can be charged via the charger 25 by inputting power through the USB connector 24. The voltage converters 26 converts the voltage from the Battery 3 to suitable violate levels. Of course the charger 25 could be left out if non-rechargeable batteries where used or if the battery would be charged externally.

The Connector to the alarm unit 27 has an interface for data communication between the Communication unit circuit board 20 and the Alarm unit 30, as well as power supply from the Communication unit circuit board 20 to the Alarm unit 30 via the battery 3. The Connector to the alarm unit 27 connects to the Alarm unit 30 via the corresponding Connector to the communication board 35 of the Alarm unit 30.

The Pressure sensors 5 can be connected to the Alarm unit 30 via the Data cable 4 and the Connector to sensors 36. A number of Amplifiers 31 amplifies the pressure signals from the Pressure sensors 5. For each Pressure sensor 5 there is a corresponding Amplifier 31, thus the number of Pressure sensors 5 should be lower or equal to the number of Amplifiers 31, normally their numbers being equal. In the current design there are 8 Amplifiers 31 and 8 Pressure sensors 5, however the invention is not limited to these numbers.

The amplified pressure signals proceeds through Connector to the communication board 35 and the Connector to the Alarm unit 27 to the Analogue to digital converter 22, where the amplified pressure signals are converted into digital signals, and finally to the microcontroller 21.

The software for the Microcontroller 21 analyses the pressure data recorded. The

Microcontroller 21 can output analysed pressure data and/or alarm signals via the Bluetooth module 23 and/or the USB connector 24. The Microcontroller 21 can also activate the sounder 32 when it has determined that an alarm situation is present. Pressure data can be logged in a memory card in the Digital memory card reader 34 as well as other relevant information such as for instance alarm history. Thus the battery operated electronic device 1 may output data and/or alarms through a number of different interfaces that can be used either individually or simultaneously and the software for the Microcontroller 21 can be modified depending on the application and the user's needs. The Microcontroller 32 could e.g. be a ATmega32, however other types of microcontrollers could be used. 1. Local alarm on the Alarm unit 30. Alarm signals are sent to the sounder 32.

2. Pressure data and/or an alarm signal are sent forward to an external unit (for example a personal computer, a telephone, a mobile phone or a network) via the Bluetooth module 23 and/or via the USB connector 24, where they can be presented or saved to an external unit, for example in a computer with a monitor and a hard disc.

3. Pressure data and/or an alarm history can be stored on a memory card in Digital memory card reader 34, which then can be removed and inserted in an external unit for analyses of the stored data.

4. An external unit attached to any of the interfaces can send preferences to the Microcontroller 21 to update its software or to change parameters.

The Pressure sensors 5 can be integrated in a protective cover for measuring under larger surfaces at a number of measuring points such as in the case of surveying the risk for pressure ulcers for a person confined to a wheel chair. The

Pressure sensors 5 can also be used loose for measuring local pressures, for instance the pressure inside a shoe, under a plaster cast, a prosthesis or for similar purposes. Of course the number of pressure sensors can be customized to a surveillance task of choice, however the number of Pressure Sensors 5 cannot exceed the numbers of Amplifiers 31.

The algorithm that determines on what occasion an alarm should be given, if this function is needed, is written in the software of the Microcontroller 32. The algorithm starts out from the pressure data that is received from the Pressure sensors 5. The micro processor's software determines when to give an alarm signal based on an algorithm. The algorithms can be exchanged and adapted for different circumstances and demands, depending on what kind of application the alarm is used for. For instance it could be necessary to use different algorithms to give an alarm to prevent pressure ulcer development for a person confined to a wheel chair than for a patient confined to lying down in a bed.

The software algorithm according to the preferred embodiment will now be described in relation to Figure 4. The variables are explained below.

Step 41: Receive pressure signals from the Analogue to digital converter 22 and calculate a new value of the variable PressureEnergy by integrating with TimeK. Raw data consisting of pressure signals and/or the determined PressureEnergy can here be sent to an external unit.

TimeK is a time constant, which is determined by the updating frequency of the pressure signals from the Pressure sensors 5. PressureEnergy is a variable that is used to hold a value that we call the pressure energy. It is defined as the pressure integrated over the time constant TimeK. Where the pressure is determined based on the amplified pressure signals from the Pressure sensors 5.

Step 42: Update the variable ReBehaviour (Relieve behaviour). This is a weighting factor which is dependent on previous situations of pressure and pressure relief. For instance if the Pressure sensors 5 have indicated that the pressure have been zero or below certain thresholds during a time period that is long enough - the variable ReBehaviour can be updated so to weight the variable PressureEnergy in step 43. E.g. if the variable ReBehaviour is equal to one PressureEnergy will not be changed in step 43, but if it has been determined that the pressure has been released the variable ReBehaviour can be set below 1. The variable can also be adjusted to take care of any special conditions. For example disease or any former problems of pressure ulcer that need special considerations, i.e. if the pressure is very critical for one patient the

ReBehaviour could be asset to be larger than 1.

Step 43: PressureEnergy is weighted by ReBehaviour and the output is called RiskLevel.

Step 44: If RiskLevel is smaller than a defined Threshold there is no alarm situation. Any earlier alarm signals are shut down by going to 45 and from there back to start. If RiskLevel is bigger than Threshold the program continues to 46

Step 46: The alarm level has been reached. The time of alarm can be marked in the data saved or sent to an external unit.

Step 47: The alarm is sent out to audible alarm device 23, where after the program returns to start.

By measuring the pressure and integrating it over time, the alarm can take into account the level of pressure and for how long it consists, or likewise for how long time a period of pressure relief lasts. This makes it possible for the alarm to go off at a correct point of time instead of giving off false alarms or missing to give off an alarm when it should. For instance if the pressure is very high the alarm will go off faster than if there is a lower pressure. If the duration of the pressure relief is short, the alarm will activate again, after a shorter time than if a long period of pressure relief had been done.

Whereas the invention has been shown and described in connection with the preferred embodiment thereof it will be understood that many modifications, substitutions, and additions may be made which are within the intended broad scope of the following claims.

For instance it should be realised that the number of external interfaces could be increased or reduced within the scope of the invention.

Further the device in one embodiment lacks a battery, i.e. it is being powered externally.

Claims

PATENT CLAIMS

1. A device for diminishing the risk of acquiring pressure ulcers in the sitting or lying position with the purpose to be placed underneath the person who is in danger of acquiring pressure ulcers, characterized by a number of pressure sensors, a central unit receiving signals from the pressure sensors corresponding to the measured pressure and a time measuring unit to also register the duration of the pressure present, and an alarm device which will sound if a too high pressure lasts too long in the same area of the body.

2. A device according to claim 1 characterized by that the sitting or lying person him- or herself will be alarmed so that the person will move or at least unload the body part subjected to the pressure.

3. A device according to claim 1 or 2 characterized by the registration also of the time of pressure unloading for the control that enough pressure unloading has occurred.

4. A device according to any of the aforementioned claims characterized by the inclusion of an organ for distant connection via radio or telephone with a unit for alarm or supervision.

5. A device according to claim 4 characterized by that it first gives a signal of alarm locally in order to activate the person sitting or lying in order to perform pressure unloading but if this does not occur a distant alarm is activated to e.g. the nursin ¹gO staff.

6. A device according to any of the previously mentioned claims, characterized by that the pressure levels will be registered during a longer time interval, either locally withe. g. a memory card or the equivalent, or in a central unit via radio or telephone fore.g. the testing of seat cushions or anti decubitus mattresses during the real activities of daily living for a care-taker.

7. A device according to any of the previous claims characterized by that it is connected toe.g. a bed with pressure unloading pulsation function mattress or massage function or other organs for pressure unloading or the alteration of pressure. A device according to any of the previous claims characterized by that the pressure sensing organ is built-in in a wheel-chair cushion or the similar which communicates with an alarm transmitting unit in the wheel-chair via radio (blue tooth) so that the cushion with transmitter and pressure sensor forms a freely movable and easily interchangeable unit while meanwhile the user of the alarm may carry the alarm in a pocket.