Display unit for chest compression signals

The invention relates to a display unit for displaying characteristics of an oscillating signal (having amplitude and frequency), wherein the display unit comprises at least one indicator device adapted to be turned on when the amplitude of the oscillating signal reaches a maximum value and / or when the amplitude of the oscillating signal reaches the minimum value.

[0002] The invention relates to a system and device intended to measure, record and provide feedback on the effectiveness of cardiopulmonary resuscitation (CPR) used for victims of cardiac arrest or on mannequins for training purposes.

Background Art [0003] Cardiopulmonary resuscitation (CPR) is a procedure performed as first aid in case of sudden cardiac arrest. The procedure includes chest compressions and ventilation. Recent publications indicate a number of problems related to how CPR is currently carried out by professionals:

[0004] Aufderheide et al showed in their publication "Hyperventilation caused by hyperventilation during cardiopulmonary resuscitation" ("Hyperventilation-Induced Hypotension During Cardiopulmonary Resuscitation"), Circulation. 2004; 109 that trained Emergency Medical Services (EMS) had problems with proper ventilation. Even after re-training, the ventilation rate was still too high compared to "Guidelines 2000 for Cardiopulmonary Resuscitation and Cardiovascular Rescue Care" Guidelines 2000 for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care, published by The American Heart Association) in cooperation with the International Liaison Committee on Resuscitation, hereinafter referred to as "the Guidelines".

[0005] van Alem, Sanou and Koster pointed to another problem with performing CPR in "Interrupting cardiopulmonary resuscitation using an automatic external defibrillator with cardiac arrest outside the hospital" (Interruption of Cardiopulmonary Resuscitation With the Use of the Automated External Defibrillator in Out-of-Hospital Cardiac Arrest "), Annals of emergency medicine 42: 4 (October 2003); even trained EMS personnel who performed CPR, had compressions or ventilations for less than 50% of the time in which they were in the place of assistance, i.e. the time of hands-off time / inactivity was too long.

[0006] Two articles published on January 19, 2005 in the Journal of the American Medical Association (JAMA), Voi 293, No. 3, "Quality of cardiopulmonary resuscitation during cardiac arrest in hospital" ("Ouality of Cardiopulmonary Resuscitation During In-Hospital Cardiac Arrest") by Abell et al. And "" "Quality of cardiopulmonary resuscitation during cardiac arrest hearts outside

"Hospital" ("Quaiity of Cardiopulmonary Resuscitation During Out-of-Hospital Cardiac Arrest") by Wik et. al, they state that the time without chest compressions was too long, the correct depth of compression was not reached, the compression rate was either too low or too high, and that hyperventilation often occurred.

[0007] The CPR device is described by Halperin et al. in the document US Pat. Well. 6,390,996, "CPR Chest Compression Monitor". This device only considers compression. The device uses an accelerometer and a gyroscope and measures continuously. This means that for a rescuer who does not decreases between pressure on the patient's chest, gradually increases the error in measurements.

[0008] Other simpler CPR assist devices base their feedback on strength and time. One such device is CPREzy from Medteq Innovations Pty. Ltd.

[0009] Some CPR assist devices are part of an Automatic External Defibrillator (AED) or manual defibrillator. One such device is CPR-Dpadz ™, which is part of the AEDPIus from Zoll Medical Corporation. This device only considers compressions, and provides audible feedback, such as voice instructions and a metronome, and visual feedback in the form of numbers on the AED screen.

[0010] Purchasing a new defibrillator with a CPR assist device is rather not an alternative to Emergency Medical Systems (EMS) that already have a well-functioning AED / Defibrillation system. Rather, such EMS systems would consider stand-alone solutions for measuring and providing CPR related feedback.

[0011] None of these systems or devices provide feedback on both operations, oppression and ventilation, and also do not provide feedback related to inactivity or incomplete hand release / reliance during the entire CPR procedure. These issues are considered very important for increasing CPR efficiency, and thus for increasing the survival rate.

[0012] Another problem associated with known systems, such as Zoll's AEDplus, for example, is that they are relatively expensive, large and complex; and therefore unprofessional rescuers will not be ready at all times.

[0013] Devices made for non-professional rescuers are described in document EP1578340 (Laerdal Medical AS), which describes devices that are force sensitive, emit sound signals to assist the rescuer, and in particular a device that is placed between the hands of the person performing the compression of the chest and the patient's chest. In particular, the device subject of EP1578340 is intended to emit sound when chest compressions are performed at a force exceeding a predetermined value, and optionally also to emit a sound indicating the desired chest compressing rate. This is achieved in an inexpensive and compact device that can be independent of the battery, and thus can be

- always ready for use, or in one embodiment - it can be a device that uses a battery and has very low power consumption.

[0014] Practice has shown that sound signals may in some cases be difficult to hear, especially in certain situations requiring urgent assistance. Feedback from prior art devices providing feedback may also often interfere with other events and other information received at the place of assistance, and the rescuer may often feel in a stressful situation that feedback is aggressive and disturbing.

[0015] Also, in some cases there is a need for more appropriate rules for providing feedback to the user. If, for example, the force applied is too high, there is a risk of injury to the patient. Therefore, in such cases there is a need for energy-saving and compact devices that provide good quality CPR feedback, where feedback is provided in a way that is reliable and likely to be picked up and noticed by the rescuer in all possible situations.

[0016] Document US-A-4,797,104 describes a system and method for testing a person for CPR efficiency and a display unit according to the preamble of claim 1. [0017] The object of the invention is to provide a display unit that can be used in a system providing feedback regarding cage compressions in CPR, which can be an independent unit and can be used by rescuers with minimal training, and which provides discreet, unambiguous and intuitive feedback that can be easily seen and understood in all environments / environments.

[0018] The object of the invention is achieved by the claims.

[0019] In particular, according to the present invention, a display unit as defined in claim 1 is provided.

[0020] The feedback system regarding chest compressions in CPR includes:

measuring unit, processing unit and display unit, where

- the measuring unit includes a depth measuring device and / or a force measuring device,

- the processing unit comprises a depth signal device, a force signal device and a threshold value device, and is adapted to produce, as an output, a signal depending on the value of the depth and force signals in relation to the threshold values, and

- the display unit comprises input means and at least one display device, and is adapted to switch on display devices based on output from the processing device.

[0021] The depth measuring device may be any suitable device capable of accurately measuring the depth of each compression. In one embodiment, the device

- the accelerometer measures the depth. Double integration of the accelerometer signal leads to a depth signal. Calculation of the depth from the acceleration signal can be done by the processing unit. Accelerometers can be one, two or many, and each accelerator can be a one- or biaxial accelerator to provide reference signals and / or measurement of movement in different directions, e.g., measurement of movement in a selected compression direction and in a direction perpendicular to it. Accelerometers can be placed inside or outside the device. In one embodiment, the system includes only one accelerometer.

[0022] The force measuring device may be any suitable device capable of measuring the compression force exerted on a patient. In one embodiment, the force measuring device is a pressure sensitive coating.

[0023] Examples of possible depth and force measuring devices are described in document EP 1057451 (Laerdal Medical AS).

[0024] The signals from the force measuring device can be used in conjunction with the signals from the depth measuring device, or the depth or force measurements can be used individually. Current international guidelines specify / recommend the correct compression depth, but the force measurements can provide additional information that will provide further quality of CPR. The ability to combine depth and force measurements provides flexibility in use and the ability to adapt to new guidelines and / or new knowledge, for example resulting from future research. For example, to achieve the same compression depth, different patients will require different forces. This means that sometimes it may be more effective to measure the compression force, while in other cases it is preferable to measure the compression depth. For a patient in a moving vehicle, the depth values ​​can be deceptive, and in this case strength measurements may be more valuable.

[0025] The system may be contained within a housing, the housing being rigid and waterproof to provide a solid device.

[0026] The system may also include a ventilation measuring device and / or a ventilation signal device to measure and provide feedback on the patient's ventilation characteristics. The ventilation measuring device may be any suitable device that can measure the volume, flow and / or frequency of the ventilation.

[0027] The processing unit is adapted to process signals representing chest compressions and includes a depth signal device and a strength signal device and a threshold value device. The threshold device includes thresholds such as upper and lower thresholds. The processing unit is adapted to produce as output signal depending on the value of the depth and strength signals in relation to the threshold values.

[0028] The processing unit may be integrated into the system, for example, by placing it in a device containing the system, or the processing unit may be partially or completely external device. The processing unit may for example be part of the defibrillator processing unit or may be adapted to cooperate and / or share resources with the defibrillator, in particular with the AED.

[0029] Threshold values ​​are values ​​that are used to compare with the values ​​of the depth and force signals. The threshold values ​​may be values ​​previously programmed in the processing unit, stored in memory in the processing unit or connected to the processing unit, or may be input from an external source. Where threshold values ​​are input into the processing unit, the processing unit includes an input unit receiving the threshold values ​​and other possible input values. The processing unit can also be adapted to define or change thresholds based on the results of measurements from the measuring unit, e.g. based on the strength / depth signal amplitude.

[0030] In one embodiment, the first upper threshold value is the maximum force value or the maximum depth value. As current international guidelines specify compression depth, the first upper threshold value will in most cases be the maximum depth value corresponding to the recommended maximum compression depth. To avoid injury to the patient, or if the guidelines change in determining the maximum force, the upper threshold may correspond to the maximum recommended compression force.

[0031] In another embodiment, the second upper threshold value is the minimum force value. For example, it will represent the minimum force that can be applied to the patient's chest without preventing blood circulation. This is often referred to as "leaning" or "incomplete release" because the rescuer often rests on the patient and does not completely relieve pressure on the chest. This can prevent blood from flowing back into the heart and thus leads to weaker circulation that could otherwise be obtained. It will therefore be important to provide feedback to the rescuer about whether he / she is not relieving enough pressure.

[0032] In one embodiment, the threshold device also includes a ventilation threshold device and thus ventilation thresholds, e.g. regarding rate, volume, flow, etc.

[0033] The memory device may be any suitable type of memory device for storing data, such as semiconductor memory, capacitor, magnetic memory, optical memory, etc. The memory device is in one embodiment included in the power supply. The storage device can be removable and / or updated so that the stored values ​​can be changed. The memory device may be dedicated to the storage of threshold values ​​or may store other values ​​for other processing purposes and software for the processing device. For example, historical data may be stored in a memory device in order to be able to evaluate a resuscitation session, which can be done by

- saving and storing simple data, such as the instantaneous or total number of compressions, a number that indicates how many times the recommended compression depth or other thresholds have been reached, frequency counting, etc., or saving more complex data, such as full or partial force / depth curves oppress.

[0034] The system may include a power supply that provides power to the metering unit and the processing unit. The power supply may be included in the processing unit. The power supply can be internal, as an integrated or detachable part of the system and / or processing unit, or the power supply can be an external power supply, and the system / processing unit can be adapted to connect to such a power supply, e.g. for hospital supply, for supplying an ambulance, defibrillator, CPR dummy or laptop computer.

[0035] In one embodiment, the processing system / unit comprises a chamber for housing a power unit and / or includes connectors for connecting to a power unit. The power supply unit may be a replaceable unit, for example, a battery (rechargeable or non-rechargeable) or a connector adapted to connect the system / processing unit to an external power source, such as power supply / hospital power supply, or an ambulance power supply as mentioned above.

[0036] If the storage device is included in the supply unit, the storage device may be replaced by changing the supply unit. This can be useful when tracking software updates / system thresholds. For example, the power unit lead may have different colors associated with different versions of the memory unit / threshold values. This means that if the thresholds should be updated, the distributor / manufacturer can instruct users to change the power supply unit so that they have their system / processing unit updated. This will be relevant, for example, when there are changes to the international guidelines for CPR (American Heart Association Guidelines on CPR ( American Heart Association (AHA) Guidelines for CPR). [0037] The depth signal device and the force signal device contain signals representing compression depth and compression force. In one embodiment, these signals are provided by a depth measuring device and a force measuring device included in the measuring unit.

[0038] The processing unit may further be able to process signals from the depth signal device and from the force signal device. Processing can lead to other CPR characteristics, such as patient's chest stiffness, compression frequency, shape of the oscillation signal of the force / depth of compression, etc. As mentioned above, depth calculation based on the accelerometer signals can be done by the processing unit. Processing may also include filtering compression strength / depth signals to obtain a clearer picture of the CPR session.

[0039] Since it is important for the rescuer to have information regarding his compressions, generally, in real time, the processing of measurement signals must provide real-time feedback. Since the processing itself takes time, measurements that require no processing or only small processing operations will be most suitable for providing feedback. Alternatively, such measurements can be used in processing to compensate for the time used for processing, thereby obtaining real time measurement signals closer to real time.

[0040] As mentioned above, the possibility of combining depth measurements with force measurements provides flexibility in use and the ability to adapt to new guidelines and new knowledge. Even if current guidelines focus on the depth of pressure, this may change in the future. For example, new tests may lead to different depth recommendations for different chest stiffness, new guidelines may be for children, etc.

[0041] In one embodiment, the compression force, measured when the compression depth (s) lies within the recommended value (s) of the depth (according to guidelines), is recorded by the processing unit, and the processing unit provides measurements of the force in to provide feedback to the user, alerting the user if the depth measurements change significantly. This will guarantee that the patient's movement in the direction of compression (i.e. essentially vertical movement) will not affect the measurements and will not give false warnings. The relationship between depth and strength can also be checked regularly to ensure that the patient's chest stiffness does not change. The processing unit can also be adapted to recognize the movement of the patient (for example, when it is transferred to the ambulance) by analyzing the depth signals / accelerometer signals, and then only switch to force measurements until the patient stops moving. When the patient is no longer moving, depth measurements can be continued / resumed.

[0042] In another embodiment, the force measurement may be used for the first few compressions, for example to initiate / initialize depth calculations, and then switch to acceleration / depth measurements. Force measurements can then be used as a zero point indicator for further measurement / processing, i.e. indicating when pressure is released.

[0043] As mentioned above, the processing unit can also be adapted to define and change thresholds based on the results of measurements from the measurement unit, for example based on the strength / depth signal amplitude. For example, if the upper force threshold value is 50kg and 50kg is measured, then a depth measurement corresponding to this force can be set by the processing unit as the upper depth threshold value. Then, depth measurements can be used to provide feedback to the user. Also, for very stiff patients (chest stiffness), the system can be adapted to provide strength feedback instead of providing depth feedback. In very stiff patients, there must be value

-8 minimum force threshold, and force measurements may not provide sufficient information. The processing device may be adapted to choose between force measurement or depth measurement based on force or depth thresholds. The processing device may for example be adapted to use the relationship between force and depth measurements as a guide which measurements to use, e.g. use only force measurements if the relationship varies significantly over time, as this may mean that the patient is in a moving vehicle and the output of the accelerometer may not be reliable.

[0044] The processing device generates a signal as an output, depending on the value of the depth signal and strength in relation to the threshold values. This signal can be used as input to the display unit to provide feedback to the user / rescuer.

[0045] The system may also be connected to a database or comprise a database with knowledge / experimental data. This may enable the processing unit to choose the right characteristics for each patient, for example by choosing the compression depth for which it has been proven to be most effective for small / large patients, children, by choosing the compression depth depending on the force used for the compression, etc. .

[0046] The display unit includes input means and at least one indicator, and is adapted to include indicator devices based on the output of the processing device.

[0047] The output from the processing device may be simple signals indicating whether the measured depth / force / ventilation is within or outside the threshold values ​​from the threshold device, whether there were no compressions within a predetermined period of time, etc. The output from the processing device, alternatively, may be a more complex signal, e.g. an oscillating signal, representing the relationship between depth and time and / or between strength and time, and / or between strength and depth, a signal representing the number of compressions over time, the rate of compressions in time, etc. The output from the processing device may also contain several types of signal and several signals.

[0048] In one embodiment, the processing device is adapted to prioritize which feedback is most important and / or should first be given to the rescuer. This can be important when there are several measurements that are outside the respective thresholds. In this case, the processing device may be able to give the most important feedback first or mark the most important feedback so that the indicating instruments emphasize this feedback when pointing to the user. For example, the processing device may hold less important feedback until more important issues are corrected. Prioritization can be accomplished by comparing the deviating characteristics with a previously remembered list. For example, this list may contain information about which characteristics must first be corrected to get the best CPR result.

[0049] In another embodiment, the feedback is placed in a queue, for example ordered according to the aforementioned priority. When feedback is given to the user, it is moved backwards in the queue, for example to the last position.

[0050] The processing device may be able to control, partly or completely, a defibrillator, e.g., an AED, in order to be able to synchronize the operation of the defibrillator and the CPR. Alternatively, the processing device may be able to communicate with the defibrillator processing device, or the defibrillator may control the operation of measuring and providing feedback. This may allow the system to coordinate compressions and ventilation and / or coordinate compressions, ventilation and shock to the defibrillator. Collaboration between the defibrillator and the feedback system can also allow for shock detection, automatic feedback on hand removal and / or countdown to the moment the impact is to be applied, and control feedback to coordinate CPR and defibrillation.

[0051] Indicator devices (display devices) are devices or systems adapted to provide the user with feedback regarding various characteristics of the CPR session, for example in graphic form and / or as part of another type of visual presentation. The pointing device (s) may be of any type, such as audible, visible, tactile, e.g. tone signal, voice message from the loudspeaker, curve, text or any symbol on the screen, one or several light-emitting diodes (LEDs), vibration generator, pulse generator, etc. Several indicators may also be given by one indicator, or several indicator devices may be included in one unit / system, for example implemented as different areas of the screen.

[0052] Indicating devices can be arranged on many levels, for example, displaying colors or lights first, then symbols and then sounds, for example to increase the importance of feedback or as the time increases since the user's last response.

[0053] In one embodiment, the input means is adapted to input an oscillating signal (having an amplitude and frequency), and wherein the at least one indicator device includes a first indicator device adapted to be turned on when the amplitude of the oscillation signal reaches a maximum value and a second indicator, adapted to be switched on when the oscillation signal amplitude reaches a minimum value.

[0054] The oscillating signal is, for example, an output signal from the processing unit that represents the depth-time or force-time relationship for compressions. It may be a sinusoid-like signal, with the amplitude and frequency corresponding to the depth or strength, and the frequency (pace) of the compressions, respectively.

[0055] According to the invention, the first and second indicator devices are light indicator devices having different light intensities depending on the number of occurrences, respectively, maximum and minimum

- 10 amplitudes of the input signal in the time interval. For example, the light intensity of an LED may increase for each case where the amplitude of the oscillating signal reaches its maximum or minimum during a predetermined number of oscillations, or it may decrease if the signal has not reached its maximum or minimum within a time interval. The maximum / minimum may correspond to or be the same as the threshold values ​​from the threshold device and may, for example, be the recommended compression depth and / or the minimum force when pressure is released during compression. In this way, the operator / rescuer will be able to see if he / she has reached the maximum / minimum during the last few compressions without having to constantly observe the indicating instrument.

[0056] In one embodiment, the display unit includes a third indicator, adapted to be turned on partially or completely, depending on the amplitude of the input signal. This gives the operator an indication of how deep the compressions are relative to the recommended depth. This can be done by using different light intensities, a sound signal, etc. In one embodiment, the third indicator comprises a number of LEDs, e.g. arranged in a row, and a number of LEDs that are turned on, depending on the amplitude of the input signal. In another embodiment, the third indicator is an OLED screen, or is implemented on an OLED screen, for example by incorporating a portion of the sector / area, wherein the size or position of the enabled sector / area is dependent on the amplitude of the input signal.

[0057] In one embodiment, the display unit includes a fourth indicator, adapted to be turned on by a secondary signal obtained from the frequency of the input signal. This secondary signal may, for example, correspond to the number of compressions performed per unit of time, and is an important factor in ensuring the quality of CPR.

[0058] In one embodiment, the fourth indicator comprises at least three zones, a central zone and at least two side zones, and the middle zone is adapted to be turned on when the signal frequency lies between the maximum and minimum values ​​and the side areas are switched on when the signal frequency is above / below the maximum and minimum values, respectively.

[0059] In one embodiment, the display unit includes a fifth indicator, adapted to be turned on when the input signal does not appear during a predetermined period of time. This is feedback that reminds the operator to continue the CPR procedure. The fifth indicator can be a constant or variable intensity light, a clock / time counter or an audible signal.

[0060] The invention will now be described by way of examples with reference to the accompanying drawings.

Fig. 1 is a schematic diagram of an embodiment of the system according to the invention.

Fig. 2 shows examples of signals used in the processing unit according to the invention.

Fig. 3 shows an embodiment of a display unit according to the invention.

Fig. 4 is a block diagram of the operation of a display unit according to the invention.

Fig. 5 shows examples of various possible pointing devices used in the display unit according to the invention.

Fig. 6 shows an example of various possible pointing devices included on the screen.

[0061] Fig. 1 is a schematic diagram of an embodiment of the system according to the invention. The system includes a measuring unit 12 comprising a force measuring device 10 and a depth measuring device 11. The depth measuring device 11 and a force measuring device 10 measure the depth and strength of pressure applied to the patient (not shown). The depth measuring device may, for example, be an accelerometer providing an acceleration signal which may be processed to provide depth.

[0062] The system further includes a processing unit 13 including a force signal device 15, a depth signal device 16 and a threshold value device 17. In this embodiment, the force signal device 15 and the depth signal device 16 receive signals from the force measuring device 10 and the depth measuring device respectively 11. In this embodiment, the threshold device includes four thresholds T1-T4.

[0063] The processing unit processes and analyzes the signals in the strength signal device 15 and the depth signal device 16. The processing / analysis result, which implies a comparison with the threshold values ​​T1-T4 from the threshold device 17, is transmitted as output to the display unit 14. In this embodiment, the display unit 14 comprises five indicator instruments. Indicator apparatus 1-Indicator apparatus 5. The display unit will turn on one or more display instruments based on the output from the processing unit 12. The display instrument provides the user with information on the quality of his / her CPR test and allows users to change the way CPR is performed to improve the quality and thus the patient's chances of survival.

[0064] Fig. 2 shows examples of signals used in the processing unit according to the invention. The force signal 20 is received directly from the force measuring device, while the depth signal 21 is the result of double integration of the accelerometer signal, the integration being carried out in the processing unit. The processing unit may also perform a filtering process to straighten signals, remove artifacts or remove phase shifts. The result of the filtering process performed on the depth 21 signal is the depth 22 signal. In the graphs, the x axis represents the time of the CRP session, and the time between compressions and the number of compressions in time can be calculated from the curves.

[0065] Fig. 3 shows an embodiment of a display unit according to the invention. The display unit includes input means for inputting an oscillating signal (having amplitude and frequency) and at least one indicator that is adapted to be on when the amplitude of the oscillating signal reaches a maximum value and / or when the amplitude of the oscillating signal reaches a minimum value.

[0066] In this embodiment, the display unit includes five indicator instruments 31-35. Indicating devices are, for example, LEDs or screen sections. The inclusion of indicator 32 means that the operator / rescuer has reached the recommended compression depth, while the inclusion of indicator 31 means that the operator / rescuer has sufficiently reduced pressure between compressions during compression. The correct CPR procedure is performed when the indicator device 31, 32 is turned on for each compression. In a CPR situation, the rescuer's attention is often distracted by other events and people around the rescuer, and he / she is not able to constantly observe the display unit to ensure that all compressions are properly performed. In one embodiment, the light intensity of the indicator device 31, 32 will vary depending on the number of times the rescuer reaches the correct depth or decreases pressure when applying pressure. For example, the light intensity of the LED may be maximum after one correct pressure, slowly weakening. This means that if the operator sees the dim light, he / she knows that he has done a good pressure in the recent past, but that the last pressure was inappropriate. If he sees a bright light, he knows that the last tribulation was adequate. Alternatively, the light intensity of the LEDs may increase for each correctly performed pressure up to the desired number, for example 2 or 3 compressions.

[0067] Between indicator 31 and 32 is a third indicator 33. The third indicator 33 includes a section / area that is turned on partially or completely depending on the depth of compression. The third indicator may be a screen section or multiple (e.g. three or more) LEDs. The third indicator indicates, together with the first and second indicators 31, 32, the depth of the compressions. In the exemplary embodiment of Fig. 3a, with five LEDs, switching on only one LED means that the rescuer presses only 20% of the sufficient pressure depth, switching on two LEDs means that the pressure is 40% of the recommended depth, and so on. Turning on all five LEDs will turn on the indicator 32 indicating that the pressure is adequate. Alternatively, only one LED is turned on at a time, such that 20% pressure is indicated by the first LED, 40% pressure by turning only the second LED, and so on. In the exemplary embodiment of Fig. 3b, the third indicator 33 'is a dedicated section / area on the screen and the sectors of the area are turned on depending on the vertical position of the hand of the rescuer, i.e. the depth of compression. This will be seen by the rescuer as a lighting point between the two max / min 31 ', 32' indicators.

[0068] In the embodiment shown in Fig. 3c, the third indicator device comprises a section 38 extending beyond the indicator device 32, which indicates that the correct compression depth is reached. Section 38 is included when the rescuer presses too deeply.

[0069] In this embodiment, the fourth indicator 34 represents the number of compressions performed per unit of time. This quantity is obtained from the depth signal, and corresponds to the oscillation frequency of the signal. Indicator 34 includes three zones 35, 36, 37, where the inclusion of center zone 36 means that the rescuer is compressing at the correct frequency. The inclusion of one of the side zones 35, 37 means that the rescuer should increase / decrease the compression frequency.

[0070] The fifth indicator 35 is turned on when there were no compressions during the time period. This pointing instrument reminds the rescuer to continue the CPR session.

[0071] Figs. 4a-c are block diagrams of the operation of a display unit according to the invention. Fig. 4a shows three thresholds T1-T3 associated with an oscillating signal that represents the number of compressions. The thresholds T1 and T2 represent the upper and lower thresholds respectively for the recommended compression depth, for example 52mm and 38mm. The threshold value T3 represents the minimum allowable compression force between compressions, for example 3 kg. In Fig. 4a all compressions are performed correctly.

[0072] Fig. 4b shows an example of the logic used to control the activation of the indicator device 32 of Fig. 3. The depth of each compression is compared at 41 with the thresholds T1 and T2. If the depth lies between T1 and T2, the indicator 32 is turned on. If the depth is outside of T1-T2, the compression force is compared to the next T4 threshold, for example 50kg. If the compression force exceeds T4, the indicator device 32 is switched on. The basis for this is that in some cases the chest makes it almost impossible to achieve the correct depth of compression, and therefore compression with 50 kg is determined as adequate compression. When T4 is used as the inclusion criterion for indicator 32, the depth corresponding to the force T4 can be measured, and this depth is set as the new T2 for the continued CPR session, or force measurements are used to enable the indicator device in the continuing CPR session. The calculation associated with the inclusion of the third indicator 33 in Fig. 3 is changed accordingly.

[0073] Fig. 4c shows an example of the logic for controlling activation of the indicator device 31 of Fig. 3. Here, the compression force is compared to the threshold value T3, and if the compression force is less than T3, the indicator device 31 is switched on.

[0074] Figs. 5a-k show examples of various possible indicator devices that can be used in the display unit according to the invention. All these pointing devices may be light-emitting display devices, for example contained as an OLED screen.

[0075] The example of Fig. 5a includes three indicator devices. The first and second indicators 61 relate to the maximum and minimum compressions respectively, i.e. the first indicator 61 is turned on when the recommended compression depth is reached and the second indicator 62 is turned on when the recommended minimum pressure between the compressions is reached. The third indicator 63 includes an area where sectors of the area are turned on depending on the amplitude of the input signal. In the figure to the left, the signal amplitude is slightly below the recommended compression depth, and sector 64 below the first indicator is turned on. In the figure to the right, the rescuer has reached the recommended compression depth, and no sector of the third indicator 63 is on, but the first indicator 61 is on. In this configuration, the rescuer can observe the "passing" indication between the first and second indicator instruments, thus having full control of his / her compression movements.

[0076] In Fig. 5b and Fig. 5c, essentially the same configuration of the first, second and third indicator devices as in Fig. 5a is used. However, in Fig. 5b and Fig. 5c, the first and second indicator instruments remain on, i.e. they are lit, within a time interval from the last time the respective thresholds were reached. Fig. 5b and Fig. 5c also contain two different embodiments of the fourth indicator 65, 65 'for indicating the compression rate, i.e. the number of compressions over time. In Fig. 5b, the indicator is in the form of a "speedometer", i.e. a radial "needle" which is attached at one end and is movable at the other end. The movable end can move in a semi-circle and indicates the pace, with the center of the semi-circle being the recommended pace In Fig. 5c the indicator is in the form of a linear scale, where the middle of the scale represents the recommended rate, also shown in the figure by the number.

[0077] Figs. 5d-5g show another embodiment of the first and second indicator devices, where the indicator device has an alternative shape and are arranged perpendicular to the direction of the indicator device of Figures 5a-5c. Figs. 5d-5g also show four different alternatives for representing the compression rate as a third indicator.

[0078] Figs. 5h-5k show various alternatives of pointing devices that can be used to provide feedback to a user. Fig. 5h contains a proposal for written messages, Fig. 5i is a battery level indicating device, Fig. 5j contains a proposal for a ventilation indicating device, where the lung drawing is filled / emptied while the patient is ventilated, and Fig. 5k is an example of indicating too long without compressing the chest, that is, the rescuer did not compress for 10 seconds.

[0079] Figs. 6a-6d show examples of various possible pointing devices implemented on the screen, for example on an OLED screen. Different symbols may have different colors and colors may change during resuscitation according to, for example, the importance of the feedback given or the time elapsed since the last action related to the feedback. Fig. 6a indicates the depth of compression as in the embodiment of Fig. 5a and Fig. 5b, but here the indicator 73 changes continuously without defining the sectors. Fig. 6b shows an example in which the arrow 75 underlines that the depth of the compressions is inadequate. The arrow 75 may be a second level indicator, for example turned on after the compression depth was not sufficient during a certain number of compressions or during a predetermined time. FIG. 6c also shows an embodiment of a fourth indicator 75 for indicating the rate of compression, i.e. the number of compressions as a function of time. Indicator 75 is similar to the embodiment shown in Fig. 5d and has the form of a "speedometer", i.e. a radial "needle" which is attached with one end and movable at the other end. The movable ending can move in a semi-circle and indicates the pace, with the middle of the semi-circle being the recommended pace. The recommended tempo can be a range of 77 and is highlighted.

[0080] Fig. 6d illustrates a possible indicator that indicates that no compressions are being carried out and to tell the user to begin compressions.

[0081] All different pointing devices and types of feedback, illustrated and described herein, can of course be used with each other in any combinations or individually.