Monitoring of biosignals, especially electrocardiograms

Description

Field of the invention

[0001] The present invention relates generally to methods, systems and computer program products for monitoring biosignals, in particular electrocardiograms, and to the use of an electrocardiogram as a reference electrocardiogram. Background of the invention

[0002] Biosignals, such as electrocardiograms, allow conclusions to be drawn about the physiological activities of organs or an organism. The evaluation of monitored biosignals is not only used by physicians as a basis for diagnostics, but increasingly also in the field of so-called home monitoring or personal tracking. Here, users monitor their physical activity or physiological parameters without the constant support of a physician. The monitoring can form the basis for a recommendation for action to the user, for example, an instruction to consult a physician for in-depth diagnostics. Furthermore, the monitoring can be used to evaluate or manage an athletic training plan, e.g., to increase endurance in marathon training.

[0003] The abnormality or inconspicuousness of monitored biosignals can be determined by comparison with a reference. The reference can be predetermined by measuring another subject, by averaging across a group of subjects, or by computer-assisted modeling of the underlying physiological and / or pathological processes.

[0004] The reliability of the comparison (determined by the proportion of false-positive and / or false-negative comparison results) depends, among other things, on the quality of the reference. Furthermore, the reliability of the comparison can be increased if the reference and control measurements are based on comparable conditions. These conditions include the physical characteristics of the subject and environmental influences.

[0005] From WO 96 / 25096 it is known to store sample electrocardiograms for certain cardiac events of known diagnosis, e.g. tachycardia or atrial fibrillation, and to compare them with a measured electrocardiogram for a more precise localization of disturbances.

[0006] WO 2016 / 014194 A1 discloses methods and devices for distinguishing supraventricular tachycardia from ventricular tachycardia during changes in body posture.

[0007] From US 2007 / 142737 A1 it is known that heart rate dependence must be taken into account when distinguishing supraventricular tachycardia from ventricular tachycardia.

[0008] WO 2016 / 086037 A1 discloses a method having the features of the preamble of claim 1.

[0009] Against this background, the object of the present invention is to provide improved methods, systems, and computer program products for monitoring biosignals, in particular electrocardiograms. The invention relates to those cases in which determining the measurement conditions does not require a diagnosis of a pathological, in particular a cardiac, event. Summary of the invention

[0010] The present invention provides methods, systems, and computer program products for monitoring biosignals, in particular electrocardiograms, according to the independent claims. The dependent claims relate to preferred embodiments.

[0011] In a first aspect, the present invention provides a method for monitoring biosignals of a subject as defined in claim 1.

[0012] In some embodiments, a biosignal can consist of a measurement curve, e.g., a temporal progression of a measured voltage. An electrocardiogram, as an example of a measurement curve, measures the temporal progression of the heart's electrical muscle activity in the form of electrical potential differences.

[0013] In some embodiments, the biosignals may include measured values, e.g., voltage values, or values ​​derived from measurements. An example of biosignals that can be derived from a measurement are ECG parameters familiar to those skilled in the art, such as QT interval, QRS complex times, ST segment, and P-wave / R-wave / T-wave measurements, which can be determined from a measured electrocardiogram.

[0014] According to the invention, the multiple reference biosignals are present continuously as multiple intervals of a time series. In examples not covered by the claims and presented merely for illustrative purposes, the multiple reference biosignals may be present discretely, e.g., in the form of database entries and / or one or more files and / or a folder structure.

[0015] A continuous time series, for example, of heart rate values, should also be understood here as quantized quasi-continuous time series. Heart rates can typically be measured at intervals of one heartbeat, which means there is a certain time interval between two measurement points. Nevertheless, these quasi-continuous time series can be considered continuous for the purposes of the present invention and for illustration purposes. In some embodiments, a quantized measurement series can be converted into a strictly continuous time series using interpolation methods.

[0016] In general, each of the multiple reference biosignals is assigned a respective value of a reference parameter. Values ​​of the reference parameter describe, at least in part, physiological states of the subject. In particular, reference parameters can influence biosignals. In general, reference parameters (or a determination of a value of a reference parameter) do not require a diagnosis of a pathological event, in particular a cardiac event. For example, according to the invention, the presence or absence of a pathological diagnosis (e.g., a cardiac arrhythmia) should not be used as a reference parameter for selecting a comparison biosignal (e.g., a comparison electrocardiogram).

[0017] In some embodiments, the reference parameter can take numerical values, optionally in conjunction with a unit. The reference parameter includes the heart rate, which can be specified in the unit "beats per minute." Depending on the reference parameter, the numerical value can take integer and / or floating-point values. In some embodiments, the reference parameter can take descriptive values. An example of a reference parameter with descriptive values ​​is the body posture, with values ​​such as "lying," "sitting," or "standing."

[0018] Examples of reference parameters whose values ​​at least partially describe the subject’s physiological states are: Heart rate, ECG parameters that can be determined from an electrocardiogram (e.g. QT time interval, times and / or amplitudes in the QRS complex, ST segment, P wave, R wave, T wave, Q wave, S wave, U wave, baseline), blood sugar level, blood pressure, oxygen content in the blood (SpO2), electrolyte levels (e.g. concentration of calcium, potassium, sodium), body temperature, respiratory rate, minute ventilation;

[0019] These examples of reference parameters can be specified by numerical values, possibly in conjunction with an appropriate unit.

[0020] Further examples of reference parameters whose values ​​at least partially describe the subject’s physiological states are: Subject's medication; subject's posture; subject's current and / or previous level of physical activity; subject's lifestyle, particularly their occupation, eating habits, and frequency of physical activity.

[0021] These further examples of reference parameters can be specified by descriptive values, optionally numerically or binary coded. For example, the reference parameter "subject's medication" can assume values ​​such as "yes," "no," "amiodarone yes," "amiodarone no," or a variety of other values ​​to be determined depending on the subject and / or the biosignal to be monitored. The reference parameter "activity state" can assume descriptive values ​​such as "resting," "exercising," "running," "just ran," "exercise on the ergometer," etc.

[0022] Values ​​of reference parameters can also at least partially describe the boundary conditions of an environment. Examples of reference parameters whose values ​​at least partially describe the boundary conditions of the subject's environment are: Time of day, ambient temperature, air pressure, humidity, season.

[0023] The examples of reference parameters mentioned here are intended to serve illustrative purposes and are not to be understood as a limiting list. Other reference parameters are also included, as long as they can influence biosignals. According to the invention, the reference parameter in any case includes a heart rate.

[0024] In some embodiments, the reference parameter may comprise multiple components. In such cases, one can speak of a multi-component reference parameter or of a reference parameter consisting of a set of multiple components. For example, the components "heart rate" and "posture" may form the set "(heart rate; posture)" as a reference parameter. Values ​​of a multi-component reference parameter are determined by the values ​​of its components. For example, "(62 beats per minute; lying down)" may be a possible value of the reference parameter "(heart rate; posture)", where "62 beats per minute" is a possible value of the "heart rate" component and "lying down" is a possible value of the "posture" component. A set of n components can be mathematically represented as an n-tuples, i.e., represented in such a way that the order of the components is not negligible.In some embodiments, the components may be weighted differently.

[0025] The method further comprises measuring a control biosignal, in particular a control electrocardiogram, of the subject, and determining a value of the reference parameter associated with the control biosignal. The determination may comprise a measurement, automatic detection, or user input.

[0026] Preferably, the assignment of the control biosignal and the determined value is based on a temporal proximity or even simultaneity of the measurement of the control biosignal and the determination of the value of the reference parameter.

[0027] The method further comprises selecting at least one comparison biosignal, in particular at least one comparison electrocardiogram, from the plurality of stored reference biosignals based on the value of the reference parameter associated with the control biosignal and on the plurality of values ​​of the reference parameter associated with the plurality of reference biosignals. Preferably, a single comparison biosignal is selected.

[0028] In some embodiments, the one of the plurality of reference biosignals is selected as the comparison biosignal whose associated value of the reference parameter is identical to or has the smallest difference with the value of the reference parameter associated with the control biosignal.

[0029] In some embodiments, the one of the plurality of reference biosignals is selected as the comparison biosignal whose associated value of the reference parameter represents the next higher or the next lower value to the value of the reference parameter associated with the control biosignal.

[0030] In some embodiments, particularly in the case of multi-component reference parameters, a norm can be defined for the purpose of comparing the multi-component values ​​of the reference parameter. As an illustrative example, consider the sentence "(heart rate; blood glucose level)" as a multi-component reference parameter: The question may arise whether a control value of (65 bpm; 105 mg / dl) is "closer to" (60 bpm; 90 mg / dl) or to (70 bpm; 110 mg / dl). To address this question, a norm can be formed for the respective multi-component sentence, for example, a Euclidean norm (weighted and / or taking units into account) or a conditional norm.A conditional norm can, for example, stipulate that only the first-mentioned parameter (in the example: heart rate) should be considered initially, and only in the case of an ambiguous result (such as an identical difference of 5 bpm in the example) should the second parameter (in the example: blood sugar level) be consulted. In the above example, in the case of this conditional norm, the value (70 bpm; 110 mg / dl) would be selected. As an alternative norm, a Euclidean norm can represent the numerical values ​​of heart rate in the unit bpm and blood sugar level in the unit mg / dl in a (possibly weighted) Euclidean coordinate system and define the difference as the length of the difference vector.

[0031] Generally, the method further comprises comparing the measured control biosignal with the selected comparison biosignal. Comparing the biosignals may additionally or alternatively include, in particular, comparing values ​​derived from the biosignals to be compared. For example, to compare two electrocardiograms, one or more of the common ECG parameters (amplitudes, temporal course, rhythm parameters, QT interval, times in the QRS complex, ST segment, P-wave / R-wave / T-wave measurements) may be compared.

[0032] In general, the reference biosignals can be regarded as unremarkable or abnormal, for example at the time of their acquisition, measurement, or retrieval. In some embodiments, for example, reference biosignals recorded from a healthy subject can be regarded as unremarkable. For a reference biosignal classified as unremarkable, a negative comparison result (i.e., a mismatch between the control and reference signals) can lead to the instruction to consult a doctor. For a reference biosignal classified as abnormal, a positive comparison result (i.e., a match between the control and reference signals) can lead to the instruction to consult a doctor.

[0033] In some embodiments, certain requirements may be placed on the data quality of the reference biosignals, such as a high signal-to-noise ratio. Biosignals that meet such requirements may be considered suitable for comparison.

[0034] In some embodiments, the measured control biosignal can be included in the set of multiple reference biosignals. The value of the reference parameter associated with the measured control biosignal can be assigned to the newly recorded reference biosignal. Thus, the set of reference biosignals can be further expanded during operation for future method implementations, as well as covering a broader or more finely resolved spectrum of values ​​of the reference parameter. Such an inclusion can be particularly advantageous if the measured control biosignal is considered unremarkable.

[0035] In some embodiments, the method may further comprise outputting or displaying information. Examples of information to be output are: the value of the reference parameter associated with the control biosignal; the value of the reference parameter associated with the selected comparison biosignal; the control biosignal; the comparison biosignal; a deviation between the control biosignal and the comparison biosignal; a deviation between the value of the reference parameter associated with the control biosignal and the value of the reference parameter associated with the selected comparison biosignal; a recommended action based on a deviation between the control biosignal and the comparison biosignal. A recommended action to be output may, for example, be directed at the subject sitting down, resting, or engaging in physical activity.

[0036] The output can be optical, acoustic, haptic or a combination of the above.

[0037] Biosignals to be monitored can generally allow conclusions to be drawn about the activities of organs or the organism of the subject. A possible diagnosis, i.e., determination of a disease by a physician, based on the monitored biosignals is not part of the method according to the invention.

[0038] Examples of biosignals to be monitored include blood pressure curves, blood counts, electrocardiograms, electroencephalograms, electromyograms, and electroretinograms. Alternatively or additionally, recordings of the composition of respiratory gas (e.g., CO2 content determined by capnography) or excretions (e.g., urine composition determined by urine test strips) can serve as biosignals.

[0039] Biosignals can be measured using suitable sensors, particularly electrical ones such as electrocardiograms. Preferably, the measurement is non-invasive.

[0040] In some embodiments, multiple control biosignals, in particular multiple control electrocardiograms, can be measured. Multiple control biosignals can, for example, be measured as a time series. This may be particularly preferred for long-term monitoring, such as a long-term ECG.

[0041] In particular, a single value of the reference parameter can be determined for the multiple control biosignals, for example, because the reference parameter does not change significantly over the course of the time series. In these cases, a single reference biosignal is selected from the multiple reference biosignals as a comparison biosignal and compared with each of the multiple control biosignals.

[0042] Alternatively, a respective value of the reference parameter can be determined for each of the multiple control biosignals, for example, because the value of the reference parameter changes over the course of the time series. In these cases, a respective comparison biosignal is selected from the multiple reference biosignals for each control biosignal and compared with the respective control biosignal.

[0043] In a second aspect, the present invention provides a computer program product as defined in claim 11.

[0044] In a third aspect, the present invention provides a system for monitoring biosignals of a subject as defined in claim 12.

[0045] The at least one sensor is designed to measure a control biosignal of the test subject. In particular, the at least one sensor can be ECG electrodes for measuring electrocardiograms. In some embodiments, the at least one sensor can be connected to components of the system, in particular to the controller, via a cable (e.g., via a USB interface) or wirelessly (e.g., via a Bluetooth interface), or can be designed to be connected. In some embodiments, the at least one sensor can be arranged in or on a common housing with at least the controller.

[0046] In some embodiments, the at least one sensor may further be configured to measure a plurality of reference biosignals of the subject.

[0047] The memory is designed to store a plurality of reference biosignals, in particular reference electrocardiograms, of the subject. Each of the plurality of reference biosignals is assigned a respective value of a reference parameter. The assigned values ​​of the reference parameter can also be stored in the memory. In some embodiments, the memory can be located remotely, for example, on a server or in a decentralized network.

[0048] The controller is configured to determine a value of the reference parameter associated with the control biosignal. This value can preferably be determined automatically, for example, by measurement by the at least one sensor or by another sensor, or manually, for example, by user input in an input interface.

[0049] Furthermore, the controller is configured to select at least one comparison biosignal, in particular at least one comparison electrocardiogram, from the plurality of stored reference biosignals based on the determined value of the reference parameter and on the plurality of values ​​of the reference parameter associated with the plurality of reference biosignals.

[0050] Furthermore, the controller is configured to compare the control biosignal and the comparison biosignal. Short description of the drawings

[0051] Embodiments of the present invention will now be described by way of example and with reference to the following figures. Fig. 1A shows a human torso with sensors for measuring electrocardiograms. Fig. 1B is a schematic representation of two measured electrocardiograms. Fig. 2illustrates three reference electrocardiograms with assigned values ​​of the reference parameter "heart rate", as well as a control electrocardiogram with assigned value of the reference parameter "heart rate" according to an embodiment. Fig. 3A illustrates three reference electrocardiograms with associated values ​​of the reference parameter "heart rate" according to another embodiment. Fig. 3B illustrates a control electrocardiogram with assigned value of the reference parameter "heart rate" according to the embodiment of Fig. 3A . Fig. 4 illustrates three reference electrocardiograms and one control electrocardiogram, each with associated values ​​of the reference parameter "posture". Fig. 5 illustrates three reference electrocardiograms and one control electrocardiogram, each with associated values ​​of the reference parameter "ambient temperature". Fig. 6shows an embodiment of a system according to the present invention, Fig. 7 shows a flowchart of a method according to the present invention. Description of preferred embodiments

[0052] The following examples deal with examples of biosignals in the form of electrocardiograms. Electrocardiograms depict the electrical activity of the heart in the form of temporal voltage curves, which can be measured, for example, using ECG electrodes on the subject's body.

[0053] Fig. 1Ashows three views of a human torso 1 of a subject with four ECG electrodes 2-5, one each at the upper end of the sternum (electrode 2), at the lower end of the sternum (electrode 3), at the right mid-axillary line at the level of the lower edge of the sternum (corresponding to the height of electrode 3) (electrode 4), and at the left mid-axillary line at the level of the lower edge of the sternum (corresponding to the height of electrode 3) (electrode 5). Other sensor arrangements for measuring electrocardiograms with a different number of ECG electrodes, for example ten electrodes, are known and can also be used for the purposes of the present invention, in particular for measuring electrocardiograms. The electrodes 2-5 can, for example, be designed as disposable electrodes for adhesive use and comprise a wet gel or dry gel.

[0054] Depending on the arrangement of the electrodes, the existing electrodes are connected in such a way that certain leads or channels are maintained. The four Fig. 1A The electrodes 2-5 shown enable, for example, according to the EASI method, the calculation of a 12-lead ECG recorded with the Einthoven (I, II, III), Goldberger (aVR, aVL, aVF), and Wilson (V1-V6) leads. Alternatively or additionally, the extended chest wall leads V7-V9 and VR3-VR9 and / or an ECG mapping can be calculated in this way. Other wiring schemes and / or leads (e.g., those according to Einthoven, Goldberger, Wilson, Nehb, Franck, or Dower) are also suitable for measuring electrocardiograms for the purposes of the present invention.

[0055] For illustrative purposes, reference is made throughout the description to a 12-lead ECG, recorded, for example, using the four electrodes 2-5. However, the present teaching can also be implemented with ECGs other than 12-lead ECGs, in particular with vector ECGs or single-lead ECGs, or with other biosignals.

[0056] Fig. 1B This is a schematic representation of two electrocardiograms (10, 14) recorded from a test subject. Each electrocardiogram is shown as a temporal variation of an electrical voltage over approximately the duration of one heartbeat. The electrocardiograms (10, 14) shown are Einthoven II derivations.

[0057] For the purposes of the present invention, the term "electrocardiogram" can refer to a single time waveform for a single lead, e.g., an Einthoven II lead, or it can refer to a plurality of time waveforms for different leads. In particular, the entirety of the twelve graphs of a 12-lead ECG can also be referred to as an "electrocardiogram."

[0058] For illustration purposes, each electrocardiogram will be represented by a graph, e.g. the Einthoven lead 11.

[0059] Electrocardiogram 10 is a schematic representation of a physiological electrocardiogram of a healthy subject. The electrocardiogram was recorded while the subject was at rest as a so-called resting ECG. It can be referred to as reference electrocardiogram 10.

[0060] Common ECG parameters such as the QT interval, QRS complex times, ST segment, P wave, R wave, and T wave measurements can be determined from the measured electrocardiogram. The following example discusses the QT interval, i.e., the time interval between the Q wave (the first negative deflection in the QRS complex caused by ventricular excitation) and the T wave (regression of excitation toward the end of the ECG trace). The QT interval of electrocardiogram 10 is schematically highlighted by duration 12.

[0061] This is also in Fig. 1BThe electrocardiogram 14 shown was recorded at a later time than electrocardiogram 10. It was recorded on the same subject as electrocardiogram 10. In particular, it may have been recorded to monitor or control cardiac activity in comparison to the reference electrocardiogram 10, which was classified as unremarkable. The later recorded electrocardiogram 14 is referred to as the control electrocardiogram 14. The control electrocardiogram 14 here shows an increased QT interval 16 compared to the reference electrocardiogram 10. The control electrocardiogram 14 can therefore be considered abnormal compared to the reference electrocardiogram 10.

[0062] A change in the QT interval can have a variety of causes. For example, an increase in heart rate can lead to a shortening of the QT interval. Medications, such as amiodarone, can also prolong the QT interval. There is also a connection between certain electrolyte concentrations in the blood and changes in the QT interval. For example, hypercalcemia or hyperkalemia can be associated with shortening of the QT interval. Furthermore, a long QT interval can also be an indicator of certain cardiac arrhythmias, such as bradycardia.

[0063] Based on a comparison of the reference electrocardiogram 10 and the control cardiogram 14, there is therefore uncertainty as to which of the above-mentioned influencing factors the change in the QT interval observed in the comparison is due.

[0064] In Fig. 2Electrocardiograms and values ​​of a reference parameter from a method according to the invention for monitoring biosignals of a subject are shown schematically.

[0065] Firstly, there are several reference electrocardiograms 20 of the subject with several heart rate values ​​22, each of the several reference electrocardiograms 20 being assigned a respective heart rate value. The respectively assigned value corresponds to the heart rate at which the respective reference electrocardiogram was measured. For example, the first reference electrocardiogram here is assigned the heart rate value 60 beats per minute (in the unit bpm, beats per minute). Alternatively, a heart rate value can be specified in a different unit, e.g., in Hertz, where 1 Hz corresponds to a heart rate of 60 beats per minute. A reference parameter "RR interval", i.e., the time interval between the R waves in the electrocardiogram of two consecutive cardiac cycles (e.g., expressed in milliseconds), also corresponds to a heart rate.The second reference electrocardiogram 20b and the third reference electrocardiogram are assigned the heart rate values ​​90 bpm and 120 bpm, respectively.

[0066] In the embodiment illustrated here, the set 20 of multiple reference electrocardiograms consists of three electrocardiograms 20a-20c. In general, the set of reference electrocardiograms can consist of two or more electrocardiograms. By increasing the number of reference electrocardiograms, the covered spectrum of reference parameter values ​​can be broadened, for example, to cover not only the range between 60 bpm and 120 bpm, but also to include lower heart rates, such as 50 bpm, and / or higher heart rates, such as 150 bpm.

[0067] Alternatively or additionally, the resolution within the covered spectrum can be increased by increasing the number of reference electrocardiograms. Thus, instead of the intervals between heart rate values ​​of 30 bpm present in the illustrated embodiment, comparatively shorter intervals, e.g., 15, 10, 5, or 1 bpm, can be achieved. This allows for more precise or reliable monitoring of the electrocardiograms.

[0068] In the present case, the multiple reference electrocardiograms 20 differ in particular in the position and shape of the T wave, i.e., the reversal of excitation at the right end of the electrocardiogram. Accordingly, the multiple reference electrocardiograms have different QT intervals, with the QT interval in the first reference electrocardiogram 20a being longer than in the other two reference electrocardiograms 20b, 20c, and the QT interval in the third reference electrocardiogram 20c being shorter than in the reference electrocardiograms 20a, 20b. This is consistent with a physiological reduction in the QT interval with increasing heart rate. The multiple reference electrocardiograms 20 were measured in a healthy subject.

[0069] Furthermore, a control electrocardiogram 24 of the subject is available, with a heart rate value 26 of 88 bpm assigned to him. The control electrocardiogram 24 was measured on the same subject at a later time point to monitor cardiac function. In conjunction with the measurement of the control electrocardiogram 24, the heart rate value 26 was also determined.

[0070] In a method according to the invention, the control electrocardiogram 24 can now be compared with at least one of the several reference electrocardiograms 20.

[0071] For this purpose, a comparison electrocardiogram is selected from the multiple reference electrocardiograms 20. This selection is based on the multiple heart rate values ​​22 assigned to the reference electrocardiograms 20, as well as on the heart rate value 26 assigned to the control electrocardiogram 24. Preferably, the one of the multiple reference electrocardiograms 20 whose assigned heart rate value 22 has the smallest difference from the heart rate value 26 (assigned to the control electrocardiogram 24) can be selected as the comparison electrocardiogram (where the difference is expressed as an absolute value). Here, the second reference electrocardiogram 20b has a difference of 2 bpm, whereas the reference electrocardiograms 20a and 20c have differences of 28 bpm and 32 bpm, respectively, from the heart rate 26 of the control electrocardiogram 24.Consequently, the second reference electrocardiogram 20b exhibits the smallest difference in heart rate. The second reference electrocardiogram 20b is selected as the comparison electrocardiogram for comparison with the control electrocardiogram 24. In other embodiments, the reference electrocardiogram selected from the plurality of reference electrocardiograms 20 may be the one whose associated heart rate value 22 represents the next lower or next higher value to the heart rate value 26 (associated with the control electrocardiogram 24). In the illustrated case, this is the first reference electrocardiogram 20a or the second reference electrocardiogram 20b, respectively.

[0072] In the present case, the control electrocardiogram shows no altered QT interval or any other significant change compared to the reference electrocardiogram 20b. It can therefore be classified as normal compared to the reference electrocardiogram.

[0073] In a method for monitoring electrocardiograms not according to the invention, where, for example, several reference electrocardiograms are not available, a control electrocardiogram would be compared with the only available reference electrocardiogram, which, for example, was measured at a heart rate of 60 bpm like electrocardiogram 20a. In this case, a deviation in the QT interval would be detected, but without allowing conclusions to be drawn about the cause (e.g., physiological frequency dependence or pathological cause). If a diagnosis were nevertheless made based on the deviation, the risk of false-positive results would increase. If the only available reference electrocardiogram lacks information about the underlying heart rate (e.g.,60 bpm), this would at least allow for a frequency-dependent adjustment of the QT interval parameter. However, this could be based, for example, on a mathematical or statistical model that can only partially account for the individual's specific circumstances. Examples of frequency-dependent adjustments of the QT interval are the Hegglin formula, Bazett formula, or Fridericia formula. The changes in the electrocardiogram can vary from subject to subject and therefore cannot be generalized.

[0074] In comparison, in some embodiments of the invention, especially with a small difference in heart rate values ​​as in the Fig. 2 In the case presented, a frequency-dependent adjustment of the QT time parameter is unnecessary.

[0075] In Fig. 3Electrocardiograms and values ​​of a reference parameter are shown schematically, as they may be present in the course of a further embodiment of a method according to the invention for monitoring biosignals of a test subject. Fig. 3A shows several reference electrocardiograms 30 and several heart rate values ​​32 as reference parameters.

[0076] The subject's multiple reference electrocardiograms 30 are measured as a continuous time series. The multiple heart rate values ​​32 are also measured as a continuous time series simultaneously with or in a synchronized manner with the multiple reference electrocardiograms. The displayed heart rate curve is based on an interpolation, which converts a quasi-continuous measurement series into a strictly continuous time series using data processing.

[0077] The multiple heart rate values ​​32 are assigned to the multiple reference electrocardiograms 30 by means of the synchronized recording and the thus common time axis.

[0078] The multiple reference electrocardiograms 30 and the multiple heart rate values ​​32 of the Fig. 3AThe heart rate values ​​of the exemplary embodiment illustrated may, for example, have been measured as a result of stimuli that increase the heart rate, such as a targeted load on the test subject on an ergometer. The test subject has been instructed (for example by a system according to the invention) to exert themselves on the ergometer up to their maximum load or for a defined time. Immediately after completion of the load, their heart rate is at a maximum. Other forms of load to initially increase the heart rate are climbing stairs or squats with a certain number of repetitions. Additionally or alternatively, the heart rate can be increased with medication.

[0079] After reaching a maximum heart rate and ending the physical exercise, the measurement of reference electrocardiograms was initiated. The heart rate was recorded simultaneously. The heart rate can be determined directly from the recorded reference electrocardiograms, namely using the RR interval. Therefore, no additional sensor arrangement (e.g., a pulsometer) is necessary. Furthermore, the synchronization of the two time series is facilitated by the direct determination from the time series of the measured reference electrocardiograms.

[0080] Over time, the heart rate slowly decreases from the maximum to the resting heart rate. In this embodiment, a wide range of heart rates from the maximum heart rate to the resting heart rate can be recorded. Depending on the rate of decrease in the heart rate, it may be possible to record and assign a reference electrocardiogram to each integer heart rate in the covered range. If this is the case, identity of the heart rate values ​​can be required for later selection for comparison with a control electrocardiogram. For illustration purposes, Fig. 3A Only a section of the time series is shown, namely three ranges at approximately 90 beats per minute. Reference electrocardiogram 30a is assigned a heart rate of 92 bpm. Reference electrocardiogram 30b is assigned a heart rate of 90 bpm. Reference electrocardiogram 30c is assigned a heart rate of 88 bpm.

[0081] Alternatively or additionally, in some embodiments, the measurement of reference electrocardiograms can be carried out during the increase in heart rate during exercise, e.g. on an ergometer.

[0082] In Fig. 3B A control electrocardiogram 34 is shown, which was measured on the same subject at a later time for monitoring purposes. At the same time, a heart rate value of 36 out of 88 beats per minute is determined and assigned to the control electrocardiogram 34.

[0083] By comparison, the heart rate value from the multiple heart rates 32 that is identical to the heart rate value 36 or has the smallest difference is determined. In the case of the illustrated embodiment, the reference electrocardiogram 30c and the control electrocardiogram 34 are assigned identical heart rate values, namely 88 beats per minute. The reference electrocardiogram 30c is selected as the comparison electrocardiogram and compared with the control electrocardiogram 34.

[0084] This allows for effective monitoring of a test subject, particularly an athlete during training or a convalescent patient during rehabilitation: During a stress ECG, the heart rate changes. According to the teachings of the present invention, particularly in the exemplary embodiment presented here, it is possible to select a suitable reference electrocardiogram for each control electrocardiogram during the stress ECG—that is, a reference electrocardiogram measured under the same or similar conditions.

[0085] This allows stress-induced changes in the ECG curve to be distinguished from changes with other causes (e.g. pathological causes such as circulatory disorders).

[0086] If two of the multiple heart rate values ​​32 have the same difference from the heart rate value 36, both associated electrocardiograms can be selected as comparison electrocardiograms and used for comparison. Alternatively, a middle comparison electrocardiogram can be formed from the two selected reference electrocardiograms. Furthermore, alternatively, one of the two reference electrocardiograms can be selected as the comparison electrocardiogram randomly or in a predetermined manner (for example, the one with the lower / higher associated value of the reference parameter; or the more recent one in the case of different recording dates).

[0087] In Fig. 4Three reference electrocardiograms 40 of a test subject with assigned values ​​42 of the reference parameter "posture", as well as a control electrocardiogram 44 of the same test subject with assigned value 46 of the reference parameter "posture" are schematically shown.

[0088] The reference parameter "posture" is a reference parameter that takes non-numeric values. In a computer-based implementation, each of these non-numeric values ​​can be assigned a corresponding numeric or binary value. For illustrative purposes, the values ​​are presented here in their descriptive word form. For example, the reference parameter "posture" takes the values ​​"lying," "sitting," or "standing."

[0089] The reference parameter "posture" influences the shape of electrocardiograms through the so-called position type, as explained below. Electrocardiograms can be interpreted as projections of a dipole in the subject's body using the various leads mentioned above. For given electrode positions, e.g., the positions shown in Fig. 1AAs shown, a measured electrocardiogram depends, among other things, on the orientation of the projected dipole. The orientations are commonly described under the term position type, for example in connection with the Cabrera circle. Examples of position types include the normal type, left type, and right type. Using the Einthoven I lead as an example (i.e., between the left and right arm), it can be seen that in a left type, this shows a strong positive R wave, whereas the R wave (in the Einthoven I lead) can even be negative in a right type. Corresponding position-type-dependent changes can also be found in the other leads and the other characteristics of the electrocardiogram (shape of the P wave, T wave, etc.). Changes in the position type can have pathological causes, e.g., hypertrophy. For example, left ventricular hypertrophy (LVH) leads to a shift from the normal type to the left type.At the same time, however, posture also influences the position type. For example, standing up can lead to changes in the electrocardiogram that resemble a right-angled type. Comparing electrocardiograms measured in different postures can therefore lead to false or unfounded comparison results. Particularly in long-term ECG studies, it can also happen that the subject changes their posture during the measurement.

[0090] In the embodiment of Fig. 4 Therefore, for comparison with the control electrocardiogram, one of the reference electrocardiograms 40 is selected whose assigned posture value 42 matches that of the control electrocardiogram 44 (i.e., "standing"). This avoids comparing electrocardiograms that were measured in different postures (and therefore have a different position type).

[0091] Fig. 5 shows three measured reference electrocardiograms 50 of a test subject with assigned values ​​52 of the reference parameter "ambient temperature", as well as a measured control electrocardiogram 54 of the test subject with assigned value 56 of the reference parameter "ambient temperature".

[0092] Values ​​of the reference parameter "ambient temperature" describe at least partially the boundary conditions of the subject's surroundings or environment during the measurement.

[0093] Based on the ambient temperature value 56 associated with the control electrocardiogram 54 and the multiple ambient temperature values ​​52 associated with the multiple reference electrocardiograms 50, a comparison electrocardiogram can be selected. In the present case of an ambient temperature value 56 of 22°C, the closest among the values ​​52 of the reference electrocardiograms 50 is the ambient temperature of 20°C. This is associated with the second of the three reference electrocardiograms 50. This second of the reference electrocardiograms 50 is thus selected as the comparison electrocardiogram and compared with the control electrocardiogram 56. This avoids comparing electrocardiograms measured under different environmental conditions.

[0094] Fig. 6shows an embodiment of a system 60 for monitoring electrocardiograms of a subject with four sensors 62, a memory 64, a controller 66 and a display 68.

[0095] The sensors 62 are designed as ECG electrodes and are designed to measure a control electrocardiogram. For this purpose, they can be used in particular according to Fig. 1 be placed on the subject. Furthermore, the sensors 62 are designed to measure multiple reference electrocardiograms.

[0096] The memory 64 is configured to store the multiple reference electrocardiograms. A respective value of a reference parameter is assigned to each of the multiple reference biosignals in the memory. The storage and assignment of reference electrocardiograms and reference parameter values ​​can be performed, for example, in a database format.

[0097] The controller 66 is configured to determine a value of the reference parameter to be assigned to the control electrocardiogram. Here, determining the value of the reference parameter involves a measurement using the sensors 62.

[0098] Furthermore, the controller 66 is configured to select a comparison electrocardiogram from the plurality of stored reference electrocardiograms based on the determined value of the reference parameter associated with the control electrocardiogram and on the plurality of values ​​of the reference parameter associated with the plurality of reference electrocardiograms.

[0099] Furthermore, the controller 66 is configured to compare the control electrocardiogram and the comparison electrocardiogram.

[0100] The display 68 is designed to output information. The display 68 is configured as an LCD screen for visually outputting the information. In particular, it is designed to indicate whether a method for monitoring electrocardiograms was performed correctly. Furthermore, it is designed to output a recommended course of action based on a comparison of the control electrocardiogram and the comparison electrocardiogram after the method has been performed correctly. A recommended course of action to be output can, for example, be directed at the subject sitting down, resting, or engaging in physical activity.

[0101] Fig. 7 shows a flowchart of a method 70 according to an embodiment. The method 70 is used to monitor biosignals of a test subject.

[0102] It comprises the steps of acquiring 72 a plurality of reference biosignals of the subject, each with a value of a reference parameter, measuring 74 a control biosignal of the subject, determining 76 a value of the reference parameter, selecting 78 a comparison biosignal from the plurality of stored reference biosignals and comparing 79 the measured control biosignal with the selected comparison biosignal.

[0103] Selecting 78 a comparison biosignal from the plurality of acquired reference biosignals is based on the value of the reference parameter determined in step 76 and on the plurality of values ​​of the reference parameter acquired in step 72.

[0104] Values ​​of the reference parameter describe physiological states of the subject and / or boundary conditions of an environment at least in part and do not require a diagnosis of a pathological, in particular a cardiac, event.

Claims

1. A method (70) for monitoring biosignals of a test subject, comprising, - recording (72) a plurality of reference biosignals, in particular reference electrocardiograms (30), of the test subject, wherein each of the plurality of reference biosignals is assigned with a respective value of a reference parameter, wherein the reference parameter comprises a heart rate; - measuring (74) a control biosignal, in particular a control electrocardiogram (34), of the test subject, using a sensor, - determining (76) a value (36) of the reference parameter assigned with the control biosignal, - selecting (78) at least one comparative biosignal, in particular at least one comparative electrocardiogram (30c), from the plurality of stored reference biosignals (30), based on a value of the reference parameter assigned to the control biosignal, and on a plurality of values of the reference parameter assigned to the plurality of reference biosignals, - comparing (76) the measured control biosignal with the selected comparative biosignal, and - outputting an action recommendation based on a deviation between the control biosignal and the comparative biosignal, wherein the values of the reference parameter describe at least partially a physiological state of the test subject, characterized in that the plurality of reference biosignals are provided continuously as multiple intervals of a time series.

2. The method according to claim 1, wherein among the plurality of reference biosignals, a reference biosignal having an assigned value of the reference parameter representing a value identical to or having the smallest difference with respect to the value of the reference parameter assigned to the control biosignal, or having an assigned value of the reference parameter representing the next higher or the next lower value with respect to the value of the reference parameter assigned to the control biosignal is selected as the comparative biosignal.

3. The method according to one of the preceding claims, wherein the reference parameter comprises a plurality of components.

4. The method according to one of the preceding claims, wherein the measured control biosignal having an assigned value of the reference parameter is recorded as another plurality of reference biosignals having an assigned value of the reference parameter.

5. The method according to one of the preceding claims, wherein the biosignal is an electrocardiogram, or the biosignal is an ECG-parameter that can be determined from an electrocardiogram, such as, a QT-time interval, times and / or amplitudes in a QRS-complex, ST-segment, P-wave, R-spike, T-wave, Q-spike, S-spike, U-wave, and zero-line.

6. The method according to one of the preceding claims, wherein the reference parameter further comprises one or more of the following: - ECG-parameters that can be determined from an electrocardiogram, blood sugar level, blood pressure, oxygen content in blood, electrolyte levels, body temperature, respiratory rate, minute ventilation; - medication of the test subject, posture of the test subject, current and / or motion state of the test subject up till now, habits of the test subject, in particular occupation, eating habits, frequency of sports activity thereof;7. The method according to one of the preceding claims, wherein values of the reference parameter furthermore at least partially describe boundary conditions of an environment.

8. A method according to the preceding claim, wherein the reference parameter further comprises one or more of the following: time of day, ambient temperature, air pressure, humidity, season.

9. The method according to one of the preceding claims , wherein the outputting further outputs at least one of the following information: the value of the reference parameter assigned to the control biosignal; the value of the reference parameter assigned to the selected comparative biosignal; the control biosignal; the comparative biosignal; a deviation between the control biosignal and the comparative biosignal; a deviation between the value of the reference parameter assigned to the control biosignal and the value of the reference parameter assigned to the selected comparative biosignal.

10. The method according to one of the preceding claims, wherein the biosignal is one of, a blood pressure curve, hemogram, electrocardiogram, electroencephalogram, electromyogram, electroretinogram, record of respiratory gas composition, record of excretion composition.

11. A computer program product stored on a computer readable medium and using a program code causes an apparatus according to claim 12 to perform the steps of the method defined by any one of claims 1 to 10.

12. A system (60) for monitoring biosignals of a test subject, comprising: - at least one sensor (62), in particular ECG electrodes, for measuring a control biosignal, in particular a control electrocardiogram of the test subject; - a memory (64) for storing a plurality of reference biosignals, in particular reference electrocardiograms, of the test subject, wherein each of the plurality of reference biosignals is assigned with a respective value of a reference parameter, wherein values of the reference parameter describe at least partially a physiological state of the test subject, and wherein the plurality of reference biosignals are provided continuously as multiple intervals of a time series; - a controller, wherein the controller is configured to, - determine a value of the reference parameter assigned to the control biosignal, wherein the reference parameter comprises a heart rate, - select at least one comparative biosignal, in particular at least one comparative electrocardiogram, from the plurality of stored reference biosignals, based on the determined value of the reference parameter and on the plurality of values of the reference parameter assigned to the plurality of reference biosignals, - compare the control biosignal and the comparative biosignal, and - output an action recommendation based on a deviation between the control biosignal and the comparative biosignal.