DE102007019624A1 - Method and apparatus for measuring stimulated heart rate variability - Google Patents

Abstract

In order to enable the output of a measured value with regard to the stimulated heart rate variability without the assistance of trained specialist personnel, a method and a device for measuring the stimulated heart rate variability are proposed, which specify a defined measuring time interval and a defined lead time.

Description

The The invention relates to a method and a device for measuring the stimulated heart rate variability. This is called as Heart rate variability the variability in the Heart rate is referred from heart beat to heart beat. This can calculated and specified by suitable mathematical methods, for example, by a standard deviation, in particular the temporal Distance between the individual heart beats. in this connection Heart rate variability is the mathematical correlate for the permanent adaptation of the heart rate to changing requirements in the human organism and in particular is also an expression of neurovegetative regulatory capacity of the body of a human.

To The prior art calculates heart rate variability On the one hand via a 24-hour ECG, which by means of a portable ECG recorder is recorded. This procedure will mostly used in cardiological issues and is proportionate consuming. In particular, it also means a considerable burden of the patient, as this is over 24 hours with the portable ECG recorder must be connected. A targeted stimulation Heart rate variability occurs in this procedure Not.

To the others, according to the prior art, the heart rate variability determined as the result of various neurophysiological functional tests, the carried out in specialized centers or institutions become. These functional tests usually include the Ewing test that Valsalva maneuver, the respiratory Sinus arrhythmia and / or short heart rate variability measurement in Rest as test procedures. These test procedures are performed by the patient even as directed by an examiner, stimulation of his cardiovascular system made that cause characteristic changes in heart rate to lead. For example, in the Ewing test, the patient becomes asked to get up from lying down quickly. During the Valsalva maneuver He is instructed to exhale firmly with the larynx lid closed and so in the chest to create an overpressure. For determination The respiratory sinus arrhythmia slows the patient down Breath rhythm with about six breaths per minute given, which he should follow. The short-term heart rate variability measurement at rest, the provisions include heart rate variability at rest without any special stimulation.

The above-mentioned functional tests are mostly used by neurologists and diabetologists to quantify heart rate variability. The importance of heart rate variability as a risk parameter has been clearly established in a large number of studies, for example in the German Evidence-based Diabetes Guideline (DDG), as of April 15, 2002 released. However, it is not known in wide circles of the population.

To The prior art is for determining heart rate variability necessary, appropriate medical device and medical To have know-how. For medical Questions are usually an electrocardiogram (ECG) registered with the appropriate equipment. Furthermore are meanwhile special systems in the market, which are an automated one and standardizing the study of heart rate variability in the professional, ie in the medically controlled Area, allow. However, these systems provide to the operating personnel high requirements regarding the level of education in the ECG registration and the subsequent determination of the Heart rate variability.

Responsible for heart rate variability are neurovegetative Reflective arches, which are used in particular for blood pressure regulation. A pharmacological blockade, for example, leads on the other hand almost completely disappearing the variation of heart rate variability depending on external influences.

The Therefore, functional tests described above include a targeted Stimulation and set heart rate variability with the stimulation signal in correlation, for example, the quality of heart rate variability to determine. The latter can be done for example via a spectral analysis the heart rate. At maximum quality of heart rate variability Essentially, only one frequency occurs in spectral analysis the heart rate, namely the respiratory rate. It understands itself that to measure the correlation between heart rate variability and stimulation is not necessarily set to a spectral analysis must become. Rather, all analytical Methods are used with which the reactions of the heartbeat Measured on a stimulation, that is, with a measure occupied can, can.

The corresponding measurement values may be made in any suitable manner, for example by outputting a value related to the correlation between heart rate variability and stimulation signal, for example as a graph, in number or in binary. Thus, for example, a graphic order of the respective distance between two heart beats over the measurement time can be made, which represents an image of the heart rate variability and whose amplitude is a measure of the quality of the heart rate variability. On the other hand, from the standard deviation or other mathematical Verfah a numerical value for the quality of heart rate variability can be determined. The same is possible by a corresponding function analysis of the spectrum of the heart rate. Likewise, such determined values can be converted into simple signals, for example, such as (good / bad), (red / green) or (+/-) for the simple statement to what extent the heart rate variability is good or bad, or correspondingly finer tuned by (red / yellow / green) or (+ / 0 / -) for a corresponding more detailed statement regarding high quality, average quality or low quality of heart rate variability. It is immediately understandable that all conceivable types of output can be used advantageously depending on the desired significance.

Also if a patient is usually at a relative simple statement regarding the correlation of heart rate variability in terms of a stimulation signal, so ultimately on a simple statement about his state of health, may be interested in the method known from the prior art such statements only by highly trained specialist staff, usually only be taken by doctors.

It is therefore an object of the present invention generic To provide methods or devices which the output a measure of stimulated heart rate variability without the assistance of trained specialist personnel.

When Solution proposes the invention on the one hand a generic Device which, by means for specifying a defined Measuring time interval distinguished. Likewise, the invention proposes generic method before, which is characterized indicates that a defined measuring interval is specified.

The Specification of a defined measuring time interval relieves the user the responsibility for a sufficient measurement period the to comply with the necessary measuring conditions without first knowing how long this measurement period will be In particular, you can users are already about to adjust for how long those necessary for a proper measurement Conditions, such as a breastfeeding, a steady Breathing or the like, must be respected. Also relieves the Specification of a defined measuring time interval the user of the Responsibility to evaluate a measurement result in retrospect, whether the measurement time was sufficiently long, or to what extent, for example for a longer measuring time, a shorter partial interval from the entire measurement period used for an evaluation should or could be. In particular, a user then also not enticed, only positive appearing measurement data to be included in the evaluation.

on the other hand the invention proposes a generic Device, which is defined by means for specifying a defined Lead time. Likewise, the invention proposes generic method before, which is characterized characterized in that a defined lead time is specified.

Cumulative or alternatively to the specification of a defined measuring time interval allows the specification of a defined lead time objective testing of the measurement environment, for example, whether a heart rate can be recorded with sufficient reliability. Also can during the lead time the physiology of the patient be appropriately soothed in advance, so that in particular the Parasympathetic the control over the body the patient can take over. This allows the specification of a lead time that the patient is up to the lead time as such does not need to deal with what, in particular the risk that the sympathetic nervous engages, minimizes.

By the specification of a defined measuring time interval or by the Specification of a defined lead time arise over it addition cumulative or alternatively reproducible frameworks for the actual measurement or for an evaluation of the Measuring results, so that the latter in particular also automated and without trained medical personnel or without a doctor, so now the stimulated Herzratenvariabilitätsmessung according to the invention also by a layman, especially by the patient himself can be.

Preferably a user is given the beginning of the measurement, which at the measuring device by any suitable means, such as a corresponding display can be made. On the one hand, it can be the user then internally adjust to the fact that now the Measurement is running and accordingly the specifications for the Measurement should be kept as possible. on the other hand This can be the end of the lead time and a while the lead time successfully completed plausibility check be communicated to the user.

Preferably, the user is given the measuring time. Again, this can be done by the measuring device by any suitable means. In this case, for example, a corresponding signal, for example a changing tone, can be output. Likewise, a counter or clock can indicate how long the measurement is running or will be running. In particular, a running on the end of the measuring clock, for example, a backward This is advantageous for ergonomic reasons because the patient or user can immediately get an idea of the remaining measurement time, increasing the acceptance of observing the prescribed conditions for measuring the stimulated heart rate variability, thus increasing the quality the measurement results can be significantly increased. In particular, this increase in quality also means that measurements must be repeated less frequently, as a result of which the acceptance for carrying out such measurements can be further increased.

The The method described here is particularly suitable for the respiratory sinus arrhythmia, so with accordingly the stimulation signal respiration should be stimulated. Consequently it is advantageous if the measuring device means for output a stimulation signal comprises, where - if necessary - also an external signal is detected and processed accordingly can. The overall arrangement, however, is particularly simple, if the measuring device has means for outputting a breathing signal, what for example by a bar, in the desired respiratory rhythm rises and falls again, can happen.

Around the user not with unnecessary measuring processes To charge, it is beneficial if within a lead time carried out a plausibility check becomes. This can be achieved by particularly simple measures be ensured that necessary boundary conditions, such as a More reliable pulse measurement via an ear clip, ei ne sufficient stability of respiration and / or a reliable Heart rate measurement, are complied with when the actual measurement starts. This plausibility check should at least during a sub-interval within the lead time, preferably between 10 s and 30 s. It It goes without saying that a plausibility check preferably also during the measurement or for quality testing The measurement can be used advantageously advantageous. Accordingly It is also advantageous if the measuring device means to carry out has a plausibility check. These implementing means In particular, statistical evaluation methods, for example to check if every heartbeat is detected whether artifacts are present or if a user is not in the right place Rhythm breathes, resulting in a falsification of the measurement result may result.

artifacts for example, by a moving average the deviations of some, for example five, pulse intervals be recognized. Is the deviation of a pulse interval greater as a certain threshold, then is highly likely an artifact that was falsely recognized as a pulse wave has been. Likewise, for example, missing heartbeats be recognized because in consequence unrecognized pulse waves of the Pulse distance of a subsequent to a previous pulse wave increased so that starting from a corresponding threshold there is a high probability of an unrecognized heartbeat. Also, by a spectral analysis of the pulse spacing, the width a frequency peak and as a measure of this be used, if ever regularly is breathed. In the present context, the distance of a Pulse wave from its predecessor wave with the term "pulse interval" denotes this concept and the term "pulse wave" in their most general form and all include body wave correlated with the heartbeat, the Pulse measurement can be used. In addition to simple pulse wave measurement For example, R-waves can also be one ECG and therefore RR distance is used in this regard if the Measurements can be carried out sufficiently easily.

Around Ensure the measurement of stimulated heart rate variability under as uniform conditions as possible, it is an advantage if already during a lead time a stimulation of heart rate variability, for example by Specification of a breath signal occurs. That way, too autonomic nervous system to appropriate measurement in appropriate Be prepared, for example, the parasympathetic nervous system can come to the fore. By the procedural predetermined stimulation during a lead time, the preferably defined, these advantages can be without external intervention, even if no trained operating personnel or even if no doctor is present is.

Especially can also check the plausibility check whether the breathing rhythm complies with the appropriate specification. This can be done for example by a spectral analysis, in which is subsequently checked, whether the frequency peak on the specification of the rhythm, for example, of 0.1 Hz.

It is immediately apparent that the measurement of stimulated heart rate variability per se is relatively complex and therefore should be reliably performed in the prior art only by trained personnel or physicians to patients. In particular, the evaluation of the measurement results is associated with very high inaccuracies. An analytical evaluation of the measurement results, however, depends very much on the reliability of the determined heart rate. For example, even a single unrecognized heartbeat is sufficient to raise the measurement results to falsify it. In addition to the plausibility check described above, a quality check during and / or after the measurement proves to be indispensable. Preferably, the corresponding measuring device accordingly comprises means for quality testing the measurement and for outputting a quality-related value, wherein cumulatively or alternatively the means for quality testing are connected to a data memory in which data on the heart rate recorded by a transducer are stored. In this way, the measuring device can perform an automated quality inspection, which ultimately allows objectively a quantitative or qualitative output of a quality-related value. By means of such an automated quality test, the measurement of stimulated heart rate variability from the field of metrology only feasible for trained personnel or physicians, in a very reliable way in the hands of an untrained user and thus put into the hands of a patient.

The Quality control can be based on the measured data using statistical methods. This can, for example the standard deviation or in particular a maximum and minimum Deviation of the heart rate are checked. In particular, you can for quality testing those already explained above Methods for the plausibility check come into use. But also more complex examination methods, who are interested in the plausibility check can not grab because of the shorter lead time, can be used. For example, it can be that is breathed at the right time, but different deep. This would make the stimulation uneven, Accordingly, the amplitudes of the vibrations would be the Heart rate varies with each respiratory cycle. This can for example by a statistical evaluation of the scattering of the amplitudes, e.g. B. by calculating the coefficient of variation, be assessed.

Especially in conjunction with the specification of a defined measuring time interval, for example between 60 s and 80 s, and / or the specification of a defined lead time, for example between 10 s and 30 s, can through the plausibility check and / or the quality inspection an objective evaluation the data present in the data storage is done, which is on the trained eye of a physician or specially trained Staff can dispense, without thereby the statement by virtue of Measurement results, especially in terms of ultimately for the patient of interest statement - is the heart rate variability okay or not - is diminished.

It It is understood that the above-described plausibility check and / or the quality inspection described above also independent of the other features present Advantageously serve the invention, the measurement of the stimulated Heart rate variability also accessible to laymen do.

includes the transducer has a heart rate monitor with an ear clip over a cable is connected to the remaining measuring device, Can via a cable drum or cable reel, with which the Cable is connected, ensuring that that Cable between measuring device and ear not tangled or jammed, to negatively affect the measurement in this way.

Preferably the cable drum is two-sided effective, as expressed in this way small and lightweight. This is due in particular to the fact that the necessary for rolling up the cable routes can be halved in this way, as compared to unilaterally effective cable drums only half the route needs to be rolled up. This is because of that at the same speed, the cable is double wound. In addition, this increases the cable diameter faster, so for this reason an effective rolling up can be guaranteed with minimal effort.

Further Advantages, objects and characteristics of the present invention illustrated by the following description of attached drawings. In the drawing show:

1 an overall view of a measuring device according to the invention;

2 a schematic front view of the measuring device according to 1 .

3 a schematic perspective of the measuring device according to 1 and 2 ;

4 the measuring arrangement after 1 in a rear view with inserted ear clip;

5 the measuring arrangement after 1 and 4 with retracted ear clip;

6 the main strands of a measuring device according to the invention;

7 a procedure for performing the measurement in the process according to 6 ;

8th the structure of the display of the measuring device according to 1 . 4 and 5 ; and

9 to 19 various displays in process states of the procedure after 7 ,

The in the 1 to 5 illustrated measuring device 1 know an ad 2 , a on-off switch 3 , a memory button 4 , a setting button 5 (SET button), a USB plug 6 and a heart rate monitor, whose ear clip 7 via a cable 8th connected to the other measuring device. With these interfaces, this measuring device succeeds 1 to implement the functionalities of the invention.

In addition, the measuring device still includes a double-acting cable drum 9 , which ensures that the cable between the remaining measuring device 1 and the ear clip 7 constantly under a slight voltage, so that the risk of a negative influence on the measurement result by a hooking cable 8th or by other influences on the cable 8th can be minimized. Due to the cable drum 9 can the ear clip 7 fast and reliable in a recess 10 on the back of the housing of the measuring device 1 be stored. In this way, the device is extremely compact and can be taken anywhere without significant risk that the cable tangled somewhere during transport.

With the keys 3 to 6 can, as in particular in 6 schematically illustrated, various operating modes are initialized. In the present embodiment, the respective end of operation takes place 11 (off) by a key that is assigned to this method point with the appropriate functionality. In alternative embodiments, the expiration of a specific time interval can be used for this purpose after the end of the corresponding, started functionality.

While through the keys 3 to 6 respectively initialized functionalities are in the present embodiment, the keys 3 and 4 redefined. Here is the button 3 an upscrolling, ie a respective increase of an appropriate value by 1, while the key 4 this serves to store a correctly set value. In this respect, a unidirectional programming with only 2 buttons is realized in this embodiment. Likewise, another programming method, such as a bi-directional programming method with two or 3 keys or a slightly more complex input option can be created, which according to the Appendix of the present embodiment as simple as possible programming or input should be provided, which is already known to an average user if possible is what is known to the average citizen especially with unidirectional keystrokes or bidirectional keystrokes with just a few buttons of watches or alarms.

With a connection of the measuring device 1 with a computer (not explicitly shown here) via the USB connector 6 in a conventional manner is in the measuring device 1 the functionality "Data + measured values to PC" 12 started. In the present exemplary embodiment, the data determined by the measuring device are exported to the PC from a data memory (not shown) which is arranged in the housing of the measuring device. These data include both personal parameters as well as measurement data and measurement results. If the connection to the PC is disconnected, the measuring device switches 1 again off, as shown by numeral 11. It is understood that in other embodiments, the interface can be made more complex, so that, for example, inputs can be made via the PC. It is also conceivable, with existing connection to the PC, the measuring device 1 only to be used as a measuring device and to have the entire evaluation and control carried out by the PC. In this regard, the most diverse concrete embodiments are readily conceivable.

By pressing the SET button 5 a user accesses the functionality "Activate / deactivate user, enter user age; Enter date + time " 13 , By pressing the button 3 The various memories "User", "Age" and "Date + Time" can be accessed 4 then you can change the corresponding values by pressing the key as often as necessary. By pressing the button again 3 the individual memory is left again and it can be activated by pressing the button 4 a new memory to be controlled. Again, it is understood that alternative key functionalities can be selected. For example, using the two buttons 3 and 4 Also bidirectional programming situations can be realized by pressing the key 3 the memory increases by the number 1 while pressing the key 4 the memory is reduced by the number 1. By pressing both buttons 3 . 4 At the same time, a storage process as such or the opening of a specific memory can then be implemented. It goes beyond that in functionality 13 further storage operations can be made without further addition.

Will the button 4 with the measuring device switched off 1 pressed, the measuring device turns off 1 into the functionality "Read memory contents + display" 14 , in this functionality, the user has the opportunity to query measurements taken, which may be useful, for example, on the occasion of a doctor's visit.

Is the key when the unit is switched off 3 "I / E-ON" pressed, so will the functionality 15 , the actual measurement, initialized. This is in detail in 7 shown, wherein in the 9 to 19 corresponding to the individual process steps appearances of the display 2 while - for the sake of completeness - the prepared advertisement with all elements in 8th can be found.

Next to a breathing bar 16 and 2 Respiratory direction indicators 17 . 18 for an inhale or exhale, the display includes three 3-digit displays 19 and a 4-digit display 20 , which depending on the functional state in connection with various unit displays in a units column 21 by which respective meanings can be assigned to the respective numbers, the user can provide the information explained herein. More details 22 to 24 complete the display options of the display 2 , Here is the partial display 24 in the present embodiment, the warning that the memory is full and has to be emptied in one way or another by reading or transfer in a PC. In this case, the memory status by the two outer ring segments already coarse warning was previously displayed when it reaches a critical level. In this context, it is understood that such partial displays can also be assigned with other meanings.

As in 7 shown, a pressure on the button starts 3 the actual measurement 15 by first performing a system check, a battery check and display check 25 is carried out. A corresponding indication at B1 is for example in 9 for a weak battery dargstellt. Is the system check 25 unsuccessful, the device switches off with a corresponding display. Otherwise, the device checks in a next step 26 whether a particular user is selected. The latter is, as already explained, about the functionality 13 carried out.

Is, as indicated by the display B2 (see 10 ), a user (user 1 in this embodiment) is selected, then in one process step 27 the age determined from the stored user data. If no user is selected, then in one process step 28 Alternatively, enter the age directly as shown in display B3 11 indicated by way of example. Alternatively to a user choice via the functionality 13 (please refer 6 ) This can also in the process step 26 done by a "non-user" or the user with the number 0 according to the display after 10 as a non-default user directly via the button 3 is selectable.

In the following process step 29 the user has the option of choosing between two measuring programs, which is shown as an example in display B4 12 is shown. In the present embodiment, therefore, only the numbers 1 and 2 are available to the user for program selection. It is understood that in this regard, other programs can be offered alternatively. In the present embodiment, the program "2" is used for heart rate variability monitoring, in which in one step 30 the heart rate variability is continuously calculated and displayed. The corresponding values are stored in the data memory of the measuring device or alternatively routed via the USB interface to a PC. Heart rate variability monitoring can be done via the button 3 be terminated by this button off the measuring device.

Alternatively, there is in the process step 29 in the 12 presented option to activate the program "1", which ultimately determines the respiratory sinus arrhythmia 32 started, which runs in the present embodiment over a defined lead time of 20 seconds. To do this, first via the breathing bar 16 as well as the breath direction indicators 17 . 18 a breathing signal is output as a stimulation signal. At the same time a pulse display 22 activates and calculates and displays the heartbeat heart rate heart rate. During the lead time, the user has the opportunity to adapt his breathing to the respiratory signal. At the same time, the ear clip signal is checked by ascertaining from the ascertained heart rate the sliding mean value of the deviation of the respectively last five pulse intervals and setting it against a threshold value. If this threshold is exceeded, it is assumed that there is either an artifact, that is, a non-existent heartbeat, or a missing heartbeat. In particular, this preliminary test can ensure that all pulses are measured correctly, which would otherwise lead to a considerable deterioration of the measurement result. In addition, a spectral analysis is performed and checks to what extent a frequency peak is at the specified respiratory rate. Suggests this plausibility check 33 fails, then an error message B6 (see 14 ) is displayed and the unit then turns off 34 ,

Otherwise the measurement will be over a defined measuring time interval 35 , in the present embodiment over 70 seconds, during which the user the display B7 is displayed. This includes in addition to the breathing signal 16 to 18 and the pulse display 19 . 21 . 22 a backwards measuring time display in the partial display 20 , which is used to output the measurement time, so that users can adjust to when the measurement ends is.

During the measurement 35 the corresponding data are stored.

This is followed by an evaluation 36 What the user through 3 bars of the partial display 19 is signaled as shown by the exemplary display B8 in 16 shown. In the meantime, quality parameters are calculated in particular, including the previously used calculation methods for plausibility checks 33 as well as refined statistical methods. In the present embodiment, this is a calculation of the coefficient of variation of the amplitude as a measure of their dispersion, so that a statement can be made about the extent to which, although breathed differently in time to the beat. If the quality is lower, this will be communicated to the user as an error message 37 , which is exemplary as display B9 in 17 is shown. After this the device switches off.

If the quality exceeds a predefined value, the evaluation is calculated age-corrected and displayed, which in a final process step 38 happens, which has a constantly changing display B10 / B11, which gives the user a variety of information, such as time and date in the partial display 20 and respiratory rate (rsa 1 / min), accuracy of respiration with respect to the score (score%) and quality (quality%), see 18 , pulse rate (1 / min pulse) and heart rate variability (% cv; ms rmssd), see 19 , indicates. Incidentally, this display form also corresponds to the display form when using the functionality in this embodiment 14 "Read memory contents + display" according to 6 ,

After reading the measurement results, the device can be activated via the button 3 be turned off again.

Through the plausibility check 33 , the quality inspection 36 and the specification of defined measuring time intervals 35 or lead times 32 In particular, this measuring device ensures that even laypersons can measure stimulated heart rate variability. In particular, the data can also be measured at almost any location, so that continuous measurement series can be recorded for the first time without too great stress on a patient, which are also available for further evaluations due to the possibility of data transfer or subsequent read-out. It is understood that details of this measuring device 1 can be modified without departing from the subject matter of the present invention. In particular, the measuring device 1 be provided with additional functionalities or have more interfaces to other transducers to allow more complex evaluations or to record even more patient data.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited non-patent literature

• - German Evidence-based Diabetes Guideline (DDG), as of April 15, 2002 [0004]

Claims (16)

Apparatus for measuring stimulated heart rate variability comprising means for determining heart rate variability, means for correlating heart rate variability with a stimulation signal, and means for outputting a value related to correlation, characterized by means for specifying a defined measurement time interval ( 35 ). A device for measuring stimulated heart rate variability comprising means for determining heart rate variability, means for correlating heart rate variability with a stimulation signal, and means for outputting a value related to correlation, characterized by means for specifying a defined lead time (Fig. 32 ). Apparatus according to claim 1 or 2, characterized by means for outputting a signal for the start of measurement. Device according to one of Claims 1 to 3, characterized by means for outputting the measuring time ( 20 ). Device according to one of claims 1 to 4, characterized by means for quality control ( 36 ) measuring and outputting a quality related value. Device according to one of claims 1 to 5, characterized by means for outputting a stimulation signal. Apparatus according to claim 6, characterized by specification of a breathing signal ( 16 . 17 . 18 ). Device according to one of Claims 1 to 7, characterized by means for carrying out a plausibility check ( 33 ). Method for measuring stimulated heart rate variability, in which the heart rate variability is determined and correlated with a stimulation signal, characterized in that a defined measuring time interval ( 35 ) will pretend. Method for measuring stimulated heart rate variability, in which the heart rate variability is determined and correlated with a stimulation signal, characterized in that a defined lead time ( 32 ) is given. Method according to claim 9 or 10, characterized the beginning of the measurement is output to a user (display B7). Method according to one of claims 9 to 11, characterized in that the measuring time output to a user becomes (display B7). Method according to one of claims 9 to 12, characterized in that during and / or after the measurement, a quality test ( 36 ) he follows. Method according to one of claims 9 to 13, characterized in that the respiration is stimulated. Method according to one of claims 9 to 14, characterized in that at least during a part-time interval within the lead time ( 32 ) a plausibility check ( 33 ) is carried out. Method according to one of claims 9 to 15, characterized in that during a lead time ( 32 ) a stimulation takes place.