DE102014212590A1 - Method and device for detecting the cardiac activity of a driver - Google Patents

Abstract

A method and a device for detecting the cardiac activity of a driver of a motor vehicle by means of the capacitive ECG method, wherein a predetermined number of electrodes are integrated in the driver's seat, perform the following steps: defining an electrode as a reference electrode, defining measurement channels as bipolar derivatives of the other electrodes with respect to the reference electrode, performing a spatiotemporal independence analysis based on the measurement channels to determine the output channels of an output vector of the independence analysis, selecting at least one output channel from the output channels of the output vector of the independence analysis, and determining heart rate and heart rate variability the at least one selected output channel.

Description

The invention relates to a method for detecting the cardiac activity of a driver of a motor vehicle according to the preamble of claim 1 and to a corresponding device according to the preamble of claim 5.

Due to the demographic development of the population structure and the ever-increasing number of older drivers, systems for medical analysis or support of the driver in an automotive environment are becoming increasingly important. An essential requirement for medical assistance systems is their ability to reliably measure vital signals, wherein one of the most important vital signals is the heartbeat, in particular its change and rhythm, ie the cardiac activity.

Detection of cardiac activity and autonomic regulation, hereafter referred to as physiological monitoring, allows the diagnosis and prediction of cardiovascular complications and may further contribute to the evaluation of conditions such as stress and fatigue. A functional physiological monitoring of motorists requires a technical solution that does not represent any restriction for the driver, which ideally requires a contactless function, works completely non-reactive and delivers reliable information despite the difficult measurement situation found in the car. The difficulties of the measurement situation are due in particular to passive and active movements of the driver.

This is how the document describes US 20090226071 A1 a device for determining the heart rate of a person by means of the analysis of optical images of a skin portion which is located above a blood-carrying capillary. The observation of the skin section takes place in the visible light range, wherein the observation can take place both in reflection and in transmission and for the irradiation of the skin section a suitable light source is used. The change in the volume flow of blood in the capillaries caused by the heartbeat can be detected in the optical images and thus used to determine the cardiac activity. However, the use of an optical method by observing the skin surface in a motor vehicle is difficult to realize.

Another possibility for the non-contact determination of cardiac activity is provided by the capacitive ECG, which is abbreviated hereafter to kEKG. The kEKG is of particular interest because it has already been shown in the clinical environment that comparable results to the clinically used reference technique, the conductive ECG, can be achieved under appropriate measurement conditions. Regarding the monitoring of drivers by kEKG first approaches are described.

In the publication U. Wiklund et al: "Adaptive Spatio-temporal filtering of disturbed ECCs: a multi-channel approach to heartbeat detection in smart clothing", Med. Bio. Closely. Comput., Vol. 45, no. 6, pp. 515-523, 2007 , a method for determining an ECG is described, wherein in a tight-fitting outer garment, such as a T-shirt, a plurality of electrodes for defining a plurality of possible measuring channels are arranged. By means of an adaptive spatial-temporal filtering method (spatio-temporal filtering) of the ECG signals, heartbeats can be determined in a strongly noisy environment.

A summary of the independence analysis, known as Independent Component Analysis ICA, can be found A. Hyvärinen: Independent Component Analysis: Recent Advances, Phil. Trans. R. Soc. A, vol. 371, no. 1984, pp. 1-19, 2013 be removed.

In T. Matsuda et al .: ECG Monitoring of a Car Driver Using Capacitively-Coupled Electrodes, Proceedings of the IEEE Engineering in Medicine and Biology, 30th Annual Conference, Vancouver, Canada 2008, 1315-1318 , A method for capacitive measurement of an ECG, ie a kEKG, described, wherein in the lower part of the driver's seat, ie in the buttocks of the driver, a signal electrode is arranged, while the steering wheel is provided with a suitable ground electrode. It was found that with this arrangement, in principle, an ECG signal can be determined, however, large-area electrodes must be used and the quality of the measurement signal depends strongly on the external driving conditions. Thus, the ECG determination in bad road conditions turns out to be extremely difficult.

In Wartzek et al: "ECG on the Road: Robust and Unobtrusive Estimation of Heart Rate", IEEE transactions on bio-medical engineering, Vol. 11, p. 3112-3120, Nov. 2011 , a device arranged in the driver's seat for determining the heart rate based on a capacitive ECG is described in the backrest of the driver's seat 6 electrodes and in the lower seat part, a so-called DRL (DRL - Driven Right Leg) are arranged, wherein the DRL electrode has the function of the ground electrode. A measurement channel is defined as the bipolar derivative of two electrodes, whereby several channels are examined and a decision is made in which of the observed channels a suitable QRS complex can be found. In this context, a QRS complex in medicine is understood to mean a group of electrocardiogram eruptions caused by the depolarization of the two heart chambers. It turns out that the determination of the ECG, for example, depends on the clothing of the test persons, so that in unfavorable clothing often no ECG could be determined and safe monitoring of the driver is not possible. Likewise, a safe exclusion of artifacts is not always possible.

The known methods for determining the cardiac activity of a driver have difficulties with the disturbing influences found in the motor vehicle, namely with regard to vehicle and driver movement as well as the individually greatly differing driver characteristics.

The invention is therefore based on the object to improve the automatic identification of cardiovascular signals of the driver of a motor vehicle.

This object is achieved by a method for detecting the cardiac activity of the driver of a motor vehicle having the features of claim 1 and by a corresponding device having the features of claim 5. Preferred embodiments of the invention are the subject of the dependent claims.

• – Festlegen einer Elektrode als Referenzelektrode,
• – Definieren von Messkanälen als bipolare Ableitungen der anderen Elektroden gegenüber der Referenzelektrode,
• – Durchführen einer räumlich zeitlichen Unabhängigkeitsanalyse basierend auf den Messkanälen zur Bestimmung der Ausgangskanäle eines Ausgangsvektors der Unabhängigkeitsanalyse,
• – Auswählen von mindestens einem Ausgangskanal aus den Ausgangskanälen des Ausgangsvektors der Unabhängigkeitsanalyse, und
• – Bestimmung von Herzrate und Herzratenvariabilität aus dem mindestens einen ausgewählten Ausgangskanal.

The inventive method for detecting the cardiac activity of a driver of a motor vehicle by means of the capacitive ECG method, wherein a predetermined number of electrodes are integrated in the driver's seat, comprises the following steps:

• Setting an electrode as a reference electrode,
• Defining measurement channels as bipolar derivatives of the other electrodes with respect to the reference electrode,
• Performing a spatiotemporal independence analysis based on the measurement channels to determine the output channels of an output vector of the independence analysis,
• Selecting at least one output channel from the output channels of the output vector of the independence analysis, and
• Determination of heart rate and heart rate variability from the at least one selected output channel.

Preferably, a preselection of the measuring channels for supplying a selection of measuring channels to the spatio-temporal independence analysis.

More preferably, the selection of at least one output channel by means of a cascaded selection process, wherein artifacts are determined and excluded.

In particular, the cascaded selection process comprises three steps, namely a primary artifact exclusion, a secondary artifact exclusion, and a channel selection.

• – eine vorgegebenen Anzahl von in dem Fahrersitz integrierten Elektroden zur Festlegung einer Anzahl bipolarer Messkanäle,
• – eine Einrichtung zur Durchführung einer räumlich-zeitlichen Unabhängigkeitsanalyse basierend auf den Messkanälen zur Bestimmung der Ausgangskanäle eines Ausgangsvektors der Unabhängigkeitsanalyse,
• – eine Einrichtung zum Auswählen von mindestens einem Ausgangskanal aus den Ausgangskanälen des Ausgangsvektors der Unabhängigkeitsanalyse, und
• – eine Einrichtung zur Bestimmung von Herzrate und Herzratenvariabilität aus dem mindestens einen Ausgangskanal.

The device according to the invention for detecting the cardiac activity of a driver of a motor vehicle by means of the capacitive ECG method, which is designed and configured to carry out the method explained above, comprises:

• A predetermined number of electrodes integrated in the driver's seat for defining a number of bipolar measuring channels,
• A device for carrying out a spatio-temporal independence analysis based on the measuring channels for determining the output channels of an output vector of the independence analysis,
• Means for selecting at least one output channel from the output channels of the output vector of the independence analysis, and
• A means for determining heart rate and heart rate variability from the at least one output channel.

The device preferably has a device for preselecting the measurement channels for supplying a selection of measurement channels to the spatio-temporal independence analysis.

Preferred embodiments of the invention are explained below with reference to the drawings. It shows

1 a first example of a system for determining a kEKG, and

2 a second example of a system for determining a kEKG.

1 shows a first example of the components of a system for determining the cardiac activity of a driver of a motor vehicle. Thereby are in the driver's seat 9 of the motor vehicle (not shown) arranged a plurality of electrodes, in the example of the 1 in the backrest 10 of the seat 9 six electrodes 1 to 6 and in the seating area 11 (Buttocks area) two more electrodes 7 . 8th , so a total of eight electrodes in the driver's seat 9 are arranged integrated.

The kEKG is controlled by the electrodes in the driver's seat 1 to 8th as bipolar leads to an electrode selected as the reference electrode 1 to 8th recorded, so that in this way seven ECG channels are measured capacitively. For example, electrode 3 used as reference electrode, the result in the following table seven ECG channels, for further formal treatment or explanation of the method used, the seven ECG channels are redefined in the formal channels x _i listed on the right: electrode combination ECG channel Formal channel 1 - 3 KN1 x ₀ 2 - 3 KN2 x ₁ 4 - 3 KN 4 x ₂ 5 - 3 KN5 x ₃ 6 - 3 KN6 x ₄ 7 - 3 KN7 x ₅ 8th - 3 CN8 x ₆

The selection of the electrode 3 As a reference electrode is to be understood as an example only, it can of course be chosen another electrode. Likewise, the total number of electrodes is exemplary and not limited to eight.

In a spatio-temporal independence analysis 12 Also referred to as spatiotemporal ICA (spatio-temporal independent component analysis), the seven ECG signals x _i are associated with time-shifted duplicates of these signals over a predetermined period of time, for example 10 seconds, thereby providing temporal and spatial filtering is reached. This is also referred to as data fusion at the raw data level. The signals of the ECG channels are regarded as signal overlays from originally independent components. By means of the independence analysis 12 the quadratic segregation matrix W is determined taking into account the central limit theorem, so that the original independent components, in the present case the driver's cardiac activity, can be determined.

wobei I die Anzahl der Kanäle i und K die Anzahl der verschobenen Versionen bedeutet. From the input signals x _i (n) of the n-th measurement of the i-th channel are in the independence analysis 12 the following quantities z _{i, k} (n) are formed for spatial-temporal filtering:

where I is the number of channels i and K is the number of shifted versions.

In this example, I = 7 channels and K = 10 time-shifted versions are considered.

The output y of the spatio-temporal independence analysis 12 arises too y = Wz, wherein the square segregation matrix W has the dimension [IK · IK]. As an output of the spatio-temporal independence analysis 12 The result is the vector y, which comprises KI = N output channels ICA1 to ICAN. In the present example, these are 70 output channels, which are also referred to as components. In principle, the spatio-temporal independence analysis 12 work with any number of input channels I and time shifts K.

The components or output signals ICA1 to ICAN of the output vector y of the spatio-temporal independence analysis 12 become a cascaded channel selection 13 fed, in which the frequency bands of the output channels are evaluated. Those output channels ICA1 to ICAN, which are not suitable for further use, are discarded. The evaluation is carried out both on the basis of the frequency characteristics generally to be expected in the ECG and also after the raw data fusion by means of the spatio-temporal independence analysis 12 expected characteristics. It assesses the severity and appearance characteristics of QRS complexes, with QRS complexes reflecting electrical cardiac excitation, ie individual heartbeats.

erfüllen, werden aussortiert. Es wird also im ersten Schritt überprüft. ob die höherfrequenten Leistungen, wie sie im Falle ausgeprägter QRS Komplexe erwartet werden, ausreichend stark gegenüber den niederfrequenten Anteilen, die Rauschen und Störungen darstellen, repräsentiert sind. The cascaded channel selection 13 involves several steps, three steps being used in the present example. The first step, the primary artifact exclusion, is the ratio of higher-frequency power p (1) / HF to low-frequency power p (1) / NF for each output channel ICA1 to ICAN or component of the output vector y determined. The sizes p (1) / HF and p (1) / NF are determined by estimates of the spectral power density, with higher frequency for the frequency range 5 to 40 Hz and low frequency for the frequency range less than 5 Hz. Channels ICA1 to ICAN or components that meet the criterion

fulfill are sorted out. It will be checked in the first step. whether the higher-frequency powers, as expected in the case of pronounced QRS complexes, are sufficiently strong in comparison with the low-frequency components that represent noise and interference.

In the remaining channels, in a second step, an amplification of the QRS complexes by means of digital filtering by means of a bandpass filter in the range 5-11 Hz is performed, which ensures that in the spectrum of suitable signals a periodic component with period of the heart rate, ie between 0 , 5 Hz and 5 Hz, together with their harmonics. This can be done by means of a smoothed derivative filter with a subsequent squaring. To classify a filtered signal as usable, the power in this frequency range should be distinct from the remaining high frequency power. The exclusion criterion now applies in the second step:

Finally, in a third step, the most suitable channel ICA_sel1 is selected from the remaining channels by evaluating the degree of distinctness of the fundamental frequency, and possibly of its harmonics. Particularly pronounced spectral peaks in the range between 0.5 Hz and 5 Hz speak for a good usable signal. You can also select multiple channels.

The third step of the cascaded channel selection 13 selected channel ICA_sel1 becomes a device 14 for determining heart rate and heart rate variability. The heart rate variability corresponds to the dynamics of the distances between two successive QRS complexes, ie heartbeats.

2 shows a second example of a system for determining a kEKG, wherein the first example identical system components with the in 1 used reference numerals are designated and will not be explained in detail. In the system after 1 takes place in a preselection device 15 a preselection of the possible channels. Also in the example of 2 eight electrodes are arranged in the driver's seat so that seven possible measuring channels KN1, KN2, KN4 to KN8 are available if one of the eight electrodes 1 - 8th , in the present example, electrode 3 , is selected as the reference electrode. Is now in the preselection device 15 recognizable that individual measuring channels provide an inadequate quality of measurement, for example, if no or too little pronounced QRS complex in the raw signal is recognizable, these channels can be sorted out directly. If, for example, only the channels KN5, KN6 and KN7 are suitable for further processing, the subsequent signal processing in the independence analysis is simplified 12 and the cascaded signal selection 13 ,

Furthermore, a feedback of the signal analysis to the preselection device 15 possible by following the various steps of artifact exclusion in the signal selection 13 present signals or their correlation to the input signals are evaluated. Thus, suitable input signals can be preselected and / or the reference electrode can be adapted adaptively if required.

LIST OF REFERENCE NUMBERS

1

electrode

2

electrode

3

electrode

4

electrode

5

electrode

6

electrode

7

electrode

8th

electrode

9

Automotive seat

10

backrest

11

seat part

12

Spatio-temporal independence analysis

13

Cascaded channel selection

14

Heart rate, heart rate variability

15

preselection

KN1

ECG channel

KN2

ECG channel

KN 4

ECG channel

KN5

ECG channel

KN6

ECG channel

KN7

ECG channel

CN8

ECG channel

ICA1

Output channel independence analysis

ICAN

Output channel independence analysis

ICA_sel1

Selected output channel

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 20090226071 A1 [0004]

Cited non-patent literature

• U. Wiklund et al: "Adaptive Spatio-temporal filtering of disturbed ECCs: a multi-channel approach to heartbeat detection in smart clothing", Med. Bio. Closely. Comput., Vol. 45, no. 6, pp. 515-523, 2007 [0006]
• A. Hyvärinen: Independent Component Analysis: Recent Advances, Phil. Trans. R. Soc. A, vol. 371, no. 1984, pp. 1-19, 2013 [0007]
• T. Matsuda et al .: "ECG Monitoring of a Car Driver Using Capacitively-Coupled Electrodes, Proceedings of the IEEE Engineering in Medicine and Biology, 30th Annual Conference, Vancouver, Canada 2008, 1315-1318 [0008]
• Wartzek et al: "ECG on the Road: Robust and Unobtrusive Estimation of Heart Rate", IEEE transactions on bio-medical engineering, Vol. 11, pp. 3112-3120, Nov. 2011 [0009]

Claims (6)

Method for detecting the cardiac activity of a driver of a motor vehicle by means of the capacitive ECG method, wherein a predetermined number of electrodes ( 1 - 8th ) in the driver's seat ( 9 ), and wherein the method comprises the steps of: defining an electrode as a reference electrode ( 3 ), Defining measurement channels (KN1, KN2, KN4-KN8) as bipolar leads of the other electrodes ( 1 . 2 . 4 - 8th ) with respect to the reference electrode ( 3 ), Performing a spatio-temporal independence analysis ( 12 ) based on the measurement channels (KN1, KN2, KN4-KN8) for determining the output channels (ICA1-ICAN) of an output vector of the independence analysis ( 12 ), Selecting at least one output channel (ICA_sel1) from the output channels of the output vector of the independence analysis ( 12 ), and determining heart rate and heart rate variability from the at least one exit channel (ICA_sel1). Method according to claim 1, characterized in that a preselection ( 15 ) of the measuring channels (KN1, KN2, KN4-KN8) for supplying a selection of measuring channels (KN5, KN6, KN7) to the spatio-temporal independence analysis ( 12 ) he follows. Method according to one of the preceding claims, characterized in that the selection of at least one output channel (ICA_sel1) by means of a cascaded selection method ( 13 ), whereby artefacts in the output channels (ICA1-ICAN) are detected and excluded. Method according to claim 3, characterized in that the cascaded selection method ( 13 ) comprises three steps, namely a primary artifact exclusion, a secondary artifact exclusion, and a channel selection. Device for detecting the cardiac activity of a driver of a motor vehicle by means of the capacitive ECG method, which is designed and arranged to carry out the method according to one of the preceding claims, with a predetermined number of integrated in the driver's seat electrodes ( 1 - 8th ) for determining a number of bipolar measuring channels (KN1, KN2, KN4-KN8), a device for carrying out a spatio-temporal independence analysis ( 12 ) based on the measurement channels (KN1, KN2, KN4-KN8) for determining the output channels (ICA1-ICAN) of an output vector of the independence analysis ( 12 ), an institution ( 13 ) for selecting at least one output channel (ICA_sel1) from the output channels (ICA1-ICAN) of the output vector of the independence analysis by means of a cascaded selection method ( 13 ), and a facility ( 14 ) for determining heart rate and heart rate variability from the at least one exit channel (ICA_sel1). Device according to claim 5, characterized in that the device comprises a preselection device ( 15 ) of the measuring channels (KN1, KN2, KN4-KN8) for supplying a selection of measuring channels (KN5, KN6, KN7) to the spatio-temporal independence analysis ( 12 ) having.

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