JP5018569B2 - ECG waveform processing device, heart rate measurement device - Google Patents

Description

  The present invention relates to an electrocardiographic waveform processing technique for executing predetermined processing on an electrocardiographic waveform measured from a measurement subject.

Conventionally, a pair of left and right electrodes are provided on the ring portion of the steering wheel, and the driver's cardiac radio waves are detected by detecting a potential difference between the electrodes when the vehicle driver grips each electrode with his / her left and right hands. An apparatus that measures a shape and measures a heart rate from the electrocardiogram waveform is known (for example, see Patent Document 1).
JP-A-6-255516

  In such a heart rate measuring device, the heart rate is obtained from the frequency analysis result of the electrocardiographic waveform measured for a certain time. This is a method of detecting the highest peak from the frequency spectrum of the electrocardiogram waveform and converting the frequency into a heart rate. For example, as shown in FIG. 14, the processing of electrocardiographic waveform measurement → high pass filter processing → FFT (Fast Fourier Transform) processing → heart rate calculation from peak frequency is sequentially performed.

  However, in the frequency spectrum, in addition to the peak of the fundamental frequency determined by the heart rate, harmonic peaks often appear, and if this harmonic peak is detected by mistake, the heart rate is measured correctly. I can't do that.

Such a problem is the same even when a pair of left and right electrode portions are provided on the ring portion of the steering wheel and the vehicle driver holding the electrode portions is the person being measured.
The present invention has been made in view of these problems, and an object of the present invention is to process an electrocardiographic waveform obtained from a subject to obtain an electrocardiographic waveform with reduced harmonic components of the frequency spectrum.

  In the electrocardiographic waveform processing apparatus according to claim 1, which is made to achieve the above object, the measuring means measures the electrocardiographic waveform of the measurement subject. It has been found that by adding processing, harmonic components of the frequency spectrum can be reduced, for example, an electrocardiographic waveform suitable for heart rate calculation can be obtained.

Therefore, processing means for executing predetermined processing on the electrocardiographic waveform measured by the measuring means performs the following processing. That is, a binarization process for generating binarized data in which 1 is recorded at a position where an R wave exists in an electrocardiogram waveform and 0 is recorded at other positions, and a binarization process created by the binarization process. Widening processing is performed in which the width of 1 in the binarized data is expanded to a width that is half of the average interval of the positions where 1 exists in the binarized data created by the binarization processing.

  If frequency analysis is performed on the binarized data thus widened, harmonic components of the frequency spectrum can be reduced. Therefore, for example, as shown in claim 6, if applied to an electrocardiogram waveform processing apparatus that performs frequency analysis on the binarized data subjected to widening processing and measures the heart rate based on the frequency analysis result, The number can be measured correctly.

By executing the widening process, the harmonic component of the frequency spectrum of the binarized data can be reduced, but the width of 1 in the binarized data created by the binarizing process is binarized. It is theoretically considered that the harmonic component can be reduced most when the width is expanded to half the average interval at the position where 1 exists in the binarized data created by the binarization processing.

The subject's electrocardiographic waveform processing apparatus such as this, for example, it is conceivable that the driver of the vehicle. In that case, as shown in claim 2 , the driver is provided with electrode portions respectively provided on the left and right grip portions of the steering wheel, and the driver is a driver who grips the steering wheel via the left and right electrode portions. It is possible.

In any of the above cases, the plurality of electrode portions may be disposed at positions where the driver can easily grip the steering wheel, but more preferably, the steering is as described in claim 3. It is desirable to arrange on the wheel side surface of the wheel.

In other words, when the driver grips the left and right sides of the steering wheel, the driver seat side surface of the steering wheel comes into contact with the base of the thumb with the thinnest skin in the palm of the driver. If an electrode part is arrange | positioned as described in Claim 3 , it will become easier to detect biosignals, such as an electrocardiogram signal, the SN ratio of a biosignal will be improved, and the measurement precision of an electrocardiogram waveform can be improved.

The measurement means may be provided anywhere in the vehicle, but for the wiring ease and noise reduction, it is desirable to place near the electrode portion, in order that, when mounted to the scan tearing the wheel Good.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of a heart rate measuring device that measures the electrocardiogram waveform of a vehicle driver, performs predetermined processing, and further measures the heart rate. FIG. 2 shows the vehicle of each part of the measuring device. It is explanatory drawing showing the arrangement state to. 2A is a front view of the steering wheel 2 viewed from the driver's seat side, and FIG. 2B is a side view of the steering wheel 2.

  As shown in FIG. 1, the heart rate measuring device of the present embodiment includes left and right electrode portions (left electrodes) provided on left and right grip portions of the steering wheel 2 in order to acquire an electrocardiogram waveform from a vehicle driver. Part 10 and right electrode part 20).

  As shown in FIG. 2, the left and right electrode portions 10 and 20 are provided in a ring portion (wheel ring) 4 of the steering wheel 2 where a left and right spoke portion (wheel spoke) 6 is connected.

  The left and right electrode portions 10 and 20 are arranged along the circumferential direction of the ring portion so that the driver can hold the left and right hands at the same time, and are arranged at the connecting portion of the left and right spoke portions 6. Each central portion is formed so as to project toward the spoke portion 6 side. This is because when the driver grips this portion, the area in contact with the palm of the driver is increased to reduce the contact impedance with the driver's palm.

  Further, each of the electrode portions 10 and 20 is provided on the driver seat side surface of the steering wheel 2 so that when the driver grips the steering wheel 2, the base of the thumb having a small skin thickness comes into contact with the palm of the driver. Is arranged. This is also for reducing the contact impedance between the electrode portions 10 and 20 and the palm of the driver.

  Further, as shown in FIG. 1, each electrode portion 10, 20 is configured as an electrode pair including a first electrode 11, 21 and a second electrode 12, 22. The electrodes 11, 12, 21, and 22 of the electrode units 10 and 20 are connected to the measurement circuit units for measuring the electrocardiogram waveform (in other words, the electrocardiogram signal) and the contact impedance via the switching circuit unit 30. Connected to.

  That is, in the heart rate measuring apparatus of the present embodiment, the amplification is connected to the left and right electrode portions 10 and 20 and generates an electrocardiogram signal by amplifying the potential difference generated between the left and right electrode portions 10 and 20. Part 40 and an impedance measuring part 50 for measuring the contact impedance between the left and right electrode parts 10, 20 and the driver's palm, and the left and right electrode parts via the switching circuit part 30. By connecting the first and second electrodes 11 and 21 to the amplifying unit 40, an electrocardiographic signal is measured through the amplifying unit 40, or each of the electrode units 10 and 20 is connected through the switching circuit unit 30. By connecting the first electrode 11, 21 and the second electrode 12, 22 to the impedance measuring unit 50, the contact impedance can be measured via the impedance measuring unit 50. .

  The switching circuit unit 30 connects the electrodes 11, 12, 21, and 22 to a reference potential (ground: GND in this embodiment) for each of the left and right electrode units 10 and 20, or the amplifier unit 40 or impedance measurement. The first changeover switch 32 for switching whether to connect to the measurement circuit unit side of the unit 50, and the electrodes 11, 12, 21, 22 switched to the measurement circuit unit side via the first changeover switch 32 are connected to the amplification unit 40. Or a second changeover switch 34 connected to the impedance measuring unit 50.

  Further, the switching of the switching circuit unit 30, the measurement of the electrocardiogram signal using the amplification unit 40, and the measurement of the contact impedance using the impedance measurement unit 50 are all configured with a CPU, ROM, RAM, etc. as the center. It is executed by a microcomputer 60 (hereinafter simply referred to as CPU).

  Further, the CPU 60 is connected to a wireless communication unit 70, and the CPU 60 conforms to a request from an external device (specifically, a portable device or an in-vehicle device possessed by the driver) connected to the wireless communication unit 70. Then, the measurement result of the contact impedance and the electrocardiogram signal is transmitted to the external device via the wireless communication unit 70.

  In addition, an information storage unit 75 is connected to the CPU 60. The information storage unit 75 includes a rewritable nonvolatile memory such as a flash memory, and can store a rotation angle α for measurement, which will be described later.

  As shown in FIG. 2, the switching circuit unit 30 is separated into the left electrode unit 10 and the right electrode unit 20, and is arranged on both the left and right sides of the central portion 8 of the steering wheel 2 where an airbag or the like is provided. The other circuit units, that is, the amplifying unit 40, the impedance measuring unit 50, the CPU 60, and the wireless communication unit 70 are mounted on a common substrate 80, and are accommodated in a substantially central position of the central portion 8 of the steering wheel 2. ing.

Next, FIG. 3 is a block diagram illustrating the configuration of the amplification unit 40.
The amplifying unit 40 detects and amplifies a potential difference generated between two electrodes connected via the switching circuit unit 30, and outputs from the differential amplifying circuit 42 at a predetermined level. A variable amplification circuit 44 capable of gain adjustment up to and a signal (electrocardiographic signal) in a frequency band (for example, about 35 Hz or less) necessary for measuring an electrocardiographic waveform from the output signal from the variable amplification circuit 44 And a band-pass filter (BPF) 46 that selectively passes only the light.

  The BPF 46 is a variable BPF capable of adjusting the cutoff frequency on the high frequency side, and the cutoff frequency of the variable BPF 46 and the gain of the variable amplification circuit 44 are output from the CPU 60 via the D / A converter 64. It is adjusted by the control signal.

Next, FIG. 4 is a circuit diagram showing the configuration of the impedance measuring unit 50.
In the present embodiment, the impedance measuring unit 50 realizes a function as a lock-in amplifier by the impedance measuring unit 50 and the arithmetic processing in the CPU 60, and between two electrodes connected via the switching circuit unit 30 (see FIG. Then, the impedance Z between the electrodes 11-12 is measured.

  That is, the impedance measuring unit 50 takes in the single frequency signal E input from the CPU 60 via the D / A converter 66 via the buffer 52 and applies it to the one electrode 11 via the reference resistor Rref. Thus, the single frequency signal E is divided by the resistance (contact impedance) Z between the reference resistor Rref and the electrodes 11-12, and the divided voltage V is output to the CPU 60 via the buffer 54.

  Then, the CPU 60 takes in the divided voltage V through the A / D converter 62, multiplies the single frequency signal E and the divided voltage V, and performs a filtering process with a low-pass filter, thereby reducing noise. The removed divided voltage V is obtained (lock-in amplifier mechanism). Further, the CPU 60 obtains a gain G of “V = G · E” by using the voltage V obtained by the lock-in amplifier mechanism and the single frequency signal E, and calculates the impedance Z. The arithmetic expression in this case is “Z = Rref × G / (1−G)”.

Next, a heart rate measurement process that is repeatedly executed by the CPU 50 during, for example, engine operation of the vehicle will be described with reference to the flowchart of FIG.
As can be seen from FIG. 5, electrocardiographic waveform measurement (S10), high-pass filter processing (S20), R wave detection (S30), binarization processing (S40), widening processing (S50), FFT processing (S60). The heart rate measurement (S70) is sequentially executed from the peak frequency. These processing contents will be described in order.

[S10 ECG waveform measurement]
First, in order to measure the contact impedance in each electrode part 10 and 20, respectively, by switching the switching circuit part 30, the first electrode 11 (or 21) and the second electrode 12 (or the electrode part 10 (or 20) are switched. 22) is connected to the impedance measuring unit 50, and then the detection signal (the voltage V described above) is taken in from the impedance measuring unit 50 to calculate the contact impedance (Imp) Zi.

  Next, the switching circuit unit 30 is switched so that the electrode units 10 and 20 are connected to the amplifier unit 40 and the differential amplifier circuit 42 is operated. Then, the induced noise Vn is measured by capturing a signal from the amplifying unit 40, and the measurement result is stored in the RAM. During this measurement, the hum noise near 50-60 Hz that affects the electrocardiogram waveform is detected by maximizing the cutoff frequency of the variable BPF 46 in the amplifying unit 40 (that is, maximizing the pass bandwidth of the variable BPF 46). It can be so. When the induced noise Vn is measured in this way, the process proceeds to S240, and the measurement result is subjected to FFT processing, thereby calculating and storing a hum noise frequency in the vicinity of 50 to 60 Hz that affects the electrocardiogram waveform.

  If the calculated contact impedance Zi is equal to or less than a preset threshold value, the electrocardiogram waveform (signal) is provisionally measured using the electrode units 10 and 20. Then, the tentatively measured electrocardiogram waveform is subjected to FFT processing, and based on the result of the FFT processing, the terminal portion of the electrocardiogram spectrum near 35 Hz which is the maximum frequency of the electrocardiogram waveform is detected, and the detection result and the above calculation Based on the hum noise frequency, the cutoff frequency of the variable BPF 46 and the gain of the variable amplifier circuit 44, which are optimal for removing unnecessary signal components in the amplifier 40, are calculated, and the electrocardiogram waveform is calculated according to the calculation result. The cutoff frequency of the variable BPF 46 and the gain of the variable amplifier circuit 44 are adjusted in all the amplifiers 40 used for measurement.

  When the characteristics of the amplification unit 40 used for measuring the electrocardiogram waveform are adjusted in this way, the electrocardiogram waveform (signal) is now formally measured. Then, the noise component is removed from the electrocardiographic waveform based on the measured induced noise Vn. The final electrocardiogram waveform is stored in the RAM. FIG. 6A shows an example of the measured electrocardiogram waveform.

[High-pass filter processing in S20]
This is a filter process for removing noise mixed in the electrocardiogram waveform (signal). FIG. 6B shows an electrocardiographic waveform after the high-pass filter processing. It can be seen that the low-frequency noise is reduced as compared with FIG.

[Detection of R wave of S30]
An R wave appearing in an electrocardiogram waveform, which is a waveform of a temporal change in electrocardiogram, is detected. Specifically, in order to detect the peak appearing in FIG. 6B as an R wave, peak detection is performed.

[Binarization processing of S40]
In this binarization processing, data is created in which 1 is recorded at the position where the R wave detected at S30 exists and 0 is recorded at other positions. The created binarized data is shown in FIG.

[S50 widening process]
This widening process is a process for expanding the width of 1 of the binarized data created in S40. As a method for expanding the width of 1 of the binarized data, for example, a moving average process or an integration process can be considered.

  7 (b) (c), 8 (a) (b) (c), and FIG. 9 (a) (b) show binarized data after widening. These are the results of changing the degree of widening. Among these, “widening 80” shown in FIG. 8B is most appropriate. Although this point will be described later, here, the width of 1 of the binarized data created in S40 is subjected to a widening process of “widening 80” as shown in FIG. 8B.

[S60 FFT processing]
An FFT (Fast Fourier Transform) process is performed for frequency analysis. FIG. 11A shows the frequency analysis result obtained by subjecting the binarized data (binarized data not subjected to the widening process) shown in FIG. 7A to FFT processing. FIGS. 11 (b) and 11 (c), FIGS. 12 (a), (b), and (c) and FIGS. 13 (a) and 13 (b) are respectively shown in FIGS. 7 (b), (c), and FIGS. (C), FIG. 9 (a) and FIG. 9 (b) show frequency analysis results obtained by performing FFT processing on the binarized data after widening.

In the process of S50, the “widening 80” widening process as shown in FIG. 8B is performed, and the result of performing the FFT process is as shown in FIG. 11B.
[Heart rate measurement from peak frequency of S70]
As clearly seen from the frequency analysis result shown in FIG. 11B, in this case, the peak in the vicinity of 1.1 Hz is a peak due to the heartbeat. Therefore, this peak frequency is converted into a heart rate. Specifically, 1.1 Hz × 60 = 66 beats / minute.

  As described above, in the heart rate measuring apparatus of the present embodiment, 1 is set at a position where an R wave exists in the electrocardiographic waveform, and 0 is set at other positions. A binarization process for creating the recorded binarized data (S40 in FIG. 5) is performed, and a widening process for expanding the width of 1 in the binarized data created by the binarization process (S50) I do.

  If the frequency analysis (S60 in FIG. 6) is performed on the binarized data thus widened, the harmonic component of the frequency spectrum can be reduced. Therefore, if the peak frequency of the frequency analysis result is converted into a heart rate, the heart rate can be measured correctly.

  The inventor of the present application has found that the harmonic component of the frequency spectrum can be reduced by adding binarization and widening processing when processing the electrocardiogram waveform, for example, an electrocardiogram waveform suitable for heart rate calculation can be obtained. However, how the harmonic components of the frequency spectrum are reduced by this “binarization and widening process” will be described with reference to FIGS.

  FIG. 11A shows the frequency analysis result obtained by performing FFT processing on the binarized data shown in FIG. 7A, that is, binarized data that has not been subjected to the widening process. According to the frequency analysis result of FIG. 11A, in addition to the peak of the fundamental frequency determined by the heart rate (here, the peak at 1.1 Hz), the peak due to the harmonics (here, around 2.2 Hz); If peaks due to the higher harmonics are erroneously detected, the heart rate cannot be detected correctly.

  On the other hand, FIGS. 7B, 7C, 8A, 8B, 9C, 9A, and 9B are respectively 20, 40, 60, 80, 100, 120, and 140 (in units). Point) The binarized data after widening is shown. The “point” used here is a unit based on resolution when binarized data is used, and is a unit physically corresponding to time. The average interval between the peaks of the binarized data in the non-widened state used in this embodiment is about 175 points.

  The frequency analysis results obtained by subjecting these widened binarized data to the FFT processing are shown in FIGS. 11B, 11C, 12A, 12B, 13C, and 13A, 13B. . It can be seen that the harmonic components are reduced compared to FIG. 11A, which is a frequency analysis result obtained by performing FFT processing on binarized data that has not been subjected to widening processing. More specifically, it can be seen that the harmonic component of the frequency spectrum is reduced as the degree of widening increases to 20, 40, 60, and 80 (unit is point). Then, as the degree of widening further increases to 80, 100, 120, and 140 (in units of points), it can be seen that, on the contrary, the harmonic component once reduced (of the frequency spectrum) increases.

  That is, in the widening process of these 20, 40, 60, 80, 100, 120, and 140 (units are points), it can be seen that the 80-point widening process contributes most to the reduction of harmonic components.

FIG. 13 is an explanatory diagram showing the peak height of the second harmonic when the peak height of the fundamental frequency is 1. The vertical axis indicates the peak height, and the horizontal axis indicates the widening point.
The peak height of the second harmonic when the width is 0 point is 1.088469682.
The peak height of the second harmonic when the width is 20 points is 0.949997621.
The peak height of the second harmonic when the width is 40 points is 0.621779597.
The peak height of the second harmonic in the case of 60 points of widening is 0.254786154
The peak height of the second harmonic in the case of 80 points of widening is 0.023383731
The peak height of the second harmonic in the case of 100 points of widening is 0.054059874
The peak height of the second harmonic in the case of 120 points of widening is 0.385462573.
The peak height of the second harmonic in the case of 140 points of widening is 1.024925871
As described above, since the average interval between the peaks of the binarized data in the non-widened state used in the present embodiment is about 175 points, theoretically, the half-width of 87 points is ideal. Also in the results shown in FIG. 11 to FIG. 13, the second-order harmonics at the widening of 80 points are the smallest and agree with the theoretical values.

As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various aspect can be taken in the range which does not deviate from the summary of this invention.
(A) In the heart rate measuring apparatus of the above-described embodiment, binarization processing (S540 in FIG. 5) and widening processing (S550) are performed on the electrocardiographic waveform, and then FFT processing (S560) is further performed. Up to the heart rate measurement (S570).

  However, it may be configured as an electrocardiographic waveform processing apparatus that performs up to the widening process, and the electrocardiographic waveform that has been subjected to the widening process is transmitted to the outside, so that FFT processing and heart rate measurement are executed in the external apparatus. That is, it can be realized as an invention as an electrocardiographic waveform processing apparatus.

  (B) In the heart rate measuring device of the above embodiment, a pair of left and right electrode portions 10 and 20 are provided on the ring portion 4 of the steering wheel 2, and the vehicle driver holding the electrode portions 10 and 20 is the person being measured. Although some cases have been described, the same applies to measurements in other situations.

It is a block diagram showing the whole structure of the heart rate measuring apparatus of embodiment. It is explanatory drawing showing the arrangement | positioning state to the steering wheel of each part of heart rate measuring apparatus. It is a block diagram showing the structure of an amplification part. It is a circuit diagram showing the structure of an impedance measurement part. It is a flowchart showing the heart rate measurement process performed by CPU. (A) is a measured electrocardiographic waveform, and (b) is an explanatory diagram showing a waveform obtained by subjecting it to a high-pass filter. (A) is binarized data in which 1 is recorded at a position where an R wave exists and 0 is recorded at other positions, and (b) and (c) are explanatory diagrams showing data subjected to widening processing. It is explanatory drawing showing the data which carried out the widening process. It is explanatory drawing showing the data which carried out the widening process. (A) is the frequency analysis result of the binarized data which does not perform a widening process, (b) (c) is explanatory drawing showing the frequency analysis result of the data which carried out the widening process. It is explanatory drawing showing the frequency analysis result of the data which carried out the widening process. It is explanatory drawing showing the frequency analysis result of the data which carried out the widening process. It is explanatory drawing which shows the peak height of the secondary harmonic when the peak height of the fundamental frequency is 1. It is a flowchart which shows the method of the conventional heart rate measurement.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Steering wheel, 4 ... Ring part, 6 ... Spoke part, 8 ... Center part, 10 ... Left electrode part, 11 ... 1st electrode, 12 ... 2nd electrode, 20 ... Right electrode part, 21 ... 1st electrode, DESCRIPTION OF SYMBOLS 22 ... 2nd electrode, 30 ... Switching circuit part, 32 ... 1st changeover switch, 34 ... 2nd changeover switch, 40 ... Amplification part, 42 ... Differential amplification circuit, 44 ... Variable amplification circuit, 46 ... Variable BPF, 50 ... Impedance measuring section, 52, 54... Buffer, 60... CPU (microcomputer), 62... A / D converter, 64, 66.

Claims (5)

A measuring means for measuring the electrocardiographic waveform of the subject,
Processing means for performing predetermined processing on the electrocardiogram waveform measured by the measuring means;
An electrocardiographic waveform processing apparatus comprising:
The processing means includes a binarization process for creating binarized data in which 1 is recorded at a position where an R wave exists in the electrocardiogram waveform and 0 is recorded at other positions, and the binarization process. performing the first width in the binarized data generated, and a widening process of enlarging to half the width of the average distance between the position 1 is present in the binarized in data created by the binarization process An electrocardiographic waveform processing apparatus characterized by the above. Provided with electrode parts respectively provided on the left and right grips of the steering wheel,
The electrocardiographic waveform processing apparatus according to claim 1, wherein the measurement subject is a driver who holds the steering wheel via the left and right electrode portions. The electrocardiographic waveform processing apparatus according to claim 2 , wherein each of the electrode portions is disposed on a driver seat side surface of a steering wheel. The electrocardiographic waveform processing apparatus according to claim 2 , wherein the measuring unit is mounted in the steering wheel. The electrocardiographic waveform processing apparatus according to any one of claims 1 to 4,
A heart rate measuring apparatus characterized by performing frequency analysis on the binarized data widened by the processing means and measuring a heart rate based on the frequency analysis result.