JP2006247221A - Pulse wave detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pulse wave detector capable of precisely judging whether a pulse wave includes a noise. <P>SOLUTION: An autocorrelation function waveform of the pulse wave detected by a cuff (pulse wave sensor) is determined by an autocorrelation function waveform determining means. When maximum points increase because of the noise mixing in the pulse wave detected by the cuff due to body motion or the like, the autocorrelation function waveform determined from the pulse wave becomes the waveform of a complicated shape having more maximum points than the autocorrelation function waveform determined from a normal pulse wave having less noise. Therefor, it becomes possible to precisely judge whether the pulse wave is normally detected from the autocorrelation function waveform. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pulse wave detection device that detects a pulse wave generated from a living body.

  Various devices for detecting a pulse wave from a living body and using it for diagnosis have been proposed. There are various methods of diagnosis based on a pulse wave, for example, a method using a feature value reflecting the shape of the pulse wave (see, for example, Patent Document 1). In Patent Document 1, as a feature value of a pulse wave, an ascending feature value such as U-time that is the time from the rising point to the peak (maximum point) of the pulse wave and the sharpness of the pulse wave are calculated, and these ascending features are calculated. Based on the value and sharpness, the stenosis of the lower limb artery is determined.

  As another diagnostic method based on the pulse wave, there is a method using the generation time and magnitude of a predetermined part such as the rising point of the pulse wave and the peak of the pulse wave (see, for example, Patent Document 1 and Patent Document 2). . In Patent Document 1, a pulse wave propagation speed, which is a speed at which a pulse wave propagates in a living body, is calculated based on the occurrence time of a predetermined part such as a rising point of the pulse wave, and the pulse wave propagation speed is calculated as the above-described rising feature value. Similarly to the sharpness, it is used to determine stenosis of the lower limb arteries. Further, in Patent Document 2, a blood pressure value is continuously determined using a predetermined relationship from the magnitude of the rising point (that is, the minimum point) and the peak (that is, the maximum point) of the pulse wave.

When making a diagnosis based on a pulse wave, it is necessary that the detected pulse wave does not contain noise due to body movement or the like. For this reason, in Patent Document 2, the amplitude of the pulse wave detected sequentially is within a predetermined range determined based on the amplitude of the pulse wave detected immediately before, or the amplitude of the pulse wave detected last time and the current time It is a pulse wave that contains noise due to body movement by judging whether the amplitude difference from the amplitude of the pulse wave is within a predetermined range determined based on the amplitude difference calculated immediately before Judging whether or not.
JP 2002-272688 A Japanese Patent No. 2664983

  In the apparatus of Patent Document 2, when the magnitude of noise mixed in the detected pulse wave is smaller than the amplitude of the pulse wave, it cannot be detected that noise has occurred. However, when noise is mixed in the pulse wave, the amplitude of the pulse wave does not always change greatly. When the noise is relatively small, the amplitude does not change so much, but the number of local maximum points increases. The wave shape may change. As such, even when the pulse wave shape changes due to noise, the diagnosis may be adversely affected.

  The present invention has been made against the background of the above circumstances, and the object of the present invention is to provide a pulse wave detection device that can accurately determine whether or not the pulse wave contains noise. is there.

  The present invention for achieving the above object includes a pulse wave sensor for detecting a pulse wave from a living body, and a correlation function waveform determining means for determining a correlation function waveform of the pulse wave detected by the pulse wave sensor. This is a characteristic pulse wave detection device.

  According to this invention, the correlation function waveform determining means determines the correlation function waveform of the pulse wave detected by the pulse wave sensor, and the correlation is determined based on the pulse wave whose maximum point has increased due to the mixing of noise. The function waveform has a complex shape with more maximum points than the correlation function waveform determined based on the normal pulse wave with less noise, so it is accurate whether the pulse wave was detected normally from the correlation function waveform. It becomes possible to judge well.

  Here, the correlation function waveform determined by the correlation function waveform determining means may be a cross correlation function waveform, but is preferably an autocorrelation function waveform. The reason is that since the autocorrelation function waveform is determined from the same two pulse waves, both pulse waves used for the determination of the autocorrelation function waveform contain the same noise. Therefore, the maximum point of the autocorrelation function waveform derived from the noise becomes large, and it is easy to determine whether or not the pulse wave is normally detected.

  Preferably, the pulse wave detection device includes an output device that outputs the correlation function waveform determined by the correlation function waveform determination means. In this way, a doctor or the like can determine whether or not the pulse wave is normally detected from the correlation function waveform output to the output device.

  Preferably, the pulse wave detection device detects whether or not the pulse wave detected by the pulse wave sensor is normally detected based on the correlation function waveform determined by the correlation function waveform determination means. A result judging means is provided. In this way, since it is automatically determined whether or not the pulse wave is detected normally, an erroneous diagnosis based on the pulse wave including noise is prevented.

  Examples of the determination method by the detection result determination means include a determination method based on the number of local maximum points of the correlation function waveform and a determination method based on the power spectrum of the correlation function waveform. Since the number of local maximum points derived from noise increases in the pulse wave as the noise increases, the number of local maximum points also increases in the correlation function waveform. Therefore, the number of local maximum points existing in the correlation function waveform is greater than or equal to a preset number. In some cases, it can be determined that the pulse wave is not normally detected. Also, as the number of local maximum points in the correlation function waveform increases, noise-derived components also increase in the power spectrum of the correlation function waveform, so it is determined whether the pulse wave has been detected normally from the power spectrum of the correlation function waveform. can do. Further, when the correlation function waveform determined by the correlation function waveform determining means is a cross correlation function waveform, the detection result determining means is based on the time point indicating the maximum value of the cross correlation function waveform, and the maximum value It is also possible to determine whether or not the pulse wave detected by the pulse wave sensor has been detected normally based on the correlation coefficient between the waveform on the minus side and the waveform on the plus side of the time point.

  Embodiments of the present invention will be described below. First, an embodiment of the present invention will be described with reference to the drawings. The pulse wave detection device of the present invention can be used for various diagnoses. This embodiment is a stenosis diagnosis device that uses a pulse wave detection device for diagnosis of arterial stenosis. FIG. 1 is a block diagram showing a circuit configuration of the stenosis diagnostic apparatus 10.

  In FIG. 1, a cuff 12 is a general ankle cuff and is wound around the ankle 14. A pressure sensor 16 and a pressure regulating valve 18 are connected to the cuff 12 by a pipe 20. The pressure regulating valve 18 is connected to an air pump 22 by a pipe 21. The cuff 12 has a structure in which a rubber bag is accommodated in a cloth belt-like bag. The pressure regulating valve 18 regulates the pressure in the cuff 12 by regulating the pressure of the high-pressure air supplied from the air pump 22 and supplying the pressure into the cuff 12 or exhausting the air in the cuff 12.

  The pressure sensor 16 detects the pressure in the cuff 12 and supplies a pressure signal SP representing the pressure to the static pressure discrimination circuit 24 and the pulse wave discrimination circuit 26, respectively. The static pressure discriminating circuit 24 includes a low-pass filter that discriminates a cuff pressure signal SC representing a steady pressure included in the pressure signal SP, that is, a compression pressure of the cuff 12 (hereinafter, this pressure is referred to as a cuff pressure PC). The pressure signal SC is supplied to the electronic control unit 30 via the A / D converter 28.

  The pulse wave discriminating circuit 26 includes a band-pass filter, and discriminates the pulse wave signal SM, which is a vibration component of the pressure signal SP, in frequency and sends the pulse wave signal SM to the electronic control unit 30 via the A / D converter 32. Supply. Since this pulse wave signal SM represents a pulse wave detected from the ankle 14, that is, an ankle pulse wave, the cuff 12 for detecting the pressure signal SP including the pulse wave signal SM functions as a pulse wave sensor.

  The electronic control unit 30 is constituted by a so-called microcomputer having a CPU 34, a ROM 36, a RAM 38, an I / O port (not shown), and the like. The CPU 34 executes signal processing while using the storage function of the RAM 38 in accordance with a program stored in advance in the ROM 36, thereby outputting a drive signal from the I / O port to output the pressure regulating valve 18 and the air via a drive circuit (not shown). The pump 22 is controlled. The CPU 34 controls the pressure in the cuff 12 by controlling the pressure regulating valve 18 and the air pump 22. In addition, the CPU 34 performs arithmetic processing on a signal supplied to the electronic control device 30, thereby determining whether or not the ankle pulse wave is normally detected and determining stenosis related information such as% MAP. Further, the CPU 34 controls the display content of the display 40 that functions as an output device.

  FIG. 2 is a functional block diagram showing the main part of the control function of the electronic control unit 30. When a measurement start button (not shown) is operated, the cuff pressure control means 50 determines the cuff pressure PC based on the cuff pressure signal SC supplied from the static pressure discriminating circuit 24 and controls the pressure regulating valve 18 and the air pump 22. By controlling, the cuff pressure PC is set to a predetermined pulse wave detection pressure. This pulse wave detection pressure is a pressure lower than the minimum blood pressure value at the site where the cuff 12 is worn (that is, the ankle 14), and the pulse wave signal SM discriminated by the pulse wave discrimination circuit 26 is sufficient. The pressure is such that the signal intensity is obtained, and is set to, for example, 50 to 60 mmHg.

  The pulse wave display means 52 is a pulse wave signal SM for one beat supplied from the pulse wave discrimination circuit 26 in a state where the cuff pressure PC is controlled to the pulse wave detection pressure by the cuff pressure control means 50, that is, one beat. The ankle pulse wave of the minute is displayed at a predetermined position of the display 40.

The autocorrelation function waveform determining means 54 is used for the ankle pulse wave signal SM for one beat supplied from the pulse wave discrimination circuit 26 in a state where the cuff pressure PC is controlled to the pulse wave detection pressure by the cuff pressure control means 50. The autocorrelation function waveform is determined, and the determined autocorrelation function waveform is displayed on the display 40. The autocorrelation function waveform is a waveform represented by the autocorrelation function R (τ) described in Equation 1.

  3 and 4 are diagrams showing an example of an ankle pulse wave and an autocorrelation function waveform displayed on the display 40 by the pulse wave display means 52 and the autocorrelation function waveform determination means 54, and FIG. FIG. 4 shows an ankle pulse wave that is detected normally and an autocorrelation function waveform that is determined from the detected ankle pulse wave that is low in noise, and FIG. As can be seen from FIGS. 3 and 4, the autocorrelation function waveform determined from the normal ankle pulse wave is a waveform having a simple shape with only one local maximum point, but not detected normally. The autocorrelation function waveform determined from the ankle pulse wave has a plurality of maximum points and has a complex shape. Therefore, the doctor or the like can determine from the autocorrelation function waveform displayed on the display 40 whether or not the ankle pulse wave has been normally detected.

  The detection result determination unit 56 determines whether or not the ankle pulse wave supplied from the pulse wave discrimination circuit 26 is a pulse wave that has been normally detected, and the maximum of the autocorrelation function waveform determined by the autocorrelation function waveform determination unit 54. Determine based on the number of points. That is, if the number of local maximum points of the autocorrelation function waveform is less than the predetermined number, it is determined that the ankle pulse wave has been detected normally, and if the number of local maximum points is equal to or greater than the predetermined number (for example, three), body motion It is determined that the ankle pulse wave is not normally detected due to noise such as the above.

  Based on the ankle pulse wave supplied from the pulse wave discrimination circuit 26, the stenosis related information determination means 58 determines stenosis related information which is biological information related to stenosis of the blood vessel, and the determined stenosis related information is displayed on the display 40. To display. The stenosis-related information includes, for example, the ascending feature value, sharpness, pulse wave velocity information described in Patent Document 1, and in this embodiment, the upstroke time (upstroke time) that is the ascending feature value. (Hereinafter referred to as U-time)) and% MAP, which is the sharpness. U-time is the time from the rising point of the pulse wave to the peak (maximum point), and% MAP is the height G of the center of gravity of the pulse wave area S relative to the peak height H (ie, pulse pressure) of the pulse wave. Ratio (= 100 × H / G). When these U-time and% MAP are displayed on the display device 40, it becomes possible to determine arterial stenosis from the values.

  FIG. 5 is a flowchart for explaining the control operation of the electronic control unit 30 shown in the functional block diagram of FIG. First, in step (hereinafter, step is omitted) S1, the air pump 22 is activated and the pressure regulating valve 18 is controlled to start increasing the cuff pressure PC. In subsequent S2, it is determined whether or not the cuff pressure PC is equal to or higher than 50 mmHg set as the pulse wave detection pressure. If the determination in S2 is negative, the determination in S2 is repeatedly executed. If the determination is positive, in the subsequent S3, the pressure control valve 18 is closed to maintain the cuff pressure PC, and the air pump 22 Stop.

  In the subsequent S4, the pulse wave signal SM supplied from the pulse wave discrimination circuit 26 is read while the cuff pressure PC is maintained. In the subsequent S5, it is determined whether or not the pulse wave signal SM has been read for one beat. to decide. If this determination is negative, the reading of the pulse wave signal SM is continued by repeatedly executing S4. If the determination is affirmative, in step S6, the pressure regulating valve 18 is released to release the cuff pressure. Exhaust PC to atmospheric pressure. In FIG. 5, S 1 to S 3 and S 6 correspond to the cuff pressure control means 50.

  Subsequent S7 corresponds to the pulse wave display means 52, and the ankle pulse wave represented by the pulse wave signal SM for one beat read by repeating S4 to S5 is displayed as shown in FIG. 3 or FIG. 4, for example. 40.

  The subsequent S8 corresponds to the autocorrelation function waveform determining means 54, and the autocorrelation function waveform of the ankle pulse wave for one beat from the above equation 1 based on the pulse wave signal SM for one beat read by repeating S4 to S5. , And the determined autocorrelation function waveform is displayed on the display 40 as shown in FIG. 3 or FIG.

  Subsequent S9 to S10 correspond to the detection result determination means 56. In S9, the number of local maximum points of the autocorrelation function waveform determined in S8 is determined, and the number of local maximum points is set to a predetermined number (for example, If three or more), it is determined that the ankle pulse wave is not normally detected, and if the number of local maximum points is less than the predetermined number, it is determined that the ankle pulse wave is normally detected. In subsequent S10, the result determined in S9 is displayed on the display 40.

  Subsequent S11 corresponds to the stenosis related information determining means 58, and U-time and% MAP are determined based on the ankle pulse wave for one beat read by repeating S4 to S5. That is, the rising point and peak of the read ankle pulse wave are determined, the time from the rising point to the peak is defined as U-time, the center of gravity position height G of the ankle pulse wave area S and the peak height of the ankle pulse wave H is determined, and the ratio of the center-of-gravity position height G of the pulse wave area S to the peak height H (= 100 × H / G) is determined as% MAP. Then, the determined U-time and% MAP are displayed on the display 40.

  In the diagnosis using the present apparatus 10, it is determined whether the ankle pulse wave is normally detected from the autocorrelation function waveform displayed in S8 or the detection result displayed in S10, and then displayed in S11. The presence or absence of stenosis is determined from the U-time and% MAP and the shape of the ankle pulse wave displayed in S7.

  According to the above-described embodiment, the autocorrelation function waveform determining means 54 (S8) determines the autocorrelation function waveform of the ankle pulse wave detected by the cuff 12, and the ankle in which the maximum point is increased due to noise mixing. The autocorrelation function waveform determined based on the pulse wave has a complex shape with more local points than the autocorrelation function waveform determined based on the normal ankle pulse wave with less noise. It is possible to accurately determine whether or not the ankle pulse wave is normally detected from the waveform.

  Further, according to the present embodiment, since the autocorrelation function waveform determined by the autocorrelation function waveform determining means 54 (S8) is displayed on the display 40, a doctor or the like can be obtained from the displayed autocorrelation function waveform. However, it can be determined whether or not the pulse wave is detected normally.

  Further, according to this embodiment, the ankle detected by the cuff 12 based on the autocorrelation function waveform determined by the autocorrelation function waveform determining means 54 (S8) by the detection result determining means 56 (S9 to S10). Since it is automatically determined whether or not the pulse wave is normally detected, it is possible to prevent an erroneous diagnosis based on an ankle pulse wave including noise.

  As mentioned above, although one Example of this invention was described based on drawing, this invention is applied also in another aspect.

  For example, the detection result determination unit 56 of the above-described embodiment determines whether or not the ankle pulse wave is normally detected based on the number of local maximum points of the autocorrelation function waveform. And determining whether or not the ankle pulse wave is normally detected from the power spectrum. FIG. 6 is a diagram illustrating an example of the power spectrum, where (a) is an example of a power spectrum of an autocorrelation function waveform determined based on a normal ankle pulse wave, and (b) is a lot of noise. It is an example of the power spectrum of the autocorrelation function waveform determined based on the mixed abnormal ankle pulse wave. When a lot of noise is mixed, as shown in FIG. 6 (b), the high frequency portion of the power spectrum increases due to the noise, and a peak can be confirmed in the high frequency portion. It is possible to determine whether the wave has been detected normally.

In the above-described embodiment, the autocorrelation function waveform is determined as the correlation function waveform. Instead, a cross correlation function waveform may be determined. The two pulse waves for determining the cross-correlation function waveform may be two pulse waves detected respectively from two different parts, or two pulse waves that are the same part but have different detection times. It may be. FIG. 7 is a diagram showing two pulse waves (first pulse wave x (t) and second pulse wave y (t)) having different detection sites, and cross-correlation function waveforms determined from the two pulse waves. is there. The cross-correlation function waveform is a waveform represented by the cross-correlation function Rxy (τ) described in Equation 2.

  When determining the cross-correlation function waveform as the correlation function waveform, the method for determining whether or not the pulse wave detected by the pulse wave sensor is normal from the cross-correlation function waveform is the same as the autocorrelation function waveform described above. A method based on the number of local maximum points or a method based on the power spectrum of the correlation function waveform may be used, but a method based on the left-right symmetry of the cross-correlation function waveform may also be used. The method based on the left-right symmetry of the cross-correlation function waveform refers to the time point (time τ = 0 in FIG. 7) at which the cross-correlation function waveform illustrated in FIG. As shown in FIG. 8, the left waveform (that is, the negative waveform) L (τ) and the right waveform (that is, the positive waveform) R (τ) are divided into the left and right waveforms, as shown in FIG. In this method, a correlation coefficient c with the waveform R (τ) is obtained, and when the correlation coefficient c is lower than a predetermined value, it is determined that the pulse wave detection has not been performed normally.

  The correlation coefficient c is a value between 0 and 1, but when there is little noise mixing in both the first pulse wave x and the second pulse wave y, the first pulse wave x and the second pulse wave Since y has a relatively similar shape, the left waveform L (τ) and the right waveform R (τ) of the cross-correlation function waveform show relatively high symmetry, and the correlation coefficient c is close to 1. . On the other hand, if noise is mixed in one of the first pulse wave x and the second pulse wave y and the shape of the first pulse wave x and the shape of the second pulse wave y are relatively different, Since the shape of the left waveform L (τ) and the shape of the right waveform R (τ) are relatively different, the correlation coefficient c is a value sufficiently smaller than 1. Therefore, the predetermined value for determining whether or not the pulse wave detection is normally performed is set to a value relatively close to 1 within a range smaller than 1.

  In the above-described embodiment, as shown in FIGS. 3 and 4, the autocorrelation function waveform is also shown for the region where the time τ is negative. However, when the correlation function is an autocorrelation function, Since the correlation function waveform is symmetric with respect to time τ = 0, it is not necessary to determine the waveform in the region where time τ is negative.

  In the above-described embodiment, when the pulse wave is detected, the stenosis related information is always determined based on the pulse wave. However, when the detection result determination unit 56 determines that the pulse wave is detected normally, Only the stenosis-related information may be determined from the pulse wave.

  In the above-described embodiment, a pulse wave for one beat is detected. However, pulse waves for a plurality of beats may be detected, and stenosis related information may be determined from the pulse waves for the plurality of beats. In addition, when using pulse waves for a plurality of beats as described above, stenosis-related information may be determined based on all pulse waves, or as described above, only for pulse waves that are determined to be normally detected. Stenosis related information may be determined.

  In the above-described embodiment, the cuff 12 functions as a pulse wave sensor. However, the pulse wave sensor is not limited to that of the above-described embodiment, and a pressure pulse wave is generated by a pressure-sensitive element provided on the pressing surface. A pressure pulse wave sensor that detects a pressure pulse wave, such as a detection type, can also be used. Also, a photoelectric pulse wave detection probe for measuring oxygen saturation, a photoelectric sensor attached to a fingertip for pulse detection, etc. A sensor that detects volume pulse waves, such as a pulse wave sensor, can also be used.

  In the above-described embodiment, the part for detecting the pulse wave is the ankle 14, but the pulse wave may be detected in another part such as the neck. Note that even if pulse waves are detected normally, the number of local maximum points differs depending on the detection site. Therefore, the number of local maximum points of the correlation function waveform varies depending on the detection site of the pulse wave. Therefore, when determining whether or not the detected pulse wave is normal based on the number of maximum points of the correlation function waveform, if the number of maximum points of the correlation function waveform is less than the number, It depends on the wave detection site.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be implemented in variously modified and improved forms based on the knowledge of those skilled in the art.

It is a block diagram which shows the circuit structure of the stenosis diagnostic apparatus provided with the function as a pulse wave detection apparatus of this invention. It is a functional block diagram which shows the principal part of the control function of the electronic controller in the stenosis diagnostic apparatus of FIG. It is a figure which shows an example of the ankle pulse wave and autocorrelation function waveform which are displayed on a display by the pulse wave display means and autocorrelation function waveform determination means of FIG. It is an autocorrelation function waveform determined therefrom. It is a figure which shows an example of the ankle pulse wave and autocorrelation function waveform which are displayed on a display by the pulse wave display means and autocorrelation function waveform determination means of FIG. The autocorrelation function waveform is shown. It is a flowchart explaining the control action of the electronic controller shown in the functional block diagram of FIG. It is a figure which shows an example of the power spectrum determined in order to determine whether the ankle pulse wave was normally detected in the detection result determination means of FIG. It is a figure which shows the cross-correlation function waveform determined from two pulse waves (1st pulse wave x (t) and 2nd pulse wave y (t)) from which a detection part differs, and the two pulse waves. It is a figure which shows the left side waveform and right side waveform of the cross correlation function waveform of FIG.

Explanation of symbols

10: Stenosis diagnosis device (pulse wave detection device)
12: Cuff (pulse wave sensor)
40: Display (output device)
52: Pulse wave display means 54: Autocorrelation function waveform determination means 56: Detection result determination means

Claims (8)

A pulse wave sensor for detecting a pulse wave from a living body;
And a correlation function waveform determining means for determining a correlation function waveform of the pulse wave detected by the pulse wave sensor. 2. The pulse wave detection device according to claim 1, wherein the correlation function waveform determined by the correlation function waveform determination means is an autocorrelation function waveform. The pulse wave detection device according to claim 1, wherein the correlation function waveform determined by the correlation function waveform determination unit is a cross-correlation function waveform. The pulse wave detection device according to any one of claims 1 to 3,
The pulse wave detection device further comprising an output device for outputting the correlation function waveform determined by the correlation function waveform determination means. The pulse wave detection device according to any one of claims 1 to 4,
The pulse further comprising detection result determination means for determining whether or not the pulse wave detected by the pulse wave sensor is normally detected based on the correlation function waveform determined by the correlation function waveform determination means. Wave detector. The pulse wave detection device according to claim 5,
The detection result determining means determines whether or not the pulse wave detected by the pulse wave sensor is normally detected based on the number of maximum points of the correlation function waveform. Detection device. The pulse wave detection device according to claim 5,
The detection result determining means determines whether or not the pulse wave detected by the pulse wave sensor is normally detected based on a power spectrum of the correlation function waveform. . The pulse wave detection device according to claim 3,
Based on the correlation coefficient between the waveform on the minus side and the waveform on the plus side with respect to the time point indicating the maximum value of the cross correlation function waveform determined by the correlation function waveform determining means, The pulse wave detection device further comprising a detection result determination means for determining whether or not the pulse wave detected by the pulse wave sensor is normally detected.

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