JP2012024320A - Device and method for measuring biological signal - Google Patents

Abstract

A measurement subject's pulsation component can be accurately extracted and detected from a measurement signal on which a noise component such as an artifact component is superimposed.
An irradiation unit that irradiates a living tissue of a person to be measured with light of two different wavelengths, and receives light of each wavelength that has been irradiated from the irradiation unit 10 and transmitted or reflected by the biological tissue 500, respectively. A light receiving unit 20 that converts the electrical signal into an electrical signal corresponding to the received light intensity of the light, a Hilbert transforming unit 34 and 35 that generates envelope data that constitutes an envelope by Hilbert transforming the electrical signal, and the generated envelope data A biological signal measuring device 100 comprising: an oxygen saturation calculating unit 40 that calculates a light attenuation ratio based on the light attenuation ratio and calculates blood oxygen saturation of an artery in the living tissue 500 based on the light attenuation ratio. provide.
[Selection] Figure 1

Description

  The present invention relates to a biological signal measuring device and a biological signal measuring method for measuring the oxygen saturation and pulse rate of arterial blood of a measurement subject.

  2. Description of the Related Art An oxygen saturation measuring device that estimates the state of peripheral circulation of a subject by noninvasively determining the oxygen saturation or pulse rate in the arterial blood of the subject (see, for example, Patent Document 1). ).

  The oxygen saturation measuring device transmits or reflects light of a plurality of wavelengths having different absorbances with respect to a target substance such as oxygenated hemoglobin to a living tissue, and continuously measures the amount of the transmitted or reflected light. A pulse oximeter in which the oxygen saturation (SpO2) in arterial blood is obtained from the pulse wave data signal obtained is generally used.

JP-A-10-216114

  By the way, the conventional pulse oximeter may not be able to accurately detect the pulsation component by superimposing a noise component such as an artifact component due to the movement of the body of the measurement subject or a cough during measurement on the measurement signal. there were. In some cases, the peak intensity of such a noise component may be larger than that of the pulsation component. Therefore, it is difficult to accurately capture the pulsation component in the method of detecting the component having the highest peak intensity as the pulsation component.

  In order to solve the above problems, the present invention provides an irradiation unit that irradiates a living tissue of a person to be measured with light of two different wavelengths, and each wavelength that is irradiated from the irradiation unit and transmitted or reflected by the biological tissue. A light receiving unit that receives the light of the light and converts it into an electrical signal corresponding to the received light intensity of each light, a Hilbert conversion unit that generates an envelope data that constitutes an envelope by converting the electrical signal into a Hilbert transform, and A biological signal measurement comprising: an oxygen saturation calculating unit that calculates a light attenuation ratio based on the envelope data and calculates blood oxygen saturation of an artery in the biological tissue based on the light attenuation ratio Providing equipment.

  The biological signal measuring device further includes a normalization processing unit that normalizes the value of the envelope data, and a pulse rate calculation unit that calculates a pulse rate based on the normalized envelope data. Is preferred.

  The present invention also provides an irradiation stage for irradiating the living tissue of the person to be measured with light of two different wavelengths, and receives the light of each wavelength transmitted or reflected by the living tissue, and the received light intensity of each light. A light receiving step for converting into an electrical signal, a Hilbert transform step for generating an envelope data that forms an envelope by converting the electrical signal into a Hilbert transform, and calculating a dimming ratio based on the envelope data, There is provided a biological signal measuring method comprising: an oxygen saturation calculating step of calculating blood oxygen saturation of an artery in the living tissue based on the dimming ratio.

  The biological signal measurement method further includes a normalization process stage that normalizes the value of the envelope data, and a pulse rate calculation stage that calculates a pulse rate based on the normalized envelope data. Is preferred.

  According to the biological signal measuring apparatus and the biological signal measuring method of the present invention, it is possible to accurately extract and detect the pulsation component of the measurement subject from the measurement signal on which the noise component such as the artifact component is superimposed. In addition, the oxygen saturation calculation unit calculates the dimming ratio based on the envelope data of the measurement signal of each wavelength generated by the Hilbert transform unit in the extraction unit, thereby directly reducing the dimming ratio from the measurement signal of each wavelength. As compared with the case of calculating, the calculated value of the dimming ratio does not become an abnormal value, and the blood oxygen saturation can be calculated more accurately.

  The conventional dimming ratio φ (oxygen saturation) is calculated by the equation φ = R / IR that divides R (red light signal) by IR (infrared light signal), and the denominator becomes zero. There was a defect that showed an abnormal value. However, according to the biological signal measuring apparatus and the biological signal measuring method of the present invention, since processing by Hilbert transform is performed, the denominator does not take zero, and the dimming ratio is rarely an abnormal value.

  Furthermore, according to the biological signal measuring apparatus and the biological signal measuring method of the present invention, since the Hilbert transformed signal is normalized, artifacts having a large amplitude are suppressed when the frequency spectrum of the biological signal (pulse wave) is obtained. As a result, the pulse wave having a small amplitude is elongated, so that the pulse wave spectrum becomes clear and measurement can be performed with high accuracy.

It is a functional block diagram of biological signal measuring device 100 concerning an embodiment of the present invention. A part of IR time waveform is shown. The relationship between frequency distribution and amplitude when the time waveform of IR shown in FIG. 2 is subjected to fast Fourier transform (FFT) is shown. An example of the time waveform of the dimming ratio calculated by the conventional method is shown. An example of an IR time waveform (IR) and an envelope (HIR) waveform obtained by Hilbert transform of the time waveform are shown. The time waveform which normalized the time waveform of IR shown in FIG. 5 with the envelope shown in the figure is shown. FIG. 7 shows the relationship between frequency distribution and amplitude when the normalized time waveform of IR shown in FIG. 6 is subjected to fast Fourier transform (FFT). An example of the time waveform of the dimming ratio calculated based on the envelope data generated from the R time waveform and the envelope data generated from the IR time waveform is shown.

  Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. In addition, not all the combinations of features described in the embodiments are essential for the solving means of the invention.

  FIG. 1 is a functional block diagram of a biological signal measuring apparatus 100 according to an embodiment of the present invention. As shown in FIG. 1, the biological signal measurement device 100 is a device that measures the oxygen saturation in the arterial blood of a measurement subject, and includes an irradiation unit 10, a light receiving unit 20, an extraction unit 30, and an arithmetic processing unit 40. And a storage unit 50 and a display unit 60. As will be described later, the arithmetic processing unit 40 functions as an oxygen saturation calculation unit and a pulse rate calculation unit in the present invention.

  The irradiation unit 10 includes a light emitting element 11, a light emitting element 12, and a drive circuit 13. The light emitting element 11 and the light emitting element 12 are driven by the drive circuit 13 so as to emit light of two different wavelengths alternately. In this example, the light emitting element 11 is a light emitting diode that emits infrared light (IR) having a wavelength of about 940 nm, and the light emitting element 12 is a light emitting diode that emits red light (R) having a wavelength of about 660 nm. It is.

  In addition, the wavelength of the light which the light emitting element 11 and the light emitting element 12 light-emit is not restricted to said wavelength. The wavelength of the light emitted from the light emitting element 11 is, for example, in a region where the difference in extinction coefficient between oxygenated hemoglobin and anoxic hemoglobin in blood is larger than a predetermined value, specifically in a band shorter than 800 nm. It is preferable that the value is set as high as possible. The wavelength of light emitted from the light emitting element 12 is, for example, a region where the difference in extinction coefficient between oxygenated hemoglobin and anoxic hemoglobin in blood is smaller than a predetermined value, specifically, longer wavelength than 800 nm. It is preferable to set the value within the region and as low as possible.

  The light receiving unit 20 includes a light receiving element 21 and an amplifier 22. When the light of the two different wavelengths is alternately irradiated from the irradiation unit 10 toward the measurement subject's biological tissue 500, the light receiving element 21 receives the light of each wavelength transmitted or reflected by the biological tissue 500. And it converts into the electric signal according to the light reception intensity | strength of each light. The amplifier 22 amplifies the electric signal from the light receiving element 21 to a predetermined level. In this example, the light receiving element 21 is a photodiode. Further, the living tissue 500 may be, for example, the fingertip or earlobe of the measurement subject.

  The extraction unit 30 includes a multiplexer 31, A / D converters 32 and 33, Hilbert conversion units 34 and 35, normalization processing units 36 and 37, and a preprocessing unit 38. The multiplexer 31 separates the electric signal amplified by the amplifier 22 for each electric signal corresponding to each optical wavelength (R or IR). One of the separated electrical signals is input to the A / D converter 32 and the other is input to the A / D converter 33. In this example, an analog electrical signal corresponding to the received light intensity of R light is input to the A / D converter 32, and the A / D converter 32 digitizes the electrical signal. An analog electrical signal corresponding to the received light intensity of IR light is input to the A / D converter 33, and the A / D converter 33 digitizes the electrical signal.

  The preprocessing unit 38 performs a predetermined process on the electrical signal digitized by each of the A / D converter 32 and the A / D converter 33. Here, the predetermined process is a known process necessary for calculating the oxygen saturation (the dimming ratio φ) and the pulse rate (PR). Specifically, there are filtering by a band pass filter or the like in a predetermined band, separation of a direct current component and an alternating current component of pulse waves in R and IR, and the like. In addition, the pre-processing unit 38 further performs a one-time difference, double rotation (for example, processing described in Japanese Patent No. 4196209) or single rotation (for example, Japanese Patent No. 4352315) with respect to the input signal as necessary. A component caused by an artifact included in an input electric signal may be removed by executing a known process such as the process described in Japanese Patent Publication.

  The Hilbert transform unit 34 performs Hilbert transform on the electrical signal corresponding to the received light intensity of R that has been digitized by the A / D converter 32 and subjected to the above-described processing in the pre-processing unit 38, and an envelope of the time waveform of the electrical signal Envelope data constituting the line is generated. Also, the Hilbert transform unit 35 performs a Hilbert transform on the electrical signal corresponding to the IR received light intensity digitized by the A / D converter 33 and subjected to the above processing in the pre-processing unit 38, and the time waveform of the electrical signal. Envelope data that constitutes the envelope is generated. Here, each of the Hilbert transform unit 34 and the Hilbert transform unit 35 more specifically, the value obtained by squaring the value of the electric signal corresponding to the received light intensity of each light input from the preprocessing unit 38 and the Hilbert transform Calculate the square root of the sum of the squared values. Each of the Hilbert transform unit 34 and the Hilbert transform unit 35 outputs the calculated value of the square root as envelope data.

  Then, the Hilbert transform unit 34 outputs the digital electrical signal corresponding to the received light intensity of the R light input from the pre-processing unit 38 to the normalization processing unit 36 in the subsequent stage as it is, and also converts the electrical signal into the Hilbert transform. The envelope data generated in this way is output to the normalization processing unit 36 and the arithmetic processing unit 40. Further, the Hilbert transform unit 35 outputs a digital electrical signal corresponding to the received light intensity of the IR light input from the pre-processing unit 38 to the normalization processing unit 37 at the subsequent stage, and also converts the electrical signal into the Hilbert transform. The envelope data generated in this way is output to the normalization processing unit 37 and the arithmetic processing unit 40.

  The normalization processing units 36 and 37 normalize the electric signals input from the Hilbert conversion units 34 and 35 based on the envelope data input from the Hilbert conversion units 34 and 35 at the same timing. More specifically, the normalization processing units 36 and 37 use the values of the electric signals input from the Hilbert conversion units 34 and 35 at one timing and the envelopes input from the Hilbert conversion units 34 and 35 at the same timing. A value divided by the line data value is calculated, and the calculated value is normalized.

  The arithmetic processing unit 40 includes an arithmetic processing circuit such as a CPU, and executes various arithmetic processes based on a program stored in a storage unit 50 constituted by a RAM or a hard disk drive. In this example, the arithmetic processing unit 40 calculates the pulsation frequency (pulse rate) of the artery of the measurement subject based on the amplitude of the frequency component corresponding to each of the normalized light of the two wavelengths. The arithmetic processing unit 40 calculates the dimming ratio (Hφ) based on the envelope data corresponding to the two wavelengths of light input from the Hilbert conversion units 34 and 35.

More specifically, the envelope data (HR) generated from the time waveform of the electrical signal corresponding to the received light intensity of the R light is input from the Hilbert transform unit 34 to the arithmetic processing unit 40, and the Hilbert transform The envelope data (HIR) generated from the time waveform of the electrical signal corresponding to the received light intensity of the IR light is input from the unit 34. Then, the arithmetic processing unit 40 calculates the dimming ratio (Hφ) from these envelope data based on the following equation (1).
Hφ = HR / HIR (1)

  The arithmetic processing unit 40 calculates a biological signal in the artery of the measurement subject based on the calculated attenuation ratio, and outputs the calculation result to the display unit 60 as time-series data. The display unit 60 is one of known display devices such as an LCD, and displays the data string from the arithmetic processing unit 40 as a time waveform. The display unit 60 may also display the pulse rate calculated by the arithmetic processing unit 40. Note that any of various known methods may be used as a method for calculating blood oxygen saturation.

  Here, the characteristic function in the biological signal measuring apparatus 100 when measuring the oxygen saturation of the arterial blood of the measurement subject using the biological signal measuring apparatus 100 according to the present embodiment will be described in more detail.

FIG. 2 shows a part of an IR time waveform which is an example of a signal waveform digitized by the A / D converter 33. As shown in FIG. 2, the IR time waveform includes various noise components such as an artifact component caused by movement of the body of the subject and coughing in addition to the frequency component corresponding to the pulsation of the artery of the subject. Superimposed. In particular, in the time width indicated by “T ₁ ” and “T ₂ ” in FIG. 2, a noise component having a larger amplitude and smaller frequency than the pulsating component is superimposed.

  FIG. 3 shows the relationship between frequency distribution and amplitude when the time waveform of IR shown in FIG. 2 is subjected to fast Fourier transform (FFT). As shown in FIG. 3, when the time waveform of IR shown in FIG. 2 is subjected to FFT analysis, it can be seen that various frequency components are included in addition to the peak of the pulsation component indicated by “P” in FIG. In particular, the band component indicated by “X” in FIG. 3 corresponds to the noise component, but includes a peak whose amplitude exceeds that of the pulsating component.

  Such noise component superposition is the same not only in the IR time waveform exemplified above but also in the R time waveform (that is, in the R time waveform digitized by the A / D converter 32). Is the same). Therefore, if these time waveforms are used as they are, it is difficult to accurately specify the frequency component according to the pulsation of the artery of the measurement subject, as is apparent from the result of the FFT. Further, when the dimming ratio is calculated by dividing the R value by the IR value at each light receiving timing in the R and IR time waveforms as in the prior art, for example, as shown in FIG. However, it is difficult to accurately capture the temporal change in blood oxygen saturation.

  In contrast, in the biological signal measuring apparatus 100 according to the present embodiment, the time waveforms of the R and IR electrical signals digitized by the A / D converters 32 and 33 are converted into the Hilbert conversion units 34 and 35 as described above. A process of converting to an envelope of the time waveform by performing Hilbert transform is executed. Then, R and IR electric signals digitized by the A / D converters 32 and 33 in the normalization processing units 36 and 37 in the subsequent stage are subjected to envelope data input from the Hilbert transform units 34 and 35 at the same timing. Normalize based on.

  FIG. 5 shows an example of an IR time waveform (IR) and an envelope (HIR) waveform obtained by Hilbert transform of the time waveform. FIG. 6 shows a time waveform obtained by normalizing the IR time waveform shown in FIG. 5 with the envelope shown in FIG. FIG. 7 shows the relationship between the frequency distribution and the amplitude when the normalized time waveform of IR shown in FIG. 6 is fast Fourier transformed (FFT).

  As shown in FIGS. 6 and 7, the normalization processing units 36 and 37 normalize the R and IR time waveforms with their envelopes, so that a frequency component (pulsation component) corresponding to the pulsation of the artery of the measurement subject is obtained. Components other than) are relatively attenuated. Accordingly, the band component indicated by “X” in FIG. 7 corresponding to the band indicated by “X” in FIG. 3 is suppressed, and as a result, the pulsation component indicated by “P” in FIG. Is relatively emphasized, the pulsating component can be accurately specified.

  Further, in the biological signal measurement device 100 according to the present embodiment, the arithmetic processing unit 40 uses the envelope data generated from the R time waveform and the envelope data generated from the IR time waveform. The ratio is calculated. FIG. 8 shows an example of the waveform of the dimming ratio calculated in the arithmetic processing unit 40. As shown in FIG. 8, the value of the dimming ratio calculated based on the envelope data generated from the R time waveform and the envelope data generated from the IR time waveform is a value regardless of the calculation timing. Therefore, the reliability of the blood oxygen saturation in the artery of the measurement subject calculated based on the dimming ratio is improved, and the temporal change can be captured more accurately.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiment.

DESCRIPTION OF SYMBOLS 10 Irradiation part 11, 12 Light emitting element 13 Drive circuit 20 Light receiving part 21 Light receiving element 22 Amplifier 30 Extraction part 31 Multiplexer 32, 33 A / D converter 34, 35 Hilbert conversion part 36, 37 Normalization processing part 38 Preprocessing part 40 Arithmetic processor (oxygen saturation calculator, pulse rate calculator)
50 Storage Unit 60 Display Unit 100 Biological Signal Measuring Device 500 Biological Tissue

Claims (4)

An irradiation unit for irradiating the living tissue of the person to be measured with light of two different wavelengths;
A light receiving unit that receives light of each wavelength irradiated from the irradiation unit and transmitted or reflected through the biological tissue, and converts the light into an electrical signal corresponding to the light reception intensity of each light;
Hilbert transforming the electrical signal to generate envelope data constituting an envelope by Hilbert transform;
A biological signal comprising: an oxygen saturation calculating unit that calculates a light attenuation ratio based on the envelope data, and calculates blood oxygen saturation of an artery in the biological tissue based on the light attenuation ratio. measuring device. The biological signal measuring device further includes
A normalization processing unit for normalizing the value of the envelope data;
The biological signal measurement device according to claim 1, further comprising: a pulse rate calculation unit that calculates a pulse rate based on the normalized envelope data. An irradiation stage for irradiating the living tissue of the measurement subject with light of two different wavelengths;
A light receiving step of receiving light of each wavelength transmitted or reflected through the living tissue and converting it into an electrical signal corresponding to the light receiving intensity of each light;
Hilbert transform stage for generating envelope data constituting the envelope by Hilbert transform the electrical signal;
A biological signal comprising: calculating an attenuation ratio based on the envelope data; and calculating an oxygen saturation level of an artery in the living tissue based on the attenuation ratio. Measuring method. The biological signal measurement method further includes:
A normalization process for normalizing the value of the envelope data;
The biological signal measurement method according to claim 3, further comprising: a pulse rate calculation step of calculating a pulse rate based on the normalized envelope data.

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