JP2022087940A - Oxygen saturation degree measuring device and oxygen saturation degree measuring method - Google Patents

Abstract

To provide an oxygen saturation degree measuring device and an oxygen saturation degree measuring method capable of measuring an oxygen saturation degree even by a signal with a small fluctuation component, by which measurement of an oxygen saturation degree is difficult on a conventional oxygen saturation degree measuring device.SOLUTION: A biological tissue is irradiated with lights of different wavelengths, and the light passing through the biological tissue or the light reflected by the biological tissue is received. Not only in the case where a peak value and a bottom value of a signal of a fluctuation component are clearly shown in a received signal, but also in the case where a peak value and a bottom value are not clear, a root mean square of the signal of the fluctuation component is calculated, and using the result of this calculation, a predetermined ratio is calculated to obtain an oxygen saturation degree.SELECTED DRAWING: Figure 2

Description

The present invention relates to an oxygen saturation measuring device and an oxygen saturation measuring method for irradiating a living tissue with light having a different wavelength and measuring the oxygen saturation in blood from the transmitted or reflected light.

An oxygen saturation measuring device that non-invasively measures the oxygen saturation in blood irradiates a living tissue with red light and infrared light, and is obtained from transmitted light or reflected light of the red light and infrared light, respectively. The oxygen saturation is measured from the ratio of the fluctuation component (pulsation component) of the absorption degree. In particular, a method of reducing an error due to noise by processing a signal of a variable component having a peak value and a bottom value has been proposed (for example, Patent Document 1).

Special Fair 02-44534 Gazette

This type of oxygen saturation measuring device is widely used in the medical field such as emergency lifesaving field and postoperative management, but most of them are permeable type worn on the fingertip or earlobe.

On the other hand, in the reflective type in which the light emitting surface and the light receiving surface are in the same plane, the signal of the variable component contained in the reflected light is small, that is, the peak value and the bottom value of the signal of the variable component are not clear, so that the oxygen saturation is high. Accurate measurement is difficult and has not been widely used. However, the reflective oxygen saturation measuring device has an advantage that the measuring position is not limited to a limited part such as a fingertip or an earlobe, but can be measured at various parts. In view of such circumstances, the present invention is an oxygen saturation measuring device and an oxygen saturation measuring method capable of measuring oxygen saturation even with a signal having a small fluctuation component, which is difficult to measure with a conventional oxygen saturation measuring device. The purpose is to provide.

In order to achieve the above object, the invention according to claim 1 of the present application comprises a light emitting portion that radiates light of at least two different wavelengths to a living body tissue, and light having the different wavelengths transmitted through or reflected by the living body tissue. It is provided with a light receiving unit that receives light, and a calculation unit that calculates the ratio of the signal of the variable component and the signal of the non-variable component of the light received by the light receiving unit, and obtains the oxygen saturation from the ratio of the calculation result. In the oxygen saturation measuring device, the calculation unit calculates the squared average square root of the signal of the variable component, and calculates the ratio of the signal of the squared average square root of the signal of the variable component to the signal of the non-variable component, respectively. However, it is characterized in that the oxygen saturation is obtained from the ratio of the calculation result.

The invention according to claim 2 of the present application irradiates a living body tissue with light having at least two different wavelengths, and receives light transmitted through the living body tissue or reflected by the living body tissue to receive a signal of a variable component of the received light. In the oxygen saturation measurement method in which the ratio between the signal of the variable component and the signal of the non-variable component is calculated and the oxygen saturation is obtained from the ratio of the calculation result, the squared average square root of the signal of the variable component is calculated and the signal of the variable component is calculated. It is characterized in that the ratio of the signal of the squared average square root of the above and the signal of the non-variable component is calculated, and the oxygen saturation is obtained from the ratio of the calculation result.

In the oxygen saturation measuring device and the oxygen saturation measuring method of the present invention, it is possible to obtain a measurement result with less noise by calculating the root mean square of the signal of the fluctuating component and calculating a predetermined ratio. As a result, it is possible to measure the oxygen saturation even when the peak value and the bottom value do not clearly appear in the signal of the fluctuating component, and there is an advantage that the applicable range is widened. In particular, it is possible to configure a reflection type oxygen saturation measuring device in which the light emitting surface and the light receiving surface are in the same plane, which is highly effective.

It is explanatory drawing of the oxygen saturation degree measuring apparatus. It is a figure explaining the oxygen saturation degree measuring method of this invention. It is a figure explaining the oxygen saturation degree measuring method of 1st Example of this invention. It is explanatory drawing of the general oxygen saturation degree measuring method. It is a figure explaining the oxygen saturation degree measuring method using the general reflection type oxygen saturation degree measuring apparatus.

The oxygen saturation measuring device and the oxygen saturation measuring method of the present invention irradiate a living tissue with light having different wavelengths, and receive light transmitted through the living tissue or reflected by the living tissue. At this time, the root mean square of the signal of the variable component is calculated not only when the peak value and the bottom value of the signal of the variable component appear clearly but also when the peak value and the bottom value of the signal received are not clear. Then, the oxygen saturation can be known by calculating a predetermined ratio using this calculation result. Hereinafter, the present invention will be described with reference to conventional examples.

First, a method of measuring the oxygen saturation in blood using a general oxygen saturation measuring device will be described. FIG. 1 schematically shows a general oxygen saturation measuring device, FIG. 1A schematically shows a transmission type oxygen saturation measuring device, and FIG. 1B schematically shows a reflection type oxygen saturation measuring device. ing. The light emitting unit 1 includes a red LED1 _R that emits red light and an infrared LED1 _IR that emits infrared light because it emits light having different wavelengths, and the red LED1 _R and the infrared LED1 _IR are either one of them. It is controlled to emit light only from. The light receiving unit 2 includes a light receiving element 2 _{R_IR} that receives red light and infrared light. The light emission of the light emitting unit 1 and the light reception of the light receiving unit 2 are controlled to be either red light or infrared light or light received by a timing control means (not shown).

When the red light radiated from the red LED _{1 R} passes through the living tissue, it is received by the light receiving element 2 _{R_IR} , and the analog signal amplified by the amplification unit 3 is converted into a digital signal by the analog / digital conversion unit 4 to be converted into a digital signal by the arithmetic unit. Enter in 5. On the other hand, when the infrared light radiated from the infrared LED 1 _IR also passes through the biological tissue, it is received by the light receiving element 2 _{R_IR} , and the analog signal amplified by the amplification unit 3 is converted into a digital signal by the analog / digital conversion unit 4. And input to the calculation unit 5.

The calculation unit 5 calculates the ratio of the absorption characteristics of red light and infrared light. Specifically, assuming that the time-series data yR (k) of red light to be input to the calculation unit 5 and the time-series data yIR (k) of infrared light are used, the calculation as shown in FIG. 4 is performed.

As shown in FIG. 4, in the calculation related to the red light, the time series data yR (k) of the red light input to the calculation unit 5 is processed. A peak value and a bottom value are detected for a signal that has passed through a bandpass filter (BPF: for example, a pass band of 0.5 to 3 Hz), and a peak value (peak value-bottom value) is calculated. This becomes the signal _RAC of the variable component.

During the period in which the signal R _AC of this variable component is calculated, the signal that has passed through the low-pass filter (LPF: for example, the cutoff frequency Fc = 0.5 Hz) becomes the signal R _DC of the non-variable component.

Similarly, in the calculation related to infrared light, the time series data yIR (k) of infrared light input to the calculation unit 5 is processed. A peak value and a bottom value are detected for a signal that has passed through a bandpass filter (BPF: for example, a pass band of 0.5 to 3 Hz), and a peak value (peak value-bottom value) is calculated. This becomes the signal IR _AC of the variable component.

During the period in which the signal IR _AC of this variable component is calculated, the signal that has passed through the low-pass filter becomes the signal IR _DC of the non-variable component.

Next, the ratio R is calculated. Ratio R is
R = (R _AC / R _DC ) / (IR _AC / IR _DC ) ... (Equation 1)
Is calculated as. Here, by normalizing the variable component with the non-variable component, the influence of the different emission amounts of the red LED1 _R and the infrared LED1 _IR is eliminated.

By obtaining the relationship between the ratio R and the known blood oxygen saturation in advance, it is possible to know the oxygen saturation in the blood to be measured once the ratio R is determined. The relationship between the ratio R and the known oxygen saturation may be stored in the calculation unit 5 or in another device that outputs the ratio R.

The ratio R calculated in order to obtain the oxygen saturation is the ratio of variable components such as transmitted light of red light and infrared light. In the measurement of fingertips and earlobe using a transmission type oxygen saturation measuring device, the peak value and bottom value of the signal of the fluctuating component clearly appear, the peak value can be calculated easily, and the ratio R can be calculated without any problem. ..

However, even when a transmission type oxygen saturation measuring device is used, the peak value and bottom value of the signal of the fluctuating component are clearly defined in the measurement of parts other than the fingertip and earlid and the reflection type oxygen saturation measuring device. It may not appear. For example, FIG. 5 shows the results of measuring the ratio R by measuring the wrist, which is a region where the pulsation is small, using a reflex-type oxygen saturation measuring device. As shown in FIG. 5, noise is included in the ratio R calculated according to the above equation (1), which makes it difficult to measure the oxygen saturation.

Therefore, the present invention proposes another calculation method as a method for calculating the ratio R in the calculation unit 5. In the present invention, the root mean square R _{AC_rms} is calculated from the variable component R _AC of red light sampled for a predetermined period, and similarly, the root mean square IR _{AC_rms} is calculated from the variable component IR _AC of infrared light sampled for a predetermined period. Then, the ratio R of the red light and the infrared light is calculated. The ratio R can be expressed by the following equation.

R = (R _{AC_rms} / R _DC ) / (IR _{AC_rms} / IR _DC ) ... (Equation 2)

In this case as well, by normalizing the variable component with the non-variable component, it is possible to eliminate the influence of the different emission amounts of the red LED1 _R and the infrared LED1 _IR . The measurement for calculating the root mean square R _{AC_rms} may be performed for about 1 second to several seconds when the sampling frequency fs is 100 Hz. This is because, with this measurement time, it is possible to sufficiently perform the measurement corresponding to one beat of a normal pulse (60 beats / minute).

In this way, the oxygen saturation can be calculated by using the value obtained by calculating the root mean square as the signal of the variable component for the calculation of the ratio R. Hereinafter, examples of the present invention will be described.

A first embodiment of the present invention will be described. The oxygen saturation measuring device of this embodiment has a different configuration of the calculation unit 5 as compared with a general oxygen saturation measuring device. That is, the difference is that the arithmetic unit 5 is provided with means for executing the oxygen saturation measuring method of the present invention.

Similar to the oxygen saturation measuring device shown in FIG. 1, the oxygen saturation measuring device of the present invention emits red LED1 _R that emits light having a wavelength of 630 nm as red light and light having a wavelength of 920 nm as infrared light in the light emitting unit 1. It is equipped with an infrared LED 1 _IR that emits light. When emitting red light or infrared light to a living tissue, control is performed so that only red light or infrared light having a period of 10 msec and a emission duty of 1% is emitted according to a signal from a timing control unit (not shown). Will be done.

The light receiving unit 2 is provided with a light receiving element 2 _{R_IR} that receives the red light and the infrared light. The light receiving element 2 _{R_IR} converts the light received at the timing when the red LED1 _R and the infrared LED1 _IR are emitting into an electric signal and outputs it to the amplification unit 3, and the analog signal output from the amplification unit 3 Is converted into a digital signal by the analog / digital conversion unit 4 and output to the calculation unit 5. Since the timing of converting the analog signal to the digital signal by the analog / digital conversion unit 4 is performed at the same timing as the red light or the infrared light is emitted, the sampling frequency fs for the red light or the infrared light is 100 Hz. Become. The above operation is the same as the operation of a general pulse oximeter.

Next, the calculation in the calculation unit 5 will be described. The time-series data of red light input to the calculation unit 5 is yR (k), and the time-series data of infrared light is yIR (k). FIG. 2 is an explanatory diagram illustrating an operation in the calculation unit 5.

As shown in FIG. 2, in the calculation related to the red light, the time series data yR (k) of the red light input to the calculation unit 5 is processed. Specifically, the root mean square is calculated for a signal that has passed through a bandpass filter (BPF: pass band 0.5 to 3 Hz). The signal that has passed through this bandpass filter becomes a signal of a variable component. The signal that has passed through the bandpass filter is defined as ybpR (k).

The root mean square (RMS) is calculated using the data from the signal ybp_R (k) that passed through the bandpass filter to the signal ybp_R (k—N) that passed through the bandpass filter T seconds ago. Here, N is the number of samples during the time T seconds, and when the sampling frequency is fs, the relationship is N = fs / T.

と、算出される。 Let yR_rms (k) be the root mean square for T seconds at time k.

Is calculated.

On the other hand, the signal that has passed through the low-pass filter (LPF: cutoff frequency Fc = 0.5 Hz) becomes a signal having a non-variable component. Assuming that the signal that has passed through the low-pass filter is ylp_R (k), the normalized signal yR_nom (k) is
yR_nom (k) = yR_rms (k) / ylp_R (k)
Will be.

Similarly, in the calculation related to infrared light, the time series data yIR (k) of infrared light input to the calculation unit 5 is processed. Specifically, the root mean square is calculated for a signal that has passed through a bandpass filter (BPF: pass band 0.5 to 3 Hz). The signal that has passed through the bandpass filter is defined as ybpIR (k).

The calculation for the root mean square (RMS) uses the data from the signal ybp_IR (k) that passed through the bandpass filter to the signal ybp_IR (k—N) that passed through the bandpass filter T seconds ago. Here, N is the number of samples during the time T seconds, and when the sampling frequency is fs, the relationship is N = fs / T.

と、算出される。 Let yIR_rms (k) be the root mean square for T seconds at time k.

Is calculated.

On the other hand, the signal that has passed through the low-pass filter (LPF: cutoff frequency Fc = 0.5 Hz) becomes a signal having a non-variable component. Assuming that the signal that has passed through the low-pass filter is ylp_IR (k), the normalized signal yIR_nom (k) is
yIR_nom (k) = yIR_rms (k) / ylp_IR (k)
Will be.

Next, the ratio R is calculated. The ratio R is the same as in the above equation (2).
R = yR_nom (k) / yIR_nom (k) ... (Equation 3)
Is calculated as.

By obtaining the relationship between this ratio R and the known oxygen saturation in advance, it is possible to know the oxygen saturation to be measured once the ratio R is determined. The relationship between the ratio R and the known oxygen saturation may be stored in the calculation unit 5 or in another device that outputs the ratio R.

FIG. 3 shows the measured values of the wrist, which is a region where the pulsation is small, where T = 2 seconds and N = 200. The signal obtained by the wrist measurement has a small fluctuation component signal, and the peak value and bottom value are not clear. As explained earlier in FIG. 5, noise is generated by the method of calculating according to the conventional formula (1). It was a lot of parts. On the other hand, in this embodiment calculated according to the equation (3), it can be seen that the noise is reduced as shown by the solid line in FIG. For comparison, the measurement results by the conventional method shown in FIG. 5 are shown by broken lines.

As described above, according to the oxygen saturation measuring device and the oxygen saturation measuring method of the present invention, a ratio R with less noise is calculated, and from the relationship between this ratio R and the oxygen saturation measured in advance, the blood to be measured is measured. The oxygen saturation can be calculated accurately.

Next, a second embodiment will be described. As described in the first embodiment described above, the oxygen saturation measuring device of the present invention has a different configuration of the calculation unit 5 as compared with the general oxygen saturation measuring device. The method for measuring oxygen saturation of the present invention is being carried out. The normal calculation unit 5 can store a plurality of measurement modes. That is, the oxygen saturation measuring device can be an oxygen saturation measuring device capable of switching between a measurement mode according to a general oxygen saturation measuring method and a measurement mode according to the oxygen saturation measuring method of the present invention.

In the measurement of large pulsating parts such as fingertips and ear pads, the results obtained from the measurement by the measurement mode according to the oxygen saturation measurement method of the present invention and the measurement by the measurement mode according to the general oxygen saturation measurement method are obtained. It will be almost the same.

Therefore, for example, for a site such as a fingertip where good measurement can be performed with a permeation type, a measurement according to a general oxygen saturation measurement method using a permeation type device and a measurement according to the oxygen saturation measurement method of the present invention can be performed. , The measurement results of both can be compared, and the reliability of the measurement results can be confirmed by the degree of deviation between the measurement results of both. Alternatively, the measurement result according to the oxygen saturation measurement method of the present invention using the fingertip transmission type device is compared with the measurement result according to the oxygen saturation measurement method of the present invention using the reflection type device, and the measurement result is similarly compared. You can check the reliability of. At this time, the same LED may be used for the light emitting unit 1. As described above, according to this embodiment, it is possible to use the measurement result of oxygen saturation in addition to obtaining oxygen saturation.

As described above, according to the oxygen saturation measuring method of the present invention, it is possible to measure the blood oxygen saturation even when the signal of the fluctuating component is small and the peak value and the bottom value do not clearly appear. As a matter of course, the oxygen saturation measuring method of the present invention can obtain the same measurement results as the conventional apparatus and method even when the peak value and the bottom value of the signal of the fluctuating component clearly appear.

1: Light emitting part, 1 _R : Red LED, 1 _IR : Infrared LED, 2: Light receiving part, 3: Amplifying part, 4: Analog / digital conversion part, 5: Arithmetic unit

Claims (2)

A light emitting part that radiates light of at least two different wavelengths to living tissue,
A light receiving unit that receives light of the different wavelength that has passed through the living tissue or is reflected by the living tissue.
In an oxygen saturation measuring device provided with a calculation unit that calculates the ratio of the signal of the variable component and the signal of the non-variable component of the light received by the light receiving unit and obtains the oxygen saturation from the ratio of the calculation result. ,
The calculation unit calculates the root mean square of the signal of the variable component, calculates the ratio between the signal of the root mean square of the signal of the variable component and the signal of the non-variable component, respectively, and from the ratio of the calculation results. An oxygen saturation measuring device characterized by obtaining an oxygen saturation. By irradiating a living tissue with light of at least two different wavelengths and receiving light transmitted through the living tissue or reflected by the living tissue, the ratio of the signal of the variable component and the signal of the non-variable component of the received light is received. In the oxygen saturation measurement method in which oxygen saturation is obtained from the ratio of the calculation results.
The root mean square of the signal of the variable component is calculated, the ratio of the root mean square signal of the signal of the variable component to the signal of the non-variable component is calculated, and the oxygen saturation is obtained from the ratio of the calculation results. A method for measuring oxygen saturation.

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