JP7257571B2 - pulse oximeter - Google Patents

Description

The present invention relates to the technical field of pulse oximeters.

This type of pulse oximeter is, for example, a ring-type pulse oximeter that is assumed to be worn at all times. A pulse oximeter has been proposed that presses a target site to be measured so as to increase the pulsation of the artery when the arterial pulsation decreases (see Patent Document 1).

Alternatively, the blood pressure value is obtained based on the pulsation component of one volume signal and the cuff pressure of two volume signals corresponding to light with different wavelengths, and the volume extracted from the pulsation component of each of the two volume signals. A device has been proposed that simultaneously and continuously measures blood pressure and blood oxygen saturation by obtaining blood oxygen saturation from a pulse wave signal (see Patent Document 2).

Japanese Patent Application Laid-Open No. 2007-330708 JP-A-6-63024

By the way, in arterial oxygen saturation (hereinafter referred to as “SpO ₂ ” as appropriate) measurement by a pulse oximeter, when the mounting pressure of the sensor constituting the pulse oximeter changes, the measurement result of SpO ₂ changes.

In the technique described in Patent Document 1, when the sensor of the finger ring type pulse oximeter is worn relatively high due to, for example, swollen fingers of the person being measured, there is a possibility that the SpO ₂ value cannot be measured correctly. There is a technical problem that exists. Moreover, the technique described in Patent Document 2 above has a technical problem that the mounting pressure of the sensor is not taken into consideration for SpO ₂ measurement.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a pulse oximeter capable of suppressing the influence of the mounting pressure of the sensor.

In order to solve the above problems, a first pulse oximeter of the present invention provides a first light emitting section that generates a first light and a second light emitting section that generates a second light having a wavelength different from that of the first light. a light receiving unit that receives each of the first return light from the living body of the first light and the second return light of the second light from the living body; and a contact that detects a signal related to contact pressure between the living body and the living body. Oxygen saturation based on pressure detection means, a signal output from the light receiving unit due to each of the first return light and the second return light, and a signal related to the detected contact pressure and output means for outputting information.

In order to solve the above problems, a second pulse oximeter of the present invention provides a first light emitting unit that emits a first light and a second light emitting unit that emits a second light having a wavelength different from that of the first light. and a light-receiving unit that receives a first return light from the living body as the first light and a second return light as the second light from the living body, the pulse oximeter comprising: and contact pressure detection means for detecting a signal related to the contact pressure with the living body, and output means for outputting information related to adjustment of the contact pressure according to the detected signal related to the contact pressure.

The operation and other advantages of the present invention will become apparent from the detailed description that follows.

1 is a schematic configuration diagram showing an overview of a pulse oximeter according to a first embodiment; FIG. FIG. 2 is a block diagram showing the essential parts of the calculation device according to the first embodiment; FIG. FIG. 4 is a diagram showing an example of a signal output from a light receiving means for each mounting pressure; FIG. 5 is a characteristic diagram showing an example of the relationship between mounting pressure and signal amplitude; FIG. 4 is a characteristic diagram showing an example of the relationship between mounting pressure and _SpO2 . FIG. 4 is a diagram showing an example of a gain correction function F(Δp) according to the first embodiment; FIG. 4 is a diagram showing an example of SpO ₂ measurement results without correction and an example of SpO ₂ measurement results with correction; FIG. 2 is a diagram showing an arrangement example of each element that constitutes the transmission-type pulse oximeter according to the first embodiment; FIG. 2 is a diagram showing an arrangement example of each element that constitutes the reflection-type pulse oximeter according to the first embodiment; It is a schematic block diagram which shows the outline|summary of the pulse oximeter based on the modification of 1st Example. FIG. 2 is a schematic configuration diagram showing an outline of a pulse oximeter according to a second embodiment; FIG. 11 is a schematic configuration diagram showing an overview of a pulse oximeter according to a modification of the second embodiment;

Embodiments of the pulse oximeter of the present invention will be described below.

<First embodiment>
A pulse oximeter according to the first embodiment includes a first light emitting section, a second light emitting section, and a light receiving section. The first light emitting unit emits first light. The second light emitter generates second light having a wavelength different from that of the first light. Here, the wavelength of one of the first light and the second light is a wavelength that is predominantly absorbed by oxygenated hemoglobin, and the wavelength of the other light of the first light and the second light is the wavelength of deoxygenated hemoglobin. Although it is desirable that the wavelength is a dominant wavelength for absorption, it is not limited to this. The pulse oximeter according to this embodiment may have three or more light emitting units.

The light receiving unit receives the first return light from the living body as the first light and the second return light from the living body as the second light. Here, "returned light" is a concept including not only light scattered or reflected by the living body but also light transmitted through the living body. That is, the pulse oximeter according to the present embodiment may be a reflective pulse oximeter or a transmissive pulse oximeter. It should be noted that the light receiving section is not limited to being composed of, for example, a single light receiving element, and may be composed of a plurality of light receiving elements.

The contact pressure detection means detects a signal related to the contact pressure between the pulse oximeter and the living body. Here, the "signal related to the contact pressure" is not limited to a signal indicating the value of the contact pressure itself. It is a concept that includes

For example, the output means, which includes a memory, a processor, etc., outputs oxygen saturation signals based on the signals output from the light receiving unit due to the first return light and the second return light and the detected contact pressure signal. Output information about the degree. Here, the "information about the oxygen saturation" is not limited to information indicating the value of the oxygen saturation itself. It is a concept that includes information that indirectly indicates

According to the studies of the inventors of the present application, the following matters have been clarified. That is, the pulse oximeter outputs information about the oxygen saturation level based on the pulsating component of the output signal of the light receiving unit caused by arterial blood. Here, arteries are the only blood vessels that pulsate in the living body, and veins that seep out from capillaries and whose blood pressure is reduced to a level that can be regarded as 0 mmHg do not pulsate. In reality, however, arterial pulsations propagate through living tissue and physically vibrate veins. As a result, the pulsation component of the output signal from the light receiving section contains more or less vein information.

When the contact pressure of the pulse oximeter with respect to the living body changes, the physical distance between arteries and veins in the living body changes, and the effect of arterial pulsation on veins also changes. In other words, when the contact pressure changes, the influence of veins on the pulsating component of the output signal also changes. Pulse oximeters are often designed to obtain accurate oxygen saturation based on the assumption of contact pressure. Therefore, depending on the contact pressure, the pulsating component of the output signal is greatly affected by veins, and an erroneous oxygen saturation may be obtained.

Therefore, in the present embodiment, the oxygen saturation level is calculated based on the signal output from the light receiving unit due to the first return light and the second return light and the signal related to the detected contact pressure by the output means. information is output.

Specifically, for example, the output unit corrects the signal output from the light receiving unit due to each of the first return light and the second return light (for example, signal amplitude is increased or decreased), and then information related to the oxygen saturation is output. Alternatively, the output means converts the information related to the oxygen saturation obtained based on the signals output from the light receiving section due to the first returned light and the second returned light to the signal related to the detected contact pressure. Correct accordingly. In any case, information on oxygen saturation with little or no effect of contact pressure is output.

As a result, according to the pulse oximeter according to the present embodiment, the influence of the contact pressure can be suppressed, and thus highly reliable information regarding the oxygen saturation can be output.

In one aspect of the pulse oximeter according to the first embodiment, the output means includes a signal output from the light receiving section due to the first return light and a signal output from the light receiving section due to the second return light. and at least one of which is changed based on the detected contact pressure signal.

For example, as the contact pressure increases, the physical distance between arteries and veins in the body becomes shorter, and the effects of arterial pulsation on veins become greater. Then, the pulsation component (signal amplitude) of the output signal increases due to the influence of the vein.

As described above, the output means outputs a signal output from the light receiving section due to the first return light and a signal output from the light receiving section due to the second return light based on the detected signal related to the contact pressure. By changing the amplification factor of at least one of the signal and the venous effect (that is, the contact pressure effect), it is possible to suppress or eliminate the effect of the vein.

Alternatively, in another aspect of the pulse oximeter according to the first embodiment, the pulse oximeter further includes second output means for outputting information related to adjustment of the contact pressure according to the detected signal related to the contact pressure.

According to this aspect, if the contact pressure of the pulse oximeter is automatically or manually adjusted according to the output information related to adjustment of the contact pressure, the oxygen saturation with the influence of the contact pressure suppressed can be achieved. Such information can be output.

It should be noted that the "information related to contact pressure adjustment" is not limited to information indicating the contact pressure adjustment value itself. It is a concept that includes prompting information, a physical quantity or parameter that directly or indirectly indicates the degree of contact pressure, and the like.

<Second embodiment>
A pulse oximeter according to the second embodiment includes a first light emitting section, a second light emitting section, and a light receiving section. The first light emitting unit emits first light. The second light emitter generates second light having a wavelength different from that of the first light. The light receiving unit receives the first return light from the living body as the first light and the second return light from the living body as the second light.

The contact pressure detection means detects a signal related to the contact pressure between the pulse oximeter and the living body. For example, the output means including a memory, a processor, etc. outputs information regarding adjustment of the contact pressure according to the detected signal regarding the contact pressure.

If the contact pressure of the pulse oximeter is automatically or manually adjusted according to the output information related to contact pressure adjustment, the oxygen saturation is measured at an appropriate contact pressure. As a result, it is possible to obtain the oxygen saturation in which the influence of the contact pressure is suppressed.

One aspect of the pulse oximeter according to the second embodiment further comprises adjusting means for adjusting the contact pressure between the pulse oximeter and the living body according to the output information relating to adjustment of the contact pressure.

According to this aspect, the contact pressure is automatically adjusted, which is extremely advantageous in practice.

An embodiment of the pulse oximeter of the present invention will be described with reference to the drawings.

<First embodiment>
A first embodiment of the pulse oximeter of the present invention will be described with reference to FIGS. 1 to 7. FIG.

In FIG. 1, the pulse oximeter 1 includes light emitting means 11, light emitting means 12, light receiving means 13 such as a PD (Photodiode), mounting pressure detecting means 14 such as a pressure sensor, and output from the light receiving means 13. and a calculation means 100 for processing the signal output from the mounting pressure detection means 14 and the signal output from the mounting pressure detection means 14 .

The light emitting means 11 includes, for example, an infrared LED (Light Emitting Diode), and generates first light having a wavelength that is predominantly absorbed by oxygenated hemoglobin. On the other hand, the light emitting means 12, for example comprising a red LED, emits a second light of a wavelength which is predominantly absorbed by the deoxygenated hemoglobin.

The first light and the second light are applied to blood vessels of human fingers (corresponding to the “living body” according to the present invention). The light receiving means 13 receives the first transmitted light (corresponding to the “first returned light” according to the present invention) of the first light transmitted through the blood vessel and the second transmitted light of the second light (“second returned light” according to the present invention). ”) and outputs a signal corresponding to the amount of light received.

Here, SpO ₂ is the signal output from the light receiving means 13 due to the first transmitted light (i.e., light with a wavelength that is predominantly absorbed by oxygenated hemoglobin) and the second transmitted light (i.e., deoxygenated light). It is obtained based on the amplitude ratio between the signal output from the light receiving means 13 due to the light having a wavelength that is predominantly absorbed by hemoglobin.

By the way, research by the inventor of the present application has revealed that the amplitude of the signal output from the light receiving means 13 is affected by the mounting pressure of the pulse oximeter 1 . Specifically, for example, as shown in FIGS. 3 and 4, the amplitude of the signal output from the light receiving means 13 changes depending on the mounting pressure of the pulse oximeter.

The "infrared light signal" and the "red light signal" in FIGS. 3 and 4 are respectively the "signal output from the light receiving means 13 due to the first transmitted light" and the "signal generated by the second transmitted light". The signal output from the light-receiving means 13 as a result of ".

In particular, when the mounting pressure of the pulse oximeter 1 increases, the rate at which the second light having a wavelength that is predominantly absorbed by deoxygenated hemoglobin is absorbed by the living body increases due to venous blood. Then, the amplitude of the signal output from the light receiving means due to the second light (second transmitted light) is lower than the amplitude of the signal output from the light receiving means 13 due to the first transmitted light. becomes difficult (see Fig. 4).

As a result, the ratio between the amplitude of the signal output from the light receiving means 13 due to the first transmitted light and the amplitude of the signal output from the light receiving means 13 due to the second transmitted light is relatively small. Become. Therefore _, if no countermeasures are _taken , as shown in FIG. possible).

Therefore, in this embodiment, in order to suppress the influence of veins, the calculation device 100 receives light according to the signal output from the wearing pressure detection means 14 (corresponding to the "signal related to wearing pressure" according to the present invention). The amplification factor of the signal resulting from the second transmitted light output from the means 13 is changed. Then, _SpO2 is calculated by the calculating device 100 based on the amplitude ratio between the signal caused by the second transmitted light whose amplification factor is changed and the signal caused by the first transmitted light output from the light receiving means 13. be done.

Specifically, in FIG. 2, the calculation device 100 includes a wearing pressure correction means 110, an amplifier 120, and an oxygen saturation output means .

The wearing pressure correction means 110 determines a correction coefficient for the amplification factor of the amplifier 120 according to the signal related to the wearing pressure output from the wearing pressure detection means 14 .

This correction coefficient is, for example, the difference Δp between the actual wearing pressure based on the signal related to the wearing pressure output from the wearing pressure detection means 14 and the predetermined reference wearing pressure, and the function F of the difference Δp. (Δp).

Such a function F(Δp) is the amplitude ratio between the signal due to the first transmitted light and the signal due to the second transmitted light at the reference mounting pressure, and the first transmitted light at an arbitrary mounting pressure. A plurality of ratios of the amplitude ratio of the signal caused by the second transmitted light and the amplitude ratio of the signal caused by the second transmitted light may be obtained, and an approximation curve for the plurality of ratios thus obtained may be obtained (see FIG. 6).

That is, the function F(Δp) can be expressed as in the following formula.

ここで、ＲＤ_ｓｔｄは、基準となる装着圧における第２透過光に起因する信号の振幅値であり、ＩＲ_ｓｔｄは、基準となる装着圧における第１透過光に起因する信号の振幅値であり、ＲＤは、任意の装着圧における第２透過光に起因する信号の振幅値であり、ＩＲは、任意の装着圧における第１透過光に起因する信号の振幅値である。

Here, RD _std is the amplitude value of the signal caused by the second transmitted light at the reference wearing pressure, and IR _std is the amplitude value of the signal caused by the first transmitted light at the reference wearing pressure. , RD is the amplitude value of the signal due to the second transmitted light at any wearing pressure, and IR is the amplitude value of the signal due to the first transmitted light at any wearing pressure.

If the above formula is modified, the amplitude ratio between the signal caused by the first transmitted light and the signal caused by the second transmitted light actually output (that is, at an arbitrary mounting pressure), the function F(Δp), and can be used to determine the amplitude ratio between the signal due to the first transmitted light and the signal due to the second transmitted light at the reference mounting pressure (in other words, appropriate mounting pressure) (see the following formula) .

上記式に従えば、装着圧補正手段１１０は、装着圧検出手段１４から出力された装着圧に係る信号に基づいて求められたＦ（Δｐ）の値を、増幅器１２０に係る増幅率の補正係数として決定する。

According to the above formula, the wearing pressure correction means 110 converts the value of F(Δp) obtained based on the signal related to the wearing pressure output from the wearing pressure detection means 14 to the correction coefficient of the amplification factor related to the amplifier 120 Determined as

By changing the amplification factor of the amplifier 120 according to the correction coefficient determined by the mounting pressure correction means 110, the amplitude of the signal caused by the second transmitted light (corresponding to "RD" in the above formula) is changed. be done. Oxygen saturation output means 130 obtains _SpO2 based on the signal due to the second transmitted light whose amplitude has been changed and the signal due to the first transmitted light.

If no measures are taken for the mounting pressure of the pulse oximeter 1, the measurement result of SpO ₂ will be as shown in FIG. 7(a), for example. However, in this embodiment, as described above, the amplification factor of the signal caused by the second transmitted light is corrected in accordance with the mounting pressure of the pulse oximeter 1, so that the measurement results shown in FIG. is obtained. That is, according to the pulse oximeter 1 according to the present embodiment, measurement results are obtained that are not or hardly affected by the wearing pressure.

The light emitting means 11 and the light emitting means 12 are driven alternately in terms of time (that is, the first light and the second light are alternately generated in terms of time). Then, for example, in the calculation device 100, the signal output from the light receiving means 13 during the driving period of the light emitting means 11 is directly input to the oxygen saturation output means 130, and during the driving period of the light emitting means 12, the light receiving means 13 A switching circuit (not shown) is provided for inputting the signal output from the oxygen saturation level output means 130 via the amplifier 120 .

The light emitting means 11, the light emitting means 12, the light receiving means 13, and the wearing pressure detecting means 14, which constitute the pulse oximeter 1, are arranged so that the light emitting means 11 and 12 are placed on the back of the finger, for example, as shown in FIG. 8(a). The light receiving means 13 and the wearing pressure detecting means 14 may be arranged on the pad of the finger. Alternatively, as shown in FIG. 8B, the light emitting means 11 and 12 and the wearing pressure detecting means 14 may be arranged on the back of the finger, and the light receiving means 13 may be arranged on the ball of the finger. Alternatively, as shown in FIG. 8C, the light emitting means 11 and 12 and the wearing pressure detecting means 14a are arranged on the back of the finger, and the light receiving means 13 and the wearing pressure detecting means 14b are arranged on the ball of the finger. may

Although the transmissive pulse oximeter 1 has been described in this embodiment, the present invention can also be applied to a reflective pulse oximeter. In this case, each of the light emitting means 11 and 12, the light receiving means 13, and the mounting pressure detecting means 14 can adopt any of the arrangements shown in FIGS. 9(a) to 9(c).

The "light emitting means 11", the "light emitting means 12", the "light receiving means 13", the "wearing pressure detecting means 14", and the "calculating device 100" according to the present embodiment are respectively the "first light emitting units" according to the present invention. , "second light emitting section", "light receiving section", "contact pressure detecting means" and "output means".

In this embodiment, as shown in FIG. 2, the amplification factor of the signal caused by the second transmitted light is changed. The amplification factor of the signal may be changed, or the amplification factor of both the signal caused by the first transmitted light and the signal caused by the second transmitted light may be changed.

<Modification>
Next, a modification of the pulse oximeter according to the first embodiment will be described with reference to FIG. FIG. 10 is a schematic configuration diagram showing an outline of a pulse oximeter according to a modification of the first embodiment.

In FIG. 10, the pulse oximeter 2 according to the modification of the first embodiment includes, in addition to the light emitting means 11, the light emitting means 12, the light receiving means 13, the wearing pressure detecting means 14 and the calculating device 100, an arithmetic device 21 and a wearing pressure It is configured with a display device 22 .

The calculation device 21, which is an example of the "second output means" according to the present invention, adjusts the wearing pressure suitable for display on the wearing pressure display device 22 based on the signal output from the wearing pressure detection means 14. Output the relevant information. Here, in particular, the wearing pressure display device 22 displays such that the wearing pressure is guided within a predetermined range.

If the user of the pulse oximeter 2 adjusts the wearing pressure of the pulse oximeter 2 with reference to the display of the wearing pressure display device 22, the SpO ₂ value can be preferably measured.

In particular, when the mounting pressure is relatively high, the correction amount is relatively large, as shown in FIG. 7, for example. Therefore, with the configuration as described above, errors due to correction can be suppressed, which is very advantageous in practice.

<Second embodiment>
A second embodiment of the pulse oximeter of the present invention will be described with reference to FIG. The second embodiment is the same as the first embodiment described above, except that the configuration of the pulse oximeter is partially different. Therefore, for the second embodiment, description overlapping with the first embodiment will be omitted, common parts on the drawings will be indicated by the same reference numerals, and only basic differences will be described with reference to FIG. explain.

In FIG. 11, the pulse oximeter 3 according to the second embodiment comprises a light emitting means 11, a light emitting means 12, a light receiving means 13, a wearing pressure detecting means 14, an arithmetic device 21, a wearing pressure display device 22 and a calculating device 100. It is configured.

Based on the signal output from the wearing pressure detection means 14 , the calculation device 21 outputs information related to adjustment of the wearing pressure suitable for display on the wearing pressure display device 22 .

When the user of the pulse oximeter 2 refers to the display of the wearing pressure display device 22 and adjusts the wearing pressure of the pulse oximeter 2 to a predetermined value, light is received as described in the first embodiment. SpO ₂ values can be conveniently measured without correction of the signal output from means 13 .

<Modification>
Next, a modification of the pulse oximeter according to the second embodiment will be described with reference to FIG. FIG. 12 is a schematic configuration diagram showing an outline of a pulse oximeter according to a modification of the second embodiment.

In FIG. 12, the pulse oximeter 4 according to the modification of the second embodiment includes a light emitting means 11, a light emitting means 12, a light receiving means 13, a wearing pressure detecting means 14, an arithmetic device 21, and a calculating device 100, and a wearing pressure It is configured to include an adjustment section 23 .

The mounting pressure adjusting portion 23 is provided between a supporting member that supports the light emitting means 11 and 12 and a supporting member that supports the light receiving means 13 and the mounting pressure detecting means 14 .

The computing device 21 controls the mounting pressure adjusting section 23 according to the signal output from the mounting pressure detecting means 14 so that the mounting pressure becomes a predetermined value. With this configuration, the SpO ₂ value can be suitably measured.

The "computing device 21" and the "wearing pressure adjusting section 23" according to this modification are examples of the "adjusting means" according to the present invention.

The present invention is not limited to the above-described embodiments, and can be modified as appropriate within the scope of the gist or idea of the invention that can be read from the scope of claims and the entire specification. is also included in the technical scope of the present invention.

1, 2, 3, 4... Pulse oximeter, 11, 12... Light-emitting means, 13... Light-receiving means, 14, 14a, 14b... Wearing pressure detecting means, 21... Computing device, 22... Wearing pressure display device, 23... Wearing Pressure adjusting unit, 100... Calculating device

Claims (1)

a first light emitting unit that emits a first light;
a second light emitting unit that generates a second light having a wavelength different from that of the first light;
a light receiving unit that receives a first return light from the living body of the first light and a second return light from the living body of the second light;
contact pressure detection means for detecting a signal related to contact pressure with the living body;
Output for outputting information related to oxygen saturation based on a signal output from the light receiving unit due to each of the first return light and the second return light and a signal related to the detected contact pressure. means and
comprising a
The output means provides an amplification factor for at least one of a signal output from the light receiving section due to the first return light and a signal output from the light receiving section due to the second return light. is changed based on the detected contact pressure signal
A pulse oximeter characterized by:

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