JP2555833Y2 - Reflective oximeter probe - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a probe used for a reflection type oximeter.

[0002]

2. Description of the Related Art A plurality of types of light emitting elements are sequentially irradiated with a plurality of types of light having different wavelengths from each other on the surface of a living body, and reflected light from the living body is detected by a common light receiving element. There is known a reflection oximeter that measures oxygen saturation in blood based on a photoplethysmographic signal representing the following equation. For example, Japanese Unexamined Patent Application Publication No. 2-111344, which was filed by the applicant of the present invention, has been disclosed. The measurement of oxygen saturation using such a reflection oximeter is based on the dermis constituting a part of the skin. It is usually done in the inner vascular bed.

[0003] The reflection type oximeter described in the above publication is
Two types of light emitting elements having different emission wavelengths are arranged alternately over the entire circumference at predetermined intervals on a circumference of a predetermined radius centered on the light receiving element, and reflected from the light emitting element on the body surface to the light receiving element. A cylindrical light blocking member for blocking incoming light is provided with a probe provided between the light receiving element and the light emitting element, and a photoelectric pulse wave signal representing the intensity of reflected light detected by the light receiving element is large. In addition to this, there is an advantage that the oxygen saturation can be measured accurately and stably even when the composition of the vascular bed is not uniform or when the posture of the probe is inclined. Further, in the reflection oximeter described in the above publication, the oxygen saturation is determined based on the ratio between the AC component and the DC component of the photoplethysmographic signal.

[0004]

However, the probe of the reflection type oximeter described in the above publication still has a problem to be solved. That is, since the distance between the light receiving element and each light emitting element is constant, the width of the optimum detection depth representing the depth from the surface of the living body where the intensity of the reflected light from the inside of the living body is sufficiently large is reduced. Therefore, if the depth position of the vascular bed from the surface of the living body varies due to the individual difference of the subject and the difference of the measurement site, the magnitude of the photoelectric pulse wave signal may decrease and the oxygen saturation may not be measured accurately. In addition, when peripheral blood circulation is reduced due to shock applied to the living body and reflected light is detected only from a deeper position in the vascular bed, the magnitude of the photoelectric pulse wave signal decreases and the oxygen saturation is measured accurately. There is a possibility that good and stable measurement cannot be performed.

The present invention has been made in view of the above circumstances, and its purpose is to accurately measure the oxygen saturation regardless of the individual difference of the subject and the difference of the measurement site. It is an object of the present invention to provide a probe for a reflection type oximeter capable of measuring oxygen saturation with high accuracy and stability regardless of a decrease in peripheral circulation.

[0006]

Means for Solving the Problems The gist of the present invention to achieve the above object is to sequentially emit a plurality of types of light having different wavelengths from a plurality of types of light emitting element groups onto the surface of a living body. was irradiated, the irradiation of a plurality of types of reflected light from the living body
In the reflection type oximeter, which detects each of the common light receiving elements by switching the timing in synchronization with each other and measures the oxygen saturation in blood based on the photoelectric pulse wave signal representing the intensity of the reflected light, Configure the element group
A light emitting element covers the entire circumference surrounding the light receiving element for each type.
Together are arranged at intervals such as to be substantially equal to I, between them the light emitting element and the light receiving element, it is reflected by the surface of the living body from the light-emitting element light shielding ring for blocking light toward the light receiving element A probe in which a member is provided, wherein the distance between the light emitting element and the light receiving element is gradually increased.
It is provided around the light receiving element so as to increase and gradually decrease in the middle .

[0007]

According to the probe for a reflection type oximeter having such a structure, a plurality of light emitting elements which emit light of a plurality of wavelengths and are provided for each kind are provided around a common light receiving element. The distance from the photo detector gradually increases
Since they are arranged so as to gradually decrease from the middle, a wide range of the optimum detection depth of the reflected light can be obtained. As a result, even if the depth position of the vascular bed from the living body surface varies due to the individual difference of the subject or the measurement site, the magnitude of the photoplethysmographic signal can be sufficiently obtained and the oxygen saturation can be accurately measured. In addition, even if the reflected light is detected only from a deeper position in the vascular bed due to a decrease in peripheral circulation, the magnitude of the photoplethysmographic signal can be sufficiently obtained and the oxygen saturation can be measured accurately and stably. I can do it.

Preferably, each minimum detection depth from the surface of the living body of the reflected light of each light emitting element detected by the light receiving element is equal to or greater than the thickness of the epidermis constituting a part of the skin of the living body. Is determined. As described above, even if the distance between the light receiving element and each light emitting element is different, the minimum detection depth of each light emitting element is set to be equal to or greater than the thickness of the epidermis, so that reflected light from the epidermis without blood vessels is received. Since the detection by the element can be preferably avoided, a large ratio between the AC component and the DC component of the photoplethysmographic signal can be secured, and the measurement accuracy of the oxygen saturation can be further improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 2 is a diagram showing an example of a configuration of a reflection type oximeter provided with a probe to which the present invention is applied. The probe 10 is mounted in a state in which the probe 10 is in close contact with a body surface 12 such as a living finger. Is done. As shown in FIGS. 1 and 2, the probes 10 are alternately and annularly arranged at predetermined intervals in a container-like housing 14 which is open in one direction, and in a portion located on the outer peripheral side of the bottom inner surface of the housing 14. A first light-emitting element 18 and a second light-emitting element 20, for example, each comprising an LED or the like, and provided on the inner surface of the bottom of the housing 14 on the inner peripheral side of the first light-emitting element 18 and the second light-emitting element 20; A light-receiving element 16 composed of a photodiode, a phototransistor, or the like; a transparent resin 22 provided integrally in the housing 14 to cover the light-receiving element 16 and the light-emitting elements 18 and 20;
And a ring-shaped light blocking member 24 provided between the light receiving element 16 and the light emitting elements 18 and 20 for blocking reflected light of the light emitted from the light emitting elements 18 and 20 from the body surface 12 toward the light receiving element 16. It is provided with.

The first light emitting element 18 is, for example, 660n.
m emits red light having a wavelength of about m, and the second light emitting element 20 emits infrared light having a wavelength of about 800 nm, for example. However, the present invention is not necessarily limited to these wavelengths, and the extinction coefficient of hemoglobin is not limited thereto. Any light may be used as long as it emits light having a wavelength at which the extinction coefficient of oxyhemoglobin differs greatly from that of oxyhemoglobin and light having a wavelength at which both extinction coefficients are substantially the same.
The first light emitting element 18 and the second light emitting element 20 emit light at a predetermined frequency in order for a predetermined time,
The reflected light from the vascular bed under the body surface 12 of the light emitted from the light emitting elements 18 and 20, that is, the portion where the thin blood vessels are densely packed in the dermis constituting a part of the skin, is reflected by the common light receiving element 16. Each is received.

The light receiving element 16 outputs an electric signal SV having a magnitude corresponding to the amount of received light to the low-pass filter 32 via the amplifier 30. This electric signal SV includes a fluctuation component due to arterial pulsation. The low-pass filter 32 removes noise having a frequency higher than the frequency of the pulse wave from the input electric signal SV, and outputs the signal SV from which the noise has been removed to the demultiplexer 34. By demultiplexer 34 is switched in synchronism with the emission of the first light emitting element 18 and the second light emitting element 20 by switching signal SC will be described later, the electrical signal SV _R by the red light sample hold circuit 36 and A / D converter 38 with sequentially supplied to the I / O port 40 via an electrical signal SV _IR by infrared light sample hold circuit 42 and a
It is sequentially supplied to the I / O port 40 via the / D converter 44. When sequentially outputting the input electric signals SV _R , SV _IR to the A / D converters 38, 44, the sample-hold circuits 36, 42 perform A / D conversion on the previously output electric signals SV _R , SV _IR. Until the conversion operation in the devices 38 and 44 is completed, the electric signals SV _R and SV _IR to be output next are respectively held.

The I / O port 40 is connected to a CPU 46, a ROM 48, a RAM 50, and a display 52 via data bus lines. The CPU 46 sets the RA
Using the storage function of M50, the measuring operation is executed in accordance with a program stored in the ROM 48 in advance, and the irradiation signal SLD is output from the I / O port 40 to the driving circuit 54, and the first light emitting element 18 and the second light emitting element 20 are output. The timing
By switching, light is emitted in sequence at a predetermined frequency for a certain period of time, while the first light emitting element 18 and the second
By switching the demultiplexer 34 by outputting the switching signal SC in synchronization with the light emission of the light emitting element 20, the electric signal SV _R is distributed to the sample and hold circuit 36 and the electric signal SV _IR is distributed to the sample and hold circuit 42. Further, the CPU 46 determines the oxygen saturation in the blood based on the photoplethysmographic waveforms represented by the electric signal SV _R and the electric signal SV _IR according to a program stored in advance, and displays the determined oxygen saturation on the display 52. To be displayed. The method of determining the oxygen saturation is described in, for example, Japanese Patent Application Laid-Open No.
This is the same as the determination method described in Japanese Patent Application Publication No. 440, and the oxygen saturation is determined based on the actual ratio from the previously obtained relationship between the ratio shown in Expression 1 and the oxygen saturation.

[0014]

(Equation 1)

In the above formula 1, V _dR and V _SR are the upper peak value and lower peak value of the _{photoplethysmographic} waveform due to red light, respectively, and V _dIR and V _SIR are the upper peak values of the _{photoplethysmographic} waveform due to infrared light, respectively. , The lower peak value. Also, V _dR −V _SR
And V _dIR −V _SIR represent the amplitude of the AC component of each _{photoplethysmographic} waveform, respectively, and V _dR + V _SR and V _dIR + V
_SIR represents the DC component of each photoelectric pulse waveform doubled.

Here, in this embodiment, the peripheral wall of the housing 14 and the light-shielding member 24 each have an oval shape, and the light-receiving element 16 is
Is provided at a position biased toward one end of the inner peripheral side. Thus, each of the light emitting elements 18 and 20 surrounds the light receiving element 16.
Provided around the light receiving element 16 such that the distance between the light receiving element 16 and the light receiving element 16 gradually increases and gradually decreases in the middle thereof at intervals so as to be substantially uniform over the entire circumference. From
As a result, the width of the optimum detection depth d _suit indicating the depth from the body surface 12 at which the intensity of the reflected light from the living body is sufficiently large can be obtained. FIG. 3 shows a state in which the reflected light detection characteristic of the probe 10 is tested using a biological model in which a reflecting mirror 60 is disposed at the bottom of a container 58 containing a suspension 56 of milk or the like. , The distance d _model between the probe 10 and the reflecting mirror 60 in the suspension 56 (corresponding to the detection depth of the reflected light from the living body) is gradually changed,
When light is irradiated from 20 toward the reflecting mirror 60, the intensity of the reflected light detected by the light receiving element 16 changes, for example, as shown in FIG. A wide detection distance width W was obtained. Accordingly, it is estimated that even when the probe 10 is mounted on the body surface 12, the width of the optimum detection depth d _suit can be widened.

Further, the light receiving element 16 and the light emitting elements 18 and 20
As the distance between them increases, the thickness t of the light shielding member 24 on the straight line connecting the light receiving element 16 and each of the light emitting elements 18 and 20 gradually increases, for example, as shown by t _{1 to} t ₄ in FIG. Has been enlarged. Thereby, the light receiving element 16
Each of the minimum detection depths d _min of the reflected light from the body surface 12 for each of the light emitting elements 18 and 20 detected respectively at the light emitting elements 18 and 20 is the same in each of the light emitting elements 18 and 20 as shown in FIGS. In addition, for example, each is set to 0.35 mm.

As described above, according to this embodiment, the distance between each of the light emitting elements 18 and 20 and the light receiving element 16 gradually increases.
Since the width of the optimal detection depth d _suit of the reflected light is widened by being provided around the light receiving element 16 so as to gradually decrease from the middle, the distance from the body surface 12 due to the individual difference of the subject and the difference of the measurement site. vascular bed depth position photoelectric pulse wave signal is also varied (SV _R, SV _IR) with the magnitude is sufficiently obtained oxygen saturation can be accurately measured, shock in addition to biological by knife or drugs, etc. Even if the peripheral circulation is reduced and reflected light is detected only from a deeper position in the vascular bed, the magnitude of the photoelectric pulse wave signal is sufficiently obtained and the oxygen saturation is measured with high accuracy and stability can do.

By the way, it is known that the thickness of the epidermis of the human body is 0.3 mm or less in the skin of almost all parts except the sole and the like.
The minimum detection depth d _min every 8, 20 is 0.35 mm, which is slightly larger than the maximum thickness of the epidermis of most parts, 0.3 mm.
Therefore, the detection of the reflected light from the epidermis having no blood vessel by the light receiving element 16 is reliably avoided. Thus, the ratio between the AC component and the DC component of the photoplethysmographic waveform, that is, (V _dR −V _SR ) / (V _dR +
(V _SR ) and (V _dIR −V _SIR ) / (V _dIR + V _SIR ) are largely secured, and the measurement accuracy of the oxygen saturation is further improved.

In the above embodiment, the light emitting elements 18, 2
The minimum detection depth d _{min for} each 0 is determined to be the same at 0.35 mm, but it is not always necessary, for example, various values of 0.3 mm or more, which is the maximum thickness of the epidermis of most parts of the human body. However, the same effect as in the above embodiment can be obtained.

Further, in the above embodiment, even when the minimum detection depth d _min is smaller than the thickness of the skin of the subject, the distance between the light emitting elements 18 and 20 and the light receiving element 16 gradually increases, and gradually from the middle. By being arranged around the light receiving element 16 so as to decrease, the oxygen saturation can be measured accurately regardless of the individual difference of the subject and the difference of the measurement site, and the oxygen saturation can be measured regardless of the decrease in the peripheral circulation. The effect of the present invention is that the degree can be measured with high accuracy and stability.

Further, in the above embodiment, the light receiving element 16 is provided at a position deviated to one end of the inner peripheral side of the light shielding member 24 having an oval ring shape. The effect of the present invention can be obtained also in the case where it is provided in the center part on the side or when a cylindrical light shielding member is used.

Further, in the above embodiment, the light emitting elements 18, 2
The 0s are arranged so that the arrangement shape is an ellipse shape, but this is not always necessary. For example, they may be arranged in a rhombus shape or a circular shape. When the light emitting elements 18 and 20 are arranged in a circular shape, the light receiving element 16 is arranged at an eccentric position in the circumference. In short, the distance between the light emitting element and the light receiving element gradually increases, and gradually decreases in the middle.
What is necessary is just to be provided around the light receiving element so as to reduce it.

In the above embodiment, the first light emitting elements 18 and the second light emitting elements 20 which emit two kinds of light having different wavelengths are arranged alternately. However, this is not always necessary. A plurality of three or more types of light-emitting elements that emit three or more different types of light may be arranged such that each type is substantially evenly distributed over the entire circumference.

In addition, the present invention can be variously modified without departing from the gist thereof.

[Brief description of the drawings]

FIG. 1 is an enlarged view of the probe of FIG. 2 viewed from an opening side of a housing thereof.

FIG. 2 is a block diagram showing a configuration example of a reflection type oximeter including a probe according to an embodiment of the present invention.

FIG. 3 is a diagram showing one state in a case where the reflected light detection characteristics of the probe of FIG. 2 are tested using a biological model having a reflecting mirror in a suspension.

FIG. 4 is a diagram showing an example of a reflected light detection characteristic of the probe of FIG. 2 obtained using the biological model of FIG. 3;

FIG. 5 is a diagram showing a minimum detection depth d _min of reflected light at a portion of the light shielding member having a thickness t ₁ of FIG. 1;

FIG. 6 is a diagram illustrating a minimum detection depth d _min of reflected light at a portion of a light shielding member having a thickness t ₂ of FIG. 1;

FIG. 7 is a diagram illustrating a minimum detection depth d _min of reflected light at a portion of a light shielding member having a thickness t ₃ of FIG. 1;

8 is a diagram showing a minimum detectable depth d _min of the reflected light in a portion of the thickness t ₄ of the shielding member of FIG.

[Explanation of symbols]

 Reference Signs List 10 probe 12 body surface 16 light receiving element 18 first light emitting element 20 second light emitting element 24 light shielding member

Claims (2)

(57) [Scope of request for utility model registration] 1. A plurality types plurality of types having different wavelengths from each other from the light emitting element group of the light sequentially applied to the surface of the living body, the timing of a plurality of types of reflected light from the living body in synchronism with the irradiation
The light-emitting element group is configured in a reflection-type oximeter that detects each of the light-receiving elements by switching over and measures the oxygen saturation in blood based on a photoplethysmographic signal representing the intensity of the reflected light. The light emitting element is substantially uniform over the entire circumference surrounding the light receiving element for each type.
While arranged at intervals, between the light-emitting element and the light-receiving element, a ring-shaped light-shielding member that shields light from the light-emitting element on the surface of the living body toward the light-receiving element is provided. A probe, wherein a distance between the light emitting element and the light receiving element gradually increases.
A reflection type oximeter probe which is provided around the light receiving element so as to gradually decrease in the middle . 2. The reflection oximeter probe according to claim 1, wherein the minimum detection depth from the surface of the living body of the reflected light of each light emitting element detected by the light receiving element is defined as one of the skins of the living body. A reflective oximeter probe characterized in that it has a thickness equal to or greater than the thickness of the skin constituting the portion.