KR20210076662A - Blood oxygen saturation sensing device for non-pulsatile extracorporeal blood circulation circuit and a control method of the same - Google Patents

Abstract

The present invention relates to an apparatus and method for measuring oxygen saturation and, more particularly, to an apparatus and method for measuring oxygen saturation in blood non-invasively using light having a predetermined wavelength. More specifically, the present invention relates to the apparatus and method for non-invasively measuring oxygen saturation in a non-pulsatile extracorporeal circuit. According to one embodiment of the present invention, the apparatus for measuring oxygen saturation comprises: a light source unit provided to irradiate light to the subject; a first light receiving unit positioned to have a first separation distance from the light source unit and provided to receive light emitted from the light source unit; a second light receiving unit positioned to have a second separation distance different from the first separation distance from the light source unit and provided to receive light emitted from the light source unit; and a processor for measuring oxygen saturation of the blood of the subject by using the difference in absorbance between the first light receiving unit and the second light receiving unit.

Description

Blood oxygen saturation sensing device for non-pulsatile extracorporeal blood circulation circuit and a control method of the same

The present invention relates to an apparatus and method for measuring oxygen saturation, and more particularly, to an apparatus and method for measuring oxygen saturation in blood non-invasively using light having a predetermined wavelength.

More specifically, the present invention relates to an apparatus and method for non-invasively measuring oxygen saturation in a non-pulsatile extracorporeal circulation circuit.

Saturation of oxygen (SpO2) refers to the amount of oxygen bound to hemoglobin (Hb) in red blood cells. It can be determined whether or not Oxygen saturation is expressed as a percentage of the concentration of oxidized hemoglobin combined with oxygen to the total hemoglobin concentration. This number is being used as an important parameter in clinical fields such as hypoxia neonatal monitoring emergency medicine.

The normal value of oxygen saturation is 95% or more, and if it is lower than that, it is a state of hypoxia, and if it is less than 905, it is an emergency state in which breathing becomes difficult due to hypoxia. In general, the oxygen saturation level decreases in a very serious condition due to multiple organ failure, and the level may also decrease in the course of recovery after anesthesia or worsening of respiratory diseases such as chronic obstructive pulmonary disease. In this case, it is necessary to perform a treatment to increase oxygen saturation through a system that artificially administers or exchanges oxygen with a ventilator and an extracorporeal membrane oxygenation (ECMO) device.

The extracorporeal membrane oxygenation device is a device that temporarily helps the heart and lungs function when it is difficult to maintain life by conventional methods due to deterioration of the heart or lung function. Therefore, it is a device applied to patients who cannot adequately supply oxygen with only a ventilator. This device consists of a membrane oxygenator that supplies oxygen to the blood instead of the lungs, a pump that circulates oxygenated blood instead of the heart, and a pump that connects to the patient's blood vessels. It is composed of a blood circuit that serves as an extracorporeal blood vessel by connecting oxidizers

In the case of a patient to which such an extracorporeal membrane oxygenation device is applied, oxygen saturation as well as partial pressure of oxygen and carbon dioxide in arterial and venous blood should be continuously monitored in order to supply adequate oxygen and carbon dioxide exchange.

As a method for measuring oxygen saturation, there are a surgical method and a non-surgical method.

The surgical method is to collect arterial blood and measure blood oxygen saturation, which is the most accurate way to measure oxygen saturation. However, there is a disadvantage that blood collection is required, and it is not easy to measure the oxygen saturation value in a short time because it takes a certain time to analyze the oxygen saturation value after blood collection. Therefore, in an environment requiring urgency, the use of surgical methods is inevitably limited.

An example of blood oxygen saturation measurement by such a surgical method is arterial blood gas analysis (ABGA). However, since ABGA equipment is expensive, it is difficult to access and use it easily.

A non-surgical method is to measure oxygen saturation through absorbance, and the most representative method is pulse oximetry.

Pulse oximetry is a method that can measure oxygen saturation continuously and non-invasively. The absorbance of two different light wavelengths (red light and near-infrared light) obtained by penetrating thin skin areas such as fingertips and earlobes is measured by the contraction of the heart. This is a method of calculating the oxygen saturation by using the amplitude ratio of the maximum and minimum values of the pulsation component caused by the relaxation action. Therefore, pulse oximetry is widely used in an emergency environment.

The basic principle of pulse oximetry follows the Beer-Lambert law, which indicates the relationship between the absorbance and concentration of the transmitted material, and measures the absorbance of oxygenated hemoglobin (HbO2) and deoxygenated hemoglobin (Hb) using two wavelengths. to measure coral saturation. That is, oxygen saturation is measured by measuring a photo-plethysmograpy (PPG) signal.

A pulse oximeter generally consists of two light sources (LEDs) and a light receiving unit (photodiode) that can detect the amount of light. The wavelength used as the light source is a wavelength of 660 nm in the red light region and a wavelength of 940 nm in the infrared region. . The reason why the wavelengths of the two regions are used is that the change in oxygenated hemoglobin can be identified by using the ratio of the red light region and the infrared light region, where the absorption coefficient difference between oxygenated hemoglobin and deoxygenated hemoglobin is large.

In other words, the red light region is a region in which the absorption coefficient of oxygenated hemoglobin is much greater than that of deoxygenated hemoglobin, and the infrared region is a region in which the absorption coefficient of deoxygenated hemoglobin is much larger than that of oxygenated hemoglobin. Accordingly, a red light region and an infrared light region having a large difference in absorption coefficient can be used.

The conventional pulse oximeter basically follows the above-mentioned Beer-Lambert law, and is a method of calculating oxygen saturation through the ratio of absorbance generated by the pulse. Equation 1 is an equation for calculating the luminance using the Beer-Lambert law.

< Equation 1 >

I = I ₀ e- ^βcl

Here, I is the light intensity, I ₀ is the initial light intensity, β is the absorbance of the material to be measured, c is the concentration of the material to be measured, and l is the movement distance of light.

The initial light intensity (I ₀ ) is not always a constant value, but a value that varies depending on the surrounding environment and the patient's tissue, and must be removed through erasing. When there is a pulse, the unit area of the blood vessel changes according to the systolic and diastolic phases, and the travel distance of light also changes. Therefore, it is possible to erase the initial light intensity in the saturation measurement equation (Equation 2) through the absorbance difference value generated by the pulse.

< Equation 2 >

ln(I _d )-ln(I _s ) = βc(l _d - l _s )

Here, I _s is the light intensity measured during systole, I _d is the light intensity measured during diastole, l _d is the light travel distance during diastole, and l _s is the light travel distance during systole. That is, Equation 2 can be said to be a saturation measurement equation in which the _{initial luminous intensity I 0 is erased.}

In other words, through the difference in luminous intensity during each systolic and diastolic phase, the initial luminous intensity can be easily canceled to calculate the oxygen saturation for pulsed arterial blood.

However, in the case of patients equipped with an extracorporeal circulation circuit, a non-pulsatile continuous blood flow in which no pulsation occurs is supplied. Therefore, because there is no pulsation, the volume change of the blood vessel does not occur or appears very small. Therefore, it is difficult to separate the luminous intensity signal between a variable that is not a measurement target such as a blood circuit and blood that is a measurement target existing inside the blood circuit. That is, in the blood circuit in which non-pulsating blood flow flows, it can be said that the separation of the light intensity signal is impossible by erasing the initial light intensity through a simple formula as in the conventional pulse oximetry method. As a result, there is a problem in that the conventional pulse oximetry cannot be applied to the non-pulsating blood circuit. It becomes impossible to calculate oxygen saturation by easily extracting the light intensity signal of the measurement target of interest.

On the other hand, recently, a lot of research on wearable medical devices has been conducted, and the oxygen saturation level described in the prior art literature can also be said to be an example of a wearable medical device. That is, as an oxygen saturation measuring device using pulse oximetry, research is being conducted in the direction of solving the problem of error due to the movement of the patient.

However, studies on an oxygen saturation measuring device capable of non-invasively measuring oxygen saturation in non-pulsatile continuous blood flow have not been conducted in spite of the necessity.

Therefore, in order to solve this problem, there is a need to provide an oxygen saturation measuring apparatus and measuring method capable of non-invasively measuring oxygen saturation even in non-pulsatile continuous blood flow without a pulsation component.

Korean Patent Application Laid-Open No. 10-2017-0076329 (published date: 2017. 7. 4.)

The present invention is to solve the above problems.

It is an object of the present invention to provide an oxygen saturation measuring device and measuring method capable of non-invasively measuring oxygen saturation even in non-pulsatile continuous blood flow.

An embodiment of the present invention aims to provide an oxygen saturation measuring device and measuring method that can measure oxygen saturation in non-pulsatile blood flow very effectively while borrowing a conventional pulse-type oxygen saturation measuring device and measuring method.

An object of the present invention is to provide an apparatus and method for measuring oxygen saturation that are easy to manufacture and use.

It is an object of the present invention to provide an economical oxygen saturation measuring apparatus and measuring method through an embodiment of the present invention.

In order to achieve the above object, according to an embodiment of the present invention, a light source unit provided to irradiate light to a subject; a first light receiving unit positioned to have a first separation distance from the light source unit and provided to receive the light emitted from the light source unit; a second light receiving unit positioned to have a second separation distance different from the first separation distance from the light source unit and provided to receive the light emitted from the light source unit; In addition, there may be provided an oxygen saturation measuring device including a processor for measuring oxygen saturation of blood of a subject by using a difference in absorbance between the first light receiving unit and the second light receiving unit.

The subject may be a blood supply tube constituting a non-pulsating extracorporeal circulation circuit.

The subject may be the body of a tachycardia patient. Specifically, the body may be a fingertip or an earlobe.

Preferably, the light source unit includes different light sources for irradiating light in different wavelength regions.

Preferably, the light source unit includes a first light source irradiating light to a red light region and a second light source irradiating light to an infrared light region.

Preferably, the light source part is made of an LED, and the first light receiving part and the second light receiving part are made of a photodiode.

The processor may calculate oxygen saturation by using a difference between signals output from the first light receiving unit and the second light receiving unit.

Preferably, the distance from the center point between the first light source and the second light source to the center point of the first light receiving unit and the distance to the center point of the second light receiving unit are the same.

A center point between the first light source and the second light source, a center point of the first light receiving unit, and a center point of the second light receiving unit may form an isosceles triangle. Due to this positional relationship, the oxygen saturation calculation may be easier.

Preferably, the processor calculates oxygen saturation through a ratio of absorbance at the first light receiving unit and the second light receiving unit based on the Beer-Lambert law.

Preferably, the processor calculates oxygen saturation by using a difference in absorbance according to the first separation distance and the second separation distance instead of a difference in absorbance caused by a pulse when calculating the oxygen saturation.

It is preferable that a holder surrounding the subject is included, and the light source unit, the first light receiving unit, and the second light receiving unit are provided inside the holder to face the measurement target. That is, the holder can be said to be a configuration for mounting the measurement sensor to the subject.

Since the measurement sensor components are mounted on the holder, the measurement sensor components can be mounted on the subject by mounting the holder on the subject.

The holder may include a first holder extending from the center of the holder to one side to which the first light receiving unit is mounted, and a second holder extending from the center to the other side to which the first light receiving unit is mounted.

An opening for inserting the subject is preferably formed between the first holder and the second holder.

The first holder and the second holder may be rotatably provided with respect to the center of the holder. Even if the size of the subject changes due to such rotation, it is possible to respond flexibly.

In order to achieve the above object, according to an embodiment of the present invention, the method comprising: irradiating light through a light source to a subject; generating a signal by receiving light from the first light receiving unit and the second light receiving unit positioned to have different separation distances from the light source; And there may be provided a method for measuring oxygen saturation comprising the step of calculating oxygen saturation by using a difference between the signal generated by the first light receiving unit and the signal generated by the second light receiving unit.

In the step of irradiating the light, it is preferable to respectively irradiate light of a first wavelength and light of a second wavelength different from the first wavelength.

It is preferable that the light irradiation of the first wavelength and the light irradiation of the second wavelength are sequentially performed. Therefore, it is preferable that the signal generation for the first wavelength and the signal generation for the second wavelength are also sequentially performed.

Preferably, the first light receiving unit and the second light receiving unit are positioned to receive the light that has passed through the subject.

The subject may be a blood supply tube constituting a non-pulsating extracorporeal circulation circuit or a body of a tachycardia patient.

In order to implement the above object, according to an embodiment of the present invention, the equation

An oxygen saturation measuring device and measuring method capable of measuring oxygen saturation through the

Here, the oxygen saturation (S or SpO2) can be simply calculated through the R value and constant values calculated through the output value of the photodiode.

Specifically, β ₁ and β ₂ are the absorption constants of oxyhemoglobin and deoxyhemoglobin for red light, and parts marked with prime are the absorption constants of oxyhemoglobin and deoxyhemoglobin for infrared light, respectively. Therefore, all of the absorption constants have constant values.

Meanwhile, R may be a ratio of a difference in absorbance of red light to a difference in absorbance of infrared light. The R value is a value calculated through the output of the photodiodes.

According to an embodiment of the present invention, the equation

Through , the calculated R value on the left side becomes the same as the equation on the right side.

Here, d1 is the separation distance between the light source and the first light receiving unit, and d2 is the separation distance between the light source and the second light receiving unit. And C1 and C2 are the blood concentrations of oxyhemoglobin and deoxyhemoglobin.

Rearranging R on the left and the formula on the right, since oxygen saturation S(SpO2) is C1/(C1+C2), the calculated value of S(SpO2) can be easily obtained through calculation of R and constant values.

According to an embodiment of the present invention, when there are two light sources, the first separation distance and the second separation distance from the first light source may be the same as the first separation distance and the second separation distance from the second light source. Therefore, the first separation distance and the second separation distance can be easily erased.

Features in the above-described embodiments may be implemented in combination in other embodiments unless they are contradictory or mutually exclusive.

According to an embodiment of the present invention, it is possible to provide an oxygen saturation measuring apparatus and a measuring method capable of non-invasively measuring oxygen saturation even in non-pulsatile continuous blood flow.

According to an embodiment of the present invention, it is possible to provide an oxygen saturation measuring device and measuring method that can measure oxygen saturation in non-pulsatile blood flow very effectively while using a conventional pulse-type oxygen saturation measuring device and measuring method.

Through one embodiment of the present invention, it is possible to provide an apparatus and method for measuring oxygen saturation that are easy to manufacture and use.

Through an embodiment of the present invention, an oxygen saturation measuring device capable of accurately measuring oxygen saturation not only in patients using a non-pulsatile extracorporeal circulation system but also in patients with non-periodic heartbeats such as tachycardia, and A measurement method can be provided.

Through one embodiment of the present invention, it is possible to provide an economical oxygen saturation measuring apparatus and measuring method.

Effects according to the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those of ordinary skill in the art to which the present invention belongs from the description of the claims and detailed description. will be able

1 shows the relationship between absorbance and time in an extracorporeal circulation circuit capable of measuring oxygen saturation through an oxygen saturation measuring device according to an embodiment of the present invention;
2 schematically shows the structure of a measuring sensor of an oxygen saturation measuring device according to an embodiment of the present invention;
3 shows a control block of an oxygen saturation measuring apparatus according to an embodiment of the present invention;
4 shows a control flow of an apparatus for measuring oxygen saturation according to an embodiment of the present invention;
5 is a graph for verifying the accuracy of the oxygen saturation measuring apparatus according to an embodiment of the present invention;
6 schematically shows a holder structure of an oxygen saturation measuring apparatus according to an embodiment of the present invention.

Hereinafter, an embodiment will be described in detail with reference to the accompanying drawings. In the description with reference to the accompanying drawings, the same components are given the same reference numerals, and redundant description thereof will be omitted.

Terms such as first, second, etc. may be used to describe the components, but the components are not limited to the above terms, and are used only for the purpose of distinguishing one component from other components.

When a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

In addition, each embodiment may be implemented independently or together, and some components may be excluded in accordance with the purpose of the invention.

As described above, the most common non-invasive method for measuring oxygen saturation is pulse oximetry. Since the oxygen saturation is measured as a ratio of two wavelengths in the presence of a pulse, there is no pulse. There is a problem in that it is impossible to measure oxygen saturation through this method in an extracorporeal circulation circuit. Accordingly, it is an object of the present invention to provide a novel oxygen saturation measuring apparatus and measuring method capable of measuring oxygen saturation through two wavelengths in non-pulsatile blood flow without a pulse.

According to an embodiment of the present invention, as a method for canceling the initial luminosity in the oxygen saturation measurement equation, two light-receiving units may be used to make the moving distance of light different. Specifically, an apparatus for measuring oxygen saturation comprising a light source unit, two light receiving units having different separation distances from the light source unit, and a control unit (processor) for calculating oxygen saturation from a difference in luminous intensity signals measured by each light receiving unit can be provided. have.

More specifically, the control unit may be provided to calculate oxygen saturation using a difference between a measurement equation similar to a pulse-type oxygen saturation measurement equation and a luminous intensity signal measured by each of the light receiving units.

Hereinafter, an apparatus for measuring oxygen saturation according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2 .

1 shows the correlation between time and absorbance in a non-pulsating extracorporeal circulation circuit in which blood flows.

The medium that absorbs the irradiated light is the extracorporeal circuit tube and blood in the tube. Since the diameter of the circuit tube is constant, it can be said that the absorbance component by the tube is constant. In addition, since it is a non-pulsating extracorporeal circulation circuit, it can be said that the absorbance component by the blood in the tube is also constant. Therefore, it can be said that the total absorbance is always constant.

On the other hand, in the case of a blood vessel in which there is a pulse, the absorbance component by venous blood and tissue is constant, but the volume change of the blood vessel is issued by the pulse, so the absorbance component in the systolic and diastolic phases is different. That is, it can be said that the total absorbance varies as much as the component due to the pulsation. However, the change in absorbance due to a constant pulse has a constant pattern (period, amplitude). It can be said that the conventional oxygen saturation measuring device calculates the oxygen saturation by using the difference in absorbance due to the beat.

However, since the total absorbance is always constant in a subject such as a non-pulsating extracorporeal circuit, it is preferable to artificially generate a difference in absorbance.

2 conceptually shows the measurement sensor 5 in the oxygen saturation measurement apparatus according to an embodiment of the present invention.

As shown in FIG. 2 , in the present embodiment, a difference in absorbance may be artificially generated through a difference in a distance through which light passes.

The tube 1 constituting the non-pulsating extracorporeal circulation circuit may be used as a subject, and the oxygen saturation of the blood 1a flowing in the subject may be measured using the light source 10 and the light receiver 20 .

Specifically, the light source unit 10 is provided to irradiate light to the tube 1 as a subject. The light source unit 10 may be positioned to irradiate light through the inside of the tube 1 . And, the light receiving unit 20 may be positioned to detect the light passing through the inside of the tube (1).

Specifically, the light irradiated from the light source unit 10 may be received by two different light receiving units 21 and 21 . Here, it is preferable that the separation distance between the first light receiving unit 21 and the second light receiving unit 21 with respect to the light source unit 10 is different from each other. That is, the first separation distance d1 between the light source unit 10 and the first light receiving unit 21 is preferably different from the second separation distance d2 between the light source unit 10 and the second light receiving unit 22 . In FIG. 2 , it is illustrated that the first separation distance d1 is greater than the second separation distance d2 as an example.

Accordingly, the absorbance of absorbing light emitted from the same light source unit 10 is different between the first light receiving unit 21 and the second light receiving unit 22 due to the difference in the separation distance. That is, a difference in absorbance between the first light receiving unit and the second light receiving unit is generated. It is possible to calculate the oxygen saturation of the blood of the subject by using the difference in absorbance.

The subject may be a body as well as a blood supply tube in a non-pulsating extracorporeal circuit. In patients with non-periodic heartbeats such as tachycardia, a steady heartbeat does not occur. In this case, the change in the distance through which light is transmitted due to the non-constant heartbeat is not constant. That is, the change in absorbance may be continuously changed in a non-uniform pattern. Therefore, in the case of tachycardia patients, it is impossible to measure oxygen saturation using the conventional pulse oximetry method. Therefore, the measurement of oxygen saturation in the blood of a tachycardia patient can be implemented through an embodiment of the present invention.

As a result, according to an embodiment of the present invention, it is possible to measure the oxygen saturation of a subject, which has not been applied in the prior art, thereby causing an epochal and innovative change in the medical field.

More specifically, the light source unit 10 may include different light sources for irradiating light in different wavelength regions. For example, the light source unit 10 may include a first light source 11 for irradiating light into a red light region and a second light source 12 for irradiating light into an infrared region. A wavelength of 660 nm may be used in the red light region and a wavelength of 860 nm may be used in the infrared region. The reason for using the wavelength in this band is that the change in oxygenated hemoglobin can be grasped by using the ratio of the red light region and the infrared light region, which has a large difference in absorption coefficient between oxygenated hemoglobin and deoxygenated hemoglobin.

Preferably, the light source unit 10 is formed of a light emitting diode (LED), and the first light receiving unit 21 and the second light receiving unit 22 are formed of a photo-diode.

On the other hand, the oxygen saturation measuring apparatus according to an embodiment of the present invention may include not only the measuring sensor 5 for irradiating light and sensing light, but also various components.

3 is a control block diagram of an oxygen saturation measuring apparatus 100 according to an embodiment of the present invention.

As an example of the light receiving unit 20 , a photodiode absorbs light, and a current signal proportional to the intensity of the absorbed light, ie, absorbance, is induced in the light receiving unit. That is, the photodiode generates a current signal. The induced current may be converted into a voltage and amplified through a current-to-voltage converter 30 or transimpedance. Thus, the current-to-voltage converter or transimpedance may comprise an amplifier.

The amplified analog voltage signal is converted into a digital electrical signal through an analog-to-digital converter (ADC) 40 , and oxygen saturation may be calculated through an operation program using the digital electrical signal.

Accordingly, the oxygen saturation measuring device 100 includes the light source unit 10 and the light receiving unit 20 as well as the current-voltage converter 30 , the ADC 40 and the communication module as an example of a UART (universal asynchronous receiver). /transmitter, 60). In addition, the oxygen saturation measuring device may include a PC 50 in which a program for calculating a digital electrical signal received through UART communication is installed. The PC itself or the processor 51 in the PC may be referred to as a processor for calculating oxygen saturation. The measured oxygen saturation may be displayed on the display of the PC.

The PC may be a portable terminal, and through a user interface (UI) including a display, a user may operate the oxygen saturation measuring device, and the measured oxygen saturation may be recognized.

The processor calculates oxygen saturation based on the ratio of absorbance in the first light receiving unit 21 and the second light receiving unit 21 based on the Beer-Lambert law. Of course, it can be said that the signal corresponding to the absorbance is converted into a digital signal and input.

The PC may include a user interface (UI) 52 as well as a processor 51 . A user may operate the oxygen saturation measuring device through the user interface, and the measured oxygen saturation may be displayed.

In addition, the processor 51 may be provided to control the operation of the light source unit 10 according to a set logic.

Hereinafter, a measuring method using an oxygen saturation measuring device will be described in detail with reference to FIG. 4 .

In order to measure oxygen saturation, a step (S10) of irradiating light through a light source to the subject may be performed. Then, a step (S20) of generating a signal by receiving the irradiated light may be performed.

Here, the generating of the signal may include generating a signal by receiving light from the first light receiving unit and the second light receiving unit positioned to have different separation distances from the light source, respectively ( S3 and S4 ).

The method may include calculating oxygen saturation by using a difference between the signal generated by the first light receiving unit and the signal generated by the second light receiving unit (S8).

The calculated oxygen saturation is displayed (S9) on the display (S9) of the user interface of the PC, so that the measurement of oxygen saturation can be ended.

In the step of irradiating the light (S10), it is preferable to irradiate the light of the first wavelength and the light of the second wavelength different from the first wavelength (S1, S2), respectively. And, it is preferable that the light irradiation of the first wavelength and the light irradiation of the second wavelength are sequentially performed.

Meanwhile, the light receiving unit may generate an analog current signal. It is possible to convert the current-voltage (S5) and amplify the analog voltage signal (S6). The amplified analog voltage signal may be converted into a digital signal (S7). Accordingly, the processor may calculate the oxygen saturation through a simple operation (S8) through the value converted into the digital signal.

Conventional pulse oximetry uses the difference in absorbance caused by the pulse, but in this embodiment, instead of using this difference, each light receiving unit 21, 22 has a different separation distance from the light source 10. The difference in absorbance is used.

Hereinafter, the derivation of a formula for calculating the oxygen saturation using the difference in absorbance generated according to the separation distance will be described in detail.

The initial luminosity must be eliminated from the formula for calculating oxygen saturation. In this embodiment, the initial luminous intensity can be erased by using the two light receiving units 21 and 22 to vary the moving distance of light.

Applying Equation 2 to this embodiment, Equation 3 for the first light receiving unit 21 and Equation 4 for the second light receiving unit 22 can be derived.

< Equation 3 >

ln(I ₀ ) - ln(I(d ₂ )) = d ₂ (β ₁ C ₁ + β ₂ C ₂ )

< Equation 4 >

ln(I ₀ ) - ln(I(d ₁ )) = d ₁ (β ₁ C ₁ + β ₂ C ₂ )

Here, d1 is the separation distance between the light source and the first light receiving unit, d2 is the separation distance between the light source and the second light receiving unit, β ₁ and β ₂ are the extinction constants of oxyhemoglobin and deoxygenated hemoglobin, and C1 and C2 are oxyhemoglobin and oxyhemoglobin It is the blood concentration of deoxygenated hemoglobin.

Looking at Equations 3 and 4, it can be seen that there is an _{initial luminance (I 0 ) factor.} Here, Equation 5 can be derived by obtaining the difference in absorbance at each light receiving unit.

< Equation 5 >

ln(I(d ₂ )) - ln(I(d ₁ )) = (d ₂ - d ₁ )(β ₁ C ₁ + β ₂ C ₂ )

Accordingly, it can be seen that the _{initial luminance (I 0} ) factor can be canceled in Equation 5 representing the difference in absorbance. Therefore, it can be seen that oxygen saturation can be calculated using the difference in absorbance even in non-pulsatile blood flow.

Meanwhile, Equation 5 may be a difference in absorbance measured by each of the light receiving units 20 and 30 with respect to the light irradiated from the first light source 11 having one wavelength, for example, a wavelength in the red light region.

With the same structure, with respect to light irradiated from the second light source 11 having a different wavelength, for example, an infrared light region wavelength, the difference in absorbance measured by each of the light receiving units 21 and 22 can be derived similarly to Equation 5. can As a result, the ratio of the red light absorbance to the difference in the infrared light absorbance can be expressed by Equation (6).

< Equation 6 >

Here, the variables corresponding to the prime are variables according to the wavelength of the infrared light region. And, the first separation distance (d ₁ ) and the second separation distance (d ₂ ) do not change according to the wavelength. That is, offset is possible. And, in Equation 6, it can be seen that _{the initial luminance I 0 is erased.}

In particular, when there are two light sources, the first separation distance and the second separation distance from the first light source may be the same as the first separation distance and the second separation distance from the second light source. In other words, the center point (see FIGS. 4 and 28 ) between the light source and the light source may be positioned at the same distance from the first light receiving unit 21 and the second light receiving unit 22 , respectively. That is, the center point between the light source and the light source, the center point of the first light receiving unit, and the center point of the second light receiving unit may form an isosceles triangle. Accordingly, the calculation for calculating the oxygen saturation can be made easier.

As a result, it can be seen that the oxygen saturation can be simply calculated by using a voltage value proportional to the intensity of the luminous intensity measured for each wavelength in each of the light receiving units. Here, the ratio of the luminous intensity measured for each wavelength is the left side of Equation 6, which may be referred to as R. Therefore, R can be said to be the right side of Equation (6).

Accordingly, since the oxygen saturation S(SpO2) is C1/(C1+C2), it can be derived as in Equation 7 using Equation 6 .

< Equation 7 >

In Equation 7, R is a value measured through the light-receiving units, β ₁ and β ₂ are the absorption constants of oxyhemoglobin and deoxyhemoglobin in the red light region, and β′ ₁ and β′ ₂ are oxyhemoglobin and deoxidation in the infrared region. It is the extinction constant of oxyhemoglibin. Therefore, the oxygen saturation S can be calculated simply by using Equation (7).

The present applicant conducted verification of a method for measuring oxygen saturation in non-pulsatile continuous blood flow.

A blood circuit for measuring oxygen saturation was constructed with the blood of a pig model. The blood circuit was composed of a blood tube to which the measurement sensor 5 can be mounted, a blood pack for blood supply, and a straight channel with a sampling port.

That is, the blood was configured to flow through the tube connected in a straight line from the blood pack, and oxygen saturation was measured through the measurement sensor 5 at the front end of the sampling port through which the blood is discharged.

In order to verify the accuracy, a value measured by an arterial blood gas analyzer, a commercial equipment, and a value measured using a measuring device according to an embodiment of the present invention were compared and analyzed. A graph of comparative analysis is shown in FIG. 5 .

The horizontal axis represents the oxygen saturation measured by the arterial blood gas analyzer as the reference oxygen saturation degree, and the vertical axis represents the measured oxygen saturation degree and the oxygen saturation measured using the measuring device according to an embodiment of the present invention. The dotted line is a calibration curve that can measure the magnitude of the error between the reference oxygen saturation and the measured oxygen saturation. When the measured oxygen saturation is located as close to the straight line as possible, it means that the error of the oxygen saturation measurement is low. Therefore, it can be confirmed that the closer the slope of the calibration curve is to 1, the smaller the error is. As shown, it can be seen that the slope of the calibration curve is approximately 0.9439, very close to 1. Therefore, it can be seen that according to the present embodiment, oxygen saturation can be calculated very accurately.

As shown, as a result of comparing a total of 11 different oxygen saturation levels, it can be seen that all values are located very close to the dotted line. Accordingly, it can be seen that the measurement of oxygen saturation through the measuring device according to an embodiment of the present invention is very accurate.

Hereinafter, the holder 25 of the oxygen saturation measuring device according to an embodiment of the present invention will be described in detail with reference to FIG. 6 .

The holder 25 can be said to be a configuration for mounting the measurement sensor 5 to the subject, for example, the tube 1 . That is, the measurement sensor 5 is provided in the holder 25 or the holder body, and the holder is mounted on the subject, so that each component of the measurement sensor 50 is positioned at the correct position.

Specifically, the holder 25 includes a first holder 26 and a second holder 27 , and an opening 29 for inserting and mounting a subject between the first holder 26 and the second holder 27 . ) can be formed.

Since the size of the subject is not always constant, it is preferable that the size of the opening 29 also varies according to the size of the subject. To this end, the first holder 26 and the second holder 27 may be provided to rotate about the same central axis.

6 the centerline 28 of the holder 25 is shown. Accordingly, the rotation centers of the first holder 26 and the second holder 27 are preferably located on the center line 28 . The holder 25 may be provided such that the opening is expanded or reduced to surround the subject like tongs. Preferably, the rotation center of the first holder 26 and the second holder 26 is preferably formed outside the center point between the first light source part and the second light source part in the radial direction. Through this, the first holder 26 and the second holder 26 can be rotated to be symmetrical with respect to the center of rotation. In other words, as the first hole 26 and the second holder 26 rotate with respect to the rotation center, the holder opening may be expanded, and more preferably, may be expanded to be symmetrical. Therefore, even if the size of the subject is changed, the isosceles triangle formed by the three central points may be maintained as described above.

As a result, the relative separation distance of the two photodiodes with respect to one light source may be maintained to be the same as the relative separation distance of the two photodiodes with respect to the other light source. Through this, the separation distance can be easily erased from the equation.

As described above, it can be seen that, according to an embodiment of the present invention, oxygen saturation can be measured very accurately non-invasively even in non-pulsating blood flow through the light receiving units provided at different positions with respect to the light source.

In addition, it can be seen that it can be economically manufactured and used, and can bring about an epochal change in relation to the coral saturation measuring device.

It will be said that the above-described embodiment can be changed in various forms. Therefore, the present invention is not limited by the embodiments disclosed herein, and all forms that can be changed by a person of ordinary skill in the art to which the present invention pertains will also fall within the scope of the present invention.

1: extracorporeal circulation blood tube 1a: blood
5: measurement sensor
10: light source unit 11: first light source
12: second light source 20: light receiving unit
21: first light receiving unit 22: second light receiving unit
25: holder body 26: first holder
27: second holder 29: holder opening
30: current-voltage converter 40: ADC
50: PC 51: control unit (processor)
52 : UI
A: the center point between the first light source and the second light source

Claims (20)

In the oxygen saturation measuring device for measuring the oxygen saturation of blood of a subject,
a light source unit provided to irradiate light to the subject;
a first light receiving unit positioned to have a first separation distance from the light source unit and provided to receive the light emitted from the light source unit;
a second light receiving unit positioned to have a second separation distance different from the first separation distance from the light source unit and provided to receive the light emitted from the light source unit; And
and a processor for measuring oxygen saturation of blood of a subject by using a difference in absorbance between the first and second light receiving units. The method of claim 1,
The oxygen saturation measuring device, characterized in that the subject is a blood supply tube constituting a non-pulsating extracorporeal circulation circuit. 3. The method of claim 2,
The oxygen saturation measuring device, characterized in that the subject is the body of a tachycardia patient. The method of claim 1,
and the light source unit includes different light sources for irradiating light in different wavelength ranges. 5. The method of claim 4,
and the light source unit includes a first light source for irradiating light to a red light region and a second light source for irradiating light to an infrared light region. 6. The method of claim 5,
The light source unit is formed of an LED, and the first light receiving unit and the second light receiving unit are formed of a photodiode. 7. The method of claim 6,
and the processor calculates oxygen saturation by using a difference between signals output from the first light receiving unit and the second light receiving unit. 6. The method of claim 5,
The oxygen saturation measuring device, characterized in that the distance from the center point between the first light source and the second light source to the center point of the first light receiving unit and the distance to the center point of the second light receiving unit are the same. 6. The method of claim 5,
A center point between the first light source and the second light source, the center point of the first light receiving unit, and the center point of the second light receiving unit form an isosceles triangle. 5. The method of claim 4,
and the processor calculates oxygen saturation through a ratio of absorbance at the first light receiving unit and the second light receiving unit based on the Beer-Lambert law. 11. The method of claim 10,
Oxygen saturation measurement, characterized in that the processor calculates oxygen saturation using a difference in absorbance according to the first separation distance and the second separation distance instead of a difference in absorbance caused by a pulse when calculating the oxygen saturation Device. 5. The method of claim 4,
A holder surrounding the subject,
and the light source unit, the first light receiving unit, and the second light receiving unit are provided inside the holder to face the measurement object. 13. The method of claim 12,
wherein the holder includes a first holder extending from the center of the holder to one side to which the first light receiving unit is mounted and a second holder extending from the center to the other side to which the first light receiving unit is mounted. Device. 14. The method of claim 13,
An oxygen saturation measuring device, characterized in that between the first holder and the second holder, an opening for inserting the subject is formed. 15. The method of claim 14,
The oxygen saturation measuring device, characterized in that the first holder and the second holder are rotatably provided with respect to the center of the holder. In the measuring method for measuring oxygen saturation of blood of a subject,
irradiating light to the subject through a light source;
generating a signal by receiving light from the first light receiving unit and the second light receiving unit positioned to have different separation distances from the light source; And
and calculating oxygen saturation by using a difference between the signal generated by the first light receiving unit and the signal generated by the second light receiving unit. 17. The method of claim 16,
In the step of irradiating the light,
A method for measuring oxygen saturation, characterized in that light of a first wavelength and light of a second wavelength different from the first wavelength are respectively irradiated. 18. The method of claim 17,
The oxygen saturation measuring method, characterized in that the light irradiation of the first wavelength and the light irradiation of the second wavelength are sequentially performed. 19. The method of claim 18,
The method for measuring oxygen saturation, wherein the first light receiving unit and the second light receiving unit are positioned to receive the light that has passed through the subject. 19. The method of claim 18,
The method for measuring oxygen saturation, characterized in that the subject is a blood supply tube constituting a non-pulsating extracorporeal circulation circuit or a body of a tachycardia patient.

Images