JP4962234B2 - Pulse oximeter - Google Patents

Pulse oximeter Download PDF

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JP4962234B2
JP4962234B2 JP2007236614A JP2007236614A JP4962234B2 JP 4962234 B2 JP4962234 B2 JP 4962234B2 JP 2007236614 A JP2007236614 A JP 2007236614A JP 2007236614 A JP2007236614 A JP 2007236614A JP 4962234 B2 JP4962234 B2 JP 4962234B2
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健一郎 日比
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Konica Minolta Optics Inc
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本発明は、動脈血流のある生体組織に赤色光と赤外光とを照射し、透過または反射した光を利用して、2つの波長の吸光特性の差から動脈血酸素飽和度を非観血的に測定するパルスオキシメータに関し、特に脈動が小さく、信号の交流成分が小さい低灌流の場合の精度の向上に関する。   The present invention irradiates biological tissue with arterial blood flow with red light and infrared light, and uses transmitted or reflected light to determine arterial oxygen saturation from the difference in absorption characteristics of two wavelengths. In particular, the present invention relates to an improvement in accuracy in the case of low perfusion with a small pulsation and a small AC component of a signal.

前記のようなパルスオキシメータでは、前記赤色光および赤外光を被験者の指などに交互に照射して、その透過光または反射光をシリコンフォトダイオードなどの受光素子で光電変換し、得られた入射光強度に応じた電流出力を、オペアンプを用いた電流電圧変換回路を用いて電圧信号として取出している。その後、前記電圧信号は更に増幅回路によって増幅され、アナログ/デジタル変換回路によってデジタル信号に変換されて演算装置に入力され、前記2つの波長の吸光特性の差から前記動脈血酸素飽和度が計算される。   The pulse oximeter as described above was obtained by alternately irradiating the subject's finger with the red light and infrared light, and photoelectrically converting the transmitted light or reflected light with a light receiving element such as a silicon photodiode. A current output corresponding to the incident light intensity is extracted as a voltage signal using a current-voltage conversion circuit using an operational amplifier. Thereafter, the voltage signal is further amplified by an amplification circuit, converted into a digital signal by an analog / digital conversion circuit, and input to the arithmetic unit, and the arterial oxygen saturation is calculated from the difference between the absorption characteristics of the two wavelengths. .

具体的には、前記赤色光および赤外光のデータは動脈の脈動に従って大きさが変化する。ある時間の中で、赤色光の変化した交流成分をRAC、赤外光の変化した交流成分をIRAC、赤色光の変化していない直流成分をRDC、赤外光の変化していない直流成分をIRDCとすると、赤色光と赤外光との変化割合の比Pは以下の式で表される。 Specifically, the size of the red light and infrared light data changes according to the pulsation of the artery. Within a certain period of time, the AC component in which red light has changed is R AC , the AC component in which infrared light has changed is IR AC , the DC component in which red light has not changed is R DC , and the infrared light has not changed When the DC component is IR DC , the ratio P of the change ratio between red light and infrared light is expressed by the following equation.

P=(RAC/RDC)/(IRAC/IRDC
そして、前記比Pは、使用している光源の波長や半値幅等の特性に合わせて前記動脈血酸素飽和度(SpO値)との関係が定義される。よって、上式によってその瞬間のSpO値を求めることができ、その瞬時のSpO値に、たとえば移動平均などの処理を施すことによって、パルスオキシメータで表示するSpO値を得ることができる。
P = (R AC / R DC ) / (IR AC / IR DC )
The ratio P is defined in relation to the arterial oxygen saturation (SpO 2 value) in accordance with characteristics such as the wavelength and half-value width of the light source used. Therefore, it is possible to obtain the SpO 2 value of that moment by the above equation, the SpO 2 value of the instantaneous, by performing processing such as moving averages for example, can be obtained SpO 2 values displayed by the pulse oximeter .

このとき、特許文献1で示されるように、前記赤色光および赤外光の各光源の発光時のA/Dカウント値から、その前後に測定した非発光時のA/Dカウント値を減算し、これを1回の発光時のデータとしている。こうして非発光時のカウント値を減算することで、定常的に入射している外光成分や、回路のオフセット成分を除去し、発光による純粋な信号成分のみを取出すようになっている。
特開2000−325330号公報
At this time, as shown in Patent Document 1, the A / D count value at the time of non-light emission measured before and after that is subtracted from the A / D count value at the time of light emission of each light source of red light and infrared light. This is used as data for one light emission. Thus, by subtracting the count value at the time of non-light emission, the externally incident external light component and the offset component of the circuit are removed, and only a pure signal component by light emission is taken out.
JP 2000-325330 A

このようなパルスオキシメータにおいて、光源から生体に光を照射し、透過または反射して得られる信号は、上述のように生体組織内の動脈の脈動によって大きさが変動する。しかしながら、その変動分、すなわち前記交流成分RAC,IRACの、非変動分、すなわち前記直流成分RDC,IRDCに対する割合は、抹消血管の状態の個人差や、周囲の寒暖の状態による血管収縮状態の違い等によって変化し、大きい場合は10%以上あるが、小さい場合には0.5%以下になることもある。 In such a pulse oximeter, a signal obtained by irradiating light to a living body from a light source and transmitting or reflecting the light fluctuates depending on the pulsation of an artery in the living tissue as described above. However, the ratio of the fluctuation component, that is, the alternating current components R AC and IR AC to the non-variation component, that is, the direct current components R DC and IR DC , is a blood vessel due to individual differences in the state of peripheral blood vessels and the surrounding cold and warm conditions. It changes depending on the difference in the contraction state, etc., and when it is large, it is 10% or more, but when it is small, it may be 0.5% or less.

上述の特許文献1では、上述のように外光成分や回路のオフセット成分については除去できるが、このような微小な交流成分RAC,IRACを良好なS/Nで測定できないという問題がある。そのために、電流電圧変換回路のフィードバック抵抗を大きくして増幅率を上げようとしても、直流成分RDC,IRDCも合わせて増幅され、オペアンプの出力が飽和して充分な増幅ができない。また、その結果、後段の増幅回路においても回路の飽和が起こらない範囲でしか増幅ができず、ここでもS/N的に不利な状況となり、安定した測定ができなくなる。 In the above-mentioned Patent Document 1, the external light component and the offset component of the circuit can be removed as described above, but there is a problem that such minute AC components R AC and IR AC cannot be measured with a good S / N. . Therefore, even if an attempt is made to increase the amplification factor by increasing the feedback resistance of the current-voltage conversion circuit, the direct current components R DC and IR DC are also amplified together, and the output of the operational amplifier is saturated and sufficient amplification cannot be performed. As a result, the amplification circuit in the subsequent stage can perform amplification only within a range where the circuit does not saturate, and this is also disadvantageous in terms of S / N, and stable measurement cannot be performed.

本発明の目的は、脈動によって変動する交流成分が小さくても、その部分を充分増幅して精度良く測定を行うことができるパルスオキシメータを提供することである。   An object of the present invention is to provide a pulse oximeter capable of performing measurement with high accuracy by sufficiently amplifying the portion even if the AC component that fluctuates due to pulsation is small.

本発明のパルスオキシメータは、動脈血流のある生体組織に光を照射し、透過または反射した光を利用して、動脈血酸素飽和度を測定するパルスオキシメータにおいて、前記生体組織に第1および第2の波長の光を照射する第1および第2の光源と、前記生体組織を透過または反射した前記第1および第2の波長の光を受光する受光素子と、所定の第1の基準電圧を基準として、前記受光素子において発生した電流を電圧に変換する電流電圧変換回路と、所定の第2の基準電圧を基準として、前記電流電圧変換された信号を増幅する増幅回路と、前記増幅されたアナログ信号をデジタル信号に変換するアナログ/デジタル変換回路と、変換されたデジタル信号から前記動脈血酸素飽和度を計算するとともに、前記第2の基準電圧よりも高く設定され、デジタル信号の非変動分に対応したレベルの前記第1の基準電圧を作成し、前記電流電圧変換回路に与える演算装置とを含むことを特徴とする。 The pulse oximeter of the present invention is a pulse oximeter that irradiates a living tissue having an arterial blood flow with light and uses transmitted or reflected light to measure arterial blood oxygen saturation. First and second light sources that emit light of a second wavelength; a light receiving element that receives light of the first and second wavelengths that is transmitted or reflected by the biological tissue; and a predetermined first reference voltage And a current / voltage conversion circuit that converts a current generated in the light receiving element into a voltage, an amplification circuit that amplifies the current / voltage converted signal based on a predetermined second reference voltage, and the amplified signal. and an analog / digital converter for converting an analog signal into a digital signal, thereby calculating the arterial blood oxygen saturation from the converted digital signal, said second reference voltage higher setting than Is to create the first reference voltage level corresponding to the non-variation of the digital signal, characterized in that it comprises a computing device for providing to the current-voltage conversion circuit.

上記の構成によれば、生体における赤色光と赤外光との2つの波長の吸光特性の差を利用して動脈血酸素飽和度を非観血的に測定するためのパルスオキシメータにおいて、2つの光源からの波長の異なる光の前記生体組織の透過光または反射光を受光素子で光電変換し、得られた電流信号を電圧信号に変換して増幅するにあたって、電流電圧変換回路は所定の第1の基準電圧を基準として、前記電流信号を電圧信号に変換して増幅を行い、さらに2段目の増幅回路において前記電圧信号の振幅を増幅する。続いて、その増幅されたアナログの電圧信号をアナログ/デジタル変換回路においてデジタルの信号に変換し、演算装置(CPU)が、その変換されたデジタル信号から前記動脈血酸素飽和度を計算する。このとき、前記第1の基準電圧を可変として、前記演算装置はまた、前記第2の基準電圧よりも高く設定され、前記デジタル信号の脈動(AC)分を除いた、非変動(DC)分に対応したレベルの前記第1の基準電圧を作成して前記電流電圧変換回路に与え、該電流電圧変換回路は、入力電流信号から前記非変動(DC)分を減算した脈動(AC)分を、該電流電圧変換回路が飽和しないレベルの大きなゲインで電圧に変換する。 According to the above configuration, in a pulse oximeter for noninvasively measuring arterial oxygen saturation using a difference in absorption characteristics of two wavelengths of red light and infrared light in a living body, When photoelectrically converting transmitted light or reflected light of the biological tissue of light having different wavelengths from a light source with a light receiving element, and converting the obtained current signal into a voltage signal and amplifying the current signal, the current-voltage conversion circuit has a predetermined first The current signal is converted into a voltage signal and amplified with reference to the reference voltage, and the amplitude of the voltage signal is amplified in a second stage amplifier circuit. Subsequently, the amplified analog voltage signal is converted into a digital signal by an analog / digital conversion circuit, and the arithmetic unit (CPU) calculates the arterial oxygen saturation from the converted digital signal. At this time, the first reference voltage is variable, and the arithmetic unit is also set higher than the second reference voltage , and the non-fluctuating (DC) component excluding the pulsation (AC) component of the digital signal. The first reference voltage of a level corresponding to is generated and applied to the current-voltage conversion circuit, and the current-voltage conversion circuit subtracts the non-fluctuation (DC) component from the input current signal to obtain a pulsation (AC) component. The current-voltage conversion circuit converts the voltage into a voltage with a large gain that does not saturate.

これによって、前記増幅回路に入力される電圧信号は、該増幅回路の中心電圧に前記脈動分のボトム値が略一致した信号となり、出力される信号は該増幅回路の動作電圧の範囲内で大きな変動幅を有する信号となる。したがって、脈動で変動する部分を充分増幅して電圧に変換することができ、特に脈動が小さく、信号の交流成分が小さい測定条件の悪い低灌流の場合にも、精度良く測定を行うことができる。   As a result, the voltage signal input to the amplifier circuit becomes a signal in which the bottom value of the pulsation substantially coincides with the center voltage of the amplifier circuit, and the output signal is large within the operating voltage range of the amplifier circuit. The signal has a fluctuation range. Therefore, it is possible to sufficiently amplify a portion that fluctuates due to pulsation and convert it into a voltage. In particular, even in the case of low perfusion with a low pulsation and a small AC component of the signal and poor measurement conditions, the measurement can be performed with high accuracy. .

また、本発明のパルスオキシメータは、前記第1および第2の光源を時間分割で相互に異なるタイミングで点灯を行わせるタイミング信号を発生する制御回路をさらに備え、前記受光素子は前記第1および第2の光源からの光を受光し、前記演算装置は、前記第1および第2の波長のそれぞれに適した基準電圧を作成し、前記タイミング信号に応答して前記電流電圧変換回路に与えるとともに、前記アナログ/デジタル変換回路からのデジタル信号を前記第1および第2の波長にそれぞれ対応したものであると認識して、前記第1の基準電圧の変化量分を補正して、前記動脈血酸素飽和度を計算することを特徴とする。 The pulse oximeter of the present invention further includes a control circuit that generates a timing signal for lighting the first and second light sources at different timings in a time division manner, and the light receiving element includes the first and second light sources. The light from the second light source is received, and the arithmetic unit creates a reference voltage suitable for each of the first and second wavelengths and supplies the reference voltage to the current-voltage conversion circuit in response to the timing signal. Recognizing that the digital signal from the analog / digital conversion circuit corresponds to the first and second wavelengths, respectively, and correcting the amount of change in the first reference voltage to obtain the arterial oxygen It is characterized by calculating the degree of saturation.

上記の構成によれば、受光素子、電流電圧変換回路、増幅回路、アナログ/デジタル変換回路を時間分割で使用して前記赤色光と赤外光との2つの波長の吸光特性を検出するにあたって、制御回路から出力され、前記第1および第2の光源を時間分割で相互に異なるタイミングで点灯を行わせるタイミング信号を前記演算装置が取込み、前記アナログ/デジタル変換回路からのデジタル信号を前記第1および第2の波長にそれぞれ対応したものであると認識して前記動脈血酸素飽和度を計算する。その際、前述のとおり赤色光と赤外光との変化の割合の比を求める必要があり、直流成分も計算に使用するので、前記電流電圧変換回路の第1の基準電圧を変化させることで入力電流信号から減算しておいた直流成分の全てまたは一部を考慮して計算を行う。 According to the above configuration, when detecting light absorption characteristics of the two wavelengths of the red light and the infrared light by using a light receiving element, a current-voltage conversion circuit, an amplification circuit, and an analog / digital conversion circuit in time division, The arithmetic unit takes in a timing signal output from the control circuit and causes the first and second light sources to be turned on at different timings in a time division manner, and receives the digital signal from the analog / digital conversion circuit as the first signal. The arterial blood oxygen saturation is calculated by recognizing that it corresponds to the second wavelength. At that time, as described above, it is necessary to obtain the ratio of the ratio of change between red light and infrared light, and since the DC component is also used in the calculation, the first reference voltage of the current-voltage conversion circuit can be changed. Calculation is performed in consideration of all or part of the DC component subtracted from the input current signal.

したがって、前記赤色光と赤外光との2つの波長の電流信号に対する第1の基準電圧を可変として前記脈動(AC)分を良好なS/Nで検出するようにしても、直流成分も含めて求める動脈血酸素飽和度を正確に求めることができる。 Therefore, even if the first reference voltage for the current signals of two wavelengths of the red light and the infrared light is made variable to detect the pulsation (AC) with a good S / N, the direct current component is also included. Thus, the arterial oxygen saturation can be accurately determined.

本発明のパルスオキシメータは、以上のように、生体における赤色光と赤外光との2つの波長の吸光特性の差を利用して動脈血酸素飽和度を非観血的に測定するためのパルスオキシメータにおいて、受光素子で得られた電流信号を電流電圧変換回路が所定の第1の基準電圧を基準として電圧信号に変換して増幅を行い、さらに2段目の増幅回路において前記電圧信号の振幅を増幅し、その増幅されたアナログの電圧信号をアナログ/デジタル変換回路においてデジタルの信号に変換し、演算装置(CPU)が、その変換されたデジタル信号から前記動脈血酸素飽和度を計算するにあたって、前記第1の基準電圧を可変として、前記演算装置はまた、前記第2の基準電圧よりも高く設定され、前記デジタル信号の脈動(AC)分を除いた、非変動(DC)分に対応したレベルの前記第1の基準電圧を作成して前記電流電圧変換回路に与え、該電流電圧変換回路が、入力電流信号から前記非変動(DC)分を減算した脈動(AC)分を、該電流電圧変換回路が飽和しないレベルの大きなゲインで電圧に変換する。 As described above, the pulse oximeter of the present invention is a pulse for non-invasively measuring arterial oxygen saturation using the difference in absorption characteristics of two wavelengths of red light and infrared light in a living body. In the oximeter, the current / voltage conversion circuit converts the current signal obtained by the light receiving element into a voltage signal with a predetermined first reference voltage as a reference, and amplifies the current signal. When the amplitude is amplified, the amplified analog voltage signal is converted into a digital signal by an analog / digital conversion circuit, and the arithmetic unit (CPU) calculates the arterial oxygen saturation from the converted digital signal. , the first reference voltage as a variable, the calculation device also, the second higher set than the reference voltage of, except for pulsation (AC) component of the digital signal, nondenaturing (DC) component to create the first reference voltage level corresponding given to the current-voltage conversion circuit, pulsating said current-voltage conversion circuit, obtained by subtracting the non-fluctuating (DC) component from the input current signal ( AC) is converted into a voltage with a large gain at a level at which the current-voltage conversion circuit does not saturate.

それゆえ、前記増幅回路に入力される電圧信号は、該増幅回路の中心電圧に前記脈動分のボトム値が略一致した信号となり、出力される信号は該増幅回路の動作電圧の範囲内で大きな変動幅を有する信号となる。したがって、脈動で変動する部分を充分増幅して電圧に変換することができ、特に脈動が小さく、信号の交流成分が小さい測定条件の悪い低灌流の場合にも、精度良く測定を行うことができる。   Therefore, the voltage signal input to the amplifier circuit is a signal whose bottom value for the pulsation substantially coincides with the center voltage of the amplifier circuit, and the output signal is large within the operating voltage range of the amplifier circuit. The signal has a fluctuation range. Therefore, it is possible to sufficiently amplify a portion that fluctuates due to pulsation and convert it into a voltage. In particular, even in the case of low perfusion with a low pulsation and a small AC component of the signal and poor measurement conditions, the measurement can be performed with high accuracy. .

図1は、本発明の実施の一形態に係るパルスオキシメータ10の電気的構成を示すブロック図である。このパルスオキシメータ10では、発光回路1が、第1の波長である赤色光Rを発する第1の光源である発光素子2aと、第2の波長である赤外光IRを発する第2の光源である発光素子2bとを交互に点灯させ、それらから発せられた光R,IRが生体3に入射し、一部が吸光された後、残りの透過光が受光素子4で検出される。シリコンフォトダイオードなどから成る前記受光素子4は、前記透過光を光電変換し、電流出力で電流電圧変換回路5に入力する。   FIG. 1 is a block diagram showing an electrical configuration of a pulse oximeter 10 according to an embodiment of the present invention. In the pulse oximeter 10, the light emitting circuit 1 has a light emitting element 2a that is a first light source that emits red light R having a first wavelength, and a second light source that emits infrared light IR having a second wavelength. The light emitting elements 2b are alternately turned on, and the light R and IR emitted therefrom are incident on the living body 3 and part of the light is absorbed, and then the remaining transmitted light is detected by the light receiving element 4. The light receiving element 4 made of a silicon photodiode or the like photoelectrically converts the transmitted light and inputs it to the current / voltage conversion circuit 5 as a current output.

前記電流電圧変換回路5は、所定の基準電圧Vref1を基準として、前記受光素子4において発生した電流を電圧に変換するとともに増幅して、次段の増幅回路6に与える。増幅回路6は、所定の基準電圧Vref2を基準として、前記電流電圧変換回路5からの電圧出力を増幅し、アナログ/デジタル変換回路7に与える。アナログ/デジタル変換回路7は、増幅回路6で増幅されたアナログ信号をデジタル信号に変換し、演算装置8に与える。演算装置8は、CPUから成り、入力された前記光R,IRに対応するデジタル信号から、後述するようにして前記動脈血酸素飽和度(SpO値)を計算するとともに、デジタル信号の非変動(DC)分に対応したレベルの前記基準電圧Vref1を作成し、Vref1調整回路9を介して、前記電流電圧変換回路5に与える。Vref1調整回路9は、デジタル/アナログ変換回路などで実現され、前記演算装置8からの出力データに対応したレベルの直流電圧を発生して、前記基準電圧Vref1として電流電圧変換回路5に与える。さらにこのパルスオキシメータ10では、全体の動作を制御する制御回路11が設けられており、該制御回路11は前記発光回路1および演算装置8にタイミング信号を出力する。なお、1つのCPUを使って、制御回路11と演算装置8との機能を、そのCPUに持たせるようにしてもよい。 The current-voltage conversion circuit 5 converts a current generated in the light receiving element 4 into a voltage and amplifies it with reference to a predetermined reference voltage Vref1, and supplies it to the amplification circuit 6 in the next stage. The amplifying circuit 6 amplifies the voltage output from the current-voltage converting circuit 5 with reference to a predetermined reference voltage Vref2, and gives it to the analog / digital converting circuit 7. The analog / digital conversion circuit 7 converts the analog signal amplified by the amplification circuit 6 into a digital signal and supplies the digital signal to the arithmetic device 8. The arithmetic unit 8 is composed of a CPU, calculates the arterial oxygen saturation (SpO 2 value) from the digital signals corresponding to the inputted lights R and IR as described later, and does not change the digital signal ( The reference voltage Vref1 having a level corresponding to (DC) is generated and applied to the current-voltage conversion circuit 5 via the Vref1 adjustment circuit 9. The Vref1 adjustment circuit 9 is realized by a digital / analog conversion circuit or the like, generates a DC voltage of a level corresponding to the output data from the arithmetic unit 8, and supplies it to the current-voltage conversion circuit 5 as the reference voltage Vref1. Further, the pulse oximeter 10 is provided with a control circuit 11 for controlling the entire operation, and the control circuit 11 outputs a timing signal to the light emitting circuit 1 and the arithmetic unit 8. In addition, you may make it give the function of the control circuit 11 and the arithmetic unit 8 to the CPU using one CPU.

図2は、前記電流電圧変換回路5への入力波形の例を示す図である。前記発光回路1は、前記タイミング信号に応答して、赤色光Rの発光素子2aと赤外光IRの発光素子2bとを、予め定める周期、たとえば16msec毎に、相互に半周期ずれて、交互に500μsecずつ点灯させる。それによる前記受光素子4の光電変換出力は、この図2に示すようなものであり、理解し易くするために、図3で示すように赤色光Rの成分のみを抜出すと、脈動によって変化する部分(AC成分)と、脈動によって変化しない部分(DC成分)とが含まれている。   FIG. 2 is a diagram showing an example of an input waveform to the current-voltage conversion circuit 5. In response to the timing signal, the light emitting circuit 1 alternates between the red light R light emitting element 2a and the infrared light IR light emitting element 2b with a predetermined period, for example, every 16 msec, shifted from each other by a half period. For 500 μsec. The photoelectric conversion output of the light receiving element 4 thereby is as shown in FIG. 2. For ease of understanding, when only the component of the red light R is extracted as shown in FIG. And a portion that does not change due to pulsation (DC component).

そこで本発明では、反転増幅のオペアンプである電流電圧変換回路5の非反転入力端に、従来ではGNDレベルや所定の固定値が入力されていたのに対して、可変の前記基準電圧Vref1を入力するようにし、この基準電圧Vref1を基準に、マイナス方向に振れて増幅を行うようにする(ダイナミックレンジを確保する)。これによって、電流電圧変換回路5のフィードバックゲイン抵抗の値を大きく取ることができ、S/Nを改善することができる。またこの電流電圧変換回路5の基準電圧Vref1を増幅回路6の基準電圧Vref2より高く設定することによって、増幅回路6にVref2基準でAC成分のみの信号を入力する。図4に、その電流電圧変換出力を示す。一方、増幅回路6と同一の固定値の基準電圧Vref2を入力した従来の電流電圧変換出力を図5に示す。   In the present invention, therefore, the variable reference voltage Vref1 is input to the non-inverting input terminal of the current-voltage conversion circuit 5 which is an operational amplifier for inverting amplification, whereas a GND level or a predetermined fixed value is input conventionally. Thus, amplification is performed by swinging in the minus direction with reference to the reference voltage Vref1 (a dynamic range is ensured). As a result, the value of the feedback gain resistance of the current-voltage conversion circuit 5 can be increased, and the S / N can be improved. Further, by setting the reference voltage Vref1 of the current-voltage conversion circuit 5 to be higher than the reference voltage Vref2 of the amplifier circuit 6, a signal having only an AC component on the basis of Vref2 is input to the amplifier circuit 6. FIG. 4 shows the current-voltage conversion output. On the other hand, FIG. 5 shows a conventional current-voltage conversion output in which a reference voltage Vref2 having the same fixed value as that of the amplifier circuit 6 is input.

したがって、前記増幅回路6に入力される電圧信号は、該増幅回路6の中心電圧に前記脈動(AC)分のボトム値が略一致した信号となり、出力される信号は、図6で示すように、該増幅回路6の動作電圧V1の範囲内で大きな変動幅を有する信号となる。これに対して、前記増幅回路6に図5で示すような従来の電圧信号が入力されると、その出力は、図7で示すように、前記動作電圧V1の範囲内で、非変動(DC)分が多く占め、変動幅の小さな信号となる。したがって、アナログ/デジタル変換回路7が同じ分解能でアナログ/デジタル変換を行い、演算装置8が演算を行った場合、脈動の割合が前記0.5%にもなると、従来では精度が確保できなくなるのに対して、本発明では充分な精度を確保できることが理解される。   Therefore, the voltage signal input to the amplifier circuit 6 is a signal in which the bottom value corresponding to the pulsation (AC) substantially coincides with the center voltage of the amplifier circuit 6, and the output signal is as shown in FIG. Thus, the signal has a large fluctuation width within the range of the operating voltage V1 of the amplifier circuit 6. On the other hand, when a conventional voltage signal as shown in FIG. 5 is input to the amplifier circuit 6, the output is non-variable (DC) within the range of the operating voltage V1, as shown in FIG. ) Occupies a large amount, and the signal has a small fluctuation range. Therefore, when the analog / digital conversion circuit 7 performs analog / digital conversion with the same resolution and the calculation device 8 performs calculation, if the pulsation ratio reaches 0.5%, the accuracy cannot be ensured conventionally. On the other hand, it is understood that sufficient accuracy can be secured in the present invention.

前記演算装置8での演算は、前記のとおり、赤色光の変化した交流成分をRAC、赤外光の変化した交流成分をIRAC、赤色光の変化していない直流成分をRDC、赤外光の変化していない直流成分をIRDCとするとき、
P=(RAC/RDC)/(IRAC/IRDC
から赤色光と赤外光との変化割合の比Pを求め、その比Pに対して、発光素子2a,2bの波長や半値幅等の特性に合わせて、図8で示すように予め対応付けて求められている動脈血酸素飽和度(SpO値)を求める。求められたSpO値は、図示しない表示装置や外部のデータ記録装置などへ出力される。
As described above, the arithmetic operation by the arithmetic unit 8 is performed by using the AC component in which the red light is changed as R AC , the AC component in which the infrared light is changed as IR AC , and the DC component as the red light is not changed as R DC and red. When the direct current component in which external light does not change is IR DC ,
P = (R AC / R DC ) / (IR AC / IR DC )
The ratio P of the change ratio between the red light and the infrared light is obtained from the above, and the ratio P is previously associated with the characteristics of the light emitting elements 2a and 2b, such as the wavelength and the half width, as shown in FIG. To determine the arterial oxygen saturation (SpO 2 value). The obtained SpO 2 value is output to a display device (not shown) or an external data recording device.

したがって、演算には直流成分RDC,IRDCが必要になるが、演算装置8は、発光回路1において発光素子2a,2bの点灯制御に使用される制御回路11からのタイミング信号に応答して、前記Vref1調整回路9に出力したデータを記憶しており、前記の演算にあたっては、そのデータに対応した前記基準電圧Vref1に、前記電流電圧変換回路5および増幅回路6におけるゲインならびにアナログ/デジタル変換回路7の1ビットあたりの信号の大きさ(分解能)を乗算して、前記直流成分RDC,IRDCを求める。 Therefore, although direct current components R DC and IR DC are required for the calculation, the calculation device 8 responds to the timing signal from the control circuit 11 used for lighting control of the light emitting elements 2a and 2b in the light emitting circuit 1. The data output to the Vref1 adjustment circuit 9 is stored, and in the calculation, the reference voltage Vref1 corresponding to the data is converted to the gain in the current-voltage conversion circuit 5 and the amplification circuit 6 and analog / digital conversion. The DC components R DC and IR DC are obtained by multiplying the magnitude (resolution) of the signal per bit of the circuit 7.

以上のように、本発明のパルスオキシメータ10は、生体における赤色光Rと赤外光IRとの2つの波長の吸光特性の差を利用して動脈血酸素飽和度を測定するにあたって、2つの発光素子2a,2bからの光の生体3での透過光を受光素子4で光電変換し、得られた電流信号を電圧信号に変換して増幅する電流電圧変換回路5の基準電圧Vref1を、直流成分RDC,IRDCを除去するレベルとし、これによって該電流電圧変換回路5が交流成分RAC,IRACのみを増幅して出力するようにし、さらにその出力信号のボトム値を次段の増幅回路6の中心電圧に略一致した信号とするので、増幅回路6から出力される信号は該増幅回路6の動作電圧の範囲内の大きな変動幅を有する信号となる。したがって、脈動で変化する部分を充分増幅して電圧に変換することができ、特に脈動が小さく、信号の交流成分が小さい測定条件の悪い低灌流の場合にも、精度良く測定を行うことができる。 As described above, the pulse oximeter 10 of the present invention uses two luminescences when measuring arterial oxygen saturation using the difference in absorption characteristics of two wavelengths of red light R and infrared light IR in a living body. The reference voltage Vref1 of the current-voltage conversion circuit 5 that photoelectrically converts the light transmitted from the elements 2a and 2b through the living body 3 with the light receiving element 4 and converts the obtained current signal into a voltage signal and amplifies the direct current component. R DC and IR DC are set to a level to be removed, so that the current-voltage conversion circuit 5 amplifies and outputs only the AC components R AC and IR AC , and the bottom value of the output signal is set to the next stage amplifier circuit. 6, the signal output from the amplifier circuit 6 is a signal having a large fluctuation range within the operating voltage range of the amplifier circuit 6. Therefore, it is possible to sufficiently amplify a portion that changes due to pulsation and convert it into a voltage. In particular, even in the case of low perfusion with a low pulsation and a small AC component of the signal and poor measurement conditions, it is possible to accurately measure. .

また、そのように可変基準電圧Vref1で直流成分RDC,IRDCを除去して交流成分RAC,IRACのみを良好なS/Nで検出するようにしても、演算装置8は、その直流成分RDC,IRDCを考慮して動脈血酸素飽和度を計算するので、該動脈血酸素飽和度を正確に求めることができる。 Further, even if the DC component R DC , IR DC is removed by the variable reference voltage Vref1 so that only the AC component R AC , IR AC is detected with a good S / N, the arithmetic unit 8 does not have the DC component. Since the arterial oxygen saturation is calculated in consideration of the components R DC and IR DC , the arterial oxygen saturation can be accurately obtained.

本発明の実施の一形態に係るパルスオキシメータの電気的構成を示すブロック図である。1 is a block diagram showing an electrical configuration of a pulse oximeter according to an embodiment of the present invention. 電流電圧変換回路に入力されるシリコンフォトダイオードの電流出力において、赤色光と赤外光との両方の波形を表す図である。It is a figure showing the waveform of both red light and infrared light in the current output of the silicon photodiode input into a current-voltage converter circuit. 前記図2で示す電流電圧変換回路に入力されるシリコンフォトダイオードの電流出力のうち、赤色光についての波形を表す図である。It is a figure showing the waveform about red light among the current outputs of the silicon photodiode input into the current-voltage converter circuit shown in the said FIG. 本発明による前記電流電圧変換回路の電圧出力のうち、赤色光の波形を表す図である。It is a figure showing the waveform of red light among the voltage outputs of the said current voltage conversion circuit by this invention. 従来技術による電流電圧変換回路の電圧出力のうち、赤色光の波形を表す図である。It is a figure showing the waveform of red light among the voltage outputs of the current-voltage conversion circuit by a prior art. 図4で示す電圧出力の増幅波形を表す図である。It is a figure showing the amplification waveform of the voltage output shown in FIG. 図5で示す電圧出力の増幅波形を表す図である。It is a figure showing the amplification waveform of the voltage output shown in FIG. (RAC/RDC)/(IRAC/IRDC)とSpO値との関係の一例を示すグラフである。It is a graph which shows an example of the relationship between (R AC / R DC ) / (IR AC / IR DC ) and SpO 2 value.

1 発光回路
2a 赤色光の発光素子
2b 赤外光の発光素子
3 生体
4 受光素子
5 電流電圧変換回路
6 増幅回路
7 アナログ/デジタル変換回路
8 演算装置(CPU)
9 Vref1調整回路
10 パルスオキシメータ
11 制御回路
DESCRIPTION OF SYMBOLS 1 Light emitting circuit 2a Red light emitting element 2b Infrared light emitting element 3 Living body 4 Light receiving element 5 Current voltage converting circuit 6 Amplifying circuit 7 Analog / digital converting circuit 8 Arithmetic unit (CPU)
9 Vref1 adjustment circuit 10 Pulse oximeter 11 Control circuit

Claims (2)

動脈血流のある生体組織に光を照射し、透過または反射した光を利用して、動脈血酸素飽和度を測定するパルスオキシメータにおいて、
前記生体組織に第1および第2の波長の光を照射する第1および第2の光源と、
前記生体組織を透過または反射した前記第1および第2の波長の光を受光する受光素子と、
所定の第1の基準電圧を基準として、前記受光素子において発生した電流を電圧に変換する電流電圧変換回路と、
所定の第2の基準電圧を基準として、前記電流電圧変換された信号を増幅する増幅回路と、
前記増幅されたアナログ信号をデジタル信号に変換するアナログ/デジタル変換回路と、
変換されたデジタル信号から前記動脈血酸素飽和度を計算するとともに、前記第2の基準電圧よりも高く設定され、デジタル信号の非変動分に対応したレベルの前記第1の基準電圧を作成し、前記電流電圧変換回路に与える演算装置とを含むことを特徴とするパルスオキシメータ。
In a pulse oximeter that measures arterial oxygen saturation by irradiating a living tissue with arterial blood flow and using transmitted or reflected light,
First and second light sources that irradiate the biological tissue with light of first and second wavelengths;
A light receiving element that receives light of the first and second wavelengths transmitted or reflected by the biological tissue;
A current-voltage conversion circuit that converts a current generated in the light receiving element into a voltage with reference to a predetermined first reference voltage;
An amplifying circuit that amplifies the current-voltage converted signal with a predetermined second reference voltage as a reference ;
An analog / digital conversion circuit for converting the amplified analog signal into a digital signal;
With calculating the converted said digital signal arterial oxygen saturation, said the second set higher than the reference voltage, creating a first reference voltage level corresponding to the non-variation of the digital signal, the A pulse oximeter comprising: an arithmetic device for giving to a current-voltage conversion circuit.
前記第1および第2の光源を時間分割で相互に異なるタイミングで点灯を行わせるタイミング信号を発生する制御回路をさらに備え、
前記受光素子は前記第1および第2の光源からの光を受光し、
前記演算装置は、前記第1および第2の波長のそれぞれに適した前記第1の基準電圧を作成し、前記タイミング信号に応答して前記電流電圧変換回路に与えるとともに、前記アナログ/デジタル変換回路からのデジタル信号を前記第1および第2の波長にそれぞれ対応したものであると認識して、前記第1の基準電圧の変化量分を補正して、前記動脈血酸素飽和度を計算することを特徴とする請求項1記載のパルスオキシメータ。
A control circuit for generating a timing signal for turning on the first and second light sources at different timings in a time division manner;
The light receiving element receives light from the first and second light sources;
The arithmetic unit creates the first reference voltage suitable for each of the first and second wavelengths, supplies the first reference voltage to the current-voltage conversion circuit in response to the timing signal, and the analog / digital conversion circuit And calculating the arterial oxygen saturation by recognizing that the digital signal from each corresponds to the first and second wavelengths respectively, and correcting the amount of change in the first reference voltage. The pulse oximeter according to claim 1, characterized in that:
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