JPS6216647B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an oximeter that non-invasively measures the absolute value of O ₂ saturation in arterial blood of a living body, and more specifically, the present invention relates to an oximeter that non-invasively measures the absolute value of O ₂ saturation in arterial blood of a living body. The present invention relates to a non-invasive oximeter that performs the above measurements by diffracting the light absorbed in the living body. BACKGROUND ART Conventionally, as an oximeter that measures oxygen saturation non-invasively without collecting blood from a living body, one that utilizes changes in absorbance due to blood pulsation is known. This device obtains information from changes in absorbance, so the steady component of the measurement output, that is,
It is not affected by the absorbance of living body tissues, and there is no need to perform ischemia of the measurement area, which was previously required to remove this effect, and as a result, oxygen saturation can be measured continuously. Has advantages. However, since this device uses variations in the measurement output as its information source, when the part to be measured moves, the effect appears as a variation component in the measurement signal, which has the disadvantage of being mixed into the measurement value as an error. The present invention aims to improve the above-mentioned drawbacks, and provides a non-invasive oximeter that can perform measurements with high accuracy even when the part to be measured is shaken. The present invention will be explained below based on the illustrated embodiments. FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, the light transmitted through the part to be measured 2 is divided into three wavelength ranges by a dichroic mirror 3, a dichroic mirror 4, an interference filter 5, an interference filter 6, and an interference filter 7. The light enters the light receiving section 9 and the light receiving section 10, respectively. Light receiving section 8, light receiving section 9, light receiving section 10
The outputs E _a1 , E _a2 , and E _a3 are respectively E _a1 =I _O1 (1+α)F ₁ 10−C{S( ¹ ε _Hbp2 − ¹ ε _Hb ) ⁺¹ ε _Hb }(d+△d) −(1) E _a2 =I _O2 (1+α)F ₂ 10−C{S( ² ε _Hbp2 − ² ε _Hb )+ ² ε _Hb }(d+△d) ―(2) E _a3 = I _O3 (1+α) F ₃ 10− It is expressed as C{S( ³ ε _Hbp2 − ³ ε _Hb ) ⁺³ ε _Hb }(d+△d) - (3). I _p1 , I _p2 , and I _p3 are the incident light intensities in the first, second, and third wavelength ranges, respectively, and F
₁ , F ₂ , and F ₃ are the transmittance of tissues other than arterial blood to light in the first, second, and third wavelength ranges, respectively, and ¹ ε
_Hbp2 , ² ε _Hbp2 , ³ ε _Hbp2 are the first, second, and
The extinction coefficient of oxyhemoglobin for light in the third wavelength range, ¹ ε _Hb , ² ε _Hb , ³ ε _Hb is the extinction coefficient of hemoglobin for light in the first, second, and third wavelength range, respectively, and C is the total hemoglobin. The concentration, d, is the thickness of blood pooled in the tissue, Δd is the variation thereof due to pulsation, S is the oxygen saturation level of arterial blood, and α is the rate of change in the intensity of the incident light due to agitation of the part to be measured. As can be seen from equations (1), (2), and (3), the output of the light receiving section includes a DC component and an AC component, respectively. 11,
12 and 13 are arithmetic circuits that calculate changes in absorbance from the outputs of the light receiving sections 8, 9, and 10, respectively. The change in absorbance can be obtained, for example, by calculating the ratio of the AC component to the DC component of the output of each light receiving section using the calculation circuits 11, 12, and 13. That is, if we rewrite equations (1), (2), and (3), E _ai 〓I _pi (1+α)F _i10 −C{S( ⁱ ε _Hbp2 − ⁱ ε _Hb )+ ⁱ ε _Hb }d X[1− ln10・C{S( ⁱ ε _Hbp2 − ⁱ ε _Hb )+ ⁱ ε _Hb }△d} 〓I _Oi Fi10−C{S( ⁱ ε _Hbp2 − ⁱ ε _Hb )+ ⁱ ε _Hb }d X[1+α−ln10・C{S( ⁱ ε _Hbp2 − ⁱ ε _Hb )+ ⁱ ε _Hb }△d] - (4) However, in the above, when i = 1, 2, 3, the formula
Three cases (1), (2), and (3) are expressed simultaneously in equation (4). Therefore, the calculation circuits 11, 12, and 13 each calculate the ratio of the AC component of E _ai to the DC component of E _ai , and the following output E _bi (i=1, 2, 3) is obtained.
get. E _bi =α−ln10・C{S( ⁱ ε _Hbp2 − ⁱ ε _Hb )+ ⁱ ε _Hb }△d −(5) As is clear from equation (5), the arithmetic circuits 11, 12,
The output of 13 is information only about changes in the intensity of light incident on the light receiving sections 8, 9, and 10. However, α, which is a factor due to the movement of the measured part, is also included in the output E _bi because it is a change in the intensity of the incident light. Conventionally, E _b1 and E _b2 were obtained for two wavelengths, and S was determined from these two outputs, but the influence of α could not be eliminated, which caused measurement errors. Therefore, in the present invention, Eb ₁ ,
Eb ₂ and Eb ₃ are input to differential amplifiers 14 and 15 to calculate (Eb ₁ −Eb ₃ ) and (Eb ₂ −Eb ₃ ), respectively. That is, the outputs Ec ₁ and Ec ₂ of the differential amplifiers 14 and 15 are respectively E _c1 =ln10・C・△d[S{( ¹ ε _Hbp2 − ³ ε _Hbp2 ) −( ¹ ε _Hb − ³ ε _Hb )}+( ¹ ε _Hb − ³ ε _Hb )] ―(6) E _c2 = ln10・C・△d[S{( ² ε _Hbp2 − ³ ε _Hbp
2 ) −( ² ε _Hb − ³ ε _Hb )}+( ² ε _Hb − ³ ε _Hb )] −(7). Determining S from equations (6) and (7), we get

[Table] 16 in Figure 1 is the known constant ¹ ε _Hb , ²
This is an oxygen saturation calculation unit that performs calculation according to equation (8) using ε _Hb , ³ ε _Hb , ¹ ε _Hbp2 , ² ε _Hbp2 , ³ ε _Hbp2 and inputs Ec ₁ and Ec ₂ . The output is displayed on the display section 17. As is clear from equations (6) and (7), the influence of α is not mixed into the calculation of S. As is clear from the above, according to the present invention, a non-invasive oximeter is provided that is capable of continuous and accurate measurement regardless of the movement of the part to be measured.

[Brief explanation of the drawing]

The drawing is a block diagram showing one embodiment of the present invention. 8, 9, 10... light receiving section, 11, 12, 13...
...Arithmetic circuit, 14, 15...Differential amplifier, 16...
...Oxygen saturation calculation section.

Claims (1)

[Scope of Claims] 1. First, second, and third light receivers that detect the amount of light of three different wavelengths absorbed by a living body including pulsating blood, and generate an output signal according to the amount of light. and calculating the change in absorbance due to blood pulsation for each of the output signals of the three light receiving means,
first, second, and third calculating means that respectively output first, second, and third absorbance signals corresponding to the calculation means; and calculating a difference between the first absorbance signal and the third absorbance signal and responding accordingly. and a second differential means that calculates a difference between the second absorbance signal and the third absorbance signal and outputs a second differential signal corresponding to the difference between the second absorbance signal and the third absorbance signal. A non-invasive oximeter comprising: differential means; and oxygen saturation calculating means for calculating the oxygen saturation of blood based on the first and second differential signals.