Device for measuring oxygen saturation degree in arterial blood

What is claimed is:

1. An oximeter device for measuring the saturation degree of oxygen in arterial blood, comprising:

a probe having light emitting means for emitting light to an organism to be measured; light receiving means for receiving light from the organism and memory means for storing data necessary for a calculation of a saturation degree of oxygen in arterial blood of an examined organism caused by said light emitting means and said light receiving means, the memory means including a storage of data representative of crosstalk of light received by the light receiving means;

a main unit having a calculation means which reads out the data stored in said memory means and calculates the saturation degree of oxygen on the basis of the read out data nd the output of said light receiving means, and

means for connecting said probe to said main unit.

2. The oximeter device according to claim 1, further comprising means for computing the remaining operative life of the emitting means and a display unit for indicating the life of said light emitting means.

3. The oximeter device according to claim 1, wherein sum check data is stored in said memory means for judging whether or not the contents of the memory means have been destroyed and whether or not the probe is operatively connected to the main unit.

4. The oximeter device according to claim 2 further including means for counting the emitting time of said light emitting means and estimating the light emitting intensity corresponding to the time of turning on said light emitting means and adjusting a driving current for said light emitting means based on the intensity and the emitting time.

5. The oximeter device according to claim 4 wherein the light emitting means includes light emitting diodes.

6. An oximeter device for measuring the saturation degree of oxygen in arterial blood, comprising:

a probe having light emitting means for emitting light to an organism to be measured, light receiving means for receiving light from the organism, and memory means for storing data necessary for a calculation of a saturation degree of oxygen in arterial blood of an examined organism caused by said light emitting means and said light receiving means;

a main unit having a calculation means which reads out the data stored in said memory means and calculates the saturation degree of oxygen on the basis of the read out data and the output of said light receiving means, and

means for detachably connecting said probe to said main unit, the memory means also storing a sum check data for enabling a judgment of whether or not the contents of the memory means are destroyed and whether or not the probe is exactly connected to the main unit.

7. An oximeter device for measuring the saturation degree of oxygen in arterial blood, comprising:

a probe having light emitting means for emitting light to an organism to be measured, light receiving means for receiving light from the organism, and memory means for storing data necessary for a calculation of a saturation degree of oxygen in arterial blood of an examined organism caused by said light emitting means and said light receiving means, said memory means storing data representative of a predetermined value corresponding to actual stored data necessary for calculation;

a main unit having a calculation means which reads out the data stored in said memory means and calculates the saturation degree of oxygen on the basis of the read out data and the output of said light receiving means;

means for detachably connecting said probe to said main unit, and

means in said main unit for reading out in a predetermined time period said stored data and comparing the stored data with the stored predetermined value data, whereby it is judged whether or not the probe is operatively connected to said main unit.

8. An oximeter device for measuring the saturation degree of oxygen in arterial blood, comprising:

a probe having light emitting means for emitting light to an organism to be measured, light receiving means for receiving light from the organism, memory means for storing data necessary for a calculation of a saturation degree of oxygen in arterial blood of an examined organism caused by said light emitting means and said light receiving means, said memory means including either an EEPROM or EPROM in which data an be rewritten, and means for counting the emitting time of said light emitting means and estimating the light emitting intensity corresponding to the time of turning on said light emitting means and adjusting a driving current for said light emitting means;

a main unit having a calculation means which reads out the data stored in said memory means and calculates the saturation degree of oxygen on the basis of the read out data and the output of said light receiving means; and

means for connecting said probe to said main unit.

9. The oximeter device according to claim 8, wherein said memory means also stores on the crosstalk of said light receiving means.

10. The oximeter device according to claim 8, further comprising a display unit means for indicating the estimated remaining life of said light emitting means.

11. An improved oximeter device comprising:

a probe having a first light emitting diode means for emitting a predetermined first wavelength on light and a second light emitting diode means for emitting a predetermined second wavelength of light, light receiving means for receiving the emitted light and converting it into electrical signals for subsequent processing, and memory means for storing data characteristic of the probe to permit a calibration for the processing of the electrical signals to determine the degree of saturation of oxygen in the blood of an examined organism, the memory means further including the storage of data representative of crosstalk of light received by the light receiving means between the first and second wavelengths of light;

a main unit having a processor circuit for receiving the data stored in the memory means of the probe unit for calculating the saturation degree of oxygen on the basis of the stored data and the electrical signals of the light receiving means, and

means for connecting the probe to the main unit.

12. The oximeter device according to claim 11, further comprising means for computing the remaining operative life of the emitting means and a display unit for indicating the life of said light emitting means.

13. The oximeter device according to claim 11, wherein sum check data is stored in said memory means for judging whether or not the contents of the memory means have been destroyed and whether or not the probe is operatively connected to the main unit.

14. The oximeter device according to claim 12 further including means for counting the emitting time of said light emitting means and estimating the light emitting intensity corresponding to the time of turning on said light emitting means and adjusting a driving current for said light emitting means based on the intensity and the emitting time.

15. In an improved oximeter device having a monitor with a processor circuit for calculating the saturation degree of oxygen, the improvement comprising:

a probe for connection to the monitor having a first light emitting means for emitting a predetermined first wavelength of light and a second light emitting means for emitting a predetermined second wavelength of light, a light receiving means for receiving the emitted light and converting it into electrical signals for subsequent processing by the processor circuit, and memory means for storing predetermined data characteristics of the probe to enable a calibrated processing of the electrical signals by the processor circuit, including the storage of data representative of the crosstalk noise of light received by the light receiving means containing a mix of first and second wavelengths of light, whereby the processor circuit can correct the processing of the electrical signals to remove the crosstalk noise.

16. The improved oximeter of claim 15 wherein the first and second light emitting means includes light emitting diodes.

17. An oximeter device for measuring the saturation degree of oxygen in arterial blood, comprising:

a probe having light emitting means for emitting light to an organism to be measured, light receiving means for receiving light from the organism, and memory means for storing predetermined data indicative of the amount of crosstalk received by said light receiving means;

a main unit having a calculation means which reads out the data stored in said memory means and calculates the saturation degree of oxygen in the basis of the read out data and the output of said light receiving means, and

means for detachably connecting said probe to said main unit.

18. An oximeter device for measuring the saturation degree of oxygen in arterial blood, comprising:

a probe having light emitting means for emitting light to an organism to be measured, light receiving means for receiving light from the organism, and memory means for storing data indicative of the total time that said light emitting means is activated to emit light;

a main unit having a calculation means which calculates the saturation degree of oxygen on the basis of a read out of the output of said light receiving means and a control means for reading out the data stored in said memory means and for estimating the intensity of light to be emitted by said light emitting means on the basis of the read out data and to adjust the driving current of said light emitting means on the basis of said estimated intensity, and

means for detachably connecting said probe to said main unit.

19. The oximeter device according to claim 18, further comprising a display unit for indicating the remaining operative life of said light emitting means.

20. An oximeter device for measuring the saturation degree of oxygen in arterial blood, comprising:

a probe having light emitting means for emitting light to an organism to be measured, light receiving means for receiving light from the organism, and first memory means for storing data necessary for measurement of a saturation degree of oxygen in arterial blood of an examined organism caused by said light emitting means and said light receiving means, and

a main unit detachably connecting said probe, having second memory means for storing the data which is read out from said first memory means when electrical power is supplied to the oximeter device, a judging means which reads out the data stored in said first memory means repeatedly at a predetermined time period and compares said read out data with the data stored in said second memory means to judge whether or not the probe is exactly connected to the main unit, and a calculation means which calculates the saturation degree of oxygen on the basis of said read out data and the output of said light receiving means when said judging means judges said probe is exactly connected to said main unit.

21. An oximeter device for measuring the saturation degree of oxygen in arterial blood, comprising:

a probe having light emitting means for emitting light to an organism to be measured, light receiving means for receiving light from the organism, and memory means for storing a plurality of first data necessary for measurement of a saturation degree of oxygen in arterial blood of an examined organism caused by said light emitting means and said light receiving means and a second data indicative of a sum of said first data, and

a main unit, detachably connecting said probe, having a judging means which reads out the data stored in said memory means and compares the read out second data with an added sum of the read out first data to judge whether or not the contents of the memory means are destroyed, and a calculation means which calculates the saturation degree of oxygen on the basis of said read out first data and the output of said light receiving means when said judging means judges that the contents of the memory means have not been destroyed.

22. An oximeter device for measuring the saturation degree of oxygen in arterial blood, comprising:

a probe having light emitting means for emitting light to an organism to be measured, light receiving means for receiving light from the organism, and memory means for storing data indicative of the intensity of light to be emitted by said light emitting means, a main unit having a reading means for reading out the data stored in said memory means, a control means for adjusting the driving current of said light emitting means on the basis of the read out of the data, and a calculation means for calculating the saturation degree of oxygen on the basis of the output of said light receiving means, and

means for connecting said probe to said main unit.

23. An oximeter device for measuring the saturation degree of oxygen in arterial blood, comprising:

a probe having light emitting means for emitting a light of a first wavelength necessary for measurement of the saturation degree of oxygen to an organism to be measured, light receiving means for receiving light from the organism, and memory means for storing data indicative of the first wavelength and the half power width of light of a first wavelength;

a main unit having a calculation means which reads out the data stored in said memory means and calculates the saturation degree of oxygen on the basis of the read out data and the output of said light receiving means, and

means for connecting said probe to said main unit.

24. The oximeter device according to claim 23, wherein said light emitting means further emits light of a second wavelength that is unnecessary for the measurement of the saturation degree of oxygen, and said memory means further stores data indicative of the second wavelength.

25. An oximeter device for measuring the saturation degree of oxygen in arterial blood, comprising:

a probe having light emitting means for emitting a first wavelength of light necessary for measurement of the saturation degree of oxygen and a second wavelength of light that is unnecessary for the measurement of the saturation degree of oxygen in an organism to be measured, light receiving means for receiving light from the organism, and memory means for storing data of the ratio of the intensity of light of the first wavelength to be emitted by said light emitting means to the intensity of light of the second wavelength to be emitted thereby;

a main unit having a calculation means which reads out the data stored in said memory means and calculates the saturation degree of oxygen on the basis of the read out data, including the ratio of intensity of the first and second wavelengths and the output of said light receiving means, and

means for connecting said probe to said main unit.

26. An oximeter device for measuring the saturation degree of oxygen in arterial blood, comprising:

a probe having light emitting means for emitting light to an organism to be measured, light receiving means for receiving light from the organism, and memory means for storing, as data, the coefficients used in an equation for calculation of the saturation degree of oxygen and corresponding to the particular characteristics of the light emitting means;

a main unit having a calculation means which reads out the coefficients stored in said memory means and calculates the saturation degree of oxygen on the basis of the read out data and the output of said light receiving means, and

means for detachably connecting said probe to said main unit.

27. An oximeter device for measuring the saturation degree of oxygen in arterial blood, comprising:

a main unit having a first memory means for storing the coefficients used in an equation for calculation of the saturation degree of oxygen;

a probe having light emitting means for emitting light to an organism to be measured, light receiving means for receiving light from the organism, and a second memory means for storing the calibration amount of the coefficients stored in said first memory means and corresponds to characteristics of the light emitting means;

means for detachably connecting said probe to said main unit;

said main unit further comprising a calculation means which reads out the calibration amount stored in said second memory means in said probe and calculates the saturation degree of oxygen on the basis of the calibration amount, the output of said light receiving means and the coefficients stored in said first memory means.

28. An oximeter device for measuring the saturation degree of oxygen in arterial blood, comprising:

a main unit having a first memory means for storing a calculation table of the reference saturation degree of oxygen;

a probe having light emitting means for emitting light to an organism to be measured, light receiving means for receiving light from the organism, and a second memory means for storing the calculation amount of the calibration table stored in said first memory means and corresponding to characteristics of the light emitting means, and

means for detachably connecting said probe to said unit,

said main unit further comprising a calculation means which reads out the calibration amount stored in said second memory means in said probe and calculates the saturation degree of oxygen on the basis of the calibration amount, the output of said light receiving means and the coefficients stored in said first memory means.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

The present invention relates to an oximeter device for measuring the oxygen saturation degree in arterial blood.

2. DESCRIPTION OF THE PRIOR ART

There has been proposed a probe calibration device of an oximeter device titled "CALIBRATED OPTICAL OXIMETER PROBE" (referred to as First Prior Example hereinafter) in the U.S. Pat. No. 4,621,643. The first prior example is characterized in that the probe device which is used together with the optical oximeter body for obtaining data of blood of a patient comprises;

light emitting means for emitting light of a known narrow wavelength range, a photosensor for detecting the intensity of the light passed through a patient to be measured, a coding means for applying the data signal of the known narrow wavelength to the optical oximeter body with respect to the probe and a connection device for attachably and removably attaching the coding means, the photosensor and the light emitting means to the oximeter body,

whereby the oximeter body receives the data signal at the coding means so as to determine the frequency of light emitted by the light emitting means, and subsequently calculate the oxygen saturation based on the determined frequency.

There has been proposed a general organism data measuring device (referred to as Second Prior Example hereinafter) in the U.S. Pat. No. 4,418,392. The above mentioned organism data measuring device measures the data of the organism and comprises;

a transducer for measuring an organism data to be required and for converting the organism data into a corresponding electrical data,

a memory means for storing a calibration data calculated in accordance with the reference characteristic of said transducer,

a calibration means for calibrating the converted organism data based on the calibration data,

a reading means for reading out the calibration data stored in the memory means, and

a calibration control means for controlling the reading means to read out the calibration data and selecting a corresponding part of the calibration data to the organism data measured by the transducer, and for controlling the calibration means to calibrate the converted organism data in accordance with the selected part of the calibrated data.

In the above mentioned first prior example, the light of a predetermined wavelength radiated from the light emitting means is applied to the photosensor through the examined organism and the output of the photosensor is processed by a predetermined calculation so as to calculate the oxygen saturation degree Sa0.sub.2 in the arterial blood of the organism. But, for example, in case the light emitting means emit not only the light of a narrow wavelength range but also the light of a comparatively wide wavelength range or emit a light of another wavelength than the main wavelength (referred to as the light of a sub-wavelength), there occurs an error in the calculation value of the oxygen saturation degree Sa0.sub.2. Moreover, in case two light emitting means, for example, are used in order to calculate the oxygen saturation degree Sa0.sub.2 and the light emitting spectrums of the two emitting devices are overlapped with each other, or in case each data of the light emitted by the above mentioned two emitting means is mixed in the process of the calculation of the oxygen saturation degree Sa0.sub.2 and can not be obtained separately at the output of the processing circuit of the above mentioned calculation so that crosstalk exists, there has been a problem that there occurs an error in the calculation value of the oxygen saturation degree Sa0.sub.2.

Furthermore, the latter second prior example comprises a calibration means for performing the calibration process of the calculation data at the time of calculating the data of the organism, but the concrete means or ways of calculating the oxygen saturation degree are not disclosed.

SUMMARY OF THE INVENTION

An essential object of the present invention is to provide an oximeter device which is able to measure the oxygen saturation degree in the arterial blood of an organism to be examined correctly even though there is dispersion of the spectrums of the light emitting devices or there is a crosstalk as mentioned above.

The oximeter device according to the present invention comprises;

a probe device comprising light emitting means, light receiving means and memory means for storing data necessary for the calculation of the oxygen saturation degree in the arterial blood of the examined organism caused by the light emitting means and the light receiving means, and

calculation means for reading out the data signal of the memory means and executing the calculation of the oxygen saturation degree on the basis of the read-out data signal and the output of the light receiving means when the probe device is connected to the oximeter device.

By the arrangement as mentioned above, the data necessary for the calculation of the oxygen saturation degree in the arterial blood of the examined organism caused by the light emitting means and the light receiving means are stored in the memory means and the data stored in the memory means are read out by the calculation means and then the calculation of the oxygen saturation degree is executed on the basis of the read-out data and the output of the light receiving means so as to obtain the oxygen saturation degree.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an embodiment of an oximeter device according to the present invention,

FIG. 2 is a block diagram showing a signal processing circuit of the oximeter device in FIG. 1,

FIG. 3 is a graph diagram showing light emitting spectrum characteristics of a red light emitting diode and an infrared ray emitting diode of the oximeter device in FIG. 1,

FIG. 4 is a diagram showing the data stored in a memory circuit in a probe of the oximeter device in FIG. 1,

FIGS. 5a-5h are a timing chart showing a wave-form of each portion of the signal processing circuit in FIG. 2,

FIG. 6 is a flow chart showing the operation of the oximeter device in FIG. 1,

FIG. 7 is a flow chart showing the operation at the time of measuring the crosstalk in the oximeter body in FIG. 1,

FIG. 8 is a timing chart showing input and output wave-forms of a revision signal generator 51 for measuring the crosstalk in the signal processing circuit in FIG. 2, and

FIGS. 9 and 10 are flow charts showing modification of the operation shown in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, the oximeter device comprises a probe 1 and a main unit 3. The probe 1 is detachably connected to the main unit 3. In the probe 1, there is provided a pair of a red light emitting diode 20 and an infrared ray emitting diode 21 disposed to project a red light and an infrared ray toward an object organism 60 such as a finger to be measured.

The red light emitting diode (referred to as RLED hereinafter) 20 emits red light 71 (see FIG. 3) of the main wavelength such as nearly 660 nm and emitting infrared ray 72 of the sub-wavelength such as 900 nm of which the light intensity is lower than that of the main wavelength light as shown in FIG. 3. The infrared light emitting diode (referred to as IRLED hereinafter) 21 emits an infrared ray 73 of the wavelength of nearly 940 nm. A temperature detecting unit 22 is provided near the RLED 20 and IRLED 21 for generating a signal representing the temperature of RLED 20 or IRLED 21. A probe discrimination generator 24 generates the signal for indicating which of a spot measuring probe or a continuous measuring probe is used. A light receiving element 25 made of a photodiode is disposed at a position opposing to said RLED 20 and IRLED 21 so as to receive the light which is radiated from RLED 20 and IRLED 21 and passed through the organism 60, thereby generating a signal corresponding to the intensity of light passed through the organism 60. Moreover, there are provided a photoelectric converter 37 for converting the output of the light receiving element 25 into a signal of a predetermined level and a non-volatile memory circuit 56 which is connected to a central processing unit (referred to as CPU) 10 in the main unit 3 through a data bus and stores the data of the luminous spectrums of RLED 20 and IRLED 21 and the data of crosstalk amount and sum check data. In the above mentioned embodiment, though the non-volatile memory circuit 56 is connected to CPU 10 via the data bus, both of the devices 10 and 56 may be connected via a single line so as to transfer the data serially.

Moreover, the memory circuit 56 may be made of an EEPROM or EPROM in which the data can be electrically written and erased and may be made by a digital switch. As shown in FIG. 4, the memory circuit 56 stores eleven items with respect to the properties of the light or ray of the RLED 20 and IRLED 21 as follows;

(1) the intensity of the main wavelength light of RLED 20 when a predetermined driving current is supplied,

(2) the intensity of the main wavelength light of IRLED 21 when a predetermined driving current is supplied,

(3) the wavelength of the main wavelength light of RLED 20,

(4) the half width of the main wavelength light of RLED 20,

(5) the wavelength of the sub-wavelength light of RLED 20,

(6) the ratio of the intensity of light of the subwavelength light to that of the main wavelength light of RLED 20,

(7) the wavelength of the light of IRLED 21,

(8) the half width of the light of IRLED 21,

(9) the crosstalk amount caused in case of mixing the light signal of RLED 20 into the processing circuit of the light of IRLED 21 (referred to as crosstalk amount from R channel to IR channel hereinafter) to be described later,

(10) the crosstalk amount caused in case of mixing the light signal of IRLED 21 into the processing circuit of the light of RLED 20 (referred to as crosstalk amount from IR channel to R channel hereinafter) to be described later, and

(11) the sum check data.

The sum check data is so determined that the sum of the data (1) to (11) amounts to a predetermined value. The sum check data is used to detect whether each of the data (1) to (10) is correctly stored or not in the memory circuit 56.

There are provided in the main unit 3 a signal processing circuit 7 for processing the output of the light receiving element 25 in the probe 1 to be described later. A multiplexer 8 selects the output of the signal processing circuit 7, an analogue to digital converter 9 (referred to as A/D converter hereinafter) for converting the analogue output signal of the multiplexer 8 into a digital signal. CPU 10 calculates the oxygen saturation degree Sa0.sub.2 in arterial blood and the pulse rate of the organism 60 and controls a display unit 13 and an operating unit 14, a read only memory (referred to as ROM hereinafter) 11, and a random access memory (referred to as RAM hereinafter) 12. The display unit 13 displays the calculated oxygen saturation degree Sa0.sub.2 in the arterial blood and the pulse rate. The operation unit 14 selects an alarm level and a measuring mode/display mode of the oximeter device. A voice generator 15 generates an alarm sound and the sound of the pulse of the organism. An input-and-output interface 16 sends and receives the data to and from a printer and an external personal computer and generates the wave-form of the pulse. An IC card input and output unit 17 sends and receives the data of the calculation value to and from the IC card 2. 18 denotes a clock portion. A light emitting diode (referred to as LED) driving portion 19 supplies power to RLED 20 and IRLED 21 for turning them on.

The principle of calculating the oxygen saturation degree Sa0.sub.2 in the arterial blood according to the present embodiment will be explained. When the lights of wavelength .lambda..sub.1 and .lambda..sub.2 are radiated to the organism 60, the luminance intensities I.sub.1 and I.sub.2 of the lights of the wavelengths .lambda..sub.1 and .lambda..sub.2 having passed through the organism 60 may be represented as follows;

I.sub.1 =Io.sub.1 .times.Tt.sub.1 .times.exp{-g.sub.1 [(E.sub.1 O-E.sub.1 H) Sa0.sub.2 /100+E.sub.1 H].times.(d+.DELTA.d)] (1)

I.sub.2 =Io.sub.2 .times.Tt.sub.2 .times.exp{-g.sub.2 [(E.sub.2 O-E.sub.2 H).times.Sa0.sub.2 /100+E.sub.2 H].times.(d+.DELTA.d)] (2),

wherein

Io.sub.1 : the intensity of the incident light of wavelength .lambda..sub.1,

Io.sub.2 : the intensity of the incident light of wavelength .lambda..sub.2,

E.sub.1 O: the absorption coefficient of oxyhemoglobin at the wavelength .lambda..sub.1 of the light,

E.sub.2 0: the absorption coefficient of oxyhemoglobin at the wavelength .lambda..sub.2 of the light,

E.sub.1 H: the absorption coefficient of hemoglobin at the wavelength .lambda..sub.1 of the light,

E.sub.2 H: the absorption coefficient of hemoglobin at the wavelength .lambda..sub.2 of the light,

Tt.sub.1 : the transmittance of the tissue other than the arterial blood at the wavelength .lambda..sub.1 of the light,

Tt.sub.2 : the transmittance of the tissue other than the arterial blood at the wavelength .lambda..sub.2 of the light,

d: the averaged thickness of the arterial blood layer,

.DELTA.d: the variable component of the thickness of the arterial blood layer,

Sa0.sub.2 : the oxygen saturation degree in the arterial blood,

g.sub.1, g.sub.2 : the coefficient of the gain.

Assuming that the DC components of the luminances I.sub.1 and I.sub.2 of the lights of each wavelength after passing through the organism 60 are represented by I.sub.1 DC and I.sub.2 DC respectively and the values log(I.sub.1 DC/I.sub.1) and log(I.sub.2 DC/I.sub.2) are represented by U.sub.1 and U.sub.2 respectively, the values U.sub.1 and U.sub.2 may be approximately represented as follows;

U.sub.1 =g.sub.1 [(E.sub.1 O-E.sub.1 H)Sa0.sub.2 /100+E.sub.1 H].DELTA.d(3)

U.sub.2 =g.sub.2 [(E.sub.2 O-E.sub.2 H)Sa0.sub.2 /100+E.sub.2 H].DELTA.d (4)

Moreover, assuming that the values U.sub.1 and U.sub.2 may be obtained as the variable components of the values log I.sub.1 and log I.sub.2 and that the variable components of the intensities of lights I.sub.1 and I.sub.2 are .DELTA.I.sub.1 and .DELTA.I.sub.2, the values U.sub.1 and U.sub.2 may be obtained as the values .DELTA.I.sub.1 /I.sub.1 DC, .DELTA.I.sub.2 /I.sub.2 DC respectively so as to obtain the expressions (3) and (4). Next, from the expressions (3) and (4), the value of the oxygen saturation degree Sa0.sub.2 in the arterial blood may be obtained as follows;

Sa0.sub.2 ={K.sub.1 (U.sub.1 /U.sub.2).sup.2 +K.sub.2 }/{K.sub.3 (U.sub.1 /U.sub.2).sup.2 +K.sub.4 }.times.100 (5)

wherein the numerals K.sub.1, K.sub.2, K.sub.3 and K.sub.4 represent respectively constant values determined by the wavelengths .lambda..sub.1 and .lambda..sub.2. In the present embodiment, the wavelengths of approximately 660 nm and 940 nm are adopted as the wavelengths .lambda..sub.1 and .lambda..sub.2.

The arrangement of the signal processing circuit 7 in the device body 3 according to the present invention is explained with reference to FIG. 2.

In the present embodiment, as described above, as the light sources there are mainly adopted RLED 20 emitting the red light of the wavelength nearly 660 nm and IRLED 21 emitting the infrared ray of the wavelength nearly 940 nm. Each of RLED 20 and IRLED 21 is respectively driven by the LED driving unit 19 which is controlled by the timing pulse generated by an oscillator included in CPU 10. The LED driving unit 19 generates two series of the driving periodic pulses having the same cycle, the phase difference of 90.degree. and the duty ratio 50%. These pulses are fed to RLED 20 and IRLED 21 so as to turn RLED 20 and IRLED 21 on respectively as shown in FIGS. 5(a) and 5(b). The light emitted from RLED 20 and IRLED 21 passes through the organism 60 and are declined and then received by the light receiving element 25, which generates electric current corresponding to the intensity of the incident light and the generated current is converted into voltage through a photoelectric converter 37 and fed to the terminal a.sub.1 of the switch S.sub.1.

In case the device body 3 is set in the measuring mode, the switch S.sub.1 is connected to the terminal a.sub.1 so that the output of the photoelectric converter 37 is amplified through an amplifier 38 and in turn inputted to a R-synchronous rectifier 39 and an IR-synchronous rectifier 40. The R-synchronous rectifier 39 is synchronized with one of the two series of the driving periodic pulses, pulse (a) in FIG. 5 generated from the LED driving unit 19 and rectify the signal of red light inputted from the converter 37. In other words, the R-synchronous rectifier 39 amplifies the input signal by a gain of 1 while RLED 20 emits the light and amplifies the input signal by a gain of -1 while RLED 20 does not emit the light. Similarly, the IR-synchronous rectifier 40 is synchronized with another series of the driving periodic pulses (b) and amplifies the input signal by a gain of 1 while IRLED 21 emits the light and amplifies the input signal by a gain of -1 while IRLED 21 does not emit the light. The time average value of the output of the synchronous rectifiers 40 corresponds to the intensity of the light of only IRLED 21 passed through the organism 60. Therefore, the outputs of a R low-pass filter 41 and an IR low-pass filter 42 corresponds respectively to the intensity of the light of wavelengths around 660 nm and 940 nm having passed through the organism 60. Thus, when a signal of the light of the light receiving element 25 is separated into the signal representing only the light of wavelengths 660 nm and another signal representing the light of 940 nm, the influence of the external disturbance light can be removed by properly selecting the driving frequencies of RLED 20 and IRLED 21.

In FIG. 2, a frequency detecting unit 53 detects the frequency of a commercial power source now in use and CPU 10 sets the driving frequency of RLED 20 and IRLED 21 to nearly (integer times of 60+30)Hz (when the commercial power source frequency is 60 Hz), or nearly (integer times of 50+25)Hz (when the commercial power source frequency is 50 Hz).

Furthermore, the outputs of the R low-pass filter 41 and the IR low-pass filter 42 are converted from analogue form to digital form (referred to as A/D hereinafter) by the A/D converter 9 via the multiplexer 8 and in turn inputted to CPU 10. CPU 10 calculates the ratio of the output of the R low-pass filter 41 to the output of the IR low-pass filter 42 and controls the LED driving unit 19 so that the ratio becomes within a predetermined range, adjusting the intensity of the light of RLED 20 and the intensity of the light of IRLED 21. By these operations, the S/N ratio of the output of the R low-pass filter 41 becomes nearly equal to the S/N ratio of the output of the IR low-pass filter 42 so as to keep a desired condition for processing the signal.

In FIG. 2, CPU 10 controls the gain of the amplifier 38 so that the outputs of the R low-pass filter 41 and the IR low-pass filter 42 are settled within a predetermined range. The output terminal of the IR low-pass filter 42 is connected to the signal line SI for the external output of the device body 3. In addition, the outputs of the R low-pass filter 41 and the IR low-pass filter 42 are respectively connected to a R logarithmic amplifier 43 and an IR logarithmic amplifier 44 and are inputted in the multiplexer 8 respectively via a R high-pass filter 45 and a R high-pass filter 47 and via an IR high-pass filter 46 and an IR high-pass filter 48. Moreover, the outputs of the R high-pass filter 47 and the IR high-pass filter 48 are inputted in the multiplexer 8 via a R inverting amplifier 49 and an IR inverting amplifier 50 respectively. In case the output of the R high-pass filter 47 or the IR high-pass filter 48 is positive, these outputs are converted from an analog form to a digital form by the A/D converter 9 via the multiplexer 8, but in case these outputs are negative, the outputs of the inverting amplifiers 49 and 50 are converted from an analog form to a digital form and applied to CPU 10. In addition, the outputs of the R low-pass filter 41 and the IR low-pass filter 42, the outputs of the R high-pass filter 47 or the R inverting amplifier 49, the outputs of the IR high-pass filter 48 or the IR inverting amplifier 50 are respectively converted from an analog form to a digital form in a predetermined sampling cycle by the A/D converter 9 and transmitted to CPU 10.

Referring to FIG. 3 showing the light emitting spectrum of RLED 20 and IRLED 21 in the probe 1, since RLED 20 emits not only the main wavelength light 71 but also the sub-wavelength light 72 and there inevitably exist dispersions of the wavelength, intensity of emitting light and half width in the spectrum characteristics of RLED 20 and IRLED 21, if the oxygen saturation degree Sa0.sub.2 in the arterial blood is calculated by using the expression (5), there occurs an unnegligible error. This is because when the light of RLED 20 and IRLED 21 is radiated to the organism 60, the intensities I.sub.1 and I.sub.2 of the respective light passing through the organism 60 are strictly represented as follows.

I.sub.1 =.intg.Io.sub.1 (.lambda.).times.T.sub.t (.lambda.).times.exp{-g.sub.1 (EO(.lambda.)-EH(.lambda.)) .times.Sa0.sub.2 /100+EH(.lambda.).times.(d+.DELTA.d)}d.lambda. (6)

I.sub.2 =Io.sub.2 (.lambda.).times.T.sub.t (.lambda.).times.exp{-g.sub.2 (EO(.lambda.)-EH(.lambda.)) .times.Sa0.sub.2 /100+EH(.lambda.).times.(d+.DELTA.d)}d.lambda. (7)

wherein Io.sub.1 (.lambda.): the light emitting spectrum character of RLED 20

Io.sub.2 (.lambda.): the light emitting spectrum character of IRLED 21

T.sub.t (.lambda.): the spectral transmittance of tissue except arterial blood

EO(.lambda.): the spectral absorption coefficient of oxyhemoglobin

EH(.lambda.): the spectral absorption coefficient of hemoglobin

d, .DELTA.d, Sao.sub.2, g.sub.1 and g.sub.2 are same as those in the expression (1).

The oxygen saturation degree Sa0.sub.2 in the arterial blood can be obtained by the calculation of the expression (5) based on the measured value inputted in CPU 10 when there is no error at the time of separating the light signal from RLED 20 and the light signal from IRLED 21 in the R synchronous rectifier 39 and the IR synchronous rectifier 40. However, in case the response speeds of the light receiving element 25, the photoelectric converter 37, the amplifier 38, the R synchronous rectifier 39 and the IR synchronous rectifier 40 are slow compared with the driving frequencies of RLED 20 and IRLED 21, and when the sub-wavelength 900 nm of the light of RLED 20 is near the wavelength 940 nm of IRLED 21 as shown in FIG. 3, the output ARl of the R synchronous rectifier 39 contains the signal representing the light from IRLED 21 as a crosstalk and similarly the output AIRl of the IR synchronous rectifier 40 contains the signal representing the light from RLED 20 as a crosstalk.

For example, in case the response speeds of the light receiving element 25, the photoelectric converter 37, the amplifier 38, the R synchronous rectifier 39 and the IR synchronous rectifier 40 are fast compared with the driving frequencies of RLED 20 and IRLED 21, the output Al of the amplifier 38, the output ARl of the R synchronous rectifier 39 and the output AIRl of the IR synchronous rectifier 40 are changed in respective levels immediately in response to the driving signal of each of RLED 20 and IRLED 21 so that the crosstalk is not produced as shown in FIGS. 5(c), 5(d) and 5(e). However, in case the response speeds of the light receiving element 25, the photoelectric conver