METHOD AND APPARATUS UTILIZING ELECTRICAL RESISTANCE RATIOS DERIVED FROM BLOODLESS AND BLOOD DATA FOR DETERMINING THE PERCENTAGE OXYGEN SATURATION IN BLOOD

• US 3,632,211 A
• Filed: 02/24/1970
• Issued: 01/04/1972
• Est. Priority Date: 02/24/1970
• Status: Expired due to Term

• Current Assignee: George F. Sedivy, William F. Sutterer
• Original Assignee: George F. Sedivy, William F. Sutterer
• Inventors: Sedivy, George F., Sutterer, William F.
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Chew, II, Orville B.
• Application Number:
  US05/013,672
• Time in Patent Office: 679 Days
• Field of Search: 356/39,40,41 250/218,226
• US Class Current: 356/41
• CPC Class Codes: G01J 1/16 using electric radiation detectors G01J1/20 takes precedence
• CPC Class Codes: G01N 21/314 with comparison of measurements at specific and non-specific wavelengths dual wavelength spectrometry G01J3/427

Abstract

Spectral data is obtained with respect to both bloodless and blood specimens. Signals are derived from this data representative of certain ratios and these signals are processed so as to obtain a direct indication of the percentage oxygen saturation without resorting to logarithmic relationships.

Claims

1. A method of determining the amount of oxygen saturation in a blood sample comprising the steps of deriving a signal in accordance with the difference between a first ratio of resistance representative of the amount of red light passing through the blood sample with respect to resistance representative of the amount of infrared light passing through said blood sample and a second ratio of resistance representative of the amount of red light passing through a bloodless sample with respect to resistance representative of the amount of infrared light passing through said bloodless sample, providing another signal in accordance with the ratio of said resistance which is representative of the amount of infrared light passing through said blood sample to said resistance which is representative of the amount of infrared light passing through said bloodless sample minus a constant substantially equal to one, and providing an output signal in accordance with the ratio of said two signals to provide an indication of the percentage oxygen saturation in the blood from which said first two resistances have been determined.

2. A method of providing an indication of the amount of oxygen saturation in a blood sample comprising the steps of passing light through a bloodless sample onto a photoresistive means responsive to infrared light whereby the resistance thereof represents the amount of infrared light transmitted through said bloodless sample, adjusting a variable resistor so that its resistance corresponds to that of said infrared responsive means, passing said light through said bloodless sample onto a photoresistive means responsive to red light whereby the resistance thereof represents the amount of red light transmitted through said bloodless sample, deriving a signal representative of the ratio of said last two resistances which has a value of substantially one owing to the general correSpondence of said resistances, comparing said ratio signal with a known signal having a value of substantially one to provide a signal representative of the difference therebetween having a value of substantially zero and thereby establishing a base level for making the oxygen saturation determination, passing said light through a blood sample onto said infrared responsive means so that the resistance thereof then represents the amount of infrared light transmitted through said blood sample, passing said light through said blood sample onto said photoresistive means responsive to red light whereby the resistance thereof represents the amount of red light transmitted through said blood sample, deriving a signal representative of the ratio of said last-mentioned red resistance with respect to said last-mentioned infrared resistance, and comparing said last-mentioned ratio signal with said first-mentioned ratio signal to obtain a signal which is an indication of the amount of difference between said ratio signals and which is an indication of the amount of oxygen saturation in said blood.

3. An oximeter for determining the amount of oxygen saturation in a blood sample comprising a circuit having first and second input terminals and an output terminal for providing a voltage at its output terminal which represents the ratio of the value of a first resistance when connected to its first input terminal with respect to a second resistance when connected to its second input terminal so that, when said first resistance corresponds to the value of the red photocell blood resistance of said sample and the second resistance corresponds to the value of the infrared photocell blood resistance of said sample, said voltage at said output terminal represents the ratio of said red photocell blood resistance to said infrared photocell blood resistance, means for comparing the voltage at said output terminal with a second voltage to provide a third voltage in accordance with any difference therebetween so that said third voltage is indicative of the amount of oxygen saturation of the blood when said second voltage represents the ratio of red photocell bloodless resistance to infrared photocell bloodless resistance.

4. An oximeter in accordance with claim 3 including potentiometer means for providing said second voltage having a value representative of the ratio of red photocell bloodless resistance to infrared photocell bloodless resistance.

5. An oximeter in accordance with claim 4 including adjustable resistance means connectable to the said second input terminal so that when a resistance corresponding to the infrared photocell bloodless resistance is connected to the first input terminal and the value of said adjustable resistance means varied so that the voltage at said output terminal has a unitary value then said adjustable resistance means provides a stored resistance corresponding to said infrared bloodless resistance, and means for applying a fourth voltage having a unitary value to said comparing means so that when the difference between the voltages being compared is substantially zero then said potentiometer means can be adjusted to store the voltage value which is representative of the ratio of red photocell bloodless resistance to infrared photocell bloodless resistance.

6. An oximeter in accordance with claim 5 in which said comparing means includes an adjustable gain operational amplifier means having a first input terminal connected to the output terminal of said ratio circuit, a ground terminal connectable to said potentiometer means, and an output terminal for providing said third voltage.

7. An oximeter in accordance with claim 6 including a meter connected to the output terminal of said amplifier means for measuring the magnitude of said third voltage.

8. An oximeter in accordance with claim 7 including first, second, third and fourth selector switches each having first, second and third contacts and each having a selector arm mechanically coupled to the sElector arms of the other selector switches, the arm of said first selector switch being connected to the second input terminal of said ratio circuit and the first contact of said first selector switch being connected to said adjustable resistance means, a photocell whose resistance varies inversely with the amount of infrared light impinging thereon, said second and third contacts of said first selector switch being connected to said infrared photocell, the selector arm of said second switch being connected to the first input terminal of said ratio circuit, a photocell whose resistance varies inversely with the amount of red light impinging thereon, said second and third contacts being connected to said red photocell, the selector arm of said third switch being connected to said second input terminal of said operational amplifier, a unitary voltage source means, the first contact of said third switch being connected to said voltage source means and the second and third contacts of said third switch being connected to said potentiometer means, the selector arm of said fourth switch being connected to said meter, the first and second contacts of said fourth switch being connected in circuit with said source means, and the third contact of said fourth switch being connected in circuit with said source means.

9. An oximeter in accordance with claim 8 including an additional adjustable resistance means for adjusting the sensitivity of said meter and an additional potentiometer means for providing an offset voltage, said additional adjustable resistance means and said additional potentiometer means being connected in circuit between the third contact of said fourth switch and said source means.

10. Apparatus for determining the amount of oxygen saturation in blood comprising a light source, a ratio circuit having first and second input terminals and an output terminal for providing an output signal representative of the ratio of signals applied to said input terminals, means for applying a first input signal to said first input terminal representative of the amount of infrared light transmitted through a saline solution from said light source, first adjustable storage means for applying a second input signal to said second input terminal having a predetermined relation to said infrared signal so that the output signal at said output terminal represents a desired ratio, means providing a reference signal having a predetermined relation to the output signal from said ratio circuit and hence having a predetermined relation with respect to said desired ratio, differential amplifier means having first and second input terminals and an output terminal for providing an output signal representative of any algebraic difference between signals applied to its said input terminals, the output terminal of said differential amplifier means providing a second output signal having a desired relation to any difference between the values of said first output signal and said reference signal, means for applying a third input signal to the first input terminal of said ratio circuit representative of the amount of red light transmitted through a sample of blood from said light source, means for applying a fourth input signal to said second input terminal of said ratio circuit representative of the amount of infrared light transmitted through said blood sample from said source whereby a third output signal is provided at the output terminal of said ratio signal which represents the ratio of said third and fourth signals with respect to each other, second adjustable storage means for applying a fifth input signal to the second input terminal of said differential amplifier means having a predetermined relation to said third output signal from said ratio circuit so that said fifth input signal represents the ratio of said third and fourth signals whereby a fourth output signal is provided at the output terminal of said differential amplifier means having a relation indicative of the change in the value of said fourth output signal from said second output signal, said fourth output signal being proportional to the oxygen saturation of said blood sample.

11. Apparatus for determining the amount of oxygen saturation in blood comprising a light source, a first photoelectric cell whose resistance varies inversely with respect to the intensity of infrared light impinging thereon, a second photoelectric cell whose resistance varies inversely with respect to the intensity of red light impinging thereon, ratio circuit means having first and second input terminals and an output terminal, variable gain operational amplifier means having first and second input terminals and an output terminal, an electrical meter connected to the last-mentioned output terminal, means for connecting the first input terminal of said ratio circuit means to said infrared responsive photocell, an adjustable resistor, means for connecting the second input terminal of said ratio circuit means to said adjustable resistor so that said adjustable resistor can be varied to correspond to the particular resistance of said infrared photocell and thereby store the value of said infrared resistance when light from said source is passing through a saline solution, said ratio circuit means then providing an output signal at its said output terminal representative of unity, means for concurrently applying a signal corresponding to said ratio signal of unity to the second input terminal of said operational amplifier means so as to provide a zero output signal at its said output terminal, said meter indicating when the adjustment of said adjustable resistor has produced said zero output signal, means for connecting the first input terminal of said ratio circuit means to said red photoelectric cell, means for connecting the second input terminal of said ratio circuit means to said input terminal of said ratio circuit means so that the output signal at the output terminal of said ratio circuit means then represents the ratio of the red resistance to infrared resistance when a saline solution is passing between said light source and said photocells, a potentiometer, means for connecting the second input terminal of said operational amplifier means to said potentiometer so that the signal applied to the second input terminal of said operational amplifier means can be adjusted to equal the output signal from the output terminal of said ratio circuit means to again provide a zero output signal at the output terminal of said operational amplifier means, said potentiometer recording a resistive value corresponding to the ratio of red to infrared resistive value corresponding to the ratio of red to infrared resistances as determined by said photocells whereby a ratio signal can thereafter be provided which represents the ratio of the resistance of said infrared cell to the value stored on said adjustable resistor and any difference between said ratio signal and said unity signal applied to the second input terminal of said operational amplifier means will provide an output signal at the output terminal of said operational means which can be reduced to a predetermined level by controlling the gain of said operational amplifier means as observed by the reading of said meter and thereafter a ratio signal provided by said ratio circuit means which represents the ratio of the red resistance to infrared resistance when blood is passing between the light source and said photocells and any difference between said last-mentioned ratio signal and the stored ratio signal on said potentiometer providing an output signal at said output terminal of the operational amplifier means which causes said meter to indicate the percentage of oxygen saturation.

12. Apparatus for determining the amount of oxygen saturation in blood comprising first means responsive to light energy in the infrared portion of the light spectrum, second means responsive to light energy in the red portion of the light spectrum, first, second, third and fourth switches eacH having first, second and third contacts and each having a selector arm, adjustable resistance means connected in circuit with the first contact of said first switch, said second and third contacts of said first switch and said first contact of said second switch being connected in circuit with said first light responsive means whereby said adjustable resistance means can be adjusted to apply an electrical signal to the first contact of said first switch corresponding to the value of the electrical signal being applied to said first contact of said second switch means, a ratio circuit having first and second input terminals and an output terminal, said first input terminal being connected to the arm of said first switch, said second input terminal being connected to the arm of said second switch and said output terminal providing an output signal representing the ratio of the resistances in circuit with the first contacts of said first and second switches, means in circuit with the first contact of said first and second switches, means in circuit with the first contact of said third switch for applying an electrical signal of constant value to the first contact of said third switch, an operational amplifier means having first and second input terminals and an output terminal, said first input terminal of said operational amplifier means being connected to the output terminal of said ratio circuit, said second input terminal of said operational amplifier means being connected to the first contact of said first switch and said output terminal of said operational amplifier means providing an output signal representative of any difference between the electrical signals applied to the first and second input terminals thereof, a potentiometer having an adjustable wiper arm, the second and third contacts of said second switch being connected to said second light responsive means and said second and third contacts of said third switch being connected in circuit with said wiper arm so as to store an electrical signal corresponding to the ratio of the resistive signals applied to the second contacts of said first and second switches by said second and first light responsive means when the arms of said second and first switches are engaged with the second contacts of said second and first switches, and measuring means connected between the output terminal of said operational amplifier means and the arm of said fourth switch, said first and second contacts of said fourth switch being connected in circuit with the power supply for said ratio circuit and said operational amplifier, second adjustable resistance means, a second potentiometer having a wiper arm, said second adjustable resistance means and said second wiper arm being connected in series with the third contact of said fourth switch.