Data processing systems and methods for pulse oximeters

• US 5,692,505 A
• Filed: 04/25/1996
• Issued: 12/02/1997
• Est. Priority Date: 04/25/1996
• Status: Expired due to Term

• Current Assignee: Spacelabs Healthcare LLC (OSI Systems Incorporated)
• Original Assignee: Spacelabs Medical Incorporated (OSI Systems Incorporated)
• Inventors: Fouts, James Michael
• Primary Examiner(s): Bahr, Jennifer
• Assistant Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US08/641,993
• Time in Patent Office: 586 Days
• Field of Search: 128/633, 128/664, 128/665, 128/666, 128/667, 356/39, 356/40, 356/41
• US Class Current: 600/336
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters

Abstract

An improved circuit for processing the received signals of a pulse oximeter includes at least first and second light-emitting diodes for transmitting light of first and second frequencies toward the finger of a user. The first diode is responsive to a first control signal for transmitting light of the first frequency. The second diode is responsive to a second control signal for transmitting light of the second frequency. Also, the first diode is responsive to a modulated control signal for transmitting a modulated light signal also of the first frequency. A photodetector is constructed to receive a first composite signal, representing the amount of light transmitted by the first diode in response to the first control signal, and a second composite signal, representing the amount of light transmitted by the second diode in response to the second control signal, wherein the first and second composite signals each include a desired signal portion and an undesired signal portion. The photodetector also receives a noise signal representing the amount of light transmitted through the finger by the first diode in response to the modulated control signal. The first and second composite signals are adaptively combined with the noise signal to provide the desired signal portion of the first and second signals, wherein the ratio of the desired signal portions represent the red to infrared ratio of the pulse oximeter. The red to infrared ratio of the pulse oximeter is combined with the second composite signal to provide the modulated control signal.

Claims

1. An improved circuit for use with a pulse oximeter to determine a signal ratio, wherein the signal ratio is used to determine the oxygen saturation levels of a blood sample, said circuit comprising:

light-emitting means responsive to first and second control signals for emitting light signals of respective first and second frequencies, said light-emitting means being further responsive to a modulation signal for emitting a modulated light signal of the first frequency;

light detector means for providing first and second composite signals respectively indicative of the amount of light received from the first and second light signals, wherein the first and second composite signals each include a desired signal portion and a noise signal portion, said light detector means also for providing a noise signal indicative of the amount of light received from the modulated light signal; and

data processing means for combining the first composite signal with the noise signal to provide a first desired signal and for combining the second composite signal with the noise signal to provide a second desired signal, said data processing means also determining the signal ratio wherein the signal ratio is a ratio of the magnitudes of the first and second desired signals, said data processing means further combining the signal ratio and the second composite signal to provide the modulation signal, said data processing means also providing the first and second control signals.

2. The improved circuit as recited in claim 1 wherein said data processing means further comprises adaptive noise canceler means responsive to the first composite signal and the noise signal for removing the noise signal portion from the first composite signal to provide the first desired signal and responsive to the second composite signal and the noise signal for removing the noise signal portion from the second composite signal to provide the second desired signal.

3. The improved circuit as recited in claim 1 wherein said light-emitting means further comprises:

a first light-emitting diode responsive to the first control signal for emitting light of the first predetermined frequency; and

a second light-emitting diode responsive to the second control signal for emitting light of the second predetermined frequency.

4. An improved pulse oximeter for measuring the oxygen content of a blood sample of a user, comprising:

a first light-emitting diode responsive to a first control signal for emitting light of a first predetermined frequency, said first light-emitting diode being constructed to be positioned proximate the user to emit light of the first predetermined frequency toward the user;

a second light-emitting diode responsive to a second control signal and a modulated control signal for emitting light of a second predetermined frequency, said second light-emitting diode being constructed to be positioned proximate the user to emit light of the second predetermined frequency toward the user;

photodetector means for providing first and second composite signals respectively indicative of the amount of light received from said first light-emitting diode in response to the first control signal and from said second light-emitting diode in response to the second control signal, wherein the first and second composite signals each include a desired signal portion and a noise signal portion, said photodetector means also for providing a noise signal indicative of the amount of light received from said first light-emitting diode in response to the modulated control signal;

adaptive noise canceler means responsive to the first composite signal and the noise signal for removing the noise signal portion from the first composite signal to provide a first desired signal and responsive to the second composite signal and the noise signal for removing the noise signal portion from the second composite signal to provide a second desired signal;

data processing means for determining a signal ratio and for determining the percentage of oxygen in the user'"'"'s blood wherein the signal ratio is a ratio of the magnitudes of the first and second desired signals, said data processing means being further constructed to combine the signal ratio and the second composite signal to provide a modulation signal, said data processing means also being constructed to provide the first and second control signals and a third control signal;

signal combining means for combining the third control signal and the modulation signal to provide the modulated control signal; and

display means responsive to said data processing means for displaying the percentage of oxygen in the user'"'"'s blood.

5. The improved pulse oximeter as recited in claim 4 wherein said photodetector means further comprises signal processing means for removing undesired portions of the frequency spectrum of the first and second composite signals and the noise signal.

6. The improved pulse oximeter as recited in claim 4 wherein said photodetector means further comprises analog to digital conversion means for converting the first and second composite signals and the noise signal into respective digital signals.

7. The improved pulse oximeter as recited in claim 4 wherein said photodetector means further comprises direct current signal processing means for removing the direct current component of the second composite signal and the noise signal, said direct current signal processing means also for removing the direct current component of the first composite signal and for normalizing the first composite signal with the direct current components of the first and second composite signals.

8. The improved pulse oximeter as recited in claim 4 wherein said data processing means further comprises memory means for storing a lookup table for correlating values of the signal ratio to the percentage of oxygen in a user'"'"'s blood.

9. The improved pulse oximeter as recited in claim 4 wherein said signal combining means further comprises a digital to analog converter coupled to receive the modulation signal and constructed to convert the modulation signal to an analog signal.

10. The improved pulse oximeter as recited in claim 4 wherein said signal combining means further comprises a multiplexer for multiplexing the second control signal and the modulated control signal to said first light-emitting diode.

11. An improved pulse oximeter for measuring the oxygen saturation levels of a blood sample of a user, comprising:

a first light-emitting diode responsive to a first control signal and a modulated control signal for emitting light of a first predetermined frequency, said first light-emitting diode being constructed to be positioned proximate the user to emit light of the first predetermined frequency toward the user;

a second light-emitting diode responsive to a second control signal for emitting light of a second predetermined frequency, said second light-emitting diode being constructed to be positioned proximate the user to emit light of the second predetermined frequency toward the user;

a photodetector for detecting the light emitted by the first and second light-emitting diodes, said photodetector including an output and providing first, second, and third light detector output signals, the first light detector output signal being associated with light received from said first light-emitting diode in response to the first control signal, the second photodetector output being associated with light received from said second light-emitting diode in response to the second control signal, and the third light detector output signal being associated with light received from said first light-emitting diode in response to the modulated control signal;

first, second, and third analog to digital converters coupled to receive the first, second, and third photodetector output signals, respectively, said first, second, and third analog to digital converters being constructed to convert the first, second, and third photodetector output signals to respective first, second and third digital signals wherein the first digital signal is associated with light received from said first light-emitting diode in response to the first control signal, the second digital signal is associated with light received from said second light-emitting diode in response to the second control signal, and the third digital signal is associated with light received from said first light-emitting diode in response to the modulated control signal;

direct current signal processing means for removing the direct current component of the first, second, and third digital signals, said direct current signal processing means being further constructed to normalize the first digital signal with the direct current components of the first and second digital signals, said direct current signal processing means providing the normalized first digital signal with the direct current component removed as the first composite signal, the second digital signal with the direct current component removed as the second composite signal, and the third digital signal with the direct current component removed as the noise signal, wherein the first and second composite signals each include a desired signal portion and a noise signal portion;

first and second adaptive noise canceler means, said first adaptive noise canceler means being responsive to the first composite signal and the noise signal for removing the noise signal portion from the first composite signal to provide a first desired signal, said second adaptive noise canceler means being responsive to the second composite signal and the noise signal for removing the noise signal portion from the second composite signal to provide a second desired signal;

memory means for storing a lookup table for correlating values of a signal ratio to the percentage of oxygen in a user'"'"'s blood;

data processing means for determining the signal ratio wherein the signal ratio is a ratio of the magnitudes of the first and second desired signals, said data processing means being further responsive to said memory means for determining the oxygen saturation level of the blood sample of the user, said data processing means being further constructed to combine the signal ratio and the second composite signal to provide a digital modulation signal, said data processing means also being constructed to sequentially provide the first control signal, the second control signal, and a third control signal;

a digital to analog converter coupled to receive the digital modulation signal and constructed to convert the digital modulation signal to an analog modulation signal and provide the analog modulation signal as its output;

a signal combiner for combining the analog modulation signal with the third control signal to provide the modulated control signal;

first, second, and third signal drivers for receiving the first, second and modulated control signals, respectively, and for supplying adequate power to the first, second, and modulated control signals to drive said first and second light-emitting diodes;

a multiplexer for multiplexing the first control signal and the modulated control signal to said first light-emitting diode; and

display means responsive to said data processing means for displaying the percentage of oxygen in the user'"'"'s blood sample.

12. An improved method for determining a signal ratio, wherein the signal ratio is combined with pulse oximetry lookup tables to determine the oxygen content of blood, the blood being positioned in a medium, said method comprising the steps of:

transmitting first and second light signals of respective first and second frequencies toward the medium;

transmitting a modulated light signal of the second frequency toward the medium, wherein the modulated light signal is a light signal of the second frequency modulated by a modulation signal;

detecting first and second composite signals respectively indicative of the amount of light transmitted through the medium by the first and second light signals, wherein the first and second composite signals each include a desired signal portion and a noise portion;

detecting a noise signal indicative of the amount of light transmitted though the blood by the modulated light signal;

combining the first composite signal with the noise signal to provide a first desired signal;

combining the second composite signal with the noise signal to provide a second desired signal;

determining the signal ratio as the ratio of the magnitudes of the first and second desired signals; and

combining the signal ratio and the first composite signal to provide the modulation signal.

13. The method as recited in claim 12 wherein said step of combining the first composite signal with the noise signal to provide a first desired signal comprises the substep of adaptively processing the first composite signal with the noise signal to remove the noise portion from the composite signal.