BLOOD OXYGENATION SENSOR WITH LED CURRENT MODULATION

• US 20170265794A1
• Filed: 03/17/2016
• Published: 09/21/2017
• Est. Priority Date: 03/17/2016
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Analog Devices Global Unlimited Company (Analog Devices, Inc.)
• Inventors: O'Donnell, John Jude, Maravilla, Javier Calpe, Lyden, Colin G., O'Dwyer, Thomas G.
• Granted Patent: US 10,582,887 B2
• Time in Patent Office: Days
• CPC Class Codes: A61B 2562/0238 Optical sensor arrangements for performing transmission measurements on body tissue
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/318 Heart-related electrical modalities, e.g. electrocardiography [ECG]
• CPC Class Codes: A61B 5/7292 Prospective gating, i.e. predicting the occurrence of a physiological event for use as a synchronisation signal

Abstract

A blood oxygenation sensor is provided comprising: a first current-powered light source to produce light having a first wavelength; a second current-powered light source to produce light having a second wavelength; a light sensor to produce a current signal having a magnitude that is indicative of intensity of light incident upon it; a current level driver circuit that includes a current source configured to couple the current source to alternatively provide current to one of the first current-powered light source and the second light current-powered light source; a processor configured to predict times of occurrence of one or more first time intervals in which arterial volume at a tissue site is at one of a maximum and a minimum; wherein the processor is configured to control the current source, to provide a first pattern of higher power-dissipation current pulses to the first and second current-powered light sources during the first time intervals, and to provide a second pattern of lower power-dissipation current pulses to at least one of the first and second current-powered light sources during second time intervals.

Claims

1. A blood oxygenation sensor comprising:

a first current-powered light source to produce light having a first wavelength;

a second current-powered light source to produce light having a second wavelength;

a light sensor to produce a current signal having a magnitude that is indicative of intensity of light incident upon it;

a current level driver circuit that includes at least one current source configured alternatively provide current to one of the first current-powered light source and the second light current-powered light source;

a processor configured,

to predict times of occurrence of one or more first time intervals in which arterial volume at a tissue site is at one of a maximum and a minimum based at least in part upon magnitude of current stimulated b the light sensor in response to light that transmitted through the tissue site and that is incident upon the light sensor during one or more second time intervals in which the arterial volume at the tissue medium site is between the minimum and maximum values, wherein the incident light during the second time intervals is produced by at least one of the first and second current-powered light sources in response to a second pattern of lower power-dissipation current pulses; and

to control the current source,

to provide a first pattern of higher power-dissipation current pulses to the first and second current-powered light sources during the first time intervals, and

to provide a second pattern of lower power-dissipation current pulses to at least one of the first and second current-powered light sources during second time intervals.

2. The sensor of claim 1,

wherein the processor is configured to determine a blood oxygenation level based at least in part upon magnitude of current stimulated by the light sensor in response to light incident upon it during the first time intervals, wherein the light incident upon the light sensor during the first time intervals is produced by the first and second current-powered light sources in response to the first pattern of higher power-dissipation current pulses, and wherein the incident light during the first time intervals has passed through the tissue site.

3. The sensor of claim 1,

wherein the processor is configured to determine a blood oxygenation level as a function of magnitude of current stimulated by the light sensor in response to light incident upon it during the first time intervals and an average magnitude current stimulated by the light sensor in response to light incident upon it during the first and second time intervals.

4. The sensor of claim 1,

wherein the first current-powered light source includes a red LED;

and

wherein the second current-powered light source includes an IR LED.

5. The sensor of claim 1,

wherein the light sensor includes a photodiode.

6. The sensor of claim 1,

wherein the current level driver circuit is configured to provide a selectable current level.

7. The sensor of claim 1,

wherein the processor is configured to predict times of occurrence of one or more first time intervals in which arterial volume at the tissue site is at one of the maximum and a minimum based at least in part upon magnitude of current stimulated by the light sensor indicating that the arterial volume at the tissue site has reached a threshold volume.

8. The sensor of claim 1,

wherein the processor is configured to predict times occurrence of one or more first time intervals in which arterial volume at the tissue site is at one of the maximum and a minimum based at least in part upon morphology of the arterial volume waveform.

9. The sensor of claim 1,

wherein the processor is configured to predict times occurrence of one or more first time intervals in which arterial volume at the tissue site is at one of the maximum and a minimum based at least in part upon a linear prediction based upon previous times of occurrence of maximums and a minimums.

10. The sensor of claim 1,

wherein the processor is configured to predict times occurrence of one or more first time intervals in which arterial volume at the tissue site is at one of the maximum and a minimum based at least in part upon at least a portion of an ECG signal.

11. The sensor of claim 1,

wherein the processor is configured to control the current source,

to provide the first pattern of higher power-dissipation current pulses at a higher level frequency to the first and second current-powered light sources during the first time intervals, and

to provide the second pattern of lower power-dissipation current pulses at a lower level frequency to the at least one of the first and second current-powered light sources during second time intervals.

12. The sensor of claim 1,

wherein the processor is configured to control the current source,

to provide the first pattern of higher power-dissipation current pulses with a higher current level to the first and second current-powered light sources during the first time intervals, and

to provide the second pattern of lower power-dissipation current pulses with a lower current level to the at least one of the first and second current-powered light sources during second time intervals.

13. The sensor of claim 1,

wherein the processor is configured to control the current source,

to provide the first pattern of higher power-dissipation current pulses with a higher current level and with a higher frequency to the first and second current-powered light sources during the first time intervals, and

to provide the second pattern of lower power-dissipation current pulses with a lower current level and with a lower frequency to the at least one of the first and second current-powered light sources during second time intervals.

14. The sensor of claim 1 further including:

a converter circuit to convert the light source current signal to a light source voltage signal; and

an ADC circuit coupled to convert the light source voltage signal to a digital signal;

wherein the processor is configured to predict times of occurrence and to control the current source in response to the digital signal.

15. The sensor of claim 1,

wherein the processor produces a digital feedback signal to control the the current source in response to the digital feedback signal;

further including;

a DAC circuit coupled to convert the digital feedback signal to an analog feedback signal;

wherein the current level driver is configured to alternatively provide current to one of the first current-powered light source and the second light current-powered light source in response to the analog feedback signal.

16. A blood oxygenation sensor comprising:

a first current-powered source of light having a first wavelength, disposed to shine the light having the first wavelength onto a tissue site;

a second current-powered source of light having a second wavelength, disposed to shine the light having the second wavelength upon the tissue site;

a light sensor to produce a current signal having a magnitude that is indicative of intensity of light incident upon it, wherein the light sensor is disposed to receive incident light from the first and second light source after the incident light has passed through the tissue site during first time intervals; and

wherein the light sensor is disposed to receive incident light from at least one of the first and second light sources after the incident light has transmitted through the tissue site during second time intervals;

a current level driver circuit that includes a current source to alternatively provide current to one of the first current-powered light source and the second light current-powered light source;

a processor configured,

to predict times of occurrence of one or more first time intervals in which arterial volume at a tissue site is at one of a maximum and a minimum based at least in part upon magnitude of current stimulated by the light sensor in response to light incident upon the light sensor during one or more second time intervals in which the arterial volume at the tissue medium site is between the minimum and maximum values, wherein the incident light during the second time intervals is produced by at least one of the first and second current-powered light sources in response to a second pattern of lower power-dissipation current pulses; and

to control the current source,

to provide a first pattern of higher power-dissipation current pulses to the first and second current-powered light sources during the first time intervals, and

to provide a second pattern of lower power-dissipation current pulses to at least one of the first and second current-powered light sources during the second time intervals.

17. For use with a blood oxygenation sensor that includes LED circuitry and a photodiode, a method comprising:

producing a first pattern of higher power-dissipation current pulses in the LED circuitry during time intervals while an arterial volume at a tissue medium site is at a maximum and during first time intervals while the arterial volume at the tissue medium site is at a minimum;

producing a second pattern of lower power-dissipation current pulses in the LED circuitry during second time intervals while the arterial volume at the tissue medium site is between minimum and maximum values;

determining a blood oxygenation measurement based at least in part upon current stimulated in the photodiode in response to light that is emitted by the LED circuitry in response to the first pattern of current pulses and that passes through the tissue medium site before reaching the photodiode; and

predicting times of occurrence of the arterial volume maximums and minimums based at least in part upon current stimulated in the photodiode in response to light that is emitted by the LED in response to the second pattern of current pulses and that passes through the tissue medium site before reaching the photodiode.

18. The method of claim 17,

wherein producing the first pattern of higher power-dissipation current pulses includes producing pulses at a higher level frequency to the first and second current-powered light sources during the first time intervals;

and

wherein producing the second pattern of lower power-dissipation current pulses includes producing pulses at a lower level frequency to the at least one of the first and second current-powered light sources during second time intervals.

19. The method of claim 17,

wherein producing the first pattern of higher power-dissipation current pulses includes producing pulses with a higher current level to the first and second current-powered light sources during the first time intervals;

and

wherein producing the second pattern of lower power-dissipation current pulses includes producing pulses with a lower current level to the at least one of the first and second current-powered light sources during second time intervals.

20. The method of claim 17,

wherein producing the first pattern of higher power-dissipation current pulses includes producing higher current level and with a higher frequency to the first and second current-powered light sources during the first time intervals;

and

wherein producing the second pattern of lower power-dissipation current pulses includes producing lower current level and with a lower frequency to the at least one of the first and second current-powered light sources during second time intervals.