Circuitry to allow low current operation of a device capable of determining a blood property

• US 9,743,868 B2
• Filed: 11/20/2014
• Issued: 08/29/2017
• Est. Priority Date: 11/20/2014
• Status: Active Grant

• Current Assignee: Philips Healthcare Informatics Incorporated (Koninklijke Philips N.V.)
• Original Assignee: Qualcomm, Inc.
• Inventors: Ballam, Robert Scott, Ganton, Robert Bruce
• Primary Examiner(s): Winakur, Eric
• Assistant Examiner(s): Fardanesh, Marjan
• Application Number:
  US14/549,167
• Publication Number:
  US 20160143566A1
• Time in Patent Office: 1,013 Days
• CPC Class Codes: A61B 2560/0204 of power management
• CPC Class Codes: A61B 2560/0214 of power generation or supply
• CPC Class Codes: A61B 2560/0412 Low-profile patch shaped housings
• CPC Class Codes: A61B 2562/0238 Optical sensor arrangements for performing transmission measurements on body tissue
• CPC Class Codes: A61B 2562/164 the sensor is mounted in or on a conformable substrate or carrier
• CPC Class Codes: A61B 5/02427 Details of sensor
• CPC Class Codes: A61B 5/02438 with portable devices, e.g. worn by the patient
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/6816 Ear lobe
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence
• CPC Class Codes: A61B 5/7292 Prospective gating, i.e. predicting the occurrence of a physiological event for use as a synchronisation signal

Abstract

Systems, methods, and devices of the various embodiments provide a device capable of determining a blood property based at least in part on the measurement of the amount of light received by a receiver circuit with a limited current capacity by charging a capacitor with a low voltage power supply and intermittently discharging the capacitor through a light emitting diode. In some embodiments the device may be a pulse oximeter capable of taking blood oxygen readings. In some embodiments the device may be a heart rate monitor to determine a heart rate based on an amount of light passed through tissue. The various embodiments may enable pulse oximeters and/or heart rate monitors to be incorporated into small unobtrusive body patches, while enabling the pulse oximeters to operate from a power output equivalent to that of a small coin cell battery or printed cell battery.

Claims

1. A device, comprising:

a capacitor configured to be charged by a low voltage power source;

at least one light-emitting diode (LED) connected to the capacitor by a switch;

a receiver circuit configured to measure light emitted by the at least one LED after the light passes through tissue of a patient, wherein the receiver circuit comprises a first photodetector; and

a processor connected to the switch and the receiver circuit, wherein the processor is configured with processor executable instructions to perform operations comprising;

determining a time of a pulse maxima and a time of a pulse minima based on measurements of light received by the first photodetector of the receiver circuit;

determining a derivative estimate of a sampled pulse curve of a group of pulse measurements taken at the determined time of the pulse maxima, wherein the group of pulse measurements are based on the measurements of light received by the first photodetector of the receiver circuit;

adjusting a time delay between the determined time of the pulse maxima and the determined time of the pulse minima based on the determined derivative estimate of the sampled pulse curve of the group of pulse measurements taken at the determined time of the pulse maxima;

controlling the switch to provide charge from the capacitor to the at least one LED to cause the at least one LED to emit light at the expiration of the adjusted time delay;

controlling the switch to isolate the capacitor from the at least one LED to cause the at least one LED to stop emitting light after a period of time;

measuring an amount of light received by the receiver circuit after the period of time; and

determining a blood property based at least in part on the measurement of the amount of light received by the receiver circuit after the period of time.

2. The device of claim 1, wherein the processor is configured with processor-executable instructions to perform operations such that determining the blood property based at least in part on the measurement of the amount of light received by the receiver circuit after the period of time comprises determining a heart rate based at least in part on the measurement of the amount of light received by the receiver circuit after the period of time.

3. The device of claim 1, wherein the processor is configured with processor-executable instructions to perform operations such that determining the blood property based at least in part on the measurement of the amount of light received by the receiver circuit after the period of time comprises determining a blood oxygen level based at least in part on the measurement of the amount of light received by the receiver circuit after the period of time.

4. The device of claim 3, wherein the processor is configured with processor-executable instructions to perform operations further comprising:

determining when the capacitor is charged by the low voltage power source to a predetermined voltage; and

controlling the switch to provide charge from the capacitor to the at least one LED to cause the at least one LED to emit light in response to determining the capacitor is charged by the low voltage power source to a predetermined voltage.

5. The device of claim 3, wherein the processor is configured with processor executable instructions to perform operations such that:

determining the blood oxygen level based at least in part on the measured amount of light received by the receiver circuit after the period of time comprises determining a blood oxygen level and a pulse waveform measurement based at least in part on the measured amount of light received by the receiver circuit after the period of time.

6. The device of claim 5, wherein the processor is configured with processor executable instructions to perform operations such that determining the time of the pulse maxima and the time of the pulse minima based on measurements of light received by the first photodetector of the receiver circuit comprises:

determining a local maxima of a sampled pulse curve of the group of pulse measurements based upon a derivative estimate of the sampled pulse curve;

determining a pulse rate and timing based on the determined local maxima of the sampled pulse curve of the group of pulse measurements; and

determining the time of the pulse maxima and the time of the pulse minima based on the determined pulse rate and timing and the determined local maxima.

7. The device of claim 3, wherein the at least one LED is two different LEDs, and wherein the two different LEDs each emit light of different wavelengths.

8. The device of claim 7, wherein the two LEDs comprise one red LED and one infrared LED.

9. The device of claim 1, wherein the low voltage source is a coin cell battery or a printed cell battery.

10. A method of measuring a blood property of a patient, comprising:

determining a time of a pulse maxima and a time of a pulse minima based on measurements of light received by a first photodetector of a receiver circuit;

determining a derivative estimate of a sampled pulse curve of a group of pulse measurements taken at the determined time of the pulse maxima, wherein the group of pulse measurements are based on the measurements of light received by the first photodetector of the receiver circuit;

adjusting a time delay between the determined time of the pulse maxima and the determined time of the pulse minima based on the determined derivative estimate of the sampled pulse curve of the group of pulse measurements taken at the determined time of the pulse maxima;

charging a capacitor with a low voltage power source;

connecting the capacitor to a light-emitting diode (LED) positioned to transmit light into tissue of the patient at the expiration of the adjusted time delay;

isolating the capacitor from the LED to cause the LED to stop emitting light after a period of time;

measuring an amount of light passing through the tissue of the patient received by the receiver circuit after the period of time; and

determining a blood property based at least in part on the measurement of the amount of light after the period of time.

11. The method of claim 10, wherein determining a blood property based at least in part on the measurement of the amount of light after the period of time comprises determining a heart rate based at least in part on the measurement of the amount of light after the period of time.

12. The method of claim 10, wherein determining the blood property based at least in part on the measurement of the amount of light after the period of time comprises determining a blood oxygen level based at least in part on the measurement of the amount of light after the period of time.

13. The method of claim 12, further comprising:

determining when the capacitor is charged by the low voltage power source to a predetermined voltage;

disconnecting the capacitor from the low voltage power source in response to determining that the capacitor is charged by the low voltage power source to a predetermined voltage; and

connecting the capacitor to a light-emitting diode (LED) positioned to transmit light into tissue of the patient in response to determining the capacitor is charged by the low voltage power source to a predetermined voltage.

14. The method of claim 13, wherein:

determining the blood oxygen level based at least in part on the measurement of the amount of light after the period of time comprises determining a blood oxygen level and a pulse waveform measurement based at least in part on the measurement of the amount of light after the period of time.

15. The method of claim 14, wherein determining the time of the pulse maxima and the time of the pulse minima based on measurements of light received by the first photodetector of the receiver circuit comprises:

determining a local maxima of a sampled pulse curve of the group of pulse measurements based upon a derivative estimate of the sampled pulse curve;

determining a pulse rate and timing based on the determined local maxima of the sampled pulse curve of the group of pulse measurements; and

determining the time of the pulse maxima and the time of a pulse minima based on the determined pulse rate and timing and the determined local maxima.

16. The method of claim 10, wherein the low voltage source is a coin cell battery or a printed cell battery.

17. A device, comprising:

means for determining a time of a pulse maxima and a time of a pulse minima based on measurements of light received by a first photodetector of a receiver circuit;

means for determining a derivative estimate of a sampled pulse curve of a group of pulse measurements taken at the determined time of the pulse maxima, wherein the group of pulse measurements are based on the measurements of light received by the first photodetector of the receiver circuit;

means for adjusting a time delay between the determined time of the pulse maxima and the determined time of the pulse minima based on the determined derivative estimate of the sampled pulse curve of the group of pulse measurements taken at the determined time of the pulse maxima;

means for charging a capacitor with a low voltage power source;

means for connecting the capacitor to a light-emitting diode (LED) positioned to transmit light into tissue of a patient at the expiration of the adjusted time delay;

means for isolating the capacitor from the LED to cause the LED to stop emitting light after a period of time;

means for measuring an amount of light passing through the tissue of the patient received by the receiver circuit after the period of time; and

means for determining a blood property based at least in part on the measurement of the amount of light after the period of time.

18. The device of claim 17, wherein means for determining the blood property based at least in part on the measurement of the amount of light after the period of time comprises means for determining a heart rate based at least in part on the measurement of the amount of light after the period of time.

19. The device of claim 17, wherein means for determining the blood property based at least in part on the measurement of the amount of light after the period of time comprises means for determining a blood oxygen level based at least in part on the measurement of the amount of light after the period of time.

20. The device of claim 19, further comprising:

means for determining when the capacitor is charged by the low voltage power source to a predetermined voltage; and

means for connecting the capacitor to a light-emitting diode (LED) positioned to transmit light into tissue of the patient in response to determining the capacitor is charged by the low voltage power source to a predetermined voltage.

21. The device of claim 20, wherein:

means for determining the blood oxygen level based at least in part on the measurement of the amount of light after the period of time comprises means for determining a blood oxygen level and a pulse waveform measurement based at least in part on the measurement of the amount of light after the period of time.

22. The device of claim 21, wherein means for determining the time of the pulse maxima and the time of the pulse minima based on measurements of light received by the first photodetector of the receiver circuit comprises:

means for determining a local maxima of a sampled pulse curve of the group of pulse measurements based upon a derivative estimate of the sampled pulse curve;

means for determining a pulse rate and timing based on the determined local maxima of the sampled pulse curve of the group of pulse measurements; and

means for determining the time of the pulse maxima and the time of a pulse minima based on the determined pulse rate and timing and the determined local maxima.

23. The device of claim 17, wherein the low voltage source is a coin cell battery or a printed cell battery.

24. A non-transitory processor readable medium having stored thereon processor executable instructions configured to cause a processor to perform operations, comprising:

determining a time of a pulse maxima and a time of a pulse minima based on measurements of light received by a first photodetector of a receiver circuit;

determining a derivative estimate of a sampled pulse curve of a group of pulse measurements taken at the determined time of the pulse maxima, wherein the group of pulse measurements are based on the measurements of light received by the first photodetector of the receiver circuit;

adjusting a time delay between the determined time of the pulse maxima and the determined time of the pulse minima based on the determined derivative estimate of the sampled pulse curve of the group of pulse measurements taken at the determined time of the pulse maxima;

charging a capacitor with a low voltage power source;

connecting the capacitor to a light-emitting diode (LED) positioned to transmit light into tissue of a patient at the expiration of the adjusted time delay;

isolating the capacitor from the LED to cause the LED to stop emitting light after a period of time;

measuring an amount of light passing through the tissue of the patient received by the receiver circuit after the period of time; and

determining a blood property based at least in part on the measurement of the amount of light after the period of time.