Pulse Oximeter With Alternate Heart-Rate Determination

• US 20090221889A1
• Filed: 05/07/2009
• Published: 09/03/2009
• Est. Priority Date: 03/08/2004
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Inventors: Baker, Clark R. JR.
• Granted Patent: US 8,007,441 B2
• Time in Patent Office: Days
• US Class Current: 600/324
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence

Abstract

A pulse oximeter which determines multiple heart rates, and selects between them based on the metrics of only one of the heart rate calculations. A primary heart rate calculation method is selected, and is used unless its metrics indicate questionable accuracy, in which case an alternative rate calculation is available and is used instead.

Claims

1. A method for determining a heart rate in a pulse oximeter comprising:

using a processor;

determining a first heart rate from a pulse oximetry signal using a first method;

determining a second heart rate from the pulse oximetry signal using a second method;

evaluating a reliability of the first heart rate using metrics applied to the pulse oximetry signal;

using the first heart rate when the metrics indicate the first method is reliable;

using the second heart rate only when the metrics indicate that the first heart rate is unreliable; and

providing an indication on a display of the first heart rate or the second heart rate.

2. The method of claim 1, comprising determining that the first heart rate is unreliable when the metrics indicate that a most recent pulse is rejected.

3. The method of claim 1, wherein the first method does not use an ensemble averaged waveform, and the second method does use an ensemble averaged waveform.

4. The method of claim 1, wherein the first method does not use an ensemble averaged waveform, and the second method does use an ensemble averaged waveform.

5. The method of claim 1, comprising filtering the pulse oximetry signal with a low pass filter.

6. The method of claim 5, wherein filter weights for the low pass filter are determined using the metrics applied to the pulse oximetry signal.

7. The method of claim 6, wherein the metrics comprise one or more of pulse shape, period variability, pulse amplitude and variability, ratio of ratios variability, or frequency content relative to pulse rate.

8. The method of claim 1, wherein determining a first or second heart rate comprises determining a pulse period.

9. A pulse oximetry system, comprising:

a sensor adapted to provide a signal related to a physiological constituent; and

a monitor adapted to process the signal to determine a pulse period, the monitor comprising;

software configured to identify one or more qualified pulses from the signal, wherein the one or more qualified pulses comprise likely arterial pulses;

software configured to determine a first pulse period from the one or more qualified pulses using a first method;

software adapted to determine a second pulse period from the one or more qualified pulses using a second method;

an evaluator configured to determine the reliability of the first pulse period using metrics applied to the pulse oximetry signal; and

a selector configured to use the first pulse period when the metrics indicate the first pulse period is reliable, and to use the second pulse period only when the metrics indicate that the first pulse period is unreliable.

10. The system of claim 9, wherein the first method does not use an ensemble averaged waveform, and the second method does use an ensemble averaged waveform.

11. The system of claim 9, wherein the first pulse period or the second pulse period is converted into a heart rate.

12. The system of claim 9, wherein the first pulse period is unreliable when the metrics indicate that a most recent pulse is rejected.

13. The system of claim 9, comprising updating the pulse period using a pulse-based variable-weight filter.

14. The system of claim 9, comprising filtering the signal with a low pass filter.

15. The system of claim 14, wherein filter weights for the low pass filter are determined using the metrics applied to the signal.

16. The system of claim 15 wherein the metrics comprise one or more of pulse shape, period variability, pulse amplitude and variability, ratio of ratios variability, or frequency content relative to pulse rate.

17. The system of claim 9, wherein the software configured to identify one or more qualified pulses from the signal comprises a neural net.

18. The system of claim 9, wherein the software configured to identify one or more qualified pulses from the signal comprises a state machine.

19. A method for determining a heart rate in a pulse oximeter comprising:

using a processor;

determining a first pulse period from a pulse oximetry signal using a first method;

evaluating a reliability of the first pulse period using metrics applied to the pulse oximetry signal;

determining a second pulse period from the pulse oximetry signal using a second method only when the metrics indicate that the first pulse period is unreliable;

converting the first pulse period into a heart rate when the metrics indicate that the first pulse period is reliable;

converting the second pulse period into a heart rate only when the metrics indicate that the first pulse period is unreliable; and

providing an indication on a display of the heart rate.

20. The method of claim 19, wherein the first method does not use an ensemble averaged waveform, and wherein the second method does use an ensemble averaged waveform.