Methods and systems for determining signal-to-noise information from a physiological signal

1. A subject monitoring pulse oximetry system for determining physiological information of a subject, comprising:

a pulse oximetry sensor configured to detect light attenuated by the subject and generate a photoplethysmographic (PPG) signal based on the detected attenuated light; and

a pulse oximeter coupled to the pulse oximetry sensor, wherein the pulse oximeter is configured to:

store a rate algorithm;

generate at least one difference signal based on the PPG signal;

sort the at least one difference signal in an order based on the values of the difference signal to generate at least one sorted difference signal;

analyze the at least one sorted difference signal to determine at least two values indicative of noise;

determine a value indicative of a signal-to-noise ratio based on the two or more values indicative of noise;

determine an algorithm setting based on the value indicative of a signal-to-noise ratio;

apply the algorithm setting to the rate algorithm stored by the pulse oximeter; and

determine the physiological information of the subject using the rate algorithm and the PPG signal, wherein the physiological information comprises pulse rate of the subject.

2. The system of claim 1 , wherein the pulse oximeter is configured to determine the value indicative of a signal-to-noise ratio using a reference of associated values indicative of noise and values indicative of signal-to-noise ratios.

3. The system of claim 1 , wherein the pulse oximeter is further configured to:

analyze the at least one sorted difference signal to determine three values indicative of noise;

select the maximum value of the three values; and

determine the value indicative of a signal-to-noise ratio based on the maximum value.

4. The system of claim 1 , wherein the pulse oximeter is further configured to:

determine a best fit line based on the at least one sorted difference signal;

generate at least one threshold based on the best fit line; and

determine a number of points of the at least one sorted difference signal that exceed the at least one threshold, wherein at least one value of the at least two values indicative of noise is based on the number of points.

5. The system of claim 1 , wherein the pulse oximeter is further configured to:

generate at least one second difference signal based on the PPG signal;

sort the at least one second difference signal in an order based on the values of the second difference signal to generate at least one second sorted difference signal;

determine a first best fit line based on the sorted difference signal;

determine a second best fit line based on the second sorted difference signal; and

compare the first best fit line and the second best fit line to determine at least one value of the at least two values indicative of noise.

6. A pulse oximetry processing module for determining physiological information of a subject, wherein the pulse oximetry processing module is configured to:

store a rate algorithm;

receive a photoplethysmographic (PPG) signal from a pulse oximetry sensor, wherein the pulse oximetry sensor detects light attenuated by the subject and generates the PPG signal based on the detected attenuated light;

generate at least one difference signal based on the PPG signal;

sort the at least one difference signal to generate at least one sorted difference signal;

analyze the at least one sorted difference signal to determine at least two values indicative of noise;

determine a value indicative of a signal-to-noise ratio based on the two or more values indicative of noises;

determine an algorithm setting based on the value indicative of a signal-to-noise ratio;

apply the algorithm setting to the rate algorithm stored by the pulse oximetry processing module; and

determine the physiological information of the subject using the rate algorithm and the PPG signal, wherein the physiological information comprises pulse rate of the subject.

7. The pulse oximetry processing module of claim 6 , further configured to determine the value indicative of a signal-to-noise ratio using a reference of associated values indicative of noise and values indicative of signal-to-noise ratios.

8. The pulse oximetry processing module of claim 6 , further configured to:

analyze the at least one sorted difference signal to determine three values indicative of noise;

select the maximum value of the three values; and

determine the value indicative of a signal-to-noise ratio based on the maximum value.

9. The pulse oximetry processing module of claim 6 , further configured to:

determine a best fit line based on the at least one sorted difference signal;

generate at least one threshold based on the best fit line; and

determine a number of points of the at least one sorted difference signal that exceed the at least one threshold, wherein at least one value of the at least two values indicative of noise is based on the number of points.

10. The pulse oximetry processing module of claim 6 , further configured to:

generate at least one second difference signal based on the PPG signal;

sort the at least one second difference signal in an order based on the values of the second difference signal to generate at least one second sorted difference signal;

determine a first best fit line based on the sorted difference signal;

determine a second best fit line based on the second sorted difference signal; and

compare the first best fit line and the second best fit line to determine at least one value of the at least two values indicative of noise.

11. A method for determining physiological information of a subject, comprising:

storing, using a pulse oximeter, a rate algorithm;

receiving, using the pulse oximeter, a photoplethysmographic (PPG) signal derived from a pulse oximetry sensor output, wherein the pulse oximetry sensor detects light attenuated by the subject and generates the PPG signal based on the detected attenuated light;

generating, using the pulse oximeter, at least one difference signal based on the PPG signal;

sorting, using the pulse oximeter, the at least one difference signal in an order based on the values of the difference signal to generate at least one sorted difference signal;

analyzing, using the pulse oximeter, the at least one sorted difference signal to determine at least two values indicative of noise;

determining, using the pulse oximeter, a value indicative of a signal-to-noise ratio based on the two or more values indicative of noise;

determining, using the pulse oximeter, an algorithm setting based on the value indicative of a signal-to-noise ratio;

applying, using the pulse oximeter, the algorithm setting to the rate algorithm stored by the pulse oximeter; and

determining, using the pulse oximeter, the physiological information of the subject using the rate algorithm and the PPG signal, wherein the physiological information comprises pulse rate of the subject.

12. The method of claim 11 , wherein determining the value indicative of a signal-to-nois ratio comprises using a reference of associated values indicative of noise and values indicative of signal-to-noise ratios.

13. The method of claim 11 , wherein analyzing the at least one sorted difference signal to determine the at least two values indicative of noise comprises analyzing the at least one sorted difference signal to determine three values indicative of noise, wherein determining a value indicative of a signal-to-noise ratio comprises:

selecting the maximum value of the three values; and

determining the signal to noise ratio based on the maximum value.

14. The method of claim 11 , wherein analyzing the at least one sorted difference signal to determine the at least two values indicative of noise comprises:

determining a best fit line based on the at least one sorted difference signal;

generating at least one threshold based on the best fit line; and

determining a number of points of the at least one sorted difference signal that exceed the at least one threshold, wherein at least one value of the at least two values indicative of noise is based on the number of points.

15. The method of claim 11 , further comprising:

generating at least one second difference signal based on the PPG signal;

sorting the at least one second difference signal in an order based on the values of the second difference signal to generate at least one second sorted difference signal, wherein analyzing the at least one sorted difference signal to determine at least two values indicative of noise comprises:

determining a first best fit line based on the sorted difference signal;

determining a second best fit line based on the second sorted difference signal; and

comparing the first best fit line and the second best fit line to determine at least one value of the at least two values indicative of noise.

16. A computer-readable medium for use in determining physiological information of a subject, the computer-readable medium comprising:

computer program instructions recorded thereon for causing a pulse oximeter storing a rate algorithm to:

receive a photoplethysmographic (PPG) signal derived from a pulse oximetry sensor output, wherein the pulse oximetry sensor detects light attenuated by the subject and generates the PPG signal based on the detected attenuated light;

generate at least one difference signal based on the PPG signal;

sort the at least one difference signal in an order based on the values of the difference signal to generate at least one sorted difference signal;

analyze the at least one sorted difference signal to determine at least two values indicative of noise;

determine a value indicative of a signal-to-noise ratio based on the two or more values indicative of noise;

determine an algorithm setting based on the value indicative of a signal-to-noise ratio;

apply the algorithm setting to the rate algorithm stored by the pulse oximeter; and

determine the physiological information of the subject using the rate algorithm and the PPG signal, wherein the physiological information comprises pulse rate of the subject.

17. The computer-readable medium of claim 16 , further comprising computer program instructions recorded thereon for causing the pulse oximeter to determine the value indicative of a signal-to-noise ratio using a reference of associated values indicative of noise and values indicative of signal-to-noise ratios.

18. The computer-readable medium of claim 16 , further comprising computer program instructions recorded thereon for causing the pulse oximeter to:

analyze the at least one sorted difference signal to determine three values indicative of noise;

select the maximum value of the three values; and

determine the value indicative of a signal-to-noise ratio based on the maximum value.

19. The computer-readable medium of claim 16 , further comprising computer program instructions recorded thereon for causing the pulse oximeter to:

determine a best fit line based on the at least one sorted difference signal;

generate at least one threshold based on the best fit line; and

determine a number of points of the at least one sorted difference signal that exceed the at least one threshold, wherein at least one value of the at least two values indicative of noise is based on the number of points.

20. The computer-readable medium of claim 16 , further comprising computer program instructions recorded thereon for causing the pulse oximeter to:

generate at least one second difference signal based on the PPG signal;

sort the at least one second difference signal in an order based on the values of the second difference signal to generate at least one second sorted difference signal;

determine a first best fit line based on the sorted difference signal;

determine second best fit line based on the second sorted difference signal; and

compare the first best fit line and the second best fit line to determine at least one value of the at least two values indicative of noise.

21. The system of claim 1 , wherein the algorithm setting affects the amount of filtering applied to the PPG signal prior to determining the physiological information of the subject.

22. The system of claim 21 , wherein the amount of filtering applied to the PPG signal prior to determining the physiological information of the subject increases when the value indicative of a signal-to-noise ratio is greater than a threshold value.

23. The method of claim 11 , wherein the algorithm setting affects the signal conditioning applied to the PPG signal prior to determining the physiological information of the subject.

24. The method of claim 23 , wherein the amount of filtering applied to the PPG signal prior to determining the physiological information of the subject increases when the value indicative of a signal-to-noise ratio is greater than a threshold value.