Methods and systems for filtering a signal according to a signal model and continuous wavelet transform techniques

• US 9,259,188 B2
• Filed: 07/31/2012
• Issued: 02/16/2016
• Est. Priority Date: 07/15/2008
• Status: Active Grant

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: Nellcor Puritan Bennett Ireland
• Inventors: Watson, James Nicholas, Addison, Paul Stanley
• Primary Examiner(s): HARWARD, SOREN T
• Application Number:
  US13/563,675
• Publication Number:
  US 20120302895A1
• Time in Patent Office: 1,295 Days
• US Class Current: 1/1
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/726 using Wavelet transforms

Abstract

According to embodiments, systems and methods are provided for filtering a signal. A first reference signal may be generated according to a signal model and a second reference signal may be generated by analyzing a continuous wavelet transform of a signal. The first and second reference signals may then both be applied to an input signal to filter the input signal according to the components of both of the reference signals.

Claims

1. A method for determining a physiological parameter, the method comprising:

generating, using a pulse oximetry sensor, a first photoplethysmograph (PPG) signal corresponding to a first wavelength of light and a second PPG signal corresponding to a second wavelength of light;

receiving, using a pulse oximeter, the first PPG signal and the second PPG signal;

performing, using the pulse oximeter, a wavelet transform of the first PPG signal to generate a first set of complex transform numbers;

generating, using the pulse oximeter, a first scalogram of real numbers based on a modulus operation performed on the first set of complex numbers;

performing, using the pulse oximeter, a wavelet transform of the second PPG signal to generate a second set of complex transform numbers;

generating, using the pulse oximeter, a second scalogram of real numbers based on a modulus operation performed on the second set of complex numbers;

summing, using the pulse oximeter, the first scalogram and the second scalogram to generate a modified scalogram; and

determining, using the pulse oximeter, the physiological parameter based on the modified scalogram.

2. The method of claim 1, wherein summing the first scalogram and the second scalogram comprises summing coefficients of the first scalogram and the second scalogram at each scale and time.

3. The method of claim 1, further comprising scaling, using the pulse oximeter, at least one of the first scalogram and the second scalogram before summing the first scalogram and the second scalogram.

4. The method of claim 3, wherein the scaling is based on noise.

5. The method of claim 3, wherein the scaling normalizes the first scalogram and the second scalogram.

6. The method of claim 1, wherein a characteristic of the wavelet transform of the first PPG signal is different than a characteristic of the wavelet transform of the second PPG signal.

7. The method of claim 1, wherein the physiological parameter is selected from the group comprising pulse rate and respiration rate.

8. A system for determining a physiological parameter, the system comprising:

a pulse oximetry sensor configured to generate a first photoplethysmograph (PPG) signal corresponding to a first wavelength of light and a second PPG signal corresponding to a second wavelength of light; and

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

receive the first PPG signal and the second PPG signal;

perform a wavelet transform of the first PPG signal to generate a first set of complex transform numbers;

generate a first scalogram of real numbers based on a modulus operation performed on the first set of complex numbers;

perform a wavelet transform of the second PPG signal to generate a second set of complex transform numbers;

generate a second scalogram of real numbers based on a modulus operation performed on the second set of complex numbers;

sum the first scalogram and the second scalogram to generate a modified scalogram; and

determine the physiological parameter based on the modified scalogram.

9. The system of claim 8, wherein the pulse oximeter is configured to sum coefficients of the first scalogram and the second scalogram at each scale and time.

10. The system of claim 8, wherein the pulse oximeter is further configured to scale at least one of the first scalogram and the second scalogram before summing the first scalogram and the second scalogram.

11. The system of claim 10, wherein the pulse oximeter is configured to scale based on noise.

12. The system of claim 10, wherein the pulse oximeter is configured to scale at least one of the first scalogram and the second scalogram to normalize the first scalogram and the second scalogram.

13. The system of claim 8, wherein a characteristic of the wavelet transform of the first PPG signal is different than a characteristic of the wavelet transform of the second PPG signal.

14. The system of claim 8, wherein the physiological parameter is selected from the group comprising pulse rate and respiration rate.