SYSTEMS AND METHODS FOR DETERMINING RESPIRATION INFORMATION FROM A PHOTOPLETHYSMOGRAPH

• US 20130079657A1
• Filed: 09/23/2011
• Published: 03/28/2013
• Est. Priority Date: 09/23/2011
• Status: Active Grant

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: Nellcor Puritan Bennett Ireland
• Inventors: Ochs, James, Watson, James, Addison, Paul S., McGonigle, Scott, Weng, Binwel
• Granted Patent: US 9,402,554 B2
• Time in Patent Office: Days
• US Class Current: 600/529
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/0803 Recording apparatus specially adapted therefor
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/7232 involving compression of the physiological signal, e.g. to extend the signal recording period
• CPC Class Codes: A61B 5/7235 Details of waveform analysis A61B5/349 takes precedence

Abstract

A signal representing physiological information may include information related to respiration. A patient monitoring system may utilize a wavelet transform to generate a scalogram from the signal. A threshold for the scalogram may be calculated, and scalogram values may be compared to the threshold. One of the scales meeting the threshold may be selected as representing respiration information such as respiration rate. The respiration information may be determined based on the selected scale.

Claims

1. A method for determining respiration information, the method comprising:

receiving a photoplethysmograph (PPG) signal;

transforming, using processing equipment, the PPG signal based at least in part on a continuous wavelet transform to generate a scalogram;

calculating, using the processing equipment, a threshold energy level based at least in part on the scalogram;

identifying, using the processing equipment, for a particular time, a scale in the scalogram associated with an energy level that is greater than the threshold, but less than a maximum energy level of the scalogram; and

determining, using the processing equipment, an estimate for respiration rate based at least in part on the scale.

2. The method of claim 1 wherein transforming the PPG signal to generate the scalogram comprises:

accessing a mother wavelet and scaling parameters; and

generating the scalogram for the signal using the continuous wavelet transform, wherein the continuous wavelet transform is based on the mother wavelet and the scaling parameters.

3. The method of claim 2 wherein the mother wavelet comprises a morlet wavelet.

4. The method of claim 2 wherein the scaling parameters comprise a number of scales and a scale resolution.

5. The method of claim 4 wherein the number of scales and scale resolution correspond to a region of interest for respiration.

6. The method of claim 4 wherein determining the estimate for respiration rate comprises determining a characteristic frequency based on a value of the scale and the scale resolution.

7. The method of claim 4 wherein transforming the PPG signal to generate the scalogram comprises:

summing across all scales to generate a sum scalogram vector; and

normalizing the sum scalogram vector to generate the scalogram.

8. The method of claim 1 wherein calculating the threshold comprises:

identifying the maximum energy level for the scalogram; and

calculating the threshold energy level based on the maximum energy level.

9. The method of claim 1 further comprising:

accessing, using the processing equipment, a previous estimate for respiration rate;

calculating, using the processing equipment, a filter weight; and

determining, using the processing equipment, a filtered estimate for respiration rate based on the estimate for respiration rate, the previous estimate for respiration rate, and the filter weight.

10. The method of claim 9, further comprising:

accessing, using the processing equipment, a previous respiration age and a current respiration age; and

determining, using the processing equipment, a combined respiration age based on the previous respiration age, the current respiration age, and the filter weight.

11. A patient monitoring system comprising:

an interface configured to receive a photoplethysmograph (PPG) signal;

a processor configured to;

transform the PPG signal based at least in part on a continuous wavelet transform to generate a scalogram;

calculate a threshold energy level based at least in part on the scalogram;

identify, for a particular time, a scale in the scalogram associated with an energy level that is greater than the threshold, but less than a maximum energy level of the scalogram; and

determine an estimate for respiration rate based at least in part on the scale.

12. The patient monitoring system of claim 11 wherein the processor is further configured to:

access a mother wavelet and scaling parameters; and

generate the scalogram for the signal using the continuous wavelet transform, wherein the continuous wavelet transform is based on the mother wavelet and the scaling parameters.

13. The patient monitoring system of claim 12 wherein the mother wavelet comprises a morlet wavelet.

14. The patient monitoring system of claim 12 wherein the scaling parameters comprise a number of scales and a scale resolution.

15. The patient monitoring system of claim 14 wherein the number of scales and scale resolution correspond to a region of interest for respiration.

16. The patient monitoring system of claim 14 wherein the processor is further configured to determine a characteristic frequency based on a value of the scale and the scale resolution, wherein the estimate for respiration rate is based on the characteristic frequency.

17. The patient monitoring system of claim 14 wherein the processor is further configured to sum across all scales in to generate a sum scalogram vector, and normalize the sum scalogram vector to generate the scalogram.

18. The patient monitoring system of claim 11 wherein the processor is further configured to locate a maximum energy level for the scalogram, and calculate the threshold energy level based on the maximum energy level.

19. The patient monitoring system of claim 11 wherein the processor is further configured to:

access a previous estimate for respiration rate;

calculate a filter weight; and

determine a filtered estimate for respiration rate based on the estimate for respiration rate, the previous estimate for respiration rate, and the filter weight.

20. The patient monitoring system of claim 19, wherein the processor is further configured to access a previous respiration age and a current respiration age, and determine a combined respiration age based on the previous respiration age, the current respiration age, and the filter weight.