Processing of photoplethysmography signals

• US 8,529,459 B2
• Filed: 08/08/2007
• Issued: 09/10/2013
• Est. Priority Date: 08/08/2007
• Status: Active Grant

• Current Assignee: Convergent Engineering, Inc., University of Florida Research Foundation, Incorporated (State University System of Florida)
• Original Assignee: Convergent Engineering, Inc., University of Florida Research Foundation, Incorporated (State University System of Florida)
• Inventors: Euliano, Neil R., Stahl, Michael W. Jr., Malker, Richard J.
• Primary Examiner(s): Mallari, Patricia
• Assistant Examiner(s): WESTON, TIFFANY C
• Application Number:
  US11/835,738
• Publication Number:
  US 20090043179A1
• Time in Patent Office: 2,225 Days
• Field of Search: 600500-507, 600529-543, 600310-344
• US Class Current: 600/500
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence

Abstract

Disclosed herein are methods and devices of processing photoplethysmography signal information. The methods for processing will allow numerous medical observations and diagnoses from a simple, non-invasive probe.

Claims

1. A method of isolating an AC component signal stream and a DC component signal stream from a raw plethysmography signal stream comprising

identifying peaks and troughs of said raw plethysmography signal stream using at least one processing device, wherein said peaks and troughs are those that exist at an expected heart rate;

identifying minimum values or midpoints between said peaks and troughs using said at least one processing device, and

interpolating between said midpoints or minimum values to define said DC component signal stream; and

extracting said interpolated DC component signal stream from said raw plethysmography signal stream using said at least one processing device, thereby separately obtaining said AC component signal stream, whereby said AC component signal stream and said DC component signal stream are individually isolated.

2. The method of claim 1 wherein said raw plethysmography signal stream is obtained from an individual by positioning at least one photodetector on said individual'"'"'s right or left nares;

and positioning at least one LED on the individual'"'"'s right or left nostril just across from said at least one photodetector.

3. The method of claim 2, wherein said at least one photodetector is positioned on top of said individual'"'"'s fibro-areolar region of said individual'"'"'s nose.

20. The method of claim 1, further comprising using said isolated AC component signal stream and/or said DC component signal stream to measure at least one of respiration rate, respiration effort and venous impedance.

21. The method according to claim 1 wherein said time varying raw plethysmography signal stream is acquired from a central source site.

4. A system for processing plethysmography signals from a patient comprising

at least one pulse oximeter probe configured for securing to a central source site of said patient and effective to generate a raw plethysmography signal stream;

and

a computer connected to and in communication with said at least one pulse oximeter probe, said computer comprising

at least one processing module,

a first computer-readable program code module configured to cause said computer to process said raw plethysmography signal stream to obtain an AC component signal stream or a DC component signal stream, or both, and

a second computer-readable program code module configured to cause said computer to analyze said AC component signal stream or said DC component signal stream, or both, to determine a decrease in amplitude of either said AC component signal stream or DC component signal stream, or both;

wherein said AC component signal stream and said DC component signal stream are isolated from each other from said raw plethysmography signal stream by said first computer-readable program code module causing said computer

to identify the peaks and troughs of said plethysmography signal stream that exist at an expected heart rate,

to identify minimum values or midpoints between said peaks and troughs,

to interpolate between said midpoints or minimum values to define said DC component signal stream, and

to extract said interpolated DC component signal stream from said raw plethysmography signal stream, thereby separately obtaining said AC component signal stream, whereby the said AC component signal stream and said DC component signal stream are individually isolated.

5. The system of claim 4, wherein said computer further comprises a display screen.

6. A computer program product for use with a computer comprising at least one processing module, said product comprising:

a non-transitory computer-usable medium comprising computer readable program code modules embodied in said computer-usable medium;

a non-transitory computer readable first program code module configured to cause said computer to process a raw plethysmography signal stream obtained from a pulse oximeter probe by separating out a AC component signal stream and a DC component signal stream,

wherein said AC component signal stream and said DC component signal stream are separated from each other from the raw plethysmography signal stream by said non-transitory computer-readable program code module configured to cause said computer to identify peaks and troughs of said raw plethysmography signal stream that exist at an expected heart rate, to identify minimum values or midpoints between said peaks and troughs, to interpolate between said midpoints or minimum values to define said DC component signal stream, and to extract said interpolated DC component signal stream from said raw plethysmography signal signal stream, thereby separately obtaining said AC component signal stream, whereby said AC component signal stream and said DC component signal stream are individually isolated; and

a non-transitory computer-readable second program code module for causing said computer to analyze said AC component signal stream or said DC component signal stream, or both, to determine a decrease in amplitude of either said AC component signal stream or said DC component signal stream, or both.

7. A method of obtaining processed photoplethysmography readings from an individual, said method comprising:

obtaining a pulse oximeter probe comprising at least one LED and at least one photodetector;

securing said probe onto said individual'"'"'s right and/or left nasal alar, whereby tissue of said nasal alar rests between said at least one photodetector and said at least one LED; and

monitoring a raw photoplethysmography signal stream generated by said probe responsive to blood flow at said tissue of said nasal alar; and

isolating an AC component signal stream and a DC'"'"'component signal stream from the raw photoplethysmography signal stream by a method comprising identifying peaks and troughs of said photoplethysmography signal stream, wherein said peaks and troughs are those that exist at an expected heart rate;

identifying minimum values or midpoints between said peaks and troughs, interpolating between said midpoints or minimum values to define said DC component signal stream;

extracting said interpolated DC component signal stream from said raw plethysmography signal stream, thereby separately obtaining said AC component signal stream, whereby said AC component signal stream and said DC component signal stream are individually isolated.

8. A method of isolating an AC and DC component signal stream from a raw plethysmography signal stream comprising

identifying extrema of said raw plethysmography signal stream using at least one processing device, whereby the extrema are those that exist at an expected heart rate;

identifying a common point relative to the extrema using said at least one processing device, interpolating between said common points to define said DC component signal stream; and

extracting said interpolated DC component signal stream from said raw plethysmography signal stream using said at least one processing device, thereby separately obtaining said AC component signal stream, whereby said AC component signal stream and said DC component signal stream are individually isolated.

9. The method of claim 8, wherein said common point is a midpoint.

10. The method of claim 8, wherein said common point is a maximum point.

11. The method of claim 8, wherein said common point is a minimum point.

12. The method of claim 8, wherein said common point is a dicrotic notch.

13. The method of claim 8, wherein said common point is a zero-crossing point.

14. The method of claim 8, wherein said common point is an inflection point.

15. The method of claim 8, wherein said common point is a point of equal areas.

16. The method of claim 8, wherein said raw plethysmography signal stream is obtained from a pulse oximeter sensor secured to a nasal alar of a patient.

17. A method of isolating from a raw plethysmography signal stream a high frequency component signal stream, a first low frequency component signal stream and a second low frequency component signal stream, said method comprising

identifying extrema of said raw plethysmography signal stream using at least one processing device, wherein said extrema are those that exist at an expected heart rate;

identifying a common point relative to the extrema using at least one processing device, interpolating between said common points to represent a low frequency content of the signal; and

extracting said interpolated low frequency content from said raw plethysmography signal stream using said at least one processing device, thereby separating said high frequency component signal stream from said low frequency content.

18. The method of claim 17, wherein said high frequency component signal stream comprises a cardiac component and said low frequency content comprises a respiratory component and a sympathetic and parasympathetic tone component.

19. The method of claim 17, further comprising separating said first low frequency component from said second low frequency component.