SYSTEMS AND METHODS FOR DETERMINING PHYSIOLOGICAL INFORMATION BY IDENTIFYING FIDUCIAL POINTS IN A PHYSIOLOGICAL SIGNAL

• US 20140243628A1
• Filed: 02/27/2013
• Published: 08/28/2014
• Est. Priority Date: 02/27/2013
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Covidien LP (Medtronic Plc)
• Inventors: Ochs, James, McGonigle, Scott
• Granted Patent: US 9,687,159 B2
• Time in Patent Office: Days
• US Class Current: 600/324
• CPC Class Codes: A61B 2562/085 combined with means for recording calibration data
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

A patient monitoring system may generate a derivative signal from a physiological signal. The derivative signal may be filtered based on a pulse rate estimate associated with the physiological signal. A plurality of crossing points may be determined for the filtered derivative signal and translated to the derivative signal. A plurality of fiducial points may be determined for the derivative signal based on the plurality of crossing points. The plurality of fiducial points may be utilized to determine physiological information from the physiological signal.

Claims

1. A method for determining physiological information from a photoplethysmograph (PPG) signal, the method comprising:

processing the PPG signal, using processing equipment, to generate a processed PPG signal;

calculating, using the processing equipment, a crossing threshold based at least in part on the processed PPG signal;

determining, using the processing equipment, a plurality of fiducial points based at least in part on the crossing threshold; and

determining, using the processing equipment, the physiological information based at least in part on the fiducial points.

2. The method of claim 1, wherein processing the PPG signal comprises:

generating a derivative signal from the PPG signal; and

filtering the derivative signal to generate the processed PPG signal.

3. The method of claim 2, wherein filtering the derivative signal comprises:

establishing a pass band for a band-pass filter; and

filtering the derivative signal based at least in part on the band-pass filter.

4. The method of claim 3, wherein establishing the pass band comprises:

receiving a pulse rate estimate signal; and

establishing a low pass cut off value and a high pass cut off value based at least in part on the pulse rate estimate signal.

5. The method of claim 1, wherein determining the plurality of fiducial points comprises:

establishing a search window of the processed PPG signal;

determining a plurality of crossing points of the processed PPG signal based at least in part on the crossing threshold and the search window; and

calculating the plurality of fiducial points based on the plurality of crossing points.

6. The method of claim 5, wherein establishing the search window comprises:

receiving a pulse rate estimate signal; and

establishing the search window based at least in part on the pulse rate estimate signal.

7. The method of claim 5, wherein calculating the plurality of fiducial points comprises:

generating a derivative signal for the PPG signal;

translating the plurality of crossing points to the derivative signal;

determining a plurality of maximum values, wherein each maximum value comprises a maximum value of the derivative signal between two consecutive crossing points; and

calculating the plurality of fiducial points based at least in part on the plurality of maximum values and a delay value.

8. A computer-readable medium for use in determining physiological information from a photoplethysmograph (PPG) signal, the computer-readable medium having computer program instructions recorded thereon for:

processing the PPG signal to generate a processed PPG signal;

calculating a crossing threshold based at least in part on the processed PPG signal;

determining a plurality of fiducial points based at least in part on the crossing threshold; and

determining the physiological information based at least in part on the fiducial points.

9. The computer-readable medium of claim 8, having further computer program instructions recorded thereon for:

generating a derivative signal from the PPG signal; and

filtering the derivative signal to generate the processed PPG signal.

10. The computer-readable medium of claim 9, having further computer program instructions recorded thereon for:

establishing a pass band for a band-pass filter; and

filtering the derivative signal based at least in part on the band-pass filter.

11. The computer-readable medium of claim 10, having further computer program instructions recorded thereon for:

receiving a pulse rate estimate signal; and

establishing a low pass cut off value and a high pass cut off value for the pass band of the band-pass filter based at least in part on the pulse rate estimate signal.

12. The computer-readable medium of claim 8, having further computer program instructions recorded thereon for:

establishing a search window of the processed PPG signal;

determining a plurality of crossing points of the processed PPG signal based at least in part on the crossing threshold and the search window; and

calculating the plurality of fiducial points based on the plurality of crossing points.

13. The computer-readable medium of claim 12, having further computer program instructions recorded thereon for:

receiving a pulse rate estimate signal; and

establishing the search window based at least in part on the pulse rate estimate signal.

14. The computer-readable medium of claim 12, having further computer program instructions recorded thereon for:

generating a derivative signal for the PPG signal;

translating the plurality of crossing points to the derivative signal;

determining a plurality of maximum values, wherein each maximum value comprises a maximum value of the derivative signal between two consecutive crossing points; and

calculating the plurality of fiducial points based at least in part on the plurality of maximum values and a delay value.

15. A patient monitoring system comprising:

an interface configured to receive a photoplethysmograph PPG signal; and

processing equipment configured to;

process the PPG signal to generate a processed PPG signal;

calculate a crossing threshold based at least in part on the processed PPG signal;

determine a plurality of fiducial points based on the crossing threshold; and

determine physiological information based on the fiducial points.

16. The patient monitoring system of claim 15, wherein the processing equipment is further configured to:

generate a derivative signal from the PPG signal; and

filter the derivative signal to generate the processed PPG signal.

17. The patient monitoring system of claim 16, wherein the processing equipment is further configured to:

establish a pass band for a band-pass filter; and

filter the derivative signal based at least in part on the band-pass filter.

18. The patient monitoring system of claim 17, wherein the processing equipment is further configured to:

receive a pulse rate estimate signal; and

establish a low pass cut off value and a high pass cut off value for the pass band of the band-pass filter based at least in part on the pulse rate estimate signal.

19. The patient monitoring system of claim 15, wherein the processing equipment is further configured to:

establish a search window of the processed PPG signal;

determine a plurality of crossing points of the processed PPG signal based at least in part on the crossing threshold and the search window; and

calculate the plurality of fiducial points based on the plurality of crossing points.

20. The patient monitoring system of claim 19, wherein the processing equipment is further configured to:

receive a pulse rate estimate signal; and

establish the search window based at least in part on the pulse rate estimate signal.