SYSTEMS AND METHODS FOR DETERMINING RESPIRATION INFORMATION FROM A PHOTOPLETHYSMOGRAPH

• US 20130079647A1
• 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: McGonigle, Scott, Watson, James N.
• Granted Patent: US 9,693,709 B2
• Time in Patent Office: Days
• US Class Current: 600/500
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• 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 5/7239 using differentiation including higher order derivatives

Abstract

A patient monitoring system may determine one or more reference points of a physiological signal. The system may select one or more fiducial points on the physiological signal relative to the reference points. The one or more fiducial points may be selected by selecting a point spaced by a time interval relative to one of the reference points. The time interval may be a predetermined constant, or the time interval may depend on physiological information. The system may generate a fiducial signal based on the selected fiducial points, calculate physiological information such as a respiration rate based on the selected fiducial points, or both.

Claims

1. A method for determining physiological information from a physiological signal, the method comprising:

determining a reference point on the physiological signal;

determining a fiducial point on the physiological signal based at least in part on the reference point and based at least in part on a time interval relative to the reference point; and

calculating physiological information based at least in part on the fiducial point.

2. The method of claim 1, wherein the physiological signal comprises a succession of samples, and wherein the time interval comprises a particular number of samples.

3. The method of claim 2, wherein the physiological signal is a photoplethysmograph signal, and wherein the time interval is about 210 milliseconds, and wherein the particular number of samples is about 16 samples.

4. The method of claim 1, wherein the time interval is a pre-determined value.

5. The method of claim 1, wherein the physiological information comprises a respiration rate.

6. The method of claim 1, further comprising creating a fiducial signal based at least in part on the determined fiducial point.

7. The method of claim 1, wherein the reference point of the physiological signal is of a type selected from the group consisting of a zero, a first derivative maximum, a first derivative zero, a first derivative minimum, a second derivative maximum, a second derivative minimum, a second derivative zero, and any combination thereof.

8. The method of claim 1, wherein the determining the reference point further comprises determining a plurality of reference points on the physiological signal, and wherein the determining the fiducial point on the physiological signal further comprises determining a plurality of fiducial points each corresponding to at least one reference point of the plurality of reference points.

9. The method of claim 8, wherein the physiological signal is a photoplethysmograph signal comprising a plurality of pulse waves, and wherein each reference point of the plurality of reference points corresponds to a single pulse wave of the plurality of pulse waves.

10. A method for determining respiratory information from a sampled signal derived from a photoplethysmograph signal or signal derived thereof, the sampled signal comprising a plurality of successive pulse waves, the method comprising:

locating two successive reference points corresponding to two successive pulse waves of the sampled signal;

locating a maximum value of the sampled signal between the two successive reference points;

selecting a fiducial point located a particular number of samples before or after the located maximum value; and

determining respiratory information based at least in part on the selected fiducial point.

11. The method of claim 10, further comprising creating a fiducial signal, the fiducial signal comprising the selected fiducial point, and wherein the determining the respiration rate is further based at least in part on the fiducial signal.

12. The method of claim 10, wherein the particular number of samples is fixed.

13. The method of claim 12, wherein the particular number of samples is fixed at about 16 samples after the earliest reference point of the two successive reference points, and wherein the 16 samples corresponds to time interval of about 210 milliseconds.

14. The method of claim 10, wherein the particular number of samples is based at least in part on a pulse period.

15. The method of claim 14, wherein the particular number of samples corresponds to a time interval of 10% of the pulse period.

16. A patient monitoring system, the system comprising:

a sensor interface configured to receive a physiological signal of a patient;

processing equipment configured to;

sample the physiological signal;

determine a reference point on the sampled physiological signal;

determine a fiducial point on the sampled physiological signal based at least in part on the reference point and based at least in part on a time interval relative to the reference point; and

calculate physiological information based at least in part on the fiducial point.

17. The system of claim 16, further comprising memory coupled to the processing equipment, wherein the memory is configured to store fiducial information comprising the time interval, and wherein the processing equipment is further configured to access the fiducial information.

18. The system of claim 16, wherein the sensor interface is configured to receive a photoplethysmograph signal comprising a plurality of pulse waves, and wherein the processing equipment is further configured to determine two successive reference points corresponding to two successive pulse waves of the sampled physiological signal.

19. The system of claim 18, wherein the processing equipment is further configured to locate a maximum value of the sampled signal between the two successive reference points, and wherein the processing equipment is further configured to select a fiducial point located a particular number of samples before or after the located maximum value.

20. The system of claim 19, wherein the processing equipment is further configured to calculate a respiration rate based at least in part on the selected fiducial point.