Systems and methods for determining respiration information from a photoplethysmograph

• US 9,693,709 B2
• Filed: 09/23/2011
• Issued: 07/04/2017
• Est. Priority Date: 09/23/2011
• Status: Active Grant

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: Nellcot Puritan Bennett Ireland
• Inventors: McGonigle, Scott, Watson, James N.
• Primary Examiner(s): Kahelin, Michael
• Assistant Examiner(s): TRAN, THO Q
• Application Number:
  US13/243,907
• Publication Number:
  US 20130079647A1
• Time in Patent Office: 2,111 Days
• Field of Search: 600501, 600502, 600504, 600507, 600500, 600484
• 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 patient monitoring system, the system comprising:

a sensor interface configured to receive a photoplethysmograph signal of a patient, the photoplethysmograph signal comprising a plurality of pulse waves;

processing equipment configured to;

sample the photoplethysmograph signal;

determine two successive reference points on the sampled photoplethysmograph signal, corresponding to two successive pulses;

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

select a fiducial point located a predetermined number of samples before or after the located maximum value and between the two successive points; and

calculate a respiration rate based at least in part on the selected fiducial point.

2. The system of claim 1, further comprising memory coupled to the processing equipment, wherein the memory is configured to store fiducial information comprising the predetermined number of samples, and wherein the processing equipment is further configured to access the fiducial information.

3. The system of claim 1, wherein the predetermined number of samples is 16 samples.

4. The system of claim 1, wherein the processing equipment is further configured to create a fiducial signal based at least in part on the selected fiducial point.

5. The system of claim 1, wherein each of the two successive reference points of the photoplethysmograph 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.

6. The system of claim 1, wherein the photoplethysmograph comprises a plurality of pulse waves, and wherein each of the two successive reference points corresponds to a single pulse wave of the plurality of pulse waves.

7. The system of claim 1, wherein the predetermined number of samples is predetermined based at least in part on a pulse period.

8. The system of claim 7, wherein the predetermined number of samples corresponds to a time interval of 10% of the pulse period.