SYSTEMS AND METHODS FOR DETERMINING DIFFERENTIAL PULSE TRANSIT TIME FROM THE PHASE DIFFERENCE OF TWO ANALOG PLETHYSMOGRAPHS

• US 20130137938A1
• Filed: 11/30/2011
• Published: 05/30/2013
• Est. Priority Date: 11/30/2011
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Inventors: Peters, Daniel J.
• Granted Patent: US 9,060,695 B2
• Time in Patent Office: Days
• US Class Current: 600/301
• CPC Class Codes: A61B 5/0002 Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network A61B5/07 takes precedence; transmission systems for measured values G08C; transmission H04B; transmission of digital information H04L; wireless communication networks H04W
• 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 5/02125 of pulse wave propagation time
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• 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

Abstract

Systems and methods are provided for patient monitors which apply phase detection operations to analog signals to identify differential pulse transit time (DPTT). Photoplethysmograph (PPG) signals measured at two sensor sites may be processed by a phase detection system to identify phase information that allows the calculation of a DPTT. The phase detection system may process analog PPG signals in the analog domain to determine phase information. In some embodiments, the phase detection system may process optical oximetry sensor signals to determine phase information using, for example, interferometric methods.

Claims

1. A method for determining physiological information about a subject, the method comprising:

receiving two or more analog physiological signals of a subject;

processing the analog physiological signals with a phase detector to generate phase information;

determining using processing equipment information indicative of differential pulse transit time based at least in part on the phase information; and

determining using processing equipment physiological information about the subject based at least in part on the information indicative of differential pulse transit time.

2. The method of claim 1, wherein each of the two or more analog physiological signals comprise a photoplethysmograph signal.

3. The method of claim 2, wherein the two or more analog physiological signals are measured at two different sites of the subject.

4. The method of claim 1, wherein the phase detector is a logarithmic amplifier based phase detector.

5. The method of claim 1, wherein the two or more analog physiological signals comprise optical oximetry sensor signals measured at two different sites of the subject.

6. The method of claim 5, wherein the phase detector is an optical phase detector.

7. The method of claim 1, wherein the determining the information indicative of differential pulse transit time is based at least in part on one or more fiducial points of the two or more analog physiological signals.

8. The method of claim 7, wherein the determining the information indicative of differential pulse transit time is based at least in part on a linear combination of the fiducial points.

9. The method of claim 1, wherein the physiological information comprises a blood pressure value.

10. A system for determining physiological information about a subject, the system comprising:

at least one signal input configured to receive two or more analog physiological signals of a subject;

a phase detector coupled to the at least one signal input, the phase detector configured to process the analog physiological signals to generate phase information; and

electronic processing equipment coupled to the at least one signal input and the phase detector, the electronic processing equipment configured to;

determine information indicative of differential pulse transit time based at least in part on the phase information; and

determine physiological information about the subject based at least in part on the information indicative of differential pulse transit time.

11. The system of claim 10, wherein each of the two or more analog physiological signals comprise a photoplethysmograph signal.

12. The system of claim 11, wherein the two or more analog physiological signals are measured at two different sites of the subject.

13. The system of claim 10, wherein the phase detector is a logarithmic amplifier based phase detector.

14. The system of claim 10, wherein the two or more analog physiological signals comprise optical oximetry sensor signals measured at two different sites of the subject.

15. The system of claim 14, wherein the phase detector is an optical phase detector.

16. The system of claim 10, wherein the electronic processing equipment is further configured to determine the information indicative of differential pulse transit time based at least in part on one or more fiducial points of the two or more analog physiological signals.

17. The system of claim 16, wherein the electronic processing equipment is further configured to determine the information indicative of differential pulse transit time based at least in part on a linear combination of the fiducial points.

18. The system of claim 10, wherein the physiological information comprises a blood pressure value.

19. Computer-readable medium for use in determining physiological information about a subject, the computer-readable medium having computer program instructions recorded thereon for:

receiving two or more analog physiological signals of a subject;

processing the analog physiological signals with a phase detector to generate phase information;

determining information indicative of differential pulse transit time based at least in part on the phase information; and

determining physiological information about the subject based at least in part on the information indicative of differential pulse transit time.

20. The computer-readable medium of claim 19, wherein the two or more analog physiological signals are measured at two different sites of the subject.