Systems and methods using induced perturbation to determine physiological parameters

• US 8,506,498 B2
• Filed: 10/09/2008
• Issued: 08/13/2013
• Est. Priority Date: 07/15/2008
• Status: Expired due to Fees

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: Nellcor Puritan Bennett Ireland
• Inventors: Sethi, Rakesh, Addison, Paul Stanley, Watson, James Nicholas
• Primary Examiner(s): Clow, Lori A
• Application Number:
  US12/248,738
• Publication Number:
  US 20100016734A1
• Time in Patent Office: 1,769 Days
• Field of Search: None
• US Class Current: 600/501
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 5/0051 by applying vibrations
• CPC Class Codes: A61B 5/0053 by applying pressure, e.g. compression, indentation, palpation, grasping, gauging
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/02108 from analysis of pulse wave characteristics
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• 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 5/726 using Wavelet transforms

Abstract

According to embodiments, systems and methods for non-invasive blood pressure monitoring are disclosed. An exciter may induce perturbations in a subject, and a sensor or probe may be used to obtain a detected signal from the subject. The detected signal may then be used to measure one or more physiological parameters of the patient. For example if the perturbations are based on a known signal, any differences between the known signal and the input signal may be attributable to the patient'"'"'s physiological parameters. A phase drift between the perturbation signal and the detected signal may be determined from a comparison of the scalograms of the exciter location and the sensor or probe location. From the scalogram comparison, more accurate and reliable physiological parameters may be determined.

Claims

1. A method for monitoring blood pressure comprising:

inducing a perturbation signal in a subject'"'"'s body;

detecting a signal from the subject'"'"'s body;

transforming the detected signal using a continuous wavelet transform to generate a scalogram, wherein the scalogram comprises three dimensional data, wherein a first dimension of the scalogram corresponds to time, wherein a second dimension of the scalogram corresponds to scale, and wherein a third dimension of the scalogram corresponds to phase;

determining, from the scalogram, a phase that corresponds to a particular time and scale;

determining, based at least in part on the phase and the perturbation signal, a phase difference; and

determining, based at least in part on the determined phase difference, a blood pressure measurement.

2. The method of claim 1 wherein determining the phase difference comprises:

generating a scalogram of the induced perturbation signal; and

comparing the scalogram of the detected signal and the scalogram of the induced perturbation signal.

3. The method of claim 2 wherein comparing the scalogram of the detected signal and the scalogram of the induced perturbation signal comprises comparing phase information from the same or similar scales at the same or similar times of the scalogram of the detected signal and the scalogram of the induced perturbation signal.

4. The method of claim 3 wherein the same or similar scales of the first and second scalograms comprises at least one scale at the characteristic frequency of the induced perturbation signal.

5. The method of claim 1 wherein determining a blood pressure measurement comprises determining an elapsed time for the induced perturbation signal to propagate a fixed distance.

6. The method of claim 5 wherein determining a blood pressure measurement comprises taking the natural log of the elapsed time.

7. The method of claim 1 wherein determining a blood pressure measurement comprises determining a time difference, T, based at least in part on the determined phase difference and solving a multi-parameter equation that includes the time difference.

8. The method of claim 7 wherein the multi-parameter equation is

p=a+b·

ln(T)

or a mathematical equivalent thereof, where p is the determined blood pressure measurement and a and b are constants.

9. The method of claim 1 further comprising performing at least one calibration of the blood pressure measurement, the calibration based at least in part on a known reference blood pressure measurement.

10. The method of claim 1 wherein inducing a perturbation signal in a subject'"'"'s body comprises inducing a known perturbation signal in the subject'"'"'s body using an ultrasonic, acoustic, or mechanical exciter.

11. The method of claim 1 wherein detecting a signal from the subject'"'"'s body comprises detecting a photoplethysmograph (PPG) signal from the subject'"'"'s body.

12. A system for monitoring blood pressure comprising:

an exciter capable of inducing a perturbation signal in a subject'"'"'s body;

a sensor capable of generating a detected signal from the subject'"'"'s body; and

a processor capable of;

transforming the detected signal using a continuous wavelet to generate a scalogram, wherein the scalogram comprises three dimensional data, wherein a first dimension of the scalogram corresponds to time, wherein a second dimension of the scalogram corresponds to scale, and wherein a third dimension of the scalogram corresponds to phase;

determining, from the scalogram, a phase that corresponds to a particular time and scale;

determining, based at least in part on the phase and the perturbation signal, a phase difference; and

determining, based at least in part on the determined phase difference, a blood pressure measurement.

13. The system of claim 12 wherein the processor is capable of determining the phase difference by:

generating a scalogram of the induced perturbation signal; and

comparing the scalogram of the detected signal and the scalogram of the induced perturbation signal.

14. The system of claim 13 wherein comparing the scalogram of the detected signal and the scalogram of the induced perturbation signal comprises comparing phase information from the same or similar scales at the same or similar times of the scalogram of the detected signal and the scalogram of the induced perturbation signal.

15. The system of claim 14 wherein the same or similar scales of the first and second scalograms comprises at least one scale at the characteristic frequency of the induced perturbation signal.

16. The system of claim 12 wherein the processor is capable of determining a blood pressure measurement by determining an elapsed time for the induced perturbation signal to propagate a fixed distance.

17. The system of claim 16 wherein the processor is capable of determining a blood pressure measurement by taking the natural log of the elapsed time.

18. The system of claim 12 wherein the processor is capable of determining a blood pressure measurement by determining a time difference, T, based at least in part on the determined phase difference and solving a multi-parameter equation that includes the time difference.

19. The system of claim 18 wherein the multi-parameter equation is

p=a+b·

ln(T)

or a mathematical equivalent thereof, where p is the determined blood pressure measurement and a and b are constants.

20. The system of claim 12 wherein the processor is capable of performing at least one calibration of the blood pressure measurement, the calibration based at least in part on a known reference blood pressure measurement.

21. The system of claim 12 wherein the exciter is capable of inducing a known perturbation signal in the subjects body using an ultrasonic, acoustic, or mechanical exciter.

22. The system of claim 12, wherein the sensor capable of generating a detected signal from the subject'"'"'s body comprises a sensor capable of generating a photoplethysmograph (PPG) signal from the subject'"'"'s body.

23. A non-transitory computer-readable medium for use in detecting an artifact in a signal, the computer-readable medium having computer program instructions recorded thereon for:

inducing a perturbation signal in a subject'"'"'s body;

detecting a signal from the subject'"'"'s body;

transforming the detected signal using a continuous wavelet transform to generate a scalogram, wherein the scalogram comprises three dimensional data, wherein a first dimension of the scalogram corresponds to time, wherein a second dimension of the scalogram corresponds to scale, and wherein a third dimension of the scalogram corresponds to phase;

determining, from the scalogram, a phase that corresponds to a particular time and scale;

determining, based at least in part on the phase and the perturbation signal, a phase difference; and

determining, based at least in part on the determined phase difference, a blood pressure measurement.