Systems and Methods for Non-Invasive Blood Pressure Monitoring

• US 20090326386A1
• Filed: 09/30/2008
• Published: 12/31/2009
• Est. Priority Date: 06/30/2008
• Status: Abandoned Application

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: Nellcor Puritan Bennett Ireland
• Inventors: Watson, James, Sethi, Rakesh
• Application Number:
  US12/242,238
• Publication Number:
  US 20090326386A1
• Time in Patent Office: Days
• US Class Current: 600/480
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/02125 of pulse wave propagation time
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence

Abstract

According to embodiments, systems and methods for non-invasive blood pressure monitoring are disclosed. A sensor or probe may be used to obtain a plethysmograph or photoplethysmograph (PPG) signal from a subject. From the signal, the time difference between two or more characteristic points in the signal may be computed. The time difference may correspond, for example, to the time for a pulse wave to travel a predetermined distance from the senor or probe to a reflection point and back to the sensor or probe. From this time difference, blood pressure measurements may be computed continuously or on a periodic basis.

Claims

1. A method for monitoring blood pressure comprising:

detecting a photoplethysmograph (PPG) signal;

identifying at least two characteristic points in the detected PPG signal;

determining the time difference between two of the at least two characteristic points in the detected PPG signal; and

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

2. The method of claim 1 wherein identifying at least two characteristic points in the detected PPG signal comprises identifying at least one stationary point or inflection point of at least one derivative of the PPG signal.

3. The method of claim 1 wherein identifying at least two characteristic points in the detected PPG signal comprises identifying a local turning point in the time domain of the PPG signal.

4. The method of claim 1 wherein identifying at least two characteristic points in the detected PPG signal comprises identifying a second peak in a second derivative of the PPG signal.

5. The method of claim 1 wherein identifying at least two characteristic points in the detected PPG signal comprises identifying two peaks in a second derivative of the PPG signal.

6. The method of claim 5 wherein identifying two peaks in the second derivative of the PPG signal comprises identifying two adjacent peaks in the second derivative of the PPG signal.

7. The method of claim 1 wherein determining, based at least in part on the determined time difference, a blood pressure measurement comprises taking a natural logarithm of the time difference.

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

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

p=a+b·

ln(T)

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

10. 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.

11. The method of claim 1 further comprising filtering the detected PPG signal one or more times prior to identifying the at least two characteristic points in the detected PPG signal.

12. A system for monitoring blood pressure comprising:

a sensor capable of generating a photoplethysmograph (PPG) signal; and

a processor capable of;

receiving the PPG signal;

identifying at least two characteristic points in the received PPG signal;

determining the time difference between two of the at least two characteristic points in the received PPG signal; and

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

13. The system of claim 12 wherein the sensor comprises a pulse oximeter.

14. The system of claim 12 wherein the processor is configured to identify at least one stationary point or inflection point of at least one derivative of the PPG signal.

15. The system of claim 12 wherein the processor is configured to identify a local turning point in the time domain of the PPG signal.

16. The system of claim 12 wherein the processor is configured to identify a second peak in a second derivative of the PPG signal.

17. The system of claim 12 wherein the processor is configured to identify two peaks in a second derivative of the PPG signal.

18. The system of claim 17 wherein the processor is configured to identify two adjacent peaks in a second derivative of the PPG signal.

19. The system of claim 12 wherein the processor is configured to determine, based at least in part on the determined time difference, a blood pressure measurement by solving a multi-parameter equation that includes the time difference.

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

p=a+b·

ln(T)

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

21. The system of claim 12 wherein the processor is configured to perform at least one calibration of the blood pressure measurement, the calibration based at least in part on a known reference blood pressure measurement.

22. The system of claim 12 where the processor is configured to filter the detected PPG signal one or more times prior to identifying the at least two characteristic points in the detected PPG signal.

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

detecting a photoplethysmograph (PPG) signal;

identifying at least two characteristic points in the detected PPG signal;

determining the time difference between two of the at least two characteristic points in the detected PPG signal; and

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