Noninvasive apparatus and method for estimating blood pressure

• US 20070032728A1
• Filed: 08/01/2006
• Published: 02/08/2007
• Est. Priority Date: 08/03/2005
• Status: Active Grant

• Current Assignee: Luca Longhini
• Original Assignee: Luca Longhini
• Inventors: Peretto, Lorenzo, Longhini, Luca
• Granted Patent: US 7,828,740 B2
• Time in Patent Office: Days
• US Class Current: 600/485
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61B 7/00 Instruments for auscultation
• CPC Class Codes: A61B 7/04 Electric stethoscopes microphones, acoustic transducers therefor H04R

Abstract

Methods and apparatus for noninvasively estimating a blood pressure are provided. A pulmonic (P) component extracted from a second heart sound (S2) signal is analyzed to obtain a number of oscillations in the P component. A predetermined relationship between the number of oscillations and PAP is used to generate a blood pressure estimate. A PCG sensor including a mechanical filter for receiving heart sounds from a chest wall is also provided. The pressure of the PCG sensor on the chest wall is adjustable.

Claims

1. A method for noninvasively estimating a blood pressure, the method comprising the steps of:

a) extracting a pulmonic (P) component from a second heart sound (S2) signal;

b) analyzing the extracted P component to obtain a number of oscillations in the P component; and

c) applying a predetermined relationship between the obtained number of oscillations and blood pressure to generate a blood pressure estimate.

2. The method according to claim 1, wherein the blood pressure includes a pulmonary artery pressure (PAP) and step (c) includes applying the predetermined relationship between the obtained number of oscillations and PAP to generate a PAP estimate.

3. The method according to claim 1, the method further including the steps of, prior to step (a):

receiving a phonocardiogram (PCG) signal; and

extracting the S2 signal from the received PCG signal,

wherein step (a) extracts the P component from the extracted S2 signal.

4. The method according to claim 1, wherein the S2 signal is a time-domain S2 signal and step (a) extracts the P component using the time-domain S2 signal.

5. The method according to claim 1, wherein step (b) determines the number of oscillations using a derivative with respect to time of the P component.

6. The method according to claim 1, wherein the predetermined relationship is determined by a linear regression between a plurality of measured numbers of oscillations and a respective plurality of measured blood pressures corresponding to the measured numbers of oscillations.

7. A computer-readable carrier including computer program instructions that cause a computer to perform the method according to claim 1.

8. The method according to claim 1, step (a) includes the steps of:

determining a P component onset time according to a maximum absolute value of a time derivative of the S2 signal; and

selecting a predetermined portion of the S2 signal as the P component using the determined P component onset time.

9. The method according to claim 1, wherein the S2 signal includes a plurality of S2 signals, and

step (a) includes extracting a corresponding plurality of P components from the plurality of S2 signals,

wherein the blood pressure estimate is generated according to the extracted plurality of P components.

10. The method according to claim 9, further including the step of determining a confidence interval measure associated with the blood pressure estimate.

11. The method according to claim 9, further including the steps of:

repeating steps (b) and (c) over the plurality of S2 signals to generate a corresponding plurality of blood pressure estimates; and

determining a mode of the plurality of blood pressure estimates to generate an average blood pressure estimate.

12. The method according to claim 9, further including the steps of:

determining a mean S2 signal from the plurality of S2 signals; and

repeating steps (b) and (c) using the mean S2 signal to generate the blood pressure estimate.

13. The method according to claim 12, wherein the step of determining the mean S2 signal further includes the steps of:

determining a plurality of discrete Fourier transform (DFT) signals corresponding to the plurality of S2 signals;

computing a mean DFT signal from the plurality of DFT signals; and

determining an inverse discrete Fourier transform (IFDT) signal from the mean DFT signal, the IFDT signal forming the mean S2 signal.

14. The method according to claim 1, the method further including the steps of, prior to step (a):

synchronously receiving a phonocardiogram (PCG) signal and an electrocardiogram (ECG) signal for a predetermined duration of time; and

extracting the S2 signal from the received PCG signal using the received ECG signal,

wherein step (a) extracts the P component from the extracted S2 signal.

15. The method according to claim 14, the step of extracting the S2 signal includes the steps of:

determining two consecutive QRS complex onset times from the received ECG signal;

calculating a time interval from the determined QRS complex onset times;

determining an S2 onset time according to the calculated time interval; and

selecting a predetermined portion of the PCG signal using the determined S2 onset time as the extracted S2 signal.

16. The method according to claim 14, wherein the PCG signal includes a plurality of PCG signals and the ECG signal includes a plurality of ECG signals corresponding to the plurality of PCG signals,

the step of synchronously receiving the PCG signal and the ECG signal includes synchronously receiving the plurality of PCG signals and the plurality of ECG signals, and

the step of extracting the S2 signal includes extracting a corresponding plurality of S2 signals,

wherein the blood pressure estimate is generated according to the extracted plurality of S2 signals.

17. The method according to claim 16, further including the step of determining a confidence interval measure associated with the blood pressure estimate.

18. The method according to claim 17, further including the step of storing at least one of the received PCG signal, the received ECG signal, the extracted S2 signal, the P component, the blood pressure estimate and the confidence interval measure.

19. The method according to claim 17, further including the step of presenting, on a display device, the blood pressure estimate and at least one of the received PCG signal, the received ECG signal, the extracted S2 signal, the P component and the confidence interval measure.

20. Apparatus for noninvasively estimating a blood pressure, the apparatus comprising:

a) means for extracting a pulmonic (P) component from a second heart sound (S2) signal;

b) means for analyzing the extracted P component to obtain a number of oscillations in the P component; and

c) means for applying a predetermined relationship between the obtained number of oscillations and blood pressure to generate a blood pressure estimate.

21. Apparatus according to claim 20, wherein the blood pressure includes a pulmonary artery pressure (PAP) and the means for applying the predetermined relationship includes means for applying the predetermined relationship between the obtained number of oscillations and PAP to generate a PAP estimate.

22. Apparatus according to claim 20, the apparatus further comprising:

means for receiving a phonocardiogram (PCG) signal; and

means for extracting the S2 signal from the received PCG signal,

wherein the means for extracting the P component includes means for extracting the P component from the extracted S2 signal.

23. Apparatus according to claim 20, the apparatus further comprising:

means for synchronously receiving a phonocardiogram (PCG) signal and an electrocardiogram (ECG) signal for a predetermined duration of time; and

means for extracting the S2 signal from the received PCG signal using the received ECG signal,

wherein the means for extracting the P component includes means for extracting the P component from the extracted S2 signal.

24. Apparatus for noninvasively estimating a blood pressure, the apparatus comprising:

a blood pressure analyzer comprising;

a pulmonary (P) component oscillation calculator configured to obtain a number of oscillations in a P component of a second heart sound (S2) signal;

a blood pressure estimator configured to generate a blood pressure estimate by applying a predetermined relationship between blood pressure and the obtained number of oscillations obtained by the P component oscillation calculator; and

an output port configured to provide the blood pressure estimate and at least one of the S2 signal and the P component.

25. Apparatus according to claim 24, wherein the blood pressure includes a pulmonary artery pressure (PAP) and the blood pressure estimator is configured to generate a PAP estimate by applying the predetermined relationship between PAP and the obtained number of oscillations.

26. Apparatus according to claim 24, wherein the P component oscillation calculator is configured to obtain the number of oscillations in the P component according to a time domain analysis of the S2 signal.

27. Apparatus according to claim 24, the apparatus further comprising:

input means for receiving a phonocardiogram (PCG) signal; and

the blood pressure analyzer further comprises;

an S2 signal extractor coupled to the input means, the S2 signal extractor being configured to extract the S2 signal from the PCG signal,

wherein the P component oscillation calculator is configured to obtain the number of oscillations in the P component of the extracted S2 signal.

28. Apparatus according to claim 27, the PAP analyzer further comprising:

a time derivative estimator configured to receive the extracted S2 signal from the S2 signal extractor and to estimate the time derivative of the extracted S2 signal; and

a P component extractor configured to extract the P component from the extracted S2 signal using the time derivative of the extracted S2 signal received from the time derivative estimator, the time derivative of the extracted P component being provided to the P component oscillation calculator;

wherein the P component oscillation calculator obtains the number of oscillations using the time derivative of the extracted P component received from the P component extractor.

29. Apparatus according to claim 27, wherein

the PCG signal includes a plurality of PCG signals,

the input means receives the plurality of PCG signals, and

the blood pressure analyzer generates the blood pressure estimate according to the plurality of PCG signals received from the input means.

30. Apparatus according to claim 29, the blood pressure analyzer further comprising a confidence interval evaluator configured to evaluate a confidence interval measure associated with the blood pressure estimate received from the blood pressure estimator.

31. Apparatus according to claim 29, wherein the S2 signal extractor extracts a corresponding plurality of S2 signals from the plurality of PCG signals and the blood pressure analyzer further comprises:

a mean S2 estimator including;

an input port configured to receive the plurality of extracted S2 signals from the S2 signal extractor,

a discrete Fourier transform (DFT) processor for generating a plurality of DFT signals corresponding to the plurality of extracted S2 signals,

a mean calculator for calculating a mean DFT signal from the plurality of DFT signals received from the DFT processor,

an inverse discrete Fourier transform processor for generating a signal from the mean DFT signal received from the mean calculator, the signal forming a mean S2 signal, and

an output port configured to transmit the mean S2 signal provided by the IFDT processor to the P component oscillator calculator, the P component oscillator calculator using the mean S2 signal to generate the PAP estimate.

32. Apparatus according to claim 27, the input means further comprising means for receiving a electrocardiogram (ECG) signal corresponding to the PCG signal, and

wherein the S2 signal extractor is configured to extract the S2 signal using the corresponding ECG signal.

33. Apparatus according to claim 32, further comprising:

a PCG sensor configured to receive the PCG signal from a chest wall;

an ECG sensor configured to receive the ECG signal from the chest wall; and

a data acquisition system configured to synchronously acquire and digitize the PCG signal and the ECG signal and configured to receive the blood pressure estimate and the at least one of the P component and the S2 signal from the output port of the blood pressure analyzer,

wherein the PCG signal and the ECG signal are each received from the chest wall at a predetermined sampling rate over a predetermined acquisition period, and

the digitized PCG signal and the digitized ECG signal being provided to the input means of the blood pressure analyzer.

34. Apparatus according to claim 33, further comprising storage means coupled to the data acquisition system for storing at least one of the received blood pressure estimate, the digitized PCG signal, the digitized ECG signal and the received at least one of the P component and the S2 signal.

35. Apparatus according to claim 33, further comprising a display coupled to the data acquisition system for presenting the received blood pressure estimate and at least one of the digitized PCG signal, the digitized ECG signal and the received at least one of the P component and the S2 signal.

36. Apparatus according to claim 33, further comprising a control interface coupled to the data acquisition system for providing control parameters to the data acquisition system and further control parameters to the blood pressure analyzer.

37. Apparatus according to claim 33, wherein the PCG sensor includes a mechanical filter.

38. Apparatus according to claim 33, further including a PCG signal conditioner to amplify the PCG signal received from the PCG sensor and to match an impedance of the PCG sensor to an impedance of the data acquisition system, the PCG signal conditioner providing a conditioned PCG signal to the data acquisition system.

39. Apparatus according to claim 38, the PCG signal conditioner further including:

a band-pass filter configured to filter the received PCG signal over a predetermined frequency range,

wherein the predetermined frequency range is about 15 Hz-550 Hz.

40. Apparatus according to claim 38, wherein the PCG sensor includes a first PCG sensor and a second PCG sensor, each of the first PCG sensor and the second PCG sensor being positioned on the chest wall, the second PCG sensor proximate to the first PCG sensor,

the first PCG sensor receiving a first PCG signal and the second PCG sensor receiving a second PCG signal, the first PCG signal including the S2 signal, the second PCG signal including the S2 signal attenuated relative to the first PCG signal, each of the first PCG signal and the second PCG signal including and a background noise signal,

the PCG signal conditioner including a noise reduction circuit that receives the first PCG signal from the first PCG sensor and the second PCG signal from the second PCG sensor, the noise reduction circuit subtracting the first PCG signal and the second PCG signal to attenuate the background noise signal.

41. Apparatus for receiving heart sounds from a chest wall, the apparatus comprising:

a sensor coupled to the chest wall and configured to receive heart sounds from the chest wall;

a cover disposed over the sensor and coupled to the chest wall;

adjusting means for adjusting the pressure of the sensor on the chest wall within the cover; and

holding means for coupling the cover to the chest wall,

wherein the holding means and the cover tend to increase a transmission of the heart sounds from the chest wall to the sensor relative to the sensor without the holding means or the cover.

42. Apparatus according to claim 41, further including a gel provided between the sensor and the chest wall for enhancing the transmission of the heart sounds from the chest wall to the sensor.

43. Apparatus according to claim 41, wherein the sensor is a piezoelectric transducer.

44. Apparatus according to claim 41, wherein the sensor is subject to background noise and the cover attenuates the background noise.