Coherent pattern identification in non-stationary periodic data and blood pressure measurement using same

• US 5,772,600 A
• Filed: 06/17/1996
• Issued: 06/30/1998
• Est. Priority Date: 06/17/1996
• Status: Expired due to Fees

• Current Assignee: BP Sure LLC
• Original Assignee: BP Sure LLC
• Inventors: Kahn, Alan R., Bahr, Dennis E., Allen, Kurt W.
• Primary Examiner(s): Getzow, Scott M.
• Application Number:
  US08/665,362
• Time in Patent Office: 743 Days
• Field of Search: 128/670, 128/680, 128/681, 128/682
• US Class Current: 600/494
• CPC Class Codes: A61B 5/02208 using the Korotkoff method
• CPC Class Codes: A61B 5/0225 the pressure being controlled by electric signals, e.g. derived from Korotkoff sounds
• CPC Class Codes: A61B 5/0285 Measuring or recording phase velocity of blood waves

Abstract

A method and apparatus for automatically recognizing meaningful patterns in non-stationary periodic data is provided. The invention may be used in making measurements of physiological phenomena, such as arterial blood pressure, wherein data of interest is undergoing small changes in timing and magnitude in succeeding cycles, and wherein noise artifacts are detected along with the data of interest. Data points of interest are identified by grouping all received data points into family groups of multi-dimensional data points wherein each data point in the family group has dimensional values similar to at least one other data point in the family. The present invention may preferably be employed for the determination of a patient'"'"'s systolic and diastolic blood pressure levels. For this application, the data points include a time dimension value corresponding to the delay time between an ECG signal and the detection of a potential blood pressure sound by a microphone placed in an inflatable cuff on the arm of a patient, and a magnitude dimension value corresponding to the cuff pressure at the time of the potential blood pressure sound detection. Data points are collected for a series of cuff pressures ranging from above the systolic blood pressure level of the patient to below the diastolic blood pressure level of the patient. The highest and lowest pressures of data points in the family containing the largest number of data points are used to derive the systolic and diastolic blood pressure levels of the patient, respectively.

Claims

1. A method for identifying blood pressure sounds of a patient, comprising the steps of:

(a) applying a plurality of pressure levels to an artery of the patient;

(b) detecting the pressure applied at each of the plurality of pressure levels;

(c) detecting a patient ECG signal at each of the plurality of pressure levels;

(d) detecting a potential blood pressure sound at each of the plurality of pressure levels;

(e) determining a time delay between the detections of the ECG signal and the potential blood pressure sound;

(f) generating a two dimensional data point at each of the plurality of pressure levels, a time dimension value of the data point corresponding to the time delay between the detected patient ECG signal at the pressure level and the detected potential blood pressure sound at the pressure level and a magnitude dimension value of the data point corresponding to the detected pressure at the pressure level, the two dimensional data points generated at each of the pressure levels forming a data set;

(g) grouping the data points in the data set into families by grouping together data points from the data set such that each data point in a family has similar time and magnitude dimension values to at least one other data point included in the family; and

(h) selecting the data points in the family of data points that includes the largest number of data points as the set of data points of interest identifying blood pressure sounds.

2. The method of claim 1 comprising additionally the step of determining a patient'"'"'s blood pressure from the data points of interest, including the steps of determining the patients'"'"'s systolic blood pressure level based on the pressure level of a data point in the set of data points of interest having a largest pressure level dimension value and determining the patient'"'"'s diastolic blood pressure level based on a detected pressure level of a data point in the set of data points of interest having a smallest pressure level dimension value.

3. The method of claim 1 wherein the step of applying a plurality of pressure levels to an artery of the patient includes the steps of:

(a) wrapping an inflatable cuff around an upper arm of the patient;

(b) inflating the cuff to a pressure level exceeding the systolic blood pressure level of the patient; and

(c) gradually deflating the cuff to a cuff pressure less than the diastolic blood pressure level of the patient to apply the plurality of blood pressure levels to an artery in the arm of the patient.

4. The method of claim 1 wherein the step of applying a plurality of pressure levels to an artery of the patient includes the steps of:

(a) wrapping an inflatable cuff around an upper arm of the patient; and

(b) gradually inflating the cuff from a cuff pressure level below the diastolic blood pressure level of the patient to a cuff pressure level above the systolic blood pressure level of a patient to apply the plurality of pressure levels to an artery in the arm of the patient.

5. The method of claim 1 wherein the step of detecting a potential blood pressure sound includes the steps of placing a microphone on the patient over the artery, the microphone producing a microphone signal in response to blood pressure sounds and noise picked up by the microphone, and processing the microphone signal to generate a potential blood pressure sound detection signal in response to microphone signals produced in response to blood pressure sounds and noise that is similar to blood pressure sounds.

6. The method of claim 1 wherein the step of grouping data points in the data set into families includes the step of determining if two data points are similar by comparing the absolute value of the difference between the time dimension values of the data points with a time delay threshold value and comparing the absolute value of the difference between the magnitude dimension values of the data points with a pressure threshold value.

7. The method of claim 1 wherein a family of data points includes at least three data points such that each data point in the family has similar time and magnitude dimension values to at least one other data point included in the family.

8. The method of claim 1 including the additional steps of:

(a) repeating the step of grouping the data points in the data set into families each time a data point is added to the data set; and

(b) displaying a two dimensional plot of the data points in the family including the largest number of data points.

9. An apparatus for measuring the blood pressure of a patient, comprising:

(a) means for applying a plurality of pressure levels to an artery of the patient;

(b) means for detecting the pressure applied at each of the plurality of pressure levels;

(c) means for detecting a patient ECG signal at each of the plurality of pressure levels;

(d) means for detecting a potential blood pressure sound at each of the plurality of pressure levels;

(e) means for determining a time delay between the detections of the ECG signal and the potential blood pressure sound;

(f) means for generating a two dimensional data point at each of the plurality of pressure levels, a time dimension value of the data point corresponding to the time delay between the detected patient ECG signal at the pressure level and the detected potential blood pressure sound at the pressure level and a magnitude dimension value of the data point corresponding to the detected pressure level, the two dimensional data points generated at each of the pressure levels forming a data set;

(g) means for grouping the data points in the data set into families by grouping together data points from the data set such that each data point in a family has similar time and magnitude dimension values to at least one other data point included in the family;

(h) means for selecting the data points in the family of data points that includes the largest number of data points as the set of data points of interest; and

(i) means for determining the patient'"'"'s blood pressure from the data points of interest.

10. The apparatus for measuring blood pressure of claim 9 wherein the means for determining the patient'"'"'s blood pressure includes means for determining the patients'"'"'s systolic blood pressure level based on the detected pressure level of a data point in the set of data points of interest having a largest pressure level dimension value and for determining the patient'"'"'s diastolic blood pressure level based on a detected pressure level of a data point in the set of data points of interest having a smallest pressure level dimension value.

11. The apparatus for measuring blood pressure of claim 9 wherein the means for applying a plurality of pressure levels to an artery of the patient includes:

(a) an inflatable cuff;

(b) means for inflating the cuff to a pressure level exceeding the systolic blood pressure level of the patient; and

(c) means for gradually deflating the cuff to a cuff pressure less than the diastolic blood pressure level of the patient to apply the plurality of blood pressure levels to an artery in the arm of the patient.

12. The apparatus for measuring blood pressure of claim 9 wherein the means for applying a plurality of pressure levels to an artery of the patient includes:

(a) an inflatable cuff;

(b) means for gradually inflating the cuff from a cuff pressure level below the diastolic blood pressure level of the patient to a cuff pressure level above the systolic blood pressure level of a patient to apply the plurality of pressure levels to an artery in the arm of the patient.

13. The apparatus for measuring blood pressure of claim 9 wherein the means for detecting the pressure applied at each of the plurality of pressure levels includes a pressure transducer.

14. The apparatus for measuring blood pressure of claim 9 wherein the means for detecting a potential blood pressure sound includes a microphone placed on the patient over the artery, the microphone producing a microphone signal in response to blood pressure sounds and noise picked up by the microphone, and means for processing the microphone signal to generate a potential blood pressure sound detection signal in response to microphone signals produced in response to blood pressure sounds and noise that is similar to blood pressure sounds.

15. The apparatus for measuring blood pressure of claim 9 wherein the means for grouping data points in the data set into families includes means for determining if two data points are similar by comparing the absolute value of the difference between the time dimension values of the data points with a time delay threshold value and comparing the absolute value of the difference between the magnitude dimension values of the data points with a pressure threshold value.

16. The apparatus for measuring blood pressure of claim 9 wherein the means for grouping the data points in the data set into families includes a digital microprocessor implementing an algorithm for grouping the data points.

17. The apparatus for measuring blood pressure of claim 9 including a display device and means for displaying a two dimensional plot of the data points in the family including the largest number of data points on the display device.

18. A method for making biological measurements, comprising the steps of:

(a) making detections of potential non-stationary periodic biological phenomena over a plurality of cycles;

(b) generating a multi-dimensional data point at each of the plurality of cycles, each data point including at least a time dimension value of the data point corresponding to a time dimension of the potential phenomenon detection and a magnitude dimension value of the data point corresponding to a magnitude dimension of the potential phenomenon detection, the multi-dimensional data points generated at each of the plurality of cycles forming a data set;

(c) grouping the data points in the data set into families by grouping together data points from the data set such that each data point in a family has similar time and magnitude dimension values to at least one other data point included in the family;

(d) selecting the data points in the family of data points that includes the largest number of data points as the set of data points of interest; and

(e) making a biological measurement from the data points of interest.

19. The method of claim 18 wherein the potential non-stationary periodic biological phenomena include ECG signals and blood pressure sounds produced by the opening of a patient'"'"'s artery to which a plurality of pressure levels are applied, wherein the time dimension value of the potential non-stationary periodic biological phenomenon detection includes a time delay between the detection of the ECG signal and the detection of the blood pressure sound at each pressure level, wherein the magnitude dimension value of the potential non-stationary periodic biological phenomenon detection includes the pressure level, and wherein the biological measurement made from the data points of interest includes systolic and diastolic blood pressure levels of a patient.

20. The method of claim 18 wherein the step of grouping data points in the data set into families includes the step of determining if two data points are similar by comparing the absolute value of the difference between the time dimension values of the data points with a time dimension threshold value and comparing the absolute value of the difference between the magnitude dimension values of the data points with a magnitude dimension threshold value.

21. The method of claim 18 wherein a family of data points includes at least three data points such that each data point in the family has similar time and magnitude dimension values to at least one other data point included in the family.

22. The method of claim 18 wherein the potential non-stationary periodic biological phenomena include pulse waveform signals produced by the opening of a patient'"'"'s artery to which a plurality of pressure levels are applied and which are detected out of phase by two separated microphones placed on the patient over the artery, wherein a multi-dimensional data point generated at each pressure level includes a time dimension value corresponding to a distance in time between peaks of the pulse waveform signals detected by each microphone, a magnitude dimension value corresponding to a ratio of amplitudes of the pulse waveform signals detected by each microphone, and a time dimension value corresponding to a ratio of widths of the pulse waveform signals detected by each microphone, and wherein the biological measurement made from the data points of interest includes systolic and diastolic blood pressure levels of the patient.