Compensation for tonometer sensor crosstalk and element spacing

• US 5,065,765 A
• Filed: 01/25/1990
• Issued: 11/19/1991
• Est. Priority Date: 06/23/1989
• Status: Expired due to Term

• Current Assignee: Omron Healthcare Company Limited (Omron Corporation)
• Original Assignee: Colin Electronics Co., Ltd.
• Inventors: Eckerle, Joseph S., Kornbluh, Roy
• Primary Examiner(s): Jaworski, Francis
• Assistant Examiner(s): Manuel, George
• Application Number:
  US07/470,241
• Time in Patent Office: 663 Days
• Field of Search: 128/672-675, 128/687-690, 128/715, 128/681, 128/901
• US Class Current: 600/485
• CPC Class Codes: A61B 2562/0247 Pressure sensors
• CPC Class Codes: A61B 2562/0261 Strain gauges
• CPC Class Codes: A61B 2562/043 in a linear array
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: Y10S 128/901 Suppression of noise in electric signal

Abstract

A method and apparatus for determining and compensating for the crosstalk behavior and element spacing of an arterial tonometer sensor in order to obtain a more accurate blood pressure measurement. The crosstalk behavior and the effects of element spacing in a tonometer sensor having a plurality of sensing elements located on a single diaphragm is derived using advanced modeling techniques. An error correction factor look-up table is computed and applied to an uncorrected blood pressure measurement, resulting in increased accuracy.

Claims

1. A method for compensating for crosstalk behavior and element spacing of the sensor of an arterial tonometer instrument, which sensor has a plurality of pressure sensing elements disposed on at least one diaphragm, the method comprising the steps of:

determining a measured artery pressure profile of a superficial artery;

using at least one characteristic of said measured artery pressure profile to determine an error correction factor;

determining an uncorrected blood pressure value; and

calculating a corrected blood pressure value by applying said error correction factor to said uncorrected blood pressure value.

2. The method of claim 1, wherein said step of determining an uncorrected blood pressure value comprises the step of determining an uncorrected diastolic pressure value.

3. The method of claim 1, wherein said step of determining an uncorrected blood pressure value comprises the step of determining an uncorrected systolic pressure value.

4. The method of claim 1, further comprising the step of sampling an entire blood pressure waveform and correcting each sampled value by applying said error correction factor.

5. The method of claim 1, wherein said at least one characteristic comprises artery width W_a.

6. The method of claim 1, wherein said at least one characteristic comprises dip depth D.

7. The method of claim 6, wherein said at least one characteristic further comprises artery width W_a.

9. The method of claim 1, wherein said error correction factor look-up table is precomputed by a method comprising the steps of:

analytically modeling said diaphragm;

using the results of said analytical modeling to obtain responses of said diaphragm to typical artery pressure profiles measured by a tonometer sensor placed over a superficial artery;

using said diaphragm responses to estimate errors in blood pressure measurements for said typical artery pressure profiles; and

calculating error correction factors necessary to compensate for said errors, and indexing them in said error correction factor look-up table according to said at least one characteristic.

8. A method for compensating for crosstalk behavior and element spacing of the sensor of an arterial tonometer instrument, which sensor has a plurality of pressure sensing elements disposed on at least one diaphragm, the method comprising the steps of:

determining a measured artery pressure profile of a superficial artery;

using at least one characteristic of said measured artery pressure profile to retrieve an error correction factor from a precomputed error correction factor look-up table;

determining an uncorrected blood pressure value; and

calculating a corrected blood pressure value by applying said error correction factor to said uncorrected blood pressure value.

10. The method of claim 8, wherein said error correction factor look-up table is precomputed by a method comprising the steps of:

modeling said diaphragm using finite element methods;

using the results of said finite element modeling to obtain responses of said diaphragm to typical artery pressure profiles measured by a tonometer sensor placed over a superficial artery;

using said diaphragm responses to estimate errors in blood pressure measurements for said typical artery pressure profiles; and

calculating error correction factors necessary to compensate for said errors, and indexing them in said error correction factor look-up table according to said at least one characteristic.

11. A method for compensating for crosstalk behavior and element spacing of the sensor of an arterial tonometer instrument, which sensor has a plurality of pressure sensing elements disposed on at least one diaphragm, the method comprising the steps of:

determining an apparent artery width W_a of a subject artery;

determining a dip depth D for said artery;

using said apparent artery width W_a and dip depth D to determine an error correction factor;

determining an uncorrected blood pressure value; and

calculating a corrected blood pressure value by applying said error correction factor to said uncorrected blood pressure value.

12. The method of claim 11, wherein said step of determining said apparent artery width Wa comprises the steps of:

locating left and right local maximums of pressure; and

calculating said apparent artery width W_a as the distance between the locations of said left and right local maximums of pressure.

13. The method of claim 11, wherein said step of determining said dip depth D comprises the steps of:

locating a spatial local minimum of pressure;

locating left and right local maximums of pressure; and

calculating said dip depth D as the average of respective differences between said left and right local maximums of pressure and said spatial local minimum of pressure.

14. The method of claim 11, wherein said apparent artery width W_a and dip depth D are utilized to retrieve said error correction factor from a precomputed error correction factor look-up table.

15. The method of claim 14, wherein said error correction factor look-up table is precomputed by a method comprising the steps of:

analytically modeling said diaphragm;

using the results of said analytical modeling to obtain responses of said diaphragm to typical artery pressure profiles measured by a tonometer sensor placed over a superficial artery;

using said responses to estimate errors in blood pressure measurements for said typical artery pressure profiles; and

calculating error correction factors necessary to compensate for said errors, and indexing them in said error correction factor look-up table according to said apparent artery width W_a and dip depth D.

16. The method of claim 15, wherein said diaphragm is analytically modeled as a plate, rigidly-clamped at four edges, of predetermined length and width which is subjected to a strip of pressure of predetermined width and magnitude that is symmetrically oriented about the minor axis of said plate, and said typical artery pressure profiles are modeled by the superposition of several pressure strips.

17. The method of claim 14, wherein said error correction factor look-up table is precomputed by a method comprising the steps of:

modeling said sensor using finite element methods;

using the results of said finite element modeling to obtain responses of said sensor to typical artery pressure profiles measured by a tonometer sensor placed over a superficial artery;

using said responses to estimate errors in blood pressure measurements for said typical artery pressure profiles; and

calculating error correction factors necessary to compensate for said errors, and indexing them in said error correction factor look-up table according to said apparent artery width W_a and dip depth D.

18. A method for compensating for crosstalk behavior and element spacing of the sensor of an arterial tonometer instrument, which sensor has a plurality of pressure sensing elements disposed on at least one diaphragm, the method comprising the steps of:

locating a sensing element that measures a maximum pulse amplitude corresponding to blood pressure pulses in a subject artery;

locating a spatial local minimum of pressures measured by said sensing elements near to the sensing element measuring said maximum pulse amplitude;

locating left and right spatial local maximums of the pressures measured by the sensing elements which are indicative of the left and right edges, respectively, of said artery;

calculating a dip depth D as the average of respective differences between said left and right local maximums of pressure and said spatial local minimum of pressure;

calculating an apparent artery width W_a as the distance between the locations of said left and right local maximums of pressure;

using said calculated dip depth D and apparent artery width Wa to retrieve an error correction factor from a precomputed error correction factor look-up table;

determining an uncorrected blood pressure value; and

calculating a corrected blood pressure value by applying said error correction factor to said uncorrected blood pressure value.

19. The method of claim 18, wherein said error correction factor look-up table is precomputed by analytically modeling said tonometer sensor diaphragm.

20. The method of claim 18, wherein said error correction factor look-up table is precomputed using finite element modeling techniques on said tonometer sensor.

21. The method of claim 18 further comprising the step of sampling an entire blood pressure waveform and correcting each sampled value by applying said error correction factor.

22. The method of claim 18, wherein said left and right spatial local maximums of pressure are located within a predetermined distance from said spatial local minimum of pressure.

23. The method of claim 22, wherein said left and right spatial local maximums of pressure are located within about 0.4 mm to 1.5 mm of said spatial local minimum of pressure for adult subjects.

24. The method of claim 23, wherein said about 0.4 mm to 1.5 mm distance is replaced with lower values when a subject is smaller than a typical adult.

25. A method for compensating for crosstalk behavior and element spacing of the sensor of an arterial tonometer instrument, which sensor has a plurality of pressure sensing elements disposed on at least one diaphragm, the method comprising the steps of:

locating a sensing element that measures a maximum pulse amplitude corresponding to blood pressure pulses in a subject artery;

locating a spatial local minimum of pressures measured by the sensing elements near to the sensing element measuring said maximum pulse amplitude;

identifying left and right locations on said at least one diaphragm at which a measured pulse amplitude is a predetermined fraction of said maximum pulse amplitude and which lie right and left, respectively, of said sensing element measuring said maximum pulse amplitude, said left and right locations being indicative of the left and right edges, respectively, of said artery;

calculating a dip depth D as the average of respective differences between the pressures at said left and right locations and said spatial local minimum of pressure;

calculating an apparent artery width W_a as the distance between said left and right locations;

using said calculated dip depth D and apparent artery width W_a to retrieve an error correction factor from a precomputed error correction factor look-up table;

determining an uncorrected blood pressure value; and

calculating a corrected blood pressure value by applying said error correction factor to said uncorrected blood pressure value.

26. The method of claim 25, wherein said predetermined fraction is about 60 to about 90 percent.

27. An apparatus for externally measuring blood pressure in an artery, said apparatus comprising:

arterial tonometer instrument means, including a sensor having a plurality of pressure sensing elements disposed on at least one diaphragm, for determining an uncorrected blood pressure value;

means for determining a measured artery pressure profile of said artery;

means for using at least one characteristic of said measured artery pressure profile to determine an error correction factor; and

means for calculating a corrected blood pressure value by applying said error correction factor to said uncorrected blood pressure value.

28. An apparatus for externally measuring blood pressure in an artery, said apparatus comprising:

arterial tonometer instrument means, including a sensor having a plurality of pressure sensing elements disposed on at least one diaphragm, for determining an uncorrected blood pressure value;

means for determining an apparent artery width W_a of said artery;

means for determining a dip depth D for said artery;

means for using said apparent artery width W_a and dip depth D to determine an error correction factor; and

means for calculating a corrected blood pressure value by applying said error correction factor to said uncorrected blood pressure value.

29. An arterial tonometer instrument, including a sensor having a plurality of pressure sensing elements disposed on at least one diaphragm, for externally measuring blood pressure in an artery, comprising:

means for locating a sensing element that measures a maximum pulse amplitude corresponding to blood pressure pulses in said artery;

means for locating a spatial local minimum of pressure measured by the plurality of pressure sensing elements near to the sensing element measuring said maximum pulse amplitude;

means for locating left and right local maximums of pressure measured by the sensing elements which are indicative of the left and right edges, respectively, of said artery;

means for determining an uncorrected blood pressure value;

means for calculating a dip depth D as the average of respective differences between said left and right local maximums of pressure and said spatial local minimum of pressure;

means for calculating an apparent artery width W_a as the distance between the locations of said left and right local maximums of pressure;

means for using said calculated dip depth D and apparent artery width W_a to retrieve an error correction factor from a precomputed error correction factor look-up table; and

means for calculating a corrected blood pressure value by applying said error correction factor to said uncorrected blood pressure value.

30. An arterial tonometer instrument, including a sensor having a plurality of pressure sensing elements disposed on at least one diaphragm, for externally measuring blood pressure in an artery, comprising:

means for locating a sensing element that measures a maximum pulse amplitude corresponding to blood pressure pulses in said artery;

means for locating a spatial local minimum of pressure measured by said plurality of pressure sensing elements near to the sensing element measuring said maximum pulse amplitude;

means for identifying left and right locations on said at least one diaphragm at which a measured pulse amplitude is a predetermined fraction of said maximum pulse amplitude, said left and right locations being indicative of the left and right edges, respectively, of said artery;

means for determining an uncorrected blood pressure value;

means for calculating a dip depth D as the average of respective differences between measured pressures at said left and right locations and said spatial local minimum of pressure;

means for calculating an apparent artery width W_a as the distance between said left and right locations;

means for using said calculated dip depth D and apparent artery width W_a to retrieve an error correction factor from a precomputed error look-up table; and

means for calculating a corrected blood pressure value by applying said error correction factor to said uncorrected blood pressure value.

31. A method for constructing an error correction factor look-up table for use in compensating for crosstalk behavior and element spacing of the sensor of an arterial tonometer instrument, which sensor has a plurality of sensing elements disposed on at least one diaphragm, the method comprising the steps of:

modeling at least one of said sensor and said diaphragm;

using the results of said modeling to obtain responses of at least one of said sensor and said diaphragm to typical artery pressure profiles measured by a tonometer sensor placed over a superficial artery;

using said responses to estimate errors in blood pressure measurements for said typical artery pressure profiles; and

calculating error correction factors necessary to compensate for said errors.

32. The method of claim 31, wherein said typical artery pressure profiles are characterized by two parameters, apparent artery width Wa and dip depth D, and said error correction factors are indexed in said error correction factor look-up table according to said two parameters.

33. The method of claim 31, wherein said diaphragm is modeled using an analytical model.

34. The method of claim 33, wherein said analytical model of said diaphragm is a plate, rigidly-clamped at four edges, of predetermined length and width which is subjected to a strip of pressure of predetermined width and magnitude that is symmetrically oriented about the minor axis of said plate, and wherein said analytical model of said diaphragm is used to obtain, by superposition of the solutions for several strips of pressure of varying widths and magnitudes, said responses to said typical artery pressure profiles.

35. The method of claim 31, wherein said sensor and diaphragm are modeled using finite element methods.

36. A method for constructing an error correction factor look-up table for use in compensating for crosstalk behavior and element spacing of the sensor of an arterial tonometer instrument, which sensor has a plurality of sensing elements disposed on at least one diaphragm, the method comprising the steps of:

analytically modeling said diaphragm as a plate, rigidly-clamped at four edges, of predetermined length and width which is subjected to a strip of pressure of predetermined width and magnitude that is symmetrically oriented about the minor axis of said plate;

using the results of said analytical modeling to obtain, by superposition of solutions for several strips of pressure of varying widths and magnitudes, responses of said diaphragm to typical artery pressure profiles measured by a tonometer sensor placed over a superficial artery;

using said responses to estimate errors in blood pressure measurements for said typical artery pressure profiles; and

calculating error correction factors necessary to compensate for said errors.

37. The method of claim 36, wherein said typical artery pressure profiles are characterized by two parameters, apparent artery width W_a and dip depth D, and said error correction factors are indexed in said error correction factor look-up table according to said two parameters.