Apparatus and process for producing sphygmometric information

• US 3,903,872 A
• Filed: 02/25/1974
• Issued: 09/09/1975
• Est. Priority Date: 02/25/1974
• Status: Expired due to Term

• Current Assignee: Baxter International Inc.
• Original Assignee: William T. Link
• Inventors: Link, William T.
• Primary Examiner(s): Gaudet, Richard A.
• Assistant Examiner(s): Cohen, Lee S.
• Application Number:
  US05/445,559
• Time in Patent Office: 561 Days
• Field of Search: 128/2.5G,2.5A,2.5M,2.5N,2.5Q,2.5Z
• US Class Current: 600/494
• CPC Class Codes: A61B 5/022 by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 7/045 Detection of Korotkoff sounds A61B5/0225 takes precedence; measuring blood pressure A61B5/021

Abstract

The invention comprises an apparatus and a process for producing sphygmometric information. The pressure in a blood pressure cuff is detected by a pressure transducer. The pressure signal is then differentiated with respect to time into a representation of a time derivative thereof. The representation is a function of two variables, the pressure applied externally adjacent an artery and time within a blood pressure pulse. The time derivative can be a first derivative, a second derivative or a higher derivative. Comparison is then made at a chosen time within a pulse of the time derivative with different applied pressures. When the first derivative is a negative maximum as a function of applied pressure the corresponding applied pressure is representative of the actual pressure within the blood vessel undistorted by the applied pressure. The apparatus and process of the present invention are particularly useful for accurately and quickly determining diastolic pressure and systolic pressure, for accurately reproducing a pressure trace corresponding substantially to the undistorted blood pressure pulse within an artery, and for providing indication of a plurality of time derivatives and the corresponding applied pressures at a measurement time within a pulse, which indication is substantially proportional to a measurement of the compliance of the artery.

Claims

1. In an apparatus for producing information indicative of the physical condition of a living test subject, said apparatus including means for applying a selectively changeable pressure to the test subject adjacent a blood vessel and means for measuring a fluctuating quantity proportional to a sum, said sum comprising a time-dependent fluctuating component representative of the pulsatile pressure within the blood vessel, plus the selectively changeable pressure applied externally adjacent the blood vessel, the improvement comprising:

means for converting said quantity into an electronic representation of a time derivative of at least the fluctuating component thereof;

means for analyzing changes in said electronic representation of said time derivative induced by changing the applied pressure; and

means for producing an output from said analyzing means indicative of the physical condition of the living test subject

2. An apparatus for producing information indicative of the physical condition of a living test subject, comprising:

means for applying a selectively changeable pressure to the test subject externally adjacent a blood vessel;

means for measuring a quantity proportional to a sum, said sum comprising;

a. a time-dependent fluctuating component representative of the pulsatile pressure within the blood vessel, plus b. the changeable pressure applied externally adjacent the blood vessel;

means for converting said quantity into a representation of a time-derivative thereof;

means for substantially maximizing the time-derivative of at least the fluctuating component of the quantity as a function of the applied pressure at a measurement time within the pulse; and

means for producing an output from said maximizing means indicative of the physical condition of the living test subject.

3. An apparatus as in claim 2, wherein the converting means comprises means for converting the quantity into a representation of a first time derivative thereof and the output producing means includes means for providing as said output a readout indicative of the applied pressure corresponding substantially to a maximum first derivative.

4. An apparatus as in claim 3 wherein the maximizing means includes means for selecting the measurement time relative to a reference time within the pulse, the reference time being the time when the first derivative changes sign from negative to positive and the blood pressure is substantially equal to the diastolic pressure of the blood vessel.

5. An apparatus as in claim 4 wherein the measurement time selecting means selects the measurement time to be adjacent to the reference time and the first derivative to be negative whereby the output is to a close approximation equal to the diastolic pressure of the blood vessel.

6. An apparatus as in claim 2 wherein the output producing means includes means for providing as said output a readout indicative of a plurality of measurement times and the corresponding applied pressures when the time derivative of the quantity is substantially maximized for each of the plurality of measurement times.

7. An apparatus as in claim 2 wherein the output producing means includes means for providing as said output a readout indicative of a plurality of time derivatives and the corresponding applied pressures at the measurement time.

8. An apparatus as in claim 2, wherein the converting means comprises means for converting the quantity into a representation of a second Time derivative and the output producing means includes means for providing as said output a readout indicative of a value of the applied pressure corresponding substantially to the maximum second derivative.

9. A sphygmometric apparatus, comprising:

means for applying a selectively changeable pressure externally adjacent a blood vessel;

means in communication with said pressure applying means for measuring a quantity proportional to a sum, said sum comprising;

a. a time-dependent fluctuation component representative of the pulsatile pressure within the blood vessel, plus b. the changeable pressure applied externally adjacent the blood vessel;

means for converting the quantity into a representation of a time-derivative thereof;

means for substantially maximizing the time derivative of at least the fluctuating component of the quantity as a function of the applied pressure at a measurement time within a pulse; and

means for producing an output from said maximizing means indicative of the physical condition of a living test subject.

10. An apparatus as in claim 9, wherein the pressure applying means includes a blood pressure cuff and the quantity measuring means comprises a pressure transducer in communication therewith.

11. An apparatus as in claim 10, wherein the converting means comprises a differentiator.

12. In a process for producing information indicative of the physical condition of a living test subject, including applying a selectively changeable pressure to the test subject externally adjacent a blood vessel and measuring a quantity proportional to a sum, said sum comprising time-dependent fluctuating component representative of the pulsatile pressure within the blood vessel, plus the changeable pressure applied externally adjacent the blood vessel, the improvement comprising:

A. converting said quantity into an electronic representation of a time derivative of at least the fluctuating component thereof;

B. electronically analyzing changes in said representation of said time derivative induced by differing said applied pressure; and

C. producing from said analyzing an output indicative of the physical condition of the living test subject.

13. A process for producing information indicative of the physical condition of a living test subject, comprising:

applying a selectively changeable pressure to the test subject externally adjacent a blood vessel;

measuring a quantity proportional to a sum, said sum comprising;

a. a time-dependent fluctuating component representative of the pulsatile pressure within the blood vessel, plus b. the changeable pressure applied externally adjacent the blood vessel;

converting said quantity into an electronic representation of a time derivative thereof;

substantially maximizing the time derivative of at least the fluctuating component of the quantity as a function of the applied pressure at a measurement time within the pulse; and

producing an output from said maximizing indicative of the physical condition of the living test subject.

14. A process as in claim 13, wherein the quantity is converted into a representation of a first time derivative, and wherein the output produced is indicative of a value of the applied pressure corresponding substantially to the maximum first derivative.

15. A process as in claim 14 including determining the measurement time relative to a reference time within the pulse, the reference time being the time when the first derivative changes sign from negative to positive and the applied pressure is substantially equal to the diastolic pressure of the blood vessel.

16. A process as in claim 15 including selecting the measurement time to be adjacent the reference time and the first derivative to be negative, whereby the output is to a close approximation equal to the diastolic pressure of the blood vessel.

17. A process as in claim 13 wherein the output producing step provides an oUtput indicative of a plurality of measurement times and the corresponding applied pressure when the time derivative of the quantity is substantially maximized for each of the plurality of measurement times.

18. A process as in claim 13 wherein the converting step converts the quantity into a representation of a first time derivative and the output producing step provides an output indicative of a plurality of first derivatives and the corresponding applied pressure at the measurement time.

19. A process as in claim 13, wherein the converting step converts the quantity into a representation of a second time derivative and the output-producing step provides an output indicative of a value of the applied pressure corresponding substantially to the maximum second derivative.

20. Apparatus for indicating the physical condition of a living test subject, comprising:

a. means for applying a selectively changeable constricting pressure to a blood vessel of said subject;

b. sensor means associated with said pressure applying means for producing an electrical signal which is a function of the sum of the applied pressure plus a representation of the pulsatile pressure fluctuations in said blood vessel;

c. electronic processing means for calculating the time derivative of at least said representation of said pulsatile pressure portion of said signal, sampling said differentiated signal at a measurement time within a pulse and determining the applied pressure corresponding to substantially a maximum value of said differentiated signal at said measurement time; and

d. means for producing an output from said electronic processing means indicative of the physical condition of said subject.

21. An apparatus for indirectly measuring the diastolic pressure of the blood in an artery of a mammal, comprising means engaging the body of the mammal external of the body and overlying an artery in the mammal, said engaging means including means for applying a changeable pressure to said artery to at least partially collapse same and transducer means for detecting pulsations representative of the pressure in the artery and providing an electrical output representing the wave form of the pressure of the blood in the artery due to the beating of the heart in the mammal with respect to time and including diastolic and systolic pressures, means differentiating the electrical output from the transducer means at least at times just prior to a rise from the diastolic pressure towards the systolic pressure to ascertain the slope of the wave form in this region during each heart beat, and means for ascertaining when the differentiated value becomes a maximum to provide the diastolic pressure.

22. An apparatus as in claim 21 wherein said means engaging the body is in the form of a cuff which surrounds the artery and wherein the transducer means measures the sum of the pressure applied by the means engaging the body plus the pulsatile pressure representative of the pressure in the artery.

23. A process for indicating the physical condition of a living test subject, comprising:

a. applying a selectively changeable constricting pressure to a blood vessel of said subject;

b. electronically sensing the sum of the applied pressure plus a representation of the pulsatile pressure fluctuations in said vessel to produce an electrical signal which is a function of said sum;

c. electronically processing said signal to (1) produce a time derivative of at least said representation of said pulsatile pressure fluctuations portion of said signal, (2) sample said differentiated signal at a measurement time within a pulse and (3) determine the applied pressure corresponding to substantially a maximum value of said differentiated signal at said measurement time; and

d. producing an output from said electronic processing indicative of the physical condition of said subject.

24. In a method for sensing the diastolic pressure in an arteRy of a mammal in which the blood pressure in the artery follows a wave form which includes a diastolic and systolic pressure for each heart beat, applying a changeable pressure to the body of the mammal external of the mammal and overlying an artery in the mammal which pressure is capable of at least partially collapsing the artery in the mammal, detecting pulsations in the blood pressure in the artery and providing an output with respect to time representing a wave form of the pressure of the blood in the artery due to the beating of the heart of the mammal and including diastolic and systolic pressures, ascertaining the slope of the wave form immediately prior to the systolic rise in the wave form for a plurality of heart beats by differentiating the output and ascertaining when said slope becomes the greatest to thereby ascertain the diastolic pressure.

25. A method as in claim 24 wherein the step of ascertaining where the slope becomes the greatest is obtained by ascertaining when the differentiated output becomes a negative maximum.

26. A method of determining diastolic blood pressure with the aid of a cuff adapted to apply a constricting pressure to a blood vessel, comprising the steps of applying pressure to the cuff, detecting the blood pressure at a point in the blood pressure pulse immediately prior to the onset of the systolic rise, differentiating said blood pressure at said point to form a first time derivative of the blood pressure at said point, maximizing said first time derivative as a function of said applied pressure and providing an output corresponding generally to a value of said applied pressure which corresponds to said first time derivative being a maximum.