Pressure sensor, pressure fluctuation detector and pulse detector using the pressure sensor

• US 5,704,363 A
• Filed: 05/15/1995
• Issued: 01/06/1998
• Est. Priority Date: 08/11/1993
• Status: Expired due to Fees

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Amano, Kazuhiko
• Primary Examiner(s): Bahr, Jennifer
• Assistant Examiner(s): GILBERT, SAMUEL G
• Application Number:
  US08/403,697
• Time in Patent Office: 967 Days
• Field of Search: 128/672, 128/675, 128/687-690
• US Class Current: 600/500
• CPC Class Codes: A61B 2562/0261 Strain gauges
• 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 5/02438 with portable devices, e.g. worn by the patient
• CPC Class Codes: A61B 5/0285 Measuring or recording phase velocity of blood waves
• CPC Class Codes: A61B 5/681 Wristwatch-type devices
• CPC Class Codes: A61B 5/6822 Neck

Abstract

The present invention has as its objective the presentation of a compact and simple pressure sensor having the ability to measure pulses, the pressure sensor 10 being composed of pressure sensing elements S₁ -S₄ and elastic rubber body 1. The measurement positions Q₁ -Q₄ of the pressure sensing elements S₁ -S₄ are on the bottom surface L of the convex-shaped elastic rubber body 1, at the same distance a from the origin of the x and y axes. If the elastic rubber body 1 is pressed in the vicinity of an artery, blood current changes in said artery, that is, vibrations from the artery occur on the exposed surface of the elastic rubber body 1, these vibrations propagate through the elastic rubber body 1 as elastic waves, and are measured as pressure waves by the pressure sensing elements S₁ -S₄. Their magnitudes decrease as the inverse square of the propagation distance of the elastic waves through the elastic rubber body 1, and the coordinates of the projection of the pressure wave generation point on the bottom surface L are calculated from the voltages V₁ -V₄ of the pressure sensing elements S₁ -S₄ and the distances from the pressure vibration generation point to the measurement positions Q₁ -Q₄. By determining these coordinates for each passage of a set time interval, the pulse front propagation speed and the artery position are able to be determined.

Claims

1. A pressure sensing apparatus including:

a flat surface;

at least three pressure measurement means for measuring pressures at different measurement positions on said flat surface, and for outputting output signals proportional to pressures measured at said measurement positions;

an elastic member having a convex shape for propagating pressure vibrations and for attenuating said pressure vibrations as they propagate across said elastic member;

an attachment means for attaching said elastic member to said flat surface so that a bottom surface of said elastic member covers said measurement positions; and

wherein

said elastic member includes an exposed surface for engagement with a measurement surface whereby pressure vibrations on said measurement surface are measured by said at least three pressure measurement means in accordance with pressure vibrations propagated across and attenuated by said elastic member.

2. A pressure sensor according to claim 1, wherein said elastic member and said at least three pressure measurement means are attached by an adhesive layer having elasticity.

3. A pressure sensor according to claim 1, wherein the number of said at least three pressure measurement means is four, their measurement positions each lie on orthogonal axes which intersect at a center of the bottom surface of said elastic member, and are positioned at equal distances from said center of the bottom surface.

4. A pressure sensor according to claim 1, wherein said at least three pressure measurement means are formed on the some semiconductor substrate.

5. A pressure sensor according to claim 4, wherein underneath the bottom surface of said elastic member, hollow chambers are provided, each opening onto a different position on said flat surface, and each of said at least three pressure measurement means are stored in one of said hollow chambers, wherein they measure the internal pressures of said hollow chambers.

6. A pressure sensor according to claim 5, wherein each of said hollow chambers is filled with a liquid substance.

7. A pressure sensor according to claim 4, the bottom surface of said elastic member further including,

hollow chambers opening onto different positions on said flat surface, and

pressure transmission routes for guiding the internal pressures of said hollow chambers to each of said at least three pressure measurement means

and each of said at least three pressure measurement means measures the internal pressure of the corresponding pressure transmission route.

8. A pressure sensor according to claim 7, wherein each of said hollow chambers and said pressure transmission routes are filled with a liquid substance.

9. A pressure sensor according to claim 7, wherein said pressure transmission routes are composed of rigid bodies.

10. A pressure sensor according to claim 1, further including a highly elastic member having a higher elasticity than said elastic member is coated on an exposed surface of said elastic member.

11. A pressure sensor according to claim 1, further including fragments of a highly elastic material having a higher elasticity than said elastic member are distributed dispersively on an exposed surface of said elastic member.

12. A pressure sensor according to claim 1, wherein each of said at least three pressure measurement means outputs signals complying with the pressure by the setting of a set bias signal,

and having a bias signal setting means for setting an equal bias signal for each of said at least three pressure measurement means.

13. A pressure sensor according to claim 12, wherein said bias signal setting means only sends bias signals to each of said at least three pressure measurement means during pressure measurement.

14. A pressure sensor according to claim 12, wherein said bias signal setting means intermittently sends bias signals to each of said at least three pressure measurement means.

15. A pressure sensor according to claim 12, wherein said bias signal is a constant current pulse.

16. A pressure sensing apparatus according to claim 1 including a converter means for converting said output signals from said at least three pressure measurement means to digital signals.

17. A pressure vibration measurement apparatus using a pressure sensor according to claim 16, wherein said converter means performs conversions to digital signals when bias signals are being sent to said at least three pressure measurement means.

18. A pressure sensing apparatus according to claim 16 including a first memory means for storing at least one of the digital signals converted by said converter means.

19. A pressure sensing apparatus according to claim 16, wherein said measurement surface is an individual'"'"'s skin and wherein a pulse from an artery in the vicinity of said elastic member in engagement with said measurement surface is measured as pressure vibrations by at least one of said at least three pressure measurement means.

20. A pressure sensing apparatus according to claim 19, including a strap for attaching said elastic member to a wrist of said individual.

21. A pressure sensing apparatus according to claim 19, further including:

a first calculation means for determining, after each passage of a set time interval, the coordinates of the projection on said flat surface of a pressure vibration point, generated on said exposed surface of said elastic member by a pulse from an artery in the vicinity of said elastic member, from ratios of measurement signals from said at least three pressure measurement means; and

a display means for plotting and displaying the coordinates determined after each passage of a set time interval by said first calculation means.

22. A pressure sensing apparatus according to claim 21, further including a time interval control means for changing the length of said time interval by discerning a size of a shift speed of said coordinates.

23. A pressure sensing apparatus according to claim 21, wherein said display means includes means for comparing and displaying measurement positions of said at least three measurement means and the coordinates determined by said first calculation means.

24. A pressure sensing apparatus according to claim 19, including a mathematical coordinate calculation means for calculating mathematical coordinates of a waveform of a pulse measured by at least one of said at least three pressure measurement means.

25. A pressure sensing apparatus according to claim 22, further including a discerning means for discerning a physical condition of said individual based on the mathematical coordinates calculated by said mathematical coordinate calculation means.

26. A pressure sensing apparatus according to claim 25, further including a first display means for displaying the physical condition of the patient discerned by said discerning means.

27. A pressure sensing apparatus according to claim 24, wherein said mathematical coordinate calculation means includes a pulse waveform mathematical coordinate calculation means for outputting a coordinate signal after measuring a minimum value of the pulse waveform and three maximal values subsequent to said minimum value.

28. A pressure sensing apparatus according to claim 19, further including:

a first calculation means for determining, after each passage of a set time interval, the coordinates of the projection on said flat surface of a pressure vibration point, generated on said exposed surface of said elastic member by a pulse from an artery in the vicinity of said elastic member, from ratios of measurement signals from said at least three pressure measurement means;

a second calculation means for determining a shift speed of the coordinates determined after each passage of a set time interval by said first calculation means; and

means for outputting said shift speed as a pulse front propagation speed of said artery.

29. A pressuring sensing apparatus according to claim 28, further including a first time interval control means for changing the length of said set time interval by discerning the size of said shift speed.

30. A pressure sensing apparatus according to claim 28, further including:

a memory means for pre-storing a correlation between a pulse front propagation speed and a normal blood pressure;

a blood pressure value calculation means for reading an output pulse front propagation speed and correlating said speed with the set individual data in said memory to output a blood pressure value of said individual being monitored.

31. A pressure sensing apparatus according to claim 30, further including a second display means for displaying an individual'"'"'s blood pressure information output by said blood pressure value calculation means.

32. A pressure sensor according to claim 1, wherein dome-shaped cavities are provided at positions covering the measurement positions of said pressure measurement means of said elastic member.

33. A pressure sensor according to claim 32, wherein, if the diameter of the bottom surface of said dome-shaped cavity is s, and the radius of the bottom surface of said elastic member is r, then said dome-shaped cavity is provided so as to satisfy the condition:

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