Inductive plethysmographic transducers and electronic circuitry therefor

• US 5,331,968 A
• Filed: 03/10/1993
• Issued: 07/26/1994
• Est. Priority Date: 10/19/1990
• Status: Expired due to Term

• Current Assignee: Adidas AG
• Original Assignee: NIMS Incorporated
• Inventors: Sackner, Marvin A., Williams, Gerald, Pak, Chu, Chong, James W., Watson, Herman
• Primary Examiner(s): Cohen, Lee S.
• Assistant Examiner(s): NASSER, ROBERT L
• Application Number:
  US08/032,835
• Time in Patent Office: 503 Days
• Field of Search: 128/734, 128/721, 128/722, 128/716, 128/719, 128/670, 128/671
• US Class Current: 600/534
• CPC Class Codes: A61B 5/0809 by impedance pneumography

Abstract

The present invention is an apparatus and method for improving the detection of the inductance "signal" generated by an inductive plethysmograph (12). Signal detection is improved by modifying the design of the inductive plethysmograph (12) and also by improving the design of the associated circuitry. By virtue of these improvements, the associated circuitry may be located remotely rather than on the transducer, as is the current practice. In one aspect of the invention, the impedance matching transformer (14) joining the inductive plethysmograph (12) to the oscillator (16) is selected such that the inductance of its primary winding is greater than about ten times the reflected inductance of the inductive plethysmograph (12) and the cable (24) joining it to the transformer (14). In accordance with another aspect of the invention, the inductive plethysmograph (12) is modified such that the conductor (20) incorporated therein encircles the relevant body portion a plurality of times. In yet a further aspect of the invention, the cable (24) connecting the inductive plethysmograph (12) to the transformer (14) is selected such that the ratio of the diameter of its screen to the diameter of its center conductor is minimized for reducing the inductance per unit length thereof.

Claims

1. In an apparatus comprising at least one inductive plethysmograph for disposition about a subject and incorporating a conductor, said conductor comprising the inductance component of an LC oscillator circuit, said conductor being electrically connected to said oscillator circuit through an impedance matching transformer with a secondary winding of the transformer being electrically connected to said conductor and a primary winding thereof being electrically connected to said oscillator circuit, the improvement comprising:

said conductor being electrically connected to said transformer via a connecting cable, said connecting cable being sufficiently long that said oscillator circuit and said transformer are disposed sufficiently remote from said plethysmograph to prevent said oscillator circuit and said transformer from contact with said plethysmograph or said subject when said subject is lying on said connecting cable; and

said transformer primary winding having an inductance greater than about ten times the reflected inductance of said conductor and said cable, whereby attenuation of changes in the inductance of said conductor and connecting cable is reduced.

2. The apparatus of claim 1, wherein the inductance of the primary winding of said transformer is about ten times the reflected inductance of said conductor and said cable.

3. The apparatus of claim 1, wherein said cable has a length of about ten feet.

4. The apparatus of claim 3, wherein said cable comprises a coaxial cable having a center conductor and a screen, wherein the ratio of a diameter of said screen to a diameter of said center conductor is minimized for reducing the inductance per unit length thereof.

5. The apparatus of claim 4, wherein the inductance per unit length of said cable is less than about 0.1 microhenries per foot.

6. The apparatus of claim 5, wherein the inductance per unit length of said cable is about 0.03 microhenries per foot.

7. The apparatus of claim 1, wherein the turns ratio of said transformer steps up the combined impedance of said inductive plethysmograph and said cable to about 150 ohms.

8. The apparatus of claim 1, wherein said cable comprises a coaxial cable having a center conductor and a screen, wherein the ratio of a diameter of said screen to a diameter of said center conductor is minimized for reducing the inductance per unit length thereof.

9. The apparatus of claim 8, wherein said conductor has a plurality of turns whereby when said inductive plethysmograph is in encircling relation about a body part said conductor encircles said body part a plurality of times for improving the sensitivity of said apparatus.

10. The apparatus of claim 9, wherein said inductive plethysmograph comprises a stretchable substrate and wherein said conductor is arranged in a zigzag pattern on said stretchable substrate.

11. The apparatus of claim 10, wherein said inductive plethysmograph comprises two free ends joinable by mating connectors and further comprises lengths of conductor supported on said substrate with one end of each conductor length being joined to one connector and the other end being joined to the other connector, whereby when said connectors are joined said conductor having a plurality of turns is formed.

12. The apparatus of claim 8, wherein the inductance per unit length of said cable is less than about 0.1 microhenries per foot.

13. The apparatus of claim 12, wherein the inductance per unit length of said cable is about 0.03 microhenries per foot.

14. The apparatus of claim 1, wherein said conductor has a plurality of turns whereby when said inductive plethysmograph is in encircling relation about a body part said conductor encircles said body part a plurality of times for improving the sensitivity of said apparatus.

15. The apparatus of claim 14, wherein said inductive plethysmograph comprises a stretchable substrate and wherein said conductor is arranged in a zigzag pattern on said stretchable substrate.

16. The apparatus of claim 15, wherein said inductive plethysmograph comprises two free ends joinable by mating connectors and further comprises lengths of conductor supported on said substrate with one end of each conductor length being joined to one connector and the other end being joined to the other connector, whereby when said connectors are joined said conductor having a plurality of turns is formed.

17. The apparatus of claim 1, wherein said connecting cable is at least ten feet.

18. In an apparatus of the type comprising at least one inductance plethysmograph adapted for placement in encircling relation about a body portion of a subject, said inductive plethysmograph incorporating a conductor which comprises the inductance component of an LC oscillator circuit, the improvement comprising:

said conductor having a plurality of turns whereby when said inductive plethysmograph is in encircling relation about said body portion said conductor encircles said body portion a plurality of times for improving the sensitivity of said apparatus,

wherein said inductive plethysmograph comprises a stretchable substrate and wherein said conductor is arranged in a zigzag pattern on said stretchable substrate,

wherein said inductive plethysmograph comprises two free ends joinable by mating connectors and further comprises lengths of conductor supported on said substrate with one end of each conductor length being joined to one connector and the other end being joined to the other connector, whereby when said connectors are joined said conductor having a plurality of turns is formed,

wherein said conductor being electrically connected to said oscillator circuit through an impedance matching transformer with a secondary winding of the transformer being electrically connected to said conductor and a primary winding thereof being electrically connected to said oscillator circuit,

wherein said conductor is electrically connected to said transformer via a connecting cable, said connecting cable being sufficiently long that said oscillator circuit and said transformer are disposed sufficiently remote from said plethysmograph to prevent said oscillator circuit and said transformer from contact with said plethysmograph or said subject when said subject is lying on said connecting cable, and

wherein said transformer primary winding having an inductance greater than about ten times the reflected inductance of said conductor and said cable, whereby attenuation of changes int he inductance of said conductor and connecting cable is reduced.

19. The apparatus of claim 18, wherein the inductance of the primary winding of said transformer is about ten times the reflected inductance said conductor and said cable.

20. The apparatus of claim 19, wherein said cable comprises a coaxial cable having a center conductor and a screen, wherein the ratio of a diameter of said screen to a diameter of said center conductor is minimized for reducing the inductance per unit length thereof.

21. The apparatus of claim 20, wherein the inductance per unit length of said cable is less than about 0.1 microhenries per foot.

22. The apparatus of claim 21, wherein the inductance per unit length of said cable is about 0.1 microhenries per foot.

23. The apparatus of claim 18, wherein said cable has a length of about ten feet.

24. The apparatus of claim 18, wherein the turns ratio of said transformer steps up the combined impedance of said inductive plethysmograph and said cable to about 150 ohms.

25. The apparatus of claim 18, wherein said cable comprises a coaxial cable having a center conductor and a screen, wherein the ratio of a diameter of said screen to a diameter of said center conductor is minimized for reducing the inductance per unit length thereof.

26. The apparatus of claim 25, wherein the inductance per unit length of said cable is less than about 0.1 microhenries per foot.

27. The apparatus of claim 26, wherein the inductance per unit length of said cable is about 0.03 microhenries per foot.

28. In an apparatus of the type comprising at least one inductive plethysmograph for disposition about a subject and incorporating a conductor, said conductor comprising the inductance component of an LC oscillator circuit, said conductor being electrically connected to said oscillator circuit through an impedance matching transformer with a secondary winding of the transformer being connected to said conductor and a primary winding thereof being electrically connected to said oscillator circuit, the improvement comprising:

said conductor being electrically connected to said transformer via a connecting cable comprising a coaxial cable comprising a center conductor and a screen, said connecting cable being sufficiently long that said oscillator circuit and said transformer are disposed sufficiently remote from said plethysmograph to prevent said oscillator circuit and said transformer from contact with said plethysmograph or said subject when said subject is lying on said connecting cable, wherein the ratio of a diameter of said screen to a diameter of said center conductor is minimized for reducing the inductance per unit length thereof, and said transformer primary winding having a first number of turns said secondary winding having a second number of turns, a ratio of the first number of turns to the second number of turns is selected so as to compensate for attenuation of changes in inductance of the conductor and the cable.

29. The apparatus of claim 28, wherein the inductance per unit length of said cable is less than about 0.1 microhenries per foot.

30. The apparatus of claim 29, wherein the inductance per unit length of said cable is about 0.03 microhenries per foot.

31. The apparatus of claim 28, wherein said coaxial cable is at least ten feet.