Intracranial pressure monitor

• US 4,026,276 A
• Filed: 04/05/1976
• Issued: 05/31/1977
• Est. Priority Date: 04/05/1976
• Status: Expired due to Term

• Current Assignee: Johns Hopkins University
• Original Assignee: Johns Hopkins University
• Inventors: Chubbuck, John G.
• Primary Examiner(s): Pellegrino, Stephen C.
• Application Number:
  US05/673,970
• Time in Patent Office: 421 Days
• Field of Search: 128/2 P, 128/2 R, 128/2.1 A, 128/2.05 E, 128/2.05 D, 73/398 R, 73/398 C, 73/399
• US Class Current: 600/407
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/031 Intracranial pressure
• CPC Class Codes: G01L 19/086 for remote indication
• CPC Class Codes: G01L 9/0038 using variations in capacitance

Abstract

Pressure monitoring apparatus implantable in the cranium to measure intracranial pressure, the apparatus comprises a passive resonant circuit having a natural frequency influenced by ambient pressure. The resonant circuit has inductance and capacitance capability for comparing the local environmental pressure to that of a volume of gas trapped inside the apparatus, the environmental pressure being measured by observation of the frequency at which energy is absorbed from an imposed magnetic field located externally of the cranium.

Claims

1. Apparatus for sensing pressure within a cavity in the body of a living entity, comprising:

means deformable in response to pressure within the cavity, said means comprising

a housing formed of non-porous and electrically non-conductive material, the housing defining a chamber,

a predetermined mass of fluid disposed within the chamber, and,

pressure responsive means carried on the housing and extending into the chamber, said pressure responsive means being formed of non-porous and elastically compliant material and being deformable by pressure imposed on the apparatus to change the volume occupied by the mass of fluid within the chamber; and

circuit means for absorbing electromagnetic radiation imposed thereon from externally of the circuit means at frequencies indicative of the deformation of the first-mentioned means.

2. The apparatus of claim 1 and further comprising:

means housing the first-mentioned means and the circuit means, the housing means being totally implantable within the aforesaid cavity;

means for imposing electromagnetic radiation on the circuit means within the implanted housing means; and

,

means for detecting the frequency at which the circuit means most efficiently absorbs the imposed electromagnetic radiation.

3. The apparatus of claim 2 and further comprising

means for converting the detected frequency to a corresponding pressure reading and for displaying the pressure reading.

4. The apparatus of claim 2 wherein at least portion of the imposing means and the detecting means are disposed on a mounting substrate, the substrate having an aperture therein for receiving discrete tool means for positioning the housing means at a desired location within the aforesaid cavity.

5. The apparatus of claim 1 wherein the fluid comprises nitrogen gas.

6. The apparatus of claim 1 and further comprising at least two electrically conductive surfaces disposed in opposing relation to each other and movable relative to each other in response to deformation of the pressure responsive means, the surfaces forming at least a capacitive portion of the circuit means.

7. The apparatus of claim 6 and further comprising inductive means disposed in proximity to the electrically conductive surfaces, the, inductive means forming an inductive portion of the circuit means.

8. The apparatus of claim 1 wherein the inductive means comprise a coil of electrically conductive material.

9. The apparatus of claim 8 wherein the coil is electrically connected to each of the electrically conductive surfaces to form a resonant circuit.

10. The apparatus of claim 1 wherein the pressure responsive means comprise at least one bellows formed of an electrically conductive material and having a substantially planar end portion extending into the chamber, the apparatus further comprising:

electrically conductive means disposed within the chamber and having a substantially planar surface opposing the planar end portion of the bellows, said surface and said planar end portion being movable relative to each other in response to deformation of the bellows, the surface of the electrically conductive means and the planar end portion of the bellows forming at least a capacitive portion of the circuit means.

11. The apparatus of claim 10 wherein the electrically conductive means is comprised of a second bellows and the substantially planar surface thereof is an end portion of the second bellows.

12. The apparatus of claim 10 and further comprising a coil of electrically conductive material, the coil being electrically connected to the bellows and to the electrically conductive means, the coil forming an inductive portion of the circuit means.

13. The apparatus of claim 12 wherein the coil is wrapped around the outer portion of the housing means.

14. The apparatus of claim 12 wherein the coil of electrically conductive material comprises a planar helix.

15. The apparatus of claim 1 and further comprising:

means encapsulating the housing means, the encapsulating means being totally implantable within the aforesaid cavity; and

a fluid disposed within the encapsulating means between interior walls of said encapsulating means and the housing means.

16. The apparatus of claim 15 and further comprising collar means for mounting the encapsulating means within the aforesaid cavity, the encapsulating means and the collar means having engaging portions formed respectively thereon, the encapsulating means being movable within the collar means to a desired location therein.

17. The apparatus of claim 16 wherein the engaging portions on the encapsulating means and on the collar means comprise mating threads.

18. The apparatus of claim 17 and further comprising slot means in at least the upper portions of the encapsulating means to facilitate rotation of the encapsulating means within the collar means.

19. The apparatus of claim 16 wherein the encapsulating means has a portion thereof which is structurally relatively thin to facilitate transfer of pressure externally imposed on the encapsulating means to the fluid disposed within the encapsulating means and externally of the housing means.

20. The apparatus of claim 1 wherein the housing has an aperture therein used for sealing the mass of fluid within the chamber, the apparatus further comprising means for sealing the aperture to prevent introduction of extraneous gaseous material into the chamber, the last-mentioned means comprising pin means insertable into the aperture, and solder means for joining the pin means to a portion of the exterior surface of the housing.

21. The apparatus of claim 20 wherein the last-mentioned means comprise a collar of metal formed about the periphery of the aperture, the solder means joining to the collar.

22. Apparatus for sensing pressure within a cavity in the body of a living entity, comprising:

means deformable in respone to pressure within the cavity, said means comprising

a first housing,

a second housing disposed within the first housing, thereby to define first and second chambers within said first housing between interior walls of the first housing and exterior walls of the second housing, the second housing defining an interior chamber therewithin and further having an aperture communicating the interior chamber with one of the aforementioned chambers,

a fluid disposed within the aforesaid chambers, and,

pressure responsive means carried on the second housing and extending into the interior chamber, the pressure responsive means being deformable by pressure imposed on the apparatus to change the volume occupied by the mass of fluid within the interior chamber; and

,

circuit means for absorbing electromagnetic radiation imposed thereon from externally of the circuit means at frequencies indicative of the deformation of the first-mentioned means.

23. The apparatus of claim 22 and further comprising at least two electrically conductive surfaces disposed in opposing relation to each other and movable relative to each other in response to deformation of the pressure responsive means, the surfaces forming at least a capacitive portion of the circuit means.

24. The apparatus of claim 22 wherein the pressure responsive means comprise at least one bellows formed of electrically conductive material and having a substantially planar end portion extending into the interior chamber, the interior of the bellows communicating with the one of the first or second chamber which does not communicate with the interior chamber through the aforementioned aperture.

25. The apparatus of claim 24 and further comprising:

electrically conductive means disposed within the interior chamber and having a substantially planar surface opposing the planar end portion of the bellows said surface and said planar end portion being movable relative to each other in response to deformation of the bellows.

26. The apparatus of claim 24 and further comprising a coil of electrically conductive material, the coil being electrically connected to the bellows and to the electrically conductive means.

27. The apparatus of claim 26 wherein the coil is wrapped about an outer portion of the second housing means.

28. The apparatus of claim 22 and further comprising inductive means disposed in proximity to the electrically conductive surfaces, the inductive means forming an inductive portion of the circuit means.

29. The apparatus of claim 28 wherein the inductive means comprise a coil of electrically conductive material.

30. The apparatus of claim 28 wherein the coil is electrically connected to each of the electrically conductive surfaces to form a resonant circuit.

31. The apparatus of claim 22 wherein the fluid comprises silcone liquid.

32. The apparatus of claim 22 and further comprising:

means housing the first-mentioned means and the circuit means, the housing means being totally implantable within the aforesaid cavity;

means for imposing electromagnetic radiation on the circuit means within the implanted housing means; and

,

means for detecting the frequency at which the circuit means most efficiently absorbs the imposed electromagnetic radiation.

33. The apparatus of claim 22 and further comprising:

means for converting the detected frequency to a corresponding pressure reading and for displaying the pressure reading.

34. Apparatus for sensing pressure within the cranial cavity of a living entity, comprising:

a first housing;

a second housing disposed within the first housing, thereby to define first and second chambers within said first housing between interior walls of the first housing and exterior walls of the second housing, the second housing defining an interior chamber therewithin and further having an aperture communicating the interior chamber with one of the aforementioned chambers;

a fluid disposed within the interior chambers and within the first and second chambers;

sealing means for sealing the first chamber from communication with the second chamber; and

,

pressure responsive means carried on the second housing and extending into the interior chamber, the pressure responsive means being deformable by pressure imposed on the apparatus to reduce the mass of fluid within the interior chamber.

35. Apparatus for sensing pressure within the cranial cavity of a living entity, comprising:

a housing formed of non-porous and electrically non-conductive material, the housing defining a chamber;

a predetermined mass of fluid disposed within the chamber;

pressure responsive means carried on the housing and extending into the chamber, said pressure responsive means being formed of non-porous and elastically compliant material and being deformable by pressure imposed on the apparatus to reduce the volume of the mass of fluid within the chamber; and

,

circuit means for absorbing electromagnetic radiation imposed thereon from externally of the apparatus at frequencies indicative of the deformation of the pressure responsive means, the circuit means including at least two electrically conductive surfaces at least one of which is carried on the pressure responsive means, the conductive surfaces being disposed in opposing relation to each other and movable relative to each other in response to deformation of the pressure responsive means, the surfaces forming at least a capacitive portion of the circuit means, the circuit means also including inductive means disposed in proximity to the electrically conductive surfaces, the inductive means forming an inductive portion of the circuit means, the inductive means being electrically connected to each of the electrically conductive surfaces to form a resonant circuit.