System for transcutaneous monitoring of intracranial pressure

• US 20070167867A1
• Filed: 10/06/2006
• Published: 07/19/2007
• Est. Priority Date: 02/24/2005
• Status: Active Grant

• Current Assignee: Erich Wolf
• Original Assignee: Erich Wolf
• Inventors: Wolf, Erich
• Granted Patent: US 8,057,401 B2
• Time in Patent Office: Days
• US Class Current: 600/561
• CPC Class Codes: A61B 2560/0219 of externally powered implanted units
• CPC Class Codes: A61B 2562/0247 Pressure sensors
• CPC Class Codes: A61B 5/0017 transmitting optical signals transmission by light H04B10/00
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/0075 by spectroscopy, i.e. measuring spectra, e.g. Raman spectroscopy, infrared absorption spectroscopy A61B5/0071 takes precedence
• CPC Class Codes: A61B 5/0077 Devices for viewing the surface of the body, e.g. camera, magnifying lens
• CPC Class Codes: A61B 5/0086 using infrared radiation
• CPC Class Codes: A61B 5/031 Intracranial pressure

Abstract

A system for measuring and converting to an observer intelligible form an internal physiological parameter of a medical patient. The invention allows transcutaneous telemetry of the measured information intracranial pressure via a system which includes a patient implanted sensor module and a processing and display module which is external of the patient and optically coupled to the sensor module via an external coupling module. A sensor within the implanted module transduces the measured information and a near infrared (NIR) emitter transmits this telemetry information when interrogated by the complementary external coupling module. Alternately, a set of tuned inductor-crystal circuits versus inductor-crystal comprised in part of a cylindrical crystal oscillator whose resonant frequency is sensed by a dipper circuit arrangement is provided. Power for the sensor module is derived inductively through rectification of a transcutaneously-applied high-frequency alternating electromagnetic field which is generated by a power source within the external coupling module, in concept much like a conventional electrical transformer. A computer within the processing and display module calculates the parameter value from the telemetry signal and represents this data either in numerical, graphical, or analog format.

Claims

1. An implantable biometric sensor comprising:

a subcutaneous case;

an access portal in the case to an internal fluid;

a sensor within the case generating a signal related to a property of the internal fluid;

a conversion circuit within the case transforming the signal into a transmitted near infrared optical form; and

an inductive power coupling providing power to the sensor and the conversion circuit.

2. The implantable biometric sensor of claim 1 wherein the sensor is an oscillated crystal comparator.

3. The implantable biometric sensor of claim 1 wherein the oscillated crystal comparator comprises:

an isolated reference crystal connected to a reference oscillator;

a transducer crystal connected to a transducer oscillator; and

a heterodyne amplifier connected to the transducer oscillator and the reference oscillator.

4. The implantable biometric sensor of claim 3 wherein the isolated reference crystal is contained within a pressure sealed container.

5. An implantable biometric sensor system comprising:

a rigid subcutaneous case;

an access portal to an internal fluid in the rigid subcutaneous case;

a dual frequency crystal oscillator, affixed to the rigid subcutaneous case and in ducted communication with the internal fluid, for sensing a pressure difference in the internal fluid; and

at least one driver coil in electrical communication with the dual frequency crystal oscillator.

6. The implantable biometric sensor system of claim 5 wherein the dual frequency crystal oscillator includes a pair of separated piezoelectric crystals.

7. The implantable biometric sensor system of claim 5 wherein the dual frequency crystal oscillator includes a pair of physically integrated piezoelectric crystals.

8. The implantable biometric sensor system of claim 5 wherein the dual frequency crystal oscillator includes a single cylindrical crystal substrate electrically separated into a pair of electrically isolated crystals.

9. The implantable biometric sensor system of claim 5 wherein the dual frequency crystal oscillator oscillates in a hoop mode.

10. The implantable biometric sensor system of claim 5 wherein the driver coil is comprised of a pair of matched inductors electrically connected to the dual frequency crystal oscillator.

11. The implantable biometric sensor system of claim 5 wherein the dual frequency crystal oscillator comprises a set of matched cylindrical crystal oscillators and the driver coil comprises a set of matched inductors connected to the set of matched cylindrical crystal oscillators.

12. The implantable biometric sensor system of claim 5 wherein the rigid subcutaneous case includes:

a cylindrical rigid probe; and

a rigid support structure adjacent the cylindrical rigid probe suspending the dual frequency crystal oscillator in ducted communication with the internal fluid and in ducted communication with a reference pressure cavity.

13. The implantable biometric sensor system of claim 5 further comprising:

a support base connecting the rigid probe and the rigid support structure and wherein the support base houses the driver coil.

14. The implantable biometric sensor system of claim 5 wherein the dual frequency crystal oscillator comprises:

a cylindrical crystal, having an exterior surface and an interior surface, supported centrally by the subcutaneous case;

a first metalized cylinder adjacent the exterior surface;

a second metalized cylinder adjacent the exterior surface;

a third metalized cylinder adjacent the interior surface;

a first inductive coil supported by the subcutaneous case electrically connected to the first metalized cylinder and the third metalized cylinder; and

a second inductive coil supported by the subcutaneous case electrically connected to the second metalized cylinder and the third metalized cylinder.

15. The implantable biometric sensor system of claim 5 wherein the dual frequency crystal oscillator comprises:

a first resonant inductor crystal circuit in communication with the internal fluid;

a second resonant inductor crystal circuit in communication with a reference pressure cavity;

an external coupling module for driving the first and second resonant inductor crystal circuits and recovering a radio frequency energy null corresponding to a resonant frequency for each of the first and second resonant inductor crystal circuits.

16. The implantable biometric sensor system of claim 15 wherein the external coupling module further comprises:

a driver coil connected to a dipper circuit;

a voltage controlled oscillator connected to the dipper circuit;

a digital to analog converter connected to the voltage controlled oscillator and a microprocessor;

a frequency counter connected to the voltage controlled oscillator and the microprocessor;

an analog to digital converter connected to the dipper circuit and the microprocessor;

wherein the microprocessor is programmed to carry out the steps of;

supplying a first digital signal to the digital to analog converter representing a desired frequency sweep;

reading the frequency sweep from the frequency counter;

reading a second digital signal from the analog to digital converter representing an output of the dipper circuit; and

translating the second digital signal into a representation of a biometric parameter.

17. The implantable biometric sensor system of claim 16 wherein the microprocessor is programmed to carry out the additional step of adjusting the representation of the biometric parameter for a protein deposit.

18. The implantable biometric sensor system of claim 5 wherein the dual frequency crystal oscillator comprises:

a first tubular crystal connected to the at least one driver coil through an externally controllable switch;

a second tubular crystal connected to the at least one driver coil through the externally controllable switch; and

wherein the externally controllable switch is configured to alternatively electrically connect the first tubular crystal to the at least one driver coil and the second tubular crystal to the at least one driver coil.

19. A method of determining intracranial fluid pressure providing the steps of:

providing a cylindrical crystal oscillator probe having a transducer section and a reference section;

providing at least one driver circuit within the cylindrical crystal oscillator probe connected to the transducer section and the reference section;

exposing the reference section to a reference pressure;

exposing the transducer section to the intracranial fluid pressure;

exciting the transducer section to provide a first radio frequency energy absorption;

exciting the reference section to produce a second radio frequency energy absorption;

measuring the first radio frequency energy absorption;

measuring the second radio frequency energy absorption;

comparing the measurement of the first radio frequency energy absorption and the measurement of the second radio frequency energy absorption to determine a difference;

relaying the difference to the reference pressure to determine the intracranial fluid pressure; and

reporting the intracranial fluid pressure.

20. The method of claim 19 wherein the steps of comparing and relating include application of the formula

P=P₀−

m(ƒ

₀−

ƒ

₁)

where;

P=intracranial pressure;

P₀=reference pressure;

m=calibration slope;

f₀=resonant frequency of reference oscillator; and

f₁=resonant frequency of transducer oscillator.

21. The method of claim 20 wherein the steps of exciting the transducer section and exciting the reference section include the steps of:

sweeping an oscillating electromagnetic field over at least one coil connected to the reference section and the transducer section to produce at least one frequency absorption null.

22. The method of claim 19 including the further steps of:

providing a memory in the crystal oscillator probe; and

storing a set of calibration data in the memory.

23. The method of claim 19 including the further steps of:

providing a memory in the crystal oscillator probe; and

storing a set of patient data in the memory.

24. The method of claim 19 comprising the additional step of adjusting the measurement of the first frequency absorption to account for a protein deposit from the intracranial fluid.

25. The method of claim 24 wherein the step of adjusting includes the step of applying the following equation:

ƒ

_r=ƒ

_measured+(ƒ

₁−

ƒ

_t)

where;

ƒ

_measured=the first frequency absorption;

ƒ

₁=an initial first frequency absorption; and

ƒ

_t=the frequency derived from an elapsed time transducer section frequency curve stored in a memory.

26. The method of claim 25 including the further step of storing the initial first frequency absorption and a time of inception in the memory.