Blood oxygen monitoring system and a lead therefor

• US 20040210263A1
• Filed: 04/16/2003
• Published: 10/21/2004
• Est. Priority Date: 04/16/2003
• Status: Active Grant

• Current Assignee: Alfred E. Mann Foundation For Scientific Research
• Original Assignee: Alfred E. Mann Foundation For Scientific Research
• Inventors: Schulman, Joseph H.
• Granted Patent: US 7,136,704 B2
• Time in Patent Office: Days
• US Class Current: 607/17
• CPC Class Codes: A61N 1/36557 controlled by chemical substances in blood
• CPC Class Codes: G01N 33/4925 measuring blood gas content, e.g. O2, CO2 , HCO3

Abstract

An oxygen monitoring system measures the oxygen concentration in a patient'"'"'s blood for use as a physiological control parameter in rate responsive pacing. The oxygen monitoring system includes an oxygen monitoring circuit embedded in a cardiac stimulation lead and monitors the blood oxygen in a patient'"'"'s venous system that passes through and into the lead. The oxygen monitoring circuit includes a working electrode, a counter electrode, a reference electrode and an IC chip electrically interconnected between the electrodes and programmed to carry out an oxygen concentration measuring process. Oxygen surrounding the electrodes causes current to flow between the electrodes and the IC chip varies the value of current generated by a current source coupled between the working electrode and counter electrode in a manner to maintain the voltage between the working electrode and reference electrode at a preselected value. The variation of the current source value is a direct measure of the blood oxygen concentration. The oxygen monitoring circuit may comprise an IC chip mounted on one side of a substrate and on the reverse side of which are mounted the electrodes or an IC chip(s) upon which the electrodes are directly mounted. Furthermore, the IC chip, with appropriate insulation may be used in place of the substrate. At least two insulated IC chips may be used, for example in a back to back arrangement, for increased overall sensitivity or redundancy.

Claims

1. An implantable cardiac stimulation system comprising:

a cardiac stimulation lead in contact with a patient'"'"'s blood stream and selected cardiac sites, said stimulation lead having at least one electrical conductor; and

a stimulation device comprising;

a processor;

an oxygen monitoring circuit electrically coupled to said at least one electrical conductor and in contact with the patient'"'"'s blood stream, said oxygen monitoring circuit configured to monitor the oxygen concentration of the patient'"'"'s blood;

a cardiac stimulation pulse generator coupled and responsive to the processor and configured to deliver cardiac stimulation pulses via the cardiac stimulation lead to the selected cardiac sites;

an oxygen monitoring pulse generator coupled to the processor and configured to generate a bi-phasic pulse train for application to the at least one electrical conductor between consecutive cardiac stimulation pulses, the pulse train defining a data frame having a pre-determined number of bits including parameter information bits, wherein the oxygen monitoring circuit interrogates the patient'"'"'s blood during an interval between consecutive cardiac stimulation pulses to measure the blood oxygen concentration utilizing respective ones of the pulse train bits for carrying commands and parameter information between the processor and oxygen monitoring circuit.

2. The system of claim 1 wherein the bi-phasic pulse train comprises pulses having opposite polarities, representative of a digital “

1” and

a digital “

0”

, respectively.

3. The system of claim 2 wherein the pulses have pulse widths in the range of about 0.1 to 100 microseconds.

4. The system of claim 1, wherein the oxygen monitoring circuit includes a re-chargeable energy source and wherein said cardiac stimulation pulses are utilized to recharge the energy source.

5. The system of claim 1, wherein the oxygen monitoring circuit includes a re-chargeable energy source and wherein the bi-phasic pulses are utilized to recharge the energy source.

6. The system of claim 1, wherein the oxygen monitoring circuit includes circuitry to generate a pulse train responsive to the oxygen monitoring pulse train in a format consistent therewith to provide the processor with the results of the interrogation request.

7. The system of claim 6, wherein the pulse train generated by the oxygen monitoring circuit is mono-phasic.

8. The system of claim 1, wherein the at least one conductor comprises two conductors and the oxygen monitoring circuit is electrically coupled across said two conductors.

9. The system of claim 1, wherein the cardiac stimulation pulse generator is housed in an electrically conductive can in contact with a patient'"'"'s tissue, and wherein the oxygen monitoring circuit is electrically coupled to the at least one electrical conductor and the patient'"'"'s tissue.

10. The system of claim 1, wherein the at least one conductor includes a pacing conductor and a return conductor wherein the oxygen monitoring circuit is electrically coupled between the pacing conductor and the return conductor.

11. The system of claim 1, wherein the at least one conductor comprises two pacing conductors and a return conductor wherein the oxygen monitoring circuit is electrically coupled between one of the pacing conductors and the return conductor.

12. The system of claim 1, wherein the at least one conductor comprises a pair of pacing conductors and a second pair of conductors, the oxygen monitoring circuit being electrically coupled across the second pair of conductors, said second pair of conductors in electrical communication with the stimulation device.

13. A cardiac stimulation lead for use with a cardiac stimulation device, the device comprising, a processor, a cardiac stimulation pulse generator coupled and responsive to the processor and configured to deliver cardiac stimulation pulses via the cardiac stimulation lead to selected cardiac sites, an oxygen monitoring pulse generator coupled to the processor and configured to generate a digital pulse train defining a data frame for application to the cardiac stimulation lead between consecutive cardiac stimulation pulses, the pulse train having a pre-determined number of bits including parameter information bits, the stimulation lead comprising:

at least one electrical conductor, said lead being in contact with a patient'"'"'s blood stream and selected cardiac sites; and

an oxygen monitoring circuit electrically coupled to said at least one electrical conductor and in contact with the patient'"'"'s blood stream, said oxygen monitoring circuit configured to monitor the oxygen concentration of the patient'"'"'s blood, wherein the oxygen monitoring circuit interrogates the patient'"'"'s blood during an interval between consecutive cardiac stimulation pulses to measure the blood oxygen concentration utilizing respective ones of the pulse train bits for carrying commands and parameter information between the processor and oxygen monitoring circuit.

14. The cardiac stimulation lead of claim 13, wherein the oxygen monitoring circuit includes a re-chargeable energy source and wherein said cardiac stimulation pulses are utilized to recharge the energy source.

15. The cardiac stimulation lead of claim 13, wherein the oxygen monitoring circuit includes a re-chargeable energy source and wherein the bi-phasic pulses are utilized to recharge the energy source.

16. The cardiac stimulation lead of claim 13, wherein the oxygen monitoring circuit includes circuitry to generate a pulse train responsive to the oxygen monitoring pulse train in a format consistent therewith to provide the processor with the results of the interrogation request.

17. The cardiac stimulation lead of claim 16, wherein the pulse train generated by the oxygen monitoring circuit is mono-phasic.

18. The cardiac stimulation lead of claim 13, wherein the cardiac stimulation pulse generator is housed in an electrically conductive can in contact with a patient'"'"'s tissue, and wherein the oxygen monitoring circuit is electrically coupled to the at least one electrical conductor and the patient'"'"'s tissue.

19. The cardiac stimulation lead of claim 13, wherein the at least one conductor includes a pacing conductor and a return conductor wherein the oxygen monitoring circuit is electrically coupled between the pacing conductor and the return conductor.

20. The cardiac stimulation lead of claim 13, wherein the at least one conductor comprises a pair of pacing conductors and a second pair of conductors, the oxygen monitoring circuit being electrically coupled across the second pair of conductors, said second pair of conductors in electrical communication with the stimulation device.

21. The cardiac stimulation lead of claim 13, wherein the at least one conductor comprises two pacing conductors and a return conductor, wherein the oxygen monitoring circuit is electrically coupled between one of the pacing conductors and the return conductor.

22. The cardiac stimulation lead of claim 13, wherein the at least one conductor comprises two conductors and the oxygen monitoring circuit is electrically coupled across said two conductors.

23. A cardiac stimulation lead for use with a cardiac stimulation device, the device comprising, a processor, a cardiac stimulation pulse generator coupled and responsive to the processor and configured to deliver cardiac stimulation pulses via the cardiac stimulation lead to selected cardiac sites, an oxygen monitoring pulse generator coupled to the processor and configured to generate a biphasic pulse train for application to the cardiac stimulation lead between consecutive cardiac stimulation pulses, the stimulation lead comprising:

at least one electrical conductor, said lead being in contact with a patient'"'"'s blood stream and selected cardiac sites; and

an oxygen monitoring circuit electrically coupled to said at least one electrical conductor and in contact with the patient'"'"'s blood stream, said oxygen monitoring circuit configured to monitor the oxygen concentration of the patient'"'"'s blood, wherein the oxygen monitoring circuit interrogates the patient'"'"'s blood during an interval between consecutive cardiac stimulation pulses to measure the blood oxygen concentration utilizing the pulse train for carrying commands and parameter information between the processor and oxygen monitoring circuit.

24. A cardiac stimulation lead for use with a cardiac stimulation device, the device comprising, a processor, a cardiac stimulation pulse generator coupled and responsive to the processor and configured to deliver cardiac stimulation pulses via the cardiac stimulation lead to selected cardiac sites, an oxygen monitoring pulse generator coupled to the processor and configured to generate a pulse train for application to the cardiac stimulation lead, the stimulation lead comprising:

at least one electrical conductor, said lead being in contact with a patient'"'"'s blood stream and selected cardiac sites; and

an oxygen monitoring circuit electrically coupled to said at least one electrical conductor and in contact with the patient'"'"'s blood stream, said oxygen monitoring circuit configured to monitor the oxygen concentration of the patient'"'"'s blood, wherein the oxygen monitoring circuit interrogates the patient'"'"'s blood to measure the blood oxygen concentration utilizing the pulse train for carrying commands and parameter information between the processor and oxygen monitoring circuit.

25. The lead of claim 24 wherein the oxygen monitoring circuit comprises:

a working electrode, a counter electrode and a reference electrode;

an integrated circuit chip electrically coupled to said electrodes and programmed to undertake an oxygen concentration measurement process;

a current source controlled by said integrated circuit chip and coupled between the working electrode and the counter electrode and configured to supply current between the working and counter electrodes;

a voltage monitor arranged to detect the voltage across the reference electrode and working electrode;

wherein the integrated circuit chip is programmed to control the level of current supplied by the current source and to monitor the detected voltage such that upon exposure of the electrodes to varying levels of oxygen concentration, varying levels of current is caused to flow between the working electrode and counter electrode and wherein the detected voltage is caused to change and further wherein the integrated circuit chip causes the current source to generate a current of a magnitude to return the detected voltage to a preselected reference value, said current magnitude being a direct measure of oxygen concentration.

26. The lead of claim 25 wherein the oxygen monitoring pulse generator generates a biphasic pulse train.

27. The lead of claim 26 wherein the lead is encased in an oxygen transmissible sheath.

28. The lead of claim 26 wherein the lead is encased in a silicone sheath extending the length thereof.

29. The lead of claim 28 wherein the electrodes are encased in an oxygen conductive gel.

30. The lead of claim of 29 wherein the oxygen conductive gel is pHema.

31. The lead of claim 25 wherein said working electrode, counter electrode and reference electrode are mounted on one face of a ceramic substrate and the integrated circuit chip is mounted on an opposing face of the substrate and wherein there are electrical conductors passing through the substrate interconnecting the electrodes with corresponding terminals of the integrated circuit chip, the conductors having a first portion extending through the substrate in a first direction and a second portion traversing through the substrate at a second direction being substantially orthogonal to the first direction.

32. A sensor for use in a cardiac stimulation lead to measure oxygen concentration in a patient'"'"'s blood comprising:

a substrate having opposite facing first and second sides, a plurality of electrodes mounted on the first side of the substrate, the electrodes immersed in an oxygen and electrically conductive gel, the gel being encased in a fluid impervious and oxygen transmissible sheath;

an IC chip mounted on the second side of the substrate, the IC chip being encased within a sealing cap hermetically sealed to the second side of the substrate; and

a plurality of electrical conductors passing through the substrate and interconnecting the electrodes to the IC chip, wherein said sensor is sized to fit within a cardiac stimulation lead.

33. The sensor of claim 32 wherein the substrate comprises a ceramic hermetic material.

34. The sensor of claim 32 further comprising an energy storage device adapted to provide energy to the IC chip.

35. The sensor of claim 34 wherein the energy storage device is a capacitor.

36. The sensor of claim 34 wherein the energy storage device is an electrical storage cell.

37. The sensor of claim 34 wherein the energy storage device forms a part of the IC chip.

38. The sensor of claim 32 comprising a plurality of pads located on the substrate outside of the sealing cap and wherein a plurality of hermetic vias selectively coupled to the IC chip and pads provides electrical communication therebetween.

39. A sensor for use in a cardiac stimulation lead to measure oxygen concentration in a patients blood comprising an IC chip having first and second sides, a plurality of electrodes mounted on the first side of the IC chip, the electrodes immersed in an oxygen conductive gel, the gel being encased in a fluid impervious oxygen transmissible sheath, a plurality of electrical conductors selectively interconnecting the electrodes to the IC chip, a plurality of pads located on the IC chip outside of the sheath and a plurality of hermetic vias selectively coupled to the IC chip and the pads for providing electrical communication between the IC chip and the pads, the sensor, other than the sheath and the pads, being encased in a fluid impervious insulating material, the fluid impervious insulating material extending about a region around the electrodes so as to insulate the IC chip from the gel, and wherein said sensor is sized to fit within a cardiac stimulation lead.

40. The sensor of claim 39 wherein the pads are covered with a waterproof material.

41. The sensor of claim 39 wherein the insulating material is aluminum.

42. The sensor of claim 39 further comprising two IC chips arranged such that the second sides thereof are arranged in abutting relationship.

43. The oxide sensor of claim 40 wherein the waterproof material is epoxy.

44. An implantable cardiac stimulation system comprising:

a cardiac stimulation lead in contact with a patient'"'"'s blood stream and selected cardiac sites, said stimulation lead having at least one electrical conductor; and

a stimulation device comprising;

a processor; and

a cardiac stimulation pulse generator coupled and responsive to the processor and configured to deliver cardiac stimulation pulses via the cardiac stimulation lead to the selected cardiac sites, said cardiac stimulation lead further comprising an oxygen monitoring circuit electrically coupled to said at least one electrical conductor and in contact with the patient'"'"'s blood stream, said oxygen monitoring circuit configured to monitor the oxygen concentration of the patient'"'"'s blood and transmit a digital signal related to said oxygen concentration to the stimulation device.

45. The cardiac stimulation system of claim 44, wherein the stimulation device further comprises an oxygen monitoring pulse generator coupled to the processor and configured to generate a bi-phasic pulse train for application to the at least one electrical conductor between consecutive cardiac stimulation pulses, the pulse train defining a data frame having a pre-determined number of bits including parameter information bits, wherein the oxygen monitoring circuit interrogates the patient'"'"'s blood during an interval between consecutive cardiac stimulation pulses to measure the blood oxygen concentration utilizing respective ones of the pulse train bits for carrying commands and parameter information between the processor and oxygen monitoring circuit.