Device for Monitoring Blood Flow to Brain

• US 20080200787A1
• Filed: 06/15/2005
• Published: 08/21/2008
• Est. Priority Date: 01/15/2002
• Status: Active Grant

• Current Assignee: Orsan Medical Technologies, Ltd.
• Original Assignee: Orsan Medical Technologies, Ltd.
• Inventors: Rappaport, Alon, Shapira, Aharon, Ben-Ari, Shlomi
• Granted Patent: US 8,702,615 B2
• Time in Patent Office: Days
• US Class Current: 600/345
• CPC Class Codes: A61B 2562/164 the sensor is mounted in or on a conformable substrate or carrier
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/0265 using electromagnetic means, e.g. electromagnetic flowmeter
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/245 specially adapted for magnetoencephalographic [MEG] signals
• CPC Class Codes: A61B 5/6814 Head
• CPC Class Codes: A61B 5/6817 Ear canal

Abstract

A method of estimating blood flow in a brain, comprising: a) causing currents to flow inside the head by producing electric fields inside the head; b) measuring at least changes in the electric fields and the currents; c) estimating changes in the blood volume of the head, using the measurements of the electric fields and the currents, where the current are produced in children or using electrodes at or near holes in the skull. Optionally, the configuration is selected to focus the flow of current to be inside the brain to a significant degree.

Claims

1. Apparatus for estimating blood flow to the brain, comprising:

(a) an impedance measurement system including at least one electrode and which generates at least one impedance measurement; and

(b) a monitor which determines changes in blood flow to the brain based on said at least one measurement,

wherein said at least one electrode is configured to cause a significant amount of at least 1% of an output current of the measurement system to flow through the interior of the skull and not through the scalp.

2. Apparatus according to claim 1, wherein said amount is at least 10%.

3. Apparatus according to claim 1, wherein said amount is at least 30%.

4. Apparatus according to any of claims 1-3, wherein the smallest convex area on the surface of the head that includes every current-carrying electrode of a same polarity is at least 1 cm across.

5. Apparatus according to any of claims 1-4, comprising:

i) a power supply comprising a controller which controls an output current of the power supply;

ii) at least two current-carrying electrodes, adapted for forming a good electrical connection to the head, and connected to the power supply, which use the power supply to produce an electric field in the head, at a safe amplitude and frequency, thereby causing the output current to flow in the head; and

iii) a voltmeter, and two voltage-measuring electrodes connected to the voltmeter, which voltage-measuring electrodes are adapted for forming a good electrical connection to the head, thereby allowing the voltmeter to determine at least changes in the electric field in the head, having sufficient precision to at least estimate changes in the impedance of the head,

wherein said monitor displays at least information telling a user when changes in the impedance of the head show a significant change in blood flow rate.

6. An apparatus according to claim 4 or claim 5, wherein said area is at least 2 cm across.

7. Apparatus according to claim 6, wherein said area is at least 5 cm across.

8. Apparatus according to claim 7, wherein said area is at least 10 cm across.

9. Apparatus according to any of claims 5-8, wherein at least a portion of one current-carrying electrode is adjacent on two opposite sides to two portions of a same voltage-measuring electrode, or at least a portion of one voltage-measuring electrode is adjacent on two opposite sides to two portions of a same current-carrying electrode, or both.

10. Apparatus according to any of claims 5-9, wherein at least a portion of one current-carrying electrode is adjacent on two opposite sides to two portions of a same voltage-measuring electrode, or at least a portion of one voltage-measuring electrode is adjacent on two opposite sides to two portions of a same current-carrying electrode, or both.

11. Apparatus according to any of claims 5-10, wherein at least a portion of one current-carrying electrode is adjacent on two opposite sides to two portions of the same voltage-measuring electrode.

12. Apparatus according to any of claims 5-11, wherein at least a portion of one voltage-measuring electrode is adjacent on two opposite sides to two portions of the same current-carrying electrode.

13. Apparatus according to any of claims 5-12, wherein at least one of said electrodes comprises an annular-shaped electrode that surrounds the electrode or the portion of the electrode that said annular-shaped electrode is adjacent to.

14. Apparatus according to any of claims 5-12, wherein at least portions of the voltage-measuring electrode and the current-carrying electrode form intertwined spirals.

15. Apparatus according to any of claims 1-4, wherein at least one electrode is adapted to be placed inside an opening in the head, near an opening in the skull, or near a thin region of the skull.

16. Apparatus according to claim 15, comprising:

a) a power supply comprising a controller which controls an output current of the power supply;

b) at least two current-carrying electrodes, adapted for forming a good electrical connection to the head, and connected to the power supply, which use the power supply to produce an electric field in the head, at a safe amplitude and frequency, thereby causing the output current to flow in the head; and

c) a voltmeter, and two voltage-measuring electrodes connected to the voltmeter, which voltage-measuring electrodes are adapted for forming a good electrical connection to the head, thereby allowing the voltmeter to determine at least changes in the electric field in the head, having sufficient precision to at least estimate changes in the impedance of the head.

17. Apparatus according to claim 15, wherein the voltage-measuring electrodes are adapted to be placed inside an opening in the head.

18. Apparatus according to claim 17, wherein the voltage-measuring electrodes are adapted to be placed inside the ears.

19. Apparatus according to claim 18, wherein the voltage-measuring electrodes are conical and padded, thereby allowing them to be pressed firmly enough into the ears to make good electrical contact, without damaging the ear drums.

20. Apparatus according to claim 18 or claim 19, and including a probe adapted for measuring blood flow photoplethysmographically in the ears, which probe is combined with the voltage-measuring electrodes.

21. Apparatus according to claim 15, wherein at least one electrode is adapted by its size and shape to be placed near an opening of the skull.

22. Apparatus according to claim 21, wherein the opening is an eye socket, and the electrode is shaped to fit over a closed eyelid.

23. Apparatus according to claim 21, wherein the opening is the foramen magnum, and the electrode is shaped to fit near the base of the skull.

24. Apparatus according to claim 21, wherein the opening is an ear, and the electrode is sized and shaped to be placed in the ear canal.

25. Apparatus according to claim 21, wherein the opening is an ear, and the electrode is sized and shaped to be placed behind the ear.

26. Apparatus according to claim 15, wherein at least one electrode is adapted by its size and shape to be placed near a thin region of the skull.

27. Apparatus according to claim 26, wherein the thin region is the temple.

28. Apparatus according to any of claims 1-4, comprising:

a) a power supply comprising a controller which controls an output current of the power supply;

b) at least two current-carrying electrodes, adapted for forming a good electrical connection to the head, and connected to the power supply, which use the power supply to produce an electric field in the head, at a safe amplitude and frequency, thereby causing the output current to flow in the head; and

c) a voltmeter, and two voltage-measuring electrodes connected to the voltmeter, which voltage-measuring electrodes are adapted for forming a good electrical connection to the head, thereby allowing the voltmeter to determine at least changes in the electric field in the head, having sufficient precision to at least estimate changes in the impedance of the head;

wherein the current-carrying electrodes are collectively sufficiently spread out in area so that a significant amount of at least 1% of the current flows through the interior of the skull, and not through the scalp, and wherein the at least two current-carrying electrodes comprise at least three current-carrying electrodes, and the power supply is capable of simultaneously applying at least three different voltages to the current-carrying electrodes, whereby a desired current distribution is produced inside the head.

29. Apparatus according to claim 28, wherein the current-carrying electrodes are adapted to be placed in locations on the head such that the desired current distribution is concentrated in a desired region of the brain.

30. Apparatus for estimating blood flow to a brain, comprising:

(a) an impedance measurement system including at least one electrode and which generates at least one impedance measurement; and

(b) a monitor which determines changes in blood flow to the brain based on said at least one measurement,

wherein the electrodes are adapted by one or both of their size and shape to be used for children.

31. Apparatus according to claim 30, wherein said system comprises:

i) a power supply comprising a controller which controls an output current of the power supply;

ii) at least two current-carrying electrodes, adapted for forming a good electrical connection to the head, and connected to the power supply, which use the power supply to produce an electric field in the head, at a safe amplitude and frequency, thereby causing the output current to flow in the head; and

iii) a voltmeter, and two voltage-measuring electrodes connected to the voltmeter, which voltage-measuring electrodes are adapted for forming a good electrical connection to the head, thereby allowing the voltmeter to determine at least changes in the electric field in the head, having sufficient precision to at least estimate changes in the impedance of the head,

wherein said monitor displays at least information telling a user when changes in the impedance of the head show a significant change in blood flow rate.

32. Apparatus according to claim 30 or claim 31, wherein the electrodes are adapted by one or both of their size and shape to be used for newborn babies.

33. Apparatus according to claim 32, wherein the electrodes are adapted by one or both of their size and shape to be used for premature babies.

34. Apparatus according to any of claims 30-33, wherein the distance between two different electrodes of said at least one electrode, or different arms of one electrode, is between 1 mm and 2 mm, thereby adapting the apparatus to be used in a patient whose scalp is between 1 mm and 2 mm thick.

35. Apparatus according to any of claims 30-33, wherein the distance between two different electrodes of said at least one electrode, or between different arms of one electrode, is between 2 mm and 5 mm thick, thereby adapting the apparatus to be used in a patient whose scalp plus skull is a total of between 2 mm and 5 mm thick.

36. Apparatus according to any of claims 30-33, wherein the at least one electrode is adapted to be used in a patient whose scalp is between 1 mm and 2 mm thick.

37. Apparatus according to any of claims 30-33, wherein the at least one electrodes is adapted to be used in a patient whose scalp plus skull is a total of between 2 mm and 5 mm thick.

38. Apparatus for estimating blood flow to the brain, comprising:

a) a power supply comprising a controller which controls an output current of the power supply;

b) at least two current-carrying electrodes, adapted for forming a good electrical connection to the head, and connected to the power supply, which use the power supply to produce an electric field in the head, at a safe amplitude and frequency, thereby causing the output current to flow in the head;

c) a voltmeter, and two voltage-measuring electrodes connected to the voltmeter, which voltage-measuring electrodes are adapted for forming a good electrical connection to the head, thereby allowing the voltmeter to determine at least changes in the electric field in the head, having sufficient precision to at least estimate changes in the impedance of the head;

d) at least one electrode structure to which at least one current-carrying electrode and at least one voltage-measuring electrode are mechanically connected; and

e) a monitor which generates a signal indicating a significant change in blood flow rate, based on said measuring.

39. Apparatus according to claim 38, wherein said connection is non-elastic.

40. Apparatus according to claim 38, wherein said connection is rigid.

41. A method of estimating blood flow in the brain of a patient, comprising:

a) causing currents to flow inside the head by placing at least two current-carrying electrodes on the head and applying at least two different voltages to the current-carrying electrodes, thereby producing electric fields inside the head;

b) measuring at least changes in the electric fields and the currents; and

c) estimating changes in the blood volume of the head, using the measurements of the electric fields and the currents, wherein the patient'"'"'s scalp is between 1 and 2 mm thick or wherein the total thickness of the patient'"'"'s scalp plus skull is between 2 and 5 mm.

42. A method of estimating blood flow in the brain, comprising:

a) causing currents to flow inside the head by placing at least two current-carrying electrodes on the head, at least one of them adjacent to an opening or thin area in the skull, and applying at least two different voltages to the current-carrying electrodes, thereby producing electric fields inside the head;

b) measuring at least changes in the electric fields and the currents; and

c) estimating changes in the blood volume of the head, using the measurements of the electric fields and the currents.

43. A method according to claim 42, wherein at least one electrode is placed at an opening.