Device for monitoring blood flow to brain

• US 20050054939A1
• Filed: 07/15/2004
• Published: 03/10/2005
• Est. Priority Date: 01/15/2002
• Status: Active Grant

• Current Assignee: Orsan Medical Technologies, Ltd.
• Original Assignee: Orsan Medical Equipment Limited
• Inventors: Rappaport, Alon, Shapira, Aharon, Ben-Ari, Shlomi
• Granted Patent: US 7,998,080 B2
• Time in Patent Office: Days
• US Class Current: 600/506
• 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 the 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; and c) estimating changes in the blood volume of the head, using the measurements of the electric fields and the currents.

Claims

1. A method of estimating blood flow in the 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; and

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

2. A method according to claim 1, wherein using the measurements of electric fields and the currents comprises calculating the impedance of the head at at least two different times.

3. A method according to claim 1, wherein producing electric fields inside the head comprises placing at least two current-carrying electrodes on the head and applying at least two different voltages to the current-carrying electrodes.

4. A method according to claim 3, wherein there is more than one current-carrying electrode at the same voltage.

5. A method according to claim 3, wherein the current-carrying electrodes are sufficiently large in area so that a significant amount of the current flows through the interior of the skull, and not through the scalp.

6. A method according to claim 3, wherein the electrodes are spread out enough in area so that a significant amount of the current flows through the interior of the skull, and not through the scalp.

7. A method according to claim 6, wherein the smallest convex area on the surface of the head which includes every current-carrying electrode of a given polarity is at least 2 cm across.

8. A method according to claim 7, wherein said area is at least 5 cm across.

9. A method according to claim 8, wherein said area is at least 10 cm across.

10. A method according to claim 3, wherein placing at least two current-carrying electrodes on the head comprises placing at least one of the electrodes adjacent to an opening in the skull.

11. A method according to claim 3, wherein placing at least two current-carrying electrodes on the head comprises placing at least one of the electrodes adjacent to a thin area of the skull.

12. A method according to claim 3, wherein measuring the electric fields comprises placing at least two voltage-measuring electrodes on the head, on a separate circuit from the current-carrying electrodes, and measuring the voltage difference between the voltage-carrying electrodes.

13. A method according to claim 12, wherein the smallest convex area which includes all of the voltage-measuring electrodes of a given polarity is at least 2 cm across.

14. A method according to claim 13, wherein said area is at least 5 cm across.

15. A method according to claim 14, wherein said area is at least 10 cm across.

16. A method according to claim 12, wherein placing at least two voltage-measuring electrodes on the head comprises placing at least one voltage-measuring electrode adjacent to an opening in the skull.

17. A method according to claim 10 or claim 16, wherein the opening is an eye socket, and said electrode is placed over the closed lid of the eye.

18. A method according to claim 10 or claim 16, wherein the opening is an ear, and said electrode is placed in the ear canal.

19. A method according to claim 10 or claim 16, wherein the opening is the foramen magnum, and said electrode is placed near the base of the skull.

20. A method according to claim 12, wherein placing at least two voltage-measuring electrodes on the head comprises placing at least one voltage-measuring electrode adjacent to a thin area of the skull.

21. A method according to claim 11 or claim 20, wherein the thin area of the skull is the temple.

22. A method according to claim 3, wherein

a) placing the current-carrying electrodes on the head comprises placing at least three current-carrying electrodes on the head;

and

b) applying different voltages to the current-carrying electrodes comprises applying at least three different voltages to the current-carrying electrodes so that a desired current distribution is produced in the head.

23. A method according to claim 22, wherein the desired current distribution is concentrated in a desired region of the brain, and estimating the blood flow in the brain comprises estimating the blood flow in the desired region of the brain.

24. A method according to claim 1, wherein producing electric fields inside the head comprises:

a) placing at least one induction coil adjacent to the head; and

b) running time-varying current through said at least one induction coils;

thereby inducing the electric fields inside the head, whereby causing currents to flow inside the head comprises causing eddy currents to flow inside the head.

25. A method according to claim 24, wherein the frequency distribution of the time-varying current running through the at least one induction coils is such that the eddy currents flowing in the head do not reduce the magnetic field at any point in the head by more than a factor of 3.

26. A method according to claim 24, wherein measuring the currents inside the head comprises measuring the magnetic field produced by the eddy currents.

27. A method according to claim 26, wherein measuring the magnetic field produced by the eddy currents comprises:

a) placing two voltage-measuring electrodes on the head;

b) measuring the induced electric field by measuring the voltage difference between the voltage-measuring electrodes; and

c) subtracting the part of the electric field induced by the magnetic field produced by the currents running in the at least one induction coils, thereby finding the part of the electric field induced by the magnetic field produced by the eddy currents.

28. A method according to claim 1, also comprising using photoplethysmography on tissue inside the head.

29. A method according to claim 28, wherein the tissue is inside the ear.

30. A method according to claim 28, wherein the tissue is inside the nose.

31. A method of monitoring a patient during surgery, comprising monitoring the blood flow in the patient'"'"'s brain during the surgery, using the method in claim 1.

32. A method of performing cardiopulmonary resuscitation (CPR) on a patient, comprising monitoring the blood flow in the patient'"'"'s brain to verify that the CPR is being performed effectively, using the method in claim 1.

33. A method of monitoring a patient with a medical condition likely to lead to loss of blood flow to the brain, comprising monitoring the blood flow in the patient'"'"'s brain using the method in claim 1.

34. An apparatus for estimating blood flow to the brain, comprising:

a) a power supply;

b) an electric field source which uses the power supply to produce an electric field in the head, at a safe amplitude and frequency, thereby producing a current in the head;

c) an electrical element which determines at least changes in the electric field in the head and at least changes in the current in the head, having sufficient precision to at least estimate changes in the impedance of the head; and

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

35. An apparatus according to claim 34, wherein:

a) the electric field source comprises at least two current-carrying electrodes, adapted for forming a good electrical connection to the head, and connected to the power supply; and

b) the electrical element comprises;

b1) a controller in the power supply which controls one of the output voltage and the output current of the power supply, or a combination of the output voltage and output current; and

b2) a meter which measures one of voltage across the head, current through the head, or a combination of voltage across the head and current through the head which is not controlled by the controller.

36. An apparatus according to claim 35, wherein the controller in the power supply controls the output current, and the meter is a voltmeter, and including two voltage-measuring electrodes, connected to the voltmeter, which voltage-measuring electrodes are adapted for forming a good electrical connection to the head.

37. An apparatus according to claim 36, wherein the current-carrying electrodes comprise at least three current-carrying electrodes, and at least two of the current-carrying electrodes are connected in parallel to the same voltage.

38. An apparatus according to claim 36, wherein the current-carrying electrodes are collectively sufficiently large in area so that a significant amount of the current flows through the interior of the skull, and not through the scalp.

39. An apparatus according to claim 36, wherein the current-carrying electrodes are collectively sufficiently spread out in area so that a significant amount of the current flows through the interior of the skull, and not through the scalp.

40. An apparatus according to claim 38, 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.

41. An apparatus according to claim 40, wherein said area is at least 2 cm across.

42. An apparatus according to claim 41, wherein said area is at least 5 cm across.

43. An apparatus according to claim 42, wherein said area is at least 10 cm across.

44. An apparatus according to claim 36, 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.

45. An apparatus according to claim 36, wherein at least a portion of one voltage-measuring electrode is adjacent on two opposite sides to two portions of a same current-carrying electrode.

46. An apparatus according to claim 44 or claim 45, 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.

47. An apparatus according to claim 44 or claim 45, wherein at least portions of the voltage-measuring electrode and the current-carrying electrode form intertwined spirals.

48. An apparatus according to claim 36, and including at least one electrode structure to which at least one current-carrying electrode and at least one voltage-measuring electrode are mechanically connected.

49. An apparatus according to claim 36, wherein the voltage-measuring electrodes are adapted to be placed inside an opening in the head.

50. An apparatus according to claim 49, wherein the voltage-measuring electrodes are adapted to be placed inside the ears.

51. An apparatus according to claim 50, 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.

52. An apparatus according to claim 50, and including a probe adapted for measuring blood flow photoplethysmographically in the ears, which probe is combined with the voltage-measuring electrodes.

53. An apparatus according to claim 35 or claim 36, wherein at least one electrode is adapted by its size and shape to be placed near an opening of the skull.

54. An apparatus according to claim 53, wherein the opening is an eye socket, and the electrode is shaped to fit over a closed eyelid.

55. An apparatus according to claim 53, wherein the opening is the foramen magnum, and the electrode is shaped to fit near the base of the skull.

56. An apparatus according to claim 53, wherein the opening is an ear, and the electrode is sized and shaped to be placed in the ear canal.

57. An apparatus according to claim 53, wherein the opening is an ear, and the electrode is sized and shaped to be placed behind the ear.

58. An apparatus according to claim 35 or claim 36, wherein at least one electrode is adapted by its size and shape to be placed near a thin region of the skull.

59. An apparatus according to claim 58, wherein the thin region is the temple.

60. An apparatus according to claim 39, 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.

61. An apparatus according to claim 60, 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.

62. An apparatus according to claim 34, wherein:

a) the power supply produces a time-varying power supply current;

b) the means for producing an electric field in the head comprises at least one induction coil, connected to the power supply, which induces an electric field in the head by producing a time-varying magnetic field in the head, the current in the head thereby being an eddy current;

c) the means for determining at least changes in the electric field in the head comprises a controller in the power supply, which determines the rate of change of the power supply current, and thereby determines the rate of change of the magnetic field in the head, and the induced electric field in the head; and

d) the means for determining at least changes in the current in the head comprises a sensor which senses the magnetic field produced by the current in the head.

63. An apparatus according to claim 62, wherein the power supply is capable of operating over at least part of the range between 10 kHz and 100 kHz.

64. An apparatus according to claim 62, wherein the power supply is capable of operating over at least part of the range between 100 kHz and 1 MHz.

65. An apparatus according to claim 62, wherein the power supply is capable of operating over at least part of the range between 1 MHz and 10 MHz.

66. An apparatus according to claim 62, wherein the power supply is capable of operating over at least part of the range between 10 MHz and 100 MHz.

67. An apparatus according to claim 62, wherein the sensor comprises at least one of the at least one induction coils.

68. An apparatus according to claim 62, wherein the sensor comprises a separate sensing coil which measures the voltage induced by changes in magnetic flux passing through it.

69. An apparatus according to claim 62, wherein the sensor comprises a solid-state magnetic field sensor.

70. An apparatus according to claim 62, wherein the sensor comprises voltage-measuring electrodes which measure an electric field induced by the time-varying magnetic field produced by the at least one induction coil.

71. An apparatus according to claim 34, and including a photoplethysmographic blood-flow measuring probe, sized and shaped to be placed in the ears.

72. An apparatus according to claim 71, where the probe is sufficiently wide at its base that it cannot damage the eardrum when inserted into the ears.

73. An apparatus according to claim 71, wherein the probe is surrounded by a holding element which, when inserted into the ear, holds the probe in a position and orientation to allow repeated optical measurements of the same location.

74. An apparatus according to claim 34, which is portable enough for use in the field by emergency medical technicians.

75. An apparatus according to claim 34, and including:

a) a head motion sensor; and

b) a controller which uses data from the head motion sensor to reduce motion artifacts in estimating the blood flow.