Method for monitoring blood flow to brain

• US 7,998,080 B2
• Filed: 07/15/2004
• Issued: 08/16/2011
• Est. Priority Date: 01/15/2002
• Status: Expired due to Fees

• Current Assignee: Orsan Medical Technologies, Ltd.
• Original Assignee: Orsan Medical Technologies, Ltd.
• Inventors: Shapira, Aharon, Rappaport, Alon, Ben-Ari, Shlomi
• Primary Examiner(s): Mallari; Patricia C
• Application Number:
  US10/893,570
• Publication Number:
  US 20050054939A1
• Time in Patent Office: 2,588 Days
• Field of Search: 600/506
• 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 monitoring blood flow in a patient'"'"'s brain during surgery, comprising:

a) performing surgery on the patient;

b) causing currents to flow inside the patient'"'"'s head by producing electric fields inside the head during the surgery, by placing at least two current-carrying electrodes on the head, and applying at least two different electric potentials to the current-carrying electrodes;

c) measuring at least changes in the electric fields and the currents during the surgery;

d) estimating changes in the blood volume of the head during the surgery, using a controller to analyze data of the measurements of the electric fields and the currents; and

e) estimating blood flow in the brain during the surgery, from the changes in blood volume of the head.

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 least two different times.

3. A method according to claim 1, wherein there is more than one current-carrying electrode at the same electric potential.

4. A method according to claim 1, 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.

5. A method according to claim 1, 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.

6. A method according to claim 5, 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.

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

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

9. A method according to claim 1, 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.

10. A method according to claim 1, 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.

11. A method according to claim 1, 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 electric potential difference between the voltage-measuring electrodes.

12. A method according to claim 11, wherein the smallest convex area which includes all of the voltage-measuring electrodes of a given polarity is at least 2 cm across.

13. A method according to claim 12, wherein said area is at least 5 cm across.

14. A method according to claim 13, wherein said area is at least 10 cm across.

15. A method according to claim 11, 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.

16. A method according to claim 11 or claim 15, wherein the opening is an eye socket, and said electrode is placed over the closed lid of the eye.

17. A method according to claim 11 or claim 15, wherein the opening is an ear, and said electrode is placed in the ear canal.

18. A method according to claim 11 or claim 15, wherein the opening is the foramen magnum, and said electrode is placed near the base of the skull.

19. A method according to claim 11, 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.

20. A method according to claim 10 or claim 19, wherein the thin area of the skull is the temple.

21. A method according to claim 1, 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 electric potentials to the current-carrying electrodes comprises applying at least three different electric potentials to the current-carrying electrodes so that a desired current distribution is produced in the head.

22. A method according to claim 21, wherein the desired current distribution is concentrated in a desired region of the brain, and estimating the changes in blood volume of the head comprises estimating the changes in blood volume in the desired region of the brain.

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

24. A method according to claim 23, wherein the tissue is inside the ear.

25. A method according to claim 23, wherein the tissue is inside the nose.

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

a) performing CPR on the patient;

b) causing currents to flow inside the patient'"'"'s head by producing electric fields inside the head during the CPR, by placing at least two current-carrying electrodes on the head, and applying at least two different electric potentials to the current-carrying electrodes;

c) measuring at least changes in the electric fields and the currents during the CPR;

d) estimating changes in the blood volume of the head during the CPR, using a controller to analyze data of the measurements of the electric fields and the currents; and

e) estimating blood flow in the brain during the CPR, from the changes in blood volume of the head.