Non-Invasive Intracranial Monitor

• US 20070287899A1
• Filed: 12/14/2006
• Published: 12/13/2007
• Est. Priority Date: 01/15/2002
• Status: Active Grant

• Current Assignee: Orsan Medical Technologies, Ltd.
• Original Assignee: Orsan Medical Technologies, Ltd.
• Inventors: Reichman, Yosef, Rappaport, Alon, Ben-Ari, Shlomi, Poupko, Ben
• Granted Patent: US 8,211,031 B2
• Time in Patent Office: Days
• US Class Current: 600/383
• CPC Class Codes: A61B 5/02 Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/026 Measuring blood flow A61B3/1233, A61B3/1241 take precedence
• 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 5/03 Detecting, measuring or recording fluid pressure within the body other than blood pressure, e.g. cerebral pressure; Measuring pressure in body tissues or organs A61B5/205 takes precedence
• CPC Class Codes: A61B 5/031 Intracranial pressure
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/4064 Evaluating the brain A61B5/031, A61B5/369, A61B5/14553 take precedence
• CPC Class Codes: A61B 5/407 Evaluating the spinal cord A61B5/4896 takes precedence
• CPC Class Codes: A61B 5/4076 Diagnosing or monitoring particular conditions of the nervous system A61B5/4821, A61B5/4824 take precedence

Abstract

A method of estimating at least one intracranial hemodynamic parameter in a subject, the method comprising: a) obtaining data of changes in electrical impedance across the subject'"'"'s head as a function of time; b) analyzing the data; and c) estimating one or more of intracranial pressure, cerebral blood volume, and a factor related to at least one of cerebral perfusion pressure and a mean transit time through cerebral capillaries.

Claims

1. A method of estimating at least one intracranial hemodynamic parameter in a subject, the method comprising:

a) obtaining data of changes in electrical impedance across the subject'"'"'s head as a function of time;

b) analyzing the data; and

c) estimating one or more of intracranial pressure, cerebral blood volume, and a factor related to at least one of cerebral perfusion pressure and a mean transit time through cerebral capillaries.

2. A method according to claim 1, wherein analyzing the data comprises one or more of smoothing the data, removing variations in the data due to the subject'"'"'s breathing cycle, and selecting data only from a portion of the subject'"'"'s cardiac cycles.

3. A method according to claim 1, wherein analyzing the data comprises finding a measure of the range of impedance, and estimating comprises estimating one or more of intracranial pressure and cerebral blood volume, responsive to the measure of the range of impedance.

4. A method according to claim 1, wherein analyzing the data comprises finding a measure of a maximum rate of fall of the impedance, and estimating comprises estimating one or more of intracranial pressure and cerebral blood volume, responsive to the measure of the maximum rate of fall.

5. A method according to claim 1, wherein analyzing the data comprises finding a measure of a maximum rate of rise of the impedance, and estimating comprises estimating the factor related to one or more of cerebral perfusion pressure and the mean transit time through cerebral capillaries, responsive to the measure of the maximum rate of rise.

6. A method according to claim 5, wherein the factor is related to cerebral perfusion pressure.

7. A method according to claim 5, wherein the factor is related to the mean transit time through cerebral capillaries.

8. A method according to claim 1, wherein analyzing the data comprises finding a measure of a height of a first local maximum of impedance, or a first local minimum in rate of rise of impedance, following the diastolic phase of the cardiac cycle, and estimating comprises estimating the factor related to one or more of cerebral perfusion pressure and the mean transit time through cerebral capillaries, responsive to the measure of the height of the first local maximum, or minimum in rate of rise, of impedance.

9. A method according to claim 8, wherein analyzing the data comprises normalizing the measure of the height of the first local maximum, or minimum in rate of rise, of impedance to a measure of a height of a second local maximum in impedance, following the diastolic phase of the cardiac cycle and the first local maximum, or minimum in rate of rise, of impedance.

10. A method according to claim 8, wherein the factor is related to cerebral perfusion pressure.

11. A method according to claim 8, wherein the factor is related to the mean transit time through cerebral capillaries.

12. A method according to claim 8, wherein analyzing the data also comprises finding a measure of a maximum rate of rise of the impedance, and estimating the factor related to one or more of cerebral perfusion pressure and the mean transit time through cerebral capillaries is responsive to a combination of the measure of a maximum rate of rise of the impedance, and the measure of a first local maximum in impedance or first local minimum in rate of rise of impedance.

13. A method according to claim 1, wherein analyzing the data comprises normalizing to a measure of the total range of impedance.

14. A method according to claim 1, wherein analyzing the data comprises finding a measure of a latency time, and estimating comprising estimating intracranial pressure responsive to the measure of the latency time.

15. A method according to claim 1, wherein analyzing the data comprises normalizing time to a cardiac period.

16. A method according to claim 1, wherein analyzing the data comprises smoothing of data over time.

17. A method according to claim 1, wherein analyzing the data comprises finding a measure of the at least one intracranial parameter and averaging the measure over a plurality of cardiac cycles.

18. A method according to claim 1, wherein analyzing the data comprises averaging data from a same phase of different cardiac cycles.

19. A method according to claim 1, wherein analyzing the data comprises excluding values of impedance, or values of rate of change of impedance, or both, that do not fall within an expected range of magnitude or do not occur within an expected range of time relative to the cardiac cycle, or both.

20. A method according to claim 1, wherein the at least one hemodynamic parameter is monitored substantially continuously for a subject undergoing surgery.

21. A method according to claim 1, wherein the at least one hemodynamic parameter is monitored substantially continuously for a subject who is a stroke patient.

22. A method according to claim 1, wherein the at least one hemodynamic parameter is monitored substantially continuously for a subject suffering from a traumatic head injury.

23. A method according to claim 1, wherein the at least one hemodynamic parameter is monitored substantially continuously for a subject suffering from a chronic condition.

24. A method according to claim 1, wherein the at least one hemodynamic parameter is monitored substantially continuously for a subject who is a neonate.

25. Apparatus for estimating one or more intracranial hemodynamic parameters, the apparatus comprising:

a) a device for obtaining electrical impedance data of the head as a function of time relative to the timing of the cardiac cycle; and

b) a controller configured to estimate at least one of intracranial pressure, cerebral blood volume, and a factor related to one or more of cerebral perfusion pressure and a mean transit time through cerebral capillaries, from the data.

26. Apparatus according to claim 25, wherein the controller is configured to analyze the data to find a measure of the range of impedance, and to estimate one or more of intracranial pressure and cerebral blood volume, responsive to the measure of the range of impedance.

27. Apparatus according to claim 25, wherein the controller is configured to analyze the data to find a measure of a maximum rate of fall of impedance, and to estimate one or more of intracranial pressure and cerebral blood volume, responsive to the measure of the maximum rate of fall of impedance.

28. Apparatus according to claim 25, wherein the controller is configured to analyze the data to find a measure of a maximum rate of rise of impedance, and to estimate the factor related to one or more of cerebral perfusion pressure and the mean transit time, responsive to the measure of the maximum rate of rise of impedance.

29. Apparatus according to claim 25, wherein the controller is configured to analyze the data to find a measure of a height of a first local maximum in impedance, or a first local minimum in rate of rise of impedance, following the diastolic phase of the cardiac cycle, and to estimate the factor related to one or more of cerebral perfusion pressure and the mean transit time, responsive to the measure of the height of the first local maximum, or minimum in rate of rise, of impedance.

30. Apparatus according to claim 25, wherein the controller is configured to analyze the data to find a measure of a latency time, and to estimate intracranial pressure, responsive to the measure of the latency time.