Cerebral perfusion monitor

• US 8,512,253 B2
• Filed: 01/17/2006
• Issued: 08/20/2013
• Est. Priority Date: 01/15/2002
• Status: Expired due to Fees

• Current Assignee: Orsan Medical Technologies, Ltd.
• Original Assignee: Orsan Medical Technologies, Ltd.
• Inventors: Reichman, Yosef, Poupko, Ben Zion, Ben-Ari, Shlomi
• Primary Examiner(s): Mallari, Patricia
• Assistant Examiner(s): WESTON, TIFFANY C
• Application Number:
  US11/921,937
• Publication Number:
  US 20090227881A1
• Time in Patent Office: 2,772 Days
• Field of Search: 600300-301, 600481-504, 600/506, 600/547
• US Class Current: 600/504
• 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 cerebral blood flow by analyzing IPG and PPG signals of the head, the method comprising:

• • a) finding a maximum slope or most negative slope or the IPG signal, within at least a portion of the cardiac cycle;
  • b) finding a maximum slope or most negative slope of the PPG signal, within at least a portion of the cardiac cycle;
  • c) finding a ratio of the maximum or most negative slope of the IPG signal to the maximum or most negative slope of the PPG signal; and
  • d) calculating a cerebral blood flow indicator from the ratio.

Claims

1. An apparatus for estimating time-varying cerebral blood flow, the apparatus comprising:

a controller configured to;

obtain a time-varying impedance plethysmography signal from a head of a subject;

use the impedance plethysmography signal to calculate a time-varying cerebral blood flow indicator; and

perform data processing on the impedance plethysmography signal and the cerebral blood flow indicator to reduce at least one of noise and artifacts, wherein performing data processing comprises discarding cardiac cycle data of the impedance plethysmography signal for a cardiac cycle which meets one or more criteria for discarding, and

wherein the criteria comprise the impedance plethysmography signal having a cross-correlation below a threshold, between the cardiac cycle and at least one of a following cardiac cycle and a preceding cardiac cycle.

2. An apparatus according to claim 1, wherein the criteria comprise having a duration of the cardiac cycle outside an expected range.

3. An apparatus according to claim 2, wherein the expected range has a maximum between 1.3 and 2 times an average duration of cardiac cycles.

4. An apparatus according to claim 1, wherein the at least one of a following cardiac cycle and a preceding cardiac cycle is a following cardiac cycle.

5. An apparatus according to claim 1, wherein the at least one of a following cardiac cycle and a preceding cardiac cycle is a preceding cardiac cycle.

6. An apparatus according to claim 1, wherein the criteria comprise impedance plethysmography signal having the cross-correlation below the threshold between +0.5 and +0.8, between the cardiac cycle and the at least one of a preceding and a following cardiac cycle.

7. An apparatus according to claim 1, wherein performing data processing comprises reducing breathing artifacts in the impedance plethysmography signal.

8. An apparatus according to claim 1, wherein performing data processing comprises smoothing the cerebral blood flow indicator.

9. An apparatus according to claim 8, wherein smoothing comprises finding an average over a time interval.

10. An apparatus according to claim 8, wherein smoothing comprises using a time scale that is adjusted adaptively, depending on behavior of the cerebral blood flow indicator as a function of time.

11. An apparatus according to claim 1, wherein the controller is further configured to determine a duration of the cardiac cycle using the impedance plethysmography signal.

12. An apparatus according to claim 1, wherein the cerebral blood flow indicator is the peak-to-peak amplitude of the impedance plethysmography signal over the cardiac cycle.

13. An apparatus according to claim 1, wherein the cerebral blood flow indicator is an average value of the impedance plethysmography signal over the cardiac cycle.

14. An apparatus according to claim 1, wherein the cerebral blood flow indicator is a maximum slope of the impedance plethysmography signal over the cardiac cycle.

15. An apparatus according to claim 1, wherein performing data processing includes adjusting the impedance plethysmography signal to have a substantially constant minimum value for a plurality of cardiac cycles.

16. An apparatus according to claim 1, wherein the controller is further configured to calculate the time varying cerebral blood flow indicator for a left hemisphere and a right hemisphere of a brain of the subject.

17. An apparatus for estimating time-varying cerebral blood flow, the apparatus comprising:

a controller configured to;

obtain a time-varying impedance plethysmography signal from a head of a subject;

use the impedance plethysmography signal to calculate a time-varying cerebral blood flow indicator; and

perform data processing on the impedance plethysmography signal and the cerebral blood flow indicator to reduce at least one of noise and artifacts,

wherein performing data processing comprises smoothing the cerebral blood flow indicator, and

wherein smoothing comprises using a time scale that is adjusted adaptively, depending on behavior of the cerebral blood flow indicator as a function of time.

18. An apparatus for estimating time-varying cerebral blood flow, the apparatus comprising:

a controller configured to;

obtain a time-varying impedance plethysmography signal from a head of a subject;

use the impedance plethysmography signal to calculate a time-varying cerebral blood flow indicator; and

perform data processing on the impedance plethysmography signal and the cerebral blood flow indicator to reduce at least one of noise and artifacts,

wherein the cerebral blood flow indicator is the peak-to-peak amplitude of the impedance plethysmography signal over a cardiac cycle.

19. An apparatus for estimating time-varying cerebral blood flow, the apparatus comprising:

a controller configured to;

obtain a time-varying impedance plethysmography signal from a head of a subject;

use the impedance plethysmography signal to calculate a time-varying cerebral blood flow indicator; and

perform data processing on the impedance plethysmography signal and the cerebral blood flow indicator to reduce at least one of noise and artifacts,

wherein performing data processing includes adjusting the impedance plethysmography signal to have a substantially constant minimum value for a plurality of cardiac cycles.

20. An apparatus for estimating time-varying cerebral blood flow, the apparatus comprising:

a controller configured to;

obtain a time-varying impedance plethysmography signal from a head of a subject;

use the impedance plethysmography signal to calculate a time-varying cerebral blood flow indicator; and

perform data processing on the impedance plethysmography signal and the cerebral blood flow indicator to reduce at least one of noise and artifacts, and

wherein the controller is further configured to calculate the time varying cerebral blood flow indicator for a left hemisphere and a right hemisphere of a brain of the subject.