Cerebral perfusion monitor

• US 20090227881A1
• Filed: 01/17/2006
• Published: 09/10/2009
• Est. Priority Date: 01/15/2002
• Status: Active Grant

• Current Assignee: Orsan Medical Technologies, Ltd.
• Original Assignee: Orsan Medical Technologies, Ltd.
• Inventors: Reichman, Yosef, Poupko, Ben Zion, Ben-Ari, Shlomi
• Granted Patent: US 8,512,253 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 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. 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.

2. A method according to claim 1 wherein finding the maximum or most negative slope comprises finding the maximum slope, for both the IPG and PPG signals, and finding a ratio comprises finding a ratio of the maximum slopes.

3. A method according to claim 2, wherein the maximum slopes are maximums within a leading portion of the cardiac cycle.

4. A method according to claim 1 wherein finding the maximum or most negative slope comprises finding the most negative slope, for both the IPG and PPG signals, and finding a ratio comprises finding a ratio of the most negative slopes.

5. A method according to claim 4, wherein the most negative slopes are most negative within a trailing portion of the cardiac cycle.

6. A method according to claim 1, wherein the maximum or most negative slope of at least one of the signals is normalized to a measure of the amplitude of said signal.

7. A method according to claim 6, wherein the measure of the amplitude is the peak-to-peak amplitude of said signal over the cardiac cycle.

8. A method according to claim 6, wherein the measure of the amplitude is an average value of said signal over the cardiac cycle.

9. A method according to claim 1, wherein the PPG signal comes from a PPG sensor on the left side of the head.

10. A method according to claim 1, wherein the PPG signal comes from a PPG sensor on the right side of the head.

11. A method according to claim 1, wherein the PPG signal is an average of signals from a PPG sensor on the left side of the head and a PPG sensor on the right side of the head.

20. A method according to claim 12, wherein calculating the cerebral blood flow indicator comprises using the method of claim 1.

12. A method of estimating time-varying cerebral blood flow, comprising:

a) obtaining a time-varying IPG signal of the head;

b) obtaining a time-varying PPG signal of the head;

c) using the IPG and PPG signals to calculate a time-varying indicator for cerebral blood flow; and

d) performing data processing on one or more of the IPG signal, the PPG signal, and the cerebral blood flow indicator, to reduce noise or artifacts or both.

13. A method according to claim 12, wherein performing data processing comprises discarding data of the IPG signal, the PPG signal, or both, for cardiac cycles which meet one or more criteria for discarding.

14. A method according to claim 13, wherein the criteria comprise having a duration outside an expected range.

15. A method according to claim 14, wherein the expected range has a maximum between 1.3 and 2 times an average duration of cardiac cycles.

16. A method according to claim 13, wherein the criteria comprise one or both of the IPG signal and the PPG signal having a cross-correlation below a threshold, between that cardiac cycle and the following cardiac cycle.

17. A method according to claim 13, wherein the criteria comprise one or both of the IPG signal and the PPG signal having a cross-correlation below a threshold, between that cardiac cycle and the preceding cardiac cycle.

18. A method according to claim 13, wherein the criteria comprise one or both of the IPG signal and the PPG signal having a cross-correlation below a threshold between +0.5 and +0.8, between that cardiac cycle and the preceding or the following cardiac cycle.

19. A method according to claim 12, wherein performing data processing comprises reducing breathing artifacts in the IPG signal, the PPG signal, or both.

21. A method according to claim 12, wherein performing data processing comprises smoothing the cerebral blood flow indicator.

22. A method according to claim 21, wherein smoothing comprises finding an average over a time interval.

23. A method according to claim 21, 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.