Dynamically variable filter

• US 20090048497A1
• Filed: 08/13/2007
• Published: 02/19/2009
• Est. Priority Date: 08/13/2007
• Status: Active Grant

• Current Assignee: Baxter Healthcare SA (Baxter International Inc.), Baxter International Inc.
• Original Assignee: Cheetah Medical Ltd. (Baxter International Inc.)
• Inventors: Keren, Hanan
• Granted Patent: US 9,095,271 B2
• Time in Patent Office: Days
• US Class Current: 600/301
• CPC Class Codes: A61B 5/02028 Determining haemodynamic parameters not otherwise provided for, e.g. cardiac contractility or left ventricular ejection fraction
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes 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 5/053 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 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/4869 Determining body composition
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence
• CPC Class Codes: A61B 5/742 using visual displays A61B5/339 takes precedence

Abstract

A method of processing a signal pertaining to at least one electrical property of an organ of a subject is disclosed. The method comprises determining a physiological condition of the subject, selecting a frequency band, filtering the signal according to the frequency band, and dynamically adapting the frequency band in response to a change in the physiological condition.

Claims

1. A method of processing a signal pertaining to at least one electrical property of an organ of a subject, comprising determining a physiological condition of the subject, selecting a frequency band, filtering said signal according to said frequency band, and dynamically adapting said frequency band in response to a change in said physiological condition, thereby processing the signal.

2. The method of claim 1, wherein said physiological condition is a heart rate of the subject.

3. The method of claim 2, wherein at least one of a lower bound of said frequency band and an upper bound of said frequency band parameter is a linear function of said heart rate.

4. The method of claim 1, wherein a lower bound of said frequency band is about 0.9*(HR/60) Hz at all times, wherein said HR is a heart rate of the subject in units of beats per minute.

5. The method of claim 1, wherein an upper bound of said frequency band is about 6+1.5*[(HR/60)−

1] Hz at all times, wherein said HR is a heart rate of the subject in units of beats per minute.

6. A filtering device, comprising:

a first input unit for receiving an input pertaining to at least one electrical property of an organ of a subject, a second input unit for receiving data pertaining to a physiological condition of the subject, and a filtering unit configured for filtering said input signal according to a frequency band which is dynamically adapted in response to a change in said physiological condition.

7. The device of claim 6, wherein said physiological condition is a heart rate of the subject.

8. The device of claim 7, wherein at least one of a lower bound of said frequency band and an upper bound of said frequency band parameter is a linear function of said heart rate.

9. The device of claim 6, wherein a lower bound of said frequency band is about 0.9*(HR/60) Hz at all times, wherein said HR is said heart rate in units of beats per minute.

10. The device of claim 6, wherein an upper bound of said frequency band is about 6+1.5*[(HR/60)−

1] Hz at all times, wherein said HR is said heart rate in units of beats per minute.

11. A system for monitoring cardiac output, comprising the device of claim 6.

12. A system for predicting at least one of:

a body cell mass, a fat free mass and total body water of a subject, comprising the device of claim 6.

13. A system for determining hematocrit of blood in a body part of a subject, comprising the device of claim 6.

14. A system for monitoring hydration status of a subject, comprising the device of claim 6.

15. A system for discriminating tissue, comprising the device of claim 6.

16. A system for calculating the circumference of a body segment, comprising the device of claim 6.

17. A method of monitoring at least one electrical property of an organ of a subject, comprising sensing input radiofrequency signals from the organ, processing said input radiofrequency signals to provide processed input signals, filtering said input signals using a dynamically variable filter to provide filtered signals, and using said filtered signals for monitoring the at least one electrical property of the organ.

18. The method of claim 17, wherein said dynamically variable filter is adapted in response to a change in a physiological condition of the subject.

19. The method of claim 18, wherein said physiological condition is a heart rate of the subject.

20. The method of claim 19, wherein at least one of a lower frequency bound and an upper frequency bound characterizing said filter is a linear function of said heart rate.

21. The method of claim 18, wherein a lower frequency bound characterizing said filter is about 0.9*(HR/60) Hz at all times, wherein said HR is said heart rate in units of beats per minute.

22. The method of claim 18, wherein an upper frequency bound characterizing said filter is about 6+1.5*[(HR/60)−

1] Hz at all times, wherein said HR is said heart rate in units of beats per minute.

23. The method of claim 17, wherein said input radiofrequency signals are indicative of impedance the organ.

24. The method of claim 17, wherein said input radiofrequency signals are indicative of hemodynamic reactance of the organ.

25. The method of claim 17, wherein said possessing comprises filtering said input radiofrequency signals using an analog filter.

26. The method of claim 17, further comprising calculating at least one quantity using said electrical property, wherein said at least one quantity is selected from the group consisting of a stroke volume, a cardiac output, a brain intra luminal blood volume and blood flow.

27. The method of claim 17, wherein said blood flow comprises at least one of:

an external carotid blood flow rate, an internal carotid blood flow rate, an ulnar blood flow rate, a radial blood flow rate, a brachial blood flow rate, a common iliac blood flow rate, an external iliac blood flow rate, a posterior tibial blood flow rate, an anterior tibial blood flow rate, a peroneal blood flow rate, a lateral plantar blood flow rate, a medial plantar blood flow rate and a deep plantar blood flow rate.

28. The method of claim 26, further comprising determining a phase shift of said input radiofrequency signals relative to output radiofrequency signals transmitted to the organ and using said phase shift for calculating said at least one quantity.

29. The method of claim 28, further comprising transmitting said output radiofrequency signals to the organ.

30. The method of claim 28, further comprising reducing or eliminating amplitude modulation of said input radiofrequency signals, so as to provide signals of substantially constant envelope.

31. The method of claim 30, wherein said reducing or eliminating said amplitude modulation comprises maintaining a phase modulation of said input radiofrequency signals.

32. The method of claim 17, further comprising mixing said input radiofrequency signals and output radiofrequency signals transmitted to the organ so as to provide a mixed radiofrequency signal.

33. The method of claim 32, wherein said mixing comprises providing a radiofrequency sum and a radiofrequency difference.

34. Apparatus for monitoring at least one electrical property of an organ of a subject, comprising:

an input unit for receiving input radiofrequency signals sensed from the organ;

a signal processing unit for processing said input radiofrequency signals to provide processed input signals;

a filtering unit configured for filtering said input signals using dynamically variable filter to thereby provide filtered signals; and

a monitoring unit for monitoring the at least one electrical property of the organ based on said filtered signals.

35. The apparatus of claim 34, wherein said dynamically variable filter is adapted in response to a change in a physiological condition of the subject.

36. The apparatus of claim 35, wherein said physiological condition is a heart rate of the subject.

37. The apparatus of claim 36, wherein at least one of a lower frequency bound and an upper frequency bound characterizing said filter is a linear function of said heart rate.

38. The apparatus of claim 36, wherein is about 0.9*(HR/60) Hz at all times, wherein said HR is said heart rate in units of beats per minute.

39. The apparatus of claim 36, wherein an upper frequency bound characterizing said filter is about 6+1.5*[(HR/60)−

1] Hz at all times, wherein said HR is said heart rate in units of beats per minute.

40. The apparatus of claim 34, wherein said input radiofrequency signals are indicative of impedance the organ.

41. The apparatus of claim 34, wherein said input radiofrequency signals are indicative of hemodynamic reactance of the organ.

42. The apparatus of claim 34, wherein said signal possessing unit comprises an analog filter for filtering said input radiofrequency signals.

43. The apparatus of claim 34, further comprising a data processor for calculating at least one quantity using said electrical property, wherein said at least one quantity is selected from the group consisting of a stroke volume, a cardiac output, a brain intra luminal blood volume and blood flow.

44. The apparatus of claim 43, further comprising a phase shift determinator configured for determining a phase shift of said input radiofrequency signals relative to output radiofrequency signals transmitted to the organ, wherein said data processor is configured for calculating said at least one quantity based on said phase shift.

45. The apparatus of claim 34, wherein said signal processing unit comprises an envelope elimination unit designed and configured to reduce or eliminate amplitude modulation of said filtered signals, so as to provide signals of substantially constant envelope.

46. The apparatus of claim 45, wherein said envelope elimination unit is designed and configured to maintain a phase modulation of said signals.

47. The apparatus of claim 34, wherein said signal processing unit comprises a mixer designed and configured to mix said input radiofrequency signals and said output radiofrequency signals transmitted to the organ so as to provide a mixed radiofrequency signal.

48. The apparatus of claim 47, wherein said mixer is operable to provide a radiofrequency sum and a radiofrequency difference.

49. A system for monitoring at least one electrical property of an organ of a subject, comprising:

a radiofrequency generator for generating output radiofrequency signals;

a plurality of electrodes, designed to be connectable to the skin of the subject, said electrodes being for transmitting said output radiofrequency signals to the organ and for sensing input radiofrequency signals from the organ; and

the apparatus of claim 34.