System, method and apparatus for measuring blood flow and blood volume

• US 8,388,545 B2
• Filed: 01/18/2006
• Issued: 03/05/2013
• Est. Priority Date: 02/15/2005
• Status: Active Grant

• Current Assignee: Baxter Healthcare SA (Baxter International Inc.), Baxter International Inc.
• Original Assignee: Cheetah Medical, Inc. (Baxter International Inc.)
• Inventors: Keren, Hanan, Simon, Avram B.
• Primary Examiner(s): Mallari, Patricia
• Assistant Examiner(s): WESTON, TIFFANY C
• Application Number:
  US11/884,227
• Publication Number:
  US 20100069765A1
• Time in Patent Office: 2,603 Days
• Field of Search: 600/504, 600/481
• US Class Current: 600/504
• 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 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

A method of calculating blood flow in an organ of a subject using output radiofrequency signals transmitted to the organ and input radiofrequency signals received from the organ, the method comprises determining a phase shift of the input radiofrequency signals relative to the output radiofrequency signals and using the phase shift to calculate the blood flow in the organ.

Claims

1. A system for measuring blood flow in an organ of a subject, the system comprising:

a radiofrequency generator configured to generate 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 of the organ; and

a signal processing unit configured to determine a phase shift of said input radiofrequency signals relative to said output radiofrequency signals, and to calculate the blood flow in the organ using a linear relationship between said phase shift and the blood flow.

2. The system of claim 1, wherein said signal processing unit comprises an envelope elimination unit designed and configured to reduce or eliminate amplitude modulation of said input radiofrequency signals so as to provide input radiofrequency signals of substantially constant envelope.

3. The system of claim 2, wherein said envelope elimination unit is designed and configured to maintain a phase modulation of said input radiofrequency signals.

4. The system of claim 2, wherein said envelope elimination unit comprises a limiter amplifier.

5. The system of claim 1, wherein said signal processing unit comprises:

a mixer, electrically communicating with said radiofrequency generator and at least a portion of said plurality of electrodes, said mixer being designed and configured to mix said output radiofrequency signals and said input radiofrequency signals, to provide a mixed radiofrequency signal being indicative of the blood flow; and

electronic circuitry configured to filter out a portion of said mixed radiofrequency signal so as to substantially increase a signal-to-noise ratio of a remaining portion of said mixed radiofrequency signal.

6. The system of claim 5, wherein said mixer is operable to provide a radiofrequency sum and a radiofrequency difference.

7. The system of claim 6, wherein said electronic circuitry comprises a low pass filter configured to filter out said radiofrequency sum.

8. The system of claim 5, wherein said electronic circuitry comprises an analog amplification circuit configured to amplify said remaining portion of said mixed radiofrequency signal.

9. The system of claim 5, wherein said electronic circuitry comprises a digitizer configured to digitize said remaining portion of said mixed radiofrequency signal.

10. The system of claim 5, wherein said electronic circuitry is designed and constructed so as to minimize sensitivity of said input radiofrequency signals to impedance differences between said plurality of electrodes and the organ of the subject.

11. The system of claim 10, wherein said electronic circuitry comprises at least one differential amplifier characterized by an impedance being substantially larger than said impedance differences between said plurality of electrodes and the organ of the subject.

12. The system of claim 5, further comprising a data processor configured to calculate at least one quantity using said remaining portion of said mixed radiofrequency signal, said at least one quantity being selected from the group consisting of a stroke volume, a cardiac output, a brain intra luminal blood flow and an artery blood flow rate.

13. The system of claim 12, wherein said artery blood flow rate is selected from the group consisting 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, a deep plantar blood flow rate.

14. The system of claim 12, further comprising a pacemaker, communicating with said data processor and operable to control a heart rate of the subject, wherein said data processor is programmed to electronically control said pacemaker, in accordance with a value of said at least one quantity.

15. The system of claim 12, further comprising a drug administrating device, communicating with said data processor and operable to administrate drugs to the subject, wherein said data processor is programmed to electronically control said drug administrating device, in accordance with a value of said at least one quantity.

16. The system of claim 12, further comprising a cardiac assist device, communicating with said data processor and operable to increase said cardiac output.

17. The system of claim 16, wherein said cardiac assist device comprises a reinforcing member designed and configured to restrict an expansion of a portion of a heart tissue, thereby to increase said cardiac output.

18. The system of claim 5, wherein a number of said plurality of electrodes is selected so as to substantially decouple said input radiofrequency signals from at least one effect selected from the group consisting of a posture changes effect, a respiration effect and a motion effect.

19. The system of claim 5, wherein said plurality of electrodes comprises two electrodes.

20. The system of claim 5, wherein said plurality of electrodes comprises three electrodes.

21. The system of claim 5, wherein said plurality of electrodes comprises four electrodes.

22. The system of claim 5, wherein at least a portion of said plurality of electrodes are designed and constructed to so as to have a substantial constant sensitivity to electrical signals transmitted through said electrodes, irrespectively of an orientation of said electrodes on the subject.

23. The system of claim 5, wherein at least a portion of said plurality of electrodes comprises at least one elongated conducting material designed and constructed to wind at least a portion of an external organ of the subject, so as to have a substantial constant sensitivity to electrical signals transmitted through said electrodes, irrespectively of an orientation of said electrodes on said external organ.

24. The system of claim 23, wherein at least a portion of said plurality of electrodes comprises an attaching material.

25. The system of claim 23, wherein said external organ is selected from the group consisting of a chest, a hip, a thigh, a neck, a head, an arm, a forearm, an abdomen, a gluteus, a leg and a foot.

26. The system of claim 5, further comprising a detector electrically communicating with at least a portion of said plurality of electrodes for detecting a voltage between a first location and a second location of the subject and for generating said input radiofrequency signals in response to said voltage, wherein said input radiofrequency signals being indicative of impedance and/or hemodynamic reactance of the organ.

27. The system of claim 26, further comprising at least one sensor configured to sense said voltage, said at least one sensor being designed and constructed to generate signals having a magnitude which is a function of blood flow in, from or to the organ.

28. The system of claim 26, wherein said electronic circuitry comprises a differentiator configured to perform at least one time-differentiation, to provide a respective derivative of said impedance and/or hemodynamic reactance of the organ.

29. The system of claim 28, wherein said derivative is selected from the group consisting of a first derivative and a second derivative.

30. The system of claim 28, wherein said differentiator is selected from the group consisting of a digital differentiator and an analog differentiator.

31. The system of claim 5, further comprising a display device for displaying the blood flow.

32. The system of claim 31, wherein said display device is capable of displaying the blood flow as a function of time.

33. The system of claim 5, wherein said signal-to-noise ratio is increased by at least 10 dB.

34. The system of claim 5, wherein said signal-to-noise ratio is increased by at least 20 dB.

35. A method of measuring blood flow in an organ of a subject, the method comprising:

generating output radiofrequency signals;

transmitting said output radiofrequency signals to the organ and sensing input radiofrequency signals of the organ; and

determining, by using a processor, a phase shift of said input radiofrequency signals relative to said output radiofrequency signals and using a linear relationship between said phase shift and the blood flow to calculate the blood flow in the organ.

36. The method of claim 35, wherein a proportion coefficient of said linear relationship comprises a systolic ejection time of a heart of the subject.

37. The method of claim 35, further comprising reducing or eliminating amplitude modulation of said input radiofrequency signals, so as to provide input radiofrequency signals of substantially constant envelope.

38. The method of claim 37, wherein said reducing or eliminating said amplitude modulation comprises maintaining a phase modulation of said input radiofrequency signals of substantially constant envelope.

39. The method of claim 37, wherein said reducing or eliminating said amplitude modulation is by a limiter amplifier.

40. The method of claim 35, further comprising mixing said output radiofrequency signals and said input radiofrequency signals so as to provide a mixed radiofrequency signal being indicative of the blood flow, and filtering out a portion of said mixed radiofrequency signal so as to substantially increase a signal-to-noise ratio of a remaining portion of said mixed radiofrequency signal.

41. The method of claim 40, wherein said mixing comprises providing a radiofrequency sum and a radiofrequency difference.

42. The method of claim 41, wherein said filtering said portion of said mixed radiofrequency signal is by a low pass filter designed and constructed for filtering out said radiofrequency sum.

43. The method of claim 40, further comprising analogically amplifying said remaining portion of said mixed radiofrequency signal.

44. The method of claim 40, further comprising digitizing said remaining portion of said mixed radiofrequency signal.

45. The method of claim 40, wherein said transmitting said output radiofrequency signals and said sensing said input radiofrequency signals are by a plurality of electrodes and the method further comprises minimizing sensitivity of said input radiofrequency signals to impedance differences between said plurality of electrodes and the organ of the subject.

46. The method of claim 45, wherein said minimizing said sensitivity of said input radiofrequency signals to said impedance differences is by at least one differential amplifier characterized by an impedance being substantially larger than said impedance differences.

47. The method of claim 40, further comprising calculating at least one quantity using said remaining portion of said mixed radiofrequency signal, said at least one quantity being selected from the group consisting of a stroke volume, a cardiac output and a brain intra luminal blood volume and an artery blood flow rate.

48. The method of claim 47, wherein said artery blood flow rate is selected from the group consisting 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, a deep plantar blood flow rate.

49. The method of claim 47, further comprising controlling a heart rate of the subject in accordance with a value of said at least one quantity.

50. The method of claim 49, wherein said controlling a heart rate of the subject is by a pacemaker.

51. The method of claim 47, further comprising using a value of said at least one quantity for selecting an amount and a type of drugs and administrating said amount and said type of drugs to the subject.

52. The method of claim 47, further comprising providing a site of surgical access to a portion of a heart of a subject and maintaining the reduction of cardiac expansion of said portion of said heart a substantial amount of time so as to increase said cardiac output.

53. The method of claim 40, wherein said transmitting said output radiofrequency signals to the organ and sensing said input radiofrequency signals of the organ is by connecting a plurality of electrodes to the skin of the subject.

54. The method of claim 53, wherein a number of said plurality of electrodes is selected so as to substantially decouple said input radiofrequency signals from at least one effect selected from the group consisting of a posture changes effect, a respiration effect and a motion effect.

55. The method of claim 53, wherein said plurality of electrodes comprises two electrodes.

56. The method of claim 53, wherein said plurality of electrodes comprises three electrodes.

57. The method of claim 53, wherein said plurality of electrodes comprises four electrodes.

58. The method of claim 53, wherein said connecting said plurality of is done so as to have a substantial constant sensitivity to electrical signals transmitted through said electrodes, irrespectively of an orientation of said electrodes on the subject.

59. The method of claim 53, wherein at least a portion of said plurality of electrodes comprises at least one elongated conducting material designed and constructed to wind at least a portion of an external organ of the subject, so as to have a substantial constant sensitivity to electrical signals transmitted through said electrodes, irrespectively of an orientation of said electrodes on said external organ.

60. The method of claim 59, wherein said external organ is selected from the group consisting of a chest, a hip, a thigh, a neck, a head, an arm, a forearm, an abdomen, a gluteus, a leg and a foot.

61. The method of claim 40, further comprising detecting a voltage between a first location and a second location of the subject and generating said input radiofrequency signals in response to said voltage, wherein said input radiofrequency signals being indicative of impedance and/or hemodynamic reactance of the organ.

62. The method of claim 61, further comprising performing at least one time-differentiation thereby providing a respective derivative of said impedance and/or hemodynamic reactance of the organ.

63. The method of claim 62, wherein said derivative is selected from the group consisting of a first derivative and a second derivative.

64. The method of claim 62, wherein said performing said time-differentiation is effected by a procedure selected from the group consisting of a digital differentiation and an analog differentiation.

65. The method of claim 40, further comprising displaying the blood flow using a display device.

66. The method of claim 65, wherein said display device is capable of displaying the blood flow as a function of time.

67. The method of claim 40, wherein said signal-to-noise ratio is increased by at least 10 dB.

68. The method of claim 40, wherein said signal-to-noise ratio is increased by at least 20 dB.