Noninvasive method of measuring physiologic parameters

• US 20020188206A1
• Filed: 05/09/2002
• Published: 12/12/2002
• Est. Priority Date: 05/09/2001
• Status: Active Grant

• Current Assignee: Hemonix, Inc.
• Original Assignee: Hemonix, Inc.
• Inventors: Harrison, Patrick D., Davis, Charles L.
• Granted Patent: US 6,749,567 B2
• Time in Patent Office: Days
• US Class Current: 600/485
• CPC Class Codes: A61B 2562/02 Details of sensors specially adapted for in-vivo measurements
• CPC Class Codes: A61B 5/0053 by applying pressure, e.g. compression, indentation, palpation, grasping, gauging
• CPC Class Codes: A61B 5/02007 Evaluating blood vessel condition, e.g. elasticity, compliance
• CPC Class Codes: A61B 5/02141 Details of apparatus construction, e.g. pump units or housings therefor, cuff pressurising systems, arrangements of fluid conduits or circuits A61B5/02233, A61B5/0235 take precedence
• CPC Class Codes: A61B 5/022 by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295

Abstract

The present invention provides means and methods for noninvasively identifying the blood pressure characteristics in each of the seven types of vessels in the circulatory system, including the central venous pressure (CVP) through a single monitoring system using fluid depletion plethysmography. Known pressure is applied to a body region in increasing amounts to force blood volume from the body region in step-wise fashion through each vessel type. Blood volume depletion for each vessel type is measured by the increasing electrical impedance of the body part during depletion and is plotted against the increasing pressure data. The resulting series of slope changes within the plotted curve reveals the blood pressure for each vessel type. The data obtained may further be used to determine vessel wall compliance/tension as well as standard measurements such as pulse and large artery systolic and diastolic pressure. Release of the applied pressure may then yield similar data by measuring blood volume replenishment against the decreasingly applied pressure during the same diagnostic operation. The method is not dependent on oscillometric or pulsatile measurement methods. The electrical leads of the impedance/volume sensor and the means for applying pressure to the body part are coextensive to ensure accurate indication of blood volume depletion and replenishment in the body region under pressure and may be incorporated into a single integrated structure.

Claims

1. A method of obtaining a physiological parameter of a body fluid compartment, comprising the steps of:

a. applying a series of known pressure values to a body region containing a body fluid to deplete or replenish a fluid volume from the body region;

b. sensing the body region under pressure to derive a series of body fluid volume indications for the body region under pressure;

c. referencing the body fluid volume indications to the series of known pressure values; and

d. identifying a linear relationship of the body fluid volume indication values referenced to the series of pressure values, thereby indicating a physiological parameter in a body fluid compartment.

2. The method according to claim 1 wherein sensing the body region is done without regard to a pulsatile body signal.

3. The method according to claim 1 wherein the physiological parameter is vessel compliance.

4. The method according to claim 1 wherein the physiological parameter is central venous pressure.

5. The method according to claim 1 wherein the physiological parameter is a nonpulsatile vessel blood pressure.

6. The method according to claim 5 wherein the physiological parameter is a nonpulsatile vessel blood pressure of the capillaries.

7. The method according to claim 5 wherein the physiological parameter is a nonpulsatile vessel blood pressure of the venuoles.

8. The method according to claim 5 wherein the physiological parameter is a nonpulsatile vessel blood pressure of the small veins.

9. The method according to claim 5 wherein the physiological parameter is a nonpulsatile vessel blood pressure of the large veins.

10. The method according to claim 5 wherein the physiological parameter is a nonpulsatile vessel blood pressure of the arterioles.

11. The method according to claim 1 wherein the physiological parameter is a pulsatile vessel blood pressure.

12. The method according to claim 11 wherein the physiological parameter is a pulsatile vessel blood pressure of the small arteries.

13. The method according to claim 11 wherein the physiological parameter is a pulsatile vessel blood pressure of the large arteries.

14. The method according to claim 13 wherein the physiological parameter is a mean blood pressure of the large arteries.

15. The method according to claim 13 wherein the physiological parameter is a systolic blood pressure of the large arteries.

16. The method according to claim 13 wherein the physiological parameter is a diastolic blood pressure of the large arteries.

17. The method according to claim 11 wherein the physiological parameter is a pulsatile vessel blood volume of the large arteries.

18. The method according to claim 1 wherein the physiological parameter is a blood oxygen level.

20. The method of obtaining a physiological parameter of claim 19, wherein the body fluid indication values are referenced to the known pressure values when the pressure is increasing.

21. The method of obtaining a physiological parameter of claim 19, wherein the body fluid indication values are referenced to the known pressure values when the pressure is decreasing.

22. The method of obtaining a physiological parameter of claim 19, wherein the body fluid indication values are referenced to the known pressure values when the pressure is increasing and when the pressure is decreasing.

23. The method of obtaining a physiological parameter of claim 19, correlating the known pressure values between the transition points to body fluid compartment types.

24. The method of obtaining a physiological parameter of claim 19, wherein at least some of the transition points are correlated to body compartments indicative of blood vessel types.

25. The method of obtaining a physiological parameter of claim 24, wherein at least one of the characteristic body fluid compartment types is indicative of central venous pressure.

26. The method of obtaining a physiological parameter of claim 19, wherein the step of applying a series of pressures includes applying pressure above a systolic pressure of the body region.

27. The method of obtaining a vascular fluid profile according to claim 26, wherein the body fluid indication values are admittance values and further including the step of graphing a first curve of admittance values to pressure values.

28. The method of obtaining a vascular fluid profile according to claim 27, further comprising the steps of:

deriving a series of non-vascular fluid admittance values above the systolic pressure value, and

graphing a second curve of the non-vascular fluid admittance values to the series of pressure values.

29. The method of obtaining a vascular fluid profile of claim 28, further including the step of subtracting the second curve from the first curve of admittance values to obtain a true representation of only vascular admittance values.

30. The method of obtaining a physiological parameter of claim 19, wherein the step of applying a series of pressures includes applying pressure starting below a lowest venous pressure of the body region.

31. The method of obtaining a physiological parameter of claim 19, wherein the sensing is done by bioimpedance.

32. The method of obtaining a physiological parameter of claim 19, further including the step of changing impedance values to admittance values.

33. The method of obtaining a physiological parameter of claim 19, further including the step of using the transition points to determine diastolic and mean pressure and deriving a vessel wall tension value therefrom.

34. The method of obtaining a physiological parameter of claim 19, wherein the step of referencing the body fluid volume indications to the series of known pressure values is done with a graphical representation.

35. The method of obtaining a physiological parameter of claim 19, wherein the body region is substantially at heart level when the series of pressures is applied.

37. The method according to claim 36, whereby at least one of the following physiological parameters is further derived from the vascular fluid profile:

a pulsatile vessel blood pressure selected from the group including;

a pulsatile vessel blood pressure of the small arteries, and a pulsatile vessel blood pressure of the large arteries and wherein the physiological parameter of the large arteries is further selected from the group including;

a mean blood pressure of the large arteries, a systolic blood pressure of the large arteries, and a diastolic blood pressure of the large arteries.

39. The method of obtaining a vascular fluid profile according to claim 38, further comprising the step of:

graphing the first curve with admittance values.

40. The method of obtaining a vascular fluid profile according to claim 39, further comprising the steps of:

deriving a series of non-vascular fluid admittance values above a highest vascular pressure value, and

graphing a second curve of the non-vascular fluid values to the series of pressure values.

41. The method of obtaining a vascular fluid profile of claim 40, further including the step of subtracting the second curve from the first curve of admittance values to obtain a true representation of only vascular admittance values.

19. A method of obtaining a physiological parameter of a body fluid compartment, comprising the steps of:

a) applying a series of known pressure values to a body region containing a body fluid to deplete or replenish a series of fluid volumes from the body region;

b) sensing the body region under pressure to derive a series of body fluid volume indication values of the body region under pressure;

c) referencing the body fluid volume indications to the series of known pressure values; and

d) identifying transition points at which a linear relationship of the body fluid volume indication values referenced to the series of pressure values changes, thereby indicating state changes in a body fluid physiological parameter between two fluid compartments having different fluid characteristics.

36. A method of obtaining a physiological parameter, comprising the steps of:

a. applying a series of known pressure values to a body region containing a body fluid to deplete or replenish a series of fluid volumes from the body region;

b. placing a plethysmographic device at the body region under pressure to derive a series of body fluid volume indication values of the body region under pressure;

c. referencing the body fluid volume indications to the series of known pressure values; and

d. identifying transition points at which a linear relationship of the body fluid volume indication values referenced to the series of known pressure values changes, thereby indicating state changes in a body fluid physiological parameter between two adjacent fluid compartments having different characteristic fluid pressures;

whereby at least one of the following physiological parameters is derived from the vascular fluid profile;

a nonpulsatile vessel blood pressure selected from the group including;

a nonpulsatile vessel blood pressure of the capillaries, a nonpulsatile vessel blood pressure of the venuoles, a nonpulsatile vessel blood pressure of the small veins, a nonpulsatile vessel blood pressure of the large veins, and a nonpulsatile vessel blood pressure of the arterioles; and

38. A method of obtaining a vascular fluid profile, comprising the steps of:

a. applying a series of known pressure values to a body region at or near a heart level of the body, to deplete or replenish a series of vascular fluid volumes from the body region;

b. placing a bioimpedance sensor on the body region under pressure to derive a series of impedance or admittance values of the body region under pressure;

c. graphing a first curve of the impedance or admittance values to the series of pressure values; and

d. identifying transition points in the curve indicating state changes in the vascular fluid profile between two vascular fluid compartments having different characteristic vascular fluid pressures;

whereby at least one of the following physiological parameters is derived from the vascular fluid profile;

vessel compliance;

central venous pressure;

a nonpulsatile vessel blood pressure selected from the group including;

a nonpulsatile vessel blood pressure of the capillaries, a nonpulsatile vessel blood pressure of the venuoles, a nonpulsatile vessel blood pressure of the small veins, a nonpulsatile vessel blood pressure of the large veins, and a nonpulsatile vessel blood pressure of the arterioles;

a pulsatile vessel blood pressure selected from the group including;

a pulsatile vessel blood pressure of the small arteries, and a pulsatile vessel blood pressure of the large arteries and wherein the physiological parameter of the large arteries is further selected from the group including;

a mean blood pressure of the large arteries, a systolic blood pressure of the large arteries, and a diastolic blood pressure of the large arteries; and

a pulsatile vessel blood volume of the large arteries.

42. Apparatus for obtaining a physiological parameter, comprising:

a. a pressure applicator for application of a series of pressures to a body region containing a body fluid so as to deplete a series of fluid volumes from the body region, the pressure applicator including means for applying the pressures at a known value;

b. a volume indicator for deriving body fluid volume indications of the body region under pressure;

c. means for referencing the body fluid volume indications to the applied pressure value; and

d. means for identifying or displaying points at which a linear relationship of the body fluid volume indications referenced to the series of pressure values changes, thereby indicating state changes in the body fluid profile between two fluid compartments having different fluid characteristics.

43. Apparatus for obtaining a physiological parameter according to claim 42, wherein the volume indicator is not dependent upon receiving a pulsatile signal to derive the body fluid volume indication.

44. Apparatus for obtaining a physiological parameter according to claim 42, wherein the pressure applicator can apply a pressure below and above a large vein pressure.

45. Apparatus for obtaining a physiological parameter according to claim 42, wherein the pressure applicator includes an inflatable cuff with a width.

46. Apparatus for obtaining a physiological parameter according to claim 42, wherein the volume indicator is a bioimpedance sensor having a sensing channel located at or near the middle of the inflatable cuff width and the sensing channel is approximately one fifth the width of the inflatable cuff.

47. Apparatus for obtaining a physiological parameter according to claim 42, wherein the pressure applicator includes a mechanical pressure cuff.

48. Apparatus for obtaining a physiological parameter according to claim 42, wherein the pressure applicator and the volume indicator are coextensive.

49. Apparatus for obtaining a physiological parameter according to claim 42, wherein the pressure applicator includes means for applying a substantially consistent pressure across that area of the cuff coextensive with the volume indicator.

50. Apparatus for obtaining a physiological parameter according to claim 42, wherein the pressure applicator includes a pressure producing plate which cannot encircle a body region.

51. Apparatus for obtaining a physiological parameter according to claim 50, wherein the pressure producing plate further has impedance plethysmography leads coextensive therewith.

52. Apparatus for obtaining a physiological parameter according to claim 50, wherein the pressure producing plate is manually operated to apply force.

53. Apparatus for obtaining a physiological parameter according to claim 42, wherein the means for referencing the fluid volume indication value to the applied pressure value includes a computer.

54. Apparatus for obtaining a physiological parameter, comprising:

a. a monitor unit comprising;

i) a system processor including;

a volume state monitor for receiving data related to fluid volumes f from, and sending control signals to, a volume indicator,

a pressure state monitor for receiving data related to a pressure applicator,

a pressure control unit for sending control signals to a pressure applicator,

a system timer for producing time values related to control of the monitor unit,

a volume/pressure analyzer for referencing pressure data to volume data, and

an input/output interface for permitting operator interaction with the apparatus,

ii) a volume sensor for applying a current source to a bioimpedance sensor, and

iii) a pressure generator for producing force to be applied to a pressure applicator;

b. a pressure applicator for application of a series of pressures to a body region containing a body fluid so as to deplete a series of fluid volumes from the body region, the pressure applicator including means for applying the pressures at a known value to a body region;

c. a bioimpedance sensor for deriving body fluid volume indications of the body region under pressure; and

d. means for identifying or displaying points at which a linear relationship of the body fluid volume indications referenced to the series of pressure values changes, thereby indicating state changes in the vascular fluid profile between two fluid compartments having different characteristic fluid pressures.

55. Apparatus for obtaining a physiological parameter according to claim 54, wherein the pressure applicator is an inflatable cuff with a width.

56. Apparatus for obtaining a physiological parameter according to claim 55, wherein the bioimpedance sensor has a sensing channel located at or near the middle of the inflatable cuff width and the sensing channel is approximately one fifth the width of the inflatable cuff.

57. A method of obtaining a physiological parameter of a body fluid compartment, comprising the steps of:

a. applying a series of known pressure values to a body region containing a body fluid to deplete or replenish a fluid volume from the body region;

b. sensing the body region under pressure to derive a series of body fluid volume indication values as changed by the pressure applied to or removed from the body region under pressure;

c. referencing the body fluid volume indication values to the series of known pressure values; and

d. identifying a linear relationship of the body fluid volume indication values referenced to the series of pressure values, thereby indicating a physiological parameter in a body fluid compartment.