Method and apparatus for the non-invasive detection of medical conditions by monitoring peripheral arterial tone

• US 6,319,205 B1
• Filed: 01/12/1999
• Issued: 11/20/2001
• Est. Priority Date: 07/30/1996
• Status: Expired due to Term

• Current Assignee: Itamar Medical Ltd. (Asahi Kasei Corporation)
• Original Assignee: Itamar Medical (C.M.) 1997 Ltd.
• Inventors: Goor, Daniel A, Sheffy, Jacob, Lavie, Peretz, Schnall, Robert P
• Primary Examiner(s): O'Connor, Cary
• Assistant Examiner(s): Natnithithadha, Navin
• Application Number:
  US09/214,788
• Time in Patent Office: 1,043 Days
• Field of Search: 600/485, 600/481, 600/490, 600/499, 600/479, 600/480, 600/454, 600/504, 600/500, 600/507
• US Class Current: 600/485
• CPC Class Codes: A61B 5/02007 Evaluating blood vessel condition, e.g. elasticity, compliance
• CPC Class Codes: A61B 5/02241 of small dimensions, e.g. adapted to fingers
• CPC Class Codes: A61B 5/1073 Measuring volume, e.g. of limbs
• CPC Class Codes: A61B 5/6806 Gloves
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6838 Clamps or clips
• CPC Class Codes: A61F 2007/0036 Hand

Abstract

A method and an apparatus for non-invasive detection of a physiological state or medical condition are disclosed. The method provides an indication of such state or condition such as myocardial ischemia or sleep apnea, by detecting the peripheral arterial tone'"'"'s response to such state or condition, based on monitoring changes in peripheral arterial tone and determining that a change in the condition of the patient has occurred when a specific change in the peripheral arterial tone has been detected. A static pressure field is applied around the distal part of a digit of the subject. Peripheral arterial tone changes and related volume changes in the distal part of the digit are detected to thereby detect or monitor a physiological state or medical condition. The apparatus includes a finger probe (20), in the form of a tube (3) accommodating the patient'"'"'s finger, which is designed to apply pressure, and a contiguous pressure cuff (40) which extends the boundary of the pressure field. The finger probe (2) either includes or is associated with a signal sensor/transducer (100, 101).

Claims

1. A method for the non-invasive detection of a change in physiological condition of a patient, comprising steps of monitoring changes in peripheral arterial tone and determining that a change in the physiological condition of the patient has occurred when a specific change in the peripheral arterial tone has been detected.

2. The method of claim 1, wherein said physiological condition is one of myocardial ischemia, on-set of REM sleep state, and sleep apnea.

3. The method of claim 1, further comprising a step of applying a pressure to the measuring site, said pressure being sufficient to (a) substantially prevent venous pooling at said measuring site (b) substantially prevent uncontrolled venous backflow at said measuring site and (c) partially unload the wall tension of, but not to occlude, the arteries at said measuring site when the measuring site is at heart level or below.

4. The method of claim 1, wherein the step of monitoring changes in peripheral arterial tone comprises monitoring changes in blood flow of skin arteries.

5. The method of claim 1, wherein the step of monitoring changes in peripheral arterial tone comprises monitoring changes in blood flow of a digit'"'"'s arteries.

67. The method of claim 1, wherein said monitoring step is performed continuously and/or in real time.

6. An apparatus for detecting a change in a physical condition of a patient, comprising:

a probe to be applied to a digit of the patient, said probe sensing the peripheral arterial tone of the digit; and

a processor receiving signals from said probe and providing an output indicating changes in the peripheral arterial tone of said digit, thereby indicating a physiological state or medical condition of the patient.

7. The apparatus of claim 6, wherein said probe comprises a membrane for applying a pressure sufficient to (a) substantially prevent venous pooling in said digit and (b) partially unload the wall tension of, but not to occlude, the arteries in said digit.

8. The apparatus of claim 7, wherein said apparatus further comprises a sensor for monitoring changes in blood volume in said digit.

9. The device of claim 6, wherein said probe further includes a pressure cuff.

68. The apparatus of claim 6, wherein said probe is adapted to sense the peripheral arterial tone continuously and/or in real time.

10. A probe to be applied to a digit for detecting peripheral vasoconstriction, said probe comprising:

a membrane for applying a pressure sufficient to partially unload the wall tension of, but not to occlude, the arteries in said digit; and

means for substantially preventing venous pooling in said digit.

11. The probe of claim 10, further comprising a sensor for monitoring changes in blood volume in said digit.

12. A method for non-invasive detection of physiological dysfunction of a patient, comprising:

applying a static pressure field around the distal end of a digit of the subject, including the extreme digit tip, which static pressure field is sufficient to (a) substantially prevent venous pooling in said distal end, (b) substantially prevent uncontrolled venous backflow in said distal end, and (c) partially unload the wall tension of, but not to occlude, the arteries in said distal end when the digit is at heart level; and

measuring changes in peripheral arterial tone and related volume changes in said distal end of the digit accompanying the arterial pulse waves.

13. The method according to claim 12, wherein said volume-related changes are measured by measuring changes in volume in said distal end.

14. The method according to claim 12, wherein said volume-related changes are measured by measuring changes in optical density in said distal end.

15. The method according to any one of claims 12-14, wherein said measured changes are monitored for indicating the existence of myocardial ischemia in the patient.

16. The method according to any one of claims 12-14, wherein said measured changes are monitored for indicating at least one of onset and duration of rapid eye movement (REM) sleep, and sleep apnea.

17. The method according to any one of claims 12-14, wherein said static pressure field is in the range of approximately 30 mm Hg to about 10% above the patient'"'"'s diastolic pressure.

18. The method according to any one of claims 14, wherein said static pressure field is applied around a portion of the finger proximal to, and including, the finger'"'"'s extreme tip.

19. The method according to claim 18, wherein said static pressure field is applied by a thimble-shaped probe including an end cap enclosing at least the most distal phalange, and a contiguous annular cuff.

20. The method according to any one of claims 12-14, wherein said static pressure field is 70 mmHg.

21. A probe for detecting changes in peripheral arterial tone, comprising:

a pressure applicator including an end cap for receiving, and for applying pressure to, the most distal phalange of a patient'"'"'s digit, and a cuff for receiving, and for applying pressure to, the phalange of the patient'"'"'s digit preceding the distal part of the digit;

said cuff acting as a venous tourniquet to prevent venous blood pooling in said digit, retrograde venous blood flow, and retrograde venous shock wave propagation into the distal part of the digit; and

said cap detecting pulsatile volume changes of the arteries in said most distal phalange, preventing venous pooling in said digit and partially unloading the wall tension of, but not occluding the arteries therein.

22. The probe of claim 21, further comprising a heating mechanism.

23. The probe of claim 22, further comprising a vertical displacement sensor.

24. The probe of claim 21, wherein said pressure compartment is defined by a deformable tubular membrane, and wherein said probe further comprises means for preventing said membrane from axial movement when pressurized, so as to avoid expelling a finger placed in the probe.

25. The probe of claim 24, wherein said deformable tubular membrane is divided into two sections at diametrically opposite sides of the finger.

26. The probe of claim 24, wherein said end cup is divided into a plurality of casing sections, each of said plurality of casing sections having a membrane section connected thereto, and wherein said plurality of casing sections are joined together to define said end cup.

27. The probe of claim 24, wherein said means for preventing said membrane from axial movement comprises a restrainer bar fixed to the casing and having a mid-portion received within the tubular membrane so as to restrain inward axial displacement of the membrane.

28. A method for calibrating a blood pressure measuring instrument, comprising the generation of a compliance curve of the measured arterial blood vessels by inducing and monitoring hydrostatic pressure changes within these blood vessels by changing the vertical position of a measurement site with respect to the heart and measuring corresponding volumes and other volume correlated features of such arterial blood vessels and then plotting such measured values and the induced hydrostatic pressure changes.

29. A method for measuring the arterial blood pressure of a subject, comprising:

heating the distal end of a digit of the subject'"'"'s body to a predetermined temperature to maximally dilate the arterial blood vessels in said digit; and

measuring volume-related changes in said distal end of the digit accompanying blood pressure waves;

and converting said measured changes to arterial blood pressure.

30. The method according to claim 29, wherein a static pressure field is applied around the distal end of the digit sufficient to substantially prevent pooling of venous blood and to partially unload the wall tension of, but not to occlude, the digit arteries when the digit is at heart level or below.

31. The method according to either of claims 29 or 30, wherein said measured changes are changes in optical density in said distal end of the digit accompanying blood pressure waves.

32. The method according to any one of claim 30 wherein said measured changes in the distal end of the digit are converted to arterial blood pressure by:

applying said static pressure field as a predetermined external counter-pressure to the digit;

vertically displacing the digit through a plurality of vertical positions with respect to the subject'"'"'s heart;

measuring the hydrostatic pressure added to the subject'"'"'s blood pressure by each vertical position of the subject'"'"'s digit with respect to the subject'"'"'s heart;

and utilizing said predetermined external counter-pressure and said hydrostatic pressure measurements for calibrating said measured changes in the outer end of the subject'"'"'s digit in terms of the arterial blood pressure of the subject and for converting said measured changes to arterial blood pressure.

33. The method according to either of claims 29 or 30, wherein said measured changes are changes in volume in said distal end of the digit accompanying blood pressure waves.

34. A probe for measuring changes in peripheral arterial tone of a subject, comprising:

a rigid casing having an open end and a closed end;

a compliant membrane disposed inside said casing and hermetically connected to the open end of said casing;

a circular pressure band provided inside said casing and positioned to press said membrane against interior wall of said casing; and

a substantially U-shaped restraining bar disposed inside the casing and positioned against the membrane so as to prevent axial shifting of the membrane when inflated to avoid expelling of a finger placed therein.

35. The probe of claim 34, wherein said pressure band divides said membrane into two hermetically sealed pressure chambers.

36. The probe of claim 34, further comprising an optical sensor.

37. An apparatus for monitoring the arterial pulse waves of a subject, comprising:

a pressure applicator including a tubular socket for receiving a predetermined length of the distal end of a digit of the subject'"'"'s body, including the extreme distal tip of the digit;

a pressure source for applying a static pressure field around the distal end, including the extreme distal tip, of the digit of the subject'"'"'s body when received in said tubular socket, which static pressure field acts as a venous tourniquet to substantially prevent pooling of venous blood in the distal end of the digit, to prevent retrograde venous blood flow and erratic venous shock wave propagation into the distal part of the digit, which could produce artifacts at the measuring site, and to partially unload the wall tension of, but not to occlude, the arteries therein when the digit is at heart level; and

,

a measuring device for measuring changes in said distal end of the digit associated with blood pressure waves.

38. The apparatus according to claim 37, wherein said measuring device measures changes in volume in said distal end of the digit associated with blood pressure waves.

39. The apparatus according to claim 37, wherein said measuring device measures changes in optical density in said distal end of the digit associated with blood pressure waves.

40. The apparatus according to any one of claims 37-39, wherein said pressure applicator applies a static pressure around the distal end of the digit which is extended in the proximal direction towards the subject'"'"'s heart for a predetermined distance from the site at which said changes are measured.

41. The apparatus according to any one of claims 37-39, wherein said pressure applicator comprises:

a casing having a deformable tubular membrane mounted therein and defining a tubular chamber with said casing; and

a fluid pressure source for applying fluid pressure to said tubular chamber to cause the tubular membrane to deform according to changes in volume of blood flow through the subject'"'"'s digit when received therein;

wherein said deformable tubular membrane is divided into a plurality of sections.

42. The apparatus according to claim 41, wherein said deformable tubular membrane is divided into two sections at diametrically opposite sides of the subject'"'"'s digit when received therein.

43. The apparatus according to claim 41, wherein said casing is divided into a plurality of sections, one for each of said membrane sections, and joined together to define said outer tubular chamber with said membrane sections.

44. The apparatus according to claim 41, wherein said tubular membrane is divided into said plurality of sections by a restrainer bar affixed to the casing and having a mid-portion received within the tubular membrane so as to restrain the inward displacement of outer periphery of each membrane section during the application of said fluid pressure to said tubular chamber.

45. The apparatus according to claim 37, wherein said pressure source applies a static pressure field in the range of 30 mm Hg to about 70 mm Hg.

46. The apparatus according to claim 37, wherein said apparatus further includes a converter for converting said measured changes in said outer end of the digit to arterial blood pressure of the subject.

47. The apparatus according to claim 46, wherein said converter includes:

a measuring device for measuring hydrostatic pressure added to the subject'"'"'s blood pressure when vertically displacing the digit through a plurality of vertical positions with respect to the subject'"'"'s heart; and

a computer utilizing said static pressure field and said hydrostatic pressure measurements for calibrating said measured changes in the outer end of the subject'"'"'s digit in terms of the arterial blood pressure of the subject, and for converting said measured changes to arterial blood pressure.

48. The apparatus according to claim 46, wherein said apparatus further includes a pre-heater for pre-heating said digit to a predetermined temperature to maximally dilate the arterial blood vessels in said digit.

49. The apparatus according to claim 37, wherein said pressure applicator is incorporated into at least one finger of a glove to be worn by the subject and to measure changes associated with blood pressure waves in the distal end of the finger of the subject'"'"'s hand received within said finger of the glove.

50. The apparatus according to claim 37, wherein said pressure applicator applies a pressure of 70 mm Hg.

51. Apparatus for monitoring a hemodynamic condition of a subject, comprising:

a tubular socket for receiving the distal end of a digit of the subject'"'"'s body;

a heater within said socket for heating the distal end of the digit of the subject'"'"'s body to a predetermined temperature to maximally dilate the arterial blood vessels in said digit; and

a measuring device for measuring changes in said distal end of the digit associated with blood pressure waves.

52. The apparatus according to claim 51, wherein said socket includes a pressure applicator for applying a static pressure field around the distal end of the digit sufficient to substantially prevent pooling of venous blood and to partially unload the wall tension of, but not to occlude, the digit'"'"'s arteries when the digit is at heart level.

53. The apparatus according to either of claims 51 or 52, wherein said measuring device measures changes in volume in said distal part of the digit associated with blood pressure waves.

54. The apparatus according to either of claims 51 or 52, wherein said measuring device measures changes in optical density in said distal part of the digit associated with blood pressure waves.

55. Apparatus for detecting cardiopulmonary distress in a subject, comprising:

a pressure applicator including a tubular socket for receiving a predetermined length of the distal end of a digit of the subject'"'"'s body, including the extreme distal tip of the digit;

a pressure source for applying a static pressure field around the distal end of said digit of the subject'"'"'s body when received in said tubular socket, which static pressure field is sufficient to substantially prevent pooling of venous blood in the distal end of the digit and to partially unload the wall tension of, but not to occlude, the arteries therein when the digit is at heart level;

a measuring device for measuring changes in said distal end of the digit associated with blood pressure waves;

and an indicator for providing an indication of the existence of cardiopulmonary distress when said measured changes exceed a predetermined percentage as compared to a normal known condition of the subject when cardiopulmonary distress is not present.

57. The apparatus according to either of claims 55 or 56, wherein said measuring device measures changes in volume in said outer end of the digit associated with blood pressure waves.

58. The apparatus according to either of claims 55 or 56, wherein said measuring device measures changes in optical density in said outer end of the digit associated with blood pressure waves.

59. The apparatus according to any one of claims 55 or 56, wherein said pressure applicator applies a pressure in the range of 30 mm Hg to 70 mm Hg.

60. The apparatus according to any one of claims 55-56, wherein said pressure applicator applies a static pressure around the distal end of the digit which static pressure field is extended in the direction towards the subject'"'"'s heart for a distance from the site at which said changes are measured.

61. The apparatus according to any one of claims 55-56, wherein said pressure applicator comprises a casing having a deformable tubular membrane mounted therein defining an outer tubular chamber with said casing, and said inner tubular socket for receiving said distal end of the subject'"'"'s digit;

said pressure source applying said static pressure field to said outer tubular chamber to cause the tubular membrane to deform according to changes in volume of the subject'"'"'s digit, when received therein, associated with blood pressure waves;

said deformable tubular membrane being divided into a plurality of sections around the subject'"'"'s digit when received therein, each section including a central region and an outer periphery, the outer periphery of each section being restrained from inward displacement, such that the pressure within the outer tubular chamber inwardly displaces the central region of each membrane section to a greater degree than the outer periphery thereof, thereby causing said inwardly displaced central regions of the plurality of membrane sections to firmly clamp the device to the subject'"'"'s digit against axial and rotary movement of the device with respect to the body extremity.

62. The apparatus according to claim 61, wherein said deformable tubular membrane is divided into two sections at diametrically opposite sides of the subject'"'"'s digit when received therein.

63. The apparatus according to claim 61, wherein said casing is divided into a plurality of sections, one for each of said membrane sections, and joined together to define said outer tubular chamber with said membrane sections, each of said membrane sections being constituted of a substantially four sided membrane secured at its peripheral edges to the peripheral edges of its respective casing section.

64. The apparatus according to claim 61, wherein said tubular membrane is divided into said plurality of sections by a restrainer bar fixed to the casing and having a mid-portion received within the tubular membrane so as to restrain the inward displacement of the outer periphery of each membrane section during the application of said fluid pressure to said outer tubular chamber.

56. Apparatus for monitoring a sleeping subject, comprising:

a pressure applicator including a tubular socket for receiving a predetermined length of the distal end of a digit of the subject'"'"'s body, including the extreme distal tip of the digit;

a pressure source for applying a static pressure field around the distal end of the digit when received in said tubular socket, which the static pressure field is sufficient to substantially prevent pooling of venous blood in the distal end of the digit and to partially unload the wall tension of, but not to occlude, the arteries therein when the digit is at heart level;

a measuring device for measuring changes in said distal end of the digit associated with blood pressure waves;

and an indicator utilizing said measured changes for providing an indication of the sleeping condition of the subject.

65. A method for non-invasive detection of a physiological condition of a patient, comprising:

monitoring changes in peripheral pulsatile volume; and

determining the physiological condition of the patient when a predetermined change in the peripheral pulsatile volume is detected.

66. A method as recited in claim 65, wherein the changes in peripheral pulsatile volume reflect changes in peripheral arterial tone.