System for quantifying blood flow in tissue with periodic updating of tissue baseline conditions

• US 7,758,511 B2
• Filed: 04/04/2003
• Issued: 07/20/2010
• Est. Priority Date: 04/05/2002
• Status: Active Grant

• Current Assignee: Thermal Technologies Incorporated
• Original Assignee: Thermal Technologies Incorporated
• Inventors: Martin, Gregory T., Bowman, H. Frederick
• Primary Examiner(s): Marmor, II; Charles A
• Assistant Examiner(s): Natnithithadha; Navin
• Application Number:
  US10/406,829
• Publication Number:
  US 20030219719A1
• Time in Patent Office: 2,664 Days
• Field of Search: 600504-507, 600/481, 600/483, 600/484, 600/549, 607/27
• US Class Current: 600/504
• CPC Class Codes: A61B 5/02055 Simultaneously evaluating both cardiovascular condition and temperature
• CPC Class Codes: A61B 5/026 Measuring blood flow A61B3/1233, A61B3/1241 take precedence
• CPC Class Codes: A61B 5/028 by thermo-dilution
• CPC Class Codes: A61B 5/413 Monitoring transplanted tissue or organ, e.g. for possible rejection reactions after a transplant

Abstract

Disclosed are methods and apparatus for determining blood flow in tissue. Particularly methods and apparatus are disclosed for establishing baseline thermal properties for the tissue and providing one or more steps for periodically determining changes in the tissue thermal properties that correspond to a need for a new baseline and establishing the new baseline.

Claims

1. A method for monitoring perfusion in living tissue comprising:

determining baseline thermal conditions for a capillary bed and establishing baseline criteria for the thermal conditions in the capillary bed;

raising the temperature in the capillary bed to a value above said thermal baseline by a heated probe immersed in the capillary bed;

computing, using a computing unit, values associated with one or more selected thermal properties of the capillary bed;

computing, using a computing unit, perfusion in the capillary bed using a value that is a function of the power required by said raising step and one or more of the selected thermal property values;

evaluating, using a computing unit, one or more conditions that may significantly change one or more of the thermal baseline and the selected thermal property values; and

determining, using a computing unit, the need for new baseline criteria using data from said evaluating step.

2. A method according to claim 1 further comprising the steps of:

repeating the second said computing step until the second said determining step indicates a need for new baseline criteria;

when a need for new baseline criteria is indicated discontinuing said raising step until said tissue location returns to an unperturbed state; and

repeating the first said determining step.

3. A method according to claim 1 wherein said evaluating step comprises evaluating selected artifact conditions for recognizing artifact conditions under which the established thermal baseline is no longer valid.

4. A method according to claim 3 wherein artifact conditions include one or more of:

ambient temperature changes,

electrical interference,

instrumentation drift,

excessive sensor-tissue contact force that can induce capillary collapse,

insufficient sensor-tissue contact force that can result in artifactual transduction of perfusion,

cross-talk between sensors, and

motion of the sensor relative to the tissue.

5. The method of claim 1 wherein said evaluating step comprises evaluating selected physiological conditions for recognizing conditions under which the established thermal baseline is no longer valid.

6. A method according to claim 5 wherein said evaluating step comprises evaluating selected artifact conditions for recognizing artifact conditions under which the established thermal baseline is no longer valid.

7. A method according to claim 5 wherein physiological conditions include one or more of:

tissue and vascular damage,

tissue edema,

tissue scar formation,

influence of a large vessel,

change in vascular status (e.g.;

blood volume, vasodilation, and vasoconstriction),

changes in perfusion,

changes in blood pressure,

changes in tissue pressure,

changes in tissue temperature,

changes in blood temperature, and

changes in tissue metabolism.

8. A method according to any one of claims 2, 3, 4, 5, 6, or 7 further comprising the step of automatically recalibrating baseline criteria for one or more of the probe and the instrumentation based on the results of the second said determining step.

9. A method for monitoring perfusion in living tissue comprising:

determining baseline thermal conditions for a capillary bed and establishing baseline criteria for the thermal conditions in the capillary bed;

raising the temperature in the capillary bed to a value above said thermal baseline;

computing, using a computing unit, values associated with one or more of an intrinsic thermal conductivity and a thermal diffusivity of the capillary bed;

computing, using a computing unit, perfusion in the capillary bed using a value that is a function of the power required by said raising step and one or more of the conductivity and diffusivity values;

evaluating, using a computing unit, one or more conditions that may significantly change the thermal baseline and one or more of the conductivity and diffusivity values;

and

determining, using a computing unit, the need for new baseline criteria using data from said evaluating step.

10. A method according to claim 9 further comprising the steps of:

repeating the second said computing step until the second said determining step indicates a need for new baseline criteria;

when a need for new baseline criteria is indicated discontinuing said raising step until the capillary bed returns to an unperturbed state; and

repeating the first said determining step.

11. A method according to claim 9 wherein said evaluating step comprises evaluating selected artifact conditions for recognizing artifact conditions under which the established thermal baseline is no longer valid.

12. A method according to claim 11 wherein artifact conditions include one or more of:

ambient temperature changes,

electrical interference,

instrumentation drift,

excessive sensor-tissue contact force that can induce capillary collapse,

insufficient sensor-tissue contact force that can result in artifactual transduction of perfusion,

cross-talk between sensors, and

motion of the sensor relative to the tissue.

13. The method of claim 9 wherein said evaluating step comprises evaluating selected physiological conditions for recognizing conditions under which the established thermal baseline is no longer valid.

14. A method according to claim 13 wherein said evaluating step comprises evaluating selected artifact conditions for recognizing artifact conditions under which the established thermal baseline is no longer valid.

15. A method according to claim 13 wherein physiological conditions include one or more of

tissue and vascular damage,

tissue edema,

tissue scar formation,

influence of a large vessel,

change in vascular status (e.g.:

blood volume, vasodilation, and vasoconstriction),

changes in perfusion,

changes in blood pressure,

changes in tissue pressure,

changes in tissue temperature,

changes in blood temperature, and

changes in tissue metabolism.

16. A method according to any one of claim 10, 11, 12, 13, 14, or 15 further comprising the step of automatically recalibrating baseline criteria based on the results of the second said determining step.