System for quantifying blood flow in tissue and updating tissue baseline conditions
First Claim
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1. A method for determining perfusion in living tissue comprising the steps of:
- (1) establishing baseline criteria, comprising(A) determining an unperturbed temperature in a capillary bed;
(B) causing the temperature in the capillary bed to change from a first unperturbed temperature to a second temperature different from said first temperature for a time period, and(C) determining a value or values for one or more thermal properties in the capillary bed during a first selected portion of said time period;
(2) calculating, using a computing unit, a perfusion value for blood in the capillary bed at a second selected portion of said time period using said thermal property value or values, and(3) evaluating, using a computing unit, one or more physiological and artifactual conditions to determine if baseline criteria established by step (1) are materially affected by said conditions and if so repeating step (1).
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Abstract
Methods and apparatus for determining blood flow in tissue are disclosed. The methods and apparatus are used to establish a baseline for both thermal properties of the tissue and non-physiologic conditions. Periodic changes in either or both constituents of the baseline are determined and, when the changes correspond to a need for a new baseline, a new baseline is established.
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Citations
23 Claims
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1. A method for determining perfusion in living tissue comprising the steps of:
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(1) establishing baseline criteria, comprising (A) determining an unperturbed temperature in a capillary bed; (B) causing the temperature in the capillary bed to change from a first unperturbed temperature to a second temperature different from said first temperature for a time period, and (C) determining a value or values for one or more thermal properties in the capillary bed during a first selected portion of said time period; (2) calculating, using a computing unit, a perfusion value for blood in the capillary bed at a second selected portion of said time period using said thermal property value or values, and (3) evaluating, using a computing unit, one or more physiological and artifactual conditions to determine if baseline criteria established by step (1) are materially affected by said conditions and if so repeating step (1).
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2. A method for determining the perfusion of blood in a volume of tissue comprising the steps of:
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(1) establishing thermal baseline criteria corresponding to thermal conditions of the volume of tissue comprising determining an unperturbed tissue temperature; (2) causing the temperature of the volume of tissue to change from the unperturbed temperature to a second temperature different from the unperturbed temperature during a time interval; (3) calculating, using a computing unit, at least one of an intrinsic thermal conductivity value and a thermal diffusivity value for the volume of tissue during a first selected portion of said time interval; (4) calculating, using a computing unit, perfusion in the volume of tissue at a second selected portion of said time interval using said value; (5) determining need for new baseline criteria for the tissue comprising evaluating one or both of physiologic and artifact conditions; and (6) repeating step (1) when indicated by step (5).
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3. A method for determining perfusion in a volume of tissue comprising the steps of:
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(1) establishing baseline criteria, comprising (A) determining an unperturbed temperature of the tissue; (B) causing the temperature of the tissue to change from a first unperturbed temperature to a second temperature different from said first temperature for a time period, and (C) determining a value or values for one or more thermal properties of tissue during said time period; (2) calculating, using a computing unit, a perfusion value for the tissue during said time period using said thermal property value or values, and (3) evaluating, using a computing unit, one or more physiological and artifactual conditions to determine if baseline criteria established by step (1) are materially affected by said conditions and if so repeating step (1). - View Dependent Claims (4)
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5. Apparatus for determining the perfusion of blood in living tissue comprising:
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means in thermal contact with the tissue for sensing the reference temperature of the tissue when the tissue is unheated; means in thermal contact with the tissue for heating the tissue; means for applying power to said heating means sufficiently rapidly to raise the temperature of said heating means to a temperature above said reference temperature so that the power necessary to maintain said heating means temperature varies as a function of time; data processing means for determining the temperature difference between said heating means temperature and said reference temperature, for determining the resistance of said heating means at said heating means temperature and for determining the time varying relationship between the power required to maintain said heating means at said heating means temperature after said temperature has been reached and the time during which said power is being applied thereto; said data processing means further being responsive to said temperature difference, said heating means resistance and said time varying power and time relationship for determining a perfusion related value; and means for evaluating conditions that affect the reference temperature of the tissue and recognizing conditions under which the reference temperature is no longer valid; and
means for providing an output in response to said evaluating and recognizing means. - View Dependent Claims (6, 7, 8, 9)
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10. Apparatus for determining the perfusion of blood in living tissue comprising:
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means adapted to contact tissue for sensing a reference temperature of the tissue when the tissue is unheated; a heating element for heating tissue including tissue contacted by said heating element, said heating element having a predetermined thermal conductivity and a predetermined thermal diffusivity; means for applying power to said heating element sufficiently rapidly to raise the temperature of said heating element above said reference temperature so that the power necessary to maintain said heating element temperature varies as a function of time; data processing means for determining the temperature difference between said heating element temperature and said reference temperature, for determining the resistance of said heating element at said heating element temperature and for determining the time varying relationship between the power required to maintain said heating element at said temperature after said temperature has been reached and the time during which said power is being applied thereto; said data processing means further being responsive to said temperature difference, said heating element resistance, said applied power in accordance with said time varying power and time relationship, said predetermined thermal conductivity and/or diffusivity of said heating element, and a change in said reference temperature for determining the thermal conductivity and/or the thermal diffusivity of the tissue; means for computing the perfusion of blood in the tissue as a function of the thermal conductivity and/or the thermal diffusivity of the tissue; and means for evaluating conditions that affect the reference temperature of the tissue and recognizing conditions under which the reference temperature is no longer valid; and
means for providing an output in response to said evaluating and recognizing means. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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Specification