Edema monitor

• US 10,052,064 B2
• Filed: 04/01/2014
• Issued: 08/21/2018
• Est. Priority Date: 04/04/2013
• Status: Active Grant

• Current Assignee: Thermal Technologies Incorporated
• Original Assignee: Thermal Technologies Incorporated
• Inventors: Bowman, H. Frederick
• Primary Examiner(s): Stout, Michael C
• Application Number:
  US13/999,906
• Publication Number:
  US 20140303513A1
• Time in Patent Office: 1,603 Days
• Field of Search: 600549
• CPC Class Codes: A61B 5/01 Measuring temperature of body parts ; Diagnostic temperature sensing, e.g. for malignant or inflamed tissue clinical contact thermometers G01K13/20
• CPC Class Codes: A61B 5/031 Intracranial pressure
• CPC Class Codes: A61B 5/4064 Evaluating the brain A61B5/031, A61B5/369, A61B5/14553 take precedence
• CPC Class Codes: A61B 5/4878 Evaluating oedema
• CPC Class Codes: A61B 5/6864 Burr holes

Abstract

An edema monitor uses patient-specific measurements of tissue conductivity and tissue perfusion and an empirically developed perfusion coefficient of thermal conductivity to obtain tissue intravascular water and tissue extravacular water components of tissue total water. Edema is an excess of tissue extravacular water. A value for edema is obtained by deducting from the obtained value for tissue extravacular water a normal value for tissue extravacular water.

Claims

1. A system for determining a value for tissue extravascular water in living tissue comprising:

a thermistor probe adapted to be inserted into living tissue for detecting in the volume of tissue surrounding the thermistor probe a thermal conductivity value indicative of the total water content of the volume of tissue;

means for determining in the volume of tissue a value indicative of perfusion in the volume of tissue as a function of the detected thermal conductivity value;

a model of the relationship in living tissue of perfusion and thermal conductivity obtained from multiple measurements of thermal conductivity and perfusion in a population of living subjects;

means for calculating a second value for thermal conductivity indicative of tissue intravascular water in the volume of tissue using the detected thermal conductivity value, the determined value indicative of perfusion and a value representing the relationship of thermal conductivity in living tissue to perfusion in living tissue provided by said model; and

means for determining a value indicative of tissue extravascular water in the volume of tissue using the detected thermal conductivity value and the calculated second value for thermal conductivity.

2. A method for determining a value for tissue extravascular water in a volume of living tissue comprising the steps of:

introducing a thermistor probe into living tissue;

heating the thermistor probe to a temperature above the baseline temperature of the surrounding tissue by means of a control circuit having a power source for energizing the thermistor probe,

as a function of the power used by the heating step detecting in the volume of tissue a value for thermal conductivity indicative of the total tissue water in the volume of tissue;

detecting in the volume of tissue a value for perfusion in the volume of tissue as a function of the detected value for conductivity in the volume of tissue; and

calculating a second value for thermal conductivity indicative of tissue extravascular water in the volume of tissue using the detected value for thermal conductivity, the detected value for perfusion and a value for the relationship in living tissue between thermal conductivity and perfusion provided by an empirically developed model of the relationship of tissue perfusion values and tissue thermal conductivity values created from multiple measurements in living tissue of thermal conductivity and perfusion in a population of subjects.

3. A system for determining a value for tissue extravascular water in a volume of living brain tissue of a subject comprising:

a thermistor probe for insertion into living brain tissue;

a control circuit having a power source for energizing the thermistor probe to raise the temperature of tissue surrounding the thermistor probe;

an empirical model of the relationship of perfusion in living brain tissue and thermal conductivity in living brain tissue; and

means responsive to the power required to heat the thermistor probe and a value for the relationship of perfusion in living brain tissue and thermal conductivity in living brain tissue provided by the model for determining a value indicative of tissue extravascular water in the tissue surrounding the thermistor probe.

4. A system according to claim 3 wherein the empirical model is obtained from multiple measurements of thermal conductivity and perfusion in living brain tissue in a population of subjects.