Blood flow monitor for shock and resuscitation

• US 20020173731A1
• Filed: 05/16/2002
• Published: 11/21/2002
• Est. Priority Date: 05/17/2001
• Status: Active Grant

• Current Assignee: Thermal Technologies Incorporated
• Original Assignee: Thermal Technologies Incorporated
• Inventors: Bowman, Harry Frederick, Martin, Gregory T.
• Granted Patent: US 6,805,672 B2
• Time in Patent Office: Days
• US Class Current: 600/549
• 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 5/026 Measuring blood flow A61B3/1233, A61B3/1241 take precedence
• CPC Class Codes: A61B 5/028 by thermo-dilution
• CPC Class Codes: A61B 5/412 Detecting or monitoring sepsis

Abstract

A shock monitor comprising one or more probes, for measuring physiological conditions indicative of shock, and a controller for calculating blood flow values, as an indicator of the state-of-shock, is disclosed. The probe is used to introduce an input signal and produces an output signal, which represents the state-of-shock of the tissue in communication with the probe. The output signal is used to calculate a blood flow value.

Claims

1. A system for monitoring shock comprising:

means for supplying heat to tissue in the inner wall of the rectum;

means for sensing in the tissue a thermal response functionally related to the perfusion of blood in the tissue; and

means for calculating a value indicative of shock as a function said thermal response.

2. The system of claim 1, wherein the means for supplying heat to tissue comprises a thermistor.

3. The system of claim 1, wherein the sensor comprises a thermal diffusion probe.

4. The system of claim 1, wherein the sensor comprises an intraluminal probe.

5. A shock monitor comprising:

a thermistor for thermal contact with tissue at a site on the inner wall of the rectum;

means for electrically energizing said thermistor to elevate the temperature of said thermistor above the baseline temperature of tissue at said site; and

means for producing an electrical signal having a value functionally related to the electrical energy supplied to said thermistor and the rate at which heat from said thermistor is transferred in said tissue;

means for producing a signal indicative of shock as a function of said electrical signal.

6. A shock monitor comprising:

thermistor means for thermally contacting living tissue at a site on the inner wall of the rectum;

means for electrically energizing and deenergizing said thermistor means cyclically to cause the temperature of said tissue to rise and fall cyclically;

means for producing a signal functionally related to the power used to energize said thermistor during each energizing and deenergizing cycle;

means responsive to the temperature change in said tissue and the power related signal from said producing means for producing a signal during each energizing and deenergizing cycle as a function of perfusion in said tissue; and

means for computing a value for blood flow in said tissue indicative of shock during each energizing and deenergizing cycle as a function of the perfusion related signal.

7. The shock monitor of claim 6, wherein the means for computing a value comprises a microprocessor.

8. The shock monitor of claim 6, wherein the means for computing a value comprises an embedded microdevice.

9. A system for producing a signal indicative of shock comprising:

a thermistor for contacting the inner wall of the rectum to establish thermal contact with tissue at a site in the inner wall of the rectum;

control means for electrically energizing and deenergizing said thermistor cyclically to cause the temperature of said thermistor to cyclically rise and fall, the rate of temperature rise in an initial time period within each energizing and deenergizing cycle being substantially a function of the intrinsic thermal conductivity of tissue in thermal contact with said thermistor;

means for producing a signal functionally related to the power used to energize said thermistor during each energizing and deenergizing cycle; and

iterative calculating means for;

calculating intrinsic thermal conductivity in the initial time interval during each energizing and deenergizing cycle as a function of the temperature rise in the initial time interval and the power related signal produced by said producing means;

calculating perfusion in a subsequent time interval during each energizing and deenergizing cycle as a function of the calculated value of intrinsic thermal conductivity;

recalculating intrinsic thermal conductivity in the first time interval using the calculated value of perfusion;

recalculating perfusion in the subsequent time interval using the recalculated value of intrinsic thermal conductivity; and

recalculating values for intrinsic thermal conductivity and perfusion, in alternating fashion, until the recalculated values of perfusion converge to a substantially unchanging value, using in each recalculation of perfusion the previously recalculated value of intrinsic thermal conductivity and in each recalculation of intrinsic thermal conductivity the previously recalculated value of perfusion.

10. A method of monitoring shock in a living subject comprising the steps of:

supplying heat to tissue in the inner wall of the rectum;

sensing in the tissue a thermal response functionally related to the perfusion of blood in the tissue; and

calculating a blood flow value indicative of shock as a function said thermal response.

11. The method of claim 10, wherein the heat is supplied using a thermistor.

12. The method of claim 10, wherein the blood flow value is calculated by comparing the thermal response with a table of thermal response values.

14. The method of claim 13, wherein the blood flow value is calculated by comparing the thermal response with a table of thermal response values.

15. The method of claim 13, wherein said calculating step comprises:

calculating intrinsic thermal conductivity in a first time interval during said energizing step;

calculating perfusion in a subsequent time interval during said energizing step using the calculated value of intrinsic thermal conductivity;

recalculating values for intrinsic thermal conductivity and perfusion in alternating fashion, until the recalculated values of perfusion converge to a substantially unchanging value, using in each recalculation of perfusion the previously calculated value of intrinsic thermal conductivity and in each recalculation of intrinsic thermal conductivity the previously calculated value of perfusion; and

calculating a blood flow value indicative of shock as a function of the converged value of perfusion.

18. A system according to claim 17, further comprising a blood flow model wherein said signal indicative of shock is a function of the relationship of said power related signal to said blood flow model.

19. A system according to claim 17, further comprising a model that relates temperature and power to tissue blood flow wherein said signal indicative of shock is a function of the relationship of said power related signal and the change in temperature produced by said energizing and deenergizing means to a blood flow value determined by said model.

20. A system according to claim 19, wherein the relationship of said power related signal and the change in temperature produced by said energizing and deenergizing means is the ratio of said power related signal to said change in temperature.

21. A system according to claim 17, 18, 19 or 20, wherein said thermistor means comprises means for thermally contacting a site on the inner wall of the rectum.

13. A method of monitoring shock comprising the steps of:

contacting the inner wall of the rectum with electrically energizable thermistor means to establish a heat transfer path between said thermistor means and tissue at a site along the inner wall of the rectum;

energizing said thermistor means to elevate the temperature of said thermistor means above the baseline temperature of said tissue;

sensing the thermal response in said tissue to the application of heat from said thermistor means; and

calculating a blood flow value indicative of shock as a function of the thermal response in said tissue sensed in said sensing step.

16. A method of monitoring shock comprising the steps of:

contacting the inner wall of the rectum with a thermistor to establish a thermal transfer path with tissue at a site in the inner wall of the rectum;

electrically energizing and deenergizing said thermistor cyclically to cause the temperature of tissue in thermal contact with said thermistor to cyclically rise and fall, the rate of temperature rise in an initial time period within each energizing and deenergizing cycle being substantially a function of the intrinsic thermal conductivity of tissue in thermal contact with said thermistor;

producing a signal functionally related to the power used to energize said thermistor during each energizing and deenergizing cycle;

calculating intrinsic thermal conductivity of tissue at said site in an initial time interval during each energizing and deenergizing cycle as a function of the temperature rise and said power related signal in the energizing and deenergizing cycle;

calculating perfusion in a subsequent time interval during each energizing and deenergizing cycle as a function of the calculated value of intrinsic thermal conductivity;

recalculating intrinsic thermal conductivity in said first time interval using the calculated value of perfusion;

recalculating perfusion in said subsequent time interval using the recalculated value of intrinsic thermal conductivity;

recalculating values for intrinsic thermal conductivity and perfusion, in alternating fashion, until the recalculated values of perfusion converge to a substantially unchanging value, using in each recalculation of perfusion the previously recalculated value of intrinsic thermal conductivity and in each recalculation of intrinsic thermal conductivity the previously recalculated value of perfusion; and

processing said substantially unchanging perfusion value during each energizing and deenergizing cycle to provide a blood flow signal indicative of shock.

17. A system for producing a signal indicative of shock comprising:

thermistor means for thermally contacting living tissue at a site on the inner wall of the rectum;

means for electrically energizing and deenergizing said thermistor means cyclically to cause the temperature of said tissue to rise and fall cyclically;

means for producing a signal functionally related to the power used to energize said thermistor during each energizing and deenergizing cycle; and

means responsive to the power related signal from said producing means for producing a signal, functionally related to blood flow and indicative of shock, during each energizing and deenergizing cycle as a function of perfusion in said tissue.