Method for determining the effective thermal mass of a body or organ using a cooling catheter

• US 6,660,028 B2
• Filed: 02/25/2002
• Issued: 12/09/2003
• Est. Priority Date: 06/02/2000
• Status: Expired due to Term

• Current Assignee: Zoll Circulation Incorporated (Asahi Kasei Corporation)
• Original Assignee: Innercool therapies Incorporated (Taxus Cardium Pharmaceuticals Group, Inc.)
• Inventors: Magers, Michael, Yon, Steven A.
• Primary Examiner(s): GIBSON, ROY DEAN
• Application Number:
  US10/082,964
• Publication Number:
  US 20020082671A1
• Time in Patent Office: 652 Days
• Field of Search: 607/96, 607/104, 607/105, 607/106, 607/113, 606/20-23, 606/27-28
• US Class Current: 607/105
• CPC Class Codes: A61B 2017/22069 Immobilising; Stabilising
• CPC Class Codes: A61B 2090/064 for measuring force, pressure or mechanical tension
• CPC Class Codes: A61B 5/20 for measuring urological functions restricted to the evaluation of the urinary system A61B5/4375 takes precedence
• CPC Class Codes: A61F 2007/0059 with an open fluid circuit
• CPC Class Codes: A61F 2007/0069 with return means
• CPC Class Codes: A61F 2007/0095 with a temperature indicator
• CPC Class Codes: A61F 2007/126 for invasive application, e.g. for introducing into blood vessels
• CPC Class Codes: A61F 7/12 Devices for heating or cooling internal body cavities
• CPC Class Codes: A61M 2025/0002 with a pressure sensor at the distal end
• CPC Class Codes: A61M 2025/0039 characterized by lumina being arranged coaxially
• CPC Class Codes: A61M 2025/0073 Tip designed for influencing the flow or the flow velocity of the fluid, e.g. inserts for twisted or vortex flow general flow characteristics A61M2206/10
• CPC Class Codes: A61M 2205/366 by liquid heat exchangers
• CPC Class Codes: A61M 2210/1085 Bladder
• CPC Class Codes: A61M 25/0029 characterized by features relating to least one lumen located at the middle part of the catheter, e.g. slots, flaps, valves, cuffs, apertures, notches, grooves or rapid exchange ports catheter shaft surface irregularities A61M2025/006
• CPC Class Codes: A61M 25/003 characterized by features relating to least one lumen located at the distal part of the catheter, e.g. filters, plugs or valves catheter tips A61M25/0067
• CPC Class Codes: A61M 25/0068 Static characteristics of the catheter tip, e.g. shape, atraumatic tip, curved tip or tip structure
• CPC Class Codes: A61M 5/44 having means for cooling or heating the devices or media

Abstract

A method and apparatus is provided for determining an effective thermal mass of a patient. The effective thermal mass is employed to determine a gain factor used in a feedback control system controlling patient temperature. The method begins by inducing hypothermia or hyperthermia in at least a selected portion of the patient with a device having a heat transfer surface. Next, power is transferred between the device and the patient. A change in temperature over time, which arises in the selected portion of the patient, is measured while performing the step of inducing hypothermia or hyperthermia. Finally, an effective thermal mass is calculated based on the measured power and the measured temperature change over time.

Claims

1. A method for determining an effective thermal mass of a patient, said method comprising the steps of:

inducing hypothermia or hyperthermia in at least a selected portion of the patient;

measuring a parameter characteristic of power transferred to or from the patient while performing the step of inducing hypothermia or hyperthermia; and

calculating an effective thermal mass based at least in part on the measured parameter.

2. The method of claim 1 further comprising the step of measuring a change in temperature of the patient while performing the step of inducing hypothermia or hyperthermia, and wherein the step of calculating the effective thermal mass includes the step of calculating the effective thermal mass based at least in part on the measured parameter and the measured temperature.

3. The method of claim 2 wherein said temperature of the patient is the whole body core temperature of the patient.

4. The method of claim 1 wherein the step of inducing hypothermia or hyperthermia includes the step of introducing a catheter into a blood vessel to transfer heat between the patient and the catheter.

5. The method of claim 4 further comprising the step of circulating a working fluid through the catheter.

6. The method of claim 5 wherein the step of measuring a parameter characteristic of the power transferred between the catheter and the patient includes the step of measuring a temperature differential between the working fluid as it enters the catheter and as it exits the catheter.

7. The method of claim 6 wherein the step of measuring a parameter characteristic of the power transferred between the catheter and the patient further includes the step of measuring the power based on the measured temperature differential and a mass flow rate of the working fluid circulating through the catheter.

8. The method of claim 4 wherein the selected portion of the patient is the brain and the catheter is introduced into the carotid artery.

9. The method of claim 4 wherein the selected portion of the patient is the whole body and the catheter is introduced into the inferior vena cava.

10. The method of claim 5 wherein the feedback control system determines the temperature of the working fluid as it enters the catheter.

11. A method for controlling the temperature of at least a selected portion of a patient, said method comprising the steps of:

introducing a catheter into a blood vessel supplying blood to the selected portion of the patient;

heating or cooling the catheter to introduce or remove heat from the selected portion of the patient, said heating or cooling being performed at a rate determined by a feedback control algorithm that employs a feedback control gain factor; and

wherein the step of heating or cooling includes the step of calculating an effective thermal mass for determining the feedback control gain factor, said calculating step including the steps of;

measuring a parameter characteristic of power transferred between the catheter and the patient; and

calculating the effective thermal mass based at least in part on the measured parameter.

12. The method of claim 11 further comprising the step measuring a change in temperature which arises in the selected portion of the patient while heating or cooling the catheter, and wherein the step of calculating the effective thermal mass includes the step of calculating the effective thermal mass based at least in part on the measured parameter and the measured temperature.

13. The method of claim 11 wherein said selected portion of the patient is an organ.

14. The method of claim 11 wherein said selected portion of the patient is the whole body of the patient.

15. The method of claim 11 wherein the heating or cooling step includes the step of circulating a working fluid through the catheter.

16. The method of claim 15 wherein the step of measuring a parameter characteristic of the power transferred between the catheter and the patient includes the step of measuring a temperature differential between the working fluid as it enters the catheter and as it exits the catheter.

18. The method of claim 15 wherein the feedback control algorithm determines the temperature of the working fluid as it enters the catheter.

19. The method of claim 15 wherein the feedback control algorithm determines a mass flow rate of the working fluid circulating through the catheter.

21. The method of claim 11 wherein the feedback control algorithm employs a PID controller.

17. The method of step 16 wherein the step of measuring a parameter characteristic of the power transferred between the catheter and the patient further includes the step of measuring the power based on the measured temperature differential and a mass flow rate of the working fluid circulating through the catheter.

20. The method of step 11 wherein the selected portion of the patient is the brain and the catheter is introduced into the carotid artery.

22. A computer readable medium for determining an effective thermal mass of a selected portion of a patient in which hypothermia or hyperthermia is to be induced with a device having a heat transfer surface, said effective thermal mass being employed to determine a gain factor used in a feedback control system controlling patient temperature, said computer readable medium containing program instructions that, when loaded into a processor, cause the processor to perform the steps of:

storing a measured value of a parameter characteristic of power transferred between the device and the patient; and

calculating and storing an effective thermal mass based at least in part on the stored value of the measured parameter.

23. The medium of claim 22 further comprising the step of storing a measured value corresponding to a change in temperature which arises in the selected portion of the patient while hypothermia or hyperthermia is being induced and wherein the step of calculating and storing an effective thermal mass includes the step of calculating and storing an effective thermal mass based at least in part on the stored values of the measured parameter and the measured temperature.

24. The medium of claim 22 wherein said selected portion of the patient is an organ.

25. The medium of claim 22 wherein said selected portion of the patient is the whole body of the patient.

26. The medium of claim 22 wherein said device having a heat transfer surface is a catheter introduced into a blood vessel supplying blood to the selected portion of the patient.

27. The medium of claim 26 wherein the step of storing a measured value of a parameter characteristic of the power transferred between the catheter and the patient includes the step of storing a measured value of a temperature differential between a working fluid as it enters the catheter and as it exits the catheter.

28. The medium of claim 27 wherein the step of storing a measured value of a parameter characteristic of the power transferred between the catheter and the patient further includes the step of storing a measured value of the power based on the measured value of the temperature differential and a mass flow rate of the working fluid circulating through the catheter.

29. The medium of claim 22 wherein the feedback control system employs a PID controller.