System and method for measuring cardiac output via thermal dilution using an implantable medical device with an external ultrasound power delivery system

• US 7,632,235 B1
• Filed: 04/05/2005
• Issued: 12/15/2009
• Est. Priority Date: 11/22/2004
• Status: Expired due to Fees

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Inventors: Boileau, Peter, Gill, Jong, Karicherla, Annapurna, Min, Xiaoyi, Bornzin, Gene A.
• Primary Examiner(s): Layno; Carl H
• Assistant Examiner(s): ANTHONY, JESSICA LYNN
• Application Number:
  US11/099,888
• Time in Patent Office: 1,715 Days
• Field of Search: 600437-439, 600454-459, 600/462, 600466-468, 600/481, 600/486, 600504-507, 600/510, 600/526, 600300-301, 600/549, 600/483, 607 17- 26, 128/905, 604/48, 604 65- 67, 604/500, 604506-510
• US Class Current: 600/526
• CPC Class Codes: A61B 2560/0209 adapted for power saving
• CPC Class Codes: A61B 2560/0214 of power generation or supply
• CPC Class Codes: A61B 5/028 by thermo-dilution
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61N 1/3627 for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy
• CPC Class Codes: A61N 1/3655 controlled by body or blood temperature

Abstract

The implantable device is capable of performing thermal dilution analysis of the cardiac output of a patient using power delivered from an external source. By using power from an external source, the implantable device conserves its power resources for other purposes, such as for pacing or defibrillation therapy. In one example, an external programmer or bedside monitor provides power through a hand-held power delivery wand via electromagnetic induction, with the power routed from a subcutaneous coil to a heating element implanted in the right atrium, which heats blood as it passes through the right atrium. In another example, the heating element is formed of a material that generates heat in response to a beam of ultrasound provided by the wand. In either case, a downstream blood temperature profile is detected using a thermistor implanted in the pulmonary artery and cardiac output is then estimated by analyzing the temperature profile.

Claims

1. An implantable system for use within a patient, the system comprising an implantable medical device adapted to be implanted within the patient, the system further comprising:

a heating element capable of generating heat in response to ultrasound, with the heating element configured for implant in proximity to blood being pumped within the patient for heating a quantity of blood in response to ultrasound generated by a source configured to be positioned external to the patient;

a blood temperature sensor configured for implant downstream from the heating element for detecting a temperature profile of blood heated by the heating element; and

a device operative to route signals representative of the blood temperature profile to the implantable medical device.

2. The system of claim 1 wherein the heating element includes an acoustic absorber absorptive at ultrasonic frequencies.

3. The system of claim 2 wherein the acoustic absorber includes a polyurethane material.

4. The system of claim 3 wherein the polyurethane material is formed of RP-6401 polyurethane.

5. The system of claim 1 wherein the heating element is adapted to be positioned within a right atrium of the patient and wherein the temperature sensor is adapted to be implanted in a pulmonary artery of the patient.

6. The system of claim 1 further including an ultrasound transducer mounted to the heating element and operative to measure incident power.

7. The system of claim 1 wherein the device operative to route signals representative of the blood temperature profile to the implantable medical device is a lead implanted within the heart of the patient.

9. The method of claim 7 wherein the heating element is adapted to be positioned within a right atrium of the patient and wherein directing a beam of ultrasound onto the heating element is performed by directing a beam of ultrasound toward the right atrium.

10. The method of claim 7 wherein the temperature sensor is adapted to be implanted in a pulmonary artery of the patient and wherein measuring the resulting temperature profile of the blood using the temperature sensor is performed to measure the temperature profile of blood passing within the pulmonary artery.

11. The method of claim 7 further comprising tracking changes in the cardiac output of the patient over time using the cardiac output detection system to detect the onset of a selected medical condition within the patient based on the changes in cardiac output over time.

12. The method of claim 11 further comprising detecting the onset of a selected medical condition within the patient based on changes in cardiac output over time.

13. The method of claim 12 further comprising tracking changes, if any, in the severity of the medical condition within the patient using the cardiac output detection system based on any changes over time in the cardiac output of the patient to detect congestive heart failure (CHF).

14. The method of claim 11 wherein the system is equipped to deliver therapy to the patient and wherein the method further comprises controlling the system to deliver therapy in response to the medical condition.

15. The method of claim 14 wherein the system is equipped with a cardiac resynchronization therapy (CRT) system and wherein the therapy includes CRT.

16. The method of claim 15 wherein the system is equipped with an implantable drug pump and wherein delivering therapy includes delivering selected medications to the patient using the drug pump.

17. The method of claim 11 wherein the system is equipped with a warning device and wherein the method further comprises generating a warning signal using the warning device in response to the medical condition.

18. The method of claim 11 wherein tracking changes in the cardiac output of the patient to detect the onset of the medical condition is performed by an external device based on signals received from the implanted device.

8. A method for measuring cardiac output within a patient having an implantable medical system equipped with a blood temperature sensor, a heating element capable of generating heat in response to ultrasound, and a cardiac output detection system, the method comprising:

directing a beam of ultrasound generated by a source configured to be positioned external to the patient onto the heating element causing the heating element to generate heat so that blood adjacent the heating element is heated;

measuring a resulting temperature profile of the blood using the temperature sensor at a location downstream from the heating element;

estimating the cardiac output of the patient using the cardiac output detection system based, in part, on the resulting temperature profile; and

employing the estimated cardiac output to control at least one system function.