System and method for monitoring thoracic fluid levels based on impedance using an implantable medical device

• US 8,032,212 B2
• Filed: 09/15/2008
• Issued: 10/04/2011
• Est. Priority Date: 09/15/2008
• Status: Expired due to Fees

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Koh, Steve, Bornzin, Gene A., Park, Euljoon
• Primary Examiner(s): Hindenburg; Max
• Assistant Examiner(s): DOUGHERTY, SEAN PATRICK
• Application Number:
  US12/210,848
• Publication Number:
  US 20100069778A1
• Time in Patent Office: 1,114 Days
• Field of Search: 600484-486, 600/506, 600/509, 600/538, 600/547, 607/2, 607/18, 607/80
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/4869 Determining body composition
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance

Abstract

Techniques are provided for monitoring thoracic fluid levels based on thoracic impedance (Z_T) and cardiogenic impedance (Z_C). In one example, the implantable device tracks the maximum time rate of change in cardiogenic impedance (i.e. max(dZ_C/dt)) to detect trends toward hypervolemic or hypovolemic states within the patient based on changes in heart contractility. The detection of these trends in combination with trends in thoracic impedance allows for a determination of whether the thoracic cavity of the patient is generally “too wet” or “too dry,” and thus allows for the titration of diuretics to avoid such extremes. In particular, a decrease in thoracic impedance (Z_T) in combination with a decrease in max (dZ_C/dt) is indicative of the thorax being “too wet” (i.e. a fluid overload). Conversely, an increase in thoracic impedance (Z_T) in combination with a decrease in max (dZ_C/dt) is indicative of the thorax being “too dry” (i.e. a fluid underload).

Claims

1. A method for monitoring thoracic fluids within a patient having an implantable medical device, the method comprising:

detecting thoracic impedance;

detecting cardiogenic impedance;

monitoring thoracic fluids based on a combination of thoracic impedance and cardiogenic impedance;

wherein monitoring thoracic fluids based on a combination of thoracic impedance and cardiogenic impedance includes detecting trends within thoracic impedance and detecting trends within time rate of change values derived from cardiogenic impedance;

wherein a decrease in thoracic impedance combined with a decrease in the time rate of change of cardiogenic impedance is deemed to be indicative of excess fluids within the thorax.

2. The method of claim 1 further including controlling therapy in response to changes in thoracic fluid levels.

3. The method of claim 2 wherein controlling therapy in response to changes in thoracic fluid levels includes one or more of initiating or increasing a dosage of diuretics in response to an excess of thoracic fluids.

4. The method of claim 2 wherein controlling therapy in response to changes in thoracic fluid levels includes one or more of suspending or decreasing a dosage of diuretics in response to a deficit of thoracic fluids.

5. The method of claim 2 wherein controlling therapy in response to changes in thoracic fluids includes controlling dosages of diuretics to maintain a thoracic fluid levels within a predetermined range.

6. The method of claim 2 wherein controlling therapy in response to changes in thoracic fluids is controlled by an expert system.

7. The method of claim 1 further including generating diagnostic information representative of changes in thoracic fluid levels.

8. The method of claim 1 further including generating warning signals indicative of thoracic fluid levels deviating from a predetermined range.

9. The method of claim 1 further including generating warning signals indicative of failure of prior therapy to maintain thoracic fluid levels within a predetermined range.

10. The method of claim 1 further including identify long-term trends within thoracic impedance and within cardiogenic impedance indicative of progression of heart failure.

11. The method of claim 1 wherein monitoring thoracic fluids based on a combination of thoracic impedance and cardiogenic impedance is performed by the implantable device.

12. The method of claim 1 wherein monitoring thoracic fluids based on a combination of thoracic impedance and cardiogenic impedance is performed by an external system based information transmitted from the implantable medical device.

13. The method of claim 1 wherein detecting thoracic impedance includes applying impedance detection pulses between one or more of a left ventricular (LV) coil shocking electrode or a LV pacing electrode and an electrode mounted to a housing of the implantable medical device.

14. The method of claim 1 wherein detecting cardiogenic impedance includes applying impedance detection pulses between at least two electrodes to obtain an impedance signal.

15. The method of claim 1 wherein detecting cardiogenic impedance includes applying impedance detection pulses between a right atrial (RA) electrode and an electrode mounted to a housing of the implantable medical device to obtain an RA-housing impedance signal.

16. A method for monitoring thoracic fluids within a patient having an implantable medical device, the method comprising:

detecting thoracic impedance;

detecting cardiogenic impedance;

monitoring thoracic fluids based on a combination of thoracic impedance and cardiogenic impedance;

wherein monitoring thoracic fluids based on a combination of thoracic impedance and cardiogenic impedance includes detecting trends within thoracic impedance and detecting trends within time rate of change values derived from cardiogenic impedance;

wherein an increase in thoracic impedance combined with a decrease in the time rate of change of cardiogenic impedance is deemed to be indicative of a deficit of fluids within the thorax.

17. A system for monitoring thoracic fluids within a patient having an implantable medical device implanted therein, the system comprising:

a thoracic impedance detector;

a cardiogenic impedance detector;

a thoracic fluid monitor that monitors thoracic fluids based on a combination of thoracic impedance and cardiogenic impedance;

wherein the thoracic fluid monitor monitors thoracic fluids based on a combination of thoracic impedance and cardiogenic impedance including detecting trends within thoracic impedance and detecting trends within time rate of change values derived from cardiogenic impedance;

wherein a decrease in thoracic impedance combined with a decrease in the time rate of change of cardiogenic impedance is deemed to be indicative of excess fluids within the thorax.

18. A system for monitoring thoracic fluids within a patient having an implantable medical device implanted therein, the system comprising:

a thoracic impedance detector;

a cardiogenic impedance detector;

a thoracic fluid monitor that monitors thoracic fluids based on a combination of thoracic impedance and cardiogenic impedance;

wherein the thoracic fluid monitor monitors thoracic fluids based on a combination of thoracic impedance and cardiogenic impedance including detecting trends within thoracic impedance and detecting trends within time rate of change values derived from cardiogenic impedance;

wherein an increase in thoracic impedance combined with a decrease in the time rate of change of cardiogenic impedance is deemed to be indicative of a deficit of fluids within the thorax.