System and method for detecting circadian states using an implantable medical device

• US 20040138716A1
• Filed: 01/10/2003
• Published: 07/15/2004
• Est. Priority Date: 01/10/2003
• Status: Active Grant

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Kon, Steve, Park, Euljoon
• Granted Patent: US 7,207,947 B2
• Time in Patent Office: Days
• US Class Current: 607/17
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/36542 controlled by body motion, e.g. acceleration
• CPC Class Codes: A61N 1/36557 controlled by chemical substances in blood

Abstract

Techniques are provided for detecting the circadian state of a patient using an implantable medical device based on selected blood carbon dioxide (CO₂) parameters. In one example, the implantable device tracks changes in end tidal CO₂ (etCO₂) levels and changes in maximum variations of pCO₂ levels per breathing cycle (Δ_cycleCO₂) over the course of the day and determines the circadian state based thereon. It has been found that average etCO₂ levels are generally highest and average Δ_cycleCO₂ levels are generally lowest while a patient is asleep and opposite while a patient is awake. Hence, by tracking changes in average etCO₂ and Δ_cycleCO₂ levels over the course of the day, circadian states can be detected. Minute ventilation and activity levels are used to assist in the determination of the circadian state. Additional techniques are directed to detecting the stage of sleep.

Claims

1. In an implantable medical device for implant within a patient, a method for detecting a circadian state of the patient, the method comprising:

detecting changes in one or more blood carbon dioxide (CO₂) parameters; and

determining the circadian state of the patient based upon the changes in the one or more blood CO₂ parameters.

2. The method of claim 1 wherein detecting changes in selected blood CO₂ parameters comprises detecting one or more of changes in end tidal CO₂ (etCO₂) levels and changes in maximum variation of pCO₂ level per breathing cycle (Δ

_cycleCO₂).

3. The method of claim 1 wherein detecting changes in selected blood CO₂ parameters comprises detecting one or more of changes in end tidal pH levels and changes in maximum variation of blood pH level per breathing cycle (Δ

_cyclepH).

4. The method of claim 1 wherein determining the circadian state of the patient based upon the changes in the selected blood CO₂ parameters comprises identifying whether the patient is asleep or awake.

5. The method of claim 1 further comprising detecting activity levels of the patient and wherein the step of determining the circadian state of the patient additionally takes into account the detected activity levels.

6. The method of claim 1 further comprising detecting minute ventilation levels of the patient and wherein the step of determining the circadian state of the patient additionally takes into account the detected minute ventilation levels.

7. The method of claim 6 further comprising determining a ratio of minute ventilation to blood CO₂ levels of the patient and wherein the step of determining the circadian state of the patient additionally takes into account the determined ratio.

8. The method of claim 7 further comprising determining a sleep stage of the patient based on the ratio of minute ventilation to blood CO₂ levels of the patient.

9. The method of claim 1 wherein detecting changes in selected blood CO₂ parameters is performed to detect changes in etCO₂ levels and changes in Δ

_cycleCO₂ and further comprising;

detecting activity levels of the patient;

detecting minute ventilation levels of the patient; and

wherein the step of determining the circadian state of the patient takes into account a combination of Δ

_cycleCO₂ levels, etCO₂ levels, activity levels and minute ventilation levels.

10. The method of claim 1 wherein determining the circadian state of the patient comprises:

generating a histogram representative of a range of values of the selected blood CO₂ parameters detected over a period of time; and

identifying the circadian state of the patient based upon the shape of the histogram.

11. The method of claim 1 further comprising controlling device functions based on the detected circadian state of the patient.

12. In an implantable medical device for implant within a patient, a system for detecting a circadian state of the patient comprising:

a sensor system operative to detect blood carbon dioxide levels (pCO₂); and

a CO₂-based circadian state detection system operative to detect maximum variations of pCO₂ levels occurring within individual breathing cycles (Δ

_cycleCO₂), track changes in Δ

_cycleCO₂, and determine the circadian state of the patient based upon the changes in Δ

_cycleCO₂.

13. The system of claim 12 wherein the sensor system also comprises an activity sensor and a minute ventilation sensor and wherein the circadian state detection system is operative to determine the circadian state of the patient based on a combination of end tidal CO₂ (etCO₂) levels, Δ

_cycleCO₂, activity levels and minute ventilation levels.

14. The system of claim 13 further comprising a controller operative to control device functions based on the detected circadian state of the patient.

15. In an implantable medical device for implant within a patient, a control system comprising:

a blood CO₂ sensor;

an activity sensor;

a minute ventilation sensor; and

a controller operative to control device functions based on a combination of blood CO₂ parameters, activity levels and minute ventilation levels.

16. In an implantable medical device for implant within a patient, a system for detecting a circadian state of the patient comprising:

means for detecting one or more blood carbon dioxide (CO₂) parameters;

means for identifying changes in the one or more blood CO₂ parameters over a plurality of breathing cycles; and

means for determining the circadian state of the patient based upon the changes in the one or more blood CO₂ parameters over the plurality of breathing cycles.

17. In an implantable medical device for implant within a patient, a method for detecting a circadian state of the patient comprising:

detecting blood carbon dioxide levels (pCO₂);

detecting minute ventilation levels;

determining a ratio of minute ventilation to pCO₂; and

determining the circadian state of the patient based upon the ratio of minute ventilation to pCO₂.

18. The method of claim 17 further comprising detecting end tidal pCO₂ levels of the patient and wherein the step of determining the circadian state of the patient additionally takes into account the end tidal pCO₂ levels.

19. The method of claim 17 further comprising determining a sleep stage of the patient based on the ratio of minute ventilation to blood CO₂ levels of the patient.