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

• US 7,207,947 B2
• Filed: 01/10/2003
• Issued: 04/24/2007
• Est. Priority Date: 01/10/2003
• Status: Expired due to Fees

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Inventors: Koh, Steve, Park, Euljoon
• Primary Examiner(s): Pezzuto; Robert E.
• Assistant Examiner(s): Malamud; Deborah
• Application Number:
  US10/339,989
• Publication Number:
  US 20040138716A1
• Time in Patent Office: 1,565 Days
• Field of Search: 607/17, 607/18, 607/22, 607/42, 600/361, 600/322, 600/345, 600529-542, 73/233, 488/84
• US Class Current: 600/529
• 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;

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

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;

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; and

detecting activity levels of the patient;

wherein detecting changes in selected blood CO₂ parameters is performed to detect changes in etCO₂ levels and changes in Δ

_cycleCO₂; 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.

2. The method of claim 1 wherein detecting changes in selected blood CO₂ parameters comprises detecting 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 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 determining a sleep stage of the patient based on the ratio of minute ventilation to blood CO₂ levels of the patient.

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

7. 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 to detect changes in etCO₂ levels and changes in Δ

_cycleCO₂ levels;

determining minute ventilation levels of the patient;

detecting activity levels of the patient; and

determining the circadian state of the patient comprising;

generating histograms representative of a range of values of the etCO₂ levels, Δ

_cycleCO₂ levels, activity levels, and minute ventilation levels detected over a period of time; and

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

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

a blood CO₂ sensor detecting changes in etCO₂ levels and changes in Δ

_cycleCO₂;

an activity sensor detecting activity levels of the patient;

a minute ventilation sensor detecting minute ventilation levels of the patient; and

a controller operative to control device functions based on a combination of Δ

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

wherein the controller determines a circadian state of the patient by taking into account a combination of Δ

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

9. 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 ) to detect changes in etCO₂ levels and changes in Δ

_cycleCO₂;

detecting minute ventilation levels;

detecting activity levels; and

determining the circadian state of the patient based upon a combination of Δ

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

10. The method of claim 9 further comprising determining a sleep stage of the patient based on the ratio of minute ventilation to blood CO₂ levels of the patient.