Method and apparatus for assessing fluid level in lungs

• US 7,704,211 B1
• Filed: 03/21/2005
• Issued: 04/27/2010
• Est. Priority Date: 03/21/2005
• Status: Expired due to Fees

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Koh, Steve
• Primary Examiner(s): Douglas; Steven O
• Assistant Examiner(s): DIXON, ANNETTE FREDRICKA
• Application Number:
  US11/086,612
• Time in Patent Office: 1,863 Days
• Field of Search: 128/200.24, 128/204.18, 128/204.21, 128/204.23, 600/547, 600/529, 600/518, 600/534, 600/527, 600/484, 600/509, 607/9, 607 17- 20, 607/32, 607/59, 607/60, 607/62, 607 4- 6
• US Class Current: 600/486
• CPC Class Codes: A61B 5/0809 by impedance pneumography
• CPC Class Codes: A61B 5/091 Measuring volume of inspired or expired gases, e.g. to determine lung capacity
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/24 Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
• CPC Class Codes: A61B 5/4818 Sleep apnoea
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• CPC Class Codes: A61F 13/4704 having preferential bending zones, e.g. fold lines or grooves
• CPC Class Codes: A61F 13/47236 characterised by an unusual contour
• CPC Class Codes: A61F 13/535 inhomogeneous in the plane of the pad, e.g. core absorbent layers being of different sizes A61F13/5323, A61F13/537 take precedence

Abstract

The invention relates to an apparatus and method to assess the fluid level in lungs. An implantable medical device or external monitor is used to sense or monitor the patient'"'"'s respiratory patterns to identify the presence of periodic breathing or Cheyne-Stokes Respiration (CSR) which is common in patients with congestive heart failure. A fluid index is used to assess the severity of congestive heart failure in a patient. A ratio of Δ blood gas/Σtotal lung volume can be used to determine the lung fluid index.

Claims

1. A method for use by an implantable medical device for assessing fluid level in a patient'"'"'s lungs, comprising:

detecting a first Cheyne-Stokes respiration cycle;

obtaining a first transition value for a respiration-dependent blood parameter during the first Cheyne-Stokes respiration cycle, wherein the first transition value is representative of a change in blood gas levels within the patient during the first Cheyne-Stokes respiration cycle;

obtaining a first tidal volume of the lungs value during the corresponding first Cheyne-Stokes respiration cycle;

deriving a first fluid index for the first Cheyne-Stokes respiration cycle from the first transition value and the first tidal volume of the lungs value; and

assessing fluid level in the lungs of the patient during Cheyne-Stokes respiration based on the first fluid index.

2. The method of claim 1 wherein:

obtaining the first transition value comprises detecting a minimum value and a maximum value of CO₂ concentration and determining the change in blood gas levels within the patient from the minimum and maximum values of CO₂ concentration.

3. The method of claim 1 wherein:

obtaining the first tidal volume of the lungs value comprises integrating phrenic nerve activity.

4. The method of claim 1 wherein:

obtaining the first tidal volume of the lungs value comprises calibrating an impedance sensor from a pneumotachometer.

5. The method of claim 1 wherein:

obtaining the first tidal volume of the lungs value comprises calibrating air flow from a thermistor cannula.

6. The method of claim 1 wherein:

obtaining the first transition value comprises detecting a minimum value and a maximum value of O₂ concentration and determining the change in blood gas levels within the patient from the minimum and maximum values of O₂ concentration.

7. The method of claim 1 further comprising:

detecting a second Cheyne-Stokes respiration cycle;

obtaining a second transition value of a respiration-dependent blood parameter, the second transition value occurring during the second Cheyne-Stokes respiration cycle;

obtaining a second tidal volume of the lungs value during the second Cheyne-Stokes respiration cycle;

deriving a second fluid index for the second Cheyne-Stokes respiration cycle from the second transition value and the second tidal volume of the lungs value; and

comparing the first fluid index and the second fluid index to obtain a further indication of the fluid level in the patient'"'"'s lungs.

8. The method of claim 1 wherein obtaining the first tidal volume of the lungs value comprises summing intrathoracic impedance.

9. A method for assessing fluid level in a patient'"'"'s lungs for use by an implantable medical device, comprising:

detecting first and second periods of Cheyne-Stokes respiration;

accumulating measurements of transitions in a respiration-dependent blood parameter during the first period of Cheyne-Stokes respiration, wherein the respiration-dependent blood parameter is representative of changes in blood gas levels within the patient during the first period of Cheyne-Stokes respiration;

accumulating measurements of tidal volume of the lungs during the first period of Cheyne-Stokes respiration;

deriving a first fluid index for the first period of Cheyne-Stokes respiration as a function of the accumulated measurements of transitions and from the accumulated measurements of tidal volume during the first period of Cheyne-Stokes respiration;

accumulating measurements of transitions in the respiration-dependent blood parameter during the second period of Cheyne-Stokes respiration;

accumulating measurements of tidal volume of the lungs during the second period of Cheyne-Stokes respiration;

deriving a second fluid index from the accumulated measurements of transitions in the respiration-dependent blood parameter and from the accumulated measurements of tidal volume during the second period of Cheyne-Stokes respiration; and

assessing a fluid level in the lungs by comparing the first fluid index and the second fluid index.

10. A method of determining a fluid level in the lungs of a patient for use by an implantable medical device, comprising:

detecting a Cheyne-Stokes respiration (CSR) cycle;

determining a blood gas level in the patient during the CSR cycle;

determining a total tidal volume of the lungs of a patient during the CSR cycle;

deriving a fluid index for the CSR cycle based on the blood gas level and the total tidal volume of the lungs; and

assessing a fluid level in the lungs of the patient based on the fluid index.

11. The method of claim 10 wherein the determining of the blood gas level comprises measuring a change in blood gas levels.

12. The method of claim 10 wherein the total tidal volume is determined using intrathoracic impedance.

13. The method of claim 10 wherein deriving a fluid index includes determining a ratio of a change in blood gas level to a tidal volume.

14. The method of claim 13 further including detecting an indication of the health of the patient by comparing the ratio against a predetermined threshold indicative of poor health.

15. The method of claim 14 further including alerting the patient if the ratio falls below the predetermined threshold indicative of poor health.