Noninvasive effective lung volume estimation

• US 20050124907A1
• Filed: 10/25/2004
• Published: 06/09/2005
• Est. Priority Date: 02/22/2000
• Status: Active Grant

• Current Assignee: RIC INVESTMENTS LLC (Respironics Incorporated)
• Original Assignee: RIC INVESTMENTS LLC (Respironics Incorporated)
• Inventors: Brewer, Lara, Kuck, Kai, Orr, Joseph
• Granted Patent: US 7,699,788 B2
• Time in Patent Office: Days
• US Class Current: 600/532
• CPC Class Codes: A61B 5/0836 Measuring rate of CO2 production
• CPC Class Codes: A61B 5/091 Measuring volume of inspired or expired gases, e.g. to determine lung capacity

Abstract

Methods for noninvasively measuring, or estimating, functional residual capacity or effective lung volume include obtaining carbon dioxide and flow measurements at or near the mouth of a subject. Such measurements are obtained during baseline breathing and during and shortly after inducement of a change in the subject'"'"'s effective ventilation. The obtained measurements are evaluated to determine the amount of time required for exhaled carbon dioxide levels to return to normal—effectively an evaluation of carbon dioxide “washout” from the subject'"'"'s lungs. Conversely, carbon dioxide and flow measurements may be evaluated to determine the amount of time it takes carbon dioxide to “wash in,” or reach peak levels within, the lungs of the subject following the change in the subject'"'"'s effective ventilation. Apparatus for effective such methods are also disclosed.

Claims

1. A method for substantially noninvasively estimating effective lung volume of a subject, comprising:

effecting a change in effective ventilation of a subject; and

determining an effective lung volume that results in a substantially linear relationship between carbon dioxide elimination measured at or near the mouth of the subject and a concentration of carbon dioxide in gas exhaled from the alveoli of the subject'"'"'s lungs when applied to the carbon dioxide elimination measured at the mouth to compensate for flow of carbon dioxide into the effective lung volume.

2. The method of claim 1, wherein determining comprises:

selecting a linear filter coefficient that creates a substantially linear relationship between the carbon dioxide elimination and the concentration of carbon dioxide.

3. The method of claim 1, wherein determining the effective lung volume comprises selecting the effective lung volume providing an optimal correlation between the carbon dioxide elimination and the carbon dioxide concentration.

4. The method of claim 1, wherein determining the effective lung volume comprises employing the following algorithm:

5. The method of claim 1, wherein effecting includes rebreathing.

6. A method for substantially noninvasively estimating effective lung volume of a subject, comprising:

effecting a change in effective ventilation of a subject while the subject continues to breathe;

considering a change in the concentration of carbon dioxide in gases residing within the alveoli of the subject'"'"'s lungs from baseline breathing to breathing in which the change in effective ventilation is effected; and

considering a change in carbon dioxide elimination from baseline breathing to breathing in which the change in effective ventilation is effected.

7. The method of claim 6, wherein considering the change in concentration and considering the change in carbon dioxide elimination comprise employing the following algorithm:

8. The method of claim 6, wherein effecting includes rebreathing.

9. A method for substantially noninvasively estimating effective lung volume of a subject, comprising:

effecting a change in effective ventilation of a subject;

considering a change in the amount of carbon dioxide in gases residing within the alveoli of the subject'"'"'s lungs from baseline breathing to breathing in which the change in effective ventilation is effected;

considering a change in carbon dioxide elimination from baseline breathing to breathing in which the change in effective ventilation is effected; and

compensating for changes in the amount of carbon dioxide in gases residing within the alveoli that occur during a breath.

10. The method of claim 9, wherein compensating comprises:

considering the change in carbon dioxide delivered to a lung from blood as a result of the change in effective ventilation that was effected.

11. The method of claim 10, wherein compensating further comprises:

considering a magnitude of the change in the amount of carbon dioxide in the alveoli from baseline breathing to breathing in which the change in effective ventilation is effected.

12. The method of claim 9, wherein effecting includes rebreathing.

13. The method of claim 9, wherein effecting includes breath-holding.

14. The method of claim 9, wherein considering the change in the concentration of carbon dioxide, considering the change in carbon dioxide elimination, and compensating for changes in the amount of carbon dioxide comprise employing the following algorithm:

15. The method of claim 9, wherein considering the change in the concentration of carbon dioxide, considering the change in carbon dioxide elimination, and compensating for changes in the amount of carbon dioxide comprise employing the following algorithm:

16. Apparatus for substantially noninvasively estimating effective lung volume of a subject, comprising:

means for effecting a change in effective ventilation of a subject; and

means for determining an effective lung volume that results in a substantially linear relationship between carbon dioxide elimination measured at or near the mouth of the subject and a concentration of carbon dioxide in gas exhaled from the alveoli of the subject'"'"'s lungs when applied to the carbon dioxide elimination measured at the mouth to compensate for flow of carbon dioxide into the effective lung volume.

17. The apparatus of claim 16, wherein the means for determining comprises:

means for selecting a linear filter coefficient that creates a substantially linear relationship between the carbon dioxide elimination and the concentration of carbon dioxide.

18. The apparatus of claim 16, wherein the means for determining the effective lung volume comprises means for selecting the effective lung volume providing an optimal correlation between the carbon dioxide elimination and the carbon dioxide concentration.

19. The apparatus of claim 16, wherein the means for determining the effective lung volume comprises means for employing the following algorithm:

20. The method of claim 16, wherein the means for effecting includes means for effecting rebreathing.

21. Apparatus for substantially noninvasively estimating effective lung volume of a subject, comprising:

means for effecting a change in effective ventilation of a subject while the subject continues to breathe;

means for considering a change in the concentration of carbon dioxide in gases residing within the alveoli of the subject'"'"'s lungs from baseline breathing to breathing in which the change in effective ventilation is effected; and

means for considering a change in carbon dioxide elimination from baseline breathing to breathing in which the change in effective ventilation is effected.

22. The apparatus of claim 21, wherein the means for considering the change in concentration and considering the change in carbon dioxide elimination comprise means for employing the following algorithm:

23. The apparatus of claim 21, wherein the means for effecting includes means for effecting rebreathing.

24. Apparatus for substantially noninvasively estimating effective lung volume of a subject, comprising:

means for effecting a change in effective ventilation of a subject;

means for considering a change in the amount of carbon dioxide in gases residing within the alveoli of the subject'"'"'s lungs from baseline breathing to breathing in which the change in effective ventilation is effected; and

means for considering a change in carbon dioxide elimination from baseline breathing to breathing in which the change in effective ventilation is effected; and

means for compensating for changes in the amount of carbon dioxide in gases residing within the alveoli that occur during a breath.

25. The apparatus of claim 24, wherein the means for compensating comprises:

means for considering the change in carbon dioxide delivered to a lung from blood as a result of the change in effective ventilation that was effected.

26. The apparatus of claim 25, wherein the means for compensating comprise:

means for considering a magnitude of the change in the amount of carbon dioxide in the alveoli from baseline breathing to breathing in which the change in effective ventilation is effected.

27. The apparatus of claim 24, wherein means for effecting includes means for rebreathing.

28. The apparatus of claim 24, wherein means for effecting includes means for effecting breath-holding.

29. The apparatus of claim 24, wherein means for considering the change in the concentration of carbon dioxide, the means for considering the change in carbon dioxide elimination, and the means for compensating for changes in the amount of carbon dioxide comprise means for employing the following algorithm:

30. The apparatus of claim 24, wherein the means for considering the change in the concentration of carbon dioxide, the means for considering the change in carbon dioxide elimination, and the means for compensating for changes in the amount of carbon dioxide comprise means for employing the following algorithm: