Method and apparatus for anatomical deadspace measurement

• US 6,599,252 B2
• Filed: 05/24/2001
• Issued: 07/29/2003
• Est. Priority Date: 06/02/2000
• Status: Expired due to Fees

• Current Assignee: RIC INVESTMENTS LLC (Respironics Incorporated)
• Original Assignee: Respironics Incorporated
• Inventors: Starr, Eric W.
• Primary Examiner(s): Hindenburg, Max
• Assistant Examiner(s): Natnithithadha, Navin
• Application Number:
  US09/864,806
• Publication Number:
  US 20010049478A1
• Time in Patent Office: 796 Days
• Field of Search: 600/529, 600/531, 600/532, 600/533, 600/538
• US Class Current: 600/532
• CPC Class Codes: A61B 5/083 Measuring rate of metabolism by using breath test, e.g. measuring rate of oxygen consumption
• CPC Class Codes: A61B 5/091 Measuring volume of inspired or expired gases, e.g. to determine lung capacity
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

An apparatus and method for determining an anatomical deadspace volume VD_ANA of a patient. The apparatus includes a sensor that measures a parameter indicative of the volume of gas exhaled by the patient and a gas analyzer that measures a concentration of a gas constituent in the patient'"'"'s expiratory flow. A controller determines the patient'"'"'s anatomical deadspace volume based on signals provided by the sensor and the gas analyzer.

Claims

1. An apparatus for determining an anatomical deadspace volume VD_ANA of a patient, the apparatus comprising:

a sensor adapted to measure a parameter indicative of a volume of gas exhaled by a patient during at least an exhalation phase of a respiratory cycle;

a gas analyzer adapted to measure a concentration of a gas constituent in such a patient'"'"'s flow of gas during an exhalation phase of a respiratory cycle; and

a controller operatively coupled to the sensor and the gas analyzer, wherein the controller determines such a patient'"'"'s anatomical deadspace volume based on signals provided by the sensor and the gas analyzer.

2. The apparatus of claim 1, wherein the sensor is a flow sensor adapted to measure a rate of flow of gas exhaled by a patient over an exhalation phase of a respiratory cycle as the parameter indicative of a volume of gas exhaled by a patient, and wherein the controller uses the measured rate of flow of gas over the exhalation phase to determine the volume of gas exhaled by such a patient.

3. The apparatus of claim 1, wherein the gas analyzer is one of a capnometer and an oxygen analyzer.

4. The apparatus of claim 1, further comprising an output device operatively coupled to the controller and adapted to display information indicative of a patient'"'"'s anatomical deadspace volume as determined by the controller.

5. The apparatus of claim 1, wherein the controller determines an anatomical deadspace volume of a patient by:

determining a time t₁ that corresponds to a point at which such a patient commences exhaling;

determining a time t₂ that corresponds to an inflection point in a waveform corresponding to the concentration of the gas constituent measured by the gas analyzer; and

determines a volume of gas exhaled by such a patient from time t₁ to time t₂ as the anatomical deadspace volume of such a patient.

6. The apparatus of claim 5, wherein (1) if the gas analyzer is a capnometer, the inflection point is determined by the controller as corresponding to a point where the waveform changes from a concave-up shape to a concave-down shape, and (2) if the gas analyzer is an oxygen analyzer, the inflection point is determined by the controller as corresponding to a point where the waveform changes from a concave-down shape to a concave-up shape.

7. The apparatus of claim 5, wherein the controller determines time t₂ by determining a first derivative of the waveform and defines time t₂ as a point where a peak value of the first derivative of the waveform occurs.

8. The apparatus of claim 5, wherein the controller determines time t₂ by determining a second derivative of the waveform and defines time t₂ as a crossover point where the second derivative of the waveform has a value of zero.

9. The apparatus of claim 8, wherein the controller determines time t₂ by determining a sign (±

) of the second derivative on opposite sides of the crossover point, and determining if the second derivative of the waveform changes sign on opposite sides of the crossover point.

10. The apparatus of claim 9, wherein the controller determines if the second derivative changes sign on opposite sides of the crossover point by also determining if the sign changes from one of positive to negative and negative to positive.

11. A method of determining an anatomical deadspace volume VD_ANA of a patient, comprising:

detecting a parameter indicative of a volume of gas exhaled by a patient;

detecting a concentration of a gas constituent in a flow of gas exhaled by such a patient; and

determining such a patient'"'"'s anatomical deadspace volume based on the detected parameter indicative of a volume of gas and the detected concentration of a gas constituent.

12. The method of claim 11, the parameter indicative of a volume of gas exhaled is a rate of flow of gas exhaled by a patient over an exhalation phase of a respiratory cycle, and determining a patient'"'"'s anatomical deadspace includes determining a volume of gas exhaled by such a patient based on the measured rate of flow of gas over the exhalation phase.

13. The method of claim 11, wherein detecting a concentration of a gas constituent includes (a) detecting a carbon dioxide as the gas constituent using a capnometer or (b) detecting oxygen as the gas constituent using an oxygen analyzer.

14. The method of claim 11, further comprising outputting information indicative of a patient'"'"'s anatomical deadspace volume.

15. The method of claim 11, wherein determining such a patient'"'"'s anatomical deadspace volume includes:

determining a time t₁ that corresponds to a point at which such a patient commences exhaling;

determining a time t₂ that corresponds to an inflection point in a waveform corresponding to the concentration of the gas constituent measured in the step of detecting a concentration of a gas constituent; and

calculating a volume of gas exhaled by such a patient from time t₁ to time t₂ as the anatomical deadspace volume of such a patient.

16. The method of claim 15, wherein (1) if the step of detecting a concentration of a gas constituent is preformed using a capnometer, the inflection point is determined as corresponding to a point where the waveform changes from a concave-up shape to a concave-down shape, and (2) if the step of detecting a concentration of a gas constituent is preformed using a gas analyzer, the inflection point is determined as corresponding to a point where the waveform changes from a concave-down shape to a concave-up shape.

17. The method of claim 15, wherein determining time t₂ includes determining a first derivative of the waveform and defining time t₂ as a point where a peak value of the first derivative of the waveform occurs.

18. The method of claim 15, wherein determining time t₂ includes determining a second derivative of the waveform and defining time t₂ as a crossover point where the second derivative of the waveform has a value of zero.

19. The method of claim 18, wherein determining time t₂ includes determining a sign (±

) of the second derivative on opposite sides of the crossover point and determining if the second derivative of the waveform changes sign on opposite sides of the crossover point.

20. The method of claim 19, wherein determining if the second derivative changes sign on opposite sides of the crossover point includes determining if the sign changes from one of positive to negative and negative to positive.

21. An apparatus for detecting an anatomical deadspace volume of a patient comprising:

sensing means for detecting a parameter indicative of a volume of gas exhaled by a patient;

gas analyzing means for detecting a concentration of a gas constituent in the flow of gas exhaled by such a patient; and

processing means for determining such a patient'"'"'s anatomical deadspace volume based on the detected volumetric flow of gas and the detected concentration of a gas constituent.

22. The apparatus of claim 21, further comprising outputting means for outputting information indicative of a patient'"'"'s anatomical deadspace volume determined by the processing means.

23. The apparatus of claim 21, wherein the processing means determines the anatomical deadspace volume of a patient by:

determining a time t₁ that corresponds to a point at which such a patient commences exhaling;

determining a time t₂ that corresponds to an inflection point in a waveform corresponding to the concentration of the gas constituent measured by the gas analyzer; and

calculating a volume of gas exhaled by such a patient from time t₁ to time t₂ as the anatomical deadspace volume of such a patient.

24. The apparatus of claim 23, wherein (1) if the gas analyzing means is a capnometer, the inflection point is determined by the processing means as corresponding to a point where the waveform changes from a concave-up shape to a concave-down shape, and (2) if the gas analyzing means is an oxygen analyzer, the inflection point is determined by the processing means as corresponding to a point where the waveform changes from a concave-down shape to a concave-up shape.

25. The apparatus of claim 23, wherein the processing means determines time t₂ by determining a first derivative of the waveform and defines time t₂ as a point where a peak value of the first derivative of the waveform occurs.

26. The apparatus of claim 23, wherein the processing means determines time t₂ by determining a second derivative of the waveform and defines time t₂ as a crossover point where the second derivative of the waveform has a value of zero.

27. The apparatus of claim 26, wherein the processing means determines time t₂ by determining a sign (±

) of the second derivative on opposite sides of the crossover point, and determining if the second derivative of the waveform changes sign on opposite sides of the crossover point.

28. The apparatus of claim 27, wherein the processing means determines if the second derivative changes sign on opposite sides of the crossover point by also determining if the sign changes from one of positive to negative and negative to positive.