Method and apparatus for determining a pulmonary function parameter for gas exchange

• US 6,302,851 B1
• Filed: 05/15/2000
• Issued: 10/16/2001
• Est. Priority Date: 11/13/1997
• Status: Expired due to Term

• Current Assignee: Maquet Critical Care AB (Getinge AB)
• Original Assignee: Siemens-Elema AB (Siemens AG)
• Inventors: Gedeon, Andras
• Primary Examiner(s): Nasser, Robert L.
• Assistant Examiner(s): Mallari, Patricia C.
• Application Number:
  US09/554,441
• Time in Patent Office: 519 Days
• Field of Search: 600/538
• US Class Current: 600/538
• CPC Class Codes: A61B 5/083 Measuring rate of metabolism by using breath test, e.g. measuring rate of oxygen consumption

Abstract

A method and apparatus for determining a pulmonary function parameter, EVG, indicative of a living subject'"'"'s effective lung volume, namely the lung volume in which gas exchange between respiratory air and pulmonary blood takes place efficiently. The apparatus carries out the steps of the method: (1) determining for a first breath during normal steady state breathing of the subject the end-tidal carbon dioxide or oxygen concentration P_et1 and the average rate of flow V_a1, over the duration T₁ of the breath, of expired carbon dioxide or oxygen, (2) determining for a second breath comprising a breath-hold period the end-tidal carbon dioxide or oxygen concentration P_et2 and the average rate of flow V_a2, over the duration T₂ of the breath, of expired carbon dioxide or oxygen, and (3) determining EVG as a quantity proportional to the ratio of the difference between said average flow rates V_a1 and V_a2 to the difference between said end-tidal concentrations P_et2 and P_et1.

Claims

1. A method for determining a pulmonary function parameter, EVG, indicative of a living subject'"'"'s effective lung volume, namely the lung volume in which gas exchange between respiratory air and pulmonary blood takes place efficiently, comprising the steps of

determining for a first breath during normal steady state breathing of the subject the end-tidal concentration P_et1 of a given component of the respiratory air, said given component being one of carbon dioxide and oxygen, and the average rate of flow V_a1, over the duration T₁ of the breath, of the quantity of said given component expired during the breath,

determining for a second breath comprising a breath-hold period the end-tidal concentration P_et2 of said given component and the average rate of flow V_a2, over the duration T₂ of the breath, of the quantity of said given component expired during the breath,

determining EVG as a quantity proportional to the ratio of the difference between said average flow rates V_a1 and V_a2 of said given component to the difference between said end-tidal concentrations P_et2 and P_et1 of said given component.

2. A method according to claim 1 in which the breath-hold period separates the inspiration and the expiration of the second breath.

3. A method according to claim 1 in which the breath-hold period precedes the inspiration of the second breath.

4. A method according to claim 1 in which the duration of the breath-hold period is 1 to 15 seconds.

5. A method according to claim 1 in which the step of determining EVG is carried out using the equation $\begin{array}{c}\mathrm{EVG}=100·\end{array}$

T2

 



(Va1-Va2)(Pet2-Pet1)(1′

)

in which V_a1, V_a2, P_et1, P_et2 and T₂ are the same quantities as above.

6. A method according to claim 1 in which the subject breathes spontaneously.

7. A method according to claim 1 in which the subject breathes with the aid of a ventilator.

8. A method according to claim 1 which comprises the additional step of determining the change of the subject'"'"'s EVG as a function of positive end-expiratory pressure, PEEP, of the subject'"'"'s lungs.

9. A method for determining lung tissue volume, V_t, of a living subject, comprising the steps of

determining the values of the subject'"'"'s EVG in accordance with claim 1 for two different non-zero breath-hold durations,

determining by linear extrapolation from the EVG values so determined a value of the subject'"'"'s EVG for zero breath-hold duration, and

determining the V_t of the subject from the known relationship of V_t to said EVG value for zero breath-hold duration and the EVG value for a non-zero breath-hold duration.

10. A method for determining lung tissue volume, V_t, of a living subject, comprising the steps of

determining the value, EVG_CO2, of the subject'"'"'s EVG in accordance with claim 1 using carbon dioxide as said given component of the respiratory gas,

determining the value, EVG_CO2, of the subject'"'"'s EVG in accordance with claim 1 using oxygen as said given component of the respiratory gas,

determining V_t from the equation

11. A device for determining a pulmonary function parameter, EVG, indicative of a living subject'"'"'s effective lung volume, namely the lung volume in which gas exchange between respiratory air and pulmonary blood takes place efficiently, comprising

means for determining for a first breath during normal steady state breathing of the subject the end-tidal concentration P_et1 of a given component of the respiratory gas, said given component being one of carbon dioxide and oxygen, and the average rate of flow V_a1, over the duration T₁ of the breath, of the amount of said given component expired during the breath,

means for determining for a second breath comprising a breath-hold period the end-tidal concentration P_et2 of said given component and the average rate of flow V_a2, over the duration T₂ of the breath, of the amount of said given component expired,

means for determining EVG as a quantity proportional to the ratio of the difference between said average flow rates V_a1, and V_a2 to the difference between said end-tidal concentrations P_et2 and P_et1.

12. Apparatus according to claim 11 including means for determining EVG using the equation $\begin{array}{c}\mathrm{EVG}=100·\end{array}$

T2

 



(Va1-Va2)(Pet2-Pet1)(1′

)

in which V_a1, V_a2, P_et2, P_et2 and T₂ are the same quantities as above.

13. Apparatus according to claim 11 including means for determining the change, Δ

EVG, of the subject'"'"'s EVG as a function of positive end-expiratory pressure, PEEP, of the lungs