99doc
Forum Elite
Topics: 52
Posts: 370
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Calculate FRC.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
Data available:
12L spirometer with 10% helium concentration. After several min of breathing, Helium concentr falls to 8%
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| mesh
Forum Guru
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Posts: 401
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2.4L.......
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| 99doc
Forum Elite
Topics: 52
Posts: 370
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how did u get it?
i don't have the correct answer
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| mesh
Forum Guru
Topics: 77
Posts: 401
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i am sorry the ans is 3L.....
helium dilution method is a closed circuit technique in which pt is allowed to breath through spirometer having fixed conc of O2 and helium....pt is allowed to breath normally and after some breaths there occurs a stage of equilibrium b/w the lungs and the spirometer..
so C1 * V1(before equilibration )=C2(V1+V2)after equilibration
C1 conc of helium before equilibration in the spirometer...which in this case is 10%
V1 volume of the gas mixture =12L
C2 conc of after equilibration=8%
V2 is the volume we want to calculate(FRC)
12*10=8(12+V2)
120=96+8V2
120-96=8V2
24=8V2
V2=3....
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| mdwannabe
Forum Guru
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Posts: 1,133
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I guess I would think of it in simpler teerms. 12L is the FVC. After introduction of Helium in to closed system, the change was 2%, that means that the RV (which is represented by the change) is 2% of the FVC, which is 2.4 L, the FRC is usually a bit larger than RV since it includes the RV and FEV. So if given the choices I d go for something close to 2.5- 3L. However, the formula given above givesone an exact amount. :-)
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| hgy
Forum Newbie
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Posts: 22
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My calculation is 3L too.
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