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13 Cards in this Set
- Front
- Back
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Lung vol and capacities that cannot be measured directly via exhaled methods
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FRC
TLC RV |
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Indirect Methods
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Open circuit Nitrogen Washout Method
Closed Circuit Helium Dilution Method Body Plethysmography (Body Box) |
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Open Circuit Nitrogen Washout Method
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The pt breathes 100% oxygen thru a valve-mpc for 7 minutes or alv. concentration of N2 decrease to1.0%
Measurements are started at end exp. Rapid response N2 analyzer measures breath by breath N2 concentration and exhaled vol Values of exhaled vol are summed to provide the total vol of N2 washout |
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FRC calc for Open Circuit Nitrogen Washout
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%N2 (final) x Exp. Vol/% N2 atm
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Washout Time
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Must be reported with results
-Indicates good/poor distrbution of vent. |
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Disadvantages of Open Circuit Nitrogen Washout & Helium Dilution Method
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Pt with signficant at trapping disease (COPD, emphysema) the gas vol measured is underestimated
Any leak introducing room air will result n overestimation of vol |
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Advantages of Open Circuit Nitrogen Washout & Helium Dilution Method
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Test is independent of pt effort
Normal tidal breathing and adequate mouthpiece seal are simple pt requirements Considered relieable, reproducible and simple to perform |
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Helium Dilution Method
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A spirometer is filled with a known vol of room air
He is added until a concentration of 10% is reached Exact vol of He is is system is measured before the test Pt breaths thru a valve-mouthpiece of a rebreathing system so a CO2 absorber is added Oxygen is added to the system only to maintain a concentration of 0.21 Valve is open at end exhalation and test lasts until -7 mins -untill stable He concentration is reached Final concentration of He is measured |
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FRC calc for Helium Dilution Method
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(Initial He %- Final He%) x V x BTPS/Final He%
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Disadvantages of Helium Dilution Method
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Pt with significant air trapping disease (COPD,emphysema) the gas vol measured in underestimated
Any leak introducing room air will result in overestimation of volume |
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Premise of the Body Box is based on...
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Boyles Law
P1xV1 = P2xV2 when temp is constant 1 = Lung 2 = Box |
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Disadvantages of Body Box
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Claustrophobia
Pt effort/understanding is essential |
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Advantages of Body Box
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Vtg measures all gas in thorax including that trapped distal to collapsed arways
More accurate FRC measurement than He dilution and N2 washout Vtg measurement is quick, precise and reproducible |
