What is functional residual capacity and describe how it is measured.

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College Answer

This question requested a definition AND a description of measurement (one method if correctly 
discussed could and did generate a pass mark) although additional marks were awarded if 
multiple measurement methods were mentioned or described. Detailed descriptions of the 
factors effecting FRC and its functions were NOT requested and scored no marks. "Fowlers 
method" uses 100% oxygen and nitrogen analysis to calculate anatomical dead space - NOT 
FRC - so scored no marks. Both Helium dilution and nitrogen washout (with 100%oxygen) 
enable calculation of FRC using C1V1=C2V2 where V2 = V1+FRC. Body plethysmography 
requires more complex calculations of P1V1= P2V2 (Boyles Law) applied twice = for the box 
and then the lung. Few candidates had a clear understanding of this method.
Most answers did not demonstrate the depth of understanding of the measurement techniques 
that was required to score highly.