Outline the abnormalities in pulmonary function testing of a person with severe obstructive lung disease (40% marks). Describe the physiological changes that explain these abnormalities (60% marks). 

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College Answer

The majority of candidates were able to state that obstructive lung disease resulted in a reduction 
in the FEV1 and the FVC. Very few gave any indication of how much these parameters might be 
reduced in severe obstructive lung disease or that FVC is usually only slightly reduced, whereas 
the FEV1 is markedly reduced and therefore so is the FEV1/FVC ratio. Candidates were also 
expected to indicate that peak expiratory flow rate is also reduced (by 50% or more in severe 
disease), that carbon monoxide diffusing capacity is also reduced, and residual volume and total 
lung capacity are increased. A reasonable proportion of candidates commented that the forced 
expiratory flow (FEF) 25-50% being reduced and this results in a ‘scalloped’ flow volume loop. 
Accurately reproducing a normal flow volume loop and a flow volume loop of a patient with 
severe obstructive lung disease on the same graph could have depicted most of the above points 
and scored the majority of marks available. 
The second part of this question was poorly answered. Whilst the majority correctly stated that an 
increase in airways resistance was present, few stated what changes gave rise to this. Dynamic 
airway compression, was mentioned by many, but why this occurred was explained poorly. The 
effect of closing capacity rising above the FRC was seldom mentioned and why the FRC 
increased again was seldom mentioned or explained. A detailed knowledge of what is a core 
subject in intensive care medicine was expected.