Tuesday, 7 September 2010

MRCP revision battle 4.1: lung function tests

After working an excessive number of hours and recovering thanks to chocolate cake (do click here to visit the ultimate chocolate cake recipe, which really is just amazing) I've managed a bit of a revision spurt, mainly through the world of lungs.

So today we have:
battle 4.1: pulmonary function tests
battle 4.2: extrinsic allergic alveolitis
battle 4.3: aspergillosis
battle 4.4: fibrosis
then bringing up the rear battle 4.5, that classic clinical sign clubbing.

Battle 4.1: Pulmonary function tests

Using a spirometer, ask your patient to blow as hard, as fast and as long as possible.  The spirometer will then give you their FEV1 (=forced expiratory volume in 1 second) and FVC (= forced vital capacity.)  These can be plotted, giving graphs that look like this.

In the exam you are far more likely to just get figures and need to be able to recognise them as representing either an obstructive or a restrictive picture.

Obstructive pattern

Obstructive lung function usually gives a very reduced FEV1 and a less severely reduced FVC.  This means that overall the FEV1/FVC ratio is <75%.

Classical causes of an obstructive pattern are COPD and asthma

Restrictive pattern

Restrictive lung function causes a reduced FVC, and FEV1/FVC remains either the same or may increase.

Causes include LONE K: lung fibrosis, obesity, neuromuscular problems, effusion, kyphoscoliosis.

That was short and sweet... onwards to battle 4.2...