D. Pulmonary fibrosis – Explanation
This is a very straightforward question but it does test your knowledge of lung
function testing thoroughly. The pulmonary indices indicate a restrictive lung
disease. The only choice that is a restrictive lung disease is pulmonary fibrosis.
Asthma, bronchiectasis, pulmonary oedema and chronic obstructive pulmonary
disease are all obstructive lung diseases.
PULMONARY FUNCTION TEST
Terms:
Total lung Capacity (TLC) – this is the amount of air in the lungs after maximal
inspiration
Residual Volume (RV) – this is the amount of air that remains in the lungs after
maximal expiration
Vital Capacity (VC) – this is the amount of air that is pushed out of the lungs after
maximal expiration
Forced Expiratory Volume in 1 second (FEV1) – this is the amount of air that is
pushed out of the lungs in one second during maximal expiration
Forced Vital Capacity (FVC) – this is the amount of air that is pushed out of the
lungs after forced maximal expiration
The following table illustrates the three main values that you need to know for the
exam and how each pulmonary index differs between obstructive and restrictive
processes
| Obstructive | Restrictive | |
|---|---|---|
| FEV1 |
↓ Less than 80% of |
↓ Less than 80% of predicted |
| FVC | N
More than 80% of |
↓ Less than 80% of predicted |
| FEV1/FVC | ↓ Less than 0.7 |
N Less than 0.7 0.7-0.8 OR t More than 0.8 |
Obstructive lung diseases
These are diseases such as asthma, cystic fibrosis and bronchiectasis. They
cause airway resistance to expiratory flow and so result in obstructed airways.
When expiratory flow is obstructed, the patient will struggle to breathe air out and
thus FEV1 will decrease. Because FEV1 is the numerator of the FEV1/FVC
ratio, any obstructive disease will also cause a decrease in the FEV1/FVC ratio.
Restrictive lung diseases
These are diseases such as pulmonary fibrosis or interstitial lung disease. They
may also be caused by obesity, chest or spine deformities and neuromuscular
disorders. Restrictive lung diseases restrict lung expansion and cause a
decrease in the amount of air that the lung can hold i.e., a decrease in the vital
capacity of the lung. This results in a decreased FVC. Because the pathology of
restrictive lung diseases also causes a decrease in lung elasticity, it also
becomes harder for the lungs to force out air. This causes a decrease in the
FEV1. Because both the FEV1 and FVC decrease in restrictive lung disease, the
FEV1/FVC ratio remains the same.
