Lung Function Test

Total Lung Capacity

IC = inspiratory capacity
IRV = inspiratory reserve volume
ERV = expiratory reserve volume
FVC = forced vital capacity
FEV1 = forced expiratory volume in 1 sec.
FER = forced expiratory ratio
= FEV1 / FVC (approx. 80%)

FRC = ERV + RV


A spirometer is used to obtain FEV and FVC. These measurements are subject to height, age and sex.

Patients with obstructive pulmonary disorder would have in their lung function report a normal (or low) FVC, a low FEV1, and thus a low FER. The obstruction of the bronchus is the cause of a low FEV1 as forced expiratory time is prolonged, which appears in asthma, chronic bronchitis, emphysema etc.

In restrictive pulmonary disorder, the capacity of patients’ lungs is reduced i.e. ‘small’ lungs, by pleural effusion, congestion etc. Thus their lung function test would show a low FVC, a low FEV1, which gives a normal (or high) FER.

A Flow-volume loop can also help differentiate between different pulmonary disorders.