Important definitions in Respiratory function tests

These are some important definitions to understand Respiratory function tests .
We will explain Tidal Volume, Residual Volume (RV), Inspiratory reserve volume (IRV), Expiratory reserve volume (ERV), Vital capacity (VC), Forced vital capacity (FVC), Maximum breathing capacity, Forced expiratory volume in 1 second (FEV1) and Total lung capacity (TLC) .

Tidal Volume :
 it is the volume of air in one breath during normal quiet breathing.

Residual Volume (RV) :
 it is the volume of gas present within lung after a maximal expiration = 1200 ml.


Inspiratory reserve volume (IRV) :
 it is the additional volume of air that can be inspired above the tidal volume = 3 L.

Expiratory reserve volume (ERV) :

 it is the volume of air that can be forcefully expired after a normal expiration.

Vital capacity (VC) :
 it is the volume of air expired after the maximal inspiration = 4600 ml.

Forced vital capacity (FVC):
 is the same as VC, except that the inhalation is performed as rapidly and forcefully as possible.

• Maximum breathing capacity = volume of air expired after the deepest
inspiration/minute.

Forced expiratory volume in 1 second (FEV1) :
The volume of air forcefully expired in the first second after a deep breath .
• In the first second --> most of vital capacity is expired, about 80% = FEV1
if  decreased  = obstructive airway disease.

Total lung capacity (TLC) :
 is the volume of gas in the lungs after a maximal inspiration, it equals the sum of the four lung volumes.

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