Lung volumes and capacities

There are many respiratory disease that affects the lung volumes and capacities.

In theses following pathological conditions the normal volumes and capacities are assessed with resultant volumes in respiratory disease-

  • Pneumonia
  • Asthma
  • Pulmonary tuberculosis
  • Emphysema
  • Cystic fibrosis

Pulmonary function test are useful in assessing the functional status of respiratory system in both physiological and pathological conditions.

So air in the lungs are classified into two divisions-

  1. Lung volumes 
  2. Lung capacities (combination of two or more volumes).

Lung volumes

There are four types of lung volumes-
  1.  Tidal volume (TV)
  2.  Inspiratory reserve volume (IRV)
  3.  Expiratory reserve volume (ERV)
  4.  Residual volume (RV)

1. Tidal volume 

The volume of air breath in and out in a single breath or respiration is called tidal volume.
Normal volume= 500ml (0.5l)

2. Inspiratory reserve volume 

It is the additional amount of air that can be inspired forcefully at the end of normal respiration beyond the tidal volume.
Normal values= 3300ml (3.3l)  

3. Expiratory reserve volume 

It is the amount of air that can be expired out forcefully after normal expiration.
Normal value= 1000ml (1l)

4. Residual volume 

It is the amount of air always remains in the lungs even after forceful expiration. It is significant because of -
  • It helps to aerate the blood in between breathing and during expiration.
  • It maintains the contour of the lungs.
Normal value= 1200ml (1.2l)

Lung capacities 

There are four types of capacities formed by combination of one or two volumes together.
  1.  Inspiratory capacity (IC)
  2.  Vital capacity (VC)
  3.  Functional residual capacity (FRC)
  4.  Total lung capacity (TLC)

1. Inspiratory capacity 

It is the maximum volume of air that can be inspired from end expiratory position.
It includes the tidal volume and inspiratory reserve volume.
IC= T.V +I.R.V

2. Vital capacity 

It is the maximum amount of air that can be expelled out forcefully after a maximum inspiration.
It includes the tidal volume, inspiratory reserve volume and expiratory reserve volume.

3. Functional residual capacity 

It is the volume of air remaining in the lungs after normal expiration.
It includes residual volume and expiratory reserve volume.

4. Total lung capacity 

It is the amount of air present in the lungs after maximal inspiration.This includes the all volumes.

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