The contraction of the diaphragm and the inter coastal muscles produces expansion of the chest cavity, so air enters into the lungs during inspiration. A forced inspiration can produce additional expansion, so more air can enter the lungs . Similarly, a forced expiration can expel an extra volume of air.

The various respiratory volumes are:

1. Vital Capacity:

Vital capacity is defined as the volume of the air that can be expelled by a forced expiration after a forced inspiration.

2. Tidal air:

Tidal air is the volume of the air passing in and out of the lungs with ordinary quiet breathing.

3. Inspiratory reserve:

Inspiratory reserve is the additional volume of air that can be taken in by forced inspiration.

4. Expiratory reserve:

Expiratory reserve is the volume of air that can be expelled by forced expiration after normal inspiration.

5. Residual Volume:

Residual volume is the volume of the air which remains in the lungs on forced expiration after normal inspiration.

6. Total Lung Capacity:

It is the sum of vital capacity and residual volume.

  Anatomy and Physiology, Medical Coding, organ systems, Respiratory System